- Email: [email protected]
Antioxidant capacity and consumer acceptability of herbal egg tofu
Accepted Manuscript Antioxidant capacity and consumer acceptability of herbal egg tofu M. Maizura, A. Aminah, W.M. Wan Aida PII:
S0023-6438(15)30080-3
DOI:
10.1016/j.lwt.2015.07.062
Reference:
YFSTL 4856
To appear in:
LWT - Food Science and Technology
Received Date: 9 March 2015 Revised Date:
22 July 2015
Accepted Date: 23 July 2015
Please cite this article as: Maizura, M., Aminah, A., Wan Aida, W.M., Antioxidant capacity and consumer acceptability of herbal egg tofu, LWT - Food Science and Technology (2015), doi: 10.1016/ j.lwt.2015.07.062. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Antioxidant capacity and consumer acceptability of herbal egg tofu
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Maizura, M.1,2 Aminah, A. 1* & Wan Aida, W.M.1 1
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School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor DE, Malaysia. 2
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School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia.
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Corresponding Author: Email: [email protected] Phone: +603-8921 5990/5963 Fax: +603-89213232
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Abstract
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A mixture design was used to optimize the herbal egg tofu formulation containing Polygonum
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minus, Curcuma longa and Zingiber officinale. The effects of the herbs on the total phenolic
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content (TPC), ferric reducing antioxidant power (FRAP) assay and scavenging activity 2,2-
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diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid
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(ABTS), texture profile (hardness, springiness, cohesiveness, gumminess and chewiness) and
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consumer preference on sensory characteristics (appearance, color, aroma, taste, texture and
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overall acceptability) of the herbal egg tofu were investigated. An increase in Curcuma longa
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content produced egg tofu with significantly higher (p<0.05) TPC and antioxidant activity
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(FRAP, ABTS and DPPH assay), but a significantly lower score for overall acceptability. An
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increase in the Polygonum minus content significantly (p<0.05) increased the springiness of
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the egg tofu. The optimum formulation of the egg tofu was determined by overlapping the
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contour plot related to sensory characteristics (color, taste and overall acceptability) and
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springiness that formed the region with optimum value. The results showed that the optimum
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predicted response value for color, taste, overall acceptability and springiness were 4.9, 4.6,
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4.8 and 0.96 mm, respectively, which were obtained from a combination of 0.7% Polygonum
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minus, 0.5% Curcuma longa and 0.8% Zingiber officinale.
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Keywords: Herbal egg tofu, antioxidant capacity, sensory analysis, optimization, response
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surface methodology (RSM), mixture design
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1. Introduction Herbs and spices have been added to food since ancient times, not only as a flavoring agent,
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and food preservative, but also as an excellent source of natural antioxidants. Antioxidant
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activities of herbs and spices have been widely studied (Hinneburg, Damien Dorman, &
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Hiltunen, 2006; Kumar, Nayaka, Dharmesh, & Salimath, 2006; Cousins, Adelberg, Chen, &
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Rieck, 2007) and the increasing use of herbs and spices as natural antioxidants in food is
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attributed to low cost and consumer’s concern about the safety of synthetic antioxidants
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(Suhaj, 2006; Yanishlieva, Marinova, & Pokorný, 2006). The incorporation of herbs and
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spices in food products, such as meat (Han & Rhee, 2005; Naveena, Muthukumar, Sen, Babji,
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& Murthy, 2006), fish, yoghurt (Burt, 2004) and dairy products (Viluda-Martos, Ruiz-
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Navajas, Fernandez-Lopez, & Angel Perez-Alvarez, 2008) has been reported. Authentic Asian
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cuisine demands the use of many fresh herbs and spices, as well as in the form of extracts and
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powders. This includes Polygonum minus, Curcuma longa and Zingiber officinale.
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Polygonum minus is usually eaten raw or added in cooking. It is known as a medicinal
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plant with natural antioxidants (Wasman Qader, Abdulla, Chua, & Hamdan, 2012). Phenolic
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compounds extracted from Polygonum minus exhibited antioxidant activities (Huda-Faujan,
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Noriham, Norrakiah, & Babji, 2007; Maizura, Aminah, & Wan Aida, 2010). In addition,
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previous research (Huda-Faujan, Noriham, Norrakiah, & Babji, 2009) also showed no
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significant difference (p>0.05) in the Fe(III) to Fe (II) reducing capacity of Polygonum minus
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extract and butylated hydroxyanisole (BHA), indeed, it was higher compared to butylated
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hydroxytoluene (BHT). Furthermore, the incorporation of Polygonum minus in duck
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meatballs was proven to reduce the lipid oxidation process (Nurul, Ruzita, & Aronal, 2010).
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ACCEPTED MANUSCRIPT Zingiber officinale is widely used in various food and beverages as a flavoring agent
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and for its health benefits. The pungent properties of Zingiber officinale (gingerols and
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shogaols) and other compounds, such as polyphenols, ascorbic acid, beta-carotene and
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flavonoids, have shown antioxidant activities (Aruoma et al., 1997; Ghasemzadeh, Jaafar, &
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Rahmat, 2010; Stoilova, Krastanov, Stoyanova, Denev, & Gargova, 2007). Murcia et al.
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(2004) reported that a 5% water extract of Zingiber officinale had almost similar antioxidant
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activity against lipid peroxidation when compared to BHT.
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Curcuma longa is an important spice used in curries as a colorant and flavoring agent
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(Chang, Jong, Huang, Nien, & Changa, 2006). Curcuma longa consists of three groups of
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Curcuminoids including curcumin, demethoxycurcumin, and bisdemethoxycurcumin.
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Curcumin, which makes up 90% of the curcuminoid content, is a lipohilic polyphenol that is
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slightly insoluble in water (Wang et al., 1997) and is responsible for the yellow color of
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Curcuma longa. Previous researches (Ishita, Kaushik, Uday, & Ranjit, 2004; Sharma,
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Gescher, & Steward, 2005; Cousins, Adelberg, Chen, & Rieck, 2007) found that the
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antioxidant activity of Curcuma longa is due to the polyphenolic compounds, such as
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curcuminoids, beta-carotene, caffeic acid, eugenol and protocatechuic acid.
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Nowadays, egg tofu is becoming popular among Asians. Egg tofu, which is also
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known as “Japanese tofu”, is a savory tofu made from soymilk, fresh egg and coagulating
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agent. The production of herbal egg tofu by incorporating Polygonum minus, Zingiber
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officinale and Curcuma longa in the egg tofu formulation is expected to enhance the
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antioxidant properties of egg tofu. By consuming herbal egg tofu, consumers can increase the
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natural antioxidant intake in their diet. However, the acceptability of the herbal egg tofu
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depends on the effects of the herbs and spices on the physical, texture and sensory
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characteristics. Therefore, the aim of this study is to determine the effects of Polygonum
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minus, Zingiber officinale and Curcuma longa on the physical, antioxidant and sensory
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properties of egg tofu and to optimize the best formulation of herbal egg tofu by using the
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response surface methodology (RSM).
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2. Materials and Methods 2.1 Materials
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Yellow soybeans (Canada), glucono-delta-lacton (GDL) and corn starch were obtained from
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Yummy’s Bakery Sdn. Bhd. (Selangor, Malaysia). Carrageenan powder was obtained from
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Omigel Sdn. Bhd. (Sabah, Malaysia), and gum arabic was obtained from Natural Prebiotics
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Sdn. Bhd. Selangor, Malaysia. Grade A eggs were obtained from Giant hypermarket
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(Selangor, Malaysia), while fresh Polygonum minus, Zingiber officinale and Curcuma longa
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were purchased from a local market in Selangor. Folin-Ciocalteu’s (FC) reagent was obtained
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from Merck (Darmstadt, Germany). Sodium carbonate, gallic acid, 2,2-diphenyl-1-
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picrylhydrazyl (DPPH), 2,4,6,-Tris (1-pyridyl)-5-triazine (TPTZ) and 2,2'-azino-bis 3-
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ethylbenzothiazoline-6-sulfonic acid (ABTS) were purchased from Sigma (Steinheim,
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Germany) and ferrous sulfate was obtained from R&M Chemicals (Essex, UK).
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2.2 Experimental design
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The response surface methodology (RSM) was applied to determine the experimental design,
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and the formulations of herbal egg tofu were selected according to the mixture design model
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“simplex-centroid’. In this study, the mixture components comprised three independent
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variables: Polygonum minus (X1), Curcuma longa (X2) and Zingiber officinale (X3). The
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mixture of these three components in egg tofu formulations at different ratios is shown in
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Table 1. The dependent variables were color (L (lightness), a (red) and b (yellow)), texture
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profile (hardness, cohesiveness, springiness, firmness and chewiness), total phenolic content
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(TPC), antioxidant activities (FRAP, ABTS and DPPH assay) and sensory characteristics
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(color, aroma, taste, texture and overall acceptability).
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Soybean seeds were soaked in water, rinsed, ground with water at a bean: water ratio of 1:3
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and filtered using muslin cloth. The slurry was cooked at 100oC for 15 min. Egg tofu was then
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prepared from a mixture of soymilk and fresh egg (2:1). Firstly, carrageenan (0.12% w/w),
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gum arabic (0.61% w/w) and corn starch (2.0% w/w) were added to the soymilk and heated to
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80oC with continuous stirring until all the ingredients were completely dissolved. The mixture
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was then cooled to 40oC followed by the addition of a filtered fresh whole egg and glucono-
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delta-lactone (GDL) (0.4% w/w). The mixture was mixed well. This was followed by the
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addition of Polygonum minus, Curcuma longa and Zingiber officinale ground beforehand
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using a blender (Waring Commercial 240V, Torrington, CT, USA) into the mixture. The
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herbal egg tofu was then poured into a plastic container (5.5 cm diameter and 4.0 cm high),
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and steamed at 90oC for 20 minutes. The herbal egg tofu samples were cooled to room
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temperature and stored at 4oC prior to analysis.
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2.4 Color measurement
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The color was measured using a colorimeter Model Minolta R-A70 Spectrophotometer
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(Japan). The sample was placed in a transparent plastic container and the Hunter values for L*
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(lightness), +a* (red), -a* (green), +b* (yellow) and –b* (blue) were determined for the
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surface of each sample. The mean value was obtained from three replicates of measurement.
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2.5 Texture profile analysis
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The texture profile of the samples was determined using a Texture Analyzer (Autograph
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AGS-J 500N universal testing machine, Shimadzu, Kyoto, Japan) fitted with 30 mm diameter
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cylinder probe, moving at a rate of 100mm/min. The penetration depth into the tofu sample (2
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cm x 2 cm) was set at 10 mm. Five replicate measurements were done to obtain the mean
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values for the textural characteristics investigated.
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2.6.1 Egg tofu extraction
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Egg tofu was freeze-dried and ground using a blender (Waring Commercial 240v Torrington,
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C.T, USA) at high speed for 30 sec, and kept in airtight bottles and stored at -20oC. The
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sample was extracted according to Kim and Lee (2002). The sample (10 g) was extracted with
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100 ml of 80% methanol and sonicated for 20 min. The sample was then filtered using filter
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paper (Sartorius grade 292) and rinsed with 50 ml 100% methanol. The residue was re-
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extracted with 50 ml of 80% methanol and the solvent was evaporated at 50oC. Subsequently,
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the sample was dissolved in 50 ml 100% methanol and made to volume (100 ml) with
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dionized water. The mixture was later centrifuged (Hermle GmbH, Germany) at 10000 RPM
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for 15 minutes. The supernatant was collected and stored at -20oC before analysis.
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2.6.2 Determination of the total phenolic content (TPC)
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The total phenolic content of sample extracts was determined using Folin-Ciocalteu reagent
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(Singleton & Rossi, 1965). Sample extracts (1 ml) were mixed with 5 ml Folin-Ciocalteu
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reagent. After 5 mins, 4 ml 7.5% sodium carbonate (Na2CO3) was added to the mixture and
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allowed to react in the dark for 2 hours at room temperature. Absorbance at 765nm was then
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measured
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Spectrophotometer, Winooski, USA). All the samples were measured in three replicates and
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the results were expressed as gallic acid equivalents (GAE) in milligrams per gram dry
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sample.
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2.6.3 FRAP assay
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The ferric reducing/antioxidant power (FRAP) assay was carried out according to the method
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of Benzie and Strain (1996). The FRAP reagent (10 mM TPTZ diluted with 40 mM HCl and
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20 mM iron (III) chloride solution in proportion of 10:1:1 (v/v), respectively) was prepared
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fresh and warmed to 37oC in the oven prior to use. Sample extracts (50 µl) were added to the
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ACCEPTED MANUSCRIPT FRAP reagent (1.5 ml) and mixed well. Absorbance at 593nm was measured after 4 minutes
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using a microplate reader spectrophotometer (EPOCH Microplate Spectrophotometer,
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Winooski, USA). The standard curve of iron (II) sulfate solutions (200, 400, 600, 800 and
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1000 mg/L) was prepared using a similar procedure and all the samples were measured in
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three replicates. The results were expressed as µmol Fe (II) /100 g dry weight sample.
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2.6.4 ABTS radical scavenging activity
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The 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activity
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was determined according to the method of Binsan et al. (2008) and Maizura, Aminah and
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Wan Aida (2013). The stock solution was prepared by mixing 7 mM ABTS solution and 2.45
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mM potassium persulfate solution in equal quantities, which was allowed to react for 16 hr in
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the dark at room temperature. The solution was then diluted with methanol to obtain an
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absorbance of 0.7 at 734nm using a microplate reader spectrophotometer (EPOCH Microplate
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Spectrophotometer, Winooski, USA). For the reaction process, the sample (100 µl) was mixed
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with ABTS solution (1000 µl) and was allowed to react for 10 minutes in the dark at room
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temperature.
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spectrophotometer. A standard curve was prepared using Trolox ranging from 5 to 300 µM.
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Samples were measured in three replicates and results were expressed as µmol TE /100 g dry
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weight sample.
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2.6.5 DPPH radical scavenging activity
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The radical scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) was determined
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using the method described by Akowuah, Ismail, Norhayati and Sadikun (2005). A
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methanolic solution of 0.1mM DPPH (200µl) was added into sample extracts (20µl) and
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mixed with methanol (80 µl). The mixture was allowed to react for 1 hour in the dark at room
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temperature.
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spectrophotometer (EPOCH Microplate Spectrophotometer, Winooski, USA). A standard
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three replicates and results were expressed as µmol TE /100 g dry weight sample.
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2.7 Sensory evaluation
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Thirty panelists (9 male and 21 female) aged between 20 to 39 years old who were students
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and staff of the Faculty of Science and Technology at Universiti Kebangsaan Malaysia,
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participated in the sensory evaluation test. Samples of egg tofu (5.5 cm diameter x 2.0 cm
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high) were taken from the refrigerator (4oC) and deep fat fried using cooking palm oil at
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180oC for 3 min. The fried samples (5.2 cm diameter x 1.8 cm high) were then cooled to room
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temperature before they were cut into three portions. Samples were served on white
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translucent plates, coded with 3-digit random numbers to be evaluated for appearance, color,
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aroma, taste, texture and overall acceptability using a 7-point hedonic scale (1= dislike very
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much and 7 like very much) (Aminah 2000). Distilled water was provided for the panelists to
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rinse their palates before and between samples. The evaluation was conducted in two sessions
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at individual booths of sensory room, with five or six samples being evaluated in a random
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order at each session.
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2.8 Statistical analysis
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Data were analyzed using Excel (Microsoft Inc.) and Statistical Package for Social Sciences
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(SPSS, version 17.0) software. Analysis of variance (ANOVA) was used to detect the
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significant difference (P<0.05) between samples. The mixture design and statistical analysis
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of data for egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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were Design Expert software package (version 6.0.10, State-Ease Inc., Minneapolis, MN,
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USA). The equation obtained using RSM for predicting response variables is as follows
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Y = β1X1 + β2X2 + β3X3 +β12X1 X2 + β13X1 X3 + β23X2 X3 + β123X1X2X3
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Where,
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Y = predicted response
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X2 = Curcuma longa
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X3 = Zingiber officinale
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β1, β2 danβ3 = Linear coefficient
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β12, β13dan β23 = Quadratic coefficient
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β123 = Cubic coefficient
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Statistical analysis of the models was evaluated with ANOVA. The criteria of the model used
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to generate the response surface plot should be significant (p<0.05), the lack-of-fit must not
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be significant (p>0.05) and the coefficient of determination R2 > 0.80.
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2.9 Optimization and model verification procedure
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Numerical optimization was performed to determine the optimum level of the independent
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variables (Polygonum minus, Curcuma longaand Zingiber officinale) that produced the
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desirable response variables of egg tofu. Contour plots for the response variables were
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created, and superimposed to obtain optimum formulation. Selected optimum formulation
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was used to calculate the predicted values of the response variables using prediction
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equations. For verification, the predicted value of the response variables obtained using
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Design Expert Software was statistically compared to the experimental value, which
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represents the mean of three replicates.
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3. Results and Discussion
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The prediction equation for color, texture, antioxidant capacity and sensory properties of
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herbal egg tofu is shown in Table 2. The statistical analysis showed that the model for color L
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(lightness) and + b (yellowness), springiness, total phenolic content, FRAP assay, ABTS and
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DPPH radical scavenging activity and sensory properties (color, taste and overall
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acceptability) were significant (p <0.05). The lack-of-fit showed no significant difference
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(p>0.05) and had a coefficient of determination R2 of more than 0.80. However, no significant
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ACCEPTED MANUSCRIPT difference (p>0.05) was observed for the model for color +a (redness), texture, such as
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hardness, cohesiveness, gumminess and chewiness and sensory characteristics, such as
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appearance, aroma and texture. This showed that the addition of Polygonum minus, Curcuma
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longa or Zingiber officinale in egg tofu formulation do not affect the response.
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3.1 Color
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The Hunter L values (lightness) and b values (yellowness) of ten formulations of egg tofu are
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shown in Table 3. The results showed that the addition of Curcuma longa contributed to the
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increase in the lightness (78.22) and yellowness (42.56) of egg tofu. However, the addition of
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Polygonum minus reduced the lightness (64.95) and yellowish (18.47) color of egg tofu. The
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mixture of Curcuma longa with Polygonum minus and Curcuma longa with Zingiber offanale
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had a positive effect and showed a significant (p<0.05) increase in the lightness of egg tofu
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(Table 2). However, the combination of Curcuma longa with Polygonum minus significantly
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(p<0.05) decreased the yellowness of egg tofu. The contour plots for the L value and b value
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of egg tofu are shown in Fig. 1. The L value on the counter decreased when approaching the
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Polygonum minus angle. This could be due to the Polygonum minus leaves changing color to
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brown and starting to float upon heating, ending up giving a dark brown color to the surface
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of the egg tofu once cooled. Increasing the contour line for the +b value when approaching
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the corner of Curcuma longa indicated that a yellow colored egg tofu was produced with the
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incorporation of Curcuma longa, which owes its yellow color to Curcuminoids.
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3.2 Texture
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The springiness of egg tofu containing Polygonum minus, Curcuma longa or Zingiber
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officinale and their combinations were between 0.93-1.57 mm (Table 3). Springiness is the
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rate at which a material when subjected to pressure will return to its original shape after
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pressure is released (Yuan & Chang 2007). Table 2 showed that, combination of Polygonum
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minus and Curcuma longa significantly (p<0.05) reduced the springiness of egg tofu. The
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the springiness values on the contour lines increased when approaching the corners of
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Polygonum minus. This could be attributed to the lower density of Polygonum minus as
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compared to Curcuma longa and Zingiber officinale, which caused it to float on the surface,
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and thus, does not interfere with the internal structure of the egg tofu. Consequently, when
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pressure is applied, egg tofu with Polygonum minus had better ability to return to its original
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shape than the egg tofu containing Curcuma longa and Zingiber officinale. The additions of
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Polygonum minus also resulted in a stronger surface of the egg tofu, thereby increasing its
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springiness compared to the control egg tofu (i.e. without herbal addition).
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3.3 Total phenolic content (TPC) and antioxidant activity
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Ten formulations of egg tofu containing Polygonum minus, Curcuma longa or Zingiber
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officinale and their combinations had a TPC of between 85.3 and 213.7 mgGAE/100 g dry
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weights sample (Table 3). Previous studies have reported that Polygonum minus (Maizura,
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Aminah, & Wan Aida, 2010), Curcuma longa (Ishita, Kaushik, Uday, & Ranjit, 2004;
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Sharma, Gescher, & Steward, 2005) and Zingiber officinale (Jeffery et al., 2003) exhibited a
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positive correlation between TPC and antioxidant activity. The results showed that, egg tofu
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containing Curcuma longa (formulation 2) had the highest TPC (213.7 mgGAE/100g dry
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sample weight) compared to the formulations containing Polygonum minus or Zingiber
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officinale. These results are consistent with previous research, which reported that the TPC in
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Polygonum minus was higher compared to the TPC in Zingiber officinale (Cai, Luo, Sun, &
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Corke, 2004; Surveswaran, Cai, Corke, & Sun, 2007; Tangkanakul et al., 2009). However, the
268
addition of Polygonum minus, Curcuma longa or Zingiber officinale had a positive and
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significant (p<0.05) linear effect on the increase in the TPC (Table 2). Figure 3 shows the
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contour plots for the TPC of egg tofu containing Polygonum minus, Curcuma longa or
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Zingiber officinale and their combinations. The TPC value of the contour line increased when
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approaching the Curcuma longa angle. This suggests that Curcuma longa is a major
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contributor to the increase of the TPC in egg tofu compared to Polygonum minus and Zingiber
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officinale. The antioxidant activity of egg tofu was determined using Ferric reducing/antioxidant
276
power (FRAP) assay, which is based on a reduction of Ferum (III) to Ferum (II) through the
277
donation of electrons (Benzie & Strain 1996). In the FRAP assay, the antioxidant activity of
278
egg tofu containing Curcuma longa (Formulation 2) was found to be the highest (3464.40
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µmol Fe(II)/100g dry weight sample) (Table 3). Conversely, the antioxidant activity of egg
280
tofu containing Zingiber officinale (formulation 3) was the lowest (2343.l6 µmol Fe (II)/100 g
281
dry weight sample). A previous study also showed higher antioxidant activity for Curcuma
282
longa (3.76 µmol TE/g dry weight sample) compared to the antioxidant activity of Zingiber
283
officinale (1.76 µmol TE/g dry sample weight) (Surveswaran, Cai, Corke, & Sun, 2007). The
284
antioxidant activity of egg tofu on the contour line increased when pointing to corner of
285
Polygonum minus and Curcuma longa (Fig. 4). This indicated Polygonum minus and
286
Curcuma longa as the contributor to the increase in antioxidant activity of egg tofu in FRAP
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assay.
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The antioxidant activity of egg tofu was also determined through scavenging of free
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radical 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS). The results showed that
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the addition of Polygonum minus, Curcuma longa or Zingiber officinale had a significant
291
(p<0.05) effect on increasing the antioxidant activity of egg tofu (Table 2). The contour plot
292
of the antioxidant activity for egg tofu in ABTS assay is shown in Fig. 5. The scavenging
293
activity of egg tofu on free radical ABTS increased when directing the corners of Polygonum
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minus, Curcuma longa or Zingiber officinale. However, the combination of all three
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components decreased (p<0.05) the antioxidant activity of egg tofu. This could be due to the
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amount of each component (Polygonum minus, Curcuma longa and Zingiber officinale) being
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insufficient to contribute to an increase in the antioxidant activity of egg tofu. DPPH (2,2-diphenyl-1-picrylhydrazyl) assay is a simple and precise method to
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determine the antioxidant activity of various plant extracts (Katalinic, Milos, Kulisic, & Jukic,
300
2006). The egg tofu containing Polygonum minus (Formulation 1), Curcuma longa
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(Formulation 2) and combination of Polygonum minus and Curcuma longa (Formulation 4)
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had 592.39, 596.70 and 594.11 µmol TE(II)/100g dry weight sample, respectively (Table 3).
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In contrast, egg tofu containing Zingiber officinale had the lowest antioxidant activity (463.19
304
µmol TE(II)/100g dry weight sample). A contour plot on the DPPH scavenging activity of egg
305
tofu is shown in Fig. 6. The DPPH scavenging activity on the contour lines increased when
306
pointing to the corner of Polygonum minus and Curcuma longa. This may be due to the
307
antioxidant activity of the flavonoids (rutin, catechin, quercetin, andkaempferol) found in
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Polygonum minus (Nanasombat & Teckchuen 2009) and several phenolic compounds
309
(curcuminoids, beta-carotene, cafficacid, protocatechuic acid) found in Curcuma longa
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(Ishita, Kaushik, Uday, & Ranjit, 2004; Sharma, Gescher, & Steward, 2005).
311
3.4 Sensory evaluation of egg tofu
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The results showed that the panelists prefer the cream color of the egg tofu containing
313
Zingiber officinale (Formulation 3) compared to other egg tofu formulations, as indicated by
314
the highest preference score of 5.5 (Table 3). The color score on the contour lines increased
315
when pointing to the corner of Zingiber officinale but decreased slightly when approaching
316
the Polygonum minus angle (Fig. 7). The panelists did not like the pale yellow color of egg
317
tofu containing Polygonum minus, or the brown color of its surface.
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Adding herbs and spices, such as basil, parsley and black pepper, enhanced the flavor
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of mayonnaise (Mihov, Nikovska, Nenov, & Slavchev, 2012). In this study, incorporation of
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herbs and spices in egg tofu affected the taste acceptability of the panelists. The taste scores
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ACCEPTED MANUSCRIPT for ten formulations of egg tofu were between 3.5 and 5.0 (dislike slightly to like slightly)
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(Table 3). The highest score was obtained for the taste of the egg tofu containing Zingiber
323
officinale (Formulation 3) while the lowest taste score was received for the egg tofu
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containing Curcuma longa (Formulation 2). The combination of Polygonum minus and
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Zingiber officinale or Curcuma longa and Zingiber officinale showed a negative effect
326
(P<0.05), and, hence, reduced the taste score (Table 2). The taste score on the contour lines
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increased when pointing to the Zingiber officinale corner (Fig. 8). This indicated that the
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panelists prefer the taste of Zingiber officinale in the egg tofu.
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The overall acceptability scores for ten formulations containing Polygonum minus,
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Curcuma longa or Zingiber officinale were in the range of 3.6 to 5.1 (Table 3). Egg tofu
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containing Zingiber officinale (Formulation 3) had the highest overall acceptability score of
332
5.1. The panelists also liked the egg tofu with a combination of Polygonum minus, Curcuma
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longa and Zingiber officinale, whereby a significant positive effect manifested itself as an
334
increase in the overall acceptability scores. The addition of Polygonum minus, Curcuma longa
335
or Zingiber officinale in egg tofu formulation contributed to the taste and a good antioxidant
336
capacity. However, the addition of the herbs and spices in large quantities affected the
337
panelists response to the sensory characteristics of egg tofu. This is because herbs and spices
338
contain polyphenolic compounds that can course spiciness, astringency, pungency and bitter
339
taste in food products (Zheng & Wang, 2001). Fig. 9 showed that the overall acceptability
340
score of egg tofu on contour lines increased when pointing to the corner of Zingiber officinale
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and declined when approaching the corners of Curcuma longa.
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3.5 Optimization of Herbal Egg Tofu Formulation and Model Verification
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The results revealed that an increase in the Polygonum minus and Curcuma longa content
344
enhanced the antioxidant capacity, but lowered the overall acceptability score of egg tofu.
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Therefore, in this study the formulation of egg tofu was optimized to obtain herbal egg tofu
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terms of the sensory characteristics. The region of optimum condition was created by
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superimposing the contour plots of the responses (springiness and sensory characteristics
349
(color, taste and overall acceptability)) in which the limits of each response were determined
350
(Fig. 10). The selection of any point within this region represented a combination of
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Polygonum minus, Curcuma longa and Zingiber officinale, which produced desirable
352
springiness and sensory characteristics.
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Point A, which is located in the overlapping area, was the optimum formulation of egg
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tofu. It contained 0.7% Polygonum minus, 0.5% Curcuma longa and 0.8% Zingiber officinale.
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Point B, which is located outside the overlapping region, contained 0.14% Polygonum minus,
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1.7% Curcuma longa and 0.16% Zingiber officinale. The predicted (from software) and
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experimental value for springiness and sensory characteristics (color, taste and overall
358
acceptability) are shown in Table 4. For verification purposes, egg tofu with the optimum
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formulation was produced and analyzed. The results from the analysis of variance showed no
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significant difference (p<0.05) between the experimental and predicted values for springiness,
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color, taste or overall acceptability at point A and point B. This indicated the validity and
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acceptability of the optimization equation obtained through the mixture design. The results
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also showed that the taste and overall acceptability scores for the egg tofu at point A were
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significantly (p<0.05) higher compared to the score for the egg tofu at point B.
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4. Conclusion
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An increase in Curcuma longa content increased the L value (brightness) and +b value
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(yellowness) of egg tofu. An increase in the Polygonum minus content, significantly (p<0.05)
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increased the springiness of the egg tofu. Curcuma longa is the major contributor to the
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increase in TPC and antioxidant activity of egg tofu. The sensory evaluation results showed
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that the panelists preferred the color, taste and overall acceptability of egg tofu containing
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minus, 0.5% Curcuma longa and 0.8% Zingiber officinale with springiness, color, taste and
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overall acceptability was 0.98mm, 4.9, 4.6 and 4.8, respectively. There were no significant
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differences (p>0.05) between the predicted values and experimental values, therefore the
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optimization equation obtained by mixture design method was acceptable.
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The usage of egg tofu in various types of cuisine is popular among Asians.
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Incorporating of herbal not only produce egg tofu with higher antioxidant activity, but also
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can provide several colors, aromas and tastes which is more attractive. In the future research,
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more formulation of herbal egg tofu with different types of herbal at several forms such as
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fresh, powder or extract should be developed to determine their effects on the physical
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chemical properties, sensory attributes characteristics and consumer acceptability.
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Acknowledgements
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The researchers would like to express their gratitude to Universiti Kebangsaan Malaysia for
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their financial support (UKM-GUP grant-NBT-08-27-103 and UKM-OUP grant-NBT-27-
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133/2) for this research as well as Universiti Sains Malaysia for the financial support for the
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first author.
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TABLES
Table 1: Mixture of Polygonum minus, Curcuma longa and Zingiber officinale in egg tofu formulations
4 5 6 7 8 9 10
SC
0 0 1 0 0.5 0 0.5 0.33 0.17 0.67 0.17
X3 (zingiber officinale) 0 0 0 1 0 0.5 0.5 0.33 0.17 0.17 0.67
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0 1 0 0 0.5 0.5 0 0.33 0.67 0.17 0.17
X2 (Curcuma longa)
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Ingredient proportion X1 (Polygonum minus)
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ABTS DPPH Sensory attributes Appearance colour Aroma Taste Texture Overall acceptability 14 15
Lack of fit
R2 Value
<0.0001 0.3025 <0.0001
0.1432 0.5150 0.1367
0.98 0.56 0.97
Y = 1.51X1* + 1.10X2* + 1.07X3* – 1.44X1X2* – 0.39X1X3 – 0.71X2X3 Y = 4.25X1 + 3.85X2 + 4.64X3 Y = 2.74X1* + 2.38X2* + 3.10X3* - 2.94X1X2 – 1.89X1X3* – 0.06X2X3* Y = 12.67X1* + 9.81X2* + 18.50X3* - 18.54X1X2 – 8.39X1X3* – 9.22X2X3* Y = 22.62X1* + 9.56X2* + 14.52X3* -37.35X1X2 – 31.32X1X3* – 3.72X2X3*
0.0066 0.5075 0.1804 0.2327 0.0506
0.6055 0.0192 0.0204 0.0003 0.0002
0.83 0.12 0.56 0.52 0.70
Y = 103.02X1* + 213.21X2* + 89.25X3* Y = 3389.31X1* + 3402.97X2* + 2343.04X3* + 136.09X1X2 – 133.85X1X3 – 651.58X2X3 – 7641.11X1X2X3* Y = 1978.58X1* + 1985.79X2* + 1884.05X3* -0.44X1X2 – 144.25X1X3 – 66.99X2X3 – 2937.10X1X2X3* Y = 598.02X1* + 603.25X2* + 465.36X3*
<0.0001 <0.0001
0.0603 0.6145
0.88 0.98
0.0153
0.0790
0.84
<0.0001
0.2502
0.96
0.1302 0.0001 0.6337 0.0006 0.2907 0.0021
0.9274 0.0802 0.9865 0.2671 0.0413 0.0698
0.31 0.80 0.10 0.94 0.57 0.91
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Y = 64.34X1* + 78.29X2* + 79.49X3* + 21.36X1X2* + 11.00X1X3 + 14.03X2X3* – 81.19X1X2X3* Y = 2.92 + 0.40X2 + 2.60X3 – 2.42 X1X2 – 1.62 X1X3 – 7.72 X2X3 – 119.42 X1X2X3 Y= 18.65X1* + 43.31X2* + 31.82X3* – 26.62X1X2* + 12.34X1X3 – 5.02X2X3
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Colour L value (Lightness) a + value (Redness) b + value (Yellowness) Texture Springiness Hardness Cohesiveness Gumminess Chewiness Antioxidant capacity TPC FRAP
Model (P<0.05)
Equation
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Parameter
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Table 2: Predicted regression equation coefficient in actual terms
Y = 4.65X1* + 5.06X2* + 5.09X3* Y = 4.39X1* + 4.71X2* + 5.43X3* Y = 4.86X1* + 4.64X2* + 4.70X3* Y= 4.26X1* + 3.64X2* + 4.99X3* + 0.60X1X2 – 1.71X1X3* – 1.27X2X3* + 13.69X1X2X3* Y = 4.26X1* + 4.26X2* + 4.66X3* + 0.06X1X2 – 0.76X1X3* – 0.90X2X3 + 13.73X1X2X3* Y = 4.60X1* + 3.79X2* + 5.07X3* + 0.16X1X2 – 2.19X1X3* – 0.54X2X3 + 14.01X1X2X3*
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*Significant difference at p<0.05. X1 = Polygonum minus, X2= Curcuma longa and X3 = Zingiber officinale.
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Table 3: Experiment results for colour, springiness, antioxidant capacity and sensory attributes
a
ABTS(µmol TE/100 g dry weight sample)
85.25 64.95 78.22 79.72 76.75 74.48 81.23 75.10 71.23 79.80 80.37
0.96 1.57 1.19 0.96 0.98 1.27 0.97 1.00 0.98 0.97 0.93
82.6 108.52 213.70 91.48 159.63 85.33 142.22 111.48 124.44 206.67 140.74
215.9 1963.33 1970.00 1886.67 1996.67 1910.00 1923.33 1856.67 1830.00 1893.33 1830.00
24.54 18.47 42.56 32.23 23.68 27.76 37.87 30.52 25.55 32.30 29.61
1134.0 3403.20 3464.40 2343.60 3436.80 2833.20 2778.00 2653.20 3012.00 3072.00 2538.00
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Antioxidant capacity TPC(mg FRAP(µmol Fe GAE/100 g (II)/ 100 g dry dry weight weight sample) sample)
DPPH (µmol TE/100 g dry weight sample) 422.62 592.39 596.70 463.19 594.11 529.08 544.05 553.83 588.36 587.21 528.80
Egg tofu formulation without addition of Polygonum minus, X2= Curcuma longa and X3 = Zingiber officinale
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Texture Springiness (mm)
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Controla 1 2 3 4 5 6 7 8 9 10
Hunter value L* +b* (lightness) (yellow)
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Formulation
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Sensory attributes Colour Taste Overall acceptability
4.8 4.5 4.6 5.5 4.7 4.8 5.2 4.7 4.7 5.0 4.8
5.2 4.4 3.5 5.0 4.2 4.2 4.0 4.7 4.2 4.0 4.6
5.0 4.7 3.6 5.1 4.2 4.4 4.3 4.9 4.3 4.4 4.5
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Table 4: Predicted and experimental values for the response variables (springiness and sensory attributes of colour, taste and overall acceptability) at point A and point B
Predicted values 0.99ab 4.7 a 3.8 b 3.9 b
Point B Experimental values 1.01 ± 0.03a 4.7 ± 0.4 a 3.9 ± 0.1 b 4.0 ± 0.1 b
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Springiness Colour Taste Overall acceptability
Predicted Values 0.98ab 4.9 a 4.6 a 4.8 a
Point A Experimental values 0.96 ± 0.03b 4.8 ± 0.2 a 4.5 ± 0.1 a 4.8 ± 0.1 a
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Response variables
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Mean score (n=3) ± standard deviation. Values with a different superscript letter within each row are significantly different (p<0.05)
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FIGURES
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Fig. 1. Contour plots for the Hunter value L (Lightness) and +b* (Yellowness) of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 2. Contour plots of springiness of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 3. Contour plots of TPC of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 4. Contour plots of FRAP of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 5. Contour plots of ABTS scavenging activity of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 6. Contour plots of DPPH scavenging activity of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 7. Contour plots of sensory evaluation for color of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 8. Contour plots of sensory evaluation for taste of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 9. Contour plots of sensory evaluation for overall acceptability of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 10. Superimposed plots of the response variables of springiness and sensory attributes (color, taste and overall acceptability) of egg tofu
ACCEPTED MANUSCRIPT Highlights Herbs and spices contributed to the higher antioxidant activity of egg tofu Herbs and spices addition affect the consumer acceptability of egg tofu Egg tofu containing Zingiber officinale is the most prefered by the consumer
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• • •
S0023-6438(15)30080-3
DOI:
10.1016/j.lwt.2015.07.062
Reference:
YFSTL 4856
To appear in:
LWT - Food Science and Technology
Received Date: 9 March 2015 Revised Date:
22 July 2015
Accepted Date: 23 July 2015
Please cite this article as: Maizura, M., Aminah, A., Wan Aida, W.M., Antioxidant capacity and consumer acceptability of herbal egg tofu, LWT - Food Science and Technology (2015), doi: 10.1016/ j.lwt.2015.07.062. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Antioxidant capacity and consumer acceptability of herbal egg tofu
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Maizura, M.1,2 Aminah, A. 1* & Wan Aida, W.M.1 1
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School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor DE, Malaysia. 2
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School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia.
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Corresponding Author: Email: [email protected] Phone: +603-8921 5990/5963 Fax: +603-89213232
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Abstract
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A mixture design was used to optimize the herbal egg tofu formulation containing Polygonum
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minus, Curcuma longa and Zingiber officinale. The effects of the herbs on the total phenolic
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content (TPC), ferric reducing antioxidant power (FRAP) assay and scavenging activity 2,2-
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diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid
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(ABTS), texture profile (hardness, springiness, cohesiveness, gumminess and chewiness) and
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consumer preference on sensory characteristics (appearance, color, aroma, taste, texture and
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overall acceptability) of the herbal egg tofu were investigated. An increase in Curcuma longa
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content produced egg tofu with significantly higher (p<0.05) TPC and antioxidant activity
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(FRAP, ABTS and DPPH assay), but a significantly lower score for overall acceptability. An
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increase in the Polygonum minus content significantly (p<0.05) increased the springiness of
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the egg tofu. The optimum formulation of the egg tofu was determined by overlapping the
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contour plot related to sensory characteristics (color, taste and overall acceptability) and
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springiness that formed the region with optimum value. The results showed that the optimum
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predicted response value for color, taste, overall acceptability and springiness were 4.9, 4.6,
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4.8 and 0.96 mm, respectively, which were obtained from a combination of 0.7% Polygonum
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minus, 0.5% Curcuma longa and 0.8% Zingiber officinale.
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Keywords: Herbal egg tofu, antioxidant capacity, sensory analysis, optimization, response
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surface methodology (RSM), mixture design
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1. Introduction Herbs and spices have been added to food since ancient times, not only as a flavoring agent,
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and food preservative, but also as an excellent source of natural antioxidants. Antioxidant
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activities of herbs and spices have been widely studied (Hinneburg, Damien Dorman, &
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Hiltunen, 2006; Kumar, Nayaka, Dharmesh, & Salimath, 2006; Cousins, Adelberg, Chen, &
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Rieck, 2007) and the increasing use of herbs and spices as natural antioxidants in food is
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attributed to low cost and consumer’s concern about the safety of synthetic antioxidants
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(Suhaj, 2006; Yanishlieva, Marinova, & Pokorný, 2006). The incorporation of herbs and
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spices in food products, such as meat (Han & Rhee, 2005; Naveena, Muthukumar, Sen, Babji,
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& Murthy, 2006), fish, yoghurt (Burt, 2004) and dairy products (Viluda-Martos, Ruiz-
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Navajas, Fernandez-Lopez, & Angel Perez-Alvarez, 2008) has been reported. Authentic Asian
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cuisine demands the use of many fresh herbs and spices, as well as in the form of extracts and
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powders. This includes Polygonum minus, Curcuma longa and Zingiber officinale.
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Polygonum minus is usually eaten raw or added in cooking. It is known as a medicinal
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plant with natural antioxidants (Wasman Qader, Abdulla, Chua, & Hamdan, 2012). Phenolic
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compounds extracted from Polygonum minus exhibited antioxidant activities (Huda-Faujan,
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Noriham, Norrakiah, & Babji, 2007; Maizura, Aminah, & Wan Aida, 2010). In addition,
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previous research (Huda-Faujan, Noriham, Norrakiah, & Babji, 2009) also showed no
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significant difference (p>0.05) in the Fe(III) to Fe (II) reducing capacity of Polygonum minus
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extract and butylated hydroxyanisole (BHA), indeed, it was higher compared to butylated
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hydroxytoluene (BHT). Furthermore, the incorporation of Polygonum minus in duck
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meatballs was proven to reduce the lipid oxidation process (Nurul, Ruzita, & Aronal, 2010).
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ACCEPTED MANUSCRIPT Zingiber officinale is widely used in various food and beverages as a flavoring agent
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and for its health benefits. The pungent properties of Zingiber officinale (gingerols and
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shogaols) and other compounds, such as polyphenols, ascorbic acid, beta-carotene and
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flavonoids, have shown antioxidant activities (Aruoma et al., 1997; Ghasemzadeh, Jaafar, &
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Rahmat, 2010; Stoilova, Krastanov, Stoyanova, Denev, & Gargova, 2007). Murcia et al.
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(2004) reported that a 5% water extract of Zingiber officinale had almost similar antioxidant
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activity against lipid peroxidation when compared to BHT.
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Curcuma longa is an important spice used in curries as a colorant and flavoring agent
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(Chang, Jong, Huang, Nien, & Changa, 2006). Curcuma longa consists of three groups of
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Curcuminoids including curcumin, demethoxycurcumin, and bisdemethoxycurcumin.
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Curcumin, which makes up 90% of the curcuminoid content, is a lipohilic polyphenol that is
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slightly insoluble in water (Wang et al., 1997) and is responsible for the yellow color of
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Curcuma longa. Previous researches (Ishita, Kaushik, Uday, & Ranjit, 2004; Sharma,
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Gescher, & Steward, 2005; Cousins, Adelberg, Chen, & Rieck, 2007) found that the
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antioxidant activity of Curcuma longa is due to the polyphenolic compounds, such as
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curcuminoids, beta-carotene, caffeic acid, eugenol and protocatechuic acid.
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Nowadays, egg tofu is becoming popular among Asians. Egg tofu, which is also
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known as “Japanese tofu”, is a savory tofu made from soymilk, fresh egg and coagulating
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agent. The production of herbal egg tofu by incorporating Polygonum minus, Zingiber
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officinale and Curcuma longa in the egg tofu formulation is expected to enhance the
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antioxidant properties of egg tofu. By consuming herbal egg tofu, consumers can increase the
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natural antioxidant intake in their diet. However, the acceptability of the herbal egg tofu
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depends on the effects of the herbs and spices on the physical, texture and sensory
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characteristics. Therefore, the aim of this study is to determine the effects of Polygonum
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minus, Zingiber officinale and Curcuma longa on the physical, antioxidant and sensory
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properties of egg tofu and to optimize the best formulation of herbal egg tofu by using the
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response surface methodology (RSM).
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2. Materials and Methods 2.1 Materials
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Yellow soybeans (Canada), glucono-delta-lacton (GDL) and corn starch were obtained from
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Yummy’s Bakery Sdn. Bhd. (Selangor, Malaysia). Carrageenan powder was obtained from
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Omigel Sdn. Bhd. (Sabah, Malaysia), and gum arabic was obtained from Natural Prebiotics
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Sdn. Bhd. Selangor, Malaysia. Grade A eggs were obtained from Giant hypermarket
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(Selangor, Malaysia), while fresh Polygonum minus, Zingiber officinale and Curcuma longa
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were purchased from a local market in Selangor. Folin-Ciocalteu’s (FC) reagent was obtained
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from Merck (Darmstadt, Germany). Sodium carbonate, gallic acid, 2,2-diphenyl-1-
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picrylhydrazyl (DPPH), 2,4,6,-Tris (1-pyridyl)-5-triazine (TPTZ) and 2,2'-azino-bis 3-
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ethylbenzothiazoline-6-sulfonic acid (ABTS) were purchased from Sigma (Steinheim,
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Germany) and ferrous sulfate was obtained from R&M Chemicals (Essex, UK).
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2.2 Experimental design
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The response surface methodology (RSM) was applied to determine the experimental design,
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and the formulations of herbal egg tofu were selected according to the mixture design model
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“simplex-centroid’. In this study, the mixture components comprised three independent
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variables: Polygonum minus (X1), Curcuma longa (X2) and Zingiber officinale (X3). The
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mixture of these three components in egg tofu formulations at different ratios is shown in
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Table 1. The dependent variables were color (L (lightness), a (red) and b (yellow)), texture
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profile (hardness, cohesiveness, springiness, firmness and chewiness), total phenolic content
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(TPC), antioxidant activities (FRAP, ABTS and DPPH assay) and sensory characteristics
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(color, aroma, taste, texture and overall acceptability).
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Soybean seeds were soaked in water, rinsed, ground with water at a bean: water ratio of 1:3
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and filtered using muslin cloth. The slurry was cooked at 100oC for 15 min. Egg tofu was then
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prepared from a mixture of soymilk and fresh egg (2:1). Firstly, carrageenan (0.12% w/w),
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gum arabic (0.61% w/w) and corn starch (2.0% w/w) were added to the soymilk and heated to
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80oC with continuous stirring until all the ingredients were completely dissolved. The mixture
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was then cooled to 40oC followed by the addition of a filtered fresh whole egg and glucono-
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delta-lactone (GDL) (0.4% w/w). The mixture was mixed well. This was followed by the
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addition of Polygonum minus, Curcuma longa and Zingiber officinale ground beforehand
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using a blender (Waring Commercial 240V, Torrington, CT, USA) into the mixture. The
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herbal egg tofu was then poured into a plastic container (5.5 cm diameter and 4.0 cm high),
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and steamed at 90oC for 20 minutes. The herbal egg tofu samples were cooled to room
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temperature and stored at 4oC prior to analysis.
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2.4 Color measurement
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The color was measured using a colorimeter Model Minolta R-A70 Spectrophotometer
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(Japan). The sample was placed in a transparent plastic container and the Hunter values for L*
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(lightness), +a* (red), -a* (green), +b* (yellow) and –b* (blue) were determined for the
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surface of each sample. The mean value was obtained from three replicates of measurement.
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2.5 Texture profile analysis
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The texture profile of the samples was determined using a Texture Analyzer (Autograph
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AGS-J 500N universal testing machine, Shimadzu, Kyoto, Japan) fitted with 30 mm diameter
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cylinder probe, moving at a rate of 100mm/min. The penetration depth into the tofu sample (2
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cm x 2 cm) was set at 10 mm. Five replicate measurements were done to obtain the mean
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values for the textural characteristics investigated.
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2.6.1 Egg tofu extraction
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Egg tofu was freeze-dried and ground using a blender (Waring Commercial 240v Torrington,
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C.T, USA) at high speed for 30 sec, and kept in airtight bottles and stored at -20oC. The
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sample was extracted according to Kim and Lee (2002). The sample (10 g) was extracted with
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100 ml of 80% methanol and sonicated for 20 min. The sample was then filtered using filter
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paper (Sartorius grade 292) and rinsed with 50 ml 100% methanol. The residue was re-
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extracted with 50 ml of 80% methanol and the solvent was evaporated at 50oC. Subsequently,
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the sample was dissolved in 50 ml 100% methanol and made to volume (100 ml) with
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dionized water. The mixture was later centrifuged (Hermle GmbH, Germany) at 10000 RPM
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for 15 minutes. The supernatant was collected and stored at -20oC before analysis.
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2.6.2 Determination of the total phenolic content (TPC)
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The total phenolic content of sample extracts was determined using Folin-Ciocalteu reagent
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(Singleton & Rossi, 1965). Sample extracts (1 ml) were mixed with 5 ml Folin-Ciocalteu
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reagent. After 5 mins, 4 ml 7.5% sodium carbonate (Na2CO3) was added to the mixture and
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allowed to react in the dark for 2 hours at room temperature. Absorbance at 765nm was then
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measured
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Spectrophotometer, Winooski, USA). All the samples were measured in three replicates and
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the results were expressed as gallic acid equivalents (GAE) in milligrams per gram dry
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sample.
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2.6.3 FRAP assay
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The ferric reducing/antioxidant power (FRAP) assay was carried out according to the method
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of Benzie and Strain (1996). The FRAP reagent (10 mM TPTZ diluted with 40 mM HCl and
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20 mM iron (III) chloride solution in proportion of 10:1:1 (v/v), respectively) was prepared
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fresh and warmed to 37oC in the oven prior to use. Sample extracts (50 µl) were added to the
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ACCEPTED MANUSCRIPT FRAP reagent (1.5 ml) and mixed well. Absorbance at 593nm was measured after 4 minutes
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using a microplate reader spectrophotometer (EPOCH Microplate Spectrophotometer,
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Winooski, USA). The standard curve of iron (II) sulfate solutions (200, 400, 600, 800 and
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1000 mg/L) was prepared using a similar procedure and all the samples were measured in
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three replicates. The results were expressed as µmol Fe (II) /100 g dry weight sample.
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2.6.4 ABTS radical scavenging activity
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The 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activity
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was determined according to the method of Binsan et al. (2008) and Maizura, Aminah and
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Wan Aida (2013). The stock solution was prepared by mixing 7 mM ABTS solution and 2.45
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mM potassium persulfate solution in equal quantities, which was allowed to react for 16 hr in
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the dark at room temperature. The solution was then diluted with methanol to obtain an
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absorbance of 0.7 at 734nm using a microplate reader spectrophotometer (EPOCH Microplate
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Spectrophotometer, Winooski, USA). For the reaction process, the sample (100 µl) was mixed
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with ABTS solution (1000 µl) and was allowed to react for 10 minutes in the dark at room
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temperature.
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spectrophotometer. A standard curve was prepared using Trolox ranging from 5 to 300 µM.
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Samples were measured in three replicates and results were expressed as µmol TE /100 g dry
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weight sample.
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2.6.5 DPPH radical scavenging activity
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The radical scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) was determined
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using the method described by Akowuah, Ismail, Norhayati and Sadikun (2005). A
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methanolic solution of 0.1mM DPPH (200µl) was added into sample extracts (20µl) and
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mixed with methanol (80 µl). The mixture was allowed to react for 1 hour in the dark at room
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temperature.
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spectrophotometer (EPOCH Microplate Spectrophotometer, Winooski, USA). A standard
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three replicates and results were expressed as µmol TE /100 g dry weight sample.
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2.7 Sensory evaluation
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Thirty panelists (9 male and 21 female) aged between 20 to 39 years old who were students
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and staff of the Faculty of Science and Technology at Universiti Kebangsaan Malaysia,
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participated in the sensory evaluation test. Samples of egg tofu (5.5 cm diameter x 2.0 cm
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high) were taken from the refrigerator (4oC) and deep fat fried using cooking palm oil at
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180oC for 3 min. The fried samples (5.2 cm diameter x 1.8 cm high) were then cooled to room
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temperature before they were cut into three portions. Samples were served on white
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translucent plates, coded with 3-digit random numbers to be evaluated for appearance, color,
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aroma, taste, texture and overall acceptability using a 7-point hedonic scale (1= dislike very
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much and 7 like very much) (Aminah 2000). Distilled water was provided for the panelists to
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rinse their palates before and between samples. The evaluation was conducted in two sessions
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at individual booths of sensory room, with five or six samples being evaluated in a random
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order at each session.
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2.8 Statistical analysis
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Data were analyzed using Excel (Microsoft Inc.) and Statistical Package for Social Sciences
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(SPSS, version 17.0) software. Analysis of variance (ANOVA) was used to detect the
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significant difference (P<0.05) between samples. The mixture design and statistical analysis
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of data for egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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were Design Expert software package (version 6.0.10, State-Ease Inc., Minneapolis, MN,
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USA). The equation obtained using RSM for predicting response variables is as follows
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Y = β1X1 + β2X2 + β3X3 +β12X1 X2 + β13X1 X3 + β23X2 X3 + β123X1X2X3
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Where,
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Y = predicted response
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X2 = Curcuma longa
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X3 = Zingiber officinale
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β1, β2 danβ3 = Linear coefficient
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β12, β13dan β23 = Quadratic coefficient
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β123 = Cubic coefficient
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Statistical analysis of the models was evaluated with ANOVA. The criteria of the model used
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to generate the response surface plot should be significant (p<0.05), the lack-of-fit must not
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be significant (p>0.05) and the coefficient of determination R2 > 0.80.
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2.9 Optimization and model verification procedure
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Numerical optimization was performed to determine the optimum level of the independent
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variables (Polygonum minus, Curcuma longaand Zingiber officinale) that produced the
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desirable response variables of egg tofu. Contour plots for the response variables were
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created, and superimposed to obtain optimum formulation. Selected optimum formulation
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was used to calculate the predicted values of the response variables using prediction
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equations. For verification, the predicted value of the response variables obtained using
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Design Expert Software was statistically compared to the experimental value, which
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represents the mean of three replicates.
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3. Results and Discussion
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The prediction equation for color, texture, antioxidant capacity and sensory properties of
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herbal egg tofu is shown in Table 2. The statistical analysis showed that the model for color L
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(lightness) and + b (yellowness), springiness, total phenolic content, FRAP assay, ABTS and
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DPPH radical scavenging activity and sensory properties (color, taste and overall
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acceptability) were significant (p <0.05). The lack-of-fit showed no significant difference
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(p>0.05) and had a coefficient of determination R2 of more than 0.80. However, no significant
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ACCEPTED MANUSCRIPT difference (p>0.05) was observed for the model for color +a (redness), texture, such as
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hardness, cohesiveness, gumminess and chewiness and sensory characteristics, such as
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appearance, aroma and texture. This showed that the addition of Polygonum minus, Curcuma
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longa or Zingiber officinale in egg tofu formulation do not affect the response.
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3.1 Color
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The Hunter L values (lightness) and b values (yellowness) of ten formulations of egg tofu are
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shown in Table 3. The results showed that the addition of Curcuma longa contributed to the
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increase in the lightness (78.22) and yellowness (42.56) of egg tofu. However, the addition of
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Polygonum minus reduced the lightness (64.95) and yellowish (18.47) color of egg tofu. The
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mixture of Curcuma longa with Polygonum minus and Curcuma longa with Zingiber offanale
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had a positive effect and showed a significant (p<0.05) increase in the lightness of egg tofu
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(Table 2). However, the combination of Curcuma longa with Polygonum minus significantly
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(p<0.05) decreased the yellowness of egg tofu. The contour plots for the L value and b value
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of egg tofu are shown in Fig. 1. The L value on the counter decreased when approaching the
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Polygonum minus angle. This could be due to the Polygonum minus leaves changing color to
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brown and starting to float upon heating, ending up giving a dark brown color to the surface
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of the egg tofu once cooled. Increasing the contour line for the +b value when approaching
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the corner of Curcuma longa indicated that a yellow colored egg tofu was produced with the
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incorporation of Curcuma longa, which owes its yellow color to Curcuminoids.
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3.2 Texture
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The springiness of egg tofu containing Polygonum minus, Curcuma longa or Zingiber
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officinale and their combinations were between 0.93-1.57 mm (Table 3). Springiness is the
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rate at which a material when subjected to pressure will return to its original shape after
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pressure is released (Yuan & Chang 2007). Table 2 showed that, combination of Polygonum
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minus and Curcuma longa significantly (p<0.05) reduced the springiness of egg tofu. The
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the springiness values on the contour lines increased when approaching the corners of
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Polygonum minus. This could be attributed to the lower density of Polygonum minus as
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compared to Curcuma longa and Zingiber officinale, which caused it to float on the surface,
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and thus, does not interfere with the internal structure of the egg tofu. Consequently, when
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pressure is applied, egg tofu with Polygonum minus had better ability to return to its original
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shape than the egg tofu containing Curcuma longa and Zingiber officinale. The additions of
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Polygonum minus also resulted in a stronger surface of the egg tofu, thereby increasing its
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springiness compared to the control egg tofu (i.e. without herbal addition).
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3.3 Total phenolic content (TPC) and antioxidant activity
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Ten formulations of egg tofu containing Polygonum minus, Curcuma longa or Zingiber
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officinale and their combinations had a TPC of between 85.3 and 213.7 mgGAE/100 g dry
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weights sample (Table 3). Previous studies have reported that Polygonum minus (Maizura,
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Aminah, & Wan Aida, 2010), Curcuma longa (Ishita, Kaushik, Uday, & Ranjit, 2004;
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Sharma, Gescher, & Steward, 2005) and Zingiber officinale (Jeffery et al., 2003) exhibited a
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positive correlation between TPC and antioxidant activity. The results showed that, egg tofu
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containing Curcuma longa (formulation 2) had the highest TPC (213.7 mgGAE/100g dry
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sample weight) compared to the formulations containing Polygonum minus or Zingiber
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officinale. These results are consistent with previous research, which reported that the TPC in
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Polygonum minus was higher compared to the TPC in Zingiber officinale (Cai, Luo, Sun, &
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Corke, 2004; Surveswaran, Cai, Corke, & Sun, 2007; Tangkanakul et al., 2009). However, the
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addition of Polygonum minus, Curcuma longa or Zingiber officinale had a positive and
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significant (p<0.05) linear effect on the increase in the TPC (Table 2). Figure 3 shows the
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contour plots for the TPC of egg tofu containing Polygonum minus, Curcuma longa or
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Zingiber officinale and their combinations. The TPC value of the contour line increased when
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approaching the Curcuma longa angle. This suggests that Curcuma longa is a major
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contributor to the increase of the TPC in egg tofu compared to Polygonum minus and Zingiber
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officinale. The antioxidant activity of egg tofu was determined using Ferric reducing/antioxidant
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power (FRAP) assay, which is based on a reduction of Ferum (III) to Ferum (II) through the
277
donation of electrons (Benzie & Strain 1996). In the FRAP assay, the antioxidant activity of
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egg tofu containing Curcuma longa (Formulation 2) was found to be the highest (3464.40
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µmol Fe(II)/100g dry weight sample) (Table 3). Conversely, the antioxidant activity of egg
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tofu containing Zingiber officinale (formulation 3) was the lowest (2343.l6 µmol Fe (II)/100 g
281
dry weight sample). A previous study also showed higher antioxidant activity for Curcuma
282
longa (3.76 µmol TE/g dry weight sample) compared to the antioxidant activity of Zingiber
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officinale (1.76 µmol TE/g dry sample weight) (Surveswaran, Cai, Corke, & Sun, 2007). The
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antioxidant activity of egg tofu on the contour line increased when pointing to corner of
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Polygonum minus and Curcuma longa (Fig. 4). This indicated Polygonum minus and
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Curcuma longa as the contributor to the increase in antioxidant activity of egg tofu in FRAP
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assay.
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The antioxidant activity of egg tofu was also determined through scavenging of free
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radical 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS). The results showed that
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the addition of Polygonum minus, Curcuma longa or Zingiber officinale had a significant
291
(p<0.05) effect on increasing the antioxidant activity of egg tofu (Table 2). The contour plot
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of the antioxidant activity for egg tofu in ABTS assay is shown in Fig. 5. The scavenging
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activity of egg tofu on free radical ABTS increased when directing the corners of Polygonum
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minus, Curcuma longa or Zingiber officinale. However, the combination of all three
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components decreased (p<0.05) the antioxidant activity of egg tofu. This could be due to the
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amount of each component (Polygonum minus, Curcuma longa and Zingiber officinale) being
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insufficient to contribute to an increase in the antioxidant activity of egg tofu. DPPH (2,2-diphenyl-1-picrylhydrazyl) assay is a simple and precise method to
299
determine the antioxidant activity of various plant extracts (Katalinic, Milos, Kulisic, & Jukic,
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2006). The egg tofu containing Polygonum minus (Formulation 1), Curcuma longa
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(Formulation 2) and combination of Polygonum minus and Curcuma longa (Formulation 4)
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had 592.39, 596.70 and 594.11 µmol TE(II)/100g dry weight sample, respectively (Table 3).
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In contrast, egg tofu containing Zingiber officinale had the lowest antioxidant activity (463.19
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µmol TE(II)/100g dry weight sample). A contour plot on the DPPH scavenging activity of egg
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tofu is shown in Fig. 6. The DPPH scavenging activity on the contour lines increased when
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pointing to the corner of Polygonum minus and Curcuma longa. This may be due to the
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antioxidant activity of the flavonoids (rutin, catechin, quercetin, andkaempferol) found in
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Polygonum minus (Nanasombat & Teckchuen 2009) and several phenolic compounds
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(curcuminoids, beta-carotene, cafficacid, protocatechuic acid) found in Curcuma longa
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(Ishita, Kaushik, Uday, & Ranjit, 2004; Sharma, Gescher, & Steward, 2005).
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3.4 Sensory evaluation of egg tofu
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The results showed that the panelists prefer the cream color of the egg tofu containing
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Zingiber officinale (Formulation 3) compared to other egg tofu formulations, as indicated by
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the highest preference score of 5.5 (Table 3). The color score on the contour lines increased
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when pointing to the corner of Zingiber officinale but decreased slightly when approaching
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the Polygonum minus angle (Fig. 7). The panelists did not like the pale yellow color of egg
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tofu containing Polygonum minus, or the brown color of its surface.
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Adding herbs and spices, such as basil, parsley and black pepper, enhanced the flavor
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of mayonnaise (Mihov, Nikovska, Nenov, & Slavchev, 2012). In this study, incorporation of
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herbs and spices in egg tofu affected the taste acceptability of the panelists. The taste scores
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ACCEPTED MANUSCRIPT for ten formulations of egg tofu were between 3.5 and 5.0 (dislike slightly to like slightly)
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(Table 3). The highest score was obtained for the taste of the egg tofu containing Zingiber
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officinale (Formulation 3) while the lowest taste score was received for the egg tofu
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containing Curcuma longa (Formulation 2). The combination of Polygonum minus and
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Zingiber officinale or Curcuma longa and Zingiber officinale showed a negative effect
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(P<0.05), and, hence, reduced the taste score (Table 2). The taste score on the contour lines
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increased when pointing to the Zingiber officinale corner (Fig. 8). This indicated that the
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panelists prefer the taste of Zingiber officinale in the egg tofu.
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The overall acceptability scores for ten formulations containing Polygonum minus,
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Curcuma longa or Zingiber officinale were in the range of 3.6 to 5.1 (Table 3). Egg tofu
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containing Zingiber officinale (Formulation 3) had the highest overall acceptability score of
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5.1. The panelists also liked the egg tofu with a combination of Polygonum minus, Curcuma
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longa and Zingiber officinale, whereby a significant positive effect manifested itself as an
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increase in the overall acceptability scores. The addition of Polygonum minus, Curcuma longa
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or Zingiber officinale in egg tofu formulation contributed to the taste and a good antioxidant
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capacity. However, the addition of the herbs and spices in large quantities affected the
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panelists response to the sensory characteristics of egg tofu. This is because herbs and spices
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contain polyphenolic compounds that can course spiciness, astringency, pungency and bitter
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taste in food products (Zheng & Wang, 2001). Fig. 9 showed that the overall acceptability
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score of egg tofu on contour lines increased when pointing to the corner of Zingiber officinale
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and declined when approaching the corners of Curcuma longa.
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3.5 Optimization of Herbal Egg Tofu Formulation and Model Verification
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The results revealed that an increase in the Polygonum minus and Curcuma longa content
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enhanced the antioxidant capacity, but lowered the overall acceptability score of egg tofu.
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Therefore, in this study the formulation of egg tofu was optimized to obtain herbal egg tofu
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terms of the sensory characteristics. The region of optimum condition was created by
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superimposing the contour plots of the responses (springiness and sensory characteristics
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(color, taste and overall acceptability)) in which the limits of each response were determined
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(Fig. 10). The selection of any point within this region represented a combination of
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Polygonum minus, Curcuma longa and Zingiber officinale, which produced desirable
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springiness and sensory characteristics.
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Point A, which is located in the overlapping area, was the optimum formulation of egg
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tofu. It contained 0.7% Polygonum minus, 0.5% Curcuma longa and 0.8% Zingiber officinale.
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Point B, which is located outside the overlapping region, contained 0.14% Polygonum minus,
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1.7% Curcuma longa and 0.16% Zingiber officinale. The predicted (from software) and
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experimental value for springiness and sensory characteristics (color, taste and overall
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acceptability) are shown in Table 4. For verification purposes, egg tofu with the optimum
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formulation was produced and analyzed. The results from the analysis of variance showed no
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significant difference (p<0.05) between the experimental and predicted values for springiness,
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color, taste or overall acceptability at point A and point B. This indicated the validity and
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acceptability of the optimization equation obtained through the mixture design. The results
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also showed that the taste and overall acceptability scores for the egg tofu at point A were
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significantly (p<0.05) higher compared to the score for the egg tofu at point B.
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4. Conclusion
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An increase in Curcuma longa content increased the L value (brightness) and +b value
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(yellowness) of egg tofu. An increase in the Polygonum minus content, significantly (p<0.05)
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increased the springiness of the egg tofu. Curcuma longa is the major contributor to the
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increase in TPC and antioxidant activity of egg tofu. The sensory evaluation results showed
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that the panelists preferred the color, taste and overall acceptability of egg tofu containing
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minus, 0.5% Curcuma longa and 0.8% Zingiber officinale with springiness, color, taste and
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overall acceptability was 0.98mm, 4.9, 4.6 and 4.8, respectively. There were no significant
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differences (p>0.05) between the predicted values and experimental values, therefore the
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optimization equation obtained by mixture design method was acceptable.
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The usage of egg tofu in various types of cuisine is popular among Asians.
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Incorporating of herbal not only produce egg tofu with higher antioxidant activity, but also
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can provide several colors, aromas and tastes which is more attractive. In the future research,
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more formulation of herbal egg tofu with different types of herbal at several forms such as
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fresh, powder or extract should be developed to determine their effects on the physical
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chemical properties, sensory attributes characteristics and consumer acceptability.
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Acknowledgements
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The researchers would like to express their gratitude to Universiti Kebangsaan Malaysia for
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their financial support (UKM-GUP grant-NBT-08-27-103 and UKM-OUP grant-NBT-27-
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133/2) for this research as well as Universiti Sains Malaysia for the financial support for the
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first author.
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TABLES
Table 1: Mixture of Polygonum minus, Curcuma longa and Zingiber officinale in egg tofu formulations
4 5 6 7 8 9 10
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0 0 1 0 0.5 0 0.5 0.33 0.17 0.67 0.17
X3 (zingiber officinale) 0 0 0 1 0 0.5 0.5 0.33 0.17 0.17 0.67
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0 1 0 0 0.5 0.5 0 0.33 0.67 0.17 0.17
X2 (Curcuma longa)
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Ingredient proportion X1 (Polygonum minus)
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ABTS DPPH Sensory attributes Appearance colour Aroma Taste Texture Overall acceptability 14 15
Lack of fit
R2 Value
<0.0001 0.3025 <0.0001
0.1432 0.5150 0.1367
0.98 0.56 0.97
Y = 1.51X1* + 1.10X2* + 1.07X3* – 1.44X1X2* – 0.39X1X3 – 0.71X2X3 Y = 4.25X1 + 3.85X2 + 4.64X3 Y = 2.74X1* + 2.38X2* + 3.10X3* - 2.94X1X2 – 1.89X1X3* – 0.06X2X3* Y = 12.67X1* + 9.81X2* + 18.50X3* - 18.54X1X2 – 8.39X1X3* – 9.22X2X3* Y = 22.62X1* + 9.56X2* + 14.52X3* -37.35X1X2 – 31.32X1X3* – 3.72X2X3*
0.0066 0.5075 0.1804 0.2327 0.0506
0.6055 0.0192 0.0204 0.0003 0.0002
0.83 0.12 0.56 0.52 0.70
Y = 103.02X1* + 213.21X2* + 89.25X3* Y = 3389.31X1* + 3402.97X2* + 2343.04X3* + 136.09X1X2 – 133.85X1X3 – 651.58X2X3 – 7641.11X1X2X3* Y = 1978.58X1* + 1985.79X2* + 1884.05X3* -0.44X1X2 – 144.25X1X3 – 66.99X2X3 – 2937.10X1X2X3* Y = 598.02X1* + 603.25X2* + 465.36X3*
<0.0001 <0.0001
0.0603 0.6145
0.88 0.98
0.0153
0.0790
0.84
<0.0001
0.2502
0.96
0.1302 0.0001 0.6337 0.0006 0.2907 0.0021
0.9274 0.0802 0.9865 0.2671 0.0413 0.0698
0.31 0.80 0.10 0.94 0.57 0.91
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Y = 64.34X1* + 78.29X2* + 79.49X3* + 21.36X1X2* + 11.00X1X3 + 14.03X2X3* – 81.19X1X2X3* Y = 2.92 + 0.40X2 + 2.60X3 – 2.42 X1X2 – 1.62 X1X3 – 7.72 X2X3 – 119.42 X1X2X3 Y= 18.65X1* + 43.31X2* + 31.82X3* – 26.62X1X2* + 12.34X1X3 – 5.02X2X3
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Colour L value (Lightness) a + value (Redness) b + value (Yellowness) Texture Springiness Hardness Cohesiveness Gumminess Chewiness Antioxidant capacity TPC FRAP
Model (P<0.05)
Equation
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Table 2: Predicted regression equation coefficient in actual terms
Y = 4.65X1* + 5.06X2* + 5.09X3* Y = 4.39X1* + 4.71X2* + 5.43X3* Y = 4.86X1* + 4.64X2* + 4.70X3* Y= 4.26X1* + 3.64X2* + 4.99X3* + 0.60X1X2 – 1.71X1X3* – 1.27X2X3* + 13.69X1X2X3* Y = 4.26X1* + 4.26X2* + 4.66X3* + 0.06X1X2 – 0.76X1X3* – 0.90X2X3 + 13.73X1X2X3* Y = 4.60X1* + 3.79X2* + 5.07X3* + 0.16X1X2 – 2.19X1X3* – 0.54X2X3 + 14.01X1X2X3*
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*Significant difference at p<0.05. X1 = Polygonum minus, X2= Curcuma longa and X3 = Zingiber officinale.
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Table 3: Experiment results for colour, springiness, antioxidant capacity and sensory attributes
a
ABTS(µmol TE/100 g dry weight sample)
85.25 64.95 78.22 79.72 76.75 74.48 81.23 75.10 71.23 79.80 80.37
0.96 1.57 1.19 0.96 0.98 1.27 0.97 1.00 0.98 0.97 0.93
82.6 108.52 213.70 91.48 159.63 85.33 142.22 111.48 124.44 206.67 140.74
215.9 1963.33 1970.00 1886.67 1996.67 1910.00 1923.33 1856.67 1830.00 1893.33 1830.00
24.54 18.47 42.56 32.23 23.68 27.76 37.87 30.52 25.55 32.30 29.61
1134.0 3403.20 3464.40 2343.60 3436.80 2833.20 2778.00 2653.20 3012.00 3072.00 2538.00
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Antioxidant capacity TPC(mg FRAP(µmol Fe GAE/100 g (II)/ 100 g dry dry weight weight sample) sample)
DPPH (µmol TE/100 g dry weight sample) 422.62 592.39 596.70 463.19 594.11 529.08 544.05 553.83 588.36 587.21 528.80
Egg tofu formulation without addition of Polygonum minus, X2= Curcuma longa and X3 = Zingiber officinale
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Texture Springiness (mm)
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Hunter value L* +b* (lightness) (yellow)
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Formulation
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Sensory attributes Colour Taste Overall acceptability
4.8 4.5 4.6 5.5 4.7 4.8 5.2 4.7 4.7 5.0 4.8
5.2 4.4 3.5 5.0 4.2 4.2 4.0 4.7 4.2 4.0 4.6
5.0 4.7 3.6 5.1 4.2 4.4 4.3 4.9 4.3 4.4 4.5
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Table 4: Predicted and experimental values for the response variables (springiness and sensory attributes of colour, taste and overall acceptability) at point A and point B
Predicted values 0.99ab 4.7 a 3.8 b 3.9 b
Point B Experimental values 1.01 ± 0.03a 4.7 ± 0.4 a 3.9 ± 0.1 b 4.0 ± 0.1 b
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Springiness Colour Taste Overall acceptability
Predicted Values 0.98ab 4.9 a 4.6 a 4.8 a
Point A Experimental values 0.96 ± 0.03b 4.8 ± 0.2 a 4.5 ± 0.1 a 4.8 ± 0.1 a
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Response variables
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Mean score (n=3) ± standard deviation. Values with a different superscript letter within each row are significantly different (p<0.05)
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FIGURES
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Fig. 1. Contour plots for the Hunter value L (Lightness) and +b* (Yellowness) of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 2. Contour plots of springiness of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 3. Contour plots of TPC of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 4. Contour plots of FRAP of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 5. Contour plots of ABTS scavenging activity of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 6. Contour plots of DPPH scavenging activity of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 7. Contour plots of sensory evaluation for color of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 8. Contour plots of sensory evaluation for taste of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
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Fig. 9. Contour plots of sensory evaluation for overall acceptability of egg tofu containing Polygonum minus, Curcuma longa and Zingiber officinale
Fig. 10. Superimposed plots of the response variables of springiness and sensory attributes (color, taste and overall acceptability) of egg tofu
ACCEPTED MANUSCRIPT Highlights Herbs and spices contributed to the higher antioxidant activity of egg tofu Herbs and spices addition affect the consumer acceptability of egg tofu Egg tofu containing Zingiber officinale is the most prefered by the consumer
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