Effect of stabilization of rice bran by domestic heating on mechanical extraction yield, quality, and antioxidant properties of cold-pressed rice bran oil (Oryza saltiva L.)

LWT - Food Science and Technology 48 (2012) 231e236

Contents lists available at SciVerse ScienceDirect

LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt

Effect of stabilization of rice bran by domestic heating on mechanical extraction yield, quality, and antioxidant properties of cold-pressed rice bran oil (Oryza saltiva L.) Amonrat Thanonkaew a, *, Surapote Wongyai b, David J. McClements c, Eric A. Decker c a

Research Unit of Local Southern Thai Foods, Department of Food Science and Technology, Faculty of Technology and Community Development, Thaksin University, Phapayom, Phatthalung 93110, Thailand Medicinal Products Department, Faculty of Oriental Medicine, Rangsit University, Paholyotin Road, Muang Aek, Patumtani 12000, Thailand c Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 May 2011 Received in revised form 10 March 2012 Accepted 20 March 2012

The effect of stabilization of rice bran by domestic heating on mechanical extraction yield, quality and antioxidant properties of cold-pressed rice bran oil (RBO) was investigated. The highest extraction yield was found in hot air heating with 5.53 g/100 g bran, followed by microwave heating (4.81 g/100 g bran), roasting (4.77 g/100 g bran) and steaming (3.41 g/100 g bran). Hot air and microwave heating were the most effective methods for stabilization of rice bran (P < 0.05), which provided a low content of acid value (AV) 6.30e6.38 mg KOH/g oil, free fatty acid (FFA) 3.51e3.17% and peroxide value (PV) 11.72 e12.13 mg Eqv/kg oil. Microwave and hot air heating stabilized RBO contained a higher content of total phenolic compounds than that of roasting and steaming stabilized RBO (P < 0.05). Hot air heating stabilized RBO had the highest content of gamma oryzanol but these were not significantly different in microwave and roasting stabilized RBO (P > 0.05). In conclusion, the stabilization of rice bran by domestic heating could be applied to RBO extraction prior to pressing to improve oil extraction yield, quality and antioxidant properties of cold-pressed RBO. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Rice bran oil Stabilization Extraction yield Quality Antioxidant Cold-pressed

1. Introduction Rice is the main staple food in Thailand and many countries in Asia. It is also the main export product of Thailand. About 20 million tons per year of rice are produced in Thailand, which produces about 1.6 million tons of rice bran (USDA Foreign Agricultural Services, 2010). However, only a small portion of rice bran is processed into edible oil. Rancidity of lipids in RBO is a major problem for utilization of rice bran. The high lipid content and a potent enzymes result in drastic quality reduction of rice bran. Storage of rice bran, especially at room temperature, for extended periods leads to degradation of triglycerides in the oil and ultimately to the formation of off-flavors and odors. Rice bran contains active enzymes. Germ and outer layers of the caryopsis have higher enzyme activities. Particular lipase, but also lipoxygenase and peroxidase, are probably most important commercially because they effect the keeping quality and shelf life of rice bran (Orthoefer, 2005). Ramarathnam, Osawa, Namiki, & Kawakishi (1989) also reported that lipid peroxidation by lipases

* Corresponding author. Tel./fax: þ66 (0) 74 693 996. E-mail address: [email protected] (A. Thanonkaew). 0023-6438/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2012.03.018

and lipoxygenases is thought to be the primary cause for bran degradation. Two main changes, oxidative rancidity and hydrolytic rancidity affect the quality of RBO. Oxidative rancidity is caused by the oxidation of the double bonds of the fatty acids while hydrolytic rancidity is caused by the removal of fatty acids from the glycerol molecule. The potent enzymes in rice bran are the key to control the reaction. The hydrolysis reaction turns triglycerides into glycerol and free fatty acids, which occurs soon after rice milling and is caused by the presence of lipase enzymes as catalyst. These free fatty acids produced by the hydrolysis reaction are harmful compounds which make RBO unsuitable for edible use. To prevent rice bran from becoming rancid, it must undergo a stabilization process or extraction of oil soon after the milling process, which are two effective methods for lipase enzyme inactivation and prohibition of rancidity of RBO (Ju & Vali, 2005). However, extraction of oil soon after the milling process is not practical for the commercial scale because of the distance and transportation of bran to the factory. Recently, various stabilization methods, applied to protect RBO degradation, have been reported such as microwave heating (Lakkakula, Lima, & Walker, 2004; Zigoneanu, Williams, Xu, & Sabliov, 2008), ohmic heating (Loypimai, Moonggarm, & Chottanom, 2009; Ramezanzadeh, Rao, Prinyawiwatkul, Marshall,

232

A. Thanonkaew et al. / LWT - Food Science and Technology 48 (2012) 231e236

& Windhauser, 2000), steaming (Juliano, 1985), extrusion (Zhu & Yao, 2006), refrigeration and pH lowering (Amarasinghe, Kumasasiri, & Gangodavilage, 2009). Heat treatment is the most common method to stabilize rice bran. High temperatures above 120  C denature the enzyme responsible for lipid degradation in RBO without destroying the nutritional value of the rice bran. Orthoefer (2005) reported that extrusion (dry heat) cookers have been ideal for stabilization because excess moisture is not added, eliminating the need for drying. The heating of the bran occurs through conversion of mechanical energy of the screw drive to heat the bran. Temperatures used for stabilization vary from 100 to 140  C. The bran is kept hot for 3e5 min after extrusion to ensure lipase inactivation. The hot bran is then cooled using ambient air. Dry extrusion was found more suitable for stabilizing bran to be used as a food ingredient. The success of stabilization of rice bran and its oil depends on temperature, duration of heat treatment, moisture content of treatment medium, pH, and other parameters (Orthoefer, 2005). Recently, mechanical pressing (cold pressing) of RBO has been used in small and medium factories for producing commercial RBO in Thailand. Mechanical pressing oil extraction is technically less expensive and less labor-intensive than the extraction solvent method. The safety and simplicity of the whole process is advantageous over the more efficient solvent extraction equipment. Furthermore, materials pressed out generally have better preserved native properties; end products are free of chemicals and it is a safer process. The cold pressing procedure involves neither heat nor chemical treatments, and it is becoming an interesting substitute for conventional practices because of consumers’ desire for natural and safe food products. Cold pressing is simple, ecologically friendly and does not require much energy; therefore it is suitable for small and medium scale industry. Over the last few years, increased interest in cold-pressed plant oils has been observed as these oils have better nutritive properties than those after refining. The consumption of new and improved products such as cold-pressed oils may improve human health and may prevent certain diseases (Singer, NogalaKalucka, & Lampart-Szczap, 2008). Developing economical methods to stabilize rice bran and extract RBO are important for the small and medium size rice bran oil factory. An economical and efficient method of stabilization is required for obtaining best results. Stabilization of rice bran with domestic heating methods could be a high potential method to pretreatment of rice bran for mechanical pressing. However, there is not much information in the literature about the application of different domestic heating methods for stabilization of rice bran and its effect on extraction yield, quality, phytochemical content and antioxidant activities of cold-pressed RBO (Oryza saltiva L.) In this experiment, hot air heating, roasting, steaming and microwaving were applied for stabilization of rice bran for using in the cold pressing process. Therefore, the aim of the present study was to investigate the impact of domestic heating on mechanical extraction yield, quality and antioxidant properties of cold-pressed RBO.

2.2. Preparation of rice bran and its stabilization by domestic heating Rice bran samples (Sangyod Phatthalung rice) (O. sativa L) were obtained by milling rice grain in a local grinding mill, Kaow Klang Village, Pantae, Khunkanun, Phatthalung, Thailand, during February to April in 2010. Freshly milled bran samples were directly collected from the milling system in polyethylene bags. The grains were immediately separated from rice bran by sieving with 177e297 mm sieves. Different domestic heating methods (as describe in Table 1) of rice bran were applied within 1 h after milling. Unstabilized rice bran was used as the control in this study. Five hundred grams of rice bran was placed in the container for domestic heating with heating condition as describe in Table 1. Temperature during domestic heating was controlled and measured with a thermocouple (Union, UN 305A, Japan). However, temperature of stabilized bran with microwave was immediately measured after heating. Then, rice bran samples were cooled down in the cooling tray about 30 min to reach room temperature. The sample was placed into the polyethylene bag and kept in a cooler (6  2  C). Each sample was collected until the rice bran reached 20 kg. Rice bran samples were separated into two portions. The first portion (1 kg) was transported to the Department of Food Science and Technology, Thaksin University. Stabilized rice brans were kept at 20  C for analysis of moisture content (AOAC, 1999). The second portion (19 kg) was transported to Ban Thai Herbs Co. Ltd, Tanhodduan, Khunkanun, Phatthalung, Thailand, for RBO extraction by pressing.

2.3. Oil extraction by pressing RBO were obtained by pressing 5 kg of stabilized and unstablilzed rice bran with a screw type expeller (475.70 w motor, Oriental Motor, Gear Head DY9 97575, Japan). This operation was carried out three times and the extracted oil was quantified. Later, all the extracted oil was collected for its analysis. Fine particles in the expressed oil were separated by vacuum filtration (Vacuumbrand, ME 2C, Germany) with a double layer of Whatman filter paper no.1. RBO samples were kept at 20  C for the further analysis. Oil extraction yield is defined as gram per hundred gram rice bran (g/100 g bran).

2.4. Color measurement Color of RBO was measured, using a colorimeter (HunterLab, Model ColorFlex, Virginia, USA), and recorded by using the CIE color system profile of L*, a* and b*. Fifteen milliliters of each oil was pipetted into a sample cup, and color value was obtained using a D65/10 setting (daylight 65 illuminant/10 observer). Table 1 Rice bran stabilization methods.

2. Materials and methods 2.1. Chemicals

a,a-diphenyl-b-picrylhydrazyl Standard gamma-oryzanol, (DPPH), ferric cyanine, bythylatedhydroxyanisole (BHA), ferulic acid and cathechin were purchased from SigmaeAldrich Chemical Co., (St. Louis, MO, USA). Hexane, heptane, dimethyl sulfoxide (DMSO) were obtained from Fisher Scientific. All chemicals and reagents were analytical grade. The remaining reagents and solvents were procured from Fluka or Merck unless stated otherwise.

Domestic heating methods

Heating conditions

Instruments

Hot air heating

150  2  C, 10 min

Roasting

150  2  C, 10 min

Steaming

130  2  C, 60 min

Microwave heating

150  2  C, 3 min Power 800 w, frequency 2450 MHz

Domestic hot air oven (TRIMOND, BO-300D-HT, China) Domestic cooking pan with diameter 60 cm Domestic cooking steamer with diameter 60 cm Domestic microwave oven (Re218H, Sharp, Japan)

A. Thanonkaew et al. / LWT - Food Science and Technology 48 (2012) 231e236

2.5. Analysis of chemical properties

233

analyses. The percentage of LA peroxidation inhibition was calculated by the following equation:

Peroxide value (PV), Acid value (AV), free fatty acid (FFA) content were determined following AOCS official methods (AOCS, 2004). FFA was calculated as oleic acid and expressed as percentage of the total lipids.

Inhibition on LA peroxidation ð%Þ h  i ¼ 1  A500 nm; sample =A500 nm; control  100

2.6. Analysis of phytochemical contents and antioxidant activity

2.7. Statistical analysis

Gamma oryzanol content in RBO was determined spectrophotometrically (UVeVIS 1700, Shimadzu, Japan) following the method of Mezouari and Eichner (2007), slightly modified. Briefly, RBO samples were diluted in heptane. The content of gamma oryzanol was determined by UV absorption at 315 nm gamma oryzanol, contents in RBO were quantified against the standard curve. The calibration curve was obtained with pure oryzanol in a concentration range of 0e200 mg/L. The concentration of gamma oryzanol was calculated and expressed as g/100 g oil. Total phenolic content of RBO was measured according to the method reported by Lai, Li, Lu, and Chen (2009) by using FolineCiocalteu reagent with some modification. A 0.1 mL RBO solution (1.0 mg/mL DMSO) was sampled into 2 mL of 0.02 mg/mL Na2CO3 and mixed for 3 min. After adding 0.1 mL of FolineCiocalteau reagent, the final mixture was left for 30 min before reading the absorbance at 750 nm (UVeVIS 1700, Shimadzu, Japan). All measurements were conducted in triplicate and the data were expressed as mg ferulic acid equivalent (FAE) per g of the oil (mg FAE/g oil), based on the calibration curve of ferulic acid. Total flavonoid content of RBO was determined according to the method reported by Jia, Tang, and Wu (1998), slightly modified. Briefly, RBO was dissolved in DMSO (1.0 mg/mL DMSO) and an appropriate dilution of RBO (250 mL) was diluted with distilled water 1.25 mL and 75 mL of 0.05 mg/mL NaNO2 solution were added. The mixture was allowed to stand at room temperature for 6 min before 150 mL of 0.1 mg/mL AlCl3 were added. This mixture was allowed to stand for a further 5 min before 0.5 mL of 1 mol/L NaOH was added. The solution was shaken vigorously before absorbance at 510 nm was measured with a UVevis spectrophotometer (UVeVIS 1700, Shimadzu, Japan). The results were expressed as mg catechin equivalents per g of the oil (mg CE/g oil). DPPH radical scavenging activity was determined using the method originally developed by Blois (1958) with slight modifications by Lai et al. (2009). A portion (0.1 mL) of the extract solution (1.0 mg/mL DMSO) in a test tube was well mixed with 3.9 ml of methanol and 1.0 mL of a,a-diphenyl-b-picrylhydrazyl (DPPH) solution (1.0 mmol/L in methanol). The mixture was kept at ambient temperature for 30 min prior to measurement of the absorbance at 517 nm. BHA was used as the reference. All measurements were done in triplicate. The scavenging effect was derived by the following equation:

The means and standard deviations of moisture content, oil extraction yield, chemical characteristics, phytochemical contents and antioxidant activity were reported in triplicate determinations for each sample. Statistical analysis of data was performed using one-way analysis of variance (ANOVA). Mean comparison was carried out using Duncan’s multiple range test (Steel & Torrie, 1980). The statistical analysis was performed by SPSS 11.0.

i h  DPPH scavengingeffect ð%Þ ¼ 1 A517 nm; sample =A517 nm; control 100 Inhibition on linoleic acid peroxidation was measured following the method of Lai et al. (2009), rice bran extract (0.5 mg) dissolved in 0.5 mL of DMSO was mixed with linoleic acid (LA) emulsion (2.5 mL, 0.02 mol/L, pH 7.0) and phosphate buffer (2.0 mL, 0.2 mol/ L, pH 7.0) in a test tube. The mixed solution was then incubated at 37  C for 72 h for completing color development rising from FeCl2ethiocyanate interaction. The absorbance at 500 nm, an index of the peroxide value, of the resultant solution was then checked (UVeVIS 1700, Shimadzu, Japan). Butylated hydroxyl anisole (BHA) was examined for reference. All data were means of triplicate

3. Results and discussion To stabilize rice bran by domestic heating for cold-pressed RBO process, experiments were carried out by using hot air, roasting, steaming and microwave heating. The effects of domestic heating on moisture content of rice bran and extraction yield of coldpressed rice bran oil are shown in Table 2. Fresh rice bran (unstabilized) had moisture of 14.56 g/100 g bran. The data show that domestic heating could reduce the moisture content of rice bran. The moisture content of steaming, hot air, microwave and roasting of stabilized rice bran were 11.41, 4.58, 4.05 and 2.12 g/100 g bran, respectively. Oil extraction yield from rice bran increased according to the application of hot air, roasting and microwave heating (P < 0.05) (Table 2). The oil extraction yield of stabilized RBO by hot air, microwave, roasting and steaming were 5.53, 4.81, 4.77 and 3.41 g/100 g bran, respectively. The stabilization of rice bran by steaming had no significant difference on oil extraction yield from the ustabilized rice bran (P < 0.05). This suggests there exists an optimal moisture content for domestic heating and the provision of a higher moisture content significantly impact on the extraction yield. The low moisture in the stabilized rice bran can make them more brittle and therefore can achieve a greater rupture of tissue and increase the extraction of oil during the mechanical pressing (Uquiche, Jerez, & Ortiz, 2008). There are two types of lipids in oilseeds: storage lipids, which are mainly triacylglycerols and which are high in quantity and localized in oil bodies of the tissues; and membrane lipids, which are mainly phospholipids (Liu & Brown, 1996). The heating may modify the cellular wall, which results in greater porosity. It also could vaporize the water of the vegetable substrate microstructure, increasing the pressure in its interior; its release causes the disintegration of the material (Aguilera & Stanley, 1999; Starmans & Nijhuis, 1996), cell membrane rupture and improves the efficiency of the pressing extraction of oil from oilseeds, enabling the passage of oil from the

Table 2 Effect of stabilization of rice bran by domestic heating on moisture content of rice bran and extraction yield of cold-pressed rice bran oil. Stabilization methods

Moisture content (g/100 g bran)

Unstabilized Hot air Roasting Steaming Microwave

14.56 4.58 2.13 11.41 4.05

    

0.08a 0.51c 0.04e 0.04b 0.13d

Extraction yield (g/100 g bran) 3.29 5.53 4.77 3.41 4.81

    

0.23c 0.16a 0.30b 0.14c 0.24b

Values (means  SD) with different index letters are statistically significantly different (P < 0.05).

234

A. Thanonkaew et al. / LWT - Food Science and Technology 48 (2012) 231e236

cell membrane (Uquiche et al., 2008). Our results were in agreement with other plants oil extraction. Azadmard-Damirchi, HabibiNodeh, Hesari, Nemati, and Achachlouei (2010) reported that pretreatment of rapeseed with microwave heating could enhance oil extraction yield of cold pressing and solvent extraction methods. Oil extraction yield from hazelnut seed increased according to the application of microwave heating (Uquiche et al., 2008). Extraction of RBO has been performed using conventional techniques like solvent extraction and mechanical pressing. But solvent extraction (hexane) is more commonly used in the RBO industry. These techniques usually use organic solvents which are expensive and sometimes toxic. Solvent oil extraction is the most efficient method; however, its application presents some industrial disadvantages such as plant security problems, emissions of volatile organic compounds into the atmosphere, high operation costs and poor quality products caused by high processing temperatures (Uquiche et al., 2008). In our previous work, we studied on yield and chemical properties of solvent extracted and cold-pressed RBO (O. saltiva L.) Rice bran sample were stabilized by hot air heating (hot air oven) at 150  C for 10 min prior to extraction with hexane and pressing. We found that solvent extraction had higher the extraction yield of oil than that of cold pressing method. But coldpressed RBO had lower values in acid, peroxide and free fatty acid but higher iodine number than that of solvent extracted RBO. Therefore, the cold-pressed extraction process gave a better crude oil quality and contained higher vitamin, phytochemical and mineral content than that of solvent extraction. Color is another important characteristic for determining visual acceptance of RBO. The influences of domestic heating on quality of cold-pressed RBO were studied. Color of RBO was determined by CIE system (Table 3). The L* value is the “lightness” of a sample from 0 to 100 with 100 being pure white; the a* value describes red (þ) to green (); the b* value represents yellow (þ) to blue (); and zero values for “a*” and “b*” represent gray. The RBO differed in their colors. Significant different were found between L*, a* and b* values of RBO (P < 0.05). Roasting and steaming could reduce the lightness of RBO and all of the heating methods could reduce the b* value of RBO (P < 0.05). However, there are no color standards for cold-pressed RBO and the L*, a* and b* measurement could thus be used for color classification. Stabilization of bran to inactivate enzyme activity is the most important factor in rice bran oil extraction. Poor or no stabilization causes the increase in AV, PV and FFA content and affects the extraction process, oil quantity and quality. The effects of stabilization of rice bran by domestic heating on chemical property of coldpressed RBO are shown in Table 4. Acid value (AV), free fatty acid (FFA) and peroxide value (PV) were the parameters used for determination of chemical quality of cold-pressed RBO. Generally, the content of AV, FFA and PV was positively related to the activity of enzyme lipase. Acid value can be used for a purity check of oil and may have already started decomposition reactions. Although refined oils are largely devoid of free fatty acids, considerable amounts may Table 3 Effect of stabilization of rice bran by domestic heating on color of cold-pressed rice bran oil. Stabilization methods

Color L*-value

Unstabilized Hot air Roasting Steaming Microwave

10.44 9.69 7.99 6.49 10.09

    

a*-value 0.27a 0.86a 0.54b 0.52c 0.92a

1.59 2.84 3.72 1.40 2.28

    

0.06cd 0.60b 0.50a 0.39d 0.33bc

b*-value 12.94 10.66 8.80 8.90 9.65

    

0.32a 0.37b 1.00b 0.58b 1.85b

Values (means  SD) with different index letters are statistically significantly different (P < 0.05).

Table 4 Effect of stabilization of rice bran by domestic heating on chemical property of coldpressed rice bran oil. Stabilization methods

Chemical property

Unstabilized Hot air Roasting Steaming Microwave

11.11 6.98 7.56 9.01 6.30

Acid value (mg KOH/g oil)     

0.84a 0.31cd 0.03c 0.40b 0.55d

Free fatty acid (%) 5.58 3.51 3.80 4.53 3.17

    

0.42a 0.16cd 0.01c 0.20b 0.27d

Peroxide value (mg Eqv/kg oil) 18.85 12.13 15.18 17.16 11.72

    

0.45a 0.22d 0.50c 0.59b 0.59d

Values (means  SD) with different index letters are statistically significantly different (P < 0.05).

be present in crude oils. Hydroperoxides are the primary products of autoxidation which in themselves are odorless. Their decomposition leads to the formation of a wide range of carbonyl compounds, hydrocarbons, furans and other products that contribute to the stale flavor of foods and may also be involved in biological oxidation (Frankel, 1991). The peroxide value (PV) measures the quantity of peroxides in the oil; these are important intermediates of oxidative reactions since they decompose via transition metal irradiation and elevated temperatures to form free radicals (Decker, 1998). Data show that different domestic heating methods provided different chemical qualities of cold-pressed RBO (P < 0.05). Steaming, roasting, hot air and microwave heating could retard the forming of AV, FFA and PV compared with unstabilized rice bran. Cold- pressed RBO of hot air and microwave heating had lower AV, FFA and PV than that of roasting and steaming methods, respectively. However, there was no significant difference between the rice bran samples treated with hot air and microwave heating (P < 0.05). This may be due to the fact that, in this condition, the heat could penetrate and effectively destroy lipase and it combined with the prevention effect of rice bran to retard the development of oxidation products in rice bran. Stabilization of rice bran with hot air and microwave heating are effective methods for controlling enzyme activity in rice bran. These results indicate that the stabilization of rice bran by domestic heating can be employed without concern as to deleterious changes to major nutrient concentrations in the bran. Our result is in agreement with Ramarathnam et al. (1989) who reported that fatty acid and proximate compositions did not change drastically in microwave-heated rice bran compared with raw samples kept under similar storage conditions. Amarasinghe et al. (2009) studied the effect of method stabilization on aqueous extraction of rice bran oil. They found that steaming, microwave and hot air heating could retard the lipolytic activity of rice bran resulting in the lower FFA when compared with unstabilized rice bran. According to CODEX standards for edible fat and oil (CODEX STAN 210, 1999), the maximum level of AV and PV of cold pressed oil are 4.0 mg KOH/g oil and 15 milliequivalents of active oxygen/kg oil, respectively. According to Tao, Rao, and Liuzzo (1993), rice bran oil with over 5% FFA is considered unsuitable for human consumption. Our results show that stabilized RBO by microwave and hot air heating had AV 6.30e6.98 mg KOH/g oil, FFA 3.17e3.51% and PV 11.72e12.13 milliequivalents of active oxygen/kg oil. The stabilized rice bran with hot air and microwave had PV lower than that of CODEX standards and had FFA 5% lower but they had a little higher AV than that of CODEX standards. Therefore, the stabilized rice bran by hot air and microwave heating could be applied to produce the cold pressed RBO for human consumption. But it may need to find some process to reduce AV to reach the CODEX standard. Rice grain contains several classes of antioxidants, including phenolic compounds, tocols and gamma oryzanol. Antioxidants reportedly are protective against oxidative damage, which has been implicated in a range of diseases, including cancer and

A. Thanonkaew et al. / LWT - Food Science and Technology 48 (2012) 231e236

Table 5 Effect of stabilization of rice bran by domestic heating on phytochemical content of cold-pressed rice bran oil. Stabilization methods

Phytochemical content

Unstabilized Hot air Roasting Steaming Microwave

11.59 15.70 13.71 13.65 16.27

Total phenolic (mg FAE/g oil)     

0.89c 3.35a 2.53b 1.79b 1.10a

Flavonoid (mg CE/g oil) 9.04 11.81 11.75 10.01 12.18

    

0.12b 1.20a 0.28a 0.69b 0.65a

Gamma oryzanol (g/100 g oil) 2.03 2.30 2.24 2.16 2.25

    

0.05c 0.08a 0.04ab 0.05b 0.02ab

Values (means  SD) with different index letters are statistically significantly different (P < 0.05).

DPPH Scavenging Effectf(%)

45 40

a

35 30

a

b

a

c

25 20 15 10 5 0 Unstabilized

Hot air

Roasting

Steaming

Microwave

Stabilization methods 45 40

Inhibition on Linoleic Acid Peroxidation (%)

cardiovascular disease. They are also one of the principal ingredients that protect food quality by preventing oxidative deterioration of lipids (Goffman & Bergman, 2004). Cold-pressed edible seed oils may be preferred by consumers because the cold pressing procedure involves neither heat nor chemicals, and may increase the retention of beneficial phytochemicals (Yu, Zhou, & Parry, 2005). It is well accepted that antioxidants may protect important cellular components such as DNA and membrane lipids from oxidative damage and suppress the pathology of cancer, cardiovascular diseases, and other aging-associated health problems. RBO rich in natural antioxidants may play a role in reducing the risk of chronic diseases. Phenolic compounds have demonstrated powerful antioxidative potential and may reduce free radical-mediated cellular damage. Phytochemical contents of stabilized cold-pressed RBO as compared to unstabilized cold-pressed RBO are displayed in Table 5. Results showed the total phenolic content ranging from 11.59 to 11.27 mg FAE/g oil, flavonoid content ranging from 9.04 to 12.18 mg CE/g oil and gamma oryzanol content ranging from 2.03 to 2.25 g/100 g oil. Stabilized rice bran with domestic heating yielded significantly higher amounts of total phenolic compounds, flavonoid content, gamma oryzanol than that of unstabilized rice bran (P < 0.05). However, steaming stabilized RBO had no significant difference in flavonoid content when compared with unstabilized RBO (P > 0.05). Microwave and hot air heating stabilized RBO contained higher contents of total phenolic compounds than that of roasting and steaming stabilized RBO. Cold-pressed RBO of hot air heating had the highest content of gamma oryzanol but there were not significantly different in microwave, roasting and steaming (P < 0.05). Rice bran contains a significant amount of natural phytochemicals such as oryzanols, tocopherols and tocotrienols that have been reported as the strongest antioxidants in rice bran (Godber & Wells, 1994; Lai et al., 2009; Orthoefer & Eastman, 2004). The total phenolic compound, flavonoid content and gamma oryzanol content of the rice bran stabilized by domestic heating were comparable to those of rice bran reported by Chotimarkorn, Benjakul, and Silalai (2008) and Lai et al. (2009). Cold-pressed RBO contained total phenolic compound content 1.44 mg CAE/100 g (Singer et al., 2008). The effects of domestic heating on antioxidant activity of coldpressed RBO are shown in Fig. 1. Free radical-scavenging and inhibition of lipid peroxidation have been studied to explain how RBO could be used as effective antioxidants. The DPPH free radical method has been used extensively to evaluate reducing substances, based on the reduction of methanolic DPPH solution in the presence of a proton-donating substance, resulting in the formation of diamagnetic molecules. The data showed that the stabilized RBO with hot air, roasting, steaming and microwave had DPPH scavenging effect and inhibition on linoleic acid peroxidation than that of unstabilized rice bran (P < 0.05). Hot air and microwave heated RBO had the inhibition on linoleic acid peroxidation higher than that roasted and steamed RBO (P < 0.05). The results indicated that the rice bran with stabilization process by domestic heating

235

35 30

a

25 20

c

b

a bc

15 10 5 0 Unstabilized

Hot air

Roasting

Steaming

Microwave

Stabilization methods Fig. 1. Effect of the stabilization of rice bran by domestic heating on DPPH scavenging effect (%) and inhibition on linoleic acid peroxidation (%) of cold-pressed rice bran oil. The different index letters are statistically significantly different (P < 0.05).

appeared to increase the oxidative stability expressed by the higher activity than unstabilized rice bran. The stabilized rice bran can reduce lipid oxidation because it contains a number of antioxidants and this result could also be indicated by the antioxidant results and bioactive compounds of RBO as shown in Table 5. The antioxidant activity of compounds is often described by its ability to delay the onset of autoxidation by scavenging reactive oxygen species, or the ability to act as chain breaking antioxidants to inhibit the propagation phase of lipid autoxidation (Yuan, Bone, & Carrington, 2005). Chotimarkorn et al. (2008) reported that the methanolic rice bran extracts produced strong results with DPPH free radicalscavenging (EC50 0.38e0.74 mg/ml), reducing power (EC50 0.10e0.53 mg/ml), ferrous ion-chelating activity (EC50 0.11e0.55 mg/ml) and inhibition of lipid peroxidation (EC50 0.14e0.57 mg/ml). Singer et al. (2008) reported that cold-pressed RBO had DPPH scavenging 23%. Additionally, there are very few studies on the effect of stabilization method of rice bran on the phytochemical content and antioxidant activity of RBO, particularly cold-pressed RBO. However, our results have similar phenomena with stabilization method of other plat oils. Azadmard-Damirchi et al. (2010) studied the effect of pretreatment with microwave on oxidative stability and nutraceuticals content of rapeseed oil. Microwave pretreatment of rapeseed can increase oil extraction yield, phytosterols and tocopherols of the oil extracted by pressing method. Oil extracted from untreated rapeseed by press had the lowest oxidative stability (1 h); this was increased to 8 h by pretreatment of rapeseed with microwaves. Higher stability of oils extracted from microwave pretreated rapeseeds may arise from their high antioxidant content. Roasted sesame seed oils are widely used in Asian and African countries. Roasting of sesame seed before pressing could increase the phytochemical which results in resistance to oxidative deterioration, distinctive flavor and extended shelf-life of sesame seed oil (Lee, Jeung, Park, Lee, & Lee, 2010). Uquiche et al. (2008) reported that stabilization of hazelnut with

236

A. Thanonkaew et al. / LWT - Food Science and Technology 48 (2012) 231e236

microwave heating prior to pressing could improve the oil recovery, quality and oxidative stability of cold pressed hazelnut oil. 4. Conclusion The results of this study suggested that stabilization of rice bran by domestic heating could be applied to RBO extraction prior to pressing to improve oil extraction yield, quality and antioxidant properties of cold-pressed RBO. Hot air and microwave heating were the most effective methods for stabilization of rice bran with a high extraction yield, and lowering of AV, FFA and PV. Those heating methods also provided higher contents of total phenolic compounds, flavonoid and gamma oryzanol while increasing the antioxidant activities of RBO. However, we suggested that microwave heating is not economical and not suitable to be used in small and medium scales in rural areas. But hot air heating is a very efficient method for stabilization and could be applicable for small and medium scale operations in rural areas. Acknowledgments This research was supported by a grant from Thailand Research Fund with a grant number of MRG5380124, grants from Institute of Research and Development of Thaksin University and Thailand Toray Science Foundation. We would also like to give a special thank you to Mr. Brian J. Moore for kindly editing the manuscript. References Aguilera, J. M., & Stanley, D. W. (1999). Microstructural principles of food processing and engineering. Gaithersburg, MD: Aspen Publishers Inc. Amarasinghe, B. M. W. P. K., Kumarasiri, M. P. M., & Gangodavilage, N. C. (2009). Effect of method of stabilization on aqueous extraction of rice bran oil. Food and Bioproducts Processing, 87, 108e114. AOAC. (1999). Official method of analysis (16th ed.). Washington, DC: Association of Official Analytical Chemists. AOCS. (2004). Official methods and recommended practices of the American Oil Chemists’ Society. Champaign, USA: American Oil Chemists’ Society. Azadmard-Damirchi, S., Habibi-Nodeh, F., Hesari, F., Nemati, M., & Achachlouei, B. F. (2010). Effect of pretreatment with microwaves on oxidative stability and nutraceuticals content of oil from rapeseed. Food Chemistry, 121, 1211e1215. Blois, M. S. (1958). Antioxidant determinations by the use of a stable free radical. Nature, 181, 1199e1200. Chotimarkorn, C., Benjakul, S., & Silalai, N. (2008). Antioxidant components and properties of five long grained rice bran extracts from commercial available cultivars in Thailand. Food Chemistry, 111, 636e641. CODEX STAN 210. (1999). CODEX standard for named vegetable oils. Decker, E. A. (1998). Antioxidant mechanisms. In C. C. Akoh, & D. B. Min (Eds.), Food lipids, chemistry, nutrition, and biotechnology (pp. 397e401). New York, USA: Marcel Dekker. Frankel, E. N. (1991). Recent advances in lipid oxidation. Journal of the Science of Food and Agriculture, 54, 489e511. Godber, J. S., & Wells, J. H. (1994). Rice bran: as a viable source of high value chemicals. Louisiana Agriculture, 37, 13e17.

Goffman, F. D., & Bergman, C. J. (2004). Rice kernel phenolic content and its relationship with antiradical efficiency. Journal of the Science of Food and Agriculture, 84, 1235e1240. Jia, Z., Tang, M., & Wu, J. (1998). The determination of flavonoid contents in mulberry and their scavenging effects on superoxides radicals. Food Chemistry, 64, 555e559. Ju, Y. H., & Vali, S. R. (2005). Rice bran oil as a potential resource for biodiesel: a review. Journal of Scientific and Industrial Research, 64, 866e882. Juliano, B. (1985). Rice bran. In B. Juliano (Ed.), Rice chemistry and technology (pp. 659). St. Paul, Minnesota, USA: The American Association of Cereal Chemist. Lai, P., Li, K. Y., Lu, S., & Chen, H. H. (2009). Phytochemicals and antioxidant properties of solvent extracts from Japonica rice bran. Food Chemistry, 117, 538e544. Lakkakula, N., Lima, M., & Walker, T. (2004). Rice bran stabilization and rice bran oil extraction using ohmic heating. Bioresource Technology, 92, 157e161. Lee, S. W., Jeung, M. K., Park, M. H., Lee, S. Y., & Lee, J. (2010). Effects of roasting conditions of sesame seeds on the oxidative stability of pressed oil during thermal oxidation. Food Chemistry, 118, 681e685. Liu, K., & Brown, E. A. (1996). Fatty acid compositions in newly differentiated tissues of soybean seedlings. Journal of Agricultural Food Chemistry, 44, 1395e1398. Loypimai, P., Moonggarm, A., & Chottanom, P. (2009). Effects of ohmic heating on lipase activity, bioactive compounds and antioxidant activity of rice bran. Australian Journal of Basic and Applied Sciences, 3, 3642e3652. Mezouari, M., & Eichner, K. (2007). Comparative study on the stability of crude and refined rice bran oil during long-term storage at room temperature. European Journal of Lipid Science and Technology, 109, 198e205. Orthoefer, F. T. (2005). Rice bran oil. In F. Shahidi (Ed.), Bailey’s industrial oil and fat Products (pp. 465e489). Hoboken, NY, USA: John Wiley & Son, Inc. Orthoefer, F. T., & Eastman, J. (2004). Rice bran and oil. In E. T. Champagne (Ed.), Rice chemistry and technology (pp. 569e593). St. Paul, Minnesota, USA: AACC. Ramarathnam, N., Osawa, T., Namiki, M., & Kawakishi, N. (1989). Studies on changes in fatty acid composition and content of endogenous antioxidant during çirradiation of rice seeds. Journal of the American Oil Chemists’ Society, 66, 105e108. Ramezanzadeh, F. M., Rao, R. M., Prinyawiwatkul, W., Marshall, W. E., & Windhauser, M. (2000). Effects of microwave heat, packaging, and storage temperature on fatty acid and proximate compositions in rice bran. Journal of Agricultural and Food Chemistry, 48, 464e467. Singer, A., Nogala-Kalucka, M., & Lampart-Szczap, E. (2008). The content and antioxidant activity of phenolic compounds in cold-pressed plants oil. Journal of Food Lipids, 15, 137e149. Starmans, D. A. J., & Nijhuis, H. H. (1996). Extraction of secondary metabolites from plant material: a review. Trends in Food Science and Technology, 7, 191e197. Steel, R. G. D., & Torrie, J. H. (1980). Principles and procedures of statistics: A biometrical approach (2nd ed.). NY, USA: McGraw-Hill. Tao, J., Rao, R., & Liuzzo, J. (1993). Microwave heating for rice bran stabilization. Journal of Microwave Power and Electromagnetic Energy, 28, 156e164. Uquiche, E., Jerez, M., & Ortiz, J. (2008). Effect of pretreatment with microwaves on mechanical extraction yield and quality of vegetable oil from Chilean hazelnuts (Gevuina avellana Mol). Innovative Food Science and Emerging Technologies, 9, 495e500. USDA Foreign Agricultural Services. (2010). Grain report: Grain and feed update Thailand. Global information network. Grant Report number: TH0025. Yu, L., Zhou, K., & Parry, J. (2005). Antioxidant properties of cold- pressed black caraway, carrot, cranberry, and hemp seed oils. Food Chemistry, 91, 723e726. Yuan, V. Y., Bone, E. D., & Carrington, F. M. (2005). Antioxidant activity of dulse (Palmaria palmate) extract evaluated in vitro. Food Chemistry, 91, 485e494. Zhu, W., & Yao, H. (2006). Visual studies on rice bran extrusion. In K. Wang, G. Kovacs, M. Wozny, & M. Fang (Eds.), International federation for information processing (IFIP), knowledge enterprise. Intelligent strategies in product design, manufacturing and management, Vol. 207 (pp. 966e971). Boston, USA: Springer. Zigoneanu, I. G., Williams, L., Xu, Z., & Sabliov, C. M. (2008). Determination of antioxidant components in rice bran oil extracted by microwave-assisted method. Bioresource Technology, 99, 4910e4918.