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Chemical and functional properties of durian (Durio zibethinus Murr.) seed flour and starch
Food Bioscience 30 (2019) 100412
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Chemical and functional properties of durian (Durio zibethinus Murr.) seed flour and starch
T
Surayani Barahenga,b, Taewee Karrilaa,∗ a b
Department of Food Science and Nutrition, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Pattani, 94000, Thailand Pattani Vocational College, Muang District, Pattani, 94000, Thailand
ARTICLE INFO
ABSTRACT
Keywords: Durian (Durio zibethinus Murr) Durian seed flour Durian seed starch Durian seed gum Durian seed mucilage
Durian (Durio zibethinus Murr.) seeds are a waste from durian paste processing that could find applications in food or non-food industries. Durian seeds are mainly composed of starch and mucilage (gum), which influence its properties and hence the potential applications. The objective of this research was to compare the properties of durian seed flour in different forms. Chemical and functional properties were compared among whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF), and durian seed starch (DS), for two varieties of durian called native (N) and Chanee (C). It was found that the durian variety made little difference in chemical and functional properties, in contrast to the processing of the sample. WDSF contained both starch and gum, and had significantly (p < 0.05) more protein, lipid, ash, and fiber than DDSF or DS. The functional properties of WDSF, especially swelling power, water absorption capacity, peak viscosity and emulsifying capacity and activity, were also significantly higher than for DDSF or starch. Among the three forms of durian seed, WDSF showed the lowest gel hardness but highest syneresis, due to its high ability to bind with water to form a weak gel network. In conclusion, the three forms of durian seeds showed different properties. Gum or mucilage in durian seeds had important roles in the functional properties.
1. Introduction Durian (Durio zibethinus Murr.) is a popular and commercially valuable fruit produced in the South-East Asian countries. Only around 30% of a durian fruit is edible while the rest is waste, among which 20–25% of the whole fruit is seeds (Amin, Ahmad, Yin, Yahya, & Ibrahim, 2007). Durian seeds have two main components: starch, and mucilage or gum. Some properties of durian seed starch have been reported previously (Tongdang, 2008). Durian seed starch is similar to rice starch in terms of the ∼4–5 μm granule size (Tongdang, 2008). However, extracting starch from durian flour has a low yield, about 10% relative to dry seed flour (Tongdang, 2008). This is because the gum in seeds absorbs a large amount of water (Amid & Mirhosseini, 2012a) making a viscous suspension that traps starch granules preventing their release. There are many studies available on durian seed gum showing its composition and functional properties, and suggesting extraction methods (Amin et al., 2007; Amid, Mirhosseini, & Kostadinović, 2012; Amid & Mirhosseini, 2012a, b, c). Durian seed gum yield is about 56% of dry seed flour with aqueous extraction (Amid & Mirhosseini, 2012a). The mucilage or gum consists of polysaccharides and proteins. The
∗
polysaccharides include galactose (48.6–59.9%), glucose (37.1–45.1%), arabinose (0.58–3.41%), and xylose (0.3–3.21%); and the proteins only contain 12 different amino acids (Amid et al., 2012). This gum has high water holding capacity, 140–274 g water/100 g gum, as well as high oil holding capacity (147 g oil/100 g gum) (Amid & Mirhosseini, 2012a). Gum from durian seeds has been used experimentally as an emulsifier in vegan mayonnaise, to replace egg yolk (Cornelia, Siratantri, & Prawita, 2015). Utilization of whole durian seed flour containing both gum and starch, i.e., without removing the gum, would allow simpler and less expensive preparation of such flour. When durian seed flour was used to partially substitute for corn flour to make gluten free pasta, a positive effect on texture was observed, but high contents (50% substitution) had negative effects on color and aroma of the pasta product (Mirhosseini et al., 2015). Durian seed flour without gum should have different functional properties from the whole seed flour. So far most studies have focused on durian seed gum, while information on whole durian seed flour remains limited. In this study a comparison of chemical and functional properties of durian seed starch, and durian seed flours with and without gum was carried out for seeds representing two varieties of
Corresponding author. E-mail addresses: [email protected] (S. Baraheng), [email protected], [email protected] (T. Karrila).
https://doi.org/10.1016/j.fbio.2019.100412 Received 7 August 2018; Received in revised form 1 May 2019; Accepted 2 May 2019 Available online 03 May 2019 2212-4292/ © 2019 Elsevier Ltd. All rights reserved.
Food Bioscience 30 (2019) 100412
S. Baraheng and T. Karrila
durian (native and Chanee varieties) that are common in Thailand.
2 min. The flour slurry was screened with a nylon cloth, to obtain the sample cake. This step was repeated three times. The filter cake was then mixed with 0.05 M NaOH and centrifuged (HARRIER 15/80 Bench Top Refrigerated Centrifuge, Sanyo Electric Co., Ltd., Osaka, Japan) at 20 °C at 1600×g for 15 min. The supernatant was drained and the yellowish upper part of the sediment was discarded. This step was repeated until a clear supernatant was obtained. The sediment starch was washed and neutralized with water and HCl (0.1 M). To remove water, the starch slurry was filtered with a porosity no. 4 (10–16 μM pore size) sintered glass funnel (Fisher Scientific Ltd., Leicester, England) connected to vacuum pump. The starch was dried at 45 °C and packed and stored as previously.
2. Materials and methods 2.1. Chemicals All chemicals used in this study were purchased from Sigma Aldrich Co. (St. Louis, MO, USA), through a local distributor in Thailand (Boss Oftical Ltd. Partnership, Songkhla, Thailand). 2.2. Durian seed samples Seeds of the two durian varieties were collected from waste of durian paste processing. Fully ripe durian fruit was dehusked, and the flesh was detached from seeds. The flesh was further processed to durian paste, mixing with sugar and stirring over low heat until thickened, while the seeds were collected and used in this study. The samples of the native variety (N) were from Ra-ngae district, Narathiwat province, southern Thailand, and those of the Chanee variety (C) were from Patong district, Rayong province, eastern Thailand. Both sites had similar production processes. Chanee has larger fruit (2.5–4.5 kg) than the native (0.5–1.2 kg), but they have similar seed size. Each fruit has ∼10–18 seeds, depending on the fruit's size. The seeds were prepared in three forms: whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF), and durian seed starch (DS).
2.3. Analysis methods 2.3.1. Chemical composition, starch content and amylose content Moisture, protein, lipid and ash contents of flour and starch were determined following AOAC procedures (AOAC, 2000). The Kjeldahl factor for protein content was 6.25. The amylose contents of the starch samples, after lipid extraction, were estimated using the iodine method (International Organization for Standardization, 1987, pp. 2–3). Defatted starch (100 mg, dw) was dispersed with 1 mL of 95% ethanol and suspended in 9 mL of 1 M NaOH. The suspension was heated for 30 min at 95 °C and then left overnight. The solution was diluted to 100 mL and a 5 mL aliquot, to which 25 mL of distilled water, 0.5 mL of 1 M acetic acid and 1 mL of iodine solution (0.2% iodine in 2% potassium iodide) were mixed and brought to 50 mL. The solution was left for ∼20 min in a dark room for color development. The absorbance was measured at 620 nm with a spectrophotometer (UV–Visible spectrophotometer, Libra S22, Biochrom, Cambridge, England). The sample blank was distilled water. Each measurement was done in triplicate. The standard curve for amylose content was prepared using mixtures of pure amylose and amylopectin. Amylose and amylopectin solutions (1 mg, dw/mL) were prepared in a similar manner to flour or starch samples. These solutions were mixed to make the proportion of amylose (by volume) range from 0 to 40%. Aliquots (5 mL) of the mixtures were reacted with the iodine solution and handled, thereafter, as previously. The standard curve was then plotted as absorbance against amylose content. The linear model from the plot was
2.2.1. Whole durian seed flour (WDSF) preparation Fresh durian seeds of about 5–7 cm length and 3–4 cm width were washed with water, and the seeds were manually dehulled by removing the brown 2–4 mm thick seed coat with a sharp knife. Dehulled seeds were then sliced with a sharp knife into thin (about 2 mm thick) chips and tray dried at 55 °C until the moisture content was below 12%, verified using a moisture analyzer (Sartorius MA150, Sartorius (Thailand), Ltd. Bangkok, Thailand) as a rapid method. The chips were ground using a laboratory grinder (Sottoria S. p. A., Marano Vicentino, Italy) into a powder, and passed through a 100 mesh (150 μm) sieve to obtain durian seed flour (WDSF). The WDSF was kept in plastic polyethylene bottles with tight lids, and stored in a refrigerator (4–5 °C) for a maximum of 54 wk. 2.2.2. Demucilaged durian seed flour (DDSF) The demucilaged durian seed flour (DDSF) was prepared from the WDSF in 2.2.1 as follows. Fifty g of WDSF was mixed with 200 mL saturated alum solution and soaked for 2.5 h. The top layer of the mixture was discarded, and the sediment was collected. Distilled water (200 mL) was added and left for 20 min, then the top layer was removed. This step was repeated a second time. The remaining flour (sediment) was mixed with 200 mL 1% NaHCO3 and soaked for 2 h. The liquid was then discarded and the flour obtained was washed with distilled water twice. The filter slurry was then mixed with 200 mL 0.075% Na2S2O5, and this slurry was filtered using a nylon cloth bought from a local shop in Muang district, Pattani provice, Thailand. The flour cake was washed with distilled water twice. The water was removed using a filter press (Kliuy Num Thai, Bangkok, Thailand) with polypropylene cloth filters (Siamnathan International Co., Samuthprakhan, Thailand). The filter cake was dried at 45 °C until its moisture content was below 14%, then milled using a mortar and pestle, and passed through a 100 mesh sieve. The DDSF obtained was packed and stored like the WDSF.
y = 0.0154x+0.4849, with R2 = 0.9916 Where: y = absorbance at 620 nm and x = amylose content (%). Each measurement was done in triplicate. Total starch content was measured using a Megazyme Assay Kit (KTSTA) (Megazyme Intl., Bray, County Wicklow, Ireland). Briefly, the 100 mg sample was wet with 0.2 mL of ethanol solution (80%, v/v). Immediately 300 units of thermostable α-amylase in 3 mL of MOPS buffer (50 mM, pH7) was added, which was then boiled for 6 min in 4 mL of sodium acetate buffer (200 mM, pH 4.5). One unit (U) of αamylase activity is the amount of enzyme required to release 1 μmol pnitrophenol from p-nitrophenyl maltoheptaoside in the presence of saturating levels of α-glucosidase and amyloglucosidase (i.e., Ceralpha αamylase assay reagent) at 40 °C and pH 6 and 11. After that, 20 units of amyloglucosidase were added and incubated at 50 °C for 30 min before adjusting with distilled water to 10 mL, and centrifuged at 1800×g for 10 min at 20 °C. One unit of amyloglucosidase is the amount of enzyme required to release 1 μmol p-nitrophenol from p-nitrophenyl β-maltoside in the presence of saturating levels of β-glucosidase, i.e., amyloglucosidase assay reagent, at 40 °C and pH 4.5 and 12.0. A 1.0 mL aliquot from the supernatant was diluted to 10 mL with distilled water. Then, 0.1 mL of this diluted solution was mixed with 3 mL of glucose oxidase peroxidase (GOPOD: a mixture of glucose oxidase > 12000 U/ L; peroxidase, > 650 U/L; and 0.4 mM 4-aminoantipyrine) and
2.2.3. Durian seed starch Durian seed starch was isolated from the DDSF following the method described in a previous report (Tongdang, 2008). The DDSF was mixed with three volumes of 1% aqueous NaCl, and blended with a kitchen blender (HR2115/02, Phillips Co., Bangkok, Thailand) for 2
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incubated at 50 °C for 20 min. Sample blanks (distilled water) and glucose control (1 mg/mL) were also prepared in the same manner as the actual samples. Absorbance was measured at 510 nm against the blank. The measurements were done in triplicates. Starch content was calculated (McCleary, Gibson, & Mugford, 1997) as:
One α-amylase inhibitory unit (IU) was defined as IU/g of dw from the maltose calibration curve. 2.3.3. Swelling power and solubility Swelling power and solubility were measured at 55, 65, 75, 85 and 95 °C (Kong, Bao, & Corke, 2009). Each sample (100 mg, dw) was mixed well with 10 mL distilled water before heating in a water bath with temperature control for 30 min. The sample was cooled to room temperature in ice water before centrifuging at 2000×g for 30 min. The supernatant was dried at 105 °C in a hot air oven until constant weight (W1) and the wet sediment was also weighed (Ws). The water solubility (WS) and swelling power (SP) were calculated as follows:
Starch (% ww) = A x F x 1000 × (1/1000) x (100/W) x (162/180) = A x (F/W) x 90 Where A = absorbance of reaction solution; F = factor to convert absorbance value to μg glucose = 100 μg glucose/absorbance of 100 μg glucose; 1000 = volume correction, i. e., 0.1 mL taken from 100 mL; 1/ 1000 = conversion from μg to mg; 100/W = conversion to 100 mg sample; 162/180 = factor to convert from free glucose, as determined, to anhydroglucose as its form in starch.
WS (%) = (W1/0.1) × 100 SP (g/g). = Ws/[0.1(100%-WS)]
2.3.2. Trypsin and α-amylase inhibitor activities Trypsin inhibitor activity (TIA) was determined according to the method described by Raj Bhandari and Kawabata (2006) with modifications. Briefly, a one g dried sample was mixed with 50 mL of 10 mM NaOH. The pH of the resulting slurry was adjusted to 9.5 ± 0.1 with 1 M NaOH or 1 M HCl. The slurry was shaken and then stirred at room temperature (28 ± 1 °C) for 3 h. After this extraction the clear suspension was used for inhibitor activity estimation. The following blends were used: in a series of 10 mL tubes: (a) reagent blank: 2 mL deionized water (MIT Technology Ltd., Bangkok, Thailand); (b) reference: standard trypsin (Sigma Aldrich Co., St. Louis, MO, USA) solution (40 mg trypsin) in 2 mL deionized water; (c) sample blank: 1 mL sample extract with 1 mL of deionized water; (d) sample: 1 mL sample extract with 1 mL deionized water and 2 mL standard trypsin solution. After mixing and preheating to 37 °C for 10 min, 5 mL of BAPNA (benzoyl-DL-arginine-p-nitroanilide hydrochloride) solution (previously warmed to 37 °C) was added and mixed. After exactly 10 min incubation at 37 °C, 1 mL acetic acid (30% v/v) was added to stop the reaction. Standard trypsin (2 mL) was then added to the reagent blank (a) and sample blank (c). After centrifugation (at 2200×g, at 20 °C for 20 min), the absorbances of the clear solutions were measured at 410 nm. The TIA was estimated in terms of weight of pure trypsin inhibited/g dw, and this is explained by Smith, Megen, Twaalfhoven, and Hitchcock (1980) (see section 2.2.4 of the reference), which explains in more detail the logic behind the formula. Since 1 μg trypsin would give an absorbance of 0.019, the weight of trypsin inhibited/mL of diluted sample extract is Ai/0.019 g (i.e., 50Ai/ 19 mg/50 mL). From this value the trypsin inhibitor activity (TIA) was calculated in terms of mg trypsin/g sample
2.3.4. Pasting properties Pasting properties were measured using a Rapid Visco Analyzer (RVA, RVA4D, Newport Scientific, Warriewood, Australia). To each 3 g (dw) sample (corrected for the 14% moisture content), distilled water was added for a total weight of 28 g. Then the paddle was inserted into the RVA sample can. To prevent clumping in the suspension, the paddle was jogged up and down 10 times before starting the actual RVA test. The pre-programmed standard temperature profile for heating and cooling was used. The sample was held at 50 °C for 1 min, heated from 50 to 95 °C in 4 min, held at 95 °C for 2 min before cooling to 50 °C in 4 min, and held at 50 °C for 2 min. For the first 10 s the stirring speed was 960 rpm, and for the remainder of the test it was 160 rpm. The Thermocline software provided with the instrument recorded the pasting curves, extracting from them the characterizing peak viscosity (PV, the highest viscosity achieved during heating from 50 to 95 °C), trough viscosity (TV, the lowest viscosity achieved during heating at 95 °C), final viscosity (FV, the paste viscosity upon cooling to 50 °C), breakdown viscosity (BV]PV-TV), setback viscosity (SV]FV-TV, indicating starch retrogradation tendency after gelatinization and cooling at 50 °C), pasting temperature (the temperature at which viscosity starts to rise), and peak time (time it takes from beginning of test to reach peak viscosity). 2.3.5. Gelatinization temperature and enthalpy The purified starches were also characterized for transition temperature and enthalpy with a differential scanning calorimeter (DSC7, PerkinElmer, Norwalk, CT, USA) following the procedure in Tongdang (2008). The temperatures of onset, (To), peak (Tpeak) and conclusion (Tc) as well as the enthalpy were measured using the software with the instrument and each type of sample was measured in triplicate.
TIA = (2.632 × Dilution factor x Ai/S) mg trypsin inhibited/g sample;
2.3.6. Water and oil absorption capacity Water absorption capacity (WAC) for durian seed flour and starch was determined as described in Maninder, Sandhu, and Singh (2007). A one g flour sample (dw) was suspended in 10 mL of distilled water in a centrifugation tube and mixed well in a Vortex shaker (VORTEXGENIE® 2, Scientific Industries, Inc., Bohemia, NY, USA.) for 2 min. The suspension was held at room temperature for 30 min before centrifuging at 3000×g for 25 min. The supernatant was decanted and the excess water in the sediment was drained for 25 min. The sediment was then weighted (Sdw). The water absorption capacity is expressed as g water absorbed/g flour (dw).
Ai is the change in absorbance, (Ab-Aa)-(Ad- Ac), due to trypsin inhibition (/mL diluted sample extract) where the subscripts (a)-(d) are described above, and S is the sample weight in g. α-Amylase inhibitor activity (AIA) was evaluated according to the method of Alonso, Orue, and Marzo (1998), as described in Raj Bhandari and Kawabata (2006). A one g sample was extracted with 10 mL of deionized water for 12 h at 4 °C and the supernatant (centrifugation at 2200×g at 20 °C for 20 min) was tested for AIA as follows: 0.25 mL of the sample extract was incubated with 0.25 mL of α-amylase enzyme (Sigma Aldrich Co.) solution (0.003% in 0.2 M sodium phosphate buffer, pH 7.0, with 0.006 M NaCl) for 15 min at 37 °C. To this mixture 0.5 mL of 1% starch solution (pre-incubated at 37 °C) was added. At the end of 3 min, the reaction was stopped by adding 2 mL of dinitrosalicylic acid and boiling for 10 min. The absorbance was measured at 540 nm. One unit of enzyme activity was defined as that which liberates one umole of reducing groups (calculated as maltose)/min at 37 °C and pH 7 from the soluble starch with the specified conditions.
WAC = (Sdw–Sw) / Sw Where Sdw is sediment weight and SW is initial sample weight. The OAC was determined similarly as WAC, but by mixing a 0.5 g sample (dw) with 6 mL of soybean oil (Thanakorn Vegetable Oil Products Co., Ltd., Samutprakarn, Thailand). 3
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Table 1 Chemical compositions and trypsin inhibitor activities (TIA) as well as α-amylase inhibitor activities (AIA) for durian seeds of native (N) and Chanee (C) varieties in the forms of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
Moisture (%)
Lipid (%, dw)
Protein (%, dw)
Fiber (%, dw)
Ash (%, dw)
Carbohydrate (%, dw)
Starch content (%, dw)
TIA (mg pure trypsin inhibited/g sample, dw)
N-WDSF N-DDF N-DS C-WDSF C-DDF C-DS
9.0 ± 0.1a 8.4 ± 0.3ab∗ 9.4 ± 0.7b∗ 9.7 ± 0.4A 9.9 ± 0.2A∗ 11 ± 0.01B∗
0.64 ± 0.05b 0.5 ± 0.1a nd 0.6 ± 0.1B 0.52 ± 0.01A nd
8.6 ± 0.4c∗ 6.7 ± 0.9b 0.17 ± 0.01a 7.2 ± 0.2B∗ 6.6 ± 0.6B 0.2 ± 0.0A
0.9 ± 0.2b 0.75 ± 0.26b 0.13 ± 0.10a 0.82 ± 0.22B 0.6 ± 0.3B 0.01 ± 0.00A
4.5 ± 0.7c 2.0 ± 0.1b∗ 0.5 ± 0.2a 4.5 ± 0.3C 3.8 ± 0.1B∗ 0.53 ± 0.04A
77 ± 1a 82 ± 1b∗ 90 ± 1c 77 ± 1A 79 ± 1A∗ 88 ± 0B
36.8 ± 0.1a 69 ± 1b 90 ± 1c 37.0 ± 0.4A 69.4 ± 0.3B 88 ± 1C
1.0 0.7 0.3 2.8 2.1 0.4
± ± ± ± ± ±
0.2c∗ 0.1b∗ 0.1a 0.1C∗ 0.1B∗ 0.1A
AIA (unit/g sample, dw)
6.4 ± 0.4c∗ 1.6 ± 0.1b∗ 0.4 ± 0.01a 4.2 ± 0.3c∗ 0.45 ± 0.01b∗ 0.38 ± 0.01a
Mean value ± standard deviation of triplicate. Carbohydrate = 100-(moisture + lipid + protein + fiber + ash). Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). Significant differences (at p < 0.5).between varieties, within the same form of sample, are indicated by *. nd = not detected. TIA=Trypsin inhibitor activity (mg pure trypsin inhibited/gram sample, dw). AIA = α-Amylase inhibitor activity (unit/g sample, dw).
2.3.7. Gel hardness The flour or starch slurry (12% w/w) in a 100 mL beaker was heated at 95 °C for 30 min, with constant stirring. After cooking the samples were allowed to cool at room temperature for 3 h. The gels were then cut with a sharp knife to 1.5 × 1.5 × 1.5 cm size. The texture profile analysis (TPA) of gels was then measured with a texture analyzer (TAXT2i, Stable Micro Systems Ltd., Surrey, UK). The modified method used the two-cycle compression test (test speed 1.0 mm/s, with 3.0 g trigger force to a distance of 2.0 mm with a P/50 probe, and 200 pps data acquisition rate). The maximum force during the first compression was recorded as hardness. Five repeated measurements were done and their average is reported. Data for the other texture parameters were lost in the software.
EA (%) = ν2 × 100/ν1 ES (%) = ν3 × 100/ν1 Where ν1 is the initial volume of the emulsion before centrifugation, ν2 is the volume of the emulsified layer, and ν3 is the volume of the remaining emulsified layer after heating. 2.4. Statistical analysis The experiments were done using a completely randomized design. Two way analysis of variance (ANOVA) was used to test the effects of sample forms, and the statistical significances were post hoc tested with the Multiple Range Duncan's test (p < 0.05). The t-test was used to compare the two varieties. The Statistical Package for the Social Sciences (V.13) statistical software (IBM, Armonk, NY, USA) was used.
2.3.8. Syneresis Sample suspension in distilled water (6%, db w/v) was prepared and heated in a water bath at 95 °C for 30 min, with constant stirring. After cooling to room temperature, the samples were placed in a still-air freezer at −20 °C for 22 h, and later placed in a 30 °C water bath for 1.5 h to thaw until equilibrated. Five such cycles of alternating freezing and thawing were done before centrifuging at 3000×g for 20 min. The separated water was measured. The syneresis was calculated as % of water released from the gel after centrifugation. Experiments were done in triplicate (Wang et al., 2010).
3. Results and discussion 3.1. Chemical composition and amylose content The chemical compositions of WDSF, DDSF and starch for both varieties are shown in Table 1. The moisture contents of flours and starches were in the range 8.95–9.69% for native variety and 9.4–11.0% for the Chanee variety. The lipid content was less than 1% in all cases. WDSF had higher lipid content than DDSF, and it was below detection level in the starches. For both varieties, protein content of WDSF was in the range 7.16–8.56% (dw), which was significantly (p < 0.05) higher than in the DDSF (6.55–6.73% dw) or in starch (0.17% dw). This shows that most proteins of durian seed flour stayed in DDSF, so they were not removed with the mucilage or gum. The protein in DDSF was mostly removed during starch isolation, so that only a very small amount remained in the starch. The choice of durian variety had no effect on the protein content, while the form of sample significantly affected protein. A previous study reported 7.6% protein in whole durian seed flour (Amin & Arshad, 2009). The crude fiber contents of both varieties, in the same form of samples, were similar. However, within a variety the fiber content of processed durian seed had the rank order WDSF > DDSF > DS, with statistically significant differences. The results (for dehulled samples, or WDSF) were lower than those reported earlier (Amin & Arshad, 2009). This happened even though the earlier study sampled the seeds of the same durian species (Durio zibethinus Murr.), while the cultivars can differ. Durian seed as biomaterial has natural variability in chemical composition. As an available example of such variation, the crude fiber
2.3.9. Emulsion activity and stability Emulsion activity (EA) and emulsion stability (ES) were determined using the methods described by Jitngarmkusol, Hongsuwankul, and Tananuwong (2008). The flour sample (1 g dw) was dispersed in 50 mL of distilled water. The mixture was homogenized with a homogenizer (X10/25, Ystral, Ballrechten-Dottingen, Germany) for 30 s before adding 25 mL of soybean oil (Thanakorn Vegetable Oil Products Co., Ltd., Samutprakarn, Thailand).The mixture was homogenized again for 30 s, and then another 25 mL of soybean oil was added. The mixtures were homogenized once more for 90 s. Each emulsified sample was divided equally into two centrifuge tubes. For emulsion activity determination the first tube was immediately centrifuged at 1500×g for 5 min, and the volume of the emulsified layer was measured (ν2). To determine the emulsion stability, the second centrifuge tube was heated in a water bath at 85 °C for 15 min, then cooled down to room temperature, and centrifuged like the first sample. The volume of the remaining emulsified layer after heating was measured (ν3). The measurements were done in triplicates. EA and ES were calculated using the following equations: 4
Food Bioscience 30 (2019) 100412
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WDSF contain both starch and non-starch polysaccharides (gums). In a previous report Malaysian researchers extracted 56% gum from the dry flour (Amid & Mirhosseini, 2012a). Apparently the DDSF had remnants of gum, despite attempted removal. Durian seed gum is considered dietary fiber (Amin & Arshad, 2009) and cannot be digested by digestive enzymes. Most of it could be soluble dietary fiber. Overall, for both varieties the secondary chemical components (lipid, protein, ash and fiber) were significantly higher in WDSF than in DDSF, and very small amounts remained in DS, while the carbohydrate contents had the opposite rank order. The amylose content was determined only for the durian seed starches (Table 1) as 23.3 and 22.9% (dw) for native and Chanee variety, respectively. This is similar to a previous report, which found 22.8% amylose (Tongdang, 2008). 3.2. Trypsin and amylase inhibitor activities (TIA and AIA) For the TIA and AIA, the rank order of activities was WDSF > DDSF > DS (Table 1). This means TIA and AIA are mostly located in the gum component of durian seed. Removing gum from seed flour significantly decreased TIA and AIA. DS showed the least AIA and TIA possibly because it had very low protein content, since protein was removed in the starch extraction process. TIA and AIA are considered anti-nutrient activity indicators. They can be found in many kinds of plant products, such as wild yam tubers (Raj Bhandari & Kawabata, 2006), and amaranth (Amaranthus hypocondriacus) seeds (ChagollaLopez, Blanco-Labran, Patthyll, Sanchez, & Pongor, 1994). The antinutrient activities could be decreased by heat treatment (Raj Bhandari & Kawabata, 2006). Fig. 1. Swelling power (a) and solubility (b) of durian seed from native variety (N) in form of whole durian seed flour (N-WDSF), demucilaged durian seed flour (N-DDSF) and durian seed starch (N-DS) at various temperatures. Error bars represent standard deviations. Different letters are significantly different (p < 0.05).
3.3. Swelling power (SP) and solubility On heating starch with water, a phase transition of the starch called gelatinization occurs. SP and solubility provide evidence of interactions between water molecules and starch chains in amorphous and crystalline domains of the starch granules (Aboubakar, Njintang, Scher, & Mbofung, 2008). The SP and solubility of flours and starches were measured at 55–95 °C as shown in Fig. 1a and b, respectively, for the native variety, and in Fig. 2a and b for the Chanee variety. Both SP and solubility increased with temperature, as expected. For N-WDSF, the SP (Fig. 1a) increased rapidly with temperatures from 55 to 75 °C, and then slowly from 75 to 95 °C, similar to the NDDSF. The SP of N-DS increased slowly in the beginning, then rapidly after 65 °C. With SP these different sample forms had the rank order WDSF > DDSF > DS. The Chanee variety showed similar swelling behavior (Fig. 2a). For both varieties, the SP of WDSF was consistently higher than those of DDSF and DS. These results suggested that the non-starch components in WDSF, particularly the mucilage, contributed significantly to water absorption (Aboubakar et al., 2008). The gum of durian seed consists of protein-polysaccharide complexes and can absorb relatively large amounts of water (Amid & Mirhosseini, 2012a). WDSF can immediately bind water at room temperature and gives very viscous mixtures. Once the mucilage was removed, the ability to bind water decreased as seen in the SP. The solubility behaviors gave the same grouping as the swelling behaviors. The WDSF of both N and C varieties had the highest solubility among the sample types at all temperatures tested, and it increased as temperature increased (Fig. 1b). Mucilage or gum in durian seeds has an important role in solubility. Once it was removed the solubility of DDSF decreased by around 50% or more at all temperatures tested. DDSF and DS did not significantly differ in solubility, and these were very sparingly soluble at 55–75 °C, although at 85 and 95 °C the DS had higher solubility than the DDSF, for both varieties. This could be due to the secondary components interacting with starch molecules during gelatinization.
of 8 cultivars of Orono dunich (Plectranthus edutis) tubers varied within the range 1.15–4.16% (Giftya, Bruno De Meulenaera, & Olangob, 2018). Durian seed flour preparation could also affect its fiber content, i. e., depending on how well the seed coat, containing cellulose, was removed in the dehulling step. For the above reasons, while the fiber content does not agree with a prior publication it can be considered reasonable. For both varieties, ash content in WDSF was higher than in DDSF or in seed starch (p < 0.05). However, only DDSF had a significant difference between the varieties, with the native variety having higher ash than Chanee. The ash content of WDSF is similar to a prior report, in which durian seed flour contained 3.8% ash (Amin & Arshad, 2009). The ash content is determined by minerals accumulated in the sample. The nutritional value of durian seed flour in food would benefit from a higher mineral content. There was very small amounts (0.5–0.6%) in whole seed and demucilaged flour, and it was not detected in starch. Starch content of durian seed samples is also shown in Table 1. It differed significantly between the three forms of each variety (p < 0.05), but not by variety for the same form of samples. Starch content in WDSF was the lowest (36–37% dw). A prior study (Srianta, Hendrawan, Kusumawati, & Blanc, 2012) reported that there was 18.9% (ww) starch in fresh (55.9% mc) durian seed. This is similar to the present work. Note that a specific analysis method was applied to determine how much starch is contained in durian seed flour. Since it is difficult to extract all of the starch from a viscous slurry, extraction results may not be reliable. DDSF contained 68–69% (dw) starch and DS showed the highest starch content (88–89%, dw). Starch content in DS is similar to its carbohydrate content, while those of WDSF and DDSF are much lower than their carbohydrate contents. This indicated that carbohydrates of 5
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The content found clearly depends on the extraction method. Durian seed gum consists of heteropolysaccharide-protein complexes. They have an important role in water holding properties and viscosity. This matches the much lower viscosity of durian seed flour after gum removal (DDSF) compared to WDSF. Durian seed starch had higher PV than DDSF. DDSF contained more lipid that could react with amylose to form amylose-lipid complexes during gelatinization. These could prevent starch molecules from binding with water, which is reflected in longer peak time and lower FV. WDSF showed higher trough viscosity than DDF and DS for both varieties, indicating higher shear resistance than the other forms. The DS and DDSF were similar in trough viscosity. This indicates the influence of mucilage. The pasting temperature did not differ between WDSF, DDSF and starch, or by durian variety: it was about 81 °C in all cases. Overall the RVA pasting behavior with the same form of sample was similar for the two varieties. 3.5. Gelatinization temperature and enthalpy Gelatinization temperatures (To, Tpeak and Tc) of durian seed starch (native variety) were 71.6 ± 0.01, 76.0 ± 0.05 and 79.9 ± 0.1 °C, respectively, and the enthalpy was 14 ± 1 J/g. For the Chanee variety, the To, Tpeak and Tc were slightly higher than those of native variety (74.3 ± 0.2, 78.7 ± 0.1, and 83.1 ± 0.1 °C, respectively). Similar gelatinization enthalpy (14.6 ± 0.5 J/g) was obtained. 3.6. Water and oil absorption capacities (WAC and OAC) The WAC represents the ability of a substance to associate with water under limited availability of water (Jitngarmkusol et al., 2008; Singh, 2001). The WAC is shown in Table 3 for all the cases tested. The WDSF had significantly higher WAC than DDSF or DS, for both durian varieties. Removing the gum from seed flour decreased its ability to absorb water. This matches well the observations of swelling power and of RVA peak viscosity. According to a previous report durian seed gum had WAC of 230–255 g/100 g gum (Mirhosseini & Tabatabaee Amid, 2013) and 1110% for local Indonesian durian seed gum (Cornelia et al., 2015). No prior report on whole durian seed flour is available. From the results, the OAC did not differ significantly between the different forms of samples, for both varieties, while the WDSF tended to have higher OAC than the other forms. The observed OAC is higher than that of durian seed gum in a prior report (113 g oil/100 g gum in Mirhosseini & Tabatabaee Amid, 2013).
Fig. 2. Swelling power (a) and solubility (b) of durian seed from Chanee variety (C) in form of whole durian seed flour (C-WDSF), demucilaged durian seed flour (C-DDSF) and durian seed starch (C-DS) at various temperatures. Error bars represent standard deviations. Different letters are significantly different (p < 0.05).
3.4. Pasting properties The RVA viscograms and parameters are shown in Fig. 3 and Table 2. In the RVA profiles, WDSF had the highest viscosity followed by DS and DDSF, for both varieties. PV of WDSF was much higher than those of DDSF and starch, and PV of starch was slightly higher than that of DDSF. The mucilage content of WDSF was 19–20%, while it has been earlier reported as 18% by Amin et al. (2007) and as 56.4% by Amid and Mirhosseini (2012a).
3.7. Gel hardness and syneresis Gel hardness of WDSF was the lowest, while DS showed the highest gel hardness. Both varieties gave similar results (Table 3). After cooling down the sample paste, it becomes a gel due to macromolecules forming a network. WDSF contains starch and mucilage (which is heteropolysaccharide-protein), so it holds a large amount of water in a weak gel network. Once the mucilage was removed the gel became stronger, and then even stronger for pure starch (DS). Syneresis or water loss from gels contributes to changes in starch gels during retrogradation, and is promoted by amylose content and lower storage temperature. For foods it is accompanied by softening of texture, drip loss during cooking, and overall deterioration of quality (Lee, Baek, Cha, Park, & Lim, 2002). The syneresis of both varieties showed significant differences between sample forms (Table 3). That of WDSF was three fold that of DDSF, while starch was similar to DDSF. This suggests that although the mucilage or gum can absorb a large amount of water it does not form a strong network, instead it easily released water during storage at low temperature.
Fig. 3. Comparison of RVA pasting profiles of durian seed from native (N) and Chanee (C) varieties in form of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). 6
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Table 2 RVA pasting characteristics of durian seeds of native (N) and Chanee (C) varieties in the forms of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
N-WDSF N-DDSF N-DS C-WDSF C-DDSF C-DS
Viscosity (mPa.s)
Peak time (min)
PV
TV
BV
(2.26 ± 0.05) x 103c∗ (1.07 ± 0.01) x 103a (1.3 ± 0.02) x 103b (2.4 ± 0.02) x 103C∗ (1.09 ± 0.02) x 103A (1.33 ± 0.02) x 103B
(1.85 ± 0.03) x 103c∗ (1.01 ± 0.01) x 103a (1.04 ± 0.01) x 103b (2.1 ± 0.1) x 103C∗ (1.04 ± 0.02) x 103A (1.06 ± 0.01) x 103B
(4.0 (6.1 (2.6 (3.2 (5.8 (2.7
FV ± ± ± ± ± ±
0.4) 0.5) 0.4) 0.2) 0.0) 0.1)
x x x x x x
102c 102a 102b 102C 102A 102B
(2.09 (1.59 (2.02 (2.33 (1.64 (2.12
SV ± ± ± ± ± ±
0.003) x 103c∗ 0.03) x 103a 0.03) x 103a 0.01) x 103C∗ 0.03) x 103A 0.03) x 103B
(2.4 ± 0.1) x 102a (5.8 ± 0.6) x 102b (9.7 ± 0.1) x 102c (2.5 ± 0.6) x 102A (6.06 ± 0.1) x 102B (10.6 ± 0.2) x 102C
5.9 ± 0.4b∗ 6.1 ± 0.5b 4.4 ± 0.4a 7.0 ± 0.0B∗ 7.1 ± 0.3B 4.77 ± 0.04A
Mean value and standard deviation of triplicate. Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). Significant differences (at p < 0.05) between varieties, within the same form of sample are indicated by *.
Table 3 Comparison of some functional properties of three forms of durian seeds of Native (N) and Chanee (C) varieties, the forms being whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
WAC* (g water/100 g sample, db)
OAC** (ml oil/100 g sample, db)
N-WDSF N-DDSF N-DS C-WDSF C-DDSF C-DS
(1.1 ± 0.03) x 102c∗ (0.70 ± 0.03) x 102b (0.55 ± 0.01) x 102a∗ (1.5 ± 0.1) x 102C∗ (0.73 ± 0.02) x 102B (0.65 ± 0.01) x 102A∗
(4.1 (4.0 (4.0 (4.8 (4.1 (4.0
± ± ± ± ± ±
0.4) 0.1) 0.2) 0.1) 0.1) 0.6)
x x x x x x
102a∗ 102a 102a 102B∗ 102A 102A
Emulsion activity (%)
Emulsion stability (%)
Gel syneresis (%)
Gel hardness (g)
31 ± 1b∗ 18.8 ± 0.5a∗ 16.1 ± 0.1a∗ 26.5 ± 0.4B∗ 15.3 ± 0.5A∗ 14.8 ± 0.1A∗
52 ± 1c∗ 25 ± 1b∗ 18.3 ± 0.2a∗ 45 ± 1B∗ 21 ± 1A∗ 21.1 ± 0.5A∗
62 ± 1b∗ 24 ± 1a∗ 25.0 ± 0.1a∗ 68.6 ± 0.5B∗ 22.0 ± 0.5A∗ 23.8 ± 0.4A∗
1.9 ± 0.1a∗ 2.2 ± 0.1b∗ 3.4 ± 0.1c∗ 1.62 ± 0.03A∗ 2.1 ± 0.1B∗ 3.54 ± 0.05C∗
Mean value ± standard deviation of at least triplicate. Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). *WAC = water absorption capacity. **OAC = oil absorption capacity. Significant differences (at p < 0.05) between varieties within the same form of sample are shown by *.
composition, which greatly influences the functional properties, as well as TIA and AIA. Gum or mucilage in WDSF has important roles in hydration properties. On comparing the two durian varieties, they appeared mostly similar, except for some RVA viscosities and syneresis being higher for the Chanee variety, while the ES was higher with the native variety. The thermal properties of purified starches also showed only a minor difference between the varieties. The WDSF required the least processing to prepare, also with least losses and correspondingly highest yield, among the forms of durian seed products tested. From that perspective it is the most attractive choice for food applications. Based on the experimental results, WDSF is suitable for moisture retention as hydrated product, for use as emulsifier, or as fat replacer, mainly due to being rich in mucilage hydrocolloids that are compatible with both water and oil. Due to the high syneresis it is not suitable in typical frozen food products, but in soft texture food or as a water binder when mixed with another flour. Application of durian seed flour in a food product could be tested in future research.
3.8. Emulsion activity (EA) and stability (EA and ES) In general, emulsifying agents either help emulsify or maintain emulsion stability, when one type of phase (oil in foods) is dispersed in another incompatible phase (water in foods). EA and ES are used to measure these abilities. WDSF had the highest EA and ES (Table 3) among the cases tested, because it contained the heteropolysaccharide–protein mucilage or gum. This hydrocolloid had a high ability to hydrate and acted as a thickener giving high viscosity, which could stabilize an emulsion by slowing the movements needed for coalescence of dispersed oil droplets. WDSF and DDSF contained 6–8% proteins. By decreasing surface tension and providing electrostatic repulsion on the surfaces of oil droplets, proteins can enable emulsification and stabilize an emulsion. Correspondingly, the EA of DS or DDSF was lower than that of WDSF, because the gum had been removed along with some other lesser components. The ES was higher than EA, especially for the WDSF cases. In the procedure of ES measurement, the heating step enhanced hydration and swelling of starch and non-starch polysaccharides, and increased viscosity. This again retarded coalescence, improving stability. Improving ES should reflect the protein and polysaccharide contents (Amid & Mirhosseini, 2012b; Jitngarmkusol et al., 2008).
Conflicts of interest The authors declare having no conflict of interest.
4. Conclusions
Acknowledgements
Functional properties of WDSF, DDSF and DS were different. The WDSF had about two-fold RVA viscosity and ES, relative to DDSF and starch, while its moisture loss by syneresis was about three-fold. Starch had the highest gel hardness and the least gel syneresis among these three sample forms. Removing gum and purifying samples (to obtain DDSF and DS, respectively) resulted in changes in chemical
This research was funded by the Halal Food Science Center, Department of Food Science and Nutrition, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Thailand (SAT531025S) and the Thai Research Fund (MRG-WII525S095). Dr. Seppo Karrila is acknowledged for language editing. 7
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Chemical and functional properties of durian (Durio zibethinus Murr.) seed flour and starch
T
Surayani Barahenga,b, Taewee Karrilaa,∗ a b
Department of Food Science and Nutrition, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Pattani, 94000, Thailand Pattani Vocational College, Muang District, Pattani, 94000, Thailand
ARTICLE INFO
ABSTRACT
Keywords: Durian (Durio zibethinus Murr) Durian seed flour Durian seed starch Durian seed gum Durian seed mucilage
Durian (Durio zibethinus Murr.) seeds are a waste from durian paste processing that could find applications in food or non-food industries. Durian seeds are mainly composed of starch and mucilage (gum), which influence its properties and hence the potential applications. The objective of this research was to compare the properties of durian seed flour in different forms. Chemical and functional properties were compared among whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF), and durian seed starch (DS), for two varieties of durian called native (N) and Chanee (C). It was found that the durian variety made little difference in chemical and functional properties, in contrast to the processing of the sample. WDSF contained both starch and gum, and had significantly (p < 0.05) more protein, lipid, ash, and fiber than DDSF or DS. The functional properties of WDSF, especially swelling power, water absorption capacity, peak viscosity and emulsifying capacity and activity, were also significantly higher than for DDSF or starch. Among the three forms of durian seed, WDSF showed the lowest gel hardness but highest syneresis, due to its high ability to bind with water to form a weak gel network. In conclusion, the three forms of durian seeds showed different properties. Gum or mucilage in durian seeds had important roles in the functional properties.
1. Introduction Durian (Durio zibethinus Murr.) is a popular and commercially valuable fruit produced in the South-East Asian countries. Only around 30% of a durian fruit is edible while the rest is waste, among which 20–25% of the whole fruit is seeds (Amin, Ahmad, Yin, Yahya, & Ibrahim, 2007). Durian seeds have two main components: starch, and mucilage or gum. Some properties of durian seed starch have been reported previously (Tongdang, 2008). Durian seed starch is similar to rice starch in terms of the ∼4–5 μm granule size (Tongdang, 2008). However, extracting starch from durian flour has a low yield, about 10% relative to dry seed flour (Tongdang, 2008). This is because the gum in seeds absorbs a large amount of water (Amid & Mirhosseini, 2012a) making a viscous suspension that traps starch granules preventing their release. There are many studies available on durian seed gum showing its composition and functional properties, and suggesting extraction methods (Amin et al., 2007; Amid, Mirhosseini, & Kostadinović, 2012; Amid & Mirhosseini, 2012a, b, c). Durian seed gum yield is about 56% of dry seed flour with aqueous extraction (Amid & Mirhosseini, 2012a). The mucilage or gum consists of polysaccharides and proteins. The
∗
polysaccharides include galactose (48.6–59.9%), glucose (37.1–45.1%), arabinose (0.58–3.41%), and xylose (0.3–3.21%); and the proteins only contain 12 different amino acids (Amid et al., 2012). This gum has high water holding capacity, 140–274 g water/100 g gum, as well as high oil holding capacity (147 g oil/100 g gum) (Amid & Mirhosseini, 2012a). Gum from durian seeds has been used experimentally as an emulsifier in vegan mayonnaise, to replace egg yolk (Cornelia, Siratantri, & Prawita, 2015). Utilization of whole durian seed flour containing both gum and starch, i.e., without removing the gum, would allow simpler and less expensive preparation of such flour. When durian seed flour was used to partially substitute for corn flour to make gluten free pasta, a positive effect on texture was observed, but high contents (50% substitution) had negative effects on color and aroma of the pasta product (Mirhosseini et al., 2015). Durian seed flour without gum should have different functional properties from the whole seed flour. So far most studies have focused on durian seed gum, while information on whole durian seed flour remains limited. In this study a comparison of chemical and functional properties of durian seed starch, and durian seed flours with and without gum was carried out for seeds representing two varieties of
Corresponding author. E-mail addresses: [email protected] (S. Baraheng), [email protected], [email protected] (T. Karrila).
https://doi.org/10.1016/j.fbio.2019.100412 Received 7 August 2018; Received in revised form 1 May 2019; Accepted 2 May 2019 Available online 03 May 2019 2212-4292/ © 2019 Elsevier Ltd. All rights reserved.
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durian (native and Chanee varieties) that are common in Thailand.
2 min. The flour slurry was screened with a nylon cloth, to obtain the sample cake. This step was repeated three times. The filter cake was then mixed with 0.05 M NaOH and centrifuged (HARRIER 15/80 Bench Top Refrigerated Centrifuge, Sanyo Electric Co., Ltd., Osaka, Japan) at 20 °C at 1600×g for 15 min. The supernatant was drained and the yellowish upper part of the sediment was discarded. This step was repeated until a clear supernatant was obtained. The sediment starch was washed and neutralized with water and HCl (0.1 M). To remove water, the starch slurry was filtered with a porosity no. 4 (10–16 μM pore size) sintered glass funnel (Fisher Scientific Ltd., Leicester, England) connected to vacuum pump. The starch was dried at 45 °C and packed and stored as previously.
2. Materials and methods 2.1. Chemicals All chemicals used in this study were purchased from Sigma Aldrich Co. (St. Louis, MO, USA), through a local distributor in Thailand (Boss Oftical Ltd. Partnership, Songkhla, Thailand). 2.2. Durian seed samples Seeds of the two durian varieties were collected from waste of durian paste processing. Fully ripe durian fruit was dehusked, and the flesh was detached from seeds. The flesh was further processed to durian paste, mixing with sugar and stirring over low heat until thickened, while the seeds were collected and used in this study. The samples of the native variety (N) were from Ra-ngae district, Narathiwat province, southern Thailand, and those of the Chanee variety (C) were from Patong district, Rayong province, eastern Thailand. Both sites had similar production processes. Chanee has larger fruit (2.5–4.5 kg) than the native (0.5–1.2 kg), but they have similar seed size. Each fruit has ∼10–18 seeds, depending on the fruit's size. The seeds were prepared in three forms: whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF), and durian seed starch (DS).
2.3. Analysis methods 2.3.1. Chemical composition, starch content and amylose content Moisture, protein, lipid and ash contents of flour and starch were determined following AOAC procedures (AOAC, 2000). The Kjeldahl factor for protein content was 6.25. The amylose contents of the starch samples, after lipid extraction, were estimated using the iodine method (International Organization for Standardization, 1987, pp. 2–3). Defatted starch (100 mg, dw) was dispersed with 1 mL of 95% ethanol and suspended in 9 mL of 1 M NaOH. The suspension was heated for 30 min at 95 °C and then left overnight. The solution was diluted to 100 mL and a 5 mL aliquot, to which 25 mL of distilled water, 0.5 mL of 1 M acetic acid and 1 mL of iodine solution (0.2% iodine in 2% potassium iodide) were mixed and brought to 50 mL. The solution was left for ∼20 min in a dark room for color development. The absorbance was measured at 620 nm with a spectrophotometer (UV–Visible spectrophotometer, Libra S22, Biochrom, Cambridge, England). The sample blank was distilled water. Each measurement was done in triplicate. The standard curve for amylose content was prepared using mixtures of pure amylose and amylopectin. Amylose and amylopectin solutions (1 mg, dw/mL) were prepared in a similar manner to flour or starch samples. These solutions were mixed to make the proportion of amylose (by volume) range from 0 to 40%. Aliquots (5 mL) of the mixtures were reacted with the iodine solution and handled, thereafter, as previously. The standard curve was then plotted as absorbance against amylose content. The linear model from the plot was
2.2.1. Whole durian seed flour (WDSF) preparation Fresh durian seeds of about 5–7 cm length and 3–4 cm width were washed with water, and the seeds were manually dehulled by removing the brown 2–4 mm thick seed coat with a sharp knife. Dehulled seeds were then sliced with a sharp knife into thin (about 2 mm thick) chips and tray dried at 55 °C until the moisture content was below 12%, verified using a moisture analyzer (Sartorius MA150, Sartorius (Thailand), Ltd. Bangkok, Thailand) as a rapid method. The chips were ground using a laboratory grinder (Sottoria S. p. A., Marano Vicentino, Italy) into a powder, and passed through a 100 mesh (150 μm) sieve to obtain durian seed flour (WDSF). The WDSF was kept in plastic polyethylene bottles with tight lids, and stored in a refrigerator (4–5 °C) for a maximum of 54 wk. 2.2.2. Demucilaged durian seed flour (DDSF) The demucilaged durian seed flour (DDSF) was prepared from the WDSF in 2.2.1 as follows. Fifty g of WDSF was mixed with 200 mL saturated alum solution and soaked for 2.5 h. The top layer of the mixture was discarded, and the sediment was collected. Distilled water (200 mL) was added and left for 20 min, then the top layer was removed. This step was repeated a second time. The remaining flour (sediment) was mixed with 200 mL 1% NaHCO3 and soaked for 2 h. The liquid was then discarded and the flour obtained was washed with distilled water twice. The filter slurry was then mixed with 200 mL 0.075% Na2S2O5, and this slurry was filtered using a nylon cloth bought from a local shop in Muang district, Pattani provice, Thailand. The flour cake was washed with distilled water twice. The water was removed using a filter press (Kliuy Num Thai, Bangkok, Thailand) with polypropylene cloth filters (Siamnathan International Co., Samuthprakhan, Thailand). The filter cake was dried at 45 °C until its moisture content was below 14%, then milled using a mortar and pestle, and passed through a 100 mesh sieve. The DDSF obtained was packed and stored like the WDSF.
y = 0.0154x+0.4849, with R2 = 0.9916 Where: y = absorbance at 620 nm and x = amylose content (%). Each measurement was done in triplicate. Total starch content was measured using a Megazyme Assay Kit (KTSTA) (Megazyme Intl., Bray, County Wicklow, Ireland). Briefly, the 100 mg sample was wet with 0.2 mL of ethanol solution (80%, v/v). Immediately 300 units of thermostable α-amylase in 3 mL of MOPS buffer (50 mM, pH7) was added, which was then boiled for 6 min in 4 mL of sodium acetate buffer (200 mM, pH 4.5). One unit (U) of αamylase activity is the amount of enzyme required to release 1 μmol pnitrophenol from p-nitrophenyl maltoheptaoside in the presence of saturating levels of α-glucosidase and amyloglucosidase (i.e., Ceralpha αamylase assay reagent) at 40 °C and pH 6 and 11. After that, 20 units of amyloglucosidase were added and incubated at 50 °C for 30 min before adjusting with distilled water to 10 mL, and centrifuged at 1800×g for 10 min at 20 °C. One unit of amyloglucosidase is the amount of enzyme required to release 1 μmol p-nitrophenol from p-nitrophenyl β-maltoside in the presence of saturating levels of β-glucosidase, i.e., amyloglucosidase assay reagent, at 40 °C and pH 4.5 and 12.0. A 1.0 mL aliquot from the supernatant was diluted to 10 mL with distilled water. Then, 0.1 mL of this diluted solution was mixed with 3 mL of glucose oxidase peroxidase (GOPOD: a mixture of glucose oxidase > 12000 U/ L; peroxidase, > 650 U/L; and 0.4 mM 4-aminoantipyrine) and
2.2.3. Durian seed starch Durian seed starch was isolated from the DDSF following the method described in a previous report (Tongdang, 2008). The DDSF was mixed with three volumes of 1% aqueous NaCl, and blended with a kitchen blender (HR2115/02, Phillips Co., Bangkok, Thailand) for 2
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incubated at 50 °C for 20 min. Sample blanks (distilled water) and glucose control (1 mg/mL) were also prepared in the same manner as the actual samples. Absorbance was measured at 510 nm against the blank. The measurements were done in triplicates. Starch content was calculated (McCleary, Gibson, & Mugford, 1997) as:
One α-amylase inhibitory unit (IU) was defined as IU/g of dw from the maltose calibration curve. 2.3.3. Swelling power and solubility Swelling power and solubility were measured at 55, 65, 75, 85 and 95 °C (Kong, Bao, & Corke, 2009). Each sample (100 mg, dw) was mixed well with 10 mL distilled water before heating in a water bath with temperature control for 30 min. The sample was cooled to room temperature in ice water before centrifuging at 2000×g for 30 min. The supernatant was dried at 105 °C in a hot air oven until constant weight (W1) and the wet sediment was also weighed (Ws). The water solubility (WS) and swelling power (SP) were calculated as follows:
Starch (% ww) = A x F x 1000 × (1/1000) x (100/W) x (162/180) = A x (F/W) x 90 Where A = absorbance of reaction solution; F = factor to convert absorbance value to μg glucose = 100 μg glucose/absorbance of 100 μg glucose; 1000 = volume correction, i. e., 0.1 mL taken from 100 mL; 1/ 1000 = conversion from μg to mg; 100/W = conversion to 100 mg sample; 162/180 = factor to convert from free glucose, as determined, to anhydroglucose as its form in starch.
WS (%) = (W1/0.1) × 100 SP (g/g). = Ws/[0.1(100%-WS)]
2.3.2. Trypsin and α-amylase inhibitor activities Trypsin inhibitor activity (TIA) was determined according to the method described by Raj Bhandari and Kawabata (2006) with modifications. Briefly, a one g dried sample was mixed with 50 mL of 10 mM NaOH. The pH of the resulting slurry was adjusted to 9.5 ± 0.1 with 1 M NaOH or 1 M HCl. The slurry was shaken and then stirred at room temperature (28 ± 1 °C) for 3 h. After this extraction the clear suspension was used for inhibitor activity estimation. The following blends were used: in a series of 10 mL tubes: (a) reagent blank: 2 mL deionized water (MIT Technology Ltd., Bangkok, Thailand); (b) reference: standard trypsin (Sigma Aldrich Co., St. Louis, MO, USA) solution (40 mg trypsin) in 2 mL deionized water; (c) sample blank: 1 mL sample extract with 1 mL of deionized water; (d) sample: 1 mL sample extract with 1 mL deionized water and 2 mL standard trypsin solution. After mixing and preheating to 37 °C for 10 min, 5 mL of BAPNA (benzoyl-DL-arginine-p-nitroanilide hydrochloride) solution (previously warmed to 37 °C) was added and mixed. After exactly 10 min incubation at 37 °C, 1 mL acetic acid (30% v/v) was added to stop the reaction. Standard trypsin (2 mL) was then added to the reagent blank (a) and sample blank (c). After centrifugation (at 2200×g, at 20 °C for 20 min), the absorbances of the clear solutions were measured at 410 nm. The TIA was estimated in terms of weight of pure trypsin inhibited/g dw, and this is explained by Smith, Megen, Twaalfhoven, and Hitchcock (1980) (see section 2.2.4 of the reference), which explains in more detail the logic behind the formula. Since 1 μg trypsin would give an absorbance of 0.019, the weight of trypsin inhibited/mL of diluted sample extract is Ai/0.019 g (i.e., 50Ai/ 19 mg/50 mL). From this value the trypsin inhibitor activity (TIA) was calculated in terms of mg trypsin/g sample
2.3.4. Pasting properties Pasting properties were measured using a Rapid Visco Analyzer (RVA, RVA4D, Newport Scientific, Warriewood, Australia). To each 3 g (dw) sample (corrected for the 14% moisture content), distilled water was added for a total weight of 28 g. Then the paddle was inserted into the RVA sample can. To prevent clumping in the suspension, the paddle was jogged up and down 10 times before starting the actual RVA test. The pre-programmed standard temperature profile for heating and cooling was used. The sample was held at 50 °C for 1 min, heated from 50 to 95 °C in 4 min, held at 95 °C for 2 min before cooling to 50 °C in 4 min, and held at 50 °C for 2 min. For the first 10 s the stirring speed was 960 rpm, and for the remainder of the test it was 160 rpm. The Thermocline software provided with the instrument recorded the pasting curves, extracting from them the characterizing peak viscosity (PV, the highest viscosity achieved during heating from 50 to 95 °C), trough viscosity (TV, the lowest viscosity achieved during heating at 95 °C), final viscosity (FV, the paste viscosity upon cooling to 50 °C), breakdown viscosity (BV]PV-TV), setback viscosity (SV]FV-TV, indicating starch retrogradation tendency after gelatinization and cooling at 50 °C), pasting temperature (the temperature at which viscosity starts to rise), and peak time (time it takes from beginning of test to reach peak viscosity). 2.3.5. Gelatinization temperature and enthalpy The purified starches were also characterized for transition temperature and enthalpy with a differential scanning calorimeter (DSC7, PerkinElmer, Norwalk, CT, USA) following the procedure in Tongdang (2008). The temperatures of onset, (To), peak (Tpeak) and conclusion (Tc) as well as the enthalpy were measured using the software with the instrument and each type of sample was measured in triplicate.
TIA = (2.632 × Dilution factor x Ai/S) mg trypsin inhibited/g sample;
2.3.6. Water and oil absorption capacity Water absorption capacity (WAC) for durian seed flour and starch was determined as described in Maninder, Sandhu, and Singh (2007). A one g flour sample (dw) was suspended in 10 mL of distilled water in a centrifugation tube and mixed well in a Vortex shaker (VORTEXGENIE® 2, Scientific Industries, Inc., Bohemia, NY, USA.) for 2 min. The suspension was held at room temperature for 30 min before centrifuging at 3000×g for 25 min. The supernatant was decanted and the excess water in the sediment was drained for 25 min. The sediment was then weighted (Sdw). The water absorption capacity is expressed as g water absorbed/g flour (dw).
Ai is the change in absorbance, (Ab-Aa)-(Ad- Ac), due to trypsin inhibition (/mL diluted sample extract) where the subscripts (a)-(d) are described above, and S is the sample weight in g. α-Amylase inhibitor activity (AIA) was evaluated according to the method of Alonso, Orue, and Marzo (1998), as described in Raj Bhandari and Kawabata (2006). A one g sample was extracted with 10 mL of deionized water for 12 h at 4 °C and the supernatant (centrifugation at 2200×g at 20 °C for 20 min) was tested for AIA as follows: 0.25 mL of the sample extract was incubated with 0.25 mL of α-amylase enzyme (Sigma Aldrich Co.) solution (0.003% in 0.2 M sodium phosphate buffer, pH 7.0, with 0.006 M NaCl) for 15 min at 37 °C. To this mixture 0.5 mL of 1% starch solution (pre-incubated at 37 °C) was added. At the end of 3 min, the reaction was stopped by adding 2 mL of dinitrosalicylic acid and boiling for 10 min. The absorbance was measured at 540 nm. One unit of enzyme activity was defined as that which liberates one umole of reducing groups (calculated as maltose)/min at 37 °C and pH 7 from the soluble starch with the specified conditions.
WAC = (Sdw–Sw) / Sw Where Sdw is sediment weight and SW is initial sample weight. The OAC was determined similarly as WAC, but by mixing a 0.5 g sample (dw) with 6 mL of soybean oil (Thanakorn Vegetable Oil Products Co., Ltd., Samutprakarn, Thailand). 3
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Table 1 Chemical compositions and trypsin inhibitor activities (TIA) as well as α-amylase inhibitor activities (AIA) for durian seeds of native (N) and Chanee (C) varieties in the forms of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
Moisture (%)
Lipid (%, dw)
Protein (%, dw)
Fiber (%, dw)
Ash (%, dw)
Carbohydrate (%, dw)
Starch content (%, dw)
TIA (mg pure trypsin inhibited/g sample, dw)
N-WDSF N-DDF N-DS C-WDSF C-DDF C-DS
9.0 ± 0.1a 8.4 ± 0.3ab∗ 9.4 ± 0.7b∗ 9.7 ± 0.4A 9.9 ± 0.2A∗ 11 ± 0.01B∗
0.64 ± 0.05b 0.5 ± 0.1a nd 0.6 ± 0.1B 0.52 ± 0.01A nd
8.6 ± 0.4c∗ 6.7 ± 0.9b 0.17 ± 0.01a 7.2 ± 0.2B∗ 6.6 ± 0.6B 0.2 ± 0.0A
0.9 ± 0.2b 0.75 ± 0.26b 0.13 ± 0.10a 0.82 ± 0.22B 0.6 ± 0.3B 0.01 ± 0.00A
4.5 ± 0.7c 2.0 ± 0.1b∗ 0.5 ± 0.2a 4.5 ± 0.3C 3.8 ± 0.1B∗ 0.53 ± 0.04A
77 ± 1a 82 ± 1b∗ 90 ± 1c 77 ± 1A 79 ± 1A∗ 88 ± 0B
36.8 ± 0.1a 69 ± 1b 90 ± 1c 37.0 ± 0.4A 69.4 ± 0.3B 88 ± 1C
1.0 0.7 0.3 2.8 2.1 0.4
± ± ± ± ± ±
0.2c∗ 0.1b∗ 0.1a 0.1C∗ 0.1B∗ 0.1A
AIA (unit/g sample, dw)
6.4 ± 0.4c∗ 1.6 ± 0.1b∗ 0.4 ± 0.01a 4.2 ± 0.3c∗ 0.45 ± 0.01b∗ 0.38 ± 0.01a
Mean value ± standard deviation of triplicate. Carbohydrate = 100-(moisture + lipid + protein + fiber + ash). Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). Significant differences (at p < 0.5).between varieties, within the same form of sample, are indicated by *. nd = not detected. TIA=Trypsin inhibitor activity (mg pure trypsin inhibited/gram sample, dw). AIA = α-Amylase inhibitor activity (unit/g sample, dw).
2.3.7. Gel hardness The flour or starch slurry (12% w/w) in a 100 mL beaker was heated at 95 °C for 30 min, with constant stirring. After cooking the samples were allowed to cool at room temperature for 3 h. The gels were then cut with a sharp knife to 1.5 × 1.5 × 1.5 cm size. The texture profile analysis (TPA) of gels was then measured with a texture analyzer (TAXT2i, Stable Micro Systems Ltd., Surrey, UK). The modified method used the two-cycle compression test (test speed 1.0 mm/s, with 3.0 g trigger force to a distance of 2.0 mm with a P/50 probe, and 200 pps data acquisition rate). The maximum force during the first compression was recorded as hardness. Five repeated measurements were done and their average is reported. Data for the other texture parameters were lost in the software.
EA (%) = ν2 × 100/ν1 ES (%) = ν3 × 100/ν1 Where ν1 is the initial volume of the emulsion before centrifugation, ν2 is the volume of the emulsified layer, and ν3 is the volume of the remaining emulsified layer after heating. 2.4. Statistical analysis The experiments were done using a completely randomized design. Two way analysis of variance (ANOVA) was used to test the effects of sample forms, and the statistical significances were post hoc tested with the Multiple Range Duncan's test (p < 0.05). The t-test was used to compare the two varieties. The Statistical Package for the Social Sciences (V.13) statistical software (IBM, Armonk, NY, USA) was used.
2.3.8. Syneresis Sample suspension in distilled water (6%, db w/v) was prepared and heated in a water bath at 95 °C for 30 min, with constant stirring. After cooling to room temperature, the samples were placed in a still-air freezer at −20 °C for 22 h, and later placed in a 30 °C water bath for 1.5 h to thaw until equilibrated. Five such cycles of alternating freezing and thawing were done before centrifuging at 3000×g for 20 min. The separated water was measured. The syneresis was calculated as % of water released from the gel after centrifugation. Experiments were done in triplicate (Wang et al., 2010).
3. Results and discussion 3.1. Chemical composition and amylose content The chemical compositions of WDSF, DDSF and starch for both varieties are shown in Table 1. The moisture contents of flours and starches were in the range 8.95–9.69% for native variety and 9.4–11.0% for the Chanee variety. The lipid content was less than 1% in all cases. WDSF had higher lipid content than DDSF, and it was below detection level in the starches. For both varieties, protein content of WDSF was in the range 7.16–8.56% (dw), which was significantly (p < 0.05) higher than in the DDSF (6.55–6.73% dw) or in starch (0.17% dw). This shows that most proteins of durian seed flour stayed in DDSF, so they were not removed with the mucilage or gum. The protein in DDSF was mostly removed during starch isolation, so that only a very small amount remained in the starch. The choice of durian variety had no effect on the protein content, while the form of sample significantly affected protein. A previous study reported 7.6% protein in whole durian seed flour (Amin & Arshad, 2009). The crude fiber contents of both varieties, in the same form of samples, were similar. However, within a variety the fiber content of processed durian seed had the rank order WDSF > DDSF > DS, with statistically significant differences. The results (for dehulled samples, or WDSF) were lower than those reported earlier (Amin & Arshad, 2009). This happened even though the earlier study sampled the seeds of the same durian species (Durio zibethinus Murr.), while the cultivars can differ. Durian seed as biomaterial has natural variability in chemical composition. As an available example of such variation, the crude fiber
2.3.9. Emulsion activity and stability Emulsion activity (EA) and emulsion stability (ES) were determined using the methods described by Jitngarmkusol, Hongsuwankul, and Tananuwong (2008). The flour sample (1 g dw) was dispersed in 50 mL of distilled water. The mixture was homogenized with a homogenizer (X10/25, Ystral, Ballrechten-Dottingen, Germany) for 30 s before adding 25 mL of soybean oil (Thanakorn Vegetable Oil Products Co., Ltd., Samutprakarn, Thailand).The mixture was homogenized again for 30 s, and then another 25 mL of soybean oil was added. The mixtures were homogenized once more for 90 s. Each emulsified sample was divided equally into two centrifuge tubes. For emulsion activity determination the first tube was immediately centrifuged at 1500×g for 5 min, and the volume of the emulsified layer was measured (ν2). To determine the emulsion stability, the second centrifuge tube was heated in a water bath at 85 °C for 15 min, then cooled down to room temperature, and centrifuged like the first sample. The volume of the remaining emulsified layer after heating was measured (ν3). The measurements were done in triplicates. EA and ES were calculated using the following equations: 4
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WDSF contain both starch and non-starch polysaccharides (gums). In a previous report Malaysian researchers extracted 56% gum from the dry flour (Amid & Mirhosseini, 2012a). Apparently the DDSF had remnants of gum, despite attempted removal. Durian seed gum is considered dietary fiber (Amin & Arshad, 2009) and cannot be digested by digestive enzymes. Most of it could be soluble dietary fiber. Overall, for both varieties the secondary chemical components (lipid, protein, ash and fiber) were significantly higher in WDSF than in DDSF, and very small amounts remained in DS, while the carbohydrate contents had the opposite rank order. The amylose content was determined only for the durian seed starches (Table 1) as 23.3 and 22.9% (dw) for native and Chanee variety, respectively. This is similar to a previous report, which found 22.8% amylose (Tongdang, 2008). 3.2. Trypsin and amylase inhibitor activities (TIA and AIA) For the TIA and AIA, the rank order of activities was WDSF > DDSF > DS (Table 1). This means TIA and AIA are mostly located in the gum component of durian seed. Removing gum from seed flour significantly decreased TIA and AIA. DS showed the least AIA and TIA possibly because it had very low protein content, since protein was removed in the starch extraction process. TIA and AIA are considered anti-nutrient activity indicators. They can be found in many kinds of plant products, such as wild yam tubers (Raj Bhandari & Kawabata, 2006), and amaranth (Amaranthus hypocondriacus) seeds (ChagollaLopez, Blanco-Labran, Patthyll, Sanchez, & Pongor, 1994). The antinutrient activities could be decreased by heat treatment (Raj Bhandari & Kawabata, 2006). Fig. 1. Swelling power (a) and solubility (b) of durian seed from native variety (N) in form of whole durian seed flour (N-WDSF), demucilaged durian seed flour (N-DDSF) and durian seed starch (N-DS) at various temperatures. Error bars represent standard deviations. Different letters are significantly different (p < 0.05).
3.3. Swelling power (SP) and solubility On heating starch with water, a phase transition of the starch called gelatinization occurs. SP and solubility provide evidence of interactions between water molecules and starch chains in amorphous and crystalline domains of the starch granules (Aboubakar, Njintang, Scher, & Mbofung, 2008). The SP and solubility of flours and starches were measured at 55–95 °C as shown in Fig. 1a and b, respectively, for the native variety, and in Fig. 2a and b for the Chanee variety. Both SP and solubility increased with temperature, as expected. For N-WDSF, the SP (Fig. 1a) increased rapidly with temperatures from 55 to 75 °C, and then slowly from 75 to 95 °C, similar to the NDDSF. The SP of N-DS increased slowly in the beginning, then rapidly after 65 °C. With SP these different sample forms had the rank order WDSF > DDSF > DS. The Chanee variety showed similar swelling behavior (Fig. 2a). For both varieties, the SP of WDSF was consistently higher than those of DDSF and DS. These results suggested that the non-starch components in WDSF, particularly the mucilage, contributed significantly to water absorption (Aboubakar et al., 2008). The gum of durian seed consists of protein-polysaccharide complexes and can absorb relatively large amounts of water (Amid & Mirhosseini, 2012a). WDSF can immediately bind water at room temperature and gives very viscous mixtures. Once the mucilage was removed, the ability to bind water decreased as seen in the SP. The solubility behaviors gave the same grouping as the swelling behaviors. The WDSF of both N and C varieties had the highest solubility among the sample types at all temperatures tested, and it increased as temperature increased (Fig. 1b). Mucilage or gum in durian seeds has an important role in solubility. Once it was removed the solubility of DDSF decreased by around 50% or more at all temperatures tested. DDSF and DS did not significantly differ in solubility, and these were very sparingly soluble at 55–75 °C, although at 85 and 95 °C the DS had higher solubility than the DDSF, for both varieties. This could be due to the secondary components interacting with starch molecules during gelatinization.
of 8 cultivars of Orono dunich (Plectranthus edutis) tubers varied within the range 1.15–4.16% (Giftya, Bruno De Meulenaera, & Olangob, 2018). Durian seed flour preparation could also affect its fiber content, i. e., depending on how well the seed coat, containing cellulose, was removed in the dehulling step. For the above reasons, while the fiber content does not agree with a prior publication it can be considered reasonable. For both varieties, ash content in WDSF was higher than in DDSF or in seed starch (p < 0.05). However, only DDSF had a significant difference between the varieties, with the native variety having higher ash than Chanee. The ash content of WDSF is similar to a prior report, in which durian seed flour contained 3.8% ash (Amin & Arshad, 2009). The ash content is determined by minerals accumulated in the sample. The nutritional value of durian seed flour in food would benefit from a higher mineral content. There was very small amounts (0.5–0.6%) in whole seed and demucilaged flour, and it was not detected in starch. Starch content of durian seed samples is also shown in Table 1. It differed significantly between the three forms of each variety (p < 0.05), but not by variety for the same form of samples. Starch content in WDSF was the lowest (36–37% dw). A prior study (Srianta, Hendrawan, Kusumawati, & Blanc, 2012) reported that there was 18.9% (ww) starch in fresh (55.9% mc) durian seed. This is similar to the present work. Note that a specific analysis method was applied to determine how much starch is contained in durian seed flour. Since it is difficult to extract all of the starch from a viscous slurry, extraction results may not be reliable. DDSF contained 68–69% (dw) starch and DS showed the highest starch content (88–89%, dw). Starch content in DS is similar to its carbohydrate content, while those of WDSF and DDSF are much lower than their carbohydrate contents. This indicated that carbohydrates of 5
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The content found clearly depends on the extraction method. Durian seed gum consists of heteropolysaccharide-protein complexes. They have an important role in water holding properties and viscosity. This matches the much lower viscosity of durian seed flour after gum removal (DDSF) compared to WDSF. Durian seed starch had higher PV than DDSF. DDSF contained more lipid that could react with amylose to form amylose-lipid complexes during gelatinization. These could prevent starch molecules from binding with water, which is reflected in longer peak time and lower FV. WDSF showed higher trough viscosity than DDF and DS for both varieties, indicating higher shear resistance than the other forms. The DS and DDSF were similar in trough viscosity. This indicates the influence of mucilage. The pasting temperature did not differ between WDSF, DDSF and starch, or by durian variety: it was about 81 °C in all cases. Overall the RVA pasting behavior with the same form of sample was similar for the two varieties. 3.5. Gelatinization temperature and enthalpy Gelatinization temperatures (To, Tpeak and Tc) of durian seed starch (native variety) were 71.6 ± 0.01, 76.0 ± 0.05 and 79.9 ± 0.1 °C, respectively, and the enthalpy was 14 ± 1 J/g. For the Chanee variety, the To, Tpeak and Tc were slightly higher than those of native variety (74.3 ± 0.2, 78.7 ± 0.1, and 83.1 ± 0.1 °C, respectively). Similar gelatinization enthalpy (14.6 ± 0.5 J/g) was obtained. 3.6. Water and oil absorption capacities (WAC and OAC) The WAC represents the ability of a substance to associate with water under limited availability of water (Jitngarmkusol et al., 2008; Singh, 2001). The WAC is shown in Table 3 for all the cases tested. The WDSF had significantly higher WAC than DDSF or DS, for both durian varieties. Removing the gum from seed flour decreased its ability to absorb water. This matches well the observations of swelling power and of RVA peak viscosity. According to a previous report durian seed gum had WAC of 230–255 g/100 g gum (Mirhosseini & Tabatabaee Amid, 2013) and 1110% for local Indonesian durian seed gum (Cornelia et al., 2015). No prior report on whole durian seed flour is available. From the results, the OAC did not differ significantly between the different forms of samples, for both varieties, while the WDSF tended to have higher OAC than the other forms. The observed OAC is higher than that of durian seed gum in a prior report (113 g oil/100 g gum in Mirhosseini & Tabatabaee Amid, 2013).
Fig. 2. Swelling power (a) and solubility (b) of durian seed from Chanee variety (C) in form of whole durian seed flour (C-WDSF), demucilaged durian seed flour (C-DDSF) and durian seed starch (C-DS) at various temperatures. Error bars represent standard deviations. Different letters are significantly different (p < 0.05).
3.4. Pasting properties The RVA viscograms and parameters are shown in Fig. 3 and Table 2. In the RVA profiles, WDSF had the highest viscosity followed by DS and DDSF, for both varieties. PV of WDSF was much higher than those of DDSF and starch, and PV of starch was slightly higher than that of DDSF. The mucilage content of WDSF was 19–20%, while it has been earlier reported as 18% by Amin et al. (2007) and as 56.4% by Amid and Mirhosseini (2012a).
3.7. Gel hardness and syneresis Gel hardness of WDSF was the lowest, while DS showed the highest gel hardness. Both varieties gave similar results (Table 3). After cooling down the sample paste, it becomes a gel due to macromolecules forming a network. WDSF contains starch and mucilage (which is heteropolysaccharide-protein), so it holds a large amount of water in a weak gel network. Once the mucilage was removed the gel became stronger, and then even stronger for pure starch (DS). Syneresis or water loss from gels contributes to changes in starch gels during retrogradation, and is promoted by amylose content and lower storage temperature. For foods it is accompanied by softening of texture, drip loss during cooking, and overall deterioration of quality (Lee, Baek, Cha, Park, & Lim, 2002). The syneresis of both varieties showed significant differences between sample forms (Table 3). That of WDSF was three fold that of DDSF, while starch was similar to DDSF. This suggests that although the mucilage or gum can absorb a large amount of water it does not form a strong network, instead it easily released water during storage at low temperature.
Fig. 3. Comparison of RVA pasting profiles of durian seed from native (N) and Chanee (C) varieties in form of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). 6
Food Bioscience 30 (2019) 100412
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Table 2 RVA pasting characteristics of durian seeds of native (N) and Chanee (C) varieties in the forms of whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
N-WDSF N-DDSF N-DS C-WDSF C-DDSF C-DS
Viscosity (mPa.s)
Peak time (min)
PV
TV
BV
(2.26 ± 0.05) x 103c∗ (1.07 ± 0.01) x 103a (1.3 ± 0.02) x 103b (2.4 ± 0.02) x 103C∗ (1.09 ± 0.02) x 103A (1.33 ± 0.02) x 103B
(1.85 ± 0.03) x 103c∗ (1.01 ± 0.01) x 103a (1.04 ± 0.01) x 103b (2.1 ± 0.1) x 103C∗ (1.04 ± 0.02) x 103A (1.06 ± 0.01) x 103B
(4.0 (6.1 (2.6 (3.2 (5.8 (2.7
FV ± ± ± ± ± ±
0.4) 0.5) 0.4) 0.2) 0.0) 0.1)
x x x x x x
102c 102a 102b 102C 102A 102B
(2.09 (1.59 (2.02 (2.33 (1.64 (2.12
SV ± ± ± ± ± ±
0.003) x 103c∗ 0.03) x 103a 0.03) x 103a 0.01) x 103C∗ 0.03) x 103A 0.03) x 103B
(2.4 ± 0.1) x 102a (5.8 ± 0.6) x 102b (9.7 ± 0.1) x 102c (2.5 ± 0.6) x 102A (6.06 ± 0.1) x 102B (10.6 ± 0.2) x 102C
5.9 ± 0.4b∗ 6.1 ± 0.5b 4.4 ± 0.4a 7.0 ± 0.0B∗ 7.1 ± 0.3B 4.77 ± 0.04A
Mean value and standard deviation of triplicate. Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). Significant differences (at p < 0.05) between varieties, within the same form of sample are indicated by *.
Table 3 Comparison of some functional properties of three forms of durian seeds of Native (N) and Chanee (C) varieties, the forms being whole durian seed flour (WDSF), demucilaged durian seed flour (DDSF) and durian seed starch (DS). Durian seed sample
WAC* (g water/100 g sample, db)
OAC** (ml oil/100 g sample, db)
N-WDSF N-DDSF N-DS C-WDSF C-DDSF C-DS
(1.1 ± 0.03) x 102c∗ (0.70 ± 0.03) x 102b (0.55 ± 0.01) x 102a∗ (1.5 ± 0.1) x 102C∗ (0.73 ± 0.02) x 102B (0.65 ± 0.01) x 102A∗
(4.1 (4.0 (4.0 (4.8 (4.1 (4.0
± ± ± ± ± ±
0.4) 0.1) 0.2) 0.1) 0.1) 0.6)
x x x x x x
102a∗ 102a 102a 102B∗ 102A 102A
Emulsion activity (%)
Emulsion stability (%)
Gel syneresis (%)
Gel hardness (g)
31 ± 1b∗ 18.8 ± 0.5a∗ 16.1 ± 0.1a∗ 26.5 ± 0.4B∗ 15.3 ± 0.5A∗ 14.8 ± 0.1A∗
52 ± 1c∗ 25 ± 1b∗ 18.3 ± 0.2a∗ 45 ± 1B∗ 21 ± 1A∗ 21.1 ± 0.5A∗
62 ± 1b∗ 24 ± 1a∗ 25.0 ± 0.1a∗ 68.6 ± 0.5B∗ 22.0 ± 0.5A∗ 23.8 ± 0.4A∗
1.9 ± 0.1a∗ 2.2 ± 0.1b∗ 3.4 ± 0.1c∗ 1.62 ± 0.03A∗ 2.1 ± 0.1B∗ 3.54 ± 0.05C∗
Mean value ± standard deviation of at least triplicate. Different letters in the same column within the same variety (N or C) indicate significant differences (p < 0.05). *WAC = water absorption capacity. **OAC = oil absorption capacity. Significant differences (at p < 0.05) between varieties within the same form of sample are shown by *.
composition, which greatly influences the functional properties, as well as TIA and AIA. Gum or mucilage in WDSF has important roles in hydration properties. On comparing the two durian varieties, they appeared mostly similar, except for some RVA viscosities and syneresis being higher for the Chanee variety, while the ES was higher with the native variety. The thermal properties of purified starches also showed only a minor difference between the varieties. The WDSF required the least processing to prepare, also with least losses and correspondingly highest yield, among the forms of durian seed products tested. From that perspective it is the most attractive choice for food applications. Based on the experimental results, WDSF is suitable for moisture retention as hydrated product, for use as emulsifier, or as fat replacer, mainly due to being rich in mucilage hydrocolloids that are compatible with both water and oil. Due to the high syneresis it is not suitable in typical frozen food products, but in soft texture food or as a water binder when mixed with another flour. Application of durian seed flour in a food product could be tested in future research.
3.8. Emulsion activity (EA) and stability (EA and ES) In general, emulsifying agents either help emulsify or maintain emulsion stability, when one type of phase (oil in foods) is dispersed in another incompatible phase (water in foods). EA and ES are used to measure these abilities. WDSF had the highest EA and ES (Table 3) among the cases tested, because it contained the heteropolysaccharide–protein mucilage or gum. This hydrocolloid had a high ability to hydrate and acted as a thickener giving high viscosity, which could stabilize an emulsion by slowing the movements needed for coalescence of dispersed oil droplets. WDSF and DDSF contained 6–8% proteins. By decreasing surface tension and providing electrostatic repulsion on the surfaces of oil droplets, proteins can enable emulsification and stabilize an emulsion. Correspondingly, the EA of DS or DDSF was lower than that of WDSF, because the gum had been removed along with some other lesser components. The ES was higher than EA, especially for the WDSF cases. In the procedure of ES measurement, the heating step enhanced hydration and swelling of starch and non-starch polysaccharides, and increased viscosity. This again retarded coalescence, improving stability. Improving ES should reflect the protein and polysaccharide contents (Amid & Mirhosseini, 2012b; Jitngarmkusol et al., 2008).
Conflicts of interest The authors declare having no conflict of interest.
4. Conclusions
Acknowledgements
Functional properties of WDSF, DDSF and DS were different. The WDSF had about two-fold RVA viscosity and ES, relative to DDSF and starch, while its moisture loss by syneresis was about three-fold. Starch had the highest gel hardness and the least gel syneresis among these three sample forms. Removing gum and purifying samples (to obtain DDSF and DS, respectively) resulted in changes in chemical
This research was funded by the Halal Food Science Center, Department of Food Science and Nutrition, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Thailand (SAT531025S) and the Thai Research Fund (MRG-WII525S095). Dr. Seppo Karrila is acknowledged for language editing. 7
Food Bioscience 30 (2019) 100412
S. Baraheng and T. Karrila
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