Effect of Fermentation on Chemical Composition

International Journal of Food Engineering Volume 7, Issue 4

2011

Article 6

Effect of Fermentation on Chemical Composition and Nutritional Quality of Extruded and Fermented Soya Products Anthony O. Ojokoh, Federal University of Technology Akure Wei Yimin, Chinese Academy of Agricultural Sciences

Recommended Citation: Ojokoh, Anthony O. and Yimin, Wei (2011) "Effect of Fermentation on Chemical Composition and Nutritional Quality of Extruded and Fermented Soya Products," International Journal of Food Engineering: Vol. 7: Iss. 4, Article 6. DOI: 10.2202/1556-3758.1857 Available at: http://www.bepress.com/ijfe/vol7/iss4/art6 ©2011 Berkeley Electronic Press. All rights reserved.

Effect of Fermentation on Chemical Composition and Nutritional Quality of Extruded and Fermented Soya Products Anthony O. Ojokoh and Wei Yimin

Abstract The effect of fermentation on chemical composition, amino acid profile and protein digestibility of extruded soya protein products was investigated. The soya protein products (low moisture extruded soya product, medium moisture extruded soya product, high moisture extruded soya product, soya meal and soya kernel) were fermented with Bacillus natto from small and large brands of soya bean cultivar. The protein content (%) ranged from 38.20 to 62.98 with the highest content in the high moisture extruded protein product fermented with Bacillus natto from large brand of soya bean cultivar. Contents of carbohydrates ranged from 14.77 to 29.08 while those of crude fibre, fat and ash were generally low. Fermentation improved protein digestibility in the raw soya meal and kernel than in the unfermented extruded and extruded fermented products. Extrusion reduced the nitrogen solubility index of the extruded samples. The contents of amino acids except arginine increased in all the samples after fermentation. Trypsin inhibitor activity decreased from 27.33 TIU/g in the unfermented soya sample to between 1.58 and 18.5 TIU/g after fermentation, whereas there was a decrease in phytic acid content only in the fermented soya meal and low moisture extruded soya sample. KEYWORDS: fermentation, extrusion, macronutrient, amino acids, soya protein products, digestibility Author Notes: Anthony O. Ojokoh, Federal University of Technology Akure, Nigeria. Wei Yimin, Chinese Academy of Agricultural Sciences. This study was funded by the Institute of Agro-Food Science and Technology through the Chinese Academy of Agricultural Science. This study was funded by the Institute of Agro-Food Science and Technology through the Chinese Academy of Agricultural Science.

Ojokoh and Yimin: Extruded and Fermented Soya Products

1.

Introduction

The soya bean is seed of the leguminous soya plant. Soya foods have been a staple part of the Chinese diet for over 4,000 years but have only been widely consumed in Western countries since 1960’s. Soya foods include tofu, tempeh, textured vegetable protein (chunks, mince etc), miso, soya sauces, soya oil, and margarine and soya dairy alternatives. Soy is widely utilized as a staple food in China and many other Asian countries. In fact out of a total of 400 million tons of soy consumed in a year, as much as 250 million tons are imported to China. The residue cake from pressing out the oil is a valuable high protein feed for livestock. It is not often realized how much soya bean is used directly in every day food products and indirectly through being fed to livestock or lost (Vegetarian Society, 2007). Extrusion- cooking is one of the most efficient and versatile food processing technologies that can be used to produce pre-cooked and dehydrated foods. A major technological advantage of extrusion is that the product is simultaneously cooked and dried, resulting in low-moisture shelf stable extrudates. This reduces the cost of post-extrusion drying and guarantees an improved shelflife of the product without the need for cooling or refrigeration and produce unique product shapes with high quality (Singh & Smith, 1998; Singh et al., 1999; Koksel et al., 2004). The reduction in protein digestibility of soya kernel in humans and animals is caused by antinutritional factors such as phytic acid and trypsin inhibitor that bind to enzymes in the digestive tract and thus inhibit utilization of proteins. This adverse effect can be overcome by fermentation, germination (Kheltarjiaul & Chauhan, 1990; Lorri & Svanberg, 1993) or extrusion (Dhalin & Lorenz, 1993). Improved protein digestibility in food is due to degradation of complex storage proteins by endogenous and microbial proteases during fermentation whereas extrusion and other forms of cooking improve digestibility by solubilization, gelatinization and formation of maltodextrins (Bjork & Asp, 1983). It is also well established that extrusion thermomechanically denatures and reorients proteins in foods leading to changes in digestibility and levels of amino acids (Bjork & Asp, 1983; Della Valle et al., 1994; Iwe et al., 2001). However, the magnitude of starch and protein transformation due to extrusion is a function of pre and post processing operations, their interactions and the type of starch and protein. Most available literature consider only the individual effects of either fermentation or extrusion on starch and protein digestibility. In this study, we determined the combined effects of extrusion and fermentation on the macronutrient composition and invitro protein digestibility of soya protein products. Comparisons were also made with (a) unfermented

Published by Berkeley Electronic Press, 2011

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International Journal of Food Engineering, Vol. 7 [2011], Iss. 4, Art. 6

extruded soya protein products (b) fermented and unfermented soya meal and kernel. 2.

Materials and methods

Extruded soya protein samples, soya meal and soya kernel used for this study were of good grade obtained from the Food and Technology Laboratory of the Institute of Agro-Food Science and Technology, Beijing. 2.1.

Bacteria strains

Bacillus natto strains were used in the study. Bacillus natto cultures were prepared from two commercial natto products (natto produced from large and small soya bean cultivars based on the physical properties, chemical composition and sensory qualities) of the Yenjing brand purchased from a local food store in Beijing. 2.2.

Preparation of soya samples as fermentation media

After removing impurities by hand picking and winnowing , the soya beans were washed, soaked in water at room temperature (25±20C) for 20h while soya meal and extruded soya protein products with moisture contents of 20% (low moisture), 32.5% (medium moisture) and 45% (high moisture) were soaked in water for 45mins and drained thereafter. The samples were inoculated immediately after steaming. 2.3.

Preparation of inocula

Preparation of inocula was done by transferring growing Bacillus natto bacteria colonies to a 200ml sterilized nutrient broth (NB) in 250mL Erlenmeyer flask followed by incubation at 250C for 24hours. Inoculum sizes of 5mL, 10mL and 15mL were used for inoculating the samples. Inoculated samples were allowed to ferment at room temperature (25±20C) for a period of 0-48 h. 2.4.

Macronutrient estimation

Moisture content was determined by direct oven drying method; the loss in weight after oven-drying was expressed as % moisture content (AOAC, 1990). Crude protein was estimated from the total nitrogen (TN) determined by the microKjeldahl method by multiplying the TN by a factor of 6.25.Crude fat was determined by using the soxhlet extraction method using petroleum ether as the

http://www.bepress.com/ijfe/vol7/iss4/art6 DOI: 10.2202/1556-3758.1857

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solvent (AOAC, 1990). Ash was measured gravimentrically after ashing at 5500C to constant weight. Carbohydrate was determined by the anthrone method according to Plummer (1971). 2.5.

Protein digestibility

In vitro protein (IVP) digestibility was determined by adding 200 mg sample to a 100 mL Erlenmeyer flask containing 35 mL 0.1 M sodium citrate tribasic dihydrate (pH 2.0) with pepsin (1.5 g pepsin/L, Sigma P-7012; activity 2650 units/mg protein). The mixture was incubated for 2 h in a shaking water bath at 370C then centrifuged at 10,000 rpm for 15 min. The supernatant was decanted and the residue was washed, dried at 800C and analyzed for nitrogen content. Digestibility was calculated by subtracting residue nitrogen from total nitrogen, dividing by total nitrogen and multiplied by 100. 2.6.

Nitrogen solubility index (NIS)

Nitrogen solubility index was determined by weighing 1 g sample into 50 mL centrifuge tube and dispersed in 20 mL distilled water. The dispersion was mechanically shaken for 1h, centrifuged at 10,000 rpm for 15 min and the supernatant collected. The residue was resuspended and centrifuged twice in 10 mL distilled water. The combined supernatants were analysed for soluble nitrogen by the Kjeldhal method. Nitrogen solubility index (NSI) was reported as soluble nitrogen expressed as a percentage of total protein. 2.7.

Amino acids

Amino acids were analysed by first hydrolyzing 20 mg sample in 6 N HCl in sealed ampoules in an oven at 1100C for 23 h. The hydrolysate was rapidly cooled in an ice-water bath before evaporating a 3 mL portion to dryness in a vacuum centrifuge. The sediment was suspended in 500 mL 0.2 M sodium citrate (pH 2.2), shaken for 1 h in a water bath then filtered through cellulose acetate (pore size 0.45 mM). The filtrate was analysed in an amino acid analyser (Pharmacia LKB-Alpha Plus, England). 2.8.

Typsin inhibitor activity

This was evaluated following the procedures by Tanteeratarm & Wwingartner (1998). Finely ground samples (1.0g) that passed 100 mesh were extracted with 50ml of 0.01N NaOH. Extracts were allowed to stand for 1h. Portions (0, 0.6, 1, 1.4 and 1.8mL) of the suspension were pipetted into duplicate sets of test-tube and


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adjusted to 2.0mL with distilled water. Trypsin solution 2.0mL was added to each test-tube, the tubes were placed in a water bath at 370C. To each tube, 5mL solution of BAPA (Benzoyl-DLarginine-p-nitroanilide) hydrate (dissolved in dimethyl sulfoxide and diluted to 100mL with Tris buffer) previously warmed to 370C was added. Exactly 10min later, the reaction was terminated by adding 1mL of 30% acetic acid. After thorough mixing, the contents of each test tube were filtered (Whatman paper No 3) and the absorbance was measured against blank at 410 nm. TIA was expressed in terms of trypsin inhibitory unit (TIU) 2.9.

Phytate

Phytate was extracted by adding 0.1g sample to 0.2mol/l hydrochloric acid and shaken for 1h before centrifuging at 5000 rpm for 15 min. The supernatant (0.5mL) was pipetted into a test tube fitted with a ground-glass stopper before adding 1mL acidic ammonium iron (III) sulphate dodecahydrate (0.2g NH4Fe(SO4)2.12H2O in 100mL 2mol/l hydrochloric acid and made up to 1000mL distilled water). The sample was boiled for 30min then rapidly cooled to 250C in an ice- water bath. 2’2’ bipyridine solution (10g 2’2’ bipyridine and 10mL thioglycolic acid in 1000mL water) was added (2mL) to the test tube and the contents mixed. Absorbance was read after 1min using an Ultrospec 1000 spectrophotometer at 519 nm against distilled water (Haug & Lantzsch, 1983). A standard curve was prepared by adding 125mg sodium phytate (Sigma Aidrich GmbH, Steinheim,Germany) to 100mL 0.2mol/l hydrochloric acid and this stock solution was used at various dilutions to give final phytate phosphorous concentrations of 3-30 g/mL. 2.10.

Statistical analysis

Analysis of variance (anova) of the samples was performed, with mean ±S.D. values being compared at 5 % significane level using Ducan’s multiple –range tests. 3.

Results and discussion

3.1 Macronutrient profile The macronutrient profile (%) of soya samples are shown in tables 1-3. There was significant increase (P< 0.05) in the protein content of the fermented samples over unfermented samples. In this study, changes in protein content in samples fermented with different inoculum sizes was highest (62.98) in the high moisture extruded soya sample fermented with 5mL of Bacillus natto from large brand of


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soya bean cultivar followed by the high moisture extruded soya sample fermented with 5ml of B. natto from small brand of soya bean cultivar which had 59.04. Table 1: Proximate composition of soya samples fermented with inoculum of Bacillus natto from large brand of soya bean cultivar (mean ± SD*) Protein Crude Ash Fat Carbohydrate fibre Samples fermented with 5mL inoculum LMESPP 57.32±0.18 1.49±0.02 7.03±0.17 0.51±0.06 20.21±0.40 MMESPP 57.61±0.24 1.55±0.04 7.27±0.06 0.40±0.00 20.12±0.31 HMESPP 62.98±0.49 1.28±0.01 6.73±0.03 0.45±0.01 16.64±0.18 SM 57.91±0.91 2.06±0.00 7.34±0.15 0.16±0.05 14.93±0.16 SK 43.22±0.58 1.58±0.02 4.68±0.16 21.33±0.12 19.76±0.24 Samples fermented with 10mL inoculum LMESPP 56.84±0.17 1.60±0.01 7.05±0.15 0.42±0.02 21.44±0.24 MMESPP 56.50±0.21 1.45±0.00 6.94±0.19 0.34±0.01 21.94±0.81 HMESPP 57.91±0.24 2.59±0.04 6.78±0.06 0.35±0.05 18.56±0.46 SM 58.04±0.40 2.55±0.01 7.52±0.03 0.21±0.00 14.77±0.24 SK 43.74±0.49 2.29±0.02 4.57±0.15 21.22±0.07 19.31±0.50 Samples fermented with 15mL inoculum LMESPP 55.42±0.91 1.12±0.05 6.34±0.06 0.31±0.04 24.49±0.46 MMESPP 56.83±0.93 1.97±0.00 7.22±0.22 0.37±0.01 21.38±0.74 HMESPP 57.49±0.58 1.68±0.04 6.73±0.15 0.40±0.00 21.56±0.31 SM 56.30±0.50 2.60±0.02 7.48±0.09 0.12±0.02 16.42±0.16 SK 41.16±0.35 1.66±0.01 5.03±0.03 21.28±0.10 22.03±0.42 LMESPP: Low Moisture Extruded Soya Protein Product, MMESPP: Medium Moisture Extruded Soya Protein Product, HMESPP: High Moisture Extruded Soya Protein Product, SM: Soya Meal, SK: Soya Kernel. * Values represent means of triplicate determinations.


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Table 2: Proximate composition of soya samples fermented with inoculum of Bacillus natto from small brand of soya bean cultivar (mean ± SD*) Protein Crude Ash Fat Carbohydrate fibre Samples fermented with 5mL inoculum LMESPP 57.6±0.68 0.80±0.03 6.89±0.05 0.49±0.02 22.92±0.19 MMESPP 57.07±0.53 0.76±0.02 6.47±0.07 0.38±0.06 22.78±0.00 HMESPP 59.04±0.91 1.26±0.03 6.47±0.02 0.46±0.05 20.25±0.83 SM 58.00±0.49 0.59±0.01 6.48±0.03 0.19±0.01 20.48±0.06 SK 42.34±0.24 2.31±0.02 4.73±0.04 21.37±0.11 21.25±0.82 Samples fermented with 10mL inoculum LMESPP 55.8±0.17 0.49±0.01 6.66±0.00 0.41±0.04 24.17±0.20 MMESPP 57.45±0.21 2.84±0.04 6.46±0.15 0.37±0.03 20.56±0.21 HMESPP 57.52±0.19 1.04±0.01 6.25±0.06 0.34±0.00 22.17±0.00 SM 58.60±0.10 2.46±0.02 6.97±0.02 0.17±0.02 19.28±0.88 SK 43.18±0.17 3.01±0.00 5.10±0.16 20.96±0.12 19.75±0.06 Samples fermented with 15mL inoculum LMESPP 55.21±0.69 0.55±0.00 6.57±0.13 0.36±0.04 26.51±0.87 MMESPP 56.85±0.40 0.88±0.00 6.75±0.22 0.39±0.00 23.29±0.21 HMESPP 58.31±0.93 3.97±0.01 6.27±0.19 0.41±0.01 18.99±0.74 SM 57.85±0.35 3.23±0.04 7.22±0.06 0.14±0.03 16.92±0.29 SK 41.53±0.16 2.66±0.01 4.61±0.03 21.06±0.09 26.75±0.18 LMESPP: Low Moisture Extruded Soya Protein Product, MMESPP: Medium Moisture Extruded Soya Protein Product, HMESPP: High Moisture Extruded Soya Protein Product, SM: Soya Meal, SK: Soya Kernel. * Values represent means of triplicate determinations.

Reade & Gregory (1975) reported that autolysis is likely to increase with initial inoculum due to disproportionate amount of nutrient and lower conversion efficiency. At lower inoculum level, cells are larger especially when competition for available nutrients was minimal (Chikwendu, 1987). Similar findings have been reported in Ojokoh & Uzeh (2005) in production of Saccharomyces cerevisiae biomass in papaya extract medium. The increase in the protein content in the high moisture extruded soya sample inoculated with Bacillus natto from large brand of soya bean cultivar was considerably higher than the increase in protein content in the high moisture extruded soya sample


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inoculated with Bacillus natto from small brand cultivar. The results indicate that selected B. natto strains have different capabilities to utilize carbohydrate during fermentation. Wei & Chang (2004) reported that there was a significantly larger concentration of protein in natto products made from Danatto soybeans harvested in 1995 than in soybeans harvested in 1996 when inoculated with B. natto NRRL B-338 strain and “Itobiki” strain. Table 3: Proximate composition of unfermented soya samples (mean ± SD*) Samples ULMESPP UMMESPP UHMESPP USM USK

Protein 53.86±0.13 52.29±0.16 53.47±0.13 52.20±0.22 38.20±0.31

Crude fibre 1.43±0.01 0.53±0.01 1.56±0.00 1.88±0.04 1.01±0.02

Ash 6.71±0.19 6.43±0.07 6.34±0.06 6.57±0.04 5.03±0.15

Fat 1.75±0.06 1.35±0.04 1.31±0.02 0.16±0.00 17.46±0.14

Carbohydrate 27.04±0.18 28.58±0.81 29.08±0.29 25.84±0.24 28.90±0.74

ULMESPP:Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP:Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP:Unfermented High Moisture Extruded Soya Protein Product, USM: Unfermented Soya Meal, USK:Unfermented Soya Kernel. * Values represent means of triplicate determinations.

The increase in protein content after fermentation is due to a decrease of carbon ratio in the total mass, resulting in redistribution of nutrient percentages. Microorganisms utilize carbohydrates as an energy source and produce carbon dioxide as a by-product. This causes the nitrogen in the fermented samples to be concentrated and thus the proportion of protein in the total mass increases. The lower protein content in the extruded samples compared to the extruded fermented samples could be due to participation of amino acids in Maillard reactions. The fat and crude fibre contents were generally low while there was no significant difference in the ash content. 3.2 Protein digestibility In vitro protein digestibility is a measure of soluble proteins digested under conditions of the pepsin assay. In vitro protein digestibility increased after fermentation because of partial degradation of complex storage proteins by endogenous and microbial proteolytic enzymes into soluble products (Chavan et al., 1988; Khetarpaul & Chauhan, 1990). Protein digestibility increased more when the samples were unfermented or extruded and fermented than in the extruded samples (Figure 1). Extrusion is a high-temperature short-time treatment that improves protein digestibility via denaturation which exposes enzyme access sites.


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Protein digestibility(%)

92 90 88 86 84 82 80

SK U

SM U

FS LM K ES U PP M M ES PP U H M ES PP U

FS M

FL M ES FM PP M ES PP FH M ES PP

78

Figure 1: Protein digestibility of soya samples FLMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.

3.3 Nitrogen Solubility Index The extent of protein denaturation is assessed by changes of protein solubility in water and is measured as NSI (Camire, 2001). The increase in NSI in the extruded fermented samples could be attributed to the proteolytic activity of endogenous and microbial enzymes (Figure 2). By contrast, NSI in the unfermented extruded samples decreased indicating polymerization, cross-linking and reorientation of the native proteins to form new fibrous structures (Pelembe et al., 2002; Iwe et al., 2001; Stanley,1989). Extrusion denatures proteins by opening up their quaternary and tertiary structures, thus inducing polymerization, cross-linking and reorientation to fibrous insoluble structures (Akdogan,1999).


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90

Nitrogen solubility index (%)

80 70 60 50 40 30 20 10

SM U

LM ES PP U M M ES PP U H M ES PP

U

FS M

FL M ES PP FM M ES PP FH M ES PP

0

Figure 2: Nitrogen solubility index of soya samples FLMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel, ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.


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3.4 Amino Acids content The contents of amino acids except arginine increased in all the samples after fermentation (Figure 3a). The increase in amino acid contents may be due to the hydrolysis of the storage proteins in the samples into peptides and amino acids by the fermenting microorganism. Non enzymatic browning reactions were responsible for the lower amino acids contents in the extruded unfermented samples (Figure 3b); and these changes are accompanied by darkening of the extrudates.

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FLMESPP FMMESPP FHMESPP FSM FSK

Amino acid (g/16g N)

10

8

6

4

2

A sp

ar a Th gin re e on in e G lu Se ta rin m ic e ac G id ly c A ine la ni Cy ne sti n V e M al et ine hi o Is nin ol e eu c Le ine u Tr cin y Ph ro e en si ya n e la ni n Ly e s H ine ist id A ine rg in in Pr e ol in e

0

Figure 3a: Amino acid content of fermented soya samples LMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel, ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.


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Ojokoh and Yimin: Extruded and Fermented Soya Products 12

ULMESPP UMMESPP UHMESPP USM USK

Amino acid (g/16 g N)

10

8

6

4

2

A sp

ar a Th gin re e on in e G lu Se ta rin m ic e ac G id ly c A ine la ni Cy ne sti ne M Val et ine hi o Is nin ol e eu c Le ine u Tr c i n y Ph ro e en si y a ne la ni n Ly e s H ine ist id A ine rg in in Pr e ol in e

0

Figure 3b: Amino acid content of unfermented soya samples LMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel, ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.

3.5 Trypsin Inhibitor Trypsin inhibitor activity decreased from 27.33 TIU/g in the unfermented soya meal to 9.52, 12.21 and 13.79 in the extruded samples and further to1.58, 1.71 and 1.85 TIU/ g in the extruded fermented samples (Figure 4). The fermented soya meal had 2.14 TIU/g trypsin inhibitor activities. The results indicated that high extrusion temperature and fermentation processing caused a reduction in the TIA of the samples to a greater extent. Similar reduction in TIA has also been reported in extruded and fermented products (Anuonye et al., 2007; Ibrahim et al., 2002)


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Trypsin inhibitor (TIU/g

30 25 20 15 10 5

SM U


U

FS M


0

Figure 4: Trypsin inhibitor activity of soya samples FLMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel, ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.

3.6 Phytic acid content There was higher phytic acid content in all the extruded samples (Figure5), while fermentation diminished the level of phytic acid in the fermented soya meal (231.5mg/100g) and in the low moisture extruded fermented sample (375.7mg/100g). The inability of extrusion cooking to degrade phytic acid has also been reported in wheat, rice and oat bran (Gualberto et al., 1997) legumes (Ummadi et al., 1995) and a high-fibre cereal (Sandberg et al., 1986). Further more, deactivation of phytase during extrusing cooking could impair mineral absorption in the stomach and intestine. It is speculated that this enzyme plays a role in phytate hydrolysis in the gastrointestinal tract and therefore its activity


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should be retained even after processing (Lopez et al., 2002). Literature research shows that activation of endogenous phytates by germination is one of the most effective ways to reduce phytate in cereals and legumes (Sandberg & Svanberg, 1991; Mbithi-Mwikya et al., 2000; Mamiro et al., 2001; Egli et al., 2002).Another effective alternative method involves use of exogenous phytates (Sandberg and Svanberg, 1991; Hurrel et al., 2003). Nevertheless even germination or use of exogenous phytases cannot reduce phytate levels that have almost no inhibitory effect on in vivo mineral iron absorption (Hurrel et al., 2003). Residual phytate levels should be less than 0.5mol/g in order to eliminate any inhibitory effect on iron availability (Sandberg & Svanberg, 1991). 450

Phytic acid (mg/100g)

400 350 300 250 200 150 100 50

SM U


U

FS M


0

Figure 5: Phytic acid content of soya samples FLMESPP: Fermented Low Moisture Extruded Soya Protein Product, FMMESPP: Fermented Medium Moisture Extruded Soya Protein Product, FHMESPP: Fermented High Moisture Extruded Soya Protein Product, FSM: Fermented Soya Meal, FSK: Fermented Soya Kernel, ULMESPP: Unfermented Low Moisture Extruded Soya Protein Product, UMMESPP: Unfermented Medium Moisture Extruded Soya Protein Product, UHMESPP: Unfermented High Moisture Extruded Soya Protein Product ,USM: Unfermented Soya Meal, USK: Unfermented Soya Kernel.


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4.

Conclusion

Fermentation of the soya samples after extrusion improved the protein content, in vitro protein digestibility and nitrogen solubility index when compared to the unfermented and extruded samples. The overall amino acid balance was higher in the extruded fermented samples than in the extruded unfermented samples. Fermenting the samples after extruding was effective in lowering trypsin inhibitor activity; whereas fermentation of the samples after extrusion decreased phytic acid content only in the fermented soya meal and low moisture extruded soya samples. References Akdogan, H.(1999). High moisture food extrusion. International Journal of Food Science and Technology, 34:195-207. Anuonye, J.C., Badifu, G.I.O., Inyang, C.U., Akpapunam, M.A., Odumudu, C.U., & Mbajika, V.I. (2007). Protein dispersibility index and trypsin inhibitor activity of extruded blends of acha/soya bean : a response surface analysis. American Journal of Food Technology, 2(6): 502–511. AOAC(1990). Official Methods of Analysis. 14 th edn, Washington, DC: Association of Official Analytical Chemists. Bjork, I., & Asp, N. G. (1983). The effect of extrusion cooking on nutritional value—A literature review. Journal of Food Engineering, 2: 281–308. Camire, M. E. (2001). Extrusion cooking: Technologies and applications. In: Guy R. (ed.), Wood head Publishing Co., Cambridge, England: CRC Press, pp. 109–129. Chavan, U. D., Chavan, J. K., & Kadam, S. S. (1988). Effect of fermentation on soluble proteins and in vitro protein digestibility of sorghum, green gram and sorghum–green gram blends. Journal of Food Science, 53(5): 1574– 1575. Chikwendu, A.E. (1987). Microbial treatment of cassava whey and single cell protein production. M.Sc. Thesis. Uni. Of Benin, Benin City, Nigeria. 162pp. Della Valle, G., Quillien, L., & Gueguen, J. (1994). Relationships between processing conditions and starch and protein modifications during extrusion-cooking of pea flour. Journal of the Science of Food and Agriculture, 64: 509–517. Dahlin, K. M., & Lorenz, K. J. (1993). Carbohydrate digestibility of laboratory extruded cereal grains. Cereal Chemistry, 70(3): 329–333.


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