Wet grinding characteristics of soybean for soymilk extraction

Wet grinding of hydrated soybean was carried out with mixer grinder, stone grinder and colloid mill which revealed that particle size had a profound effect on the protein recovery in the extracted milk with a maximum recovery of 89.3%. Greater reduction in particle size was achieved with mixer grinder (180 μm) with 5 min of grinding while reduction was not significant beyond 18 min (233 μm) in stone grinder. Specific energy consumption in colloid mill was only one-fourth of the mixer grinder while stone grinder required twice the energy. Although Kick’s, Rittinger’s and Bond’s laws could not be applied for total grinding duration, all the three classical laws were found suitable after the initial grain break-up period (2 min). Temperature and duration of thermal treatment given during hot extraction influenced protein recovery and viscosity of soymilk. The results suggest that colloid mill is a potential device for industrial scale operation.     

Okara flours from chickpea and soy are thickeners: increased dough viscosity and moisture content in gluten-free bread

The by-product of plant-based beverages, okara, can be dried in a nutritious flour, but it generates dense bakery products due to high water absorption. Gluten-free bread often tastes dry, so the objective of this work was evaluating okara flour as thickener for mouthfeel enhancement. Proximate analysis revealed that chickpea okara contained more starch than soy (35.3 vs. 3.41 g/100 g), less insoluble fibre (43.3 vs. 57.0 g/100 g) and protein (9.51 vs. 18.1 g/100 g). Water absorption capacity was higher in okara than flour and for soy (8.29 vs. 6.01 g g⁻¹, respectively). When added to a gluten-free batter, both okara flours significantly increased viscosity. Upon addition of either okara to gluten-free bread (2% w/w) moisture content increased from 31.6 to 33.5 and 36.5 g/100 g, while crumb hardness increased by up to 45% and specific loaf volume decreased by up to 42%. Soy okara flour enhanced moistness of gluten-free bread.     

Effect of lipoxygenase activity in defatted soybean flour on the gelling properties of soybean protein isolate

Soybean lipoxygenase was inactivated to different degrees by dry heating of defatted soybean flour for 0, 5, 10, 15, 20 and 25 min and soy protein isolates were prepared thereof by isoelectric precipitation of the water extract of the defatted soybean flour. The fluorescence emission intensity at 420 nm of the chloroform–methanol extract of soy protein isolates, which was indicator of the existence of peroxidized lipid, varied in parallel with the lipoxygenase residual activity in defatted soybean flours. The dispersion of soy protein isolate showed an increasing turbidity with the increase of lipoxygenase residual activity in the starting defatted soybean flour, suggesting an elevated tendency to form insoluble aggregates during the preparation of soy protein isolate. Small deformation rheological test revealed that the gelling times were shorter for those soy protein isolates derived from low lipoxygenase activity defatted soybean flours than that of high lipoxygenase activity. Frequency sweep showed that G′ of soy protein isolate derived from low lipoxygenase defatted soybean flour was independent of oscillation frequency in contrast to that of derived from non dry-heated defatted soybean flour, the latter showed a marked frequency dependence. Large deformation test revealed that the gel hardness increased about 10 times after dry heating of defatted soybean flour for 20 min. As the increase of the lipoxygenase residual activity, the gel permeability increased markedly, suggesting that soy protein isolate from high lipoxygenase defatted soybean flour produced coarser textured gel, which corresponded well with the results of scanning electron microscopy.     

豆渣酱制曲工艺条件优化

在制酱工艺中,利用豆渣代替黄豆和豆粕生产酱产品,并通过单因素实验和正交实验确定了优化的制曲条件:湿豆渣和干面粉质量比7:4,高压蒸煮30 min,接种酱油曲精0.05%,制曲室中培养36 h。按照此条件制得的豆渣酱与传统豆酱风味和口感相差不大。实验结果表明,采用豆酱工艺生产豆渣酱为豆渣的有效利用开辟了新的途径。     

Soybean seeds and its by-product okara as sources of dietary fibre. Measurement by AOAC and Englyst methods

The composition of soybean seeds and its by-product okara has been studied in this work. Dietary fibre was analysed by Englyst et al. method, by enzymatic–gravimetric methods of AOAC and by the quantification of the monomers obtained from the AOAC residues after acid hydrolysis (AOAC plus hydrolysis). Total dietary fibre by the enzymatic–gravimetric methods of AOAC in okara (55.48 g/100 g dry matter) is more than twice that of soybean seeds (24.37 g/100 g dry matter). The proportion IF/SF is 11 in okara and 6 in soybean seeds. Dietary fibre results from enzymatic–gravimetric AOAC methods are higher in okara and soybean seed samples than those from the Englyst method (okara: 41.14 g/100 g dry matter; soybean seeds: 15.05 g/100 g dry matter), and AOAC plus hydrolysis (okara: 44.91 g/100 g dry matter; soybean seeds: 16.38 g/100 g dry matter). In the case of the insoluble fibre from both samples, AOAC plus hydrolysis gives significantly (p < 0.001) higher values than the Englyst method, whilst for soluble fibre the opposite occurs (p < 0.001). The main monomers in soybean seeds and okara fibre are glucose, galactose, uronic acids, arabinose and xylose. The proportion of each monomer is similar in soybean seeds and okara, so the healthy properties of soybean seeds fibre are also claimed for okara.     

Effects of particle size distributions of rice flour on the quality of gluten-free rice cupcakes

The particle size distributions (PSD) of rice flour and milling processes are important in making gluten-free products. The dry rice flour was prepared by grinding dried rice grains after soaking. Effects of PSD on the quality of rice cupcakes were investigated using the newly-developed rice flour. The flour properties passed through 80, 120, 160, and 200 (<180, <125, <95, and <75 μm) meshsieves, and batters and cupcakes prepared from their flours were analyzed. The PSD patterns showed two peaks containing cells and free starch fractions, in which the starch fraction peak intensity increased as a particle size decreased. While damaged starch, water binding capacity, solubility and lightness increased, crude protein and yellowness decreased as a particle size decreased. The final and setback viscosities increased as a particle size decreased. The specific volume of cupcakes was the highest in the cupcakes made with rice flour passed through under 95 μm. Hardness and springiness decreased as a particle size decreased. The air cell sizes decreased as a particle size decreased with homogeneity. Air cell homogeneity, volume, hardness, and softness of cakes determined by the different test, and appearance, texture, and overall quality determined by the preference test were all significantly different (p < 0.05).     

Effect of high-fat diets supplemented with okara soybean by-product on lipid profiles of plasma,liver and faeces in Syrian hamsters

The main components of okara, a by-product from soybean, are dietary fibre and protein. In this study we fed okara based diets with different amounts of fibre, protein and isoflavones to determine their effect on the lipid profile in the plasma, liver and faeces of an animal model. Male golden Syrian hamsters were fed high-fat diets supplemented with okara for 3 weeks. The supplemented diets contained 13% or 20% of okara fibre (OK-13 and OK-20), low-protein okara with 13% of fibre (OK1-13), and isoflavone-free okara with 13% of fibre (OK2-13). Okara supplemented diets did not produce significant differences in the feed intake or body weight gain (p > 0.05). The plasma levels of triglycerides, VLDL- plus LDL cholesterol and total cholesterol in hamsters fed OK-20 decreased significantly (p < 0.05) with respect to the 20% control group (C-20). However, no significant differences (p > 0.05) were found in LDL- and HDL-cholesterol plasma levels in all experiments. Total lipids, triglycerides, total and esterified cholesterol concentrations in liver were reduced by OK-20 diet. Regarding the hamsters fed OK-13 diets, the mean values of the total lipid, triglyceride and cholesterol in the plasma and liver decreased as compared to the control (C-13), but the differences were not statistically significant. All of the okara diets assayed increased the faecal excretion of total lipids, triglycerides, free cholesterol and total nitrogen (p < 0.05) compared to their respective controls. Our results suggest that the main components of okara, dietary fibre and protein, could be related with the total lipids and cholesterol decrease in the plasma and liver, as well as with the faecal output increase in high-fat fed hamsters. Okara might play an interesting role in the prevention of hyperlipidemia and could be used as a natural ingredient or supplement for functional food preparation.     

Production of okara and soy protein concentrates using membrane technology

Microfiltration (MF) membranes with pore sizes of 200 and 450 nm and ultrafiltration (UF) membranes with molecular weight cut off of 50, 100, and 500 kDa were assessed for their ability to eliminate nonprotein substances from okara protein extract in a laboratory cross-flow membrane system. Both MF and UF improved the protein content of okara extract to a similar extent from approximately 68% to approximately 81% owing to the presence of protein in the feed leading to the formation of dynamic layer controlling the performance rather than the actual pore size of membranes. Although normalized flux in MF-450 (117 LMH/MPa) was close to UF-500 (118 LMH/MPa), the latter was selected based on higher average flux (47 LMH) offering the advantage of reduced processing time. Membrane processing of soy extract improved the protein content from 62% to 85% much closer to the target value. However, the final protein content in okara (approximately 80%) did not reach the target value (90%) owing to the greater presence of soluble fibers that were retained by the membrane. Solubility curve of membrane okara protein concentrate (MOPC) showed lower solubility than soy protein concentrate and a commercial isolate in the entire pH range. However, water absorption and fat-binding capacities of MOPC were either superior or comparable while emulsifying properties were in accordance with its solubility. The results of this study showed that okara protein concentrate (80%) could be produced using membrane technology without loss of any true proteins, thus offering value addition to okara, hitherto underutilized. Practical Application: Okara, a byproduct obtained during processing soybean for soymilk, is either underutilized or unutilized in spite of the fact that its protein quality is as good as that of soy milk and tofu. Membrane-processed protein products have been shown to possess superior functional properties compared to conventionally produced protein products. However, the potential of membrane technology has not been exploited for the recovery of okara protein. Our study showed that protein content of okara extract could be improved from approximately 68% to approximately 81% without losing any true proteins in the process.     

Indigestible fraction of okara from soybean: composition,physicochemical properties and in vitro fermentability by pure cultures of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> and <Emphasis Type="Italic">Bifidobacterium bifidum</Emphasis>

Major non-digestible components of soybean seeds and okara were determined by an in vitro enzymatic-physiological method, alternative to dietary fibre. Total indigestible fraction was higher in okara (41.6%) than in seeds (28.5%), and consisted of soluble and insoluble fractions, mainly composed of non-starch polysaccharides, klason lignin and resistant protein. Total protein was lower in okara (32.29%) than in seeds (46.97%), as were oil (14.72% okara–20.89% seeds) and ash contents (3.18% okara–4.60% seeds). In vitro digestibility of protein was lower for okara (84.3%), than for soybean seed (91.8%). Moreover, okara showed high swelling (10.54 ± 0.14 mL/g d.w.) and water retention capacity (8.87 ± 0.06 g/g d.w.) and was fermented in vitro to a greater extent by Bifidobacterium bifidum (29.8%), than by Lactobacillus acidophilus (8.3%). For its composition, physico-chemical properties and bifidogenic capacity in vitro, okara is a potential candidate to be a prebiotic fibre-rich ingredient of new functional foods. An erratum to this article can be found at     

High-power ultrasonication-assisted extraction of soybean isoflavones and effect of toasting

The effect of high-power ultrasonication (HPU) on extraction of soybean isoflavones and components, including total phenolic and DPPH radical scavenging activities (RSA) were evaluated. Isoflavones from defatted soybean flakes were extracted using a bench scale HPU system at 20 kHz and varying amplitudes (18–54 μm) for 1 and 3 min. Aqueous acetonitrile, and aqueous ethanol based solvents were evaluated for extraction at samples-to-solvent ratios of 0.1:1 and 0.2:1. The non-sonication control extraction was with mixing with magnetic stirrer for 2 h. Preliminary data indicated 1.2–1.5 times more genistein recovery at 1, and 3 min sonication compared to control, however, total phenolic decreased. The genistein recovery was lower at higher sonication levels. RSA also decreased to 40% for HPU-assisted extractions. Total isoflavones recovery in HPU-assisted extractions increased from 600 to 5813 μg/g. The concentration of major isoflavone components, genistein, daidzein, and glycitein also increased by 10-fold. HPU for 3 min reduced the average particle size of treated soy flakes from 530 μm to 60 μm. Toasting at 150 °C of defatted soy flake for longer period of time led to higher aglycone concentration in extract; however, 2 h toasting was sufficient prior to HPU-assisted extraction.     

Urinary isoflavone excretion in Korean adults: comparisons of fermented soybean paste and unfermented soy flour

BACKGROUND: This study compared the 24 h urinary excretion of isoflavone algycones after the consumption of fermented soybean paste or unfermented soy flour in a population of healthy Koreans (four males and five females). An equivalent amount (20 mg) of total isoflavone was consumed as either 52 g of soybean paste or 12.2 g of soy flour in a randomised, crossover trial consisting of two single‐time‐point feedings and having 3 day run‐in and washout periods between feedings. RESULTS: Analysis of starting materials indicated that daidzein (1.4%) and genistein (1.4%) constituted a smaller proportion of the total isoflavones in soy flour as compared with soybean paste (55.3% daidzein and 45.7% genistein). Free and glycosidic forms of isoflavones differed significantly between the two soy products. Levels of β‐glycosides as well as total glycosides (β‐glycosides, malonyl and acetyl forms) were two‐fold higher in soy flour as compared with soybean paste. Malonyl forms predominated in soy flour. CONCLUSIONS: The consumption of soybean paste resulted in significantly higher urinary excretion of both daidzein and genistein as compared with soy flour (P < 0.05 and P < 0.01 respectively). Copyright © 2007 Society of Chemical Industry     

Effects of sources of carbon and nitrogen on production of α-glucosidase inhibitor by a newly isolated strain of Bacillus subtilis B2

This study examined production of α-glucosidase inhibitors by Bacillus subtilis B2 in Luria-Bertani (LB) fermentation with okara, soy powder, starch or pectin as additional source of carbon and nitrogen. All the fermentation broths of B. subtilis B2 exhibited gradual increase in α-glucosidase inhibitory activity during the fermentation process with or without supplemented source of carbon or nitrogen. Addition of okara into the LB medium greatly enhanced the strength (nearly twice as much of that without okara supplement) of α-glucosidase inhibitory activity of fermentation broth. The α-glucosidase inhibitory activity of B. subtilis B2 fermentation broth was positively correlated (p < 0.05) with the bacterial populations grown in LB medium containing okara. Glucose and sucrose were not detected in LB medium during the entire fermentation process and were both reduced drastically in media containing okara, soy powder, starch or pectin after 6 days of fermentation. The fermented LB medium containing okara by B. subtilis B2 possessed very strong α-glucosidase inhibitory activity and contained little glucose and sucrose, suggesting that fermentation of B. subtilis B2 in LB added with okara might be considered as a strategy for preparing functional foods for diabetic patients.     

Enhancing protein and sugar release from defatted soy flakes using ultrasound technology

This research focused on the use of high-power ultrasound prior to soy protein extraction to simultaneously enhance protein and sugar release in the extract. Defatted soy flakes dispersed in water were sonicated for 15, 30, 60 and 120 s using a bench-scale ultrasound unit. The ultrasonic amplitudes used were: 0, 21, 42, 63 and 84 μm_pp (peak-to-peak). The respective power densities were 0.30, 0.87, 1.53 and 2.56 W/ml. Scanning electron micrographs of sonicated samples showed the structural disruption of soy flakes. The particle size decreased nearly 10-fold following ultrasonic treatment at high amplitudes. Sonication at high amplitude for 120 s gave the highest increase in total sugar released (50%) and protein yield (46%) when compared with non-sonicated samples (control). Ultrasonic pretreatment was also carried out with and without cooling for temperature moderation. The heat generated during sonication had no significant effect on protein and sugar release from defatted soy flakes. The use of ultrasound can significantly improve protein yield and reduce the overall cost of producing soy protein from flakes.     

Soybean okara: Effect of ultrasound on compositional and emulsifying properties

High-intensity ultrasound is widely used to modify the functional properties of macromolecules (proteins, polysaccharides, etc.) and to expand their range of potential applications. This work is aimed at studying the effects of ultrasound treatments on the composition of different soybean okara samples and their potential as an emulsifying agent. Defatted solvent-free soybean flour (DSF) was extracted by adjusting dispersion to pH 9.0. Insoluble residues obtained after centrifugation were dried, and an unsonicated okara sample (UOK) was obtained. Furthermore, the soybean flour dispersion was subjected to treatment in a probe-type ultrasonic homogeniser before or after the alkaline extraction process, thus producing SOK and OKS samples, respectively. The sonication process generated compositional and structural changes in okara soybeans. SOK had higher yield and protein content than UOK and OKS due to the insolubilisation of the glycinin (11S) fraction of soybean storage proteins. Due to these characteristics, the SOK sample showed the best emulsifying activity.     

Preparation of β-glucan and antioxidant-rich fractions by stone milling of hull-less barley

Stone milling of hull-less barley in combination with size-based separation of the milled fractions was used for preparation of flours with different compositions of macronutrients and bioactive compounds. According to similar compositions, specific milled fractions were combined to define three flours. The flour with the largest mass fraction (~70%) comprised particle sizes < 124 μm, which showed lower fibre, residual ash and antioxidant contents than the unfractionated flour. The flour with particles from 124 to 250 μm (~20% mass fraction) had >twofold greater β-glucan content, and the flour with particles > 250 μm (~10% mass fraction) had >threefold greater content of antioxidants than unfractionated flour. Each of these three flour fractions represents valuable material that can be incorporated into bakery products to enhance functional and health-related properties. Large enrichment factors of bioactive compounds in barley flours can be obtained using small-scale and widely available milling equipment.     

Preparation of low-fat uptake frying batter composite by dry particle coating of microparticulated soybean hull

This study examined the influence of soybean hull-coated frying batter composite on fat uptake during deep fat frying. Soybean hull was microparticulated by impact mill at impact mill speed (IMS) of 6000, 10,000 and 14,000 rpm, and air-classified into coarse and fine fractions at Air Classifying Wheel Speed (ACWS) of 4000, 8000 and 12,000 rpm, respectively. Each soybean hull was dry-coated into wheat flour by dry particle coating system. As the difference in particle size between wheat flour and soybean hull got larger, the coating process became more effective, which indicates the size difference between wheat flour and soybean hull was important for coating effectiveness. When the ratios of wheat flour to soybean hull were 99:1 and 95:5, there were about 3.3 (g/100 g) and 24.4 (g/100 g) of fat content reduction, respectively. Inner crust structures showed slight reduction in cell size and improved cellular integrity with shrinkage in the cell membrane, with increase in soybean hull content. This means soybean hull can form a protective layer and can be applied to the food industry as a frying batter composite to reduce fat uptake.     

Functional attributes of soybean seeds and products,with reference to isoflavone content and antioxidant activity

The concentrations of isoflavones, especially daidzein and genistein, were determined by high performance liquid chromatography in 4 soybean cultivars and 26 soybean products. The total isoflavone content of the soybean cultivars was in the range of 525–986 mg per kg, and for soy products it was 32.9–795 mg per kg. Amongst the soybean products, the isoflavone content decreased in the order: soy sprouts, soy seeds, soy flour, soy milk, soy meals and soy sauce. Significant differences in the concentration of genistein and daidzein were observed between the commercial soy products and also within the soybean cultivars. The antioxidant activity of soybean and soy products correlated well with total phenolic content (TPC) and total isoflavones (TI), whereas TPC showed higher correlation with TI.     

Protein–polysaccharide interactions: Phase behaviour of pectin–soy flour mixture

Biopolymers mixed systems have been widely studied in the past two decades, resulting in advances in knowledge of the key parameters involved in macromolecules–macromolecules interactions. Sound understanding and control of these parameters should enable food scientists to design coating or film with desired functional properties. In this study the phase behaviour of high methoxyl pectin and soy flour at pH 4.6 was investigated. The aim was to investigate the effect of different concentrations of pectin (P) and soy flour (SF) solution and different P/SF ratios on mixture phase behaviour. Pectin suspensions at 16 mg ml⁻¹ and 8 mg ml⁻¹ concentrations and soy flour suspensions at 13 mg ml⁻¹ and 6.5 mg ml⁻¹ concentrations were prepared and mixed together in different ratios (10/90, 25/75, 50/50, 75/25, 90/10). Turbidity and rheological measurements were performed to obtain information on pectin–soy flour interaction in electrostatic compatibility conditions. The experimental data show that soy flour solution is a non-stable system in which complexes may be formed during aging. It becomes insoluble and settles to the bottom of the suspension. By blending charged soy flour, at high concentration, with anionic pectin an associative interaction between biopolymers occurs which stabilizes the protein in solution. The best pectin and soy flour suspension for forming film with a continuous network was at concentrations of 16 mg ml⁻¹ and 13 mg ml⁻¹.     

Preparation and functional properties of protein from heat-denatured soybean meal assisted by steam flash-explosion with dilute acid soaking

The combined pretreatment of heat-denatured soybean meal using steam flash-explosion (SFE) with sulfuric-acid soaking was investigated to prepare protein from soybean meal. When soybean meal was pretreated by SFE at 1.8 MPa, 2.2 MPa for 8 min and at 2.0 MPa for 8 min and 10 min, combined with 0.9% sulfuric-acid soaking, the extraction yield of protein increased to 67.72%, 70.54%, 69.47% and 71.21% respectively, compared to untreated soybean meal. Scanning electron micrograph of pretreated samples showed the structural disruption of soybean meal. After pretreatment, the protein yield was improved, while protein content of soy protein isolate (SPI) decreased slightly. The functional properties of SPI from pretreated soybean meal were all improved compared to untreated soybean meal and the relationship between functional properties and the changes of surface hydrophobicity of SPI was discussed. The emulsification properties and fat-binding capacity of pretreated SPI were superior to those of SPI prepared from white flakes.     

Indigestible fraction of okara from soybean: composition,physicochemical properties and in vitro fermentability by pure cultures of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> and <Emphasis Type="Italic">Bifidobacterium bifidum</Emphasis>

Major non-digestible components of soybean seeds and okara were determined by an in vitro enzymatic-physiological method, alternative to dietary fibre. Total indigestible fraction was higher in okara (41.6%) than in seeds (28.5%), and consisted of soluble and insoluble fractions, mainly composed of non-starch polysaccharides, klason lignin and resistant protein. Total protein was lower in okara (32.29%) than in seeds (46.97%), as were oil (14.72% okara–20.89% seeds) and ash contents (3.18% okara–4.60% seeds). In vitro digestibility of protein was lower for okara (84.3%), than for soybean seed (91.8%). Moreover, okara showed high swelling (10.54 ± 0.14 mL/g d.w.) and water retention capacity (8.87 ± 0.06 g/g d.w.) and was fermented in vitro to a greater extent by Bifidobacterium bifidum (29.8%), than by Lactobacillus acidophilus (8.3%). For its composition, physico-chemical properties and bifidogenic capacity in vitro, okara is a potential candidate to be a prebiotic fibre-rich ingredient of new functional foods.