Volatile compounds in Bacillus‐fermented soybeans

Thua nao, a traditional, proteolytic, fermented soybean condiment of northern Thailand, was prepared from cooked whole soybeans by natural flora fermentation. The microbial flora during the fermentation was dominated by Bacillus species. The formation of volatile compounds during the fermentation was studied. In addition, the volatile compounds of two samples of commercial dried thua nao and two samples of commercial Japanese natto were analysed. Fermentation led to a large increase in the concentration of total volatile compounds, from 35 µg kg^?1 wet weight in cooked soybeans to 3500 µg kg^?1 wet weight in 72 h fermented material. The major volatile compounds in fermented beans were 3‐hydroxybutanone (acetoin), 2‐methlybutanoic acid, pyrazines, dimethyl disulphide and 2‐pentylfuran. Sun drying of 72 h fermented material resulted in the loss of 65% of total volatiles, including important aroma compounds. The commercial dried thua nao samples had low concentrations of total volatile compounds (380 µg kg^?1 wet weight). It is suggested that improved drying/preservation methods are needed to retain aroma compounds in the traditional products. The natto samples were devoid of aldehydes, aliphatic acids and esters, and sulphur compounds, whereas the thua nao samples contained a diversity of these compounds. Previous investigators have reported these compounds in natto and it is not possible to suggest the existence of systematic differences between the volatile compounds in traditional thua nao prepared with an undefined, mixed microbial flora and those in natto fermented with Bacillus subtilis. © 2001 Society of Chemical Industry     

EXTRACTION YIELD OF SOLUBLE PROTEIN AND MICROSTRUCTURE OF SOYBEAN AFFECTED BY MICROWAVE HEATING

A laboratory‐scale microwave (MW)‐assisted extraction system was constructed and compared with a conventional shaking water bath regarding the extraction of soluble proteins in soybeans. Dynamic reaction was monitored by response surface methodology in the MW‐assisted extraction system. The yield of soluble protein increased until either temperature (T) or water/solid (W/S) ratio reached an optimum point (60.1C, 12.6 mL/g), and then decreased with further increase of T or W/S ratio. In addition, the yield of soluble protein increased with time within a range of 30 min, and no critical point was observed. The molecular mass of soluble protein was distributed from 19.3 to 81.3 kDa estimated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Scanning electron microscopy showed the destruction of the microstructure of soybean cells, which increased the extraction of soluble soy protein.     

Characterization of fermented black soybean natto inoculated with Bacillus natto during fermentation

BACKGROUND: To make nutrients more accessible and further increase biological activity, cooked black soybeans were inoculatedwith Bacillus natto and fermented at 37 °C for 48 h. The changes in physiochemical properties of fermented black soybean natto were investigated. RESULTS: The inoculation procedure significantly increased moisture, viscosity, color, polyphenol compounds and anthocyanin, and significantly decreased hardness after 48 h fermentation. Fibrinolytic and caseinolytic protease, β‐glucosidase activities, TCA‐soluble nitrogen, and ammonia nitrogen contents in the inoculated samples significantly increased as fermentation time increased. Genistin and daidzin concentrations gradually decreased with increased fermentation time. However, genistein and daidzein increased with fermentation time, which reached 316.8 and 305.2 µg g^?1 during 48 h fermentation, respectively. DPPH radical scavenging activities of the fermented black soybeans increased linearly with fermentation time and concentration. Compared with the soaked black soybeans and cooked black soybeans, the fermented black soybeans with B. natto resulted in higher scavenging activity towards DPPH radicals, which correlated well with the content of total phenols (r = 0.9254, P < 0.05) and aglycone isoflavone (r = 0.9861, P < 0.05). CONCLUSION: Black soybean natto fermented by B. natto has the potential to become a functional food because of its high antioxidant activity. Copyright © 2010 Society of Chemical Industry     

Recent progress of soybean protein foods: Chemistry,technology, and nutrition

Abstract

The most important chemical reactions during the process of soybean protein foods are the intermolecular reactions among the residues exposed on the surface of the protein molecules through the denaturation process. In native soybean protein molecules, most amino acid residues responsible for the reactions—such as cysteine (‐SH), cystine (S‐S), and hydrophobic amino acid residues—are buried in the inside region of the molecule, inaccessible to water. These residues become reactable with each other through the exposure from the inside by heat denaturation during processing. The unique textures of soybean protein foods, such as tofu, kori‐tofu, yuba, and texturized products produced by extruder, etc., are the results of both the intermolecular interchange reaction between the exposed ‐SH and S‐S groups and the intermolecular hydrophobic reaction among the exposed hydrophobic amino acid residues. The exposure of amino acid residues is also important for the hydrolysis of soybean proteins by enzymes, through which soy sauce is produced, because the cleavage of the peptide bonds is carried out after binding between the active sites of the enzymes and the enzyme‐specific amino acid residues exposed through denaturation. These facts indicate the importance of the three‐dimensional structures of soybean protein molecules in the technology of soybean protein foods. Recently great progress has been made in the manufacturing techniques of soybean protein foods, such as soy milk, tofu, abura‐age, textured protein products, and soy sauce. The quality of soy milk and tofu was very much improved by controlling the action of the biologically active substances such as lipoxygenases and β‐glucosidases which are contained in soybeans and responsible for the production of off‐flavor. A new abura‐age, whose texture does not deteriorate during frozen storage or drying, was developed by using soybean protein isolate and oil as materials. A new type of textured protein product was also developed: a deep‐fat‐fried nugget with unique texture and flavor. This product is textured through a twin‐type extruder. For soy sauce manufacturing new biotechnology has been applied on the pilot‐plant scale. This is a system of continuous fermentation through bioreactors with the immobilized whole cells of microorganisms, by which the fermentation term is shortened strikingly. New and important discoveries were made on the nutrition of soybean proteins. According to recent experiments using human beings, the amino acid score of soybean proteins is 100 for persons more than 2 years old, indicating that the nutritive value of soybean proteins is equal to animal proteins. Further, it was elucidated that soybean proteins have cholesterol‐lowering action. A discussion is presented on the future of the soybean protein foods.     

INFLUENCE OF HEAT TREATMENT AND GRAIN GERMINATION ON THE ISOFLAVONE PROFILE OF SOY MILK

Soy foods have attracted much attention for their possible effects on human health because of their phytochemical content, mainly isoflavones. Twelve forms of isoflavones have been identified in soybeans and soy products. Technological processes like heat treatment or fermentation can change the isoflavone profile of soy products. In this study, the effects of heat treatment and grain germination on isoflavone profile of soy milk prepared from BRS 213 soybean variety were evaluated. Isoflavone forms were separated and quantified by reversed‐phase high‐performance liquid chromatography. Heat treatment by autoclaving for 5 min did not affect the total isoflavone content, but led to a 90% decrease in malonyl forms, whereas β‐glycosides increased by 70%. Autoclaving for 15 min led to a 20% loss of total isoflavones. Germination for 3 days did not change the total isoflavone content, but changed the distribution profile (15% increase of malonyl forms and 30% decrease of β‐glycosides). Germination for 7 days increased the bioavailability of aglycone isoflavones in soy milk by seven times.     

Making soy sauce using direct fermentation of defatted soybean meal without the meju (soybean Koji) preparation process

Soy sauce prepared via direct fermentation of defatted soybean meal (DFSM) using halophiles without addition of dried, fermented soybeans or meju was evaluated. DFSM was fermented using single and mixed cultures of Oceanobacillus kimchii and Bacillus pumilus under 18% salinity conditions. Amounts of total organic nitrogen, free amino acids, and organic acids in soy sauce prepared with the mixed culture were slightly higher than sauces prepared with single culture. The ingredient content was higher in soy sauce prepared via direct fermentation of DFSM than soy sauce prepared with meju. Microorganisms detected in DFSM fermentation were not detected in the meju culture, except for the 2 halophiles, based on metagenomic analysis. Direct fermentation of DFSM is better than using meju for preparation of soy sauce.     

Recent progress on biotechnology of soybean proteins and soybean protein food products

Recently it has been recognized that the action of the enzymes contained in soybeans has negative effects on the qualities of soybean protein foods. Based upon these findings, new manufacturing techniques for high quality soybean protein foods have been developed through the control of such enzyme action. For instance, new soybean seeds lacking lipoxygenases have been developed which reduce the production of grassy‐beany flavors. The gel hardness of tofu can also be controlled through the action of the lipoxygenases contained in soybeans. In addition objectionable after‐tastes develop through the hydrolysis of soybean isoflavones by the ß‐glucosidases which are found in soybeans.

Genetic engineering of soybean proteins made a great progress in improving their functional and nutritional qualities through the modifications of genes encoding for soybean storage proteins. The application of a bioreactor for soy sauce is also described as an example of the progress on the biotechnology.     

Oil Bodies Extracted from High‐Fat and Low‐Fat Soybeans: Stability and Composition During Storage

Soybeans contain oil bodies (OBs) that encapsulate triacylglycerols (TAGs) with a phospholipid monolayer carrying scattered proteins. In nature, soybean OBs can form natural emulsions in aqueous media and may serve as natural, minimally processed, stable, and pre‐emulsified oil for addition into appropriate food systems. In this study, OBs were obtained by aqueous extraction from the mature seeds of 2 soybean crop cultivars, high‐fat soybean and low‐fat soybeans. The compositions of the extracted OBs were analyzed during storage at room temperature up to 14 d (pH = 7). The oxidative stability of these OBs, stored at 60 °C, was evaluated by measuring the presence of primary (lipid hydroperoxides) and secondary lipid oxidation products (malondialdehyde) by determining the standard peroxide value (PV) and thiobarbituric acid‐reactive substances (TBARS) value. During storage, the contents of unsaturated fatty acids, phospholipids, and tocopherols declined in both OBs, while their mean particle diameters (d₃₂) and ζ‐potentials increased. The changes in PV and TBARS values exhibited a similar trend for both OBs, but the OBs from low‐fat soybeans had significantly lower PV and higher TBARS values than the OBs from high‐fat soybean cultivars (P < 0.05). Overall, the OBs from both soybean cultivars had good stability during storage.     

Source and changes of proteinase activities of Indian anchovy (Stolephorus spp.) during fish sauce fermentation

Trypsin‐like proteinases exhibited the highest activity in viscera and muscle of Indian anchovy (Stolephorus spp.). The molecular weights (MWs) of proteinases in viscera were estimated to be 31, 35, 44, 49 and 57 kDa by activity staining in the presence of 4 mol L^?1 NaCl. The MW of proteinase extracted from muscle was 56 kDa. This reflects that only one proteinase was extracted from muscle whereas five proteinases were extracted from viscera. Trypsin‐like, chymotrypsin‐like and cathepsin L‐like proteinases were found in commercial fish sauce samples throughout 12 months of fermentation, suggesting that these proteinases were stable at high salt concentrations (250–300 g kg^?1 NaCl) and under acidic conditions (pH 5.2–5.8). In contrast, leucine aminopeptidase activity was detected only in the first month. The MWs of proteinases found in fish sauce after various fermentation periods were estimated to be 37, 47 and 53 kDa, which coincided with the MWs of proteinases found in Indian anchovy. Copyright © 2006 Society of Chemical Industry     

Effect of a halophilic aromatic yeast together with Aspergillus oryzae in koji making on the volatile compounds and quality of soy sauce moromi

Koji making is an essential step in the production of high‐quality soy sauce. In this study, we inoculated koji with a halophilic aromatic yeast (Zygosaccharomyces rouxii) and Aspergillus oryzae and investigated the effects on the volatile compounds and quality of soy sauce moromi. Our results suggest that the optimal yeast inoculation was approximately 1.5 × 10⁶ yeast per gram of koji, and excessive yeast greatly decreased A. oryzae enzyme activity. In comparison with the control group, there were no significant changes in the concentrations of amino nitrogen, total titratable acids, total soluble nitrogen and reducing sugar by extending the fermentation time during the first fermentation month, whereas the concentration of glutamate in the yeast‐inoculated sample increased by 46.16% and the arginine concentration decreased by 61.07%. After the second fermentation month, 17, 38 and 38 volatile components were identified by GC–MS in C1, C2 and C5, respectively. Moreover, a large number of volatile components, such as 2‐Methoxy‐4‐vinylphenol, ethyl acetate and 1‐Octen‐3‐ol were found in C2 and C5. And the total contents of volatile compounds in C2 were obviously higher than C5. This work furthers our understanding of the traditional multistrain koji making and provides a new method for enhancing the quality and flavour of soy sauce.     

INFLUENCE OF TRANSGLUTAMINASE-INDUCED CROSS-LINKING ON IN VITRO DIGESTIBILITY OF SOY PROTEIN ISOLATE

The influence of covalent cross‐linking by microbial transglutaminase (MTGase) on the sequential in vitro pepsin and trypsin digestion process and the digestibility of soy protein isolate (SPI), was investigated by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and nitrogen release analyses. Various subunits of β‐conglycinin and acidic subunits of glycinin were cross‐linked by MTGase to form high molecular weight (MW) biopolymers, while basic subunits of glycinin were unaffected. SDS‐PAGE analysis indicated that the cross‐linking mainly affected in vitro pepsin digestion pattern of various subunits of β‐conglycinin, while the trypsin digestion pattern of native SPI was nearly unaffected. Nitrogen release analysis showed that the in vitro pepsin or/and trypsin digestibility of native SPI (at the end of pepsin or trypsin ingestion) was significantly decreased (P ≤ 0.01) by the MTGase treatment (for more than 2 h). The cross‐linking by MTGase also significantly decreased the in vitro digestibility of preheated SPI. These results suggest that the cross‐linking by means of transglutaminase may negatively affect the nutritional properties of food proteins.     

Physical and Chemical Changes in Fermented Peanut and Soybean Pastes Containing Kojis Prepared Using Aspergillus oryzae and Rhizopus oligosporus

Studies were made to determine and compare physical and chemical changes occurring during 90 days of fermentation of miso-like products containing peanuts and soybeans as well as a combination of these oilseeds. Two koji molds (Aspergillus oryzae and Rhizopus oligosporus) and two levels of NaCl (6 and 12%) were evaluated. The L color values decreased more rapidly in misos containing A. oryzae koji compared to misos containing R. oligosporus koji and changes occurred earlier in low-salt formulae than in high-salt formulae. The type of mold koji had no apparent effect on changes in viscosity. The free fatty acid content of misos increased dramatically during the first 4 days of fermentation. Misos containing A. oryzae koji had higher soluble nitrogen and free amino acid content in the final product than did those containing R. oligosporus kojis. Peanut miso products had higher soluble nitrogen contents than did respective soybean products; however, the type of oilseed had little effect on accumulation of free amino acids.     

Chromohalobacter is a Causing Agent for the Production of Organic Acids and Putrescine during Fermentation of Ganjang,a Korean Traditional Soy Sauce

Ganjang, a Korean traditional fermented soy sauce, is prepared by soaking doenjang‐meju (fermented soybeans) in approximately 20% (w/v) solar salt solution. The metabolites and bacterial communities during ganjang fermentation were simultaneously investigated to gain a better understanding of the roles of the microbial population. The bacterial community analysis based on denaturing gradient gel electrophoresis of 16S rRNA gene sequences showed that initially, the genus Cobetia was predominant (0 to 10 d), followed by Bacillus (5 to 74 d), and eventually, Chromohalobacter became predominant until the end of the fermentation process (74 to 374 d). Metabolite analysis using ¹H‐NMR showed that carbon compounds, such as fructose, galactose, glucose, and glycerol, probably released from doenjang‐meju, increased rapidly during the early fermentation period (0 to 42 d). After removal of doenjang‐meju from the ganjang solution (42 d), the initial carbon compounds remained nearly constant without the increase of fermentation products. At this point, Bacillus species, which probably originated from doenjang‐meju, were predominant, suggesting that Bacillus is not mainly responsible for ganjang fermentation. Fermentation products including acetate, lactate, α‐aminobutyrate, γ‐aminobutyrate, and putrescine increased quickly with the rapid decrease of the initial carbon compounds, while Chromohalobacter, probably derived from the solar salts, was predominant. Multivariate redundancy analysis indicated that the Chromohalobacter population was closely correlated with the production of the organic acids and putrescine during the ganjang fermentation. These results may suggest that Chromohalobacter is a causing agent responsible for the production of organic acids and putrescine during ganjang fermentation and that the solar salts, not doenjang‐meju, is an important microbial source for ganjang fermentation.     

Effect of glasswort (<Emphasis Type="Italic">Salicornia herbacea</Emphasis> L.) and rice (<Emphasis Type="Italic">oryza sativa</Emphasis> L.) on quality of <Emphasis Type="Italic">Ganjang</Emphasis> (Korean Soy Sauce)

Four types of meju were made from 100%(w/w) defatted soybean (DFS), a mixture of 80%(w/w) defatted soybean, and 20%(w/w) glasswort (DFS-G), a mixture of 80%(w/w) defatted soybean and 20%(w/w) rice (DFS-R), and a mixture of 60%(w/w) defatted soybean, 20%(w/w) glasswort, and 20%(w/w) rice (DFS-GR). Four types of Korean traditional soy sauce were prepared from the 4 types of meju. Mineral and antioxidant contents in the soy sauce made of DFS-G and DFS-GR were significantly higher than others. Citric, malic, succinic, lactic, and pyroglutamic acid contents in soy sauce made of DFS-R and DFS-GR were 1.3–1.5 times higher than others. Total nitrogen and free amino acid contents in soy sauce were correlated with DFS concentration in the meju. The bacterial community in the non-fermented meju-making ingredients was replaced largely by Bacillus sp. in the fermented meju. The use of glasswort and rice in the meju-making process did not alter the bacterial community responsible for the fermentation of meju.     

PHENOLIC ANTIOXIDANT ENRICHMENT OF SOY FLOUR-SUPPLEMENTED GUAVA WASTE BY RHIZOPUS OLIGOSPORUS-MEDIATED SOLID-STATE BIOPROCESSING

In this paper, we investigated the potential for Rhizopus oligosporus to produce enhanced levels of free phenolics from guava residue mixed with soy flour as the nitrogen source.β‐glucosidase activity and antioxidant activity in crude extracts were evaluated. Two substrates were studied based on carbon and nitrogen ratios: A, 90% guava residue : 10% soy flour (G9) and B, 50% guava residue : 50% soy flour (G5). Bioprocessing increased water extractable phenolics 12.9% with G9 substrate and 98.6% with G5 substrate. For both substrates, antioxidant activity increased during early stages of fungal growth but decreased thereafter. Phenolic antioxidant mobilization during bioprocessing was associated withβ‐glucosidase activity and hypothesized to involve the mobilization of polymeric phenolics. The bioconversion of soy flour‐supplemented guava residue by R. oligosporus represents a novel strategy for the enhancement of phenolic antioxidant content and potential commercial value of guava wastes.     

Comparison of folate losses in soybean during the preparation of tempeh and soymilk

The changes in undeconjugated and total folate content of soybean during various stages of tempeh and soymilk preparation were studied. Total folate was extracted by the tri‐enzyme technique. The ratio of total folate to undeconjugated folate was compared in all samples. Raw soybeans used for tempeh and soymilk preparation contained 4.04 and 4.50 mg total folate kg^?1 respectively. Soaking and boiling soybean caused a significant loss of folate during tempeh and soymilk preparation. Leaching was identified as the major cause of folate loss, as soaking and cooking waters were found to contain a large amount of folate. Rhizopus fermentation of boiled soybean caused an increase of 68 and 100% in undeconjugated and total folate contents respectively. Frying reduced the folate content of tempeh significantly. Milling of boiled soybean in soymilk preparation significantly reduced the undeconjugated folate content of blanched soybean but increased the total folate. UHT treatment of soymilk caused a loss of 9 and 14% of undeconjugated and total folates respectively. The total folate content of deep‐fried tempeh and soymilk was 2.35 and 2.76 mg kg^?1 respectively. Analysed values are expressed on a dry weight basis. © 2002 Society of Chemical Industry     

大豆不同前处理方式对豆浆品质的影响

为探讨大豆不同前处理方式对豆浆品质的影响,选择5 种前处理方式,对所制得豆浆的感官品质、色泽、稳定性、主要营养成分及抗营养因子含量进行对比分析。结果表明：大豆不同前处理方式对豆浆品质有不同的影响。干豆直接制浆虽方便快捷,但所得豆浆品质较差,其感官品质、稳定性均差于浸泡大豆,且主要营养成分如蛋白质、多糖得率低,抗营养因子含量高;高温高压蒸煮大豆制浆,其感官品质、稳定性及抗营养因子的去除效果均差于浸泡大豆,且色泽偏暗,蛋白质损失严重,含量低于干豆制浆;与干豆直接制浆相比,浸泡处理大豆可明显改善豆浆感官品质及其稳定性,且其蛋白质、可溶性固形物、多糖含量显著提高（P＜0.05）,抗营养因子含量显著下降（P＜0.05）;免浸泡豆和NaHCO3溶液泡豆制得豆浆色泽最亮,综合品质最好。     

Bioavailability of Zinc in Fermented Soybeans

The bioavailability of zinc in soybean meal fermented by lactic acid-producing bacteria (LAPB) and by Rhizopus oligosporus in tempeh fermentation was evaluated with the rat bioassay, using the slope ratio method and log total femur zinc or weight gain versus zinc intake as response parameters. Fermentation significantly increased (P < 0.05) the RBV of zinc from 73.0% in boiled non-fermented soybeans (pH 6.7) to 84.5% in boiled LAPB fermented soybeans. The highest RBV (95.3%) was found in the autoclaved and LAPB fermented product (pH 6.5). Rhizopus oligosporus fermentation resulted in a RBV of 89.0%. Thus, fermentation in the processing of soybeans will improve zinc bioavailability in this food.     

Immunoreactivity reduction of soybean meal by fermentation,effect on amino acid composition and antigenicity of commercial soy products

Food allergy has become a public health problem that continues to challenge both the consumer and the food industry. The objectives of this study were to evaluate the reduction of immunoreactivity by natural and induced fermentation of soybean meal (SBM) with Lactobacillus plantarum, Bifidobacterium lactis, Saccharomyces cereviseae, and to assess the effect on amino acid concentration. Immunoreactivity of commercially available fermented soybean products and ingredients was also evaluated. ELISA and western blot were used to measure IgE immunoreactivity using plasma from soy sensitive individuals. Commercial soy products included tempeh, miso and yogurt. Fermented SBM showed reduced immunoreactivity to human plasma, particularly if proteins were <20 kDa. S. cereviseae and naturally fermented SBM showed the highest reduction in IgE immunoreactivity, up to 89% and 88%, respectively, against human pooled plasma. When SBM was subjected to fermentation with different microorganisms, most of the total amino acids increased significantly (p < 0.05) and only few of them suffered a decrease depending on the type of fermentation. All commercial soy containing products tested showed very low immunoreactivity. Thus, fermentation can decrease soy immunoreactivity and can be optimized to develop nutritious hypoallergenic soy products. However, the clinical relevance of these findings needs to be determined by human challenge studies.     

Effect of koji fermentation on generation of volatile compounds in soy sauce production

The generation of aroma compounds and the changes in sensory characteristics through the soy sauce koji fermentation were investigated to evaluate the crucial impact of the koji fermentation on soy sauce aroma. The sensory analysis showed a marked increase in ‘musty’ and ‘soy sauce‐like’ odours, whereas the beany attribute decreased significantly during koji fermentation. Aldehydes and alcohols were the major volatile classes present in the koji samples. Gas chromatography–olfactometry was used to identify the aroma‐active compounds in harvested koji, and the results showed that 1‐octen‐3‐ol, 3‐octanol, (E)‐2‐octenal, di‐epi‐α‐cedrene, benzeneacetaldehyde and 3‐(methylthio)‐propanal exhibited the greatest aroma intensities in harvest koji. Moreover, relative contents of (E)‐2‐octenal, benzeneacetaldehyde, 3‐(methylthio)‐propanal and 2‐phenylpropenal were found to be positively related to ‘musty’ and ‘soy sauce‐like’ odours. Results from principal component analysis showed that the growth and sporulation of Aspergillus oryzae had the important impacts on the volatile evolution.