Processing effect on soybean storage proteins and their relationship with tofu quality

Tofu was prepared from 13 soybean varieties according to three different methods (bench, pilot, and production methods). Different soybean varieties showed significant differences in storage protein composition (glycinin and beta-conglycinin). The beta-conglycinin (7S) and glycinin (11S) contents were 7.3-9.9 and 14.1-22.9% on the dry matter basis, respectively. The 11S/7S protein ratio varied from 1.64 to 2.51 among the varieties. Glycinin content and 11S/7S protein ratio of the 13 varieties did not change significantly from soy milk to tofu for the production and pilot methods. Soybean 11S/7S protein ratio positively correlated with the 11S/7S ratio of soy milk and tofu (0.57 < or = r < or = 0.83, p < or = 0.01). The correlation coefficient depended on the processing method. Processing method affected 7S and 11S protein contents of tofu and their contribution to tofu hardness, yield, and sensory quality. This may explain in part the contradictory findings of the relationships between storage proteins and tofu quality because processing methods differed in various studies.     

Composition of proteins in okara as a byproduct in hydrothermal processing of soy milk

Protein quality, based on its subunit composition, in okara obtained as a byproduct during hydrothermal cooking of soy milk was assessed. The composition of 7S and 11S protein fractions was correlated with the physicochemical properties of protein in okara produced from six soybean varieties. The basic 7S globulin (Bg7S) and 11S protein were two main proteins in okara. Investigated soybean genotypes produced okara with mainly acidic A(5) and basic B(1,2,4) polypeptides of 11S proteins. Soybean 11S content was not an indicator of okara protein recovery or extractability. Of all tested relationships, extractable soluble protein content of okara was influenced only by soybean Bg7S (r = 0.86; p < 0.05) and its light subunit contents (r = 0.93; p < 0.05). Okara protein recovery depended on Bg7S heavy subunit content in soybeans (r = 0.81; p < 0.05). The high quantity of vegetable protein in okara (around 35%) and very high protein extractability (around 85%) qualify this byproduct for potential application in food preparation as a functional ingredient.     

Effect of soy milk characteristics and cooking conditions on coagulant requirements for making filled tofu

The amount of coagulant added to soy milk is a critical factor for tofu-making; particularly it affects the textural properties of tofu. Earlier research indicated that the critical point of coagulant concentration (CPCC) is a characteristic parameter of soy milk and could be used as an effective indicator of optimal coagulant concentration (OCC) for making filled tofu. The objective of this study was to investigate the possible correlations between CPCC and the characteristics of soy milk made from various soybean samples and the effect of soy milk cooking and dilution conditions on CPCC. CPCC was determined by a titration method. Calcium chloride and magnesium chloride were used as coagulants. Soy milk characteristics including solid, protein, phytate, pH, titratable acidity, mineral content, and 11S/7S protein and these characteristics as affected by heating rate, heating time, and sequence of dilution and heating were studied. The results showed that the CPCC was significantly (p < 0.05) positively correlated with phytate content (grams per gram of protein), pH, and 7S protein content but negatively correlated with protein content, 11S protein content, 11S/7S ratio, titratable acidity, and original calcium content. Within the same soybean material, more proteins required more coagulant, but higher protein concentration during cooking resulted in less coagulant required by each gram of protein during coagulation. The CPCC decreased with increasing soy milk heating time or decreasing heating rate. The sequence of heating and diluting for preparing soy milk also had an effect on CPCC.     

Protein recovery in soymilk and various soluble fractions as a function of genotype differences, changes during heating, and homogenization

Harovinton, a variety of tofu type soybean, and 11 derived null soybean genotypes lacking specific glycinin (11S) and beta-conglycinin (7S) protein subunits were investigated to determine whether changes in protein composition affected the protein recovery in soymilk and its soluble fractions after various centrifugation steps. As both heating and homogenization have a marked effect on the increase in protein solubility, the changes occurring during these processing steps were studied for each soybean genotype. Harovinton and 11S-null genotypes showed significantly higher protein yields than the other genotypes evaluated. Subunits of group I (A(1), A(2)) of glycinin had a negative impact on protein solubility in all treatments, but this effect was the greatest in unheated soymilk samples. Samples containing a high beta-conglycinin to glycinin ratio showed an effect of heating on the solubility of the protein, as beta-conglycinin subunits aggregate with heating. The presence of the alpha' subunit of beta-conglycinin aids in the recovery of protein in the supernatant prepared from lines containing group I (A(1,4) A(2)) glycinin. The results of this study will help determine which specific protein composition will confer an increased stability in soymilk and soymilk-derived products.     

不同品种大豆加工豆浆的品质分析及评价模型

东北是中国大豆的主产区,也是传统豆制品的重要原料生产基地。为明确该产区大豆原料与其加工制得豆浆的品质、特点,该研究选取47个东北大豆品种为原料,分析其大豆粗脂肪、粗蛋白、钙、磷含量等理化指标,比较其加工豆浆的蛋白浓度、总固形物含量、感官评价、风味物质含量等品质差异。结果得到豆浆质量得率、动力粘度、总固形物、非豆腥味活性与豆腥味活性比值最高的品种分别是吉育102、吉92、吉育70、吉小8号、吉青3号。大豆籽粒理化指标分析结果显示,粗蛋白、粗脂肪、钙、磷含量最高的品种分别为垦丰17、GY07Y16、吉82、杂交豆3号。豆浆的豆腥味与脂肪氧化酶活性、油酸、亚油酸、亚麻酸含量呈显著正相关,脂肪含量与风味活性比呈负相关。利用因子分析法提取出4个因子方程,确定豆浆各项指标在综合品质中所占比重,进一步建立了豆浆品质评价模型,模型系数可以根据加工目的进行相应调整。综合得分最高的5个品种为吉45(9.52)、吉育70(9.43)、吉青1号(9.28)、吉育66(9.27)、吉育102(9.21)。结合对应的大豆理化指标排序发现,豆浆品质是大豆理化成分综合作用的结果,并非蛋白含量越高所得产品越好,脂肪含量高的品种并不适宜加工豆浆。该研究为用于加工豆浆的东北大豆品种分级提供了参考,实现了豆浆品质的综合判别及大豆加工基础数据的分析、整合。     

Effect of calcium sulfate concentration in soymilk on the microstructure of firm tofu and the protein constitutions in tofu whey

The effects of calcium sulfate concentration in soymilk on the microstructure of tofu and the constitutions of protein in tofu whey were investigated. The firm tofu made with 0.4% CaSO(4).2H(2)O was found to be most uniform and continuous in the microstructure. This tofu gave the maximal tofu yield, maximal solid and protein recoveries, and the best water retention ability. The results of gel electrophoresis and the ratio of amino nitrogen to total organic nitrogen indicated that the low molecular weight proteins in tofu whey were at their lowest when the tofu was made with 0.4% CaSO(4).2H(2)O. The SEM observations suggested that the tofu made with 0.4% CaSO(4).2H(2)O has the most uniform and homogeneous microstructure and, consequently, can most efficiently retain soybean proteins and water in the tofu gel.     

Self-diffusion coefficient of water in tofu determined by pulsed field gradient nuclear magnetic resonance

The self-diffusion coefficient of water in soybean protein dispersion and tofu was measured by pulsed field gradient (PFG) NMR. A soy protein isolate (SPI) dispersion (6 and 12%, w/w) in water, calcium cross-linked precipitate, and tofu were used for comparison. The self-diffusion coefficient of water (D) in the SPI dispersion, 2.23 x 10(-9) m2/s, was estimated lower than that of free water, 2.6 x 10(-9) m2/s at 25 degrees C, and decreased as the SPI concentration increased. It further decreased by the addition of calcium chloride, reflecting the obstruction effect induced by the precipitates in addition to the hydration and hydrodynamic interaction in the protein dispersion. The two water regions in tofu were interpreted by the two-site K?rger model: D1 and D2 of soft tofu were 2.26 (+/-0.11) x 10(-9) and 6.84 (+/-0.34) x 10(-11) m2/s, respectively. The relative amount of proton (water) was p1 = 0.98 and p2 = 0.02 at 100 ms of diffusion time. The self-diffusion coefficients of water decreased in pressed tofu, and their relative amounts of water changed to p1 = 0.93 and p2 = 0.07. It was suggested that D1 corresponded to obstructed water in the network structure and D2 corresponded to hydrated water on the surface layer of pores formed in the protein network of tofu. The pore sizes estimated from the diffusion length of obstructed water were 21.3 microm in soft tofu and 20.8 microm in pressed tofu. The removal of fat from pressed tofu led to a decrease in D2 from 6.26 (+/-0.31) x 10(-11) to 3.53 (+/-0.18) x 10(-11) m2/s, and the relative amount of hydrated water increased from 0.07 to 0.14, which indicated hydrophobic hydration.     

晋豆24~(60)Coγ射线诱变后代种子贮藏蛋白的研究

选用晋豆24及其60Coγ射线辐照诱变后代为试验材料,利用SDS-PAGE聚丙烯酰胺凝胶电泳研究了诱变后代大豆贮藏蛋白亚基11S和7S的组分含量、亚基组成和各亚基的含量及其变异规律。结果表明:大豆贮藏蛋白种质资源中,同一品种的不同亚基和不同品种的同一亚基间均有较大变异;11S球蛋白与7S球蛋白呈极显著负相关,与11S/7S比值呈极显著正相关;聚类分析根据11S/7S比值将诱变后代群体分为比值较高(平均为1.70)、居中(平均为1.25)和较低(平均为0.79)3类,为诱变育种选育优质专用大豆新品种提供了依据。     

空间坏境对大豆主要农艺性状及蛋白品质的诱变效应

以“实践八号”育种卫星搭载的3个大豆品种中黄28、中黄29、中黄31为材料,调查了空间诱变后代SP1、SP2代的主要农艺性状分析检测SP2、SP3种子的蛋白质组分（11S/7S球蛋白）、Kunitz胰蛋白酶抑制剂（SKTI）等品质性状分析检测,以为利用空间诱变技术改良大豆品质提供理论依据。结果表明,3个大豆品种对空间环境的反应敏感性不同,中黄28和中黄29的SP1代分别获得3株和12株变异株,变异率分别为0.417 %和1.667 %,而中黄31的SP1代没有发现变异植株,且中黄28的2株（01-SP2-1、01-SP2-2）和中黄29的5株（02-SP2-2、02-SP2-5、02-SP2-6、02-SP2-7、02-SP2-8）变异株在SP2代发生性状分离;空间环境使大豆11S 蛋白亚基发生变异,SKTI基因发生突变。空间诱变既可改良农艺性状,也可改良品质性状。     

Development of enzyme-linked immunosorbent assay for evaluation of chapati-making quality of wheat varieties

An indirect enzyme-linked immunosorbent assay (ELISA) has been developed for evaluation of chapati-making quality of wheat varieties. Polyclonal antibodies against gliadin, low molecular weight glutenin (LMG), and high molecular weight glutenin (HMG) were developed and utilized in the ELISA. Twenty-eight Indian wheat varieties were utilized in the ELISA. Out of these antibodies, an antigliadin antibody response was negatively correlated with farinograph water absorption (r = -0.89 at P < 0.01), chapati dough water absorption (r = -0.91 at P < 0.01), overall chapati sensory score (r = -0.95 at P < 0.01), chapati puffed height score (r = -0.95 at P < 0.01), and positively correlated with shear value of chapati (r = 0.76 at P < 0.01). Anti-LMG antibody response was not correlated with any of these parameters, whereas anti-HMG response positively correlated with chapati dough water absorption (r = 0.44 at P < 0.05), farinograph water absorption (r = 0.45 at P < 0.05), and overall chapati sensory score (r = 0.44 at P < 0.05), and negatively correlated with shear value (r = -0.38 at P < 0.05) and chapati puffed height (r = -0.44 at P < 0.05). The results indicate that wheat varieties with good chapati-making quality were having less antigliadin antibody response.     

Growth characteristics,phytate contents,and coagulation properties of soymilk from a low-phytate Japanese soybean (Glycine max (L.) Merr.) line

The phytic acid (myo-inositol hexakisphosphate or InsP₆) content of seed crops is important to their nutritional quality. Since it represents 75?±?10% of the total seed phosphorus (P), phytic acid is also important regarding the management of P in agricultural production. A low-phytate F5 line, No. T-2-250-4-20, was selected from the progeny of a cross between the low-phytate soybean line CX1834 and the Japanese commercial cultivar Tanbakuro. This line and its parents were grown in a field nursery, and the growth characteristics, phytate accumulation, and processing suitability for tofu were evaluated. At full maturity, the weight of seeds per plant of line T-2-250-4-20 was 5.2- and 1.3-fold higher than that of CX1834 and Tanbakuro, respectively. The amount of phytate-phosphorus as a percentage of the total P content in seeds was 23% in line T-2-250-4-20-34, 30% in CX1834, and 69% in Tanbakuro. No significant difference was observed among the three cultivars/lines in their seed magnesium (Mg), potassium (K), crude protein, and sugar. However, the calcium (Ca), crude fat and ash contents in seeds of line T-2-250-4-20-34 and Tanbakuro was lowered compared to that of CX1834. The breaking stress of tofu was estimated employing a rheometer with a decreasing concentration of the coagulant magnesium chloride (MgCl₂), starting at 15.7?mmol?L^?1. In tofu made from Tanbakuro, the concentration of MgCl₂ required to achieve the maximum breaking stress was 12.6?mmol?L^?1; however, it was 9.5?mmol?L^?1 for tofu made from T-2-250-4-20-34 and CX1834. The tofu made from Tanbakuro was soft and broke at 6.3?mmol?L^?1 MgCl₂, but, in line T-2-250-4-20-34, harder tofu was made with lower MgCl₂ concentrations. No difference was observed among the cultivars/lines in the SDS-PAGE patterns of protein in soymilk. These results indicate that we have developed a low-phytate soybean with adequate productivity, and confirmed that tofu made from the low-phytate T-2-250-4-20-34 soybean becomes coagulated and harder at a lower MgCl₂ concentration than that from high-phytate soybean cultivars.     

稀释介质种类对豆乳蛋白胶体粒子zeta电位测定效果的影响

蛋白粒子zeta电位是衡量豆乳体系稳定性的一个重要指标,而在电位分析前常采用稀释介质对豆乳进行预处理。为了确保zeta电位测定的准确性和科学性,必须选择合适的稀释介质。因此,该研究采用去离子水、豆乳超滤液两种稀释介质分别对豆乳进行稀释,并比较了这2种稀释介质对zeta电位、粒径分布、pH值以及电导率的影响。结果表明,若以去离子水为稀释介质,zeta电位的绝对值会随着稀释倍数的升高而显著增加（*P<0.05）,这主要是由于豆乳蛋白胶体粒子发生解聚导致粒径减小,而pH值的升高和电导率的降低则说明豆乳的离子强度显著降低。相比之下,选用豆乳超滤液稀释豆乳时,体系的 zeta 电位、粒径分布、pH值以及电导率都未随稀释倍数的增加而改变（*P>0.05）,说明此法能够较好地维持豆乳蛋白粒子的荷电稳定性。由此可知,豆乳超滤液可做为豆乳zeta电位测定的理想稀释介质。     

Development of a rapid titration method for predicting optimal coagulant concentration for filled tofu

A rapid titration method was developed for predicting the optimal coagulant concentration for making filled tofu. Cooked soymilk (350 mL, 20 degrees C) in a 400 mL beaker was stirred by a magnetic stirrer to form a swirl. The quick-acting coagulant solution (20.0 Brix) was added into the soymilk at 1.0 mL/min. The swirl depth decreased when the soymilk viscosity increased as a result of increasing the concentration of coagulant in the soymilk. At a suitable stirrer speed, the swirl finally disappeared but the soymilk still maintained rotation, and then the swirl reappeared after around 1 min. The critical point of coagulant concentration (CPCC) was calculated on the basis of the volume of coagulant consumed to get the swirl to disappear. The influences of several factors on the CPCC were investigated, including coagulant addition rate, soymilk temperature, soymilk concentration, soymilk volume, stir bar length, and container size. For validation, 33 soybean samples were used to determine their CPCCs and make filled tofus. The results indicated that CPCC was a characteristic parameter of soymilk and could be used as an effective indicator for predicting optimal coagulant concentration.     

Comparison of protein chemical and physicochemical properties of rapeseed cruciferin with those of soybean glycinin

Rapeseeds contain cruciferin (11S globulin), napin (2S albumin), and oleosin (oil body protein) as major seed proteins. The effects of oil expression and drying conditions on the extraction of these proteins from rapeseed meal were examined. The conditions strongly affected the extraction of oleosin and only weakly affected the extraction of cruciferin and napin. The protein chemical and physicochemical properties of cruciferin, the major protein present, were compared with those of glycinin (soybean 11S globulin) under various conditions. In general, cruciferin exhibited higher surface hydrophobicity, lower thermal stability, and lower and higher solubility at mu= 0.5 and mu = 0.08, respectively, than did glycinin. At the pHs (6.0, 7.6, and 9.0) and ionic strengths (mu= 0.08 and 0.5) examined, the emulsifying ability of cruciferin was worse than that of glycinin, except at mu= 0.08 and pH 7.6. The emulsifying abilities of cruciferin and glycinin did not correlate with thermal stability and surface hydrophobicity. Higher protein concentration, higher heating temperature, higher pH, and lower ionic strength were observed to produce harder gels from cruciferin. Gel hardness partly correlated with the structural stability of cruciferin.     

高温杀菌对预浸泡豆杆货架期品质变化的影响

为研究高温杀菌对预浸泡豆杆产品在货架期内品质变化的影响,本试验对经过105℃、15 min和110℃、10 min 2个杀菌条件处理的预浸泡豆杆在货架期内的主要微生物、感官和理化指标的变化情况及相关性进行了分析。结果表明,随着储存时间的延长,2个杀菌条件处理的预浸泡豆杆的菌落总数、硬度和咀嚼性均显著增加(P<0.05),水分含量、pH值、感官评分和亮度L^*值均显著降低(P<0.05),蛋白质含量、脂肪含量和弹性变化不显著(P>0.05)。对2个杀菌条件下的各项指标进行相关性分析,其结果与各指标在货架期内的变化趋势基本一致,预浸泡豆杆的表观指标和内部理化指标存在显著的相关性,并确定感官品质和色泽是储存过程中影响预浸泡豆杆品质的关键指标。本研究证实经110℃、10 min杀菌处理的预浸泡豆杆在货架期内能更好地保留预浸泡豆杆的品质。该研究结果为预浸泡豆杆货架期内产品品质的稳定和货架期的延长等问题提供了理论依据。     

Comparison of Chapatti and Breadmaking Quality of Wheat Genotypes

The chapatti and breadmaking quality of nine (eight Indian and one Australian) wheat (Triticum aestivum L.) cultivars was compared. The extension of a chapatti strip measured with a Kieffer dough extensibility rig correlated with chapatti scores for overall quality (r = 0.84), pliability (r = 0.91), hand feel (r = 0.72), chapatti eating quality (r = 0.68), and taste (r = 0.80). Overall chapatti quality also correlated with the resistance to extension of a chapatti strip (r = 0.68) when tested for uniaxial extension with a texture analyzer. The texture analyzer provided objectivity in the scoring of chapatti quality. The high‐molecular‐weight glutenin subunit protein composition assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis did not correlate with the overall chapatti score. A negative correlation was found between chapatti and bread scores (r = −0.77). The different requirements for chapatti and bread quality complicate the breeding of new wheat varieties and the exchange of germplasm between regions producing wheat for chapatti and those supplying bread producers.     

Effect of water-to-bean ratio on the contents and compositions of isoflavones in tofu

The present study investigated the changes of the bioavailable isoflavones, including daidzin, genistin, daidzein, and genistein, during the making of tofu. The amount of extracted daidzin and genistin in soy milk increased with increasing water-to-bean ratios from 5 to 9 and reached the maximum level at the ratios of 9-11. On the other hand, the amount of extracted free isoflavones (daidzein and genistein) was not affected by the water-to-bean ratio at the range of 5-11, and their extracted amounts in soy milk were 2-4-fold those in raw soybean. It is suggested that these free isoflavones are mainly derived from daidzin, genistin, malonyldaidzin, and malonylgenistin through enzymatic hydrolysis during the making of soy milk. Tofu made with water-to-bean ratios of 9:1 and 10:1 had the maximal retentions of daidzin and genistin, which were due to the fine homogeneous network microstructure that is supposed to be more effectively retained through hydrophilic interaction with protein. On the contrary, the retained amount of free isoflavones decreased significantly as the water-to-bean ratio increased from 7 to 11, due to their weakening hydrophobic interaction with protein. In this study it was found that the homogeneous microstructure of tofu improved the retention of hydrophilic daidzin and genistin and that the increased amount of drained water does not significantly reduce their retention in the final tofu products as generally imagined.     

Quantification of the group B soyasaponins by high-performance liquid chromatography

High-performance liquid chromatographic methods were developed for the isolation and quantitative determination of the group B soyasaponins, including 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP)-conjugated soyasaponins alphag, betag, and betaa, and their non-DDMP counterparts, soyasaponins V, I, and II, respectively, with formononetin used as the internal standard. The limits of quantification for soy products were 0.11-4.86 micromol/g. The within-day and between-days assay coefficients of variation were <9.8 and < 14.3%, respectively. The group B soyasaponin concentrations in 46 soybean varieties ranged from 2.50 to 5.85 micromol/g. Soy ingredients (soybean flour, toasted soy hypocotyls, soy protein isolates, textured vegetable protein, soy protein concentrates, and Novasoy) and soy foods (commercial soy milk, tofu, and tempeh) contained the group B soyasaponins from 0.20 to 114.02 micromol/g. There was no apparent correlation between isoflavone and soyasaponin concentrations in the soy products examined.     

Thermal Behavior and Nonfreezing Water of Soybean Protein Components

Thermal denaturation and hydration of two soybean protein components were studied using differential scanning calorimetry (DSC). Results showed that temperature of denaturation (T_d) of both 11S and 7S globulins decreased sharply with an increase in water content. Enthalpy of denaturation (ΔH_d) of 11S increased with increasing water content at first, and then leveled off at high water content. However, ΔH_d of both 7S and 11S components in 7S samples first increased and then decreased at high water content. The preparation method of samples influenced the ΔH_d value significantly but had little effect on the T_d. Nonfreezing water was determined from the DSC results. It increased in both 11S and 7S as water content increased but was more abundant in 7S, probably because of different compositions and structures. Threshold value of water content for the appearance of freezing water was 0.30–0.32 h (g of water/g of protein, mass ratio) for 11S. The water absorbed by both 11S and 7S during denaturation increased quickly at low water contents and remained almost constant at high water contents. The results were attributed to different structure and conformation of proteins before and after denaturation.     

Quality indicators of cultured Newfoundland blue mussels (Mytilus edulis) during storage on ice: microbial growth, pH, lipid oxidation, chemical composition characteristics, and microbial fatty acid contents

To devise proper strategies to evaluate and maintain the quality of cultured blue mussels (Mytilus edulis) during storage on ice, this study examined the potential use of microbial growth, pH, lipid oxidation, and composition characteristics as quality indicators. It also evaluated the use of individual (i15:0, ai15:0, i16:0, ai16:0, i17:0, ai17:0, 17:0) and total bacterial fatty acid contents as a rapid method to examine the microbial quality of stored mussels. Linear regression analyses of the storage period of mussels vs various quality indicators indicated that the strongest correlation was between the storage period and microbial growth (r = 0.973, p < 0.0001) followed by the microbial fatty acid ai15:0 content (r = 0.903, p < 0.0001) and ash content (r = 0.819, p = 0.0002). All other correlations between the storage period and quality indicators were moderate (r = 0.500-0.700 and p < 0.05), poor (r < 0.500 and p > 0.05), or negative (r = -0.657 and p = 0.027).