Changes of soybean quality during storage as related to soymilk and tofu making

ABSTRACT:  Soybeans are stored and transported under various humidity and temperature conditions. Soymilk and tofu are two of the most important foods made from whole soybeans. The objective of this study was to investigate the influence of storage conditions on soybean quality as related to soymilk and tofu-making properties. Soybeans of 3 different genotypes (Proto, IA2032, and Vinton 81) were stored in varying conditions: temperature ranging from 4 to 50 °C, relative humidity from 55% to 80%, initial moisture content from 6% to14%, and storage time up to 15 mo depending upon storage conditions. The effects of different storage conditions on soybean color, solids and protein extractability, soymilk pH, tofu yield, tofu solids and protein contents, tofu color, and texture were investigated. While no significant changes occurred for the soybeans stored at 4 °C, the soybeans stored at high temperatures (30 to 50 °C) exhibited significant quality loss ( P < 0.05). The degradation of soybean lightness (Hunter L ), color difference (Δ E ), and solid extractability exhibited a linear relationship with time. Soak weight decreased at high temperature and relative humidity, but increased at mild storage conditions. Several combinations of storage conditions at temperatures exceeding 30 °C produced a drastic loss in tofu yield. Storage also affected the tofu making process by reducing optimum mixing time to produce the highest tofu yield. Varietal difference in soybean storability was observed. The results provided useful information for the soybean processing industry to store soybeans using the optimal storage conditions and to estimate soybean quality after storage.     

Yield and Quality of Tofu as Affected by Soybean and Soymilk Characteristics: Glucono-delta-lactone Coagulant

Nine light hilum soybean [Glycine max (L.) Merr] cultivars were used to study characteristics that affect yield and quality of tofu (soybean curd) coagulated with glucono-delta-lactone (GDL). Pressed and packed (nonpressed) curds were examined. Yield of tofu was not affected by size of beans. Protein and total solids in soymilk increased when protein and moisture increased in soybeans. Yield of pressed GDL tofu increased with protein content of soybeans (or soymilk) plus decreased calcium content. Fracturability of pressed GDL tofu increased with levels of phosphorus. Hardness of packed tofu increased with protein content in soymilk. Yield of pressed GDL tofu was 20% higher than CaSO₄ tofu.     

Stability of soybean seed composition and its effect on soymilk and tofu yield and quality

Soymilk was made from 10 soybean [Glycine max (L.) Merr.] lines grown at three locations for 2 years, using an 18:1 water/soy protein ratio. Tofu was made with either glucono-delta-lactone (GDL) or calcium sulphate dihydrate (CS). Genotype and year effects were substantially greater than location effects on soybean protein content and seed composition; soymilk and tofu yield, solids levels, and pH; and tofu colour, hardness, and firmness. Genotype by location and genotype by year interaction effects were minor relative to the genotype and year effects. Yield of soymilk, GDL tofu, and CS tofu, which averaged 7.39 l, 6.29 kg, and 6.15 kg per kg soybeans, respectively, were all positively correlated with seed protein and stachyose, and negatively correlated with seed oil, free sugar, sucrose and remainder content. Seed protein was positively correlated with tofu hardness and firmness, while seed oil, free sugar, sucrose, and remainder content were generally negatively correlated with tofu quality parameters. Results of stepwise regression analysis showed that seed protein was the major determinant of soymilk yield and solids content, while soymilk yield was, in turn, the major factor determining GDL tofu yield. Procedures used in making soymilk and tofu play a major role in determining which seed component has a major effect on soymilk and tofu yield and quality.     

Comparison of Two Small-Scale Processing Methods for Testing Silken Tofu Quality

In developing a simple, reliable, small-scale method to assess silken tofu quality in our soybean improvement program, we examined two processing methods and two coagulants, glucono-δ-lactone (GDL) or nigari (magnesium chloride) in two experiments. Silken tofu was prepared from a commercial soybean variety (expt 1) or seven soybean varieties (V1–V7) which were grown and harvested together (expt 2). The soybeans were soaked overnight (the soak method, with 55 g soybeans) or ground dry first (the dry method, with 60 g soybeans) before processing. The quality of the silken tofu was evaluated and compared among varieties and coagulant-processing methods and their interactions. Moisture and protein content in soymilk and soybean seeds, soymilk yield and protein and solid recovery in soymilk were determined. Compared with the dry method, the soak method allowed faster soymilk extraction, produced soymilk with lower solid and higher protein content and firmer silken tofu with either GDL or nigari as coagulant. Depending on whether nigari or GDL was used as coagulant, the soak method also produced silken tofu with the highest or the lowest water loss which correlated strongly and negatively with tofu hardness (r?=??0.93***). Differences were detected among varieties for the key quality attributes. Taken together, the soak method with GDL as coagulant would be the preferred combination to use to assess tofu quality.     

The Role of Composition and Content of Protein Particles in Soymilk on Tofu Curding by Glucono-δ-lactone or Calcium Sulfate

ABSTRACT: The effects of composition and content of protein particles on tofu curding were investigated by using soymilk prepared from mixtures of glycinin-rich and β-conglycinin-rich soybeans. The breaking stress of tofu curds increased with the increase of protein particle content in soymilk. The soymilk from glycinin-rich soybeans had a high protein particle content and formed harder tofu curds. There is a significant positive correlation between the content of protein particles and the breaking stress of tofu curds. It is suggested that the increase of the quantity of protein particles reinforces the combination among protein particles during the tofu curding, thus forming a stronger network of tofu curds.     

Yield and Quality of Tofu as Affected by Soybean and Soymilk Characteristics. Calcium Sulfate Coagulant

Nine light hilum soybean (Glycine max (L.) Merr.) varieties were used to study the characteristics of soybeans and soymilk that affect the yield and quality of tofu coagulated with calcium sulfate. The yield of tofu was not affected by the size of soybeans. Soybean varieties high in protein, fat and phosphorus contents produce tofu with higher protein, fat and phosphorus contents. Two models for predicting the yield of tofu were proposed. According to model one, soymilk with higher pH and total solids gives a higher yield of tofu. According to model two, soybeans high in protein and ash and low in phosphorus give a higher yield of tofu.     

RELATIONSHIPS BETWEEN SOYBEAN COMPONENTS AND TOFU TEXTURE1

Tofu was prepared from samples of Amsoy 71 and Vinton or Vinton 81 soybeans grown in different environments. Relationships between soybean, soymilk and tofu protein, lipid, phytic acid, calcium, copper and iron were examined. All components except lipid in soybeans were significantly correlated with the same component in soymilk, but only phytic acid, copper and iron were significantly correlated in soybeans and tofu (moist basis). When relationships were examined on a dry basis, soybean and tofu protein were significantly correlated (r = 0.93). Soybean phytic acid was significantly correlated with tofu calcium (r = 0.90). Tofu calcium and hardness (r = 0.73) and springiness (r = 0.83). were significantly related, and tofu protein was significantly related to fracturability (r = 0.75). The higher-protein varieties (Vinton/Vinton 81) generally produced tofu that had a higher protein content and a firmer, more springy texture than that of the Amsoy 71 beans. Phytic acid may preferentially bind the calcium coagulant, altering the curd structure and the yield, composition and texture of the resulting tofu.     

EFFECT OF SOYBEAN STORAGE ON TOFU AND SOYMILK PRODUCTION1

Century 84 and Century -L₂L₃ (lacking lipoxygenase isozymes 2 and 3) near isogenic soybean varieties were stored at five temperature and relative humidity conditions for up to three months. At one-month intervals, soybeans were retrieved from storage and processed into soymilk and tofu. Chemical and physical characteristics of the soybeans, soymilk, and tofu were analyzed. In general, soybean storage above 25C and 50% relative humidity adversely affected the characteristics of the soymilk (reduced pH and solids content) and tofu (decreased yield and moisture content, and darker color) produced. Century -L₂L₃ soybeans were more resistant to changes during adverse storage than were Century 84 soybeans.     

Statistical and Kinetic Studies of the Changes in Soybean Quality during Storage as Related to Soymilk and Tofu Making

ABSTRACT:  The objective of this study was to develop statistical equations and kinetic models to describe the changes of soybean quality during storage. Significant correlations ( P  < 0.0001) were found among most of quality attributes including color parameters (Hunter L , a , b , and Δ E ), solid extractability (as expressed by soymilk solids content), soymilk pH and protein content, tofu yield, hardness, and protein content. Regressed linear equations were developed between color indices ( L/L ₀, ΔE ) and soymilk/tofu making properties. Empirical equations were developed to relate soybean color indices ( L/L ₀, ΔE ) and storage conditions including variables of initial moisture content (MC), relative humidity (RH), temperature ( T ), and duration ( t ). Kinetics of the changes in soybean color and extractability during storage at 70% RH and 22 to 40 °C were investigated. The kinetics was well described by zero-order kinetics. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for all parameters, from which the activation energies and rate constant were obtained. The equations developed in this study provided simple methods to monitor soybean quality and predict quality changes of soybeans during storage at various conditions.     

PHYSICOCHEMICAL CHARACTERISTICS OF SOFT TOFU FORMULATED FROM SELECTED SOYBEAN VARIETIES1

Currently, hundreds of soybean varieties with a wide range of quality attributes are available. The majority of these soybean varieties have not been evaluated for their quality in soymilk and tofu. In this research, tofu was prepared using the hot ground method by coagulating soymilk from four soybean varieties (Macon, Saturn, OHIOFG1 and OHIOFG2) with calcium sulfate dihydrate. Soybean variety significantly affected yield, held water, color parameters, viscosity, storage modulus, and textural properties of tofu cakes. Soymilk with higher pH, viscosity, and protein produced tofu with higher protein, water held, and yield. Varietal differences should be considered in selecting soybeans for tofu production. Macon soybeans produced the best tofu with regards to quality attributes.     

两种工艺生产豆腐的营养成分与品质特性的关系

本研究以12 个大豆品种为原料,分别采用生浆工艺和熟浆工艺制作豆腐,并测定豆腐中的蛋白质及其组分含量、脂肪含量,同时分析豆腐的得率、保水性、色度以及质构特性。在对上述实验结果进行分析整理之后,通过显著性分析得到在豆腐生产过程中,熟浆工艺相比于生浆工艺更具有一定优势的结论,熟浆工艺不仅能够很好地保留大豆中的营养成分,还对豆腐的得率及品质特性有较好的提升。     

Variation in the phytic acid content of soybeans and its effect on consistency of tofu made from soybean varieties with high protein content

The relationships of contents of phytic acid and protein to the breaking stress of tofu were examined using soybeans of three Japanese varieties with high protein content harvested in different locations from the years 2001 to 2003. The phytic acid content was more variable than protein content within different cultivating locations and years for the same variety and showed significant negative correlation to the breaking stress of tofu made with 0.25% MgCl₂ for all the varieties (P < 0.001, r = ?0.60). In particular, Sachiyutaka variety was characterized by the highest negative correlation between the breaking stress of tofu and the phytic acid content in soymilk (P < 0.001, r = ?0.73). As MgCl₂ concentration increased, the correlation between the phytic acid content and the breaking stress of tofu was reduced, and finally there was no significant correlation between them when the breaking stress reached a maximum at the particular MgCl₂ concentration which is probably concerned with varietial characteristics of soybeans. These results support the idea that the variation in the content of phytic acid, which can act as a buffer against coagulation of soy protein, accounts for the fluctuation in consistency of tofu made with lower MgCl₂ concentrations (ca. 0.25%) using soybeans of the same variety with different cultivating conditions. Copyright © 2005 Society of Chemical Industry     

大豆组分与北豆腐得率及品质的相关性研究

选取11种大豆为原料,研究了大豆组分与制成的北豆腐得率、品质指标(保水性、质构指标)之间的关系。结果表明:北豆腐湿基、干基得率及保水性均与大豆中蛋白质含量、水溶性蛋白质含量、11S亚基含量以及11S/7S呈显著正相关,与大豆中脂肪含量呈显著负相关。北豆腐硬度与大豆蛋白质、水溶性蛋白质、11S亚基含量以及11S/7S均呈显著负相关;北豆腐弹性与7S、11S亚基含量呈显著负相关;北豆腐黏聚性与大豆水溶性蛋白质、植酸含量呈显著负相关,与7S、11S亚基含量呈极显著正相关;胶着性与大豆水溶性蛋白质呈极显著负相关。聚类分析结果显示,用郑9525、郑94059和郑0102这3种大豆制作的北豆腐得率、保水性及质构特性均较好。     

An interlaboratory test of a procedure to assess soybean quality for soymilk and tofu production

A method for preparing soymilk and tofu has been developed to be used in assessing the suitability of new soybean varieties for soyfood production; the coagulants were glucono-delta-lactone and CaSO_4·2H₂O. The method was tested in two separate laboratories using four soybean varieties developed in Canada, three were food grade and the fourth was an oilseed variety. The soymilk and tofu pH was similar regardless of variety or lab. For soymilks yield and total solids there were significant differences (P⩽0.01) detected among varieties and between laboratories. For tofu yield and total solids the variety effects were significant in both locations (laboratories). Although reproducibility was very good within each laboratory, for each treatment there was some lack of reproducibility across laboratories. The method is best suited for use in comparative studies using a base standard as reference and is a good tool for assessing the quality of new soybean varieties for food use.     

点浆条件对酸浆豆腐品质的影响

为探究点浆时豆乳温度、点浆后蹲脑温度和蹲脑时间对酸浆豆腐品质的影响,提高酸浆豆腐品质,本研究利用质构分析、SDS-PAGE和低场核磁等技术分析了豆腐品质、豆乳中蛋白凝固过程、大豆蛋白各亚基含量和水分分布的变化规律。结果表明,点浆时豆乳温度对豆乳沉淀中蛋白和大豆蛋白各亚基含量无显著影响,但对豆腐品质和水分分布有较大影响。当点浆时豆乳温度为75℃时,豆腐的硬度最小,而其弹性、得率、含水量、保水性、感官得分和T₂₁弛豫时间最大。蹲脑温度和蹲脑时间对豆腐品质、豆乳沉淀中蛋白含量和大豆蛋白各亚基含量影响显著,当蹲脑温度75℃和蹲脑时间20 min时,豆腐硬度最小为15.80 N,而弹性、得率、含水量、保水性和T₂₁弛豫时间最佳,分别为5.15 mm、241.3%、76.36%、65.68%、43.29 ms,且豆腐品质豆乳沉淀中蛋白含量最佳。当点浆时豆乳温度为75℃、蹲脑温度为75℃和蹲脑时间20 min时,豆腐品质和感官得分最优。     

Quality and Antioxidative Activity of Black Soybean Tofu as Affected by Bean Cultivar

ABSTRACT: Two black soybeans, green-cotyledon (T3) and yellow-cotyledon (T5), were compared for possible tofu manufacturing. The tofu made by T5 black soybean has a higher yield, a higher protein content, and a harder, smoother, and lighter surface. The antioxidative activity in the T5 black soybean tofu was similar to the T3 black soybean tofu. The T5 black soybean should be a better cultivar for tofu processing than the T3 black soybean.     

Coagulation of soymilk and quality of tofu as affected by freeze treatment of soybeans

The present study was carried out to investigate the effects of freezing of soybeans on the coagulation of soymilk and quality of tofu. Soymilk, prepared from frozen soybeans, was found to coagulate faster in the presence of coagulant and produced a more uniform-structured gel than that from unfrozen soybeans. Tofu, prepared from frozen soybeans, showed a more orderly and denser network structure than that from unfrozen soybeans, thereby inducing an increase in some textural parameters such as hardness, springiness, gumminess and chewiness as well as syneresis. Freezing also brought about some changes in tofu quality: lower yield, lower fat and higher protein contents. Results of sensory evaluation showed that tofu from frozen soybeans had better sensory properties in terms of flavour and mouthfeel. From these results, it was concluded that freezing promoted the coagulation process of soymilk and changed the quality of tofu in a positive way.     

Tofu Yield and Textural Properties from Three Soybean Cultivars as Affected by Ratios of 7S and 11S Proteins

Crude 11S and 7S proteins of three soybean cultivars were fractionated, and tofu was prepared from soymilk with 11S/7S protein ratios of 1.6 to 3.2. Higher 11S/7S ratio produced lower yield (p≤0.05) of Vinton and Sturdy tofu. Higher 11S/7S ratio resulted in higher firmness of Proto and Sturdy tofu. Increase in 11S/7S ratio increased cohesiveness of Sturdy tofu. The maximum extent of decreasing Vinton tofu yield and increasing Proto and Sturdy tofu firmness was ∼10% of the unmodified tofu. Results indicated that tofu characteristics were cultivar dependent and manipulation of 11S/7S ratio may not result in substantial effects on tofu yield or quality.     

Relationships between protein and other chemical composition and texture of tofu made from soybeans grown in different locations

Understanding quantitative relationships between protein and other chemical components in diverse soybean genotypes (lines) grown in different locations and the firmness of tofu can provide scientific insight for selecting soybean suitable for tofu making. Locations showed significant effects on seed components, including total protein, major storage proteins, subunits and polypeptides of the major storage proteins, and calcium, but not magnesium or phytic acid. Results showed that 11S content, but not 11S/7S ratio, was only correlated with filled tofu firmness when analyzed over all locations. A strong and positive correlation between firmness and A₃ polypeptide of the 11S protein content was found for both pressed tofu (r = 0.80, p < 0.001) and filled tofu (r = 0.76, p < 0.001) over three locations (overall pooled data) and within most individual locations. The correlation of filled tofu firmness and A₃ polypeptide was significant for each of the three individual locations. However, the correlation of pressed tofu firmness and A₃ polypeptide content was significant at two of three locations. Mean calcium content was positively correlated with mean pressed and filled tofu firmness over all locations, but calcium was not correlated with pressed tofu firmness at any individual location, and only one location showed a significant correlation of calcium and filled tofu firmness. In addition, pressed tofu firmness was found to be negatively correlated with tofu yield. The findings that A₃ polypeptide's strong relationship with tofu firmness within certain locations may be used by the food industry to select proper soybean for manufacturing tofu and to facilitate tofu soybean breeding for tofu making.     

Soybean variety and storage effects on soymilk flavour and quality

Soymilk prepared from five soybean cultivars, grown in Ontario, were analysed for protein, oil, mineral composition, viscosity, colour, lipoxygenase (LOX) activities and flavour profile. Among the five soybean cultivars, the Vinton 81 variety contained the highest protein and the lowest fat. The yield of soymilk from all five cultivars was similar. Major differences were observed in viscosity and in the composition of both the soymilk and the okara. Higher protein and fat extractability was found in soymilk made from S08‐80 and Vinton 81 varieties. Their okara protein contents were also among the highest. Minimum extractability was observed with S03W4 cultivar. Soymilk made from S 03W4 and Vinton 81 cultivars had the whitest colour (lowest ΔE values). Viscosity values were the highest for S08‐80, FG1 and S20‐20 varieties. Headspace solid‐phase microextraction gas chromatography was used to analyse volatile compounds in soymilk. A total of fourteen volatiles were identified, among which aldehydes and their corresponding alcohols were the major compounds. Similar volatile compounds were identified in all the samples analysed but at different concentrations. The highest LOX activity was observed in the Vinton 81 and S20‐20 soybean cultivars, which had the highest total volatile and hexanal contents. A positive correlation (correlation coefficient = 0.82) between enzymatic activity and the total volatiles was observed. Vinton 81 cultivar was subjected to storage (at 18 °C and 50% relative humidity) for a period of 10 months. Soymilk was prepared at different times during storage. The results showed that the soymilk colour, LOX and total volatiles were significantly (P < 0.05) affected by the storage of the soybeans over time.