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.     

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.     

STORAGE CONDITIONS AFFECT SOYBEAN COLOR, CHEMICAL COMPOSITION AND TOFU QUALITIES

Soybeans stored under four sets of conditions were analyzed for the changes in color, composition and their effects on yield and textural properties of tofu. Soybeans stored under the adverse conditions (84% relative humidity (RH), 30C) exhibited significant changes in tofu yield and textural quality as well as in color and total free sugar content with storage time. Significant correlations existed between soybean color and tofu yield within 6 months under the adverse storage conditions. Color changes may provide a rapid method for predicting soybean quality for making tofu after storage. Soybeans stored under mild (57% RH, 20C), cold (4C) and uncontrolled ambient conditions (garage) exhibited no significant changes in their color or composition except for moisture contents, and maintained good qualities for tofu making for up to 18 months.     

Yield and Textural Properties of Tofu as Affected by the Changes of Phytate Content During Soybean Storage

ABSTRACT: Soybeans stored under 4 conditions were analyzed for the degradation of phytate and its effects on tofu qualities. Phytate in soybeans was hydrolyzed significantly under the adverse conditions for 9 mo, but decreased slightly under 3 mild conditions for 18 mo. Phytate degradation contributed to an increase in titratable acidity. When the phytate contents of soymilk were selectively reduced by 11.3% and 17.5% by phytase, while other components remained unchanged, tofu yield increased significantly but texture became softer. Tofu yield decreased and hardness increased in beans stored in the adverse conditions. Phytate degradation during adverse storage played a minor, indirect role in the deterioration of soybeans for tofu making.     

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.     

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.     

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.     

Effect of Soybean Varieties and Growing Locations on the Physical and Chemical Properties of Soymilk and Tofu

ABSTRACT: Soybean varieties and growing location greatly affected the protein content and color of soymilk and the protein content and yield of tofu ( P < 0.05). Protein content of soybeans was the most important affecting factor for the qualities of soymilk and tofu. There were significant correlations between the protein contents of soybeans and soymilks ( P < 0.05). There were also significant correlation between the soybean protein and the total solid content of soymilk (P < 0.05). Tofu moisture content had significant effect on the hardness and yield of tofu (P < 0.05). The correlation between soybean protein and tofu yield was significant at P < 0.05. The protein content and yield of tofu can be predicted by analyzing soybean protein.     

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.     

不同储存期大豆提取的大豆分离蛋白对千页豆腐的影响

研究不同储存期大豆提取的大豆分离蛋白(SPI)对千页豆腐的硬度、弹性和色值的影响。结果表明:品质最好的千页豆腐所用SPI的大豆的最佳储存期为9～18个月;在大豆最佳储存期提取的SPI生产的千页豆腐与刚收获的大豆相比,硬度提高了26. 9%～39. 4%,弹性提高了5. 5%～7. 8%,L值降低1. 6%～3. 6%,b值升高5. 3%～12. 8%;大豆储存期超过18个月后,整体趋势看,千页豆腐的硬度和弹性开始降低,口感变差,L值降低不明显,但b值升高明显,造成千页豆腐外观明显偏黄,卖相变差;同时受季节影响较大,特别是夏季储存的大豆制作的千页豆腐品质较差。     

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.     

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.     

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。     

EFFECT OF PRESSURE AND STORAGE TIME ON TEXTURE PROFILE PARAMETERS OF SOYBEAN CURD (TOFU)

The pressure applied to soybean curd during processing into tofu has a profound effect on the moisture content, yield and some textural parameters of tofu. As the pressure increased from 0.186P to 0.744 P the moisture content decreased from 82% to 60% and yield decreased from 2.0 kg to 1.2 kg per kg whole dry soybeans. Hardness-1, hardness-2, chewiness andgumminess increased linearly with increasing pressure. Springiness, cohesiveness, adhesiveness and stringiness were hardly affected by increasing pressure. During storage in water at 2–3°C for 3 weeks, hardness, gumminess, and adhesiveness increased moderately; springiness decreased moderately and the other texture parameters were almost unchanged.     

Tofu Production from Soybeans or Full-Fat Soyflakes Using Direct and Indirect Heating Processes

We compared processing yield, composition, and quality of tofu from soybeans and from full-fat soyflakes. Tofu was made using a steam-jacketed kettle and a commercial steam-injected cooker. Hydration time was 10 min for flakes and 12h for whole beans. Regardless of cultivar, a higher tofu yield was obtained from the steam-injected cooker system than from the steam-jacketed kettle system. Utilization of flakes required 62--65% less water during soymilk production. Independent of cultivar, tofu produced from full-fat soyflakes was lower in fat (26% d.b.) than whole soybean tofu (40% d.b.).     

Effect of Grinding Temperature on Hydroperoxide and Off-flavor Contents during Soymilk Manufacturing Process

ABSTRACT: Hydroperoxides and n -hexanal of soymilk made at different temperatures in the soybean grinding process were investigated. Both hydroperoxides and n -hexanal showed maximum amounts at 30°C, 37.78 μmol/g, and 1.94 mg/g, respectively. However, at 3°C and 80°C, amounts of hydroperoxides were about half of that at 30°C. N -hexanal showed high correlation with hydroperoxides except for at 80°C. It suggests that controlling the grinding temperature is effective to reduce hydroperoxidation and off-flavor content. Protein solubility an important index of soymilk, was decreased as the temperature increased. Grinding soybeans at low temperature is considered an economical method to produce soymilk having less off-flavor and high protein.     

Interconversions of Isoflavones in Soybeans as Affected by Storage

ABSTRACT: Conversions of isoflavones in soybeans under 4 conditions were investigated. Soybeans were stored in 84% RH, 30 °C for 9 mo and in 57% RH, 20 °C, cold (4 °C), and an uncontrolled ambient garage for 18 mo. Isoflavones were analyzed by HPLC. In 84% RH, 30 °C, the interconversion between aglycones and β-glucosides was significant ( p < 0.001). The percentage of β-glucosides and malonylglucosides in total isoflavones decreased from 99% to 3% in 9 mo. In contrast, the aglycones increased from 1% to 97%. In 57% RH, 20 °C, and ambient conditions, the glucoside forms increased with storage time, but malonylglucosides tend to decrease. In the 4 °C condition, isoflavone distribution had no significant ( p > 0.05) changes during storage.     

CHANGES IN QUALITY OF DEHYDRATED KIBBLED ONIONS DURING STORAGE

SUMMARY— Dehydrated kibbled onions. of the Egyptian variety, containing 4-5% moisture, were stored under different conditions and their keeping quality as influenced by storage variables determined. 3 packaging materials, namely cans, polyethylene and Saran pouches were used. Samples were stored at temperatures of 15, 25 and 35°C at 44% relative humidity for 39 wk. Temperature of storage was found to have the largest effect on product quality. The can package was found to be superior to the flexible pouches; however, Saran pouches could be used under certain conditions. Moisture content increased significantly in polyethylene pouches at all temperatures, but in Saran pouches only at 25° C Absorbance of onion extracts, as measure of browning, increased significantly with storage temperature and to a smaller extent due to packaging materials. Products in polyethylene deteriorated most, while the difference between Saran- and can-packed products was small. A similar trend in results was found in tristimulus color determinations. All products stored at 15° C and those in cans at 25°C were found to be of good organoleptic quality. The pyruvic acid development potential could not be used as a sensitive indicator for determination of product quality.     

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.     

紫薯保健豆腐的工艺研究

以黄豆和紫薯为主要原料,通过传统豆腐工艺加工制作新型豆腐.通过单因素与多因素正交试验,确定紫薯豆腐的最佳配方工艺条件.结果表明:温度对产品感官品质的影响最大,其次是豆浆和紫薯汁比例、石膏量、黄豆和紫薯水的添加量;最后确定了最佳的工艺配方:黄豆500 g,紫薯250 g,分别加入水1000mL制备豆浆汁与紫薯汁,豆浆与紫薯汁比例为6:1,石膏量为3.5 g,温度为100℃.产品感官性状良好,不仅含有独特的紫薯营养功能,还为开发新品种豆腐提供了理论参考.