Studies on the Yield and Quality Characteristics of Tofu

Tofu made from imported U.S. soybeans and local Ta-Lien soybeans showed a similar yield. The yield of tofu from whole soybean was higher than that of defatted soybean flake. Significant different qualities of tofu products were prepared by using various coagulants. It was found that calcium sulfate (gypsum) and bittern (called nigari in Japanese) were suitable coagulants for making the Chinese-style tofu, but not glucono-δ-lactone. Other coagulants were not desirable for manufacturing good quality Chinese-style tofu. Commercial tofu products in Taiwan had various rheological properties.     

凝固剂混合方式对盐卤豆腐品质特性的影响

为明确凝固剂混合方式对盐卤豆腐的品质特性的影响,本研究分别比较了在60、120、180、240 r/min条件下加入凝固剂,搅拌10、20、30 s后,制备盐卤豆腐的品质差异,并在最佳搅拌条件下进一步比较不同批次（分1～4 次）加入凝固剂,制备盐卤豆腐的品质差异。结果表明：凝固剂一次性加入时,在120 r/min搅拌30 s条件下豆腐的得率最高为282.0 g/100 g,在240 r/min搅拌30 s时豆腐的得率最低为183.9 g/100 g。在凝固剂的加入方式上,研究发现分批次加入凝固剂后,豆腐的保水性增强,品质特性有所改善,分3 次加入凝固剂制备的豆腐差异最明显,豆腐的硬度、内聚性和胶着性分别增大了19.9%、6.9%和30.0%。     

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.     

Effect of soy protein subunit composition on tofu quality

Tofu was made, using two coagulants, from soybean lines which lacked specific glycinin and β-conglycinin protein subunits and the quality evaluated to determine the effects of specific protein subunits. The group IIb (A₃) glycinin subunit played the major role in contributing to tofu firmness, regardless of coagulant, while the group IIa (A₄) subunit had a negative effect on tofu quality in 2002. Soybeans with the group I (A₁A₂) subunit resulted in tofu with textural properties about one-third higher, expressed as a percent of Harovinton’s values, than tofu prepared from soybeans without the group I subunit. The individual components of group I had contradictory effects on GDL tofu quality in 2002, with the A₁ subunit having a negative effect and A₂ having a major positive effect. Lack of the α′ subunit of β-conglycinin increased gel hardness relative to the complete 7S protein.     

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.     

不同凝固剂对豆腐品质特性及风味成分的影响

为探究不同凝固剂对豆腐品质特性和风味成分的影响,利用质构分析、扫描电镜分析和固相微萃取-气相色谱-质谱联用（SPME-GC-MS）等技术以及聚类分析和主成分分析等分析方法研究了MgCl₂、CaSO₄、乳酸、醋酸、葡萄糖酸内酯（GDL）和酸浆对豆腐得率、质构、色差、微观结构以及挥发性物质组成的影响。结果表明:酸浆豆腐和GDL豆腐含水量和得率显著高于其他凝固剂豆腐（P<0.05）;醋酸豆腐的硬度（244.04 mN）和咀嚼性（176.34 mJ）最大,而L*值（82.77）最低;CaSO₄豆腐和GDL豆腐具有致密的网状结构,醋酸豆腐表面粗糙,具有孔隙。从豆乳和不同种凝固剂豆腐中共检测出醇类、醛类、酮类、酯类、酸类、酚类等100种挥发性风味物质,且豆乳中挥发性物质总量显著高于不同凝固剂豆腐的挥发性物质总量（P<0.05）。酸浆豆腐挥发性物质种类最多,但致“豆腥味”挥发性物质含量最低。聚类分析表明乳酸豆腐、醋酸豆腐和MgCl₂豆腐的挥发性风味特征相似度高,CaSO₄豆腐和GDL豆腐的挥发性风味特征相似度高。主成分分析表明对豆腐风味贡献较大的挥发性物质有2, 4-壬二烯醛、(E)-2-辛烯醛、1-己醇、(E)-2-癸烯醛和(E, E)-2, 4-癸二烯醛。感官评价表明CaSO₄豆腐和酸浆豆腐优于其他凝固剂豆腐。综上,不同凝固剂对豆腐得率、质构、色差、微观结构、风味物质和感官评价影响显著,其中CaSO₄豆腐和酸浆豆腐与其他凝固剂豆腐相比,拥有更佳的质地、风味和更高的消费吸引力。     

Changes in quality characteristics of tofu with freezing treatment of soybeans

The aim of this study was to investigate the influence of length of freezing time (?18°C for 5 or 24 h) on the quality characteristics of tofu. The yield and moisture content of tofu obtained from frozen soybean were lower than control tofu. Tofu made from frozen soybeans showed higher hardness, gumminess and chewiness than the control. Freezing treatment also made the microstructure of the tofu more uniform than the control. However, after 24-h freezing, hardness decreased and the microstructure of tofu appeared to form pores. Sensory evaluation showed that mouth-feel decreased with an increase of freezing time. Among all of tofu frozen at ?18°C, 5-h freezing treatment showed the highest overall acceptability. These results indicate that the length of time that soybeans are frozen before making tofu affects the quality of tofu.     

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.).     

Laboratory Scale Production of Winged Bean Curd

Procedures for the preparation of 100% winged bean or mixed winged bean-soybean curd employing the essential steps of soy curd production have been developed and optimized. Use of magnesium chloride, gluconodelta lactone, acetic acid and calcium sulfate as coagulants was investigated. The results showed that while curd formation was not facilitated by acetic acid, sticky and less cohesive curds could be formed with magnesium chloride and gluconodelta lactone. Calcium sulfate precipitation resulted in a semi-solid and appreciably cohesive curd from winged bean. Winged bean curd had very low hardness value in comparison to soy tofu. Curd products prepared from five ratios of winged bean-soybean mixtures indicate that 50:50 and 25:75 winged bean-soybean combinations by weight resulted in satisfactory products.     

Quality improvement of kenaf-based tofu: effects of kenaf seed substitution,and coagulant types and concentrations on the physicochemical quality,texture profile and microstructure of the tofu

Tofu was made by substituting kenaf seed (K) with soybean (S) at 100 (positive control), 50%, 40%, 30%, 20%, 10% and 0% (negative control). The results indicated that kenaf seed substitution at all ratios significantly increased the soluble solids and protein content of the milky extracts. The yield, moisture and protein content of the tofu were significantly increased with the increase in kenaf seed substitution, while the lipid content was significantly decreased. The tofu made with kenaf seed substitution of 50%, 40% and 30% had the same protein content (43.76–45.36 g/100 g) with the positive control (45.36 g/100 g), but a significantly higher lipid content (32.00–35.75 g/100 g) than that of the positive control (27.50 g/100 g). The microstructure of the tofu revealed that only the positive control had a honey-comb structure, whilst the tofu made from kenaf seed-soybean blends had a pseudo-honey like structure. Up to 30% of soybean can be added into the kenaf-based tofu, without any negative effect on the textural and colour properties and, protein content, but significantly improved the essential amino acids content of the kenaf-based tofu. Therefore, the blend of 70K:30S ratio using 0.5 g% glucono delta-lactone as a coagulant is recommended to produce kenaf seed-soybean tofu.     

Rapid Method for Determining Optimum Coagulant Concentration in Tofu Manufacture

Four methods of determining optimum coagulation levels in tofu manufacture were compared. Full-fat soyflakes were used to produce 5% solids soymilk. Each soymilk batch was coagulated with calcium sulfate dihydrate (0.000–0.0450 N). Electrical conductance of the coagulating batches was recorded at 72°C and 21°C. Coagulated batches were pressed to make tofu and whey volume, pH, transmittance (400 nm) and tofu composition were measured. Whey transmittance and conductance correlated with coagulant concentration (r=0.87). Tofu yield, conductivity, and absorbance data were also related. Measuring the conductance of the coagulating soymilk was faster than obtaining pH and spectrophotometric values. Conductivity and transmittance could be used to optimize tofu coagulation.     

蔬菜豆腐加工工艺研究

以大豆和芹菜为主要原料制作蔬菜豆腐具有很高的营养、保健价值。确定了蔬菜豆腐的最佳工艺参数为:芹菜汁添加量15%,豆浆浓度为25%,GDL添加量为0.35%,此工艺下制得的蔬菜豆腐呈浅绿色,具有纯正的豆香味及芹菜特有的风味。     

Effect of different coagulants on the isoflavone levels and physical properties of prepared firm tofu

The objective of this study was to understand the effect of different coagulants in their ability to retain isoflavones in prepared firm tofu. Harovinton beans were processed to obtain soymilk and a specific amount of this soymilk was coagulated using different types of coagulants for the preparation of tofu. A reversed phase high performance liquid chromatographic method was used for determining the concentration of isoflavones in tofu and whey. Quality parameters such as the texture, color and moisture of tofu, prepared from different coagulants were also determined in this study. Tofus coagulated with different coagulants were found to contain different amounts of isoflavones. Calcium sulfate was found to be the most suitable coagulant for tofu making in terms of its high yield, retention of maximum amount of isoflavones and in obtaining a firm, but not hard texture of tofu.     

Preparation of tofu using chitosan as a coagulant for improved shelf-life

The potential of chitosan as a coagulant in commercial tofu preparation was investigated with six chitosans of different molecular weights using various treatments. The following optimum processing conditions for tofu preparation were proposed: chitosan with a molecular weight of 28 kDa; chitosan solution type, 1% chitosan/1% acetic acid; chitosan solution to soymilk ratio, 1 : 8; coagulation temperature, 80 °C; coagulation time, 15 min. However, the sensory quality of tofu was notably improved using a 1 : 1 mixture of 1% acetic acid and 1% lactic acid instead of 1% acetic acid alone as a chitosan solvent. Tofu prepared with chitosan had lower ash and higher protein content than those of commercial products tested. In storage tests, the chitosan‐tofu had a longer shelf‐life, about 3 days, than tofu made with CaCl₂. This added shelf‐life is significant in view of the magnitude (366 000 tonnes year^?1) of tofu produced from commercial tofu plants (1407 plants as of 1998) in Korea.     

高温冷冻豆腐的研究

研究高温冷冻豆腐的加工工艺,考察加热温度、加热时间和储存时间的影响,发现加热温度对于豆腐的质构和颜色是高度影响因素,而加热时间对颜色是显著影响因素,储藏温度不显著以普通硫酸钙豆腐作为对照,发现得到高温冷冻豆腐凝胶网络弱于普通硫酸钙豆腐,生产类似普通硫酸钙豆腐的最佳工艺是:加热温度112℃,加热时间为30min,储藏时间取9.3d,得到的高温冷冻豆腐的硬度为7.21±0.15N.     

Process Optimization for Soft Tofu

Response surface methodology (RSM) was used to determine the optimum combinations of four factors, solids content of soy milk (10–14 °Brix), concentration of coagulant (0.25–0.41%, W/V), mixing temperature (75–91°C) and stirring time (5–25 sec) for producing soft tofu on a small pilot scale. Neither brittleness nor elasticity of the top part of tofu were influenced significantly by any factors. Yield was affected (p < 0.05) by soymilk solids content and coagulant concentration. Solids and protein content of tofu were affected (p < 0.05) by 3 factors except mixing temperature. Solids content of soy milk was the most important factor affecting texture. Optimum combinations were soymilk solids 11.8 to 12.3 °Brix, coagulant 0.27 to 0.32%, mixing temperatures 85 to 91°C, and stirring times 5 to 11.3 sec.     

Imitation Cheese Manufacture Using Rapid Visco-Analyzer and Its Optimization

Imitation cheeses in a laboratory-scale (100-g) made by a rapid visco analyzer (RVA) at different stirring speeds (200, 300, 450 rpm) were investigated with a control (Stephan cooker at 1,500 rpm) at 85 °C through functional properties, microstructure and sensory evaluation. Compared to the cheeses made by the Stephan cooker, the cheese made by RVA was significantly (P < 0.05) more green, more yellow and noticeably less white than all other cheeses, which had a decrease in the L* values and an increase in a* and b* values. TPA values of imitation cheese made by the RVA at 450 rpm were lower than that cheese made by other speed. However, the imitation cheeses of 450 rpm was significantly (P < 0.05) higher, which was similar with the fat leakage of imitation cheese manufactured by Stephan cooker. The melt of imitation cheese significantly (P < 0.05) reduced by increasing the stirring speed of RVA. While significant, the melt of the 1,500 rpm cheese was smaller than all other cheeses. Increasing the stirring speed of RVA showed a more effective fat emulsification and a uniform protein matrix. Sensory analysis showed the imitation cheese made by RVA at 450 rpm was similar to the control made by Stephan cooker. Subsequently, the stirring speed, mixing time and heating temperature were optimized at 450 rpm, 7.50 min and 86 °C by response surface methodology (RSM). Results indicated that RVA could make imitation cheeses as well as the functional properties of the control in a laboratory-scale.     

EFFECTS of THERMAL TREATMENTS ON TEXTURE of SOY PROTEIN ISOLATE TOFU

Effects of three thermal treatments; boiling at 100C and retorting at 110 and 121C, on texture of soy protein isolate tofu were studied for a range of heating times. Retorted tofu showed a shrinkage of 18–25% of its original size and a loss of 6–12% of its original moisture. Tofu processed at high temperatures and long heating times developed higher values of texture profile parameters than tofu processed at lower temperature and shorter heating times. the thermal treatment of tofu at elevated conditions also caused an increase in sensory hardness and a decrease in moistness and overall acceptability of the tofu. the increase in texture profile values appeared to be mirrored by a decrease in protein solubility in 1% sodium dodecyl sulfate solvent and a reduction in moisture content of the tofu. the formation of disulfides linkages at elevated temperatures and during heating at 100C stabilized protein aggregates that were initially formed by hydrophobic interactions. Formation of the disulfides and shrinkage of tofu as a result of moisture loss were suggested as the major reason for decreased sensory values of thermally processed soy protein isolate tofu.     

Optimizing Cholesterol Removal in Cream Using β-Cyclodextrin and Response Surface Methodology

Average cholesterol reduction increased as β-cyclodextrin concentration increased, regardless of other factors. The process was optimized using RSM. When β-cyclodextrin addition was 10%, the effect of stirring speed was more noticeable than that of stirring time. When stirring speed was at 1,600 rpm, 94.2% of cholesterol was reduced in 30 min. When stirring time was 20 min, the cholesterol was reduced 97.99% using 15%β-cyclodextrin. When stirring speed was 1,200 rpm, the effect of β-cyclodextrin addition was greater than that of stirring time. Although the percentage of cholesterol reduction varied with different factors and conditions, about 94% of cholesterol was removed from cream.     

Micronization Effects on Composition and Properties of Tofu

The effect of infra-red heating (micronization) was investigated on the composition and textural, biochemical and nutritional properties of soymilk and tofu. The yield, protein content and textural properties of tofu made from micronized beans using the common procedures (70°C as coagulating temperature and CaSO₄2H ₂O as coagulating agent) were lower than those of tofu from unprocessed beans; tofu prepared from micronized beans and coagulated at 90°C using a mixture of citric acid (0.01M) and calcium sulfate (0.03M) showed improved characteristics. The microstructure of tofu prepared from micronized beans lacked the regularity of the honeycomb-like structure shown by tofu from unprocessed beans. The heat treatment by micronization had little effect on the protein components of soymilk and tofu as determined by polyacrylamide disc gel electrophoresis.