Inhibition of Undesirable Gas Production in Tofu

Of 100 gas-producing bacterial isolates, 65% were Gram-negative. Bacterial growth and gas production in commercial tofu was accompanied by acidification, and pH decreases as low as 5.2. Coliform bacteria constituted 15% of the total bacterial flora. Sporeformers and yeast counts remained < 10³ CFU/mL. Pasteurization was effective in lowering the bacterial counts, and retarded gas production. The addition of lactic acid (reducing pH to 5.5) or lactic acid bacteria (2 × 10⁷ CFU/g) to tofu helped reduce gas production by about 50%. Addition of both lactic acid and Lactobacillus plantarum stopped gas production in contaminated tofu.     

多波长高效液相色谱法测定米豆腐中4种色素

目的建立多波长高效液相色谱法监测米豆腐中添加柠檬黄、胭脂红、日落黄、亮蓝等4种人工色素。方法氨碱性条件下用水作溶剂超声提取米豆腐中色素,提取液用柠檬酸溶液调节p H值至弱酸性,高效液相色谱在线分离。经Waters C_(18)色谱柱(250 mm×4.6 mm,5μm)分离;以0.02 mol/L乙酸铵(p H值5.5)—甲醇为流动相进行梯度洗脱,流速为1.0 m L/min,柱温30℃,以各组分的最大吸收波长为检测波长,外标法定量。结果 4种组分在1.00~100μg/m L范围内线性关系良好,相关系数在0.9993~0.9997(n=7),平均加标回收率在87.4%~89.5%(n=3)。结论该斱法同时测定米豆腐中4种人工色素,前处理简单、快速,定量准确,灵敏度高,可用于米豆腐的质量控制。     

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.     

膜技术提取大豆低聚糖的研究

利用膜分离技术从加工制作豆腐产生的废水对大豆低聚糖的提取进行了研究.实验结果表明：用截留分子量为10KDa的中空纤维聚砜膜超滤豆腐废水,对蛋白和低聚糖的分离有较好的效果.经预处理和超滤后大豆低聚糖的含量为5.80g/L,回收率为81.0%.较好的预处理条件为：豆腐废水经真空抽滤后加入CaCl2,使其浓度达到3wt%,用HCl调至pH值4.3～4.6,离心20min.较适宜的超滤条件为：料液体积流量20 L/h,膜两侧平均压力差0.10MPa,室温,pH=6.4～7.较好的清洗条件可使膜通量恢复90%以上,即：浓缩液体积流量20L/h,清水超滤30min（0.03MPa,室温）,0.1wt%的NaOH超滤30min（0.10 MPa,45℃）;0.3wt%H2O2浸泡16h.     

Changes in biogenic amines during the conventional production of stinky tofu

This study was carried out to investigate the changes in ten biogenic amines and chemical properties in stinky tofu and brine during conventional production. Results show that the free amino acid nitrogen was positively correlated with fermentation time in stinky tofu and brine except during the primary fermentation (0–24 h) in stinky tofu. Of the amines analysed, putrescine, cadaverine, spermidine, spermine and agmatine were detected in stinky tofu, putrescine, cadaverine and spermidine were detected in stinky brine, and only putrescine and cadaverine exhibited a significant positive correlation (P < 0.05) with time in both sample types during extended fermentation (24–144 h). From a toxicological point of view, stinky tofu poses no risk to health; nevertheless, an increase in total biogenic amines in stinky tofu during extended fermentation may be harmful. The results indicate that the fermentation time should be <48 h and a suggested optimum time is 12–18 h.     

Physiochemical Properties of Polysaccharides Extracted from Tofu Processing Wastewater

ABSTRACT: Yield, gelation, viscosity, emulsifying properties, and sugar composition of polysaccharides extracted from tofu processing wastewater under acidic conditions at different temperature levels and incubation times were determined. Optimum extraction for water-soluble polysaccharides was at pH 1.5 and 100 °C over an incubation period of 6 hours. Extraction ratio (%) and yield of high-molecular-weight polysaccharides were higher at pH ranges of 1.5 to 3.0 with extraction temperatures of 80 to 100 °C. Most water-soluble polysaccharides extracted under strong acidic conditions and above 80 °C remained fluid, while most extracted within the range of 45 to 80 °C gelled. Pure polysaccharides exhibited better emulsifying properties than water-soluble polysaccharides. Apparent viscosities of water-soluble polysaccharides were dependent on sugar concentration.     

冻豆腐微波解冻工艺优化

为改善传统解冻耗时长、易污染的缺点,适应现代化餐饮业需要,利用微波技术对冻豆腐进行解冻。设定不同微波功率和微波时间对冻豆腐进行处理,以基本成分、质构特性、p H、色泽、感官品质为评价指标,并与新鲜豆腐进行对比,考察微波解冻对豆腐品质的影响。确定最佳解冻参数为微波功率150 W、解冻时间90 s。     

The viscoelastic properties of soybean curd (tofu) as affected by soymilk concentration and type of coagulant

The viscoelastic properties of different types of tofu were investigated. Soymilk concentrations were 5, 6, 7, 8 and 9%. Coagulants used were 30 mm CaSO₄ or 30 mm glucono‐delta‐lactone (GDL). As the concentration of soymilk was increased viscosity and handling difficulties increased. A high concentration of soymilk in tofu gave a high break stress and produced hard tofu. The four‐element Burgers model fitted the creep behaviour and both viscous and elastic parameters could be acquired from model analysis, reflecting changes in elasticity and viscosity of tofu. The constant viscous parameter in the model increased with increasing soymilk concentration. The viscous parameters of viscoelastic materials like tofu gel, obtained from small deformation tests, seemed to correlate, to some extent, with the break stress obtained from large deformation tests. For hard tofu production increasing the soymilk concentration within a certain range and the partial replacement of calcium sulphate coagulant by GDL could be effective options.     

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.