| Abstract | The acceptable levels of quality indices including moisture content, protein content, yellowness, lightness, and textural properties including hardness, springiness, cohesiveness, gumminess, and chewiness was investigated from the seven commercial tofu samples in Thai market, and established basing on preference of consumer from sensory evaluation. Their values were 71.67-75.32%, 55.72-59.81%, 17.30-19.89, 80.54-84.71, and for the textural properties were 1119.70-2787.66 g, 0.801-0.879 mm, 0.323-0.386, 473.07¬907.54 g, and 389.06-779.10 g mm, respectively. The effect of different soybean varieties on the quality of tofu was investigated from the three soybean varieties namely SoIjor, Chiangmai 60, and Chiangmai 2. Different varieties of soybean contained different amount of moisture content, protein content, fat content, and color of seed coat that influenced on the quality of tofu. The maximum amount of protein content was observed from SoIjor variety exhibited at 61.31 % (db), and the minimum amount of protein content was found at Chiangmai 2, which was 52.44% (db). The correlation coefficient analysis showed that protein content, and fat content of tofu produced from Sorjor, Chiangmai 60, and Chiangmai 2 appeared the positive association with those individual values of soybean varieties exhibited at 0.999 and 1.000, respectively. Protein content and the textural properties positively correlated with each other, but between the syneresis and protein content, there were the negative association. SoIjor variety was the most suitable for making hard tofu, Chiangmai 60 variety was proper for making regular tofu, and the soft tofu could be made from Chiangmai 2 variety. Freezing process at temperature -4°C and -20°C for 3, 6, and 9 hr on soybean enhanced the amount of protein content. More potential in increasing protein was observed at tofu made from frozen soybean at temperature -4°C, and the amount of protein content was increased by 1.84% to 3.17% when extending longer period for 3 to 9 hr, respectively. At temperature -20°C, extending the freezing time had no effect on protein content in tofu. The textural properties were influenced from the freezing process mechanism. Tofu made from frozen soybean was more brittle and had higher chance in fracture than tofu made from unfrozen soybean. The differentiation in textural properties was observed among tofu produced from frozen soybean at -4°C and -20°C. Extending the time for freezing soybean at -4°C made hardness value continuously decrease and easier brittle whereas at - 20 °C, longer period for freezing did not affect the textural properties of tofu. Potential of alginate, CMC, and iota-carrageenan at concentration 0.05% and 0.10% increased moisture content, yield, syneresis rate resulted to decreasing the values of textural properties including hardness, springiness, cohesiveness, gumminess, and chewiness. The maximum ability was observed from tofu with the addition of CMC. It expressed the maximum rate in increasing moisture content, yield, syneresis rate, and the maximum rate in decreasing the values of textural properties in tofu. The addition of hydrocolloids at higher 0.10% was found negative effect in tofu. The excess trapped water in tofu made tofu lose the ability to form the uniform shape. The result of sensory evaluation clarified that the addition of CMC at concentration 0.05% enhanced the highest score of texture characteristic and overall acceptability, which was indicated at 6.55 and 6.68, respectively. Alginate, CMC, and iota-carrageenan disabled to enhance the ability of freeze-thaw for preventing water separation during centrifugation. If the ability to prevent the syneresis did not occur, and the higher in syneresis rate was performed, the addition of hydrocolloids might result in the lower quality when extending the storage time and shelf life might shorter than tofu without hydrocolloid. |