Development and Research on the Manufacturing of Functional Tofu

• Main Authors: Fuh-Juin Kao, 高馥君
• Other Authors: Min-Hsiung Lee, Ph.D.
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/15331540273130168498

博士 === 國立臺灣大學 === 農業化學研究所 === 92 === It was found that the firm tofu made with the water-to-bean ratio at 9:1 and 10:1 and with 0.4% calcium sulfate gave the maximum tofu yield, the maximum protein and solid recovery, the best water retention ability, as well as the maximal retention of isoflavone-β-glucosides. This tofu was found to be most uniform and continuous in the microstructure. The results of gel electrophoresis and the ratio of amino nitrogen to total organic nitrogen indicated that the low molecular weight proteins in tofu whey were at their lowest when the tofu was made the water-to-bean ratio at 10:1 and with 0.4% CaSO4.2H2O. The SEM observations suggested that this tofu had the most uniform and homogenous microstructure and, consequently, could most efficiently retain soybean proteins, water and isoflavone-β-glucosides in the tofu gel. The hardness, gumminess and chewiness of firm tofu increased as the calcium sulfate concentration increased and as the water-to-bean ratio decreased. The amount of extracted isoflavone-β-glucosides (daidzin and genistin) in soymilk increased with increasing water-to-bean ratios from 5 to 9, and reached the maximum level at the ratios of 9 to 11. On the other hand, the amount of extracted free isoflavones (daidzein and genistein) was not affected by the water-to-bean ratio, and their extracted amounts in soymilk were 2 - 4 folds of those in raw soybean. We suggested that these free isoflavones were mainly derived from the isoflavone-β-glucosides through enzymatic hydrolysis during the soymilk heating process. Tofu made with water-to-bean ratios of 9:1 and 10:1 had the maximal retention of isoflavone-β-glucosides, which we supposed to be due to the fine homogeneous network microstructure that effectively retained more isoflavone-β-glucosides through the hydrophilic interaction with protein. On the contrary, the retained amount of free isoflavones decreased significantly as the water-to-bean ratio increased from 7 to 11, due to their weakening hydrophobic interaction with protein. The process for “tofu whey recycling in tofu making” was developed to solve the water pollution problem caused by the discharged tofu whey. The drained tofu whey from the water-to-bean ratios of 9-11 was added back to the raw soybeans, and the mixture was ground, filtered and heated to boiling. After cooling to 73℃, the recycled tofu whey of the same temperature was added to soymilk and the mixture were stirred at a speed of 75 rpm, and then a calcium sulfate suspension was added to give the final CaSO4.2H2O concentration of the soymilk to be 0.4% (w/w). After incubation for 20 min, the bean curd was molded and pressed to drain the tofu whey. The tofu yield (238 g tofu/100 g soybean), protein recovery (68.3%), solid recovery (53.3%), water retention ability (73.0), and textural properties of the tofu made with the recycling tofu whey, were comparable to those of conventional tofu. In order to manufacture the “fiber and isoflavone enriched tofu”, namely “functional tofu”, the okara should be macerated to pass through 40-mesh sieve (particle diameter < 0.42 mm), and could obtain well-coagulated tofu with 0.4% CaSO4.2H2O as the coagulum. It was found that this “functional tofu” gave the maximum tofu yield, the maximum protein and solid recoveries as well as the best water retention ability at the water-to-bean ratio of 12. However, there still needs further research on the coagulating conditions for “functional tofu ” to get much higher protein and solid recovery, as well as the water retention ability。