Relations between the Behavior of Oils and the Flavor of Soy Milk

(1)目的。酶促脂质过氧化反应对豆浆的风味和口感有影响。本研究对大豆香精的前体正己醛脂质过氧化产物的行为进行了研究。研究了大豆蛋白与羰基化合物的化学反应。(2)方法。用各种物质与豆浆反应，测定脂质过氧化程度和正己醛含量。SDS-PAGE法测定大豆蛋白分子量的变化。(3)结果。加热至37℃时，豆浆的TBA值在前10 min有所上升，60 min时趋于平稳。升温0 min时TBA值较高。在豆浆制备过程中，添加脂氧化酶抑制剂SnCl_2或槲皮素，与未添加豆浆相比，升温0 min时的TBA值显著降低，说明均质过程中酶的作用使TBA值升高。添加乙醇和SDS使TBA值升高，DTAC降低TBA值，Tween 20和卵磷脂对TBA值无影响。DTAC的加入增加了己醛的产量，SDS的加入降低了己醛的产量，而乙醇的加入则没有变化。亚油酸的加入降低了TBA值。溶解氧的减少与TBA值相关。HPLC电化学测定表明，与不添加乙醇或SDS的体系相比，添加乙醇或SDS的体系中过氧化三甘油酯的含量降低。由上述结果可以推测，三酰甘油是酶促过氧化产物，其产物分解为二次氧化产物的过程与游离脂肪酸过氧化产物的分解途径不同。通过与正己醛的作用，破坏了大豆蛋白中的赖氨酸、蛋氨酸和色氨酸残基，并观察到蛋白质的聚合和羰基化合物的添加。

(1) Purpose. Enzymatic lipid peroxidation reaction have influence on the flavor and taste of soy milk. In this study, the behavior of lipid peroxidation products, which were the precursors of soy flavor, n-hexanal, was investigated. The chemical reaction of soybean proteins with carbonyl compounds was also investigated.(2) Methods. Various substances were made reaction with soy milk and the degree of lipid peroxidation and n-hexanal contents were determined. The change of molecular weight of soybean protein was determined by SDS-PAGE.(3) Results. By warming to 37ﾟC, TBA value of soy milk rose up in the first 10 min, and the value reached to plateau at 60 min. The TBA value at 0 min-warming was fairly high. By the addition of lipoxigenase inhibitors, SnCl_2 or quercetin, during preparation of soy milk, TBA value at 0 min-warming wa remarkably lowered compared with no addition soy milk, indicating the increase of TBA value caused by enzymatic action during homogenization. Addition of ethanol and SDS increased the TBA values, but DTAC lowered it, while Tween 20 and lecithin caused no change. The amount of hexanal produced increased by the addition of DTAC, but lowered with SDS, while no change with ethanol. Addition of linoleic acid lowered the TBA value. Decreasing of solubilized oxygen was correlative with TBA value. Electro-chemical determination in HPLC showed a decrease of triacylglycerol hydroperoxide in ethanol or SDS containing system compared with the system of no addition. It was presumed from the results mentioned above that triacylglycerol were peroxidized enzymatically, and the products were decomposed to secondary oxydized products via a process which differed from the decompose pathway of the peroxidized products of free fatty acid. By the action with n-hexanal, Lys, Met and Trp residues in soybean protein were damaged, and polymerization of proteins and addition of carbonyl compounds to protein were observed.