Studies on the Functional Properties of Egg Yolk

研究了蛋黄及其组分的起泡性和热凝固性.颗粒可以在高于0.3M NaCl下溶解。增溶颗粒的起泡力低于低密度脂蛋白（LDL），但泡沫稳定性高于LDL。在低于4的pH值下，颗粒沉淀并且不表现出发泡性。蛋黄的起泡特性与LDL相似，而与颗粒相似.添加少量糖或明胶可提高蛋黄的泡沫稳定性，而不降低蛋黄的起泡力。但添加量过多会降低蛋黄的起泡力。蛋黄的起泡力也随着牛奶的添加而降低。在油脂存在下，不能得到稳定的蛋白泡沫，但由于蛋黄的乳化特性，可以得到稳定的蛋黄泡沫.在许多方面，全蛋的起泡特性与蛋黄而不是蛋白的起泡特性非常相似。添加少量蛋黄可降低蛋清的泡沫性，但添加少量蛋黄可提高蛋清的泡沫性，尤其是蛋黄的泡沫稳定性。结果表明，全蛋的起泡力主要来自蛋黄，蛋白对泡沫稳定性有一定的贡献. NaCl浓度对颗粒和蛋黄的热凝性影响较大，而对LDL的影响较小。pH值对各样品热凝性的影响随NaCl浓度的不同而不同。不加NaCl时，蛋黄凝胶强度随pH值的变化与LDL凝胶相似，而加2%NaCl时，蛋黄凝胶强度随pH值的变化与颗粒凝胶相似。

Foamability and thermal coagulability of egg yolk and its components were investigated.1. Granules could be solubilized at above 0.3M NaCl. Foaming power of solubilized granules was lower than that of low density lipoprotein(LDL), but foam stability of granules was larger than that of LDL. At pH values below 4, granules precipitated and did not exhibit foamability. Foaming properties of yolk were similar to those of LDL rather than granules.2. The addition of small amount of sugar or gelatin improved foam stability of yolk without decreasing foaming power. However, many amount of them decreased foaming power of yolk. Foaming power of yolk decreased also with addition of milk. At the presence of oil, stable albumen foam could not be obtained but stable yolk foam was obtained because of emulsifying properties of yolk.3. On many points, foaming properties of whole egg were much similar to those of yolk rather than albumen. Foaminess of albumen decreased with the addition of small amount of yolk, but that of yolk increased with the addition of small amount of albumen, especially in its foam stability. Those results suggest that foaming power of whole egg is primarily due to yolk, and albumen contributes to foam stability.4. The effect of NaCl concentration on thermal coagulability of both granules and yolk was large, on the contrary, its effect was small in case of LDL. The effect of pH on thermal coagulability of each samples varied with NaCl concentration. Without NaCl, the changes of gel strangth of yolk-gel with pH changes were similar to those of LDL-gel, but when 2% NaCl was added they were similar to those of granules-gel.