Studies on the Functional Properties of Egg Yolk

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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.