Effects of Heating and Ultrasonication on Soy Bean Protein

Abstract

Changes in viscosity and amounts of sulfhydryl groups of soy bean milk(protein, 4.8%)by heating were investigated. The heated milk was ultrasonicated at room temperature to clarify the effects of ultrasonication on the aggregation of soy bean proteins. The results obtained were as follows: 1)When the milk was heated in 90°C bath, amounts of sulfhydryl groups increased within 1 min., and decreased after 2 min., showing decrease of 7S proteins. Viscosity of the milk increased at the same time. But the viscosity of the milk masked with N-ethylmaleimide(NEM) increased more rapidly during heating for 8 min. The existence of sulfhydryl group was assumed to be not necessary for the aggregation of the protein. 2)Soy bean milk was heated in water bath(90°C)to reach 80-85°C and ultrasonicated after cooling. Viscosity of the milk decreased within 30 sec., and the amounts of sulfhydryl groups increased rapidly. By the ultrasonication, decomposition of a component of 11S proteins was observed which lead to decrease of the viscosity and increase of the sulfhydryl groups. These results were confirmed by a successive process, such as heating, sonication, heating, sonication and re-heating.