Foaming Properties of Fibroin Solution Prepared from Silk Yarn, and Utilization of Foam for Making Sponge Cake

Abstract

A fibroin solution was prepared from sericin-removed silk yarn by dissolving it with 50% calcium chloride at 83-87°C for 8 hrs and by subsequent dialysis in order to remove calcium chloride, followed by additional dialysis of the dialysate for 4-5 days after the pH had been adjusted to 2.8. On the other hand, a thawed-fibroin solution was prepared in the same manner except that the fibroin solution was subsequently frozen and thawed before the pH of the thawed solution was adjusted. The foaming properties of the fibroin solutions were examined. In addition, the physical and sensory properties of sponge cake made by using the fibroin foam as a raw material were analyzed. The freezing and thawing of the fibroin solution improved the foaming properties. The overrun of the thawed fibroin solution was particularly higher than that of the fibroin solution without freezing. The volume of separated serum in form from the thawed fibroin solution prepared from the thawed-fibroin solution was less when stirred for more than 6 min, as compared to that stirred for shorter time, and was also less when prepared at about 55°C, at which denaturation and coagulation of fibroin occurred, than at the temperatures below 45°C. Foam stability lowered with an addition of the egg yolks, but other food additives or chemicals such as sodium chloride, sugar and potassium tartarate significantly improved the foaming properties, with dextrin being the most effective. Sponge cake made by using both the fibroin solution and baking powder was inferior in physical properties when compared to that made using egg whites. However, the sponge cake made in this fashion scored significantly higher in sensory evaluation tests, especially in color, hardness, elasticity, smoothness and sweetness as compared with that made using egg whites of the fibroin solution as a foaming agent.