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Development of Soymilk-based Yoghurt-type Product
Dissertation Abstract:
The study primarily aimed o investigate the possibility of modifying the conventional method of preparing yoghurt by partially or totally replacing milk protein with the less expensive soymilk production.
Yoghurt-type products were prepared from cow's milk and soymilk in different percentages using Lactobacillus bulgaricus and Streptococcus thermophilus separately and in combination. Chemical and physical analyses were performed on the raw materials and the products.
Statistical analysis indicated that addition of soymilk significantly decreased the total solid values for the three types of cultures. It also reduced the fat content of the products except for yoghurt treated with S. thermophilus (dry basis). Addition of soymilk decreased titratable acidity of the products in all cultures used.
The pH of 40 percent soymilk yoghurt treated with the mixed culture was similar to those of pure cow's milk yoghurt (control) and 20 percent soymilk yoghurt similarly treated. The 40 percent soymilk yoghurt treated with mixed culture of L. bulgaricus alone and pure cow's milk yoghurt treated with only L. bulgaricus had almost the same firmness as the control. The products' color darkened with the addition of soymilk. In terms of consistency and flavor, high scores were given to 40 percent soymilk blend-yoghurt and the control.
Sugar analysis using High Pressure Liquid Chromatography (HPLC) showed that the soymilk sucrose as the major sugar, with fructose in small amount, and raffinose and stachyose only in trace amounts. Lcatose was the major sugar found in cow's milk. Yoghurt with 40 percent soymilk showed the presence of more sugars with lactose and galactose present in larger amounts.
The typical pattern of cow's milk protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed the presenceof proteins and/or sub-unit resolved with estimated molecular weights (EMW) of 15,500-107,000, but its fermented products did not have bands at EMW higher than 35,000. The soymilk protein bands were found to have EMW varying from 15,500 to 46,000. Upon fermentation, the presence of protein bands with higher EMW (111,000) were observed.
From the different analyses performed in this study, it can be concluded that the best product that can be developed from soymilk-based yoghurt-type product was yoghurt made from 40 percent soymilk blend with 60 percent cow's milk which was treated with mixed culture.