Development of soymilk-based yoghurt-type product [Philippines]

Statistical analysis indicated that the addition of soymilk decreased significantly the total solid values for all 3 types of cultures. It also reduced the fat content of the products except for yoghurt treated with Streptococcus thermophilus (dry basis). However, as more soymilk was added, the protein values of the products increased significantly for all 3 types of cultures (dry basis). The addition of soymilk decreased titratable acidity of the products in all cultures used. The pH of 40% soymilk yoghurt treated with the mixed culture has similar pH value with those of pure cow's milk yoghurt (control), and 20% soymilk yoghurt similarly treated. The 40% soymilk yoghurt treated with mixed culture or Lactobacillus bulgaricus alone and pure cow's milk yoghurt treated with only L. bugaricus had almost the same firmness when compared to the control. The color of the products darkened with the addition of soymilk. In terms of consistency and flavor, high scores were given to 40% soymilk blend-yoghurt and the control. Sugar analyses with High Pressure Liquid Chromatography (HPLC) showed that the soymilk contained sucrose as the major sugar, with fructose in small amount, and raffinose and stachyose only in trace amounts. Lactose was the major sugar found in cow's milk. Yoghurt with 40% 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 dodecy sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed the presence of proteins and/or sub-unit resolved with estimated molecular weights (EMW) of 15,500 to 107,000, while 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