18F-24

S. GOKAVI¹, T. Pinkham, and M. Guo. (1) Dept. of Nutrition and Food Sciences, Univ. of Vermont, 210 Carrigan Hall, 536 Main street, Burlington, VT 05405

Consumption of soy foods is increasing worldwide because of its health benefits. The objectives were to study the effects of Inoculation Rate (IR) and Incubation Time (IT) on (1) acid development and texture of soy yogurt, and (2) probiotic counts. Two dairy starters, Yofast-10 and Yofast-20, both containing S. thermophilus, L. delbruecki subsp. bulgaricus, L. acidophilus, L. casei and Bifidobacteria obtained from Chr-Hansen were used for the study. Acidification of the product was studied by measuring pH and titratable acidity (TA) and texture by measuring viscosity. Four samples of soy yogurt were made with (A) Yofast-10, (B) Yofast-20, (C) Yofast-10 + 1% inulin, and (D) Yofast-20 + 1% inulin. A two-factor experimental design was used for each sample. Inoculation rates were 0.04, 0.06, and 0.08%, and incubation times were 2, 3, 4, and 5 hr. The soy milk (control) had pH, TA, and viscosity of 6.61 ± 0.021, 0.18 ± 0.02%, and 15.7 ± 3.37 mPaS, respectively. In all four samples, IT and IR had significant effect on pH and TA. They decreased to 4.43 ± 0.041 (4.38 to 4.52) and 0.51 ± 0.044% (0.46% to 0.59%), respectively, at 5 hr of incubation. IR did not show any effect on viscosity of the product, but IT significantly increased the viscosity from 15.7 ± 3.37 mPaS (0 hr) to 1299.7 ± 194.1 mPaS (5 hr), indicating gelation of soy protein induced by acidification. Probiotic counts were carried out for 5 hr incubated samples. All the samples had 10⁴, 10⁶, and 10⁵ cfu/g of L. acidophilus, Bifidobacteria, and L. casei, respectively. It is concluded that 0.08% of starter culture and 5 hr of incubation is suitable for making soy yogurt with acceptable pH; however, it is required to supplement with probiotics in order to have required probiotic population in the product. Future studies include supplementation and survivability of probiotics, chemical analysis, and microstructure of soy yogurt gel.

Session 18F, Product Development: General
2:00 PM - 5:30 PM, Sunday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana