| Probiotics are currently added as supplemental cultures into yogurts. Due to the acidity of yogurts and antagonism by traditional starter cultures, the survival of probiotics in such products is often limited. Thus, using probiotics as starters may be a more efficient way to deliver these health beneficial organisms to consumers. Our objective was to determine if an acceptable soy yogurt-like product could be manufactured by using the probiotic bacterium, Lactobacillus paracasei or Lactobacillus rhamnosus GG together with the other yogurt starter culture, Streptococcus thermophilus . The yogurt base was made using commercial soymilks mixed with sugar and nonfat dry milk. Cultures, consisting of a S. thermophilus, and L. paracasei or L. rhamnosus GG at a 1:1 ratio, were used to ferment the base, while a Lactobacillus bulgaricus starter, served as the control. Strawberry and vanilla flavors were added and fermentation proceeded at 37°C until the pH reached 4.5--4.6. Microbial counts, titratable acidity and pH were measured, while descriptive sensory analysis, flavor and carbohydrate analyses were performed during storage. Lactobacilli counts of 108 CFU/ml were established and maintained in vanilla- and strawberry-flavored soy yogurts for 30 days of refrigerated storage. The numbers of L. bulgaricus, on the other hand, significantly declined by 3--5 log CFU/ml within 10 days and to as low as <10 CFU/ml by the end of storage. The cultures tested had significant effects on the aroma, flavor and texture attributes of the yogurt samples. The concentration of raffinose, stachyose and FOS either slightly decreased or did not change in the soy yogurts. The results suggest that a soy yogurt can be successfully manufactured by using the probiotics, L. paracasei and L. rhamnosus GG together with S. thermophilus . The high counts of the probiotics maintained in the yogurts would ensure sufficient numbers to be delivered to consumers. |
