Selection of starter cultures for the fermentation of soya milk

The growth of four cultures selected on the basis of their ability to produce lactic acid in soya milk and/or utilize oligosaccharides, namely Streptococcus thermophilus, Lactobacillus delbrueckii subsp bulgaricus, Lactobacillus fermenti and Lactobacillus fermentum, was examined in reconstituted, low fat, spray-dried soya milk powder (12% total solids). The single culture of S. thermophilus produced a drop in pH from 6.5 to 4.7 over a 10-h period, and reduced the level of stachyose from 8.5 mg ml(-1) in the original milk to 3.2 mg ml(-1), after 24 h fermentation, pH fell to 4.5, and the stachyose concentration to 3.0 mg ml(-1). The paired culture of S. thermophilus and L, fermentum behaved in a similar fashion, but with only a slight improvement in stachyose utilization. When yeast extract (0.3%) and glucose (1.0%) were added to the soya milk, acid production by ail the cultures increased dramatically and L. delbrueckii subsp bulgaricus alone or in combination with S. thermophilus lowered the pH of the milk to 4.3 over 10 h. This combination of S, thermophilus and L. delbrueckii subsp bulgaricus was considered to be a likely combination for the production of a fermented product from soya milk or modified soya milk, as neither L, fermenti nor L. fermentum were appreciably more effective in lowering the concentrations of oligosaccharides. (C) 1999 Academic Press.