Metabolism of oligosaccharides and aldehydes and production of organic acids in soymilk by probiotic bifidobacteria

Four strains of Bifidobacterium were assessed for (alpha)-galactosidase activity in MRS broth using p-nitrophenyl-(alpha)-d-galactopyranoside as substrate. Bifidobacteria were then used to ferment soymilk prepared from soy protein isolate (SPI), with and without d-glucose and lcysteine supplementation. Measurements of pH and the quantification of oligosaccharides, organic acids and aldehydes in soymilk were done after 0, 12, 24, 36 and 48 h of incubation. The presence of draffinose stimulated the (alpha)-galactosidase activity of B. longum BB536 (BB536) and B. pseudolongum 20099 (BP20099). In soymilk, oligosaccharides and aldehydes were effectively metabolized by Bifidobacterium; d-glucose and l-cysteine supplementation enhanced the hydrolysis of raffinose and stachyose. BB536 and BP20099 degraded a significantly greater level of oligosaccharides and aldehydes than B. animalis Bb-12 and B. longum 1941 (P (greater than) 0.05). Raffinose and stachyose were completely metabolized by BB536 after 48 h. In soymilk without any supplementation, hexanal and pentanal were not detected after 12 h of fermentation with BB536 and BP20099. BB536 was the highest producer of organic acids, with an average acetic acid/l(+)-lactic acid ratio of 0.7.