Compositional Changes in Isoflavones and Oligosaccharides in Soymilk Fermentations by Lactic Acid Bacteria

Abstract

Three species of lactic acid bacteria namely, Lactobacillus rhamnosus, L. bulgaricus ATCC 118 and Bifidobacterium bifidoum, which in preliminary experiments showed ability to produce α-galactosidase and β-glucosidase in laboratory media, were used in soymilk fermentation for biotransformation of isoflavones and degradation of oligosaccharides. In the first experiment, lactic acid bacteria were used in the biotransformation of glycosidic isoflavones to aglyconic bioactive compounds in soymilk. Results indicated the ability of the selected bacteria to convert the glycosidic isoflavone genistin, as its concentration reduced gradually during fermentation. L. bulgaricus ATCC 118 was the best and reduced this compound by 0.158mg/ 100ml after 48hrs of fermentation. On the other hand, the concentration of the aglyconic isoflavones daidazein and genstein were gradually increased as fermentation proceeded up to 48hrs. For daidazein, L. rhamnosus and L. bulgaricus ATCC 118 were the best and they increased the concentration of the compound by 0.295mg/ 100ml, while for genistein, L. bulgaricus ATCC 118 was the best and increased its concentration by 0.386mg/ 100ml. In the second experiment, lactic acid bacteria were used for the hydrolysis of the oligosaccharides that cause digestion disturbance and flatulence, raffinose and stachyose, in soymilk. Results indicated that the bacterial strains were effective in reducing their concentration. For raffinose, L. rhamnosus was the best and reduced raffinose concentration by 1.87mg/ 100ml, while L. bulgaricus ATCC 118 was the best in reduction of stachyose as its concentration was reduced by 2.83mg/ 100ml, after 48hrs of fermentation.