RESUMO
The objective of this study was to evaluate the changes in oligosaccharides and isoflavone aglycone content in soymilk during fermentation with commercial kefir culture. Soymilk was fermented with kefir culture at 25 °C for 30 h. The counts of lactic acid bacteria, Lactococcus lactis, Leuconostoc sp and yeasts; measurements of pH, acidity, α-galactosidase and ß-glucosidase activity, sugar and isoflavone contents were performed at the intervals of time. In the fermented soymilk, the lactic acid bacteria counts increased from 7.6 log to 9.1 CFU g(-1), pH reached to 4.9 and lactic acid reached 0.34 g 100 g(- 1). The α-galactosidase was produced (0.016 AU g(-1)) with 100% raffinose and 92% stachyose hydrolysis being observed after the depletion of galactose, glucose and sucrose. Kefir culture produced ß-glucosidase (0.0164 AU g(-1)), resulting in 100% bioconversion of glycitin and daidzin and 89% bioconversion of genistin into the corresponding aglycones. The fermented soymilk presented 1.67 µmol g(-1) of daidzein, 0.28 µmol g(-1) of glicitein and 1.67 µmol g (-1) of genistein.
Assuntos
Produtos Fermentados do Leite/química , Fermentação , Isoflavonas/química , Oligossacarídeos/química , Leite de Soja/química , beta-Glucanas/química , Sobrevivência Celular , Contagem de Colônia Microbiana , Manipulação de Alimentos , Microbiologia de Alimentos , Genisteína/química , Concentração de Íons de Hidrogênio , Hidrólise , Levilactobacillus brevis/metabolismo , Lactococcus lactis/metabolismo , Leuconostoc/metabolismo , Rafinose/química , Saccharomyces cerevisiae/metabolismo , alfa-Galactosidase/metabolismo , beta-Glucosidase/metabolismoRESUMO
The objective of this work was to optimise conversion of ß-glucoside isoflavones to aglycones in soymilk processing and to evaluate their thermal stability. The soymilk was assessed for time and temperature effects of incubating supplied to central composite design 2(2). The response functions were investigated for ß-glucosidase activity and isoflavone contents. The ß-glucosidase activity was reduced through soybean slurry incubation at approximately 64°C and 3.42h. Maximum conversion of ß-glucosides into isoflavone aglycones involved soaking the soybeans at 5°C for 14h at a 1:3 ratio (soybean:water, w:v), homogenising them at a 1:8 ratio (soybean soaked:water, w:v) and incubation at 50°C for 2.7h. In evaluation of thermal stability of isoflavones in soymilk at 97°C for 25min, the daidzein and genistein aglycone contents were maintained, the glycitein and ß-glucosides contents increased and the malonylglucoside content decreased.
