β-Glucosidase from almonds and yoghurt cultures in the biotransformation of isoflavones in soy milk

Abstract

β-Glucosidase is an enzyme that hydrolyzes the isoflavone bonds and develops the active form of aglycones providing various health benefits. The potential of β-glucosidase from two sources: almonds and soy yoghurt cultures (lactic cultures) to react with soy in the biotransformation of soy isoflavones was studied. This study investigated 1) the optimum amount of culture (1, 2, 3, 4%) and incubation temperature (30, 35, 42 °C) for fermentation of soymilk (SM); 2) the production of β-glucosidase and its ability to react with isoflavones with and without the addition of skim milk powder (SMP). The ability of β-glucosidase to convert isoflavones into aglycones was measured using spectrophotometry and reverse-phase high-pressure liquid chromatography. The results showed that a 1% lactic acid culture at 30 °C produced the highest viable count of lactic acid bacteria (~108 CFU/ml) in fermented SM. Fermentation at 30 °C and 1% inoculation showed the maximum β-glucosidase activity (4.28 U/ml) while 8 U/ml of β-glucosidase from almonds had the highest activity (daidzein: 1.48 g/l and genistein: 0.78 g/l). Among the yoghurt cultures, 2% inoculation in soymilk led to the highest aglycones (daidzein: 1.14 g/l and genistein: 0.50 g/l). Supplementing soymilk with skim milk powder led to aglycone levels similar to β-glucosidase from almond.