Contents and bioconversion of β‑glycoside isoflavones to aglycones in the processing conditions of soybean tempeh

Abstract

The objective of this work was to evaluate the effect of the processing conditions of soybean tempeh on the contents of β‑glycoside isoflavones and on their bioconversion into aglycones. Different times of soaking (6, 12, and 18 hours), cooking (15, 30, and 45 minutes), and fermentation (18, 24, and 30 hours) with Rhizopus oligosporus at 37°C were evaluated for tempeh preparation. Grains from the cultivar 'BRS 267' were used, and the experiment was carried out according to a central composite design (23). The response functions comprised the contents of genistin, malonyldaidzin, malonylgenistin, daidzein, and genistein, quantified by ultraperformance liquid chromatography (UPLC). Soaking, cooking, and fermentation times change the content, profile, and distribution of the different forms of isoflavones in tempeh. The highest bioconversion of glycoside isoflavones into aglycones occurred in 6‑hour soaked soybean grains, whose cotyledons were cooked for 15 minutes and subjected to 18‑hour fermentation.