Effect of the fermentation of whole soybean flour on the conversion of isoflavones from glycosides to aglycones

The effect of fermentation of whole soybean flour (WSF) on the conversion of isoflavone glycosides to the aglycone form was analysed by liquid chromatography. WSF (200 g) with 35% moisture, was autoclaved at 121 °C for 20 min (AWSF), cooled and inoculated with 2 mL of spores of the fungus Aspergillus oryzae CCT 4359, and then incubated for 24 h and 48 h. The fermented flour was dried in a vacuum oven and 10 g of each flour, non-fermented and fermented, sieved and defatted. One gram of each flour was used for extraction of the isoflavones with 10 mL of an 80% methanol solution. Aliquots were injected into the HPLC under the following conditions: C18 column, 30 °C, gradient elution, mobile phase of (A) water: 5% acetic acid (v/v) and (B) methanol. The results showed that the FAWSF-48 h contained predominantly isoflavone aglycones (75.51%) when compared to the AWSF (6.94%) and WSF (2.67%).

► Soybean is highlighted as an important source of isoflavones. ► The aglycone form is better for absorption in the intestine than the glycoside form. ► The composition of isoflavones in products depends on the techniques used. ► Fermentation promoted a transformation of isoflavone glycoside isomer into aglycone.