Effects of oven-drying, roasting, and explosive puffing process on isoflavone distributions in soybeans

Distributions of isoflavones in soybeans treated with oven-drying, roasting, or explosive puffing were analysed using high-performance liquid chromatography (HPLC). As oven-drying time increased from 0 to 120 min at 100 °C, concentration (μmol/g) of malonyl derivatives of isoflavones decreased and β-glucosides increased significantly with over 0.99 coefficient of determination (R2) (P < 0.05). Roasting at 200 °C for 7, 14, and 21 min and explosive puffing at 490, 588, and 686 kPa decreased malonyl derivatives significantly and increased acetyl-β-glucosides and β-glucosides significantly (P < 0.05). Total isoflavones (TI) in 21 min roasted and 686 kPa puffed soybeans decreased by 25.46% and 10.42%, respectively, while TI in 120 min oven-dried soybeans was not significantly different (P > 0.05) compared to untreated samples. Regression analysis showed that malonyl-β-genistin had higher slopes of decreases (μmol/g/min) than malonyl-β-daidzin in oven-dried soybeans. This is the first report on the effects of explosive puffing and the changes of isoflavone profiles in soybeans.