The fate of phenolics, soysaponins, major isoflavones and antioxidant activity in soy milk by-product during conventional drying process

Abstract

Soy milk by-product (SMB), the insoluble fraction of the soybean cotyledon, is a rich source of phytochemicals such as isoflavones, soysaponins and other phenolic compounds. However, they are susceptible to degradation due to high moisture content in SMB. Therefore, drying is needed to remove moisture content in SMB for further applications and to prevent spoilage. This study aimed to determine the fate of phenolics, soysaponins, major isoflavones and antioxidant activity in SMB during two conventional drying processes, including fan forced oven (FFO) and vacuum oven (VO), and then compare with freeze drying to identify the most suitable drying conditions. Results showed that FFO did not significantly affect retention of phenolics, soysaponins and antioxidant capacity but had a significant impact on diadzin and genistin. FFO at 100 °C for 140 min was the most suitable condition for drying SMB. In contrast, VO did not significantly affect soysaponin, diadzin and genistin, but significantly influenced phenolic content and antioxidant capacity. VO at 60 °C for 330 min was the most suitable condition for drying SMB. In comparison with freeze drying, FFO at 100 °C for 140 min retained better soysaponin (55.96 mg ESE/g), diadzin (79.60 µg/g) and genistin (159.4 µg/g) and consumed less energy, thus this condition is recommended for dehydration of SMB for further applications.

Keywords

• Drying conditions
• Drying kinetics
• Soy milk by-product
• Okara
• Phytochemicals
• Antioxidant properties