Effects of infrared treatment on tocopherols, total phenolics and antioxidant activity of soybean samples

Abstract

In this study, infrared treatment at different powers (814, 1,003, 1,208, 1,342 W) was applied to unsoaked and soaked (30 min, 45 min) soybeans (cvs. Adasoy and Nazlican) for 10 or 15 min. Effects of infrared treatment on tocopherols (α-, β+γ-, δ-tocopherol), total phenolic contents and DPPH (1,1-diphenyl 2-picrylhydrazyl) radical scavenging activity of soybeans were investigated. Infrared treated soybeans generally had higher total phenolic contents as compared to control. Total phenolic content increased as the infrared power or treatment time increased. Unsoaked soybeans had significantly higher total phenolic content as compared to soaked counterparts. Infrared treatment caused only slight changes in tocopherol contents of soybeans (except unsoaked sample treated at 1,342 W for 15 min). Minor reductions in DPPH radical scavenging activity were observed as the infrared power increased. Infrared conditions adequate for inactivation of undesirable components (trypsin inhibitor and lipoxygenase) appear to be favourable for retention of tocopherols and DPPH radical scavenging activity, especially in soaked soybeans. Increase in total phenolic contents after infrared treatment of soybean is also promising. Overall results and discussions demonstrated that the correct selection of infrared conditions is important to guarantee the quality of soybean in terms of health beneficial components and undesirable components.