Changes in content of antioxidants and hydrolytic stability of black rice bran after heat- and enzymatic stabilizations and degradation kinetics during storage

Abstract

This research aimed to compare heat and enzymatic stabilization methods in terms of hydrolytic stability and changes in antioxidant compounds of rice bran during ambient storage. Raw non-pigmented and black rice bran (RNB and RBB) showed high lipase activity (269.0 and 241.9 U/kg, respectively). Heat-stabilized non-pigmented and black rice bran samples (HNB and HBB) and enzymatically stabilized non-pigmented and black rice bran samples (ENB and EBB) had much lower lipase activity (25.8 to 32.8 U/kg). Lipase activity was not increased in the stabilized samples during 8-week storage and had high hydrolytic stability. Compared with raw rice bran, tocols, and anthocyanin contents in HNB and HBB decreased significantly, but γ-oryzanol increased significantly, while all antioxidant compounds in ENB and EBB increased significantly. Antioxidant contents of rice bran decreased during storage following zero- and first-order reaction kinetics. EBB showed the lowest k and the highest t1/2 values, indicating more stability of these antioxidants. Novelty impact statement: In this study, the effects of stabilization processes (including heat and enzymatic methods) on lipase inhibition and antioxidant contents in black rice bran are reported for the first time. Moreover, the changes in antioxidant contents in rice bran have been little studied, with no studies on black rice bran. This work proposes enzymatically stabilized black rice bran with high antioxidant content and high storage stability as a potent source of natural antioxidants suitable for use in the food industry.