Lipase activity, phenolics content and antioxidant activity of rice bran stabilized using natural versus forced convective drying

Abstract

Importance of the work: Some studies show that thermal stabilization may degrade the phenolic components in rice bran, while others indicates the opposite. Objectives: To evaluate the effects of natural convective stabilization (NCS) and forced convective stabilization (FCS) on rice bran stability. Materials & Methods: Freshly milled rice bran was distributed uniformly on aluminum pans to a thickness of 0.8 cm. Then, the pans were placed in a preheated oven. Thermal stabilization was performed at 70°C, 90°C, 110°C or 160°C with time intervals of 10 min, 30 min or 60 min for each type of stabilization. The lipase activity, total phenolics content (TPC) and antioxidant activity were determined Results: Stabilization treatments that began at 90°C or higher lowered the lipase activity in rice bran. The operating conditions of 160°C for 60 min produced the most significant decrease in lipase activity and the highest improvement in the TPC and antioxidant activity. The enhancement of total phenolics and antioxidant activity of rice bran was more effective using FCS compared to NCS. FCS decreased the lipase activity by 73.2%, while increasing the TPC and antioxidant activity by 12.5% and 8.8%, respectively. Ultrahigh-performance liquid chromatography analysis revealed the presence of a peak found only in FCS rice bran. This peak might be a marker of adequate rice bran stabilization. Main finding: Forced convective stabilization may be considered as an alternative approach for effectively inhibiting lipase activity in rice bran, while increasing its phenolics content and antioxidant activity. Thus, this approach can improve the nutritional value and economic viability of rice bran.