Effects of thermal processing methods and simulated digestion on the phenolic content and antioxidant activity of lotus leaves

The release and antioxidant activity of the phenolics in lotus leaves were changed by various processing methods and in vitro simulated gastric fluid (SGF) and intestinal fluid (SIF) digestion. The total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity of FRAP and ABTS were the highest in the sample processed by microwave vacuum drying. The SGF treatment significantly reduced the TFC in lotus leaves treated by various thermal processing methods but had no significant effect on the TPC. However, SIF digestion reduced the TPC in lotus leaves treated with different thermal processing methods but increased the TFC. The SGF digestion reduced the ABTS of lotus leaves, whereas SIF digestion had no significant effect on the ABTS antioxidant capacity. However, both SGF and SIF digestion increased the FRAP antioxidant capacity. Previous steam heated followed by microwave vacuum drying is the optimal method for drying lotus leaves, after considering all factors. PRACTICAL APPLICATIONS: Phenolics and flavonoid from lotus leaf have antioxidant capacity that brings health benefits. However, the antioxidant capacity is affected by various processing methods and digestion. Therefore, the development of processing methods is very important. Our results show that previous steam heated followed by microwave vacuum drying is the optimal method for drying lotus leaves, considering the antioxidant capacity and flavor.