Antioxidant and prooxidant activity of acid‐hydrolyzed phenolic extracts of sugar beet leaves in oil‐in‐water emulsions

This study aimed to enhance the oxidative stability of soybean oil‐in‐water emulsions using acid‐hydrolyzed and unhydrolyzed extracts obtained from sugar beet leaves. The optimum extraction process, which includes 8 min of ultrasonication followed by a 2‐h acid hydrolysis, released new phenolics (e.g., catechin, myricetin, etc.) and increased the total phenolic content (TPC) from 586.24 ± 11.45 to 982.42 ± 6.61 μmol gallic acid equivalent (GAE)/L, and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical inhibition from 46.63 ± 1.39 to 60.87 ± 1.12%. Acid hydrolysis increased the cupric chelating activity of the extracts while decreasing ferrous chelating activity and trans‐ferulic acid concentration significantly (p < 0.05). The acid‐hydrolyzed extract at a TPC of 100 μmol GAE/L prolonged the lag phase of hexanal accumulation in the emulsion from 0 to 8 days, while 400 μmol GAE/L TPC of unhydrolyzed extract increased the lag phase to 12 days. The results show that acid‐hydrolyzed extracts in high concentrations may act as prooxidants.