Antioxidant and anti-browning activities of leaf extracts from paper mulberry (Broussonetia kazinoki)

This study evaluated the antioxidant and anti-browning properties of paper mulberry (PM, Broussonetia kazinoki) leaf extracts prepared using different solvents, water, 30% ethanol, and 70% ethanol. The total polyphenol and flavonoid contents of the extracts varied between 37.00 to 46.91 mg tannic acid equivalents per gram and 26.32 to 46.73 mg quercetin equivalents per gram, respectively, with the PM 70% ethanol extract (PME70) showing the highest levels. PME70 exhibited remarkable radical scavenging activity, with RC50 values of 39.88 for the ABTS radical and 56.30 for the DPPH radical, and demonstrated greater antioxidant stability than L-ascorbic acid over two weeks. Additionally, PME70 effectively inhibited potato polyphenol oxidase (PPO) in a dose-dependent manner, reaching an inhibition rate of 86.51% and an IC50 of 1.16 mg/mL. In anti-browning tests on apple slices, PME70-treated samples maintained significant color stability (∆L and ∆E values) compared to controls, including L-ascorbic acid, after 24 h of storage. These results highlight the potential of paper mulberry leaf extracts as a rich source of natural anti-browning agents for food applications.