Antioxidant and antityrosinase activity of extractable condensed tannins from durian shells with antibrowning effect in fresh-cut asparagus lettuce model

Abstract

Inhibiting tyrosinase activity is considered as an effective strategy to prevent the enzymatic browning of fruits and vegetables. In this study, the extractable condensed tannins (ECTs) isolated from durian shells usually disposed as agricultural wastes were found to strongly inhibit on both monophenolase and diphenolase of tyrosinase, and the inhibition of diphenolase by ECTs was proved to be reversible and mixed-type. FT-IR, ESI-MS, MALDI-TOF-MS, reversed-phase thiolysis-HPLC-ESI-MS and normal-phase HPLC-ESI-MS revealed that ECTs were predominately constituted by B-type procyanidins with a small amount of propelargonidins and prodelphinidins as well as a low degree of 3-O-galloylation. Analyses of fluorescence quenching, metal-ion chelation and UV-scanning indicated that ECTs could bind with tyrosinase to form a complex, chelate copper ions and reduce the formation of dopaquinone, which in turn led to the decline of enzyme catalytic property. Besides, ECTs exhibited potent DPPH and ABTS radical scavenging activity, ferric reducing antioxidant power and inhibitory capacity against β-carotene bleaching. Also, antibrowning test demonstrated that ECTs effectively delayed the surface browning of fresh-cut asparagus lettuce. These results suggested that ECTs from durian shells were potential antioxidants and tyrosinase inhibitors and might provide a theoretical basis for the application of ECTs as novel antibrowning agents in food industry.