Structural effect of polygalacturonase modified pectin on polyphenol enzymatic oxidation

Pectin structure plays a vital role in determining the quality of food systems. This study investigated the impact of pectin structural variations on polyphenol oxidase (PPO)-catalyzed catechin oxidation using a series of pectin fractions prepared through polygalacturonase (PG) treatment. PG progressively degraded homogalacturonan (HG) regions, reduced molecular weight, and increased the exposure of hydroxyl and carboxyl groups, thereby converting the pectin matrix from a compact to a disordered state. Among these fractions, pectin enriched in rhamnogalacturonan I (RG-I) with an extended conformation, characterized by longer RG-I chains and fewer branches, exhibited weaker interactions with PPO and catechin, resulting in disordered aggregation and the lowest catalytic efficiency. Integration with molecular docking further revealed that high-HG pectin formed compact hydrophobic networks that restricted substrate access, resulting in high Vmax but low affinity. Conversely, low-HG pectin promoted hydrogen bonding with PPO and catechin, as well as facilitated ordered aggregation. Despite a lower Vmax, it exhibited a markedly reduced Km, resulting in enhanced overall catalytic efficiency. These findings demonstrate that pectin modulates PPO-catalyzed oxidation through steric hindrance, affinity interactions, and aggregation behavior, providing new insights for controlling enzymatic browning in food systems through structural modulation of pectin.