Abstract: The effect of kojic acid on the enzymatic activity and structure of phenoloxidase (PO) from Penaeus vannamei was investigated. The PO enzyme purified from shrimp heads was treated with different concentrations (0–1.5 mmol/L) of kojic acid. Kojic acid was found to be able to inhibit PO activity. The type of inhibition was determined and the effect of different concentrations (0–1.1 mmol/L) of kojic acid on the spatial structure of the PO enzyme was examined by measuring changes in the intrinsic fluorescence spectrum, surface hydrophobicity and secondary structure contents. The results showed that the residual PO activity gradually decreased to 9.8% of the initial activity with increasing kojic acid concentration up to 1.5 mmol/L, and the change in browning index was 3.02, suggesting prominent browning inhibition. Kojic acid could effectively inhibit PO activity, and the type of inhibition was competitive. The intrinsic fluorescence intensity of PO continuously decreased with increasing kojic acid concentration and the maximum emission wavelength (λmax) was red shifted. The surface hydrophobicity of PO decreased after an initial increase. In addition, as the concentration of kojic acid increased, the α-helix and β-sheet contents decreased, but β-turn and random coil increased. It was speculated that the spatial structure of PO was changed due to its reaction with kojic acid.

Key words: Penaeus vannamei, kojic acid, phenoloxidase, enzymatic activity, tertiary structure, secondary structure