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Tyrosinase is a copper-dependent enzyme involved in melanin biosynthesis, and its increased activity is associated with hyperpigmentation. Due to the limitations of some synthetic inhibitors, natural polyphenol-rich plant extracts are increasingly investigated as safer alternatives. Prokupac grapes are of particular interest because of their specific phenolic profile and potential for the valorisation of local viticultural resources.
The aim of this study was to investigate the tyrosinase-inhibitory potential of extracts obtained from grape skin, pulp, and seeds of the Prokupac variety, with emphasis on the influence of extraction pH. The extracts were prepared using 50 mM buffer solutions with pH values ranging from 4.0 to 8.0. Tyrosinase activity was determined spectrophotometrically by monitoring dopachrome formation from L-DOPA at 475 nm, while inhibition was calculated in relation to a control sample without inhibitor. The dry residue of the extracts was also determined. Statistical analysis was performed using two-way ANOVA and Tukey’s post hoc test, with p < 0.05 considered significant.
The results showed that tyrosinase-inhibitory activity depended significantly on both the berry part and extraction pH. Grape skin extracts exhibited the strongest activity, with inhibition ranging approximately from 70 to 95%, while seed extracts showed moderate to high activity. Pulp extracts demonstrated considerably lower inhibitory potential. The highest inhibition was recorded at pH 6, where skin, seed, and pulp extracts inhibited tyrosinase activity by 94.81%, 78.94%, and 58.20%, respectively. The highest dry residue values were also observed at pH 6, suggesting a possible relationship between the amount of extracted compounds and biological activity.
These results indicate that Prokupac grape skin and seeds are promising sources of natural tyrosinase inhibitors. Their activity may be associated with polyphenolic compounds capable of affecting enzyme activity, including through copper ion chelation. Prokupac grape extracts therefore show potential for use as natural active ingredients in dermocosmetic formulations aimed at regulating melanogenesis and treating hyperpigmentation.
Keywords: Prokupac, grape, tyrosinase, inhibition, polyphenols, hyperpigmentation.