Evaluation of tyrosinase inhibitory activity of persimmon leaf tea fermented using Koji

Abstract

Fermentation using koji mold has garnered attention in recent years for its capacity to produce beneficial substances. Green tea fermented with koji mold yields polyphenols with whitening effects. Persimmon leaf tea, known as Kakinoha-cha, contains ingredients similar to green tea; however, it contains higher levels of gallic acid. Given that the inhibitory effect (IC50) of gallic acid against tyrosinase is similar to that of kojic acid, which is known for its activity as a tyrosinase inhibitor, persimmon leaf tea itself can be said to have high tyrosinase inhibitory activity. Additionally, persimmon leaf tea contains gallate catechins, akin to green tea, which are decomposed by yeast into gallic acid and hydrolyzed catechins. Therefore, persimmon leaf tea inherently possesses high tyrosinase inhibitory activity. Consequently, fermentation of persimmon leaf tea using koji mold is expected to have a stronger whitening effect than green tea because of the increased formation of gallic and kojic acid levels and their tyrosinase inhibitory activity. In this study, we fermented persimmon leaf tea using Aspergillus Oryzae (NBRC30113, RIB40) and Aspergillus Awamori (NBRL 4388) for seven days and evaluated its whitening effect and the associated factors. The evaluation of whitening action involved assessing its tyrosinase inhibitory activity. Inhibitory factors, the levels of kojic acid and total polyphenols in fermented persimmon leaf tea were assessed, followed by an investigation into their respective tyrosinase inhibitory activities. Results showed a significant increase in tyrosinase inhibitory activity after four days for the fermentation using NBRC30113 and RIB40, and after six days for NBRL 4388. Total polyphenol content exhibited an increasing trend during the seven-day fermentation, whereas kojic acid content remained unchanged. Comparison of tyrosinase inhibitory activity between 45 mg/L gallic acid solution and 0.03 mg/mL kojic acid solution (the highest concentration in this experiment), revealed higher activity with gallic acid suggesting that polyphenols play a significant role in the tyrosinase inhibitory activity of fermented persimmon leaf tea.