Experimental and theoretical studies on inhibition against tyrosinase activity and melanin biosynthesis by antioxidant ergothioneine.

Ergothioneine, a natural derivative of histidine with a thiol/thine tautomeric structure, exhibits exceptional antioxidant properties and inhibition activities on tyrosinase. In this study, enzyme kinetics experiments and chromatographic spectral analysis revealed that ergothioneine inhibited tyrosinase in a reversible and non-competitive manner, with an inhibition constant of 0.554 mg/mL (2.41 mM). As the concentration of ergothioneine increased, the extremely flexible loop structure of tyrosinase extended from 40.1 % to 41.0 %, effectively covering the active center or binding site. Theoretical molecular docking simulation results show that ergothioneine forms complexes with tyrosinase through hydrogen bonding and salt bridges in the active center of Cu ions. Additionally, it was observed that ergothioneine's antioxidant had a stronger reducing impact on dopaquinone, an intermediate in melanin production, than the effect of ascorbic acid at an equivalent concentration (0.5 mg/mL). Ergothioneine reduced the intracellular reactive oxygen species to lower levels than the control group without UVA radiation and regulated the proliferation and differentiation in B16-F10 melanocytes. Clinical trials have shown that a 0.1 % concentration of ergothioneine can effectively suppress melanin production in irradiated skin. The significant reduction in melanin index and an increase in the individual type angle (ITA°) degree were measured after 4 weeks. These results collectively suggest that ergothioneine may be a promising inhibitor of natural antioxidant tyrosinase. Furthermore, due to its safety and efficacy, ergothioneine could be considered one of the bioactive substances for further study on diseases related to melanin production and tyrosinase activity which is of great significance for the cosmetics, medicine and food industries.

Optimization of Ultrasonic Cellulase-Assisted Extraction and Antioxidant Activity of Natural Polyphenols from Passion Fruit.

In this paper, ultrasonic cellulase extraction (UCE) was applied to extract polyphenols from passion fruit. The extraction conditions for total phenol content (TPC) and antioxidant activity were optimized using response surface methodology (RSM) coupled with a Box-Behnken design (BBD). The results showed that the liquid-to-solid ratio (X2) was the most significant single factor and had a positive effect on all responses. The ANOVA analysis indicated quadratic models fitted well as TPC with R2 = 0.903, DPPH scavenging activity with R2 = 0.979, and ABTS scavenging activity with R2 = 0.981. The optimal extraction parameters of passion fruit were as follows: pH value of 5 at 30 °C for extraction temperature, 50:1 (w/v) liquid-to-solid ratio with extraction time for 47 min, the experimental values were found matched with those predicted. Infrared spectroscopy suggested that the extract contained the structure of polyphenols. Furthermore, three main polyphenols were identified and quantified by HPLC. The results showed the content of phenolic compounds and antioxidant activity of the optimized UCE were 1.5~2 times higher than that determined by the single extraction method and the Soxhlet extraction method, which indicates UCE is a competitive and effective extraction technique for natural passion fruit polyphenols.