Fermentation-Mediated Enhancement of Safety, Thermal Stability, Bioaccessibility, and Health-Promoting Potential of Watermelon Peel Polyphenol Extract.

Fruit wastes contain significant levels of polyphenols with various health-related effects. However, polyphenols have several limitations that hinder their industrial applications. In this study, solid-state fermentation was used as a pre-extraction treatment to not only increase the extraction efficiency of polyphenols from watermelon peel (WP), but also to overcome their drawbacks and improve other properties. Specifically, optimal conditions in the integrated process, fermentation and extraction, were determined by response surface methodology for the highest polyphenol recovery from WP. The post-process extract showed a dramatic improvement in polyphenol content with an increase in various phenolic compounds determined by UHPLC-MS/MS and a significant decrease in cytotoxicity. In addition, two limitations of polyphenols, low stability and bioaccessibility, were significantly improved. Various health potentials of WP were also enhanced: antioxidant (radical scavenging and ferric reduction), anti-inflammatory (inhibition of heat-induced hemolysis, protein denaturation and protease), selectively antibacterial (anti-growth, anti-survival and anti-biofilm for pathogenic bacteria), prebiotic (promotion of probiotic growth and biofilm formation), anti-diabetic (α-glucosidase and α-amylase inhibition), and anti-melanogenic (tyrosinase inhibition). The mechanisms of enzyme inhibition for anti-diabetic and anti-melanogenic capacity were further elucidated by enzyme kinetic studies. Overall, the study suggests an efficient process to convert WP into high-value products with prospects in the circular economy.