Guava processing waste: Biological activity profile of a natural and sustainable source of phenolic antioxidants

Guava (Psidium guajava L.) is a widely-consumed tropical fruit that can be industrially processed and generate several food products. However, about 30% of the total volume of processed guava is lost as processing waste, a homogenous fraction containing peels, seeds, and residual pulp. The valorization of the discard fraction is necessary in upcycling due to its richness of bioactive components. Therefore, the phenolic composition and biological activity of guava's processing waste and its pulp counterpart were investigated. Guava's pulp (22.32 mg gallic acid equivalents (GAE)/g) and waste (21.99 mg GAE/g) contained similar levels of total phenolic content (TPC), with the majority of phenolics occurring in the free and esterified forms. Besides, a strong positive correlation was observed between TPC and the antioxidant activity of extracts. Through HPLC-UV-MS-TOF analysis, 27 phenolic compounds were identified across the pulp (25) and waste (18) portions, with a predominance of gallic, vanillic, and ellagic acids and their derivatives. While free and esterified phenolic fractions showed higher efficiency as α-glucosidase inhibitors (84.94–98.85%), pancreatic lipase was better inhibited by the insoluble-bound phenolics in the extracts (41.55–43.31%). Guava waste's insoluble-bound phenolics strongly protected supercoiled DNA against hydroxyl radicals (80.09%). Oxidation protection by guava phenolics was also observed towards human LDL-cholesterol (10.82–22.98%), an indication of their potential cardioprotective effect. As such, guava processing waste demonstrates nutraceutical potential and should be considered as a value-added ingredient in functional foods and other related applications.