Valorization of quince peel into functional food ingredients: A path towards “zero waste” and sustainable food systems

Quince (<i>Cydonia oblonga</i> Mill.) is an astringent fruit widely processed into marmalade and other sweets through processes that discard the peel as a by-product. Therefore, this study was performed to characterize the quince peel composition in nutrients and phytochemicals and evaluate its <i>in vitro</i> biological activity, following a "zero waste" approach. The quince peel dry powder was particularly rich in fiber (20.2 g/100 g), fructose (34 g/100 g), malic acid (7.2 g/100 g), and potassium (692 mg/100 g). Extracts prepared by dynamic hydroethanolic maceration and hot water extraction yielded 4.70 and 4.27 mg/g of phenolic compounds, respectively, with a prevalence of flavan-3-ols. The hydroethanolic extract was the most effective in inhibiting lipid peroxidation and oxidative hemolysis, and also presented better antimicrobial effects against foodborne pathogens, which agreed with the highest flavan-3-ol contents. The extracts were better than control synthetic food additives against some tested fungal and bacterial strains. On the other hand, no ability to inhibit nitric oxide production or toxicity to the tumor and non-tumor cell lines was observed. Furthermore, the solid residues remaining after extraction contained 35-37 g/100 g of fiber. Overall, quince peel can be upcycled into fiber-rich and bioactive ingredients to endow the value chain with natural food fortifiers, preservatives, and health promoters.