Upcycling Quince Peel into Bioactive Ingredients and Fiber Concentrates through Multicomponent Extraction Processes

This study aimed to promote the total upcycling of quince (Cydonia oblonga Mill.) peel into bioactive extracts (BEs) and fiber concentrates (FCs). The multicomponent extraction processes were optimized using response surface methodology (RSM) coupled with a 20-run experimental design, where the effects of time (1–120 min), temperature (25–95 °C), and EtOH percentage (0–100%) were combined. In addition to the extraction yields, BEs were analyzed for phenolic compounds, organic acids, and other water-soluble constituents, while FCs were characterized for their color and dietary fiber content. Statistically valid theoretical models were obtained by fitting these dependent variables to a quadratic equation and used to predict optimal extraction conditions. Those obtained for phenolic compounds and malic acid were experimentally validated, yielding 9.3 mg/g and 7.6 g/100 g of these bioactive constituents, respectively, and about 51% (w/w) FC. These BEs showed in vitro antioxidant activity and antimicrobial effects against foodborne fungi and bacteria, standing out in some aspects in relation to synthetic food additives, mainly the malic acid-enriched BE. Overall, the developed extraction processes allowed valorizing of quince peel in FCs and BEs that could be used as natural fortifiers or preservatives in the formulation of foods, beverages and dietary supplements.