Enhancing the extraction of phenolic compounds from biofortified apple peel by-products: ultrasound-assisted recovery, bioaccessibility, and in vitro bioactivity.

This study modeled and optimized ultrasound-assisted extraction (UAE) of phenolic compounds from 'Granny Smith' apple peel (RM) and biofortified peel subjected to controlled abiotic stresses (RM-E). A Box-Behnken design evaluated the effects of extraction ratio, ethanol concentration, and ultrasound power on total phenolic compounds (TPC), while extraction kinetics were described using the Peleg model. Optimal conditions were 1:36 w/v, 76% ethanol, and 52% ultrasound power, yielding extracts with 20-23 g kg-1 TPC and a profile dominated by flavonols and flavan-3-ols. After simulated gastrointestinal digestion, the biofortified UAE extract (USRM-E) showed 39.8% TPC bioaccessibility. Its intestinal fraction exhibited antiproliferative effects against HT-29 and Caco-2 colorectal cancer cells and showed antioxidant, anti-inflammatory, and anti-adipogenic responses in vitro. Overall, combining abiotic stress-induced biofortification with UAE improved phenolic recovery and bioaccessibility, supporting apple peel by-products as sustainable sources of bioactive ingredients for functional food applications through green extraction technologies and valorization strategies.