Micronization Combined Ultrasound-Assisted Extraction Enhances the Sustainability of Polyphenols from Pineapple and Lemon Peels Utilizing Acidified Ethanol

Pineapple and lemon processing generates large volumes of peel waste, which is a valuable source of dietary polyphenols and flavonoids with potent antioxidant activity. This study employed a strategy of micronization and ultrasound-assisted extraction (UAE) with acidified ethanol to valorize pineapple peel (PP) and lemon peel (LP). Physicochemical characteristics, total polyphenol content, total flavonoid content, and antioxidant activities (DPPH, FRAP, and ABTS⁺) were evaluated under varying particle sizes, ethanol concentrations, extraction times, and pH conditions. Optimal extraction was achieved with 30 min of UAE using 75% ethanol acidified with citric acid at pH 5 for PP (96.6 µm) and pH 4 for LP (91.7 µm). These conditions maximized polyphenol yields, with the LP micropowder produced containing 65.7 µg/mg of hesperidin and 23.2 µg/mg of eriocitrin. Contour plots and principal component analysis confirmed that the antioxidant extraction selectivity of micropowder was dependent on pH and extraction time. Microstructural and Fourier-transform infrared spectroscopy analyzes further supported that short-dried period and a lower particle size significantly improve solute release. This study not only demonstrates the efficacy of micronization and UAE in enhancing the selective extraction of antioxidants from fruit peels but also offers a digital visualization strategy for optimizing extraction processes to support sustainable bioprocessing and functional ingredient development.