Processing-Induced Changes in Bioactive Compounds and Antioxidant Activity of Orange-Fleshed Sweet Potato (Ipomoea batatas L.): Steaming Versus Air-Frying

Orange-fleshed sweet potato (OFSP) is a rich source of carotenoids, phenolics, flavonoids, and starch that are influenced by thermal processing. This study compared the effects of steaming (15–45 min) and air-frying (5–15 min) on the color, bioactive composition, starch content, and antioxidant properties of OFSP peel and flesh to assess processing-induced changes. Unprocessed samples served as the baseline for evaluating percentage and fold changes. Results revealed tissue-specific responses. Steaming preserved flesh brightness (L*, 79) and moderately enhanced carotenoids (0.68 µg/g), anthocyanins (up to 40.5 µg/g in peel), phenolics (2.19–2.27 mg GAE/g), and flavonoids (up to 3.32 mg QE/g). Air-frying induced more pronounced increases in peel bioactives, with carotenoids (4.79 µg/g, 14-fold), phenolics (6.86 mg GAE/g, more than 3-fold), flavonoids (11.75 mg QE/g, more than 20-fold), and transient anthocyanin elevation (61.62 µg/g at 5 min), but prolonged exposure caused degradation in flesh. Starch remained stable in the peel but decreased in the flesh. Antioxidant activity showed similar tissue- and treatment-specific patterns. Steaming preserved structural integrity and bioactive stability, whereas short-duration air-frying maximized peel carotenoids and phenolics. These findings provide insights for optimizing thermal processing to enhance nutritional quality and functional properties in OFSP.