This study investigated the effects of steaming and air frying on pigments, phenolic compounds, starch and antioxidant capacity responses in the peel and flesh of purple-fleshed sweet potato (PFSP, Ipomoea batatas L.). Steaming was performed at 100°C for 15 to 45 minutes and air frying at 160°C for 5 to 15 minutes, with all measurements reported on a dry-weight basis. Quantitative analyses included anthocyanins, carotenoids, total phenolic content (TPC), total flavonoid content (TFC), starch and colour, while antioxidant capacity was assessed using DPPH, ABTS and FRAP assays. Chemometric analyses, including principal component analysis and partial least squares-discriminant analysis, were applied to identify compositional markers distinguishing processing conditions and tissue types. Steaming yielded higher measured anthocyanin values in the flesh than air frying, whereas air frying substantially increased TPC, TFC and ABTS/FRAP responses, particularly in the peel. These findings indicated that moist- and dry-heat treatments differentially influence the extractability and degradation of tissue-associated compounds, rather than uniformly maintaining all bioactive constituents. Correlation and chemometric analyses further revealed that air-fried peel was more strongly associated with TPC, TFC, ABTS and FRAP, while steamed samples were more closely linked to anthocyanin- and starch-dominant profiles. Steaming was associated with higher measured anthocyanin-rich profiles, whereas air frying produced stronger peel-associated reducing-capacity responses. These results demonstrate process-dependent changes in PFSP tissue chemistry and support the targeted use of peel and flesh fractions in the development of functional foods.
Pan-utai et al. (Fri,) studied this question.