Effects of Thermal Aging and Subsequent Autoclave Treatment on the Phytochemical Fingerprint, Antioxidant Capacity, and In Vitro Carbohydrate-Hydrolyzing Enzyme Inhibitory Activity of Lychee Pulp Extracts

Background: This study evaluated the effects of aging and subsequent autoclave treatment on the proton nuclear magnetic resonance (1H NMR) spectral-feature profile and biological activities of lychee pulp extracts. Methods: Dried lychee (DL), aged lychee (AL), and autoclave-treated aged lychee (ATAL) extracts were compared using 1H NMR spectroscopy, total phenolic content (TPC), total flavonoid content (TFC), antioxidant assays, carbohydrate-hydrolyzing enzyme inhibitory assays, and endothelial cell viability. Results: Sixteen phytochemical spectral features were putatively annotated, and their relative signal intensities differed among the extracts (p < 0.001). Relative to DL, ATAL exhibited higher signal intensities for most features, including taxifolin (8.32-fold) and procyanidin B2 (7.44-fold), whereas epicatechin was particularly prominent in AL (12.31-fold). TPC increased from 0.53 ± 0.07 mg gallic acid equivalents (GAE)/g extract in DL to 8.39 ± 0.19 and 9.07 ± 0.10 mg GAE/g extract in AL and ATAL, respectively. AL and ATAL also showed higher TFC and antioxidant activities than DL. The α-amylase IC50 values were 247.00 ± 45.00, 129.17 ± 8.56, and 126.27 ± 3.90 mg/mL for DL, AL, and ATAL, respectively, while the corresponding α-glucosidase IC50 values were 187.93 ± 8.20, 66.71 ± 6.84, and 50.30 ± 2.72 mg/mL. No significant reduction in endothelial cell viability was detected after multiplicity adjustment. Exploratory principal component analysis (PCA) explained 99.8% of the total variance and revealed distinct processing-associated spectral-feature profiles. Conclusions: Aging followed by autoclave treatment enhanced the phytochemical profile, antioxidant activity, and in vitro carbohydrate-hydrolyzing enzyme inhibition of lychee pulp extracts.