Phenolic Acid Composition and In Vitro Antioxidant Capacity in the Flesh of Thirty-Three Cucurbita pepo Accessions

To characterize intraspecific variation in phenolic acid composition and in vitro antioxidant capacity, color parameters, total phenolic contents (TPC), hydrolyzable phenolic acid profiles, and DPPH and ABTS radical scavenging capacities were systematically determined in the flesh of 33 Cucurbita pepo accessions. All accessions exhibited bright yellow flesh, with significant variation in red-green value (a). TPC and antioxidant capacity differed markedly among accessions and generally followed right-skewed distributions, indicating that a limited number of accessions accumulated high levels of phenolics and antioxidant activity. Eight phenolic acids were quantified by high-performance liquid chromatography (HPLC), with p-hydroxybenzoic acid (8.97–341.98 μg/g), p-coumaric acid (2.42–761.88 μg/g), and ferulic acid identified as the major compounds. Ferulic acid and caffeic acid showed strong positive associations with both DPPH and ABTS scavenging capacities. Hierarchical clustering separated the accessions into two major groups, with Group 2 exhibiting higher TPC (208.89–657.69 µg GAE/g), total phenolic acid content (109.92–890.85 µg/g), and ABTS antioxidant capacity than Group 1. The high-antioxidant accessions may serve as promising candidates for antioxidant-enriched C. pepo products and quality-oriented breeding.