Phytochemicals, Antioxidation, and Heat Stability of Aqueous Extracts from Cherry (<i>Prunus serrulata</i>) Petals

Consumers are increasingly demanding natural colorants that are safe and offer health benefits. In addition to their ornamental characteristics, Kanzan cherry (KC) blossoms present a promising source of red-hued natural colorants and functional bioactive substances. This research utilized distilled water to extract KC petals (KCP) and their ground powders (KCPP) under varying temperatures (30°C–90°C) and times (30–180 min). The total monomeric anthocyanins (TMAC) and total phenolics (TPC) in the extracts were evaluated via the pH differential and Folin–Ciocalteu methods. Antioxidant capacities were assessed by DPPH free radical scavenging ability and reducing power. Results indicated that the optimal extraction of TMAC and TPC from KCP occurred at 90°C for 30 min, and the resulting extracts exhibited the highest antioxidant activities among all tested temperatures and durations. Compared to different particle sizes, the finest KCPP generally produced extracts with the highest TMAC, TPC, and antioxidant activity, due to enhanced mass and heat transfer. When compared with the acidified alcohol method, hot water extraction resulted in 68.23% and 71.41% TMAC yields for petals and powders, respectively, while TPC levels were similar or higher. TMAC or TPC showed a significantly positive correlation (p < 0.01) with the antioxidant activities. These findings demonstrate that hot water extraction is a viable and environmentally friendly alternative for phytochemical recovery from KC. Additionally, elevated extraction temperature and pH accelerated anthocyanin degradation and shortened its half-life, while higher pH also lowered the activation energy, enthalpy, entropy, and Gibbs free energy. Thus, red–orange KC extracts with rich bioactivity may serve as promising ingredients for functional foods having acidic pH levels.