Impact of Postharvest Handling, Cooking, and Freezing on Flavonoids and Radical Scavenging Capabilities in Spinach

The functional properties of vegetables are influenced by the processing methods. In this study, the effects of postharvest handling, cooking, and freezing on spinach flavonoids were investigated. Fresh spinach was harvested and processed into five forms. Flavonoids were analyzed by UHPLC-UV-HRESI-MSn, and total phenolics and the radical scavenging capacity were also measured. Processing-induced changes in physicochemical properties were examined by near-infrared (NIR) spectroscopy and scanning electron microscopy (SEM). Ten of the 17 identified flavonoids were quantified. Food processing decreased total flavonoid content by 7.1–33.5%, though the impact on individual flavonoids depended on the processing method and the chemical structure. Multivariate data analysis showed three major patterns of flavonoids. Total phenolics increased only in steamed samples, and radical scavenging capabilities followed a similar pattern. NIR fingerprints and SEM examination revealed different patterns between the raw and processed spinach samples. Postharvest processing and cooking reduced the flavonoid concentration and altered the physicochemical properties of spinach.