Impact of post-harvest handling, cooking and freezing on flavonoids and radical scavenging capabilities in spinach

Authors: TAREQ, FAKIR - University Of Maryland; LEE, ETHAN - University Of Maryland; WANG, XIAOJUAN - University Of Maryland; SINGH, JASHBIR - Oak Ridge Institute For Science And Education (ORISE); WANG, IAN - University Of Maryland; JANSEN, ANDREW - Former ARS Employee; Bukowski, Michael; Luthria, Devanand; Pehrsson, Pamela; Wu, Xianli

Submitted to: ACS Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2026
Publication Date: 5/13/2026
Citation: Tareq, F.S., Lee, E.Y., Wang, X., Singh, J., Wang, I., Jansen, A., Bukowski, M.R., Luthria, D.L., Pehrsson, P.R., Wu, X. 2026. Impact of post-harvest handling, cooking and freezing on flavonoids and radical scavenging capabilities in spinach. ACS Food Science and Technology. 6(6). Article 5c01214. https://doi.org/10.1021/acsfoodscitech.5c01214.
DOI: https://doi.org/10.1021/acsfoodscitech.5c01214

Interpretive Summary: The nutritional and functional properties of plant-based foods are influenced by processing methods. In this study effects of post-harvest handling, cooking, and freezing on spinach flavonoids were investigated. Freshly harvested spinach was processed into samples representing commonly consumed forms, including grocery store fresh, domestic cooking (boiling and steaming) and industrial freezing. Flavonoids were analyzed in all samples, and total phenolic content and the radical scavenging capacity were also measured. Processing-induced changes in physiochemical properties were also examined. Ten of 17 identified flavonoids were quantified. Food processing decreased flavonoid content, though the impact on individual flavonoids depended on the processing method and the chemical structure. Multivariate data analysis showed three major patterns of flavonoids with unprocessed samples, blanched and frozen samples, and two cooked samples. Total flavonoids decreased after processing and longer thermal processing time led to greater loss, whereas total phenolics increased only in steamed samples, and radical scavenging capabilities followed a similar pattern. Compositional and physical examinations revealed different patterns between raw and thermally processed spinach samples. In conclusion, post-harvest processing and cooking reduced flavonoid concentration and altered the physicochemical properties of spinach.

Technical Abstract: 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.