Cold plasma treatment induces protein oxidation and nitration, but enhances protein digestibility

Cold plasma is a promising non-thermal processing technology, however, its effects on protein oxidation and digestibility remain insufficiently understood. This study quantified oxidation, nitration, and ᴅ-amino acid formation in milk proteins [bovine serum albumin (BSA), β-lactoglobulin (β-LG)] and plant proteins [pea protein isolate (PPI), mung bean protein isolate (MBPI)] following 1-10 min of cold plasma exposure. Cys, Met, Trp, and Lys were the most reactive residues, with losses ranging from 5% to 100%, generating oxidation products at ng/g-μg/g protein levels, while Ile, Leu, and Ala were partially racemized to their corresponding ᴅ-forms as measured by the UHPLC-FLD chiral derivatization method. Secondary structure analysis revealed up to a 40% decreased α-helical content and a corresponding increase in β-sheets after 10 min treatment. INFOGEST in vitro digestion showed moderate increase in protein digestibility by 16%, 7%, 6%, and 4% for BSA, β-LG, MBPI, and PPI, respectively. Correlation analysis indicated that α-helix-to-β-sheet conversion positively correlates with digestibility.