Effect of l ‐Cysteine on Enzymatic Browning, Antioxidant Activity, and GSH Stability in Fresh‐Cut Quince: A Comparative Evaluation With Potassium Metabisulfite

ABSTRACT This study evaluates the effectiveness of l ‐cysteine and sodium metabisulfite (1% solutions) in reducing enzymatic browning and preserving antioxidant properties in fresh‐cut quince slices during 9 days of cold storage (4°C). Key quality parameters assessed included color values ( L *, a *, b *), polyphenol oxidase (PPO) activity, total phenolic content (TPC), glutathione (GSH) levels, and antioxidant capacity (via DPPH and FRAP assays). Results show that l ‐cysteine was more effective than sodium metabisulfite in maintaining color brightness (higher L * values), suppressing red‐brown discoloration, and enhancing antioxidant activity in the early storage period. l ‐cysteine acts by inhibiting PPO and scavenging free radicals, thereby reducing the formation of brown pigments and preserving phenolic compounds. However, in terms of GSH preservation, sodium metabisulfite performed better. The rapid loss of GSH in both l ‐cysteine‐treated and untreated samples indicates that it undergoes rapid conversion to maintain cellular redox balance or that the 1% application of l ‐cysteine—which possesses pro‐oxidant properties—is not solely used for the preservation of GSH. Prioritizing the elimination of redox imbalance in the environment suggests that there is a limitation of l ‐cysteine's effect over time. Overall, l ‐cysteine presents a promising alternative to sulfite‐based preservatives in fresh‐cut fruit preservation, demonstrating strong browning inhibition and antioxidant protection—particularly, for short‐ to mid‐term storage—while offering a potentially lower risk of health concerns associated with sulfites.