Incorporation of ascorbic acid and L-cysteine in sodium carboxymethyl cellulose coating delays color deterioration and extends the shelf-life of fresh-cut asparagus lettuce (Lactuca sativa var. angustata)

In this study, a series of analyses were performed in an attempt to understand more fully the effects and related mechanisms of chemical additives, edible coatings, and their combination on postponing the color deterioration of fresh-cut asparagus lettuce. Fresh-cut asparagus lettuce was dipped into solutions of 0.67% sodium carboxymethyl cellulose (CMC-Na), 0.38% ascorbic acid (AsA) + 0.85% L-cysteine (L-cys), and their combination for 10 min, respectively. CMC-Na, AsA + L-cys, and their combination repressed discoloration and browning, allowing fresh-cut asparagus lettuce to retain its appearance of freshness during storage; however, the combination solution had a more pronounced and synergistic effect. The repression of discoloration/browning of fresh-cut asparagus lettuce was associated with a reduction in the activity and transcription of browning enzymes (polyphenol oxidase and peroxidase) and the phenol content. The solution treatments inhibited chlorophyll breakdown, retarded green loss by repressing the activity and expression of chlorophyll-degrading enzymes (chlorophyllase, pheophytinase, Mg-dechelatase and chlorophyll-degrading peroxidase), and prevented massive accumulation of reactive oxygen species (ROS) (O2·- and H2O2), which mitigate browning and chlorophyll breakdown. Additionally, these treatments maintained antioxidase capacity (superoxide dismutase and ascorbate peroxidase) and antioxidant (AsA) activity at a higher level, as evidenced by the expression of their related genes in fresh-cut asparagus lettuce. In conclusion, our findings indicated that CMC-Na, AsA + L-cys, and their combination protect fresh-cut asparagus lettuce from color deterioration by regulating enzymatic browning, chlorophyll metabolism, and ROS stress. The results provide a possible method for delaying color deterioration of fresh-cut produce.