CO2-responsive multifunctional label based on chitosan and hyaluronic acid for visualizing and maintaining postharvest freshness

Microbial infections result in significant postharvest losses of fresh produce. Microbial metabolism and variation in the quality of fruit and vegetables caused by microbial infection are accompanied by significant carbon dioxide (CO 2 ) production, contributing to a decreased pH value of the headspace microenvironment. Hence, the work aimed to design a CO 2 -responsive label with freshness indication, stimuli-responsive release antimicrobials, and adhesion for postharvest preservation. The multifunctional label (Eug/CPDH) was prepared by incorporating a mixed methyl red/bromothymol blue dye as an indicator and eugenol (Eug) as an antimicrobial agent into a matrix constructed by crosslinking 3-carboxyphenylboronic acid-grafted chitosan and dopamine-grafted hyaluronic acid (CPDH) through acid-sensitive borate bonds. The microbial infection could be indicated to visualize the freshness. Meanwhile, the label showed a CO 2 -responsive release ability, as confirmed by the release experiment. The antimicrobial test showed that the label had excellent inhibition properties against Escherichia coli , Staphylococcus aureus , and Botrytis cinerea . More importantly, the label could be conveniently adhered to the inner surface of the packaging and its effectiveness was verified by strawberry preservation experiments. At room temperature, the strawberry's reduction in hardness, vitamin C , total phenolic content, anthocyanins , and antioxidant capacity was effectively suppressed, and the shelf life was extended to 5 days. Overall, the CO 2 -responsive label provided a new strategy for developing multifunctional freshness preservation materials.