4D printed pH-responsive labels of methacrylic anhydride grafted konjac glucomannan for detecting quality changes in respiring climacteric fruits

To enhance the monitoring of quality changes in respiring climacteric fruits during storage, pH-responsive labels were developed using methacrylic anhydride (MA)-grafted konjac glucomannan (KGM) through a combination of 4D printing and light-curing technology. Anthocyanin was used as the color indicator. The response of these labels, prepared through 4D printing and molding, to changes in the quality of kiwi fruits was determined and compared. MA was successfully grafted onto KGM, achieving the highest grafting degree of 15%. The concentration of the maximally MA-grafted KGM (KGM-MA-HDG) had a significant effect on printability and color response of the printed labels. A 3% (w/w) concentration of KGM-MA-HDG was chosen to produce 4D printed pH-responsive labels. Compared to casted and 4D printed labels with higher infill, the printed labels with a lower infill rate better responded to the different quality levels of kiwi fruits in terms of color change, which was attributed to the stronger ability to absorb water and the lower masking degree of discolored areas from internal anthocyanin migration.