A starch-based 3D printed intelligent colorimetric film co-loaded natural pigments for visualizing food freshness: Effect of nozzle size on gel structure formation

Freshness intelligent visualization packaging is an innovative form for fresh/pre-made foods. Here, a highly responsive 3D printed intelligent colorimetric film (CF) was prepared by incorporating blueberry anthocyanin-phycocyanin (BA-PC) as an indicator and chondroitin sulfate (CS) as a co-pigment/co-carrier into a potato starch (PS) matrix. Enhanced sensitivity and stabilizing effect of CS on BA-PC were demonstrated to perform through sulfate group complexation and hydrogen bonding. CF was formed by modulating the 3D printed nozzle size from 0.2 mm to 0.6 mm, where CF 0.4 (nozzle diameter=0.4 mm) presented the smoothest and homogeneous gel structure, with the highest sensitivity to ammonia response (35.43%) by the action of appropriate ink extrusion. Besides, CF 0.4 exhibited high antioxidant activity (DPPH and ABTS radical scavenging rates > 75%), biosafety, and degradability. The film responded efficiently to the freshness of salmon and beef, and this colorimetric monitoring reflection was transferred to digitized freshness color signals by recognizing RGB values via a smartphone App, which reduced inter-individual differences in visual recognition. Overall, the findings broaden the diverse applications of 3D printing technology in the intelligent food packaging industry.