Smart packaging films based on gelatin/κ‐carrageenan integrated with gromwell root extract rich in shikonin and carbon dots for real‐time monitoring of shrimp freshness

Multifunctional pH-responsive gelatin/κ-carrageenan (GC) blend films containing gromwell (Lithospermum erythrorhizon [LE]) root ethanolic extract (LE-EE) rich in shikonin or shikonin rich extract (SRE) and carbon dots (LE carbon dots [LE-CDs]) were prepared and characterized. The hydrothermal method was adopted for the synthesis of LE-CDs, which displayed a blue color under UV light. The obtained LE-CDs possessed exceptional UV barrier, antioxidant and antimicrobial activities. The enhanced activities were recorded when the level of LE-CDs upsurged (p < 0.05). Transmission electron microscopic (TEM) and Fourier transform infrared (FTIR) results revealed the typical morphology and chemical composition of LE-CDs. LE-CDs of 1 and 3% (w/w) were incorporated as the active fillers along with SRE into the GC blend film by the solvent casting method. Developed films showed a slight decrease in tensile and water vapor barrier properties with the inclusion of both additives. Color and opaqueness of the film became darker as the additives were incorporated, whereas the thermal property was greatly enhanced. Film containing 3% LE-CDs blocked UV-A and UV-B by 93.30 and 99.81%, respectively. GC/SRE/^3%CD film exhibited strong radical scavenging and antibacterial activities against Listeria monocytogenes and Escherichia coli, in which the growth was terminated after 12 h. Film had a pH-dependent color change, depending on various pH levels (2-12). Shrimp freshness could be monitored as indicated by the shift to bluish color after 48 h. Therefore, this finding indicated that incorporating biomass-derived CDs and natural colorants into biopolymer films, especially GC blend films, could offer diverse strategies for maintaining safety and prolonging shelf life in response to the growing need for smart packaging for food applications.