Fabrication and characterization of chitosan/sodium alginate/gellan gum hydrogels containing black bean anthocyanins as colorimetric indicators for beef freshness monitoring.

Fresh beef is highly susceptible to quality deterioration during storage and distribution, necessitating reliable and rapid freshness indicators. In this study, a pH-responsive colorimetric chitosan-based hydrogel was developed for visual monitoring of beef freshness using anthocyanins extracted from black bean seed coats. Anthocyanins were obtained via ultrasonic extraction and stabilized with sodium chloride (NaCl, 0.1 M). The hydrogel was fabricated through physical cross-linking of chitosan, sodium alginate, and low-acyl gellan gum with 40 mg anthocyanin-enriched extract (ACNS). The CS-SA-LAG-ACNS-NaCl hydrogel exhibited favorable rheological properties (G' > G"), improved mechanical strength (compressive strength increased from 50.79 ± 0.73 N to 56.78 ± 0.42 N), and good biocompatibility (cell viability >83%). In addition, NaCl improved the color stability of the hydrogel, with the color difference (ΔE) decreasing from 11.41 to 1.71 after 7 days of storage. A distinct color change from red to dark yellow was observed as beef spoilage progressed (1-7 days), during which TVB-N increased from 4.31 ± 0.12 mg/100 g to 32.28 ± 1.34 mg/100 g, TBA increased from 0.08 mg/100 g to 1.32 ± 0.04 mg/100 g, and TVC exceeded 2.5 × 105 CFU/g on day 7, demonstrating its effectiveness as a visual freshness indicator with promising applications in intelligent meat quality monitoring.