Antibacterial Chitosan/HEMA/MAA/CQDs composite film incorporated with Syzygium Cumini Anthocyanins as a colorimetric indicator for monitoring chicken freshness

• Colorimetric indicator was developed to indicate chicken freshness via pH variation. • Syzygium cumini-derived natural dye and CQDs were incorporated for eco-friendly functionality. • Antibacterial properties of CICF were enhanced by incorporating CQDs. • Chicken spoilage were quantitatively analyzed using the CIE Lab color system. • SEM confirmed the formation of porous film, favorable for sensing performance. In this study, a colorimetric indicator based on pH-sensitive composite film with antibacterial properties was developed using Syzygium cumini anthocyanin, chitosan, 2- hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA). To improve the antibacterial properties of the colorimetric indicator composite film (CICF), carbon quantum dots (CQDs) were synthesized from different parts of Syzygium cumini as a green source. The composite film was characterized using Fourier-transform infrared (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The colorimetric sensitivity of the extracted anthocyanin was examined in aqueous and polymeric solutions, as well as in the solid state applying a composite film at different pHs, by UV-Vis spectrophotometry. The fluorescence and colorimetric properties of the quantum particles were analyzed using a UV-Vis spectrophotometer and a photoluminescence spectrophotometer. The antibacterial properties of the colorimetric indicator composite film (CICF) and the CQDs-containing colorimetric indicator composite film (CQDs-CICF) were evaluated using the colony count method. The comparison between CICF and CQD-CICF shows an improvement in the reduction percentage, from 95% to 99%, along with a decrease in viable cell count from 5×10³ to 1×10³ after 1 hour of exposure to S. aureus. Similarly, for E. coli, the reduction percentage increased from 80% to 90%, with the viable cell count decreased from 2×10⁴ to 1×10⁴. Moreover, chicken fillet spoilage was monitored using CICF and CQDs-CICF, which were detectable by naked-eye. The film composite, with colorimetric changes from purplish-red to brownish-green, indicated spoilage of the chicken fillet. The colorimetric sensitivity of the composite film to pH during spoilage was studied using CIE L*a*b* colorimetric values at white and black backgrounds. At pH 7, the colorimetric response of CICF exhibited a noticeable hue shift under both white and black standard backgrounds. The recorded values under the white background were L* = 65.11, a* = 1.39, and b* = 26.86, compared to L* =23.99, a* = -0.43, and b* = 3.34 under the black background. These findings emphasize the ability of the prepared indicator to deliver a perceptible and quantifiable colorimetric response, as well as excellent antibacterial capacity, for use in the food packaging industry for freshness monitoring and food preservation.