A Fast-Response Acidic and Basic Vapor Visual Indicator Film Based on Black Wolfberry Anthocyanin for Monitoring Chicken and Shrimp Freshness

Natural anthocyanins are considered favorable indicators for new sensing materials because of their wide pH color range. In this study, a smart visual indicator film was developed by introducing black wolfberry (BW) anthocyanins to a solid matrix composed of polyvinyl alcohol (PVA) and methyl cellulose (MC). Fourier transform infrared and X-ray photoelectron spectroscopy showed that the introduction of BW anthocyanins enhances hydrogen-bond interactions among the polymers and that the anthocyanins were well fixed in the polymer matrix. Differential scanning calorimetry, X-ray diffraction, water sensitivity analysis, and mechanical testing suggested that 5% BW could improve the stability of the PVA/MC/BW film and increase its tensile strength and breakage elongation by 63.2% and 53.0%, respectively. Optical observations and freshness monitoring suggested that the film loaded with 5% BW, i.e., PVA/MC/BW-5%, could respond to acidic and basic vapors within 10 s and as low as 25 ppm NH 3 in chicken and shrimp during storage at 4 °C. Therefore, PVA/MC/BW-5% may potentially be used as a smart sensor to determine freshness in practical applications