Porous pH natural indicators for acidic and basic vapor sensing

Herein, the development of biobased colorimetric pH porous indicators composed of a polyvinyl alcohol, polyvinyl pyrrolidone and microcrystalline cellulose functionalized with anthocyanins deriving from red cabbage, is presented. As revealed, the presence of 62.5%wt. of microcrystalline cellulose in the composite improves the stability of the porous system in aqueous environments, enhances the porosity, the pores’ interconnectivity and reduces the pores’ size that in turn significantly improves the responsiveness of the porous indicator to acidic or basic vapors. Specifically, the developed material shows distinct color change when subjected to acidic or basic vapors with a response 6 times faster compared to the indicator without any microcrystalline cellulose content. The color changes are reversible, making possible the use of the same indicator for several times. When the developed material was introduced in a package containing fresh prawns or chicken, its color was efficiently modified after one day of storage at ambient conditions demonstrating the possibility to be used as a food spoilage indicator. We prove by CIELab analysis that all color changes can be easily perceived visually, as the differences between the initial and the final color of the indicator after its interaction with the modified environment are well above the limit for visual perception. Therefore, the presented colorimetric porous indicator is suitable for multiple applications dealing with environmental protection and intelligent food packaging.