Development of a colorimetric pH indicator based on bacterial cellulose nanofibers and red cabbage (Brassica oleraceae) extract.

This work aimed to develop and characterize a smart label for pH monitoring based on bacterial cellulose (BC) nanofibers doped with anthocyanins extracted from red cabbage (Brassica oleracea). The relationship between the concentration of anthocyanins (32 and 193mgL) and the morphological properties and color response efficiency of pH indicator labels was investigated. The FT-IR results reflected that some new interactions have occurred between BC membrane and anthocyanins. The XRD analyses showed a decrease in diffraction intensities of BC by addition of concentrated form of anthocyanins. SEM results indicated that concentrated anthocyanins caused to partial disintegration and deformation of the cellulose microfibrils with more cracks on the labels. But the intrinsic morphology and structure of the BC nanofibers were preserved by addition of diluted anthocyanins. A concentration dependent decrease was observed in the tensile strength of anthocyanin loaded labels but elongation percentage and moisture absorption of BC was increased by addition of anthocyanins. The color variation in different pH range (2-10) was measured with the CIELab methodology. The label containing diluted anthocyanins showed a more clear response to pH variation. Therefore, it has potential to be used as a visual indicator of the pH variations during storage of packaged food.