Preparation of a visual pH-sensing film based on tara gum incorporating cellulose and extracts from grape skins

Extracts from grape skins (EGS) were incorporated into tara gum (TG)/cellulose nanocrystal (CNC) matrix to prepare a colorimetric pH-sensing film. The UV-vis spectra of EGS in the pH range of 1-10 were studied and the color clearly changed from bright red to dark green. Fourier transform -infrared spectroscopy, scanning electron microscopy and thermal analysis were used to characterize TG/CNC/EGS films, and the effects of EGS addition on mechanical properties, oxygen permeability and optical properties were also tested. The results revealed that EGS was successfully introduced into the TG/CNC matrix without obvious interactions. The EGS addition decreased the compact and continuous structure, thermal stability and barrier properties of the films. With EGS addition from 0 to 15 g/100 g TG, the tensile strength and light transmittance of films gradually decreased from 65.50 to 44.32 MPa and from 65.11 to 41.71% at 660 nm, respectively; however, the elongation at break of films increased significantly from 30.10 to 54.80%. The films were also immersed in different buffers to evaluate the response to pH changes. The color range of TG/CNC/EGS film varied from red (in acid pH) to slightly green (in alkali pH). The pH -sensing film was also evaluated by an activation test on milk, with evident change in the coloration of the film, indicating that the film could be applied in food packaging for information concerning the packaged food. (C) 2016 Elsevier B.V. All rights reserved.