Chitosan and Starch Based Intelligent Films with Anthocyanins from Eggplant to Monitor pH Variations

Abstract

The objective of this study was to develop and characterize a pH indicator based on chitosan (C) and starch (S) including anthocyanins from eggplant to indicate food quality changes through the detection of changes in the pH of packaged food products. Anthocyanins were extracted with solvents including ethanol and water (7:3, V:V) (EgP-E) and water (EgP-W) in acidic pH. The pH indicator films were obtained incorporating anthocyanin as 1.5 g extract/100 g film solution. The optical, mechanical and water vapor permeability properties were used to characterize the pH indicator films. The total monomeric anthocyanin content and phenolic content of extract solutions were also determined. Color variations of pH indicator films were measured by a colorimeter after immersion in different pH buffers (pH 2.0–10.0). Initially, dried C films and S based films were observed in a violet color and a magenta color, respectively. C and S films with anthocyanins showed color variations from pink (in acidic pH) to bluish-green (in neutral pH) and to violet (in basic pH) in different pH values. The water vapor permeability of films with anthocyanins was higher than films without anthocyanins. Additionally, C and S based films including anthocyanins extracted with water showed better permeability values. C:EgP-W and S:EgP-W films presented higher elasticity values when compared with films including ethanolic extracts (p<0.05) due to the plasticizing effect of water. As expected, opacity values of films including both E and W extracts were higher than those obtained in films without extracts. The developed pH indicator films have potentials to be used as a diagnostic tool for the detection of food spoilage with the advantages of a simple manufacturing process, biodegradability, and usage of natural and safe compounds.