Plasticizers' effect on pH indicator film based on starch and red grape skin extract for monitoring fish freshness

Abstract

This work aimed to develop a novel colorimetric indicator film from cassava starch, isomalt and glycerol with 20% wt.% of grape skin extract (GSE) by casting to be used as an indicator of fish freshness. The plasticizers were used in the concentration of 33% at five levels: 100/0, 70/30, 60/40, 50/50 and 0/100 (%w/w isomalt/glycerol). Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and RGB colour analysis showed the homogenous distribution of GSE in the starch matrix. The presence of GSE reduces the thermal stability, k1 value, solubility, swelling values and the %E and increases the tensile strength (TS), revealing its plasticizing potential action in the presence of isomalt. The influence of pH on the colours of the film containing GSE and its indicator activity were evaluated. The results showed that the film produced operates in a wide pH range, being an excellent candidate as an indicator for monitoring fish freshness.