Abstract: Indicator films were prepared through using starch (S) and sodium carboxymethyl cellulose (CMC-Na) as the film forming material and purple sweet potato anthocyanins (PA) as the indicator. The effects of S/CMC-Na ratio, anthocyanin concentration and glycerol concentration on the tensile strength (TS), elongation at break (EAB), water solubility and color (a value) of films were investigated. Using the comprehensive score of indicator film performance was as the response value, the process parameters were optimized by the response surface methodology, and the optimal indicator film was characterized. The results demonstrated that the optimum formulation of indicator films was determined as follows: starch/CMC-Na ratio 6:4, anthocyanin concentration 0.5%, and glycerol concentration 0.6%. The overall score of the indicator film prepared using the optimized formulation were the highest, up to 63.8, and it showed tensile strength of (21.48 ± 0.12) MPa, elongation at break of (28.88 ± 0.08)%, water solubility of (19.24 ± 0.21)%, and a value of 4.95 ± 0.02. The results of Fourier-transform infrared (FT-IR) spectroscopy, X-ray-differentiation (XRD) and scanning electron microscopy (SEM) indicated that the cross section of the SCA film was smooth and showed a good compatibility among the ingredients. Furthermore, the indicator film was used to monitor the freshness of grass carp. When the total volatile basic nitrogen (TVB-N) value, pH and total viable count reached 21.55 mg/100 g, 7.58 and 7.3 (lg(CFU/g)), respectively, the indicator film changed from red to blue-violet. These research results provide a basis for the application of indicator films for food shelf life evaluation.

Key words: indicator film, potato starch, carboxymethyl cellulose, purple sweet potato anthocyanins, properties optimization, structure characterization