Abstract: Indicator films were prepared through using starch (S) and carboxymethyl cellulose (CMC) as film forming material, purple sweet potato anthocyanins (PA) were used as the indicator. The effects of S and CMC ratio, anthocyanin concentration and glycerol concentration on the physical properties such as tensile strength (TS), elongation at break (EAB), water soluble (WS) and color (a) had been investigated. The comprehensive score of indicator film performance is used as the response value, the process parameters were optimized by the response surface method, and the optimal indicator film was characterized. The results demonstrated that the optimum formula of indicator films were starch and CMC ratio of 6:4, anthocyanin concentration of 0.5%, glycerol concentration of 0.6%. The score of indicator films were the best overall as high as 63.8 under these optimal conditions, and the properties of indicator films showed tensile strength of (21.48±0.12) MPa, elongation at break of (28.88±0.08)%, water soluble of (19.24±0.21)%, color of (4.95±0.02). Results of FT-IR, XRD and SEM indicated that the cross section of the SCA film was smooth and good compatibility of the ingredients. Furthermore, the indicator film was used to monitor the freshness of the grass carp. The total volatile basic nitrogen (TVB-N) value, pH and the total viable count reached at 21.55 mg/100g, 7.58，7.3 lg CFU/g, respectively. And simultaneously the indicator film changed from red to blue-violet. The research results can provide reference for the use of indicator films for food shelf life judgment applications.

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