Abstract: In order to improve the stability of natural anthocyanins as freshness indicators in food packaging, a novel packaging film, consisting of a protective dense outer layer formed from chitosan and polyvinyl alcohol and an inner layer formed from gellan gum and mulberry anthocyanins, was developed by layer-by-layer assembly as an intelligent indicator and applied for monitoring salmon freshness. The bilayer film with a chitosan-to-polyvinyl alcohol ratio of 1:1 (V/V) had the best mechanical properties. The tensile strength and elongation were 40.65 MPa and 54.36%, respectively. The film had the lowest water vapor transmission rate. The scanning electron microscopic image showed that the film has the best structure compatibility imparting the best stability to anthocyanins incorporated. When applying this film to detect salmon freshness, total volatile basic nitrogen (TVB-N) content increased with stored time at 4 ℃, reaching a level greater than 30 mg/100 g on the 4th day. At this time, thiobarbituric acid reactive substances (TBARs) value was 0.921 mg/kg and pH was 6.75. In addition, macroscopic observation showed that the color of the film changed from dark red to lavender, and then bluish brown, indicating that the fish were spoiled. In conclusion, the developed bilayer film improves the oxidative stability of anthocyanins incorporated and hence can be used as an intelligent indicator for salmon freshness.

Key words: intelligent packaging material, salmon, stability, mulberry anthocyanins, fish freshness