Abstract: Intelligent indicator films based on natural anthocyanins from roselle were developed for real-time monitoring of pork freshness. Three kinds of composite films were prepared by using binary combinations of starch, chitosan and polyvinyl alcohol as the solid substrate. The mechanical properties, water content, microstructure and color stability of the composite films were characterized and compared. The results showed that the chitosan/polyvinyl alcohol/roselle anthocyanins composite film had the highest tensile strength (98.28 MPa), and the starch/polyvinyl alcohol/roselle anthocyanins (SPR) composite film had the highest elongation at break (88.16%), lowest water content and greatest color stability. Scanning electron microscopic photographs showed that the composite films had different microstructures. Finally, the SPR film was selected to indicate the freshness of pork stored at 25 ℃. Total volatile basic nitrogen (TVB-N) value of pork samples increased over time. In particular at 36 h, the TVB-N value was higher than 15 mg/100 g, indicating the occurrence of pork spoilage. Accordingly, the color of the SPR composite film changed into mauve and eventually into brown (at 60 h) with the increase of TVB-N. Overall, these results can help develop intelligent indicator films for monitoring pork freshness.

Key words: indicator films, pork, freshness, roselle anthocyanins, starch, chitosan, polyvinyl alcohol