Preparation of a Composite-Based Thin Film and Its Sensing Application for Detecting Beef Freshness

In order to improve the stability of polyphenols anthocyanidins as freshness indicator in food packaging, in this study, gellan (GL), grape-skin anthocyanidins (GSAC) and chitosan-polyvinyl alcohol (CHPA) were prepared as a composite film to protect beef and indicate the beef freshness for visual detection. The results indicated that the composite film appears good mechanical properties. The results of scanning electron microscopy showed that when the composite film were added into CHPA, the structure compatibility and stability of the film was the best. Then the complicate film was used to indicate the beef freshness and the beef was stored at 4 degrees C, the total volatile base nitrogen content of beef had increased continuously with the extension of storage time. After 6 days, the total volatile base nitrogen content was 35.65 mg/100 g, the thiobarbituric acid reaction product value was 1.005 mg, and pH value was 6.96. It can be seen directly with the naked eyes that the color of the film changed from dark red to mauve, and finally to blue brown, suggesting that the beef had been rotten. To sum up, the composite film made up of CHPA and gellan (GL) anthocyanin (AC) can not only reduce the oxidation of anthocyanin and improve its stability, but also be used as an indicator of meat freshness.