Two colorimetric films based on chitin whiskers and sodium alginate/gelatin incorporated with anthocyanins for monitoring food freshness

Intelligent food packaging materials from natural resources has attracted increasing attention nowadays. In this paper, two fresh colorimetric films were obtained by incorporating natural pigment anthocyanins extract (LRM) as pH-sensitive pigments into two polyelectrolyte complex films composed of chitin whiskers (CW) and sodium alginate (SA)/gelatin (GE), respectively. The analysis results of FTIR, SEM and DSC show that, compared with the single polysaccharide system of SA or GE, the composite film with addition of CW has better water resistance and thermal stability, due to the existence of hydrogen bonds and electrostatic interactions. Meanwhile, the adhesion to LRM is also enhanced. At the same time, through Ritger–Peppas kinetic model analysis, the release process of anthocyanins in the two film systems was analyzed. The CW/SA/LRM system membrane showed good responsiveness to lactic acid and was successfully used in the detection of milk freshness; while the CW/GE/LRM system membrane showed good responsiveness to amine gases and has been successfully used in the detection of pork freshness. The study revealed that the above colorimetric films demonstrate excellent durability and accuracy in food freshness monitoring.