Fabrication and characterization of alizarin colorimetric indicator based on cellulose-chitosan to monitor the freshness of minced beef

This study was aimed to develop a colorimetric indicator for real-time freshness monitoring of minced beef. The indicator fabricated by incorporation of alizarin (1% w/v) in cellulose-chitosan film developed by sol-gel method and then characterized. Addition of alizarin did not change the swelling index, while water solubility decreased. Fourier-transform infra-red analysis showed successful binding between alizarin and film, and scanning electron microscopic images presented the compact structure of the indicator. The indicator showed a clear color response from yellow to brown and purple at pH 2-11 and had more color stability at 4 degrees C as compared with 25 degrees C during storage for 2 months. Importantly, the indicator revealed color variation from brown to purple when total volatile basic nitrogen (TVB-N) reached the critical amount of 20.53 mg N/100 g. Pearson correlation coefficient represented a strong correlation between total color difference and TVB-N. Therefore, the alizarin based cellulose-chitosan pH-sensitive indicator has the ability to track the freshness of minced beef during the storage through perceptible color changes.