Application of on-pack pH indicators to monitor freshness of modified atmospheric packaged raw beef

Abstract

Objectives: To deveop on-pack visual indicators for the real-time monitoring of raw beef steaks in a modified atmospheric packaging (MAP). Materials and Methods: Three indicators were prepared by spray deposition of a nanocellulose suspension (1.5%, in mass) with the desired concentration of the pH-sensitive indicators, either red cabbage (RC) extract, black carrot (BC) extract, or chlorophenol red (CPR). The responsiveness of the colorimetric pH indicators, assessed visually and by CIE-Lab quantitative analysis, to the freshness of raw beef steaks stored under MAP conditions at 4 °C or 20 °C, was analysed over 7 d. Results: All the indicators showed a colour change for beef steak stored at 4 °C for 7 d that was noticeable with the naked eye and had a ΔE value>12. The sensitivity of the RC pH indicator was superior to that of the BC and CPR pH indicators. A study linking total microbial count (aerobic+Escherichia coli+coliform) and the quantitative colorimetric response of the indicators (ΔE) revealed a strong linear correlation. Conclusions: The developed colorimetric pH indicators could be used to monitor the freshness of raw beef and as an alternative to the best-before date commonly used in pre-packaged meat.