Application of On-Pack pH Indicators to Monitor Freshness of Modified Atmospheric Packaged Raw Beef

Abstract

Abstract Three on-pack visual indicators for the real-time monitoring of raw beef steaks in a modified atmospheric packaging (MAP) environment were developed. The indicators were prepared by spray deposition of a nanocellulose (NC) suspension (1.5 wt. %) 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 days. All indicators gave a colour change for beef steak stored at 4 °C for 7 days that was noticeable with the naked eye and had a ΔE value >12. The sensitivity of the RC pH indicator was superior to 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. Thus, it was concluded that 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.