Using beef meat colorimetrics to predict microbial loading following chilled-then-frozen storage

This study evaluated the relationship between the changes in colorimetric measures and microbial loading of beef stored chilled (for 0, 2, 3 and 5 weeks) and then frozen (for 0, 4, 8 and 12 weeks). Forty-eight beef m. longissimus lumborum (LL) were randomly selected, sub-sampled (n = 128) and assigned to chilled-then-frozen storage treatments. Samples were then stored under simulated retail display conditions where colorimetric measurements (L*, a*, b*) and the ratio of reflectance at 630 nm and 580 nm (R630/580) were taken at 1 day intervals over a 3 day period (0, 1, 2 and 3 days). LL samples were removed at day 0 of display and analysed for loading of lactic acid bacteria (LAB), Enterobacteriaceae (ENT), Clostridium perfringens, Brocothrix thermospacta and Escherichia coli. LAB was found to have significant positive correlations to all colorimetric measures, L* an exception, with these correlations generally increasing as the display period increased. Only ΔE (the change in colorimetric measures over display period) was negatively correlated with ENT (P < 0.05). Note that these correlations, whilst significant, were relatively low at around 20-30% magnitude. At least some of the remaining variation in ENT and LAB loading, after allowing for colorimetric measurements, was related to storage duration (P < 0.001). Insufficient loading of the other microbial species limited further investigation. These results suggest that colorimetrics may have an application in monitoring the microbial content of beef, although the observed correlation strength would restrict any practical application without further investigation.