Microbiological and Physico-Chemical Parameters for Predicting Quality of Fat and Low-fat Raw Ground Beef During Refrigerated Aerobic Storage

The aim of the current study was to identify quality indicators of fat (14.50±0.75%) and low fat (4.79±0.63%) raw ground beef by monitoring changes in physico-chemical and microbiological parameters during aerobic refrigerated storage, such as water holding capacity, pH, thiols, carbonyl compounds, thiobarbituric acid reactive substances (TBARS), metmyoglobin, deoxymioglobin, oxymyoglobin color indices, pseudomonads, Brochothrix thermosphacta and total viable counts. Meat packaged in air-permeable polyethylene plastic film was stored under controlled isothermal conditions (0, 5, 10 and 15°C). A population level of pseudomonads equal to 7.0±0.5 log10 cfu/g was considered as the potential spoilage level. Using Principal Component Analysis, samples were distinguished on the basis of their microbial load. A significant positive correlation between microbial population and carbonyls, metmyoglobin, TBARS, water holding capacity, and a negative correlation with thiols and color parameters (L*, Chroma), were observed. Two different approaches were followed to estimate the quality status of samples: (i) the partial least square (PLS) regression with R2 0.93 and RMSEP for prediction 0.44 for pseudomonads, using the above physico-chemical characteristics as the dominant input variables, which allowed prediction of the microbiological status of ground beef regardless of time-temperature storage profile and fat content, and (ii) a square root-type model (adjusted R2 0.952) that satisfactorily predicted the growth of spoilage pseudomonads under isothermal and dynamic conditions, regardless of the above physico-chemical changes. The above results suggest that depending on the available input data, the two modelling approaches can accurately (and complementarily) assess quality of aerobically stored ground beef.