Rapid Impedimetric Method for Determining the Potential Shelf-Life of Pasteurized Whole Milk

Potential shelf-life of 100 pasteurized whole milk samples, obtained from retail outlets and from dairy processors, was investigated. Parameters studied were: organoleptic evaluation, Standard Plate Count (SPC), psychrotrophic bacteria count (PBC), modified psychrotrophic bacteria count (mPBC), Moseley test (MSPC), and impedance detection time (IDT) at 18 and 21°C. Correlation coefficients were obtained for all possible data combinations in an attempt to detect significant relationships between the parameters studied and the true shelf-life of the product. None of the direct counts (SPC, PBC, and mPBC) correlated well enough with shelf-life to allow shelf-life prediction. Moseley test (MSPC) appeared to possess an adequate relationship to shelf-life with a correlation coefficient at -0.84. IDT 21°C and IDT 18°C proved to have the most significant relationships to shelf-life with correlation coefficients of 0.88 and 0.87, respectively. Therefore, the impedance method had three advantages over the Moseley test: (a) it was a better predictor of shelf-life, (b) it was less labor intensive, and (c) it required only 1-2 d, as opposed to 7-9 d to complete.