Estimation of Potential Shelf-life of Pasteurized Fluid Milk Utilizing a Selective Preliminary Incubation

Selective preliminary incubation, followed by bacterial enumerations or detection techniques, was used to indicate potential shelf-life of pasteurized fluid milk. Commercial whole milk samples, stored at 7°C, were analyzed for bacterial and biochemical parameters and potential shelf-life using daily organoleptic evaluation. Prior to analysis, each sample was subjected to the following preliminary incubations: milk alone, milk with benzalkonium chloride, milk and broth, milk and broth with benzalkonium chloride, and milk and a dairy gram-negative broth. The following bacterial enumerations were conducted: Psychrotrophic Bacteria Count, modified Psychrotrophic Bacteria Count (Petrifilm and agar methods), and Moseley Keeping Quality test (Petrifilm and agar methods). Catalase detection (headspace pressure and flotation time) and impedance detection times were also determined. Initial Standard Plate and Coliform counts (Petrifilm and agar methods) were conducted on each fresh sample but were not used for shelf-life prediction. Many of the preliminary incubations, in conjunction with enumeration or detection combinations, (especially modified Psychrotrophic Bacteria Count and impedance microbiology) gave good correlations to shelf-life (-0.89 and 0.91, respectively). Thus, these methods could be used to indicate the potential shelf-life of pasteurized fluid milk.