Impact of milk components in recovery of the MS2 bacteriophage as an indicator of enteric viruses

The objective of this study was to characterize the role of milk components in the recovery of viral particles from raw milk. For such characterization, four model milk formulations (A-D) were constituted by mixing different combinations of lactose, whey protein, casein, and fat into water. Each model formulation was spiked with six concentrations of bacteriophage MS2. The soluble and insoluble components of each model milk formulation were separated by centrifugation at 40,000 x g and viruses were enumerated in each supernatant fluid and pellet by the double agar layer (DAL) method. When samples were spiked with MS2 at concentrations lower than 4.8 x 10(5) pfu/ml, milk components did not significantly impact the overall recovery. However, the impact of milk components was measurable at higher concentrations. In general, higher numbers of MS2 were recovered from supernatant fluids of model milk formulations containing no fat. The highest number of viral particles were recovered from the pellet of model C (lactose+whey protein+casein). The recovery efficiency of MS2 was correlated with the dry matter contents of each model milk formulation and the initial spiking concentration of coliphage using response surface modeling.

HPLC/UV analysis of proteins in dairy products using a hydrophobic interaction chromatographic column

High-performance liquid chromatography using a Chrompack P-300-RP column containing a polystyrene-divinylbenzene copolymer-based packing was examined to analyze bovine milk protein components. The separation of major raw-milk proteins could be performed rapidly and reliably with this HPLC/UV method. The determinations were performed in the linear ranges of 0.01-2.0 mg/ml for alpha-lactalbumin, 0.04-2.5 mg/ml for caseins and 0.02-2.0 mg/ml for beta-lactoglobulin. The validity of the method was verified. Since the chromatographic column enabled the quantification of only "native" milk proteins, the extent of denaturation and loss of milk proteins could be examined. Thus, evaluation of heat-induced proteins denaturation was carried out in raw milk heated for 5 min at pre-determined temperatures.