Milk from an on-site herd of healthy Holstein cows was used to conduct the experiments in this study. Milk was obtained from individual weigh jars at the time of milking, transported to the laboratory, and stored at 4 o C overnight. The bacteria were sonicated to disperse clumps that may have formed during processing, which resulted in more accurate quantitation of CFU of bacteria on agar slants. A control standard curve for serial dilutions of the bacterial stock preparations was prepared simultaneously to monitor the viability of the cultures. Briefly, this unit consists of a heater, a cooler, and a regenerator.
Raw milk is placed in a feed tank and is then pumped to the regenerator for heat exchange.
The holding tube is designed to allow heating of the fluid at the set temperature for 15 s. Variation of the holding time is not possible with this pasteurizer unit. Any product not at the required temperature after it passes through the holding tube is diverted back to the feed tank by a diverter valve through the action of the temperature controller. The water is heated by an immersion heater in a closed system also controlled by the temperature controller. The product then passes back through the regenerator and the cooling section for storage or output. The sensitivity of bacterial detection, as determined by previous experiments, allowed us to decrease the bacterial concentrations of the inocula in these experiments.