Application of the Decimal Reduction Time Principle to a Study of the Resistance of Coliform Bacteria to Pasteurization

Abstract

The decimal reduction time (time for 90% bacterial death calculated according to the monomoleeular reaction rate equation) in whole milk at 61[degree]C (142[degree]F) has been detd. for 66 strains of Escherichia from varied sources. The data are interpreted to indicate that few, if any, coliform bacteria survive proper pasteurization under ordinary circumstances, none of the DRTs being over 2 min., only 4 over 1 min., and the majority below 0.5 min. A DRT of about 6 min. is needed to survive 30 min. pasteurization. The methods of determining the margins of safety of a pasteurization process are noted. The DRTs of a number of other bacteria in milk are tabulated, based upon published data of other workers. DRT determination might be used as an adjunct to the coliform test for pasteurized milk contamination, to eliminate the possible cases of pasteurization survival by resistant strains. The DRT concept should be employed for the evaluation of all processes involving the thermal destruction of bacteria.