Prediction of the keeping quality of pasteurized milk by the detection of cytochromecoxidase

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Abstract
The keeping quality (KQ) of pasteurized milk samples stored at 5.degree. C and 10.degree. C was satisfactorily predicted after 18 h pre-incubation with 0.05% benzalkonium chloride at 20.degree. C, by estimating the numbers of Gram-negative psychrotrophic bacteria using the simple, cheap and rapid (5 min) assay of cytochrome c oxidase. Correlation coefficients for the relationship between cytochrome c oxidase activity at 20.degree. C and KQ at 5.degree. C or 10.degree. C of -0.89 and -0.84 respectively were obtained. The method correctly predicted the KQ of more than 89% of the samples of pasteurized milk. The assay was not satisfactory for use on samples after pre-incubation at 30.degree. C.