Milk: colimetry, phosphatase dosage and global count assays. Considerations on the detention of irregularities in the milk pasteurization line, by using the colimetry assay in dilutions of samples and in increasing concentrations

Abstract

After introductory remarks about the use of milk pasteurization, the author performs a comparative study among the coli counting methods employed as a routine in the laboratories of milk sanitary control and the coli counting process of the increasing concentration. Considering that the study of the presumptive presence of the coliform organisms registers only the bacterial densities of flora at the moment, when the pasteurized milk is already recontamined, the author states that the sanitization procedures would always affect next day mi1k. Then the author experimented a process that allowed a forecast of the results in order that the product could be maintained within the standard level and offering even a certain safety margin. So, as the Federal Regulation demands absence of coliform organisms in 0.1 ml, for milk classified as C type, the author performed inoculations in increasing concentrations - 0.1, 1, 2, 4, 6, 8, 10 ml or more. He built a series of 21 fermentation tubes, brilliant green-lactose-bile broth, with 3 tubes for each portion of milk. When a positive result is obtained, for instance in the three last tubes (10 ml), the upper level of safety would be at 8 ml, Inoculations of 0.1, 1, 2, 4, 6, 8 ml would be called safety margin. Whenever the upper level decreases, dragging with it the safety margin, the whole procedure of sanitization and regulation of the equipment must be intensified. By the usage of the increasing concentrations the factor surprise does not count, and the operation is safely executed, giving through the study of the present data the picture of the future results. Through the application of the method of the computation of the most probable numbers (M.P.N.), using 3 tubes and 3 different volumes - 0.1, 1, 10 ml - pertaining to the series of 21 fermentation tubes the author reached to some conclusions. He observed that when there is a positive result in 10 ml, a new indication could only be obtained when the positive result reached 1 ml. This silent period in a test is too large. This disadvantage of the M.P.N. test shows the superiority of the process of inoculations in increasing concentrations in forecasting the defects in pasteurization. In relation to the presence of perforations in the plates, at the level of the Regenerative Section, in a A.P.V. equipment, the author observed that while the milk of the Tubular Holding System, showed a high upper level (8 ml), coliform organisms were present in 0.1 ml, even in the Regenerative Section. The author knowing that the phosphatase test does not indicate the presence of raw milk in quantities smaller than 1%, he essayed an experimental work in order to detect the volume of raw milk that was being mixed with pasteurized milk in the regenerative section. In this complementary test the author is able to calculate the volume of raw milk mixed to the pasteurized one. For this purpose he selected 8 litres of pasteurized milk obtained from the tubular holding system, and added to them increasing quantities of raw milk - 0.01, 0.03, 0.05, 0.01, 0.5, 0.7, 1 and  2 ml - that is quantities that are below and above the detection power of the phosphatase test. Through the usage of the increasing concentrations process the author observed that the pasteurized milk of the tubular holding system, with an upper level of 8 ml, showed figures gradually lower until a positive result in 0.1 ml - pasteurized milk plus 0.1 ml of raw milk. This all happened when the inoculated volume of raw milk was    0.1 ml. Hence, he concluded that the volume of raw milk that passed through the perforations of the plates presented a percentage of 0.1 ml %. The author explains that in this case, the raw milk acted as a coliform "inoculum", and not as a phosphatase inoculation that could be detected. After these coments he concludes that this test used for the detection of coliform organisms is more accurate than the phosphatase test in observing the recontamination with raw milk. Phosphatase is completely inactivated through a correct pasteurization. Hence the author reaches to the conclusion that when the pasteurization presents light defects, the imperfectly treated milk coud act as raw milk passing in very small portions, undetected by phosphatase test but indícated by the test for coliform organisms, Consequently, this last test being so exact should be used as a routine procedure employed in checking .the efficiency of pasteurization, as well as the rate of detected recontamination.