L'épreuve de la réductase dans le contrôle de la qualité des laits pasteurises
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Reviews of the progress of dairy science 637.0:576.8 SECTION B. BACTERIOLOGY AND MYCOLOGY APPLIED TO DAIRYING PAGE Thom6 (39) has studied the change in flora during the incubation of samples in the methyleneblue test. The proportion of the different types, which consisted mainly of streptococci, micrococci and coliform organisms, changed during incubation. Initially the flora of different samples consisted of 7-100% streptococci, 0-95% micrococci and 0-6% coliform organisms; at the time of reduction the proportions were respectively 20-88, 9 r 65 and 0-24%. The reducing ability of pure cultures of representatives of the three groups, in terms of the time taken for an inoculum of 1 million organisms per ml. to reduce methylene blue in 'sterile' milk, was approximately the same, though at the time of reduction counts were higher for streptococci and coliform organisms than for micrococci. With mixed cultures, the rates of increase of each type were changed with varying proportions of inoculum, although the time for complete reduction was not materially affected. Morris (40) has observed that proliferation of psychrophilic bacteria of the genus Pseudomonas, derived from the water supplies used on the producing farms, may lead to a shortening of the reduction time after overnight storage of milk samples in a refrigerator. Reviews of the progress of dairy scienceMany papers dealing with different aspects of the resazurin test have appeared during the period under review. Resazurin has been synthesized (4J) and standards have been suggested for preparations intended for milk testing; these standards have been adopted for resazurin used for official milk tests in this country (42). According to Johns (43) resazurin tablets approved for use in North America are approximately 60% stronger than those used in this country. The use of the stronger solution made colour differentiation easier, especially when dealing with cream, colostrum, and milks tending to give a grey tinge when mixed with the dye, but it delayed by about 30 mm, the time taken to reach the pink stage, although there was no difference in the time taken to reach the Munsell P7/4 colour standard (about half-way between the initial blue and the full pink stage). Thomas(44), however, found that doubling the concentration of resazurin only slightly delayed the time taken to reach Lovibond disk 4, 2 or 0.The interpretation of results obtained by workers in different countries is complicated by the use of different colour standards for the intermediate stages of reduction. Golding & Jorgensen (45) have compared the colour standards of a Munsell colour grader with those of the Lovibond disk; the average disk values were 6 for Munsell A, 4-95 for B, 3-85 for C and 2-35 for D. In some European countries a colour chart (Dr Kloz) graduated in four classes is used(ll): class I corresponds to the initial colour (blue) of resazurin in milk, class IV to the mixture of resorufin and milk (pink), and classes II and III represent the transitions between these two extremes. A...
Reviews of the progress of dairy science 637.0:576.8 SECTION B. BACTERIOLOGY AND MYCOLOGY APPLIED TO DAIRYING PAGE Thom6 (39) has studied the change in flora during the incubation of samples in the methyleneblue test. The proportion of the different types, which consisted mainly of streptococci, micrococci and coliform organisms, changed during incubation. Initially the flora of different samples consisted of 7-100% streptococci, 0-95% micrococci and 0-6% coliform organisms; at the time of reduction the proportions were respectively 20-88, 9 r 65 and 0-24%. The reducing ability of pure cultures of representatives of the three groups, in terms of the time taken for an inoculum of 1 million organisms per ml. to reduce methylene blue in 'sterile' milk, was approximately the same, though at the time of reduction counts were higher for streptococci and coliform organisms than for micrococci. With mixed cultures, the rates of increase of each type were changed with varying proportions of inoculum, although the time for complete reduction was not materially affected. Morris (40) has observed that proliferation of psychrophilic bacteria of the genus Pseudomonas, derived from the water supplies used on the producing farms, may lead to a shortening of the reduction time after overnight storage of milk samples in a refrigerator. Reviews of the progress of dairy scienceMany papers dealing with different aspects of the resazurin test have appeared during the period under review. Resazurin has been synthesized (4J) and standards have been suggested for preparations intended for milk testing; these standards have been adopted for resazurin used for official milk tests in this country (42). According to Johns (43) resazurin tablets approved for use in North America are approximately 60% stronger than those used in this country. The use of the stronger solution made colour differentiation easier, especially when dealing with cream, colostrum, and milks tending to give a grey tinge when mixed with the dye, but it delayed by about 30 mm, the time taken to reach the pink stage, although there was no difference in the time taken to reach the Munsell P7/4 colour standard (about half-way between the initial blue and the full pink stage). Thomas(44), however, found that doubling the concentration of resazurin only slightly delayed the time taken to reach Lovibond disk 4, 2 or 0.The interpretation of results obtained by workers in different countries is complicated by the use of different colour standards for the intermediate stages of reduction. Golding & Jorgensen (45) have compared the colour standards of a Munsell colour grader with those of the Lovibond disk; the average disk values were 6 for Munsell A, 4-95 for B, 3-85 for C and 2-35 for D. In some European countries a colour chart (Dr Kloz) graduated in four classes is used(ll): class I corresponds to the initial colour (blue) of resazurin in milk, class IV to the mixture of resorufin and milk (pink), and classes II and III represent the transitions between these two extremes. A...
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