Relationship between Resazurin Test and Standard Agar Plate Count in Bacteriological Test of Raw Milk

Abstract

A total of 251 samples of raw milk collected in Kanagawa Prefecture were subjected comparatively to the standard plate count and the resazurin test tube method. The correlation coefficient 0 was determined between the time required for discoloration in the resazurin test and the standard plate count of a raw-milk sample at each range of discoloration. As a result, it was 0.633, 0.629, 0.584, and 0.675 at ranges 1, 2, 3, and 4 of the color-tone tabe of the lactester A, respectively. All the values were proved to be significant at a level of 1 per cent.Then a regression formula was devised to estimate the standard plate count of a raw-milk sample from the time required for discoloration in the resazurin test tube method. A confidence limit was also examined.
The same experimental method was applied to 92 samples of raw milk collected in Tokyo and Saitama Prefectures, with an exception that the resazurin test paper method was used instead of the test tube method. As a result, the correlation coefficients were 0.636, 0.729, 0.768, 0.822, 0.844, 0.762, and 0.765 at ranges of discoloration represented by disc Nos. 5, 4, 3, 2, 1, and 0 and a range of complete decoloration, respectively. These values were proved to be significant at a level of 1 per cent. A regression formula was devised and the confidence limit examined also this time.