Resazurin reduction time after storage as a keeping quality test for pasteurized market cream

Abstract

Reduction of resazurin to the white end-point at 37°C after KQ storage for 24 hr at 20 ° C bas been used as a keeping quality test for pasteurized cream. A reduction time of not less than 1 1/2 hr would seem to be a suitable standard. Resazurin reduction at 20°C after KQ storage gave less satisfactory results.
The resazurin reduction time at 37°C showed a significant correlation with the total bacterial count after KQ incubation. Most creams with a resazurin reduction time of less than H hr after KQ incubation were classified as unsatisfactory on the results of initial bacteriological tests for total count, psychrophilic count and presence of coliform organisms. If a psychrophilic count was not performed, the results of total bacterial count and the coliform test did not show the unsatisfactory quality of some samples which had high total bacterial counts after KQ storage and which failed the keeping quality test.
The BCP grading test was performed on some samples. Results in this test were also significantly correlated with total bacterial count after KQ incubation. Creams classed as unsatisfactory on the results of total bacterial counts, psychrophilic counts or coliform counts were usually of Grade 3 or 4 in this test.