IMPROVED ESTIMATIONS OF TOTAL AND PSYCHROTROPHIC MICROFLORA IN RAW MILK USING REFLECTANCE COLORIMETRY AT 32°C¹

Abstract

A rejlectance colorimeter with 32°C incubationldetection temperature successfully quantitated total and psychrotrophic microjlora in raw milk. Correlations between rejlectance colorimetry and the Standard Plate Count improved with preliminary incubation time: .50 (no preliminary incubation), .74 (24 h at T C ) , to .84 (48 h at 7°C). Correlations between rejectance colorimetry and the Psychrotrophic Bacterial Count were better than those achieved with the Standard Plate Count and improved: .53 (no preliminary incubation), .80 (24 h at 7"C), to .91 (48 h at 7°C). The 48 h preliminary incubation method would cost less and data would be available in 48 to 72 h compared to the 98 to 240 h f o r psychrotrophic plating methods. A second sample set (no preliminary incubation) could be analyzed to identib high-count samples in less than 24 h. Color detection times following sample refrigeration for 24 h at 0 , 4 , and 7°C were signijcantly different from samples tested before refrigeration. Identical sample timeltemperature storage conditions are suggested.'Contribution number 4 I28 of the Agricultural Experiment Station. Approved by the Director.