A reflectance color meter has been combined with a Zymate II robot and incubator to measure microbial and enzymatic activity in dairy and food products. Microwells are automatically filled with samples, dyes, and media, and the plates are intermittently removed during incubation to measure color changes of the dye(s). Traditional pH, metabolic, or O/R dyes can be used. The instrument can be programmed and media/dye selected for more rapid estimation of antibiotics, microbial numbers, abnormal milks, coliform counts, product shelf life stabilities, yeast counts, staphylococcal counts, enzymes and culture activity tests, etc. Antibiotic test data are similar to that obtained with impedance instrumentation. Where fewer samples per day are processed, models requiring manual sample preparation are described.
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.
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