ABSTRACTA radiometric bacterial detection system was investigated as an alternate method to the agar plate count for estimating total microbial population in frozen concentrated orange juice (FCOJ). Basically, the technique involves detection of1 4CO2produced by microorganisms from labeled glucose. Additional labeled nutrients were added to the test medium (tryptic soy broth plus labeled glucose) for certain lactic acid bacteria found in orange juice that do not produce gas from glucose.The organisms used in this study included four strains of yeast (Zygosaccharomyces rouxii, Z. vini, and two isolates from FCOJ), two strains ofLeuconostocsp., and two cultures of Lactobacilli (L. caseiandL. plantarum). Standard curves were prepared from the known cultures by plotting time required for radiometric detection versus concentration as determined using routine plating procedures. Results indicate concentrations of 104yeast,Leuconostoc, andLactobacillusper ml can be detected in 6, 7, and 10 hr respectively. Of 600 orange juice samples examined, 44 positives (104/ml) were detected in 12 hr, 41 of which were positive in 8 hr. Two false positive results were obtained with the radiometric technique but no false negatives were observed.
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