100A-19 |
Application of rapid chromogenic Limulus amoebocyte lysate endpoint assay for determination of microbial level in raw milk |
M. S. RHEE and D. H. Kang. Food Science and Human Nutrition, Washington State University, Pullman, WA 99164 Conventional plating method requires about 24 and 48 h incubation for coliform and total microbial load (APC) in raw milk, respectively. Therefore, a rapid and simple method for determination of microbial level is necessary. Previously developed rapid methods (ATP, microbial phosphatase, etc.) are relying on the color reactions, which are not applicable to directly raw milk tests. Newly developed chromogenic Limulus amoebocyte lysate (LAL) endpoint test was used to monitor the microbial contamination of beef carcass. To date, no research works has been reported to use chromogenic LAL for determination of microbial level in raw milk. This study was to investigate the application of rapid chromogenic LAL endpoint assay for enumeration of APC and coliform counts in raw milk. Raw milk samples (n=25) were storage in a refrigerator (2°C) and then analyzed at regular interval (1, 5, 10, and 15 days). The raw milk sample was 3-fold diluted in a 96-well plate with pyrogen free water and assayed with LAL kit (QCL-1000, BioWhittaker Inc., MD) to find the final reaction point. The LAL results based on endpoint were compared to the actual APC and coliform counts determined with conventional plating methods. The results of LAL method were strongly correlated to conventional APC plating method (n=100, R2=0.93). The relationship between LAL method and coliforms plating method was (n=100, R2=0.74) also high. Classifying the chromogenic LAL results into categories of APC and coliform counts were effectively differentiated. Clearly, the chromogenic LAL test can be applied for determination of microbial level in raw milk. The chromogenic LAL assay is a rapid (within 20 min) and simple (not requiring specific instruments) method for monitoring microbial levels in raw milk. In dairy industry, this method can be successfully implemented to rapidly determine highly microbial contaminated raw milk.
Session 100A, Food Microbiology: General II
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