100A-31 |
Use of genetically engineered bioluminescent organisms for shelf life testing |
N. G. BRIGHT, L. D. Terry, J. G. Patrick, B. D. Auman, R. J. Carroll, and B. M. Applegate, Sr. Food Science, Purdue University, 1160 Food Science Bldg, West Lafayette, IN 47907 Shelf life studies are routinely performed to ascertain growth rates of spoilage organisms in food products. Methodology consists of inoculating the test food product with a challenge organism followed by incubation at various test temperatures to simulate both storage and abuse conditions over time. Bacteria are enumerated by spread plating serial dilutions of sample, which is labor intensive and requires substantial materials. Bioluminescent bacteria offer an alternative approach for measuring biomass due to the correlation of bioluminescence and cell number. We hypothesize that surrogate bioluminescence organisms can be utilized in shelf life studies by examining the increase in bioluminescence as an indirect measure of increasing biomass. Our objective was to develop an alternative assay to plate counting for shelf life studies utilizing bioluminescent bacteria as challenge organisms. A previously constructed salicylate inducible bioluminescent reporter Pseudomonas fluorescens 5RL was used to inoculate pasteurized egg product. Bacteria were grown to a predetermined OD in LB containing 50ppm salicylate. Bioluminescing cells were then blended into the product at an initial concentration of 500 cells per mL in 200 mL samples. One mL samples were removed from three replicates and measured for bioluminescence using a Zylux luminometer and reported in photons/sec. Replicates were then incubated at 25°C, 10°C, and 4.4°C to simulate storage and abuse conditions. Egg products were sampled daily for the duration of the study. Bioluminescence increased in the 25°C samples 25 fold over the 4.4°C sample. The 10°C showed 5 fold increase over the 4.4°C sample but was 5 fold less than the 25°C samples. The 4.4°C samples remained constant a level 10 fold over background. Results demonstrated an increase in bioluminescence with increasing temperatures showing increased biomass with temperature abuse. Bioluminescence can be used to replace classical plate count methods to provide a less labor and material intensive assay.
Session 100A, Food Microbiology: General II
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