Background and Aim:Food safety is an increasing public health problem worldwide. Although approaches such as hazard analysis critical control point (HACCP) programs have significantly improved safety of our food supply, changes in food processing, products, practices, and human behavior have had influence on the emergence of food related diseases. Given the difficulties in determining the hazardous amount of preservative by techniques such as chromatography as they are time consuming and costly, we decided to use a luminescent microbial biosensor to see how it reacts to different amount of preservatives used in milk. Methods:Bacterial strain Escherichia coli SM10S1 luxAB was previously constructed using mini-Tn5 luxAB insertional mutagenesis and its luminescence light output stability and growth behavior were also characterized. Ten ml milk sample were transferred to a 15 ml falcon and hydrogen peroxide solution was added in concentration of 0.05% and 0.1%. Another preservative (potassium dichromate) was similarly added to milk sample in concentration of 0.8% and 1%. Then samples were inoculated with 107 to 108 lux-marked E.coli SM10 S1 culture medium. After incubation at 5, 10 and 15 min, samples were centrifuged at 10,000 rpm for 9 minutes and pellet obtained was dissolved in 450 ml phosphate buffer. Following that, 10 Zl of remaining solution was used for measuring of luminescence light output using luminometer and counting cfu by micro colony method. Results:Results showed no significant differences between authorized and unauthorized concentrations of hydrogen peroxide during 5 minutes incubation time. However at concentrations of 0.05% hydrogen peroxide, after incubation for 10 and 15 min only 2 and 4 colonies was detected respectively while at concentration of 0.1% hydrogen peroxide, 4 and 7 colonies observed. Luminescence light output measurement showed that at similar incubation time at 0.05% hydrogen peroxide concentration could decrease the light emition down to 15%, 90% while 0.1% hydrogen peroxide effects on luminescence light output were 82% and 99% respectively. Similar results were also observed when samples treated with 0.8 % and 1 % potassium dichromate during 5, 10 and 15 min incubation time when cfu declined to 1, 2, and 4 colonies for 0.8% and 2, 4 and 7 colonies for 1% potassium dichromate. Light output decrease at these times for 0.05%, were 20%, 50%, 89% and for 0.1% were 75%, 83% and 99% respectively. Changes in light output between preservatives permitted concentrations (0.05% hydrogen peroxide and 0.8% potassium dichromate) and their nonpermitted (0.1% hydrogen peroxide and 1% potassium dichromate concentrations), could be an indication for evaluation of the amount of preservatives in milk. Conclusion:Results showed that when concentration and contact time of preservatives increased, number of bacterial decreased. Similarly luminescence light output intensity decreased in accordance with cell number. Bioluminescence marker system could be an efficient and sensitive method to study the hazardous characteristics of various concentrations of food preservatives.

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