Date of Award

2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Science

First Advisor

Ibrahim, Salam A.

Abstract

The early detection of chemical contaminants in milk at the farm level is essential to prevent them entering into the food chain. The overall objective of this study was to determine the effect of selected rodenticides on the acidic and enzymatic coagulation properties of milk by using selected strains of lactic acid bacteria (LAB) and to evaluate the suitability of lactic acid bacteria as a biomarker for early detection of toxins in milk. Specific objectives of this study were (a) to determine the optimum growth temperature for lactic acid bacteria in MRS broth for early detection of rodenticides; (b) to determine the effect of selected rodenticides on the growth and activity of different strains of lactic acid bacteria in MRS broth; and (c) to determine the effect of selected rodenticides on the growth and activity of different strains of lactic acid bacteria in milk. Serially diluted rodenticides were added to tubes containing MRS broth/milk. Commercial yogurt culture was then inoculated into the medium and incubated at 42 °C for 6 hours. The pH of the broth was recorded at 2, 4, and 6 hour intervals. The bacterial counts, lactic acid production, α-galactosidase and β-galactosidase activity were also measured at the end of incubation. In the MRS broth, the yogurt cultures YF001 and YI 885 showed highest sensitivity to diphacinone at the level of 0.005 mg/ml. YF001 showed detectable sensitivity to brodifacoum and bromadiolone at the level of 0.02 mg/ml. YG011 showed detectable sensitivity to brodifacoum, bromadiolone and diphacinone at the levels of 0.02, 0.04, and 0.02 mg/ml, respectively. The growth of YI 885 was inhibited by brodfacoum and bromadiolone at the levels of 0.01 and 0.04 mg/ml, respectively. In milk, the yogurt cultures YG011 and YI 885 showed highest sensitivity to diphacinone at the level of 0.04 mg/ml. YF001 showed detectable sensitivity to brodifacoum, bromadiolone and diphacinone at the levels of 0.12, 0.08, and 0.08mg/ml, respectively. The growth of YG011 was inhibited by brodfacoum and bromadiolone 2 at the levels of 0.08 and 0.16mg/ml, respectively. YI 885 showed detectable sensitivity to brodifacoum and bromadiolone at the levels of 0.08 and 0.16mg/ml, respectively. A significant (p < 0.05) growth inhibition of all the yogurt cultures was observed in the presence of all the three rodenticides. There were significant differences (p < 0.05) in the bacterial count, pH, lactic acid production, α-galactosidase and β-galactosidase activity in the presence of rodenticides in the medium. The results indicate that yogurt culture could be used as a biomarker for the early detection of rodenticides in milk. With some adjustments, this process could be utilized as a fast and accurate test for the presence of rodenticides in dairy food products.

Download

Share

COinS