Theses and Dissertations


Weiien Weng

Issuing Body

Mississippi State University


Silva, Juan

Committee Member

White, Charles

Committee Member

Ma, Din-Pow

Committee Member

Matta, Frank

Committee Member

Mikel, Benjy William

Date of Degree


Document Type

Dissertation - Open Access


Food Science and Technology

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Food Science, Nutrition and Health Promotion


Enterobacter sakazakii has been associated with powdered infant formula outbreaks which caused high mortality rate illnesses in infants in recent years. Current research was mainly focused on searching for natural antimicrobial agents which may be incorporated into baby foods to control this emerging pathogen. Yogurt and muscadine products were used in this study. The antimicrobial effects of yogurt were evaluated on agar plates and in a simulated gastrointestinal model. In the agar spot tests, diluted yogurt sample containing lactic acid bacteria at 106 CFU/mL was antagonistic toward E. sakazakii. However, the antimicrobial effect of yogurt on E. sakazakii in the simulated GI model was not noted. Certain numbers of tested E. sakazakii and lactic acid bacteria in yogurt were able to survive the acidic gastric condition and recovered in the intestinal model. By measuring the viable E. sakazakii cells in liquid cultures, the strong antimicrobial activities of muscadine juices and muscadine seed extracts were demonstrated. Within two hours, all inoculated E. sakazakii at 106 CFU/mL were decreased to non-detectable level. Juice and seed extract from dark-skinned muscadine demonstrated stronger antimicrobial activities than those form white-skinned muscadine. The characteristics of muscadine juices and seed extracts were also analyzed. The high phenolics and organic acid contents, such as ellagic, gallic, tannic, and tartaric acids in muscadine were correlated to the inhibitory effect observed.