Xujian Qiu

Date of Award

12-2007

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Food and Nutrition Sciences

Advisor

Vivian Chi-Hua Wu

Second Committee Member

Alfred A. Bushway

Third Committee Member

Rodney J. Bushway

Abstract

Food safety is a worldwide concern. Traditional preservatives are widely used to protect food from contamination. However, consumers are increasingly interested in natural, safe, and healthy food. The objective of this research was to explore the potential application of natural ingredients as food preservatives to improve food microbiological safety. Cranberry concentrate, cranberry and blueberry concentrate combination, and a powder blend were found to have significant antimicrobial effects on Escherichia coli 0157:H7, Salmonella Typhimurium, Staphylococcus aureus, and Listeria monocytogenes in laboratory media. Antimicrobial effects of cranberry concentrate (10% w/w) in ground beef were also studied. The antimicrobial effects were more effective at 21 °C than at 7 °C. E. coli 0157:H7 and S. Typhimurium (Gram negative) were more sensitive to the cranberry concentrate than S. aureus and L. monocytogenes (Gram positive). Sensory evaluation studies showed that burgers with berry concentrate could be accepted by consumers. Cornus fruit extract (3% w/w) was added to apple juice to test the survival of E. coli 0157:H7. Antimicrobial effects were influenced by temperature, pH, and time. The most dramatic reduction of E. coli 0157:H7 was observed in apple juice with Cornus fruit extract stored at room temperature. Thin Agar Layer medium was more efficient than MacConkey sorbitol agar for recovery of injured cells. Major organic acids like malic acid, citric acid, and quinic acid play a major role for the antimicrobial activity of this cranberry concentrate. Other bioactive compounds may play a minor role due to the limited quantity. Transmission electron microscopy images showed that lesions on the cell wall induced by cranberry concentrate treatment may be the major reason for the death of E. coli 0157:H7 and S. Typhimurium. In contrast, cranberry concentrate did not cause very obvious cell wall damage for L. monocytogenes and S. aureus. The real-time polymerase chain reaction (PCR) study showed that cell gene expression was inhibited by cranberry concentrate. Cranberry concentrate may interact with the cell outer membrane first. By disruption of the outer membrane, bioactive compounds could enter the cell and inhibit gene transcription. The inhibition of DNA transcription may happen rapidly.

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