Doctor of Philosophy (PhD)
School of Nutrition and Food Sciences
Escherichia coli O157:H7 has become an important problem for human health in the United States. Scientific studies indicate cattle herds as primary reservoirs of E. coli O157:H7. To diagnose this pathogen, proper isolation and identification methods are crucial. From five different culture media, CT-SMAC and CHROMagar™ O157 results analyzed simultaneously were the best option for an effective detection of environmental E. coli O157. Despite extensive research at feedlots and dairy farms, there is limited information available on the prevalence of E. coli O157:H7 at cow/calf operations. From 28 small-scale cow/calf operations in the state of Louisiana, we observed an 8% prevalence of this pathogen, with no significant difference between fecal matter, water, and swabs from surfaces as a source of contamination. In a different context but also important for the state of Louisiana, hot sauce has become a large industry with more than 35 brands available in the market. Production of hot pepper sauce may require fermentation of red hot pepper mash in barrels from 2 weeks to 3 years. Physicochemical and microbiological changes during mash natural fermentation were studied over a period of 18 months. A significant reduction of pH was observed, which had a reverse correlation with production of lactic acid. There were minor changes in color of mash. Aroma was analyzed based on six volatile compounds which had a significant increase during the first 60 days of fermentation. We observed four stages during the fermentation of the mash, where LAB and yeast were the main microorganisms isolated, presenting a symbiotic association that stopped at 18 months of fermentation. As part of the fermentation process, 7% of red hot chili pepper mash will develop undesired changes in color, texture, and aroma. Bacillus firmus, Bacillus pumilus, Brevibacillus laterosporus, Enterococcus avium, and Aerococcus viridans were isolated from spoiled mash. When fresh pepper mash was inoculated with this isolates, spoilage of mash was produced after 60 days of storage at 35°C. These microorganisms were also isolated from naturally fermented not spoiled pepper mash. In conclusion, to prevent loses due to spoilage of the mash, fermentation should be stopped after 18 months.
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Gutierrez Barberena, Myriam Evelyn, "Isolation and Identification of Foodborne Pathogens and Spoilage Bacteria in Environmental and Food Samples" (2016). LSU Doctoral Dissertations. 2885.