Browsing by Subject "Lactic acid bacteria"
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Item Comparison of dairy yogurt with imitation yogurt fermented by different lactic culture from soybean milk(Texas Tech University, 1988-12) Cheng, Yeeru JenniferNot availableItem Quantification of the Antimicrobial Substances Produced by Lactic Acid Bacteria used as an Intervention to Inhibit Escherichia coli O157:H7 and Salmonella in vitro and on Fresh Spinach (Spinacia oleracea)(2012-02-14) Calix Lara, ThelmaThe metabolic activity of bacterial microorganisms may influence the growth and metabolic activities of other microbes that are present in any specific niche. Lactic acid bacteria (LAB) are antagonistic to some microbial pathogens by the metabolic production of compounds with antimicrobial activity. Consequently, investigators have measured the effects of those antimicrobials to inhibit specific pathogens. However, the mode(s) of action of LAB against foodborne pathogens on products and/or in broth is not completely understood. Therefore, the objectives of this research were to (i) determine the LAB dose required for inhibition of Escherichia coli O157:H7 and Salmonella enterica in vitro and on spinach, and (ii) identify and quantify the major antimicrobial substances synthesized by LAB as a function of postinoculation storage conditions. Assays were performed at 7 degrees C under aerobic conditions. The foodborne pathogens dose responses were assessed in a liquid microbiological medium (in vitro) and on spinach leaf surfaces. Different levels of foodborne pathogens and LAB cultures were used. The addition of LAB cultures did not reduce E. coli O157:H7 or Salmonella enterica populations when performed in vitro. However, when LAB cultures were sprayed on the surfaces of spinach leaves at 8.0 log10 CFU/g, there were significant reductions on E. coli O157:H7 of 1.62 and 0.73 log10 CFU/g (after 3 days) and on Salmonella enterica of 1.85 and 0.71 log10 CFU/g (after 6 days) for treatments inoculated with an initial level of 2.0 and 4.0 log10 CFU/g, respectively. After quantification of the antimicrobial compounds synthesized by LAB cultures, they were correlated against the population growth of targeted pathogens. The highest Llactic acid (3.71 plus/minus 0.14 micromoles/ml, day 12) and hydrogen peroxide (3.72 plus/minus 3.34 microM, day 6) production were obtained from the in vitro sample inoculated with 8.0 log10 CFU/ml of LAB and 0.0 log10 CFU/ml of pathogens. The highest bacteriocin production (0.1 plus/minus 0.01 mg/ml) was obtained from the in vitro sample with 8.0 log10 CFU/ml of LAB and 2.0 log10 CFU/ml of pathogens. In conclusion, the LAB cultures were able to produce detectable amounts of antimicrobials that may be used as intervention and/or sciencebased practice against foodborne pathogens by producers and the industry.Item Spoilage characteristics of ground beef with added lactic acid bacteria at abusive and refrigerated temperatures packaged in modified atmosphere and traditional packaging(2005-05) Hoyle, Amy R.; Brashears, Mindy M.; Brooks, Chance J.; Thompson, Leslie D.Lactic acid bacteria (LAB) can reduce Escherichia coli O157:H7 and Salmonella spp. in ground beef during storage. Two packaging studies evaluated if LAB masked changes typically associated with the spoilage of ground beef displayed under refrigerated (0°C) or abusive (10°C) temperatures. Packaging consisted of traditional (foam trays wrapped with permeable film) and MAP packaging (80% O2 and 20% CO2). To mimic industry practice, one-half of MAP samples contained 1000 ppm added rosemary oleoresin. Microbial and sensory analyses were conducted to determine spoilage endpoints. At 0°C, traditionally packaged LAB samples had significantly lower yeast and mold (YM) counts than controls throughout display. Among traditional packages, there were no significant differences in coliform, Brochothrix thermosphacta, and Pseudomonas spp. counts between LAB treatments. At abusive display temperatures, there were no significant differences in coliform, YM, B. thermosphacta, and Pseudomonas spp. counts between traditionally packaged LAB treatments. At 0°C and 10°C, total plate counts and LAB populations in both traditional and MAP packaged LAB inoculated samples were significantly higher than the control. In MAP packaging, no significant differences existed between LAB treatments for YM, coliform, B. thermosphacta, and Pseudomonas spp. No significant differences in trained or consumer sensory color and odor scores existed between LAB and controls for traditional and MAP packaging indicating spoilage was not masked. Therefore, LAB can be added to ground beef as an antimicrobial agent in traditional and MAP packaing. In addition, LAB may slow lipid oxidation in traditionally packaged ground beef.Item Spoilage characteristics of ground beef with added lactic acid bacteria at abusive and refrigerated temperatures packaged in modified atmosphere and traditional packaging(Texas Tech University, 2005-05) Hoyle, Amy R.; Brashears, Mindy M.; Brooks, Chance J.; Thompson, Leslie D.Lactic acid bacteria (LAB) can reduce Escherichia coli O157:H7 and Salmonella spp. in ground beef during storage. Two packaging studies evaluated if LAB masked changes typically associated with the spoilage of ground beef displayed under refrigerated (0°C) or abusive (10°C) temperatures. Packaging consisted of traditional (foam trays wrapped with permeable film) and MAP packaging (80% O2 and 20% CO2). To mimic industry practice, one-half of MAP samples contained 1000 ppm added rosemary oleoresin. Microbial and sensory analyses were conducted to determine spoilage endpoints. At 0°C, traditionally packaged LAB samples had significantly lower yeast and mold (YM) counts than controls throughout display. Among traditional packages, there were no significant differences in coliform, Brochothrix thermosphacta, and Pseudomonas spp. counts between LAB treatments. At abusive display temperatures, there were no significant differences in coliform, YM, B. thermosphacta, and Pseudomonas spp. counts between traditionally packaged LAB treatments. At 0°C and 10°C, total plate counts and LAB populations in both traditional and MAP packaged LAB inoculated samples were significantly higher than the control. In MAP packaging, no significant differences existed between LAB treatments for YM, coliform, B. thermosphacta, and Pseudomonas spp. No significant differences in trained or consumer sensory color and odor scores existed between LAB and controls for traditional and MAP packaging indicating spoilage was not masked. Therefore, LAB can be added to ground beef as an antimicrobial agent in traditional and MAP packaing. In addition, LAB may slow lipid oxidation in traditionally packaged ground beef.Item The use of lactic acid bacteria as a post-harvest intervention to control escherichia coli O157:H7 in fresh spinach(2008-12) Gragg, Sara E.; Brashears, Mindy M.; Brooks, Chance J.; Miller, Markus F.; Thompson, Leslie D.In recent years, fresh spinach has been identified as a vehicle for Escherichia coli (E. coli) O157:H7 transmission. Multiple studies have demonstrated the ability of lactic acid producing bacteria (LAB) to reduce the presence of Escherichia coli O157:H7 in food products and the efficacy of LAB cultures as a post – harvest intervention in fresh spinach production should be evaluated. To determine the effect of spinach inoculated with Escherichia coli O157:H7, spinach samples were rinsed with sterile distilled water and a four – strain LAB cocktail at a target concentration of 2.0x108 CFU/mL. Both treatments were compared to an inoculated control over a 24 – hour time period at 7oC. According to composite LS means data obtained for each treatment, water and LAB resulted in significant reductions of 0.88 logs (p<0.0001) and 1.03 logs (p<0.0001) in comparison to the control, respectively. The improved reduction of LAB was significantly better than that of water (p=0.0363), making it the most effective treatment. A triangle test was conducted to determine if a statistically significant difference in sensory characteristics exists when LAB is applied to fresh spinach. Two samples were rinsed with tap water and considered to be identical. The remaining sample was rinsed with LAB at a concentration of 2.0x108 CFU/mL. 40 panelists participated in the test and 16 correctly identified the LAB – treated spinach as being the one unique sample. These results indicate that a statistically significant difference does not exist (á=0.05, 0.01) when LAB is applied to fresh spinach and that the use of LAB may be acceptable from a consumer acceptance standpoint. The ability of LAB to control E. coli O157:H7 populations in combination with the industry standard chlorine rinse was determined in a 12 day shelf – life study at 7oC. The multi – hurdle intervention was evaluated in comparison to water, LAB and chlorine rinses. LAB cultures were applied at a concentration of 2.0x108 CFU/mL, while chlorine was utilized at the 200 ppm level. As indicated by composite LS means data, significant reductions in comparison to control populations were achieved by the LAB (p=0.0215), chlorine (p=0.0002) and multi – hurdle treatments (p<0.0001). However, the multi – hurdle treatment produced the greatest reductions with 1.35 logs. This reduction was significantly improved upon LAB (p=0.0012) and chlorine (p=0.0815), indicating that the application of chlorine and LAB is most effective as a combination treatment.