The effect of probiotics on food pathogen E. coli 0157:H7 during fermentation and storage of home - made yogurt | |
| Author | Batjantsan, Khishigjargal |
| Call Number | AIT Thesis no.FB-07-12 |
| Subject(s) | Probiotics Yogurt industry |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. FB-07-12 |
| Abstract | Escherichia coli 0157:H7 produces a powerful toxin that can cause severe illness and is a leading cause of foodborne illnesses. Antimicrobial activities of some probiotics against strongly pathogenic E. toll 0157:H7 were studied using three methods namely Deferred Inhibition, Well diffusion, and Paper disc diffusion assay. Probiotic L. acidophilus was found to give the best results in initial in-vitro studies and hence was selected for further analysis. The survival parameters of E. coli 0157:H7 during fermentation (inoculated with 10³ or 10⁷ CFU/ml) and storage of home-made yoghurt (traditional and acidophilus) at refrigeration temperatures (4 or 8°C) were studied. Counts of E. coli 0157:H7 increased at 10³ CFU/ml, from 3.72 to 4.94 log CFU/ml during fermentation, and it was not detected after 18 and 8 days at 4 and 8°C, respectively in traditional yogurt (without probiotic). When E. coli 0157:H7 was inoculated at 10⁷ CFU/ml, the counts decreased from 7.72 to 6.84 log CFU/ml during fermentation, and was not detected after 30 and 17 days at 4 and 8°C, respectively in traditional yogurt (without probiotic). The E. coli 0157:H7 at 10³ CFU/ml inoculations, its counts increased from 3.69 to 4.51 log CFU/ml during fermentation, and was not detected after 14 and 5 days when stored at 4 and 8°C, respectively, in yogurt containing probiotic L. acidophilus. In samples inoculated with 10⁷ CFU/ml, E. coli 0157:H7 counts decreased from 7.83 to 6.76 log CFU/ml and it was not detected after 22 and 13 days at 4 and 8°C, respectively in yogurt containing probiotic L. acidophilus. The microorganisms grew faster when milk was inoculated with low level of inoculation in acidophilus yogurt (generation time=1.94 h) than traditional yogurt (1.79 h) during the fermentation. The death time (td) decreased with the increase of the refrigeration temperature (from 0.97d at 4°C to 0.36d at 8°C and from 1.22d at 4°C to 0.57d at 8°C in acidophilus and traditional yogurt, respectively) in yogurts with low level of inoculation. Similar results were observed in yogurts with inoculated 10⁷ CFU/ml E. coli 0157:H7. The pH values of the yoghurt ranged from 3.7 to 4.6. The results show that it might be safe to consume the yogurt possibly contaminated by E. coli 0157:H7 after probiotics have destroyed all of them (after 5 days) and are not detectable. In home-made yogurt E. coli 0157:H7 counts will be much lower than experimental level (10⁷ CFU/ml) hence it might be safe to consume the product on production. The results of this study indicate that probiotic containing acidophilus yogurt was more effective in preventing the survival of E. coli 0157:H7 than traditional yogurt during the fermentation and storage period. iii |
| Year | 2007 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. FB-07-12 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Rakshit, Sudip Kumar; |
| Examination Committee(s) | Athapol Noomhorm;Ranamukhaarachchi, S. L.; |
| Scholarship Donor(s) | Ministry of Education, Culture & Science, Mongolia AIT Fellowship; |
| Degree | Thesis (M.Sc.) - Asian Institute of Technology, 2007 |