Sample Questions

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Sample Questions

Practice QuestionsFood MicrobiologyAssume each of the questions below are worth ten points. Don’t let any fancy languageput you off – that’s just to throw you off the scent! The questions aren’t in any particularorder and remember that you may have information from more that one lecture (or perhapseven module) that would relate to any single question, so take a few minutes to thinkabout the answer and to write some rough notes before you start.1. Write notes on:(a) Bacterial toxins(b) Clostridium perfringens(c) Chemical preservatives.2. What are the main sources of water for drinking?3. Many vegetables are eaten raw. Discuss what microbiological concerns the consumershould have for these vegetables.4. Discuss the mechanisms by which a low A w value produces an antimicrobial effect.5. Discuss the factors that influence the ability of foods to support the growth ofmicroorganisms.6. Discuss the importance of Gram positive bacteria in food fermentations.7. Describe the immunological tests that might be performed to indicate the presence ofbacterial toxins.8. Having a source of potable water “on tap” is taken for granted in the UK. Describe thesteps that are taken to ensure that our drinking water supply is free from pathogens –you may wish to consider potential sources of contamination, water treatment, the useof indicator organisms and the tests used to assess the safety of potable water supplies,in your essay.9. What is a food preservative? Discuss how and why preservatives are used.10. List the microorganisms that are able to survive in properly processed canned foodsand discuss their significance.11. Identify two characteristic species associated with the following and discuss theirsignificance in the following contexts:a. psychrotrophic bacteria in raw milkb. high thermoduric bacteria in raw milk to be used for pasteurised grade A milkc. > 10 coliforms per ml in pasteurised grade A milk.12. Discuss the need for using indicator bacteria for enteric pathogens in food.13. What is the principle behind the control of the growth of microbes using the autoclave,and what is the difference between moist heat sterilisation, pasteurisation andappertisation?14. List the microbiological objectives of low-temperature preservation of food. How dothese objectives differ from food preserved by heat?15. List and discuss five factors that are important in reducing microbial access to foods.16. Describe what you believe are the main function(s) and goal(s) of foodmicrobiologists?S.J.Dewar@hw.ac.uk


17. List and discuss three important factors that differentiate foodborne infection fromfoodborne intoxication. Give an example of each.18. Pooled raw milk at the processing plant has bacterial population of 4x10 5 /mL. It is tobe processed at 79°C for 21 seconds. The average D value at 65°C for the mixedpopulation is 7 min. The Z value is 7°C. How many organisms will be left afterpasteurisation? What time would be required at 65°C to accomplish the same degree oflethality?19. Define the terms “D” value and “z” value as applied to the control of microorganismsusing heat. Explain how these measurements can be used to make milk safe for humanconsumption without affecting the flavour. Use a graph to illustrate your answer.20. Discuss the influence of intrinsic factors associated with microbial spoilage of fruitsand fruit juices and the nature of spoilage of these products produced by thepredominant microflora.21. In the 1920s a typical heat treatment for olives canned in glass jars was 30 min at 210°F. If you know that the D250° F for C. botulinum is 0.1 min and the Z value is 10° F,what would the D210° F be?A 1 minuteB 10 minutesC 30 minutesD 100 minutesE 1000 minutes22. The Z value for Bacterium B is 30° C. The Z value for Nutrient N is 10° C. Given justthese facts, which pasteurisation condition would be the best to maximise the killing ofBacterium B and minimise the destruction of Nutrient N?A Low temperature for a short timeB Low temperature for a long timeC High temperature for a short timeD High temperature for a long timeE None of the above - the Z values don’t provide any guidance23. Define or Explain the Following in Relationship to Their Importance in the FoodIndustry:A Food preservationB D valueC Starter CultureD z valueE 12 D conceptS.J.Dewar@hw.ac.uk

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