Many students have problems in understanding the mathematics describing the destruction of microorganisms by heat. Log reductions of pathogens and equivalent time-temperature treatments along with the associated lethalities account for a large part of the harder to understand topics. The quiz below is a simple test of of some of the basic concepts. Note Z value is not dealt with in this quiz. If there is sufficient interest I will provide the answers.

Heat Processing Quiz

1. An important aspect of thermal processing is obtaining the requisite number of log10 (or decimal) reductions of target pathogens.

If a sous vide sea-food dish contains 1000 spores / g of non-proteolytic Clostridium botulinum before processing and the heat process reduces their number by 6 log reductions what is the final concentration of Cl. botulinum in the product?

2.What do you understand by a 12 D process?

3. Non-proteolytic Cl.  botulinum is particularly important in minimally processed food that is refrigerated and hermetically sealed.

3.1 Why is it important in these products?

3.2 How is it controlled?

4.There are two main types of Clostridium botulinum important in heat-processed food.
Give 3 significant differences between them that are important technologically.




5. What Fo value must be achieved in heat-processing low acid foods?

6. You have been advised that a batch of canned mushrooms received a heat treatment equivalent to 2 minutes at 121.1°C. What would you do with this product if you were the production manager e.g. reject, approve, release or other action?

7. The D value for proteolytic Cl. botulinum at 121.1°C is 0.21 minutes.  How many log reductions of Cl. botulinum would be achieved if a Fo value of 12 was achieved?

8. Food processors are required to achieve a heat treatment of  ?  minutes at ? °C  or equivalent and a minimum of  ? log reductions of non-proteolytic Clostridium botulinum in a refrigerated, hermetically sealed product that will be held for more than 10 days at 5°C?

9. Proteolytic Cl. botulinum can grow at 5°C. True or false?

10. Proteolytic Cl. botulinum cannot grow below 10°C. True or false?

11. Non-proteolytic Cl. botulinum can grow at 5°C. True or false?

12. A sous vide lamb joint receives a heat treatment equivalent to 3 minutes at 90°C. Assume a D value of this organism of 1.1 minutes at 90°C.

12.1. Calculate the number of log reductions of non-proteolytic Cl. botulinum in this product.

12.2. If you were the QA manager what would you do with this product?

13. A sous vide lamb joint receives a heat treatment equivalent to 8 minutes at 90°C. Assume the D value of non-proteolytic Cl. botulinum is 1.1 minutes at 90°C.

13.1. Calculate the number of log reductions of non-proteolytic Cl. botulinum.

13.2. If you were the QA manager what would you do with this product?

14. If cooling is too slow after heating following sous vide production, spoilage and potentially food poisoning can occur.

14.1. Name the organism that is the major cause of food poisoning as a consequence of slow cooling of meat.

14.2. Why is this organism so dangerous?

14.3. How is this organism controlled?

15. In determining the heat process for a soup being processed using a heat exchanger it is necessary to calculate the type of fluid flow that is taking place.

15.1. Names the types of fluid flow.

15.2. Why is the type of fluid flow important?

16.  Where should the thermocouple be placed during process validation of a heat-treated food product?

17. You have determined that the critical target pathogen for a novel pasteurised meat product is Listeria monocytogenes.  How would you calculate the minimum process time to render the product safe?

How to cite this article

Mullan, W.M.A. (2015). [On-line]. Available from: . Accessed: 23 March, 2023.  

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