Thermal processing
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- Written by Super User
Food technologists producing acidic foods such as pickles and sauces often find it difficult to get information on the processing conditions required to obtain commercially sterile products. Following experience of working with processors experiencing technical issues including spoilage problems and difficulties in exporting products I have produced a focussed and concise Ebooklet that:
1) Identifies the potential spoilage organisms of acidic foods
2) Discussed the decimal reduction times and Z-values of the major spoilage organisms of acid foods
3) Lists F or P values and reference temperatures for ensuring the production of commercially sterile acid foods
4) Explains how to calculate F values and the number of log reductions of spoilage organisms following processing
5) Explains the importance of measuring pH over the shelf life of acidified products
6) Provides a summary insight to some causes of spoilage of acidic foods and their control
7) Lists literature concerning the manufacture and control of acid foods.
The booklet can be used on an IPhone or Android device that can view PDF files.
This 16 page booklet contains 15 pages, 5 tables and 16 references (figure 1).
It is divided into the following sections:
Introduction
Microorganisms that are of significance in processing acidic foods and their resistance to heat
Sensitivity of spoilage organisms to pH and acids
Destruction of microorganisms by heat
Calculating the number of log reductions of a spoilage organism by a thermal process
Spoilage of acidified foods
Time–temperature recommendations for the heat treatment of acidic foods
Public health significance of spoilage in acidic foods
Monitoring changes in pH throughout product shelf life
Conclusions
Copyright and legal matters
Literature cited
Annex 1. Glossary of terms used.
Figure 1. Ebook
It is available as an immediate download following a donation to the Diary Science and Food Technology website. Only make this donation if you understand that you are receiving an educational aid to help you understand the scientific and technological factors influencing the production of commercially sterile acid and acidified foods.
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- Written by Michael Mullan
In this section we are going to use simple mathematical techniques, associated with thermobacteriology, to investigate the survival of Mycobacterium avium subsp. paratuberculosis during high temperature short time, HTST, pasteurisation. This organism is often abbreviated M. paratuberculosis, M. avium sub. paratuberculosis or MAP. Two simple equations describing the death of microorganisms by thermal processing have been used to construct several calculators that make it fairly easy for students and others to predict MAP levels in milk following thermal processing.
The methodology used could also be used to investigate the effects of pasteurisation on the destruction of salmonella or say Enterobacter sakazakii ( E. sakazakii has recently been reclassified as a number of distinct species within a new Genus, Cronobacter).
Why study MAP? MAP is interesting for several reasons e.g. there is public health concern about this organism since it has been linked to Crohn’s disease and there is also debate regarding whether it is killed by HTST treatments.
At the end of the article there is an assignment that can be undertaken using the calculators.
This exercise with appropriate adaption should be suitable for second and third year undergraduates in microbiology or food science and students undertaking taught Masters Degrees in Microbiology/Food Science/Food Technology. The exercise could also be used as part of an in company staff development programme. Note prior to undertaking this exercise some prior knowledge of the effects of temperature on the death of microorganisms is required. The calculators can also be used to investigate the effects of thermal processing on the survival of pathogens and thermoduric/thermophilic organisms.
PUBLIC HEALTH SIGNIFICANCE OF MAP
Both Crohn’s disease, a human illness of unknown cause and Johne’s disease,a disease of cattle and other ruminants caused by MAP, are chronic, incurable, inflammatory bowel diseases.
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- Written by Michael Mullan
The calculator converts temperature readings to lethal rates, plots the lethal rates against time, and determines F values for a heat process. The area under the curve is determined using the trapezoid rule. Accurate F determinations for most thermal processes can be obtained. In general the more values, the more accurate the value for F will be.
The lethal effect of high temperatures on microorganisms is dependent on both temperature and holding time.
