Fundamental Food Microbiology, Third Edition - Fuad Fathir

CONTROL BY HEAT 465
always be used, other methods are used mainly to prevent growth of microorganisms
as well as to maintain acceptance qualities of food. One such method is low temperature
and is discussed in Chapter 33.
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REFERENCES
1. Olson, J.C., Jr. and Nottingham, P.M., Temperature, in Microbial Ecology of Foods,
Vol. 1, Silliker, J.H., Ed., Academic Press, New York, 1980, p. 1.
2. Gould, G.W., Heat induced injury and inactivation, in Mechanism of Action of Food
Preservation Procedures, Gould, G.W., Ed., Elsevier Applied Science, New York,
1989, p. 11.
3. Pflug, I.J., Calculating F t- values for heat preservation of shelf stable low acid canned
foods using the straight-line semilogarithmatic model, J. Food Prot., 50, 608, 1987.
4. Anonymous, Sterilization methods: principles of operation and temperature distribution
studies — symposium, Food Technol., 44(12), 100, 1990.
5. Heddleson, R.A., and Doores, S., Factors affecting microwave heating of foods and
microwave induced destruction of foodborne pathogens, J. Food Prot., 57, 1026, 1994.
6. Anonymous, Dielectric and ohmic sterilization: symposium, Food Technol., 46(12),
50, 1992.
QUESTIONS
1. Discuss the ideological differences in the use of heating in food preservation
before and after 1870 A.D.
2. List the microbiologically related objectives of heating a food.
3. Describe the mechanisms of sublethal and lethal heat injury in bacterial cells and
spores. How can stress proteins alter this effect in food processed slowly at low
heat?
4. List three important factors that one should consider in designing thermal preservation
of a food. Discuss the implications of one of the factors.
5. Define D value, Z value, F value, and 12D value. Draw hypothetical plots to show
how D and Z values can indicate relative heat resistance of two microbial species.
6. List the objectives of pasteurization of food. How do these objectives differ from
those used in commercial sterilization of foods? Use a food system for each
method of treatment to justify your explanations.
7. How does microwave heating differ from conventional heating to ensure food
safety?
8. The SPC/ml of raw milk from two suppliers is as follows: (A) SPC/ml 95,000
(with thermodurics 15,000/ml) and (B) SPC/ml 65,000 (with thermodurics
25,000/ml). Briefly discuss D value differences that a processor has to adopt to
meet the legal bacterial counts for pasteurized Grade A milk. Can both be sold
as Grade A pasteurized milk? Explain.