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Category: Applied and Industrial Microbiology; Food Microbiology
Physical Methods of Food Preservation, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815912/9781555814076_Chap32-1.gif /docserver/preview/fulltext/10.1128/9781555815912/9781555814076_Chap32-2.gifAbstract:
Physical methods of food preservation are those that utilize physical treatments to inhibit, destroy, or remove undesirable microorganisms without involving antimicrobial additives or products of microbial metabolism as preservative factors. Microorganisms can be destroyed by established physical microbicide treatments such as heating (including microwave heat treatment), UV or ionizing radiation, and emerging methods of new nonthermal treatments, such as the use of high hydrostatic pressure, pulsed electric fields (PEFs), oscillating magnetic fields, photodynamic effects, and a combination of physical processes such as heat irradiation, dehydroirradiation, and manothermosonication. Mechanical removal of microorganisms from food may be accomplished by membrane filtration of food liquids. This chapter discusses the microbiological fundamentals of the physical preservation methods outlined above, with the exception of mechanical removal. One of the oldest methods for preserving food is dehydration, and water is one of the most important factors controlling the rate of deterioration of food, by either microbial or nonmicrobial effects. The most effective and most widely used method for destroying microorganisms and inactivating enzymes is heat treatment. Sensitization of microorganisms with the aim of lowering the dose can be obtained by heating and chemical means. During recent years, several other physical treatments such as the use of high hydrostatic pressure and electric and magnetic fields have attracted much interest as promising tools for food processing and preservation and for the creation of new types of food products.
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Bacterial survival curve showing logarithmic order of death and the concept of the D value.
Thermal death time curve showing definition of z value and F value. Tr, reference temperature; τ, death time; lg, log; Dr, D value at the reference temperature; tgα, slope of the thermal death time curve.
Typical radiation survival curves. N, survivors of radiation dose; N 0, original number of viable cells; 1, exponential survival curve; 2, curve characterized by an initial shoulder; 3, concave curve with a resistant tail.
aws of various foods a
Moisture contents of various dry or dehydrated food products when their aw is 0.70 at 20°C a
Minimal aw levels required for growth of foodborne microorganisms at 25°C a
Minimal aw requirements for growth of and mycotoxin production by some toxigenic molds a
Shelf-life extension for raw foods by cool storage a
Relative levels of heat resistance by some vegetative bacteria a
Approximate heat resistance levels (D values) for some bacterial spores
Preservative effects of ionizing radiation
Approximate doses of radiation needed to kill various organisms a
Typical radiation resistance levels of some foodborne microorganisms in fresh and frozen foods of animal origin
Dose requirements for various applications of food irradiation