Lecture - Physical Preservation Methods

Lecture - Physical Preservation Methods - PHYSICAL METHODS...

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Click to edit Master subtitle style PHYSICAL METHODS OF FOOD PRESERVATION Physical methods of food preservation are those that utilize physical treatments to inhibit, destroy or remove undersirable microorganisms without using additives or products of microbes.
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PHYSICAL DEHYDRATION PROCESSES Water is one of the most important factors controlling the rate of spoilage of food by microbial or non- microbial effects. The availability of water is measured by the water activity (aw) of a food, defined as the ratio of the vapor pressure of water in a food, P, to the vapor pressure of pure water, Po at
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Click to edit Master subtitle style Water activity Aw = P/Po
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Water activity Most spore forming bacteria do not grow below Aw 0.93. Germination and outgrowth of spores of Bacillus cereus are prevented at 0.97-0.93. Minimum aw for growth and spore germination C. perfringens is 0.97- 0.95.
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Water activity In general, among bacteria, gram negative species (Enterobacteriaceae 0.96) have the highest water activity requirement (Pseudomonas 0.93). Less sensitive to reduced water activity are gram- positive non-spore forming bacteria (Lactobacillus/0.94). Staphylococci are unique among nonhalophilic
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Water activity Several species of yeasts have aw requirements much lower than those of bacteia. Salt tolerant species such Debaryomyces and Hansenula and Candida may grow well on cured meats and pickles at salt concentrations of 11% (aw=0.93). Some osmophilic species (Zygosaccharomyces) are able to
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Water activity In general, molds have aw requirements much lown than those for other groups of foodborne microorganisms. However, molds with sporangiospores have greater moisture requirements and germination of their spores may be inhibited at aw 0.93. The most common xerotolerate
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Water activity The minimal aw for their growth is in the range of 0.71-0.77. The relationship of aw and toxin production is complex . It is of great public health importance that the minimal aw is higher than that for growth. (when molds grow they do not produce toxin) Differences in aw limits for growth
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DRYING Hot air drying of solid foods has two functions . It transfers heat to evaporate water from the food and carries away the vapor produced. In the process of drying microorganisms on the raw food are affected by the drying temperature and changes in the aw. The aw of dried foods us usually lower than the
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FREEZE-DRYING Freeze-drying (lyophilization) is a combined method of food preservation. The principle is dehydration of foods
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Lecture - Physical Preservation Methods - PHYSICAL METHODS...

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