Drying can be used to control the growth of microorganisms because when water is removed from cells

Drying can be used to control the growth of microorganisms because when water is removed from cells

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Drying can be used to control the growth of microorganisms because when water is removed from  cells, they shrivel and die. To dry foods, they are mixed with salt or sugar. Either draws water out of  microbial cells by osmosis, and they quickly die. One method for achieving drying is lyophilization, a  process in which liquids are quick-frozen and then subjected to evacuation, which dries the material.  Salted meat and sugared fruits are preserved this way.  Cold temperatures are used in the refrigerator to control microbial growth. At low temperatures,  microbial metabolism slows considerably, and the reproductive rate is reduced. However, cold  temperatures do not necessarily kill microorganisms. At freezing temperatures, ice crystals kill many  microorganisms present.  Radiations are also used to control microorganisms when food or other materials are subjected to 
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Unformatted text preview: gamma rays or X rays. The radiations change the chemical composition of microorganisms by forming ions in the organic materials of the cytoplasm. Highly reactive toxic radicals also form. Nonionizing radiations are typified by ultraviolet light. Ultraviolet light affects the nucleic acids of microorganisms, inducing adjacent thymine residues in DNA molecules to bind to one another forming dimers. This binding changes the character of the DNA, making it unable to function in protein synthesis. Cell death soon follows. Although microwaves are a form of radiation, their direct effect on microorganisms is minimal. Microwaves induce water molecules to vibrate at high rates, creating heat. The heat is the killing agent rather than the microwaves....
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This note was uploaded on 11/11/2011 for the course BIO 101 taught by Professor Pesthy during the Fall '07 term at Texas State.

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