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Radiation shorter wavelengths have more energy and

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Unformatted text preview: ficient time (~12 hours) Limitations: irritates the skin so not an antiseptic Chemical Methods Chemical Methods 8. Heavy Metals: i.e. mercury, zinc, arsenic, copper, silver Combine with proteins and inactivate them, sometimes precipitate proteins Benefits: good germicides Limitations: extremely toxic and ‘burn’ on skin Used as antiseptics­ Mercurachrome, zinc oxide, silver nitrate (newborns’ eyes) Used as disinfectants: copper sulfate in swimming pools and fountains Chemical Methods Chemical Methods 9. Radiation: Shorter wavelengths have more energy, and are more destructive Gamma rays: ionizing radiation Produces biologically harmful reactive molecules (superoxide and hydroxyl radicals) that then damage different cellular components Used for heat­sensitive materials, medical equipment, drugs & some foods; can be done after packaging Chemical Methods Chemical Methods 9. Radiation Ultraviolet radiation: sunlight Damages nucleic acids (DNA) by creating thymine dimers (result is poor transcription and bad proteins) Actively multiplying microbes killed, but endospores are resistant UV rays penetrate tissues poorly but damage skin and eyes Chemical Methods Chemical Methods 9. Radiation Microwaves Do not kill organisms directly, but can with heat they generate Damage is considered “indirect” Preservation of Perishables Preservation of Perishables Chemical preservatives prevent or slow the growth of microbes Food preservatives must be safe Benzoic acid and sorbic acids may alter the cell membranes and energy generation of bacteria Nitrites and nitrates are used in meats Low temperature storage may be used (refrigerate or freeze) Preservation of Perishables Preservation of Perishables Prevent water from being available for pathogens: Add large amounts of sugar (as in jams), and salt (as in salted fish, pickles); water leaves the cell Dessication (drying) can use natural means (sun­drying) Lyophilization (freeze drying), food is frozen and dried in a vacuum...
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