Control of microorganisms by using temperature

Control of microorganisms by using temperature

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  Assignment Topic : Controlsof Microorganisms by using Temperature Presented By : Muhammad Farooq Collage Roll no : 870 Subject : Microbiology BS Zoology, 7th Semester
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  Temperature  Microorganisms havea minimum, an optimum, and a maximum temperature for growth.  Temperatures below the minimum usually have a static action on microorganisms. They inhibit microbial growth by slowing down metabolism but do not necessarily kill the organism.  Temperatures above the maximum usually have a cidal action, since they denature microbial enzymes and other proteins. Temperature is a very common and effective way of controlling microorganisms. 1. Low Temperature 2. High Temperature
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  1-Low Temperature  Lowtemperature inhibits microbial growth by slowing down microbial metabolism. Examples include, Refrigeration and Freezing : • Refrigeration at 5°C slows the growth of microorganisms and keeps food fresh for a few days. • Freezing at -10°C stops microbial growth, but generally does not kill microorganisms, and keeps food fresh for several months.
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  2-High Temperature  Vegetativemicroorganisms can generally be killed at temperatures from 50°C to 70°C with moist heat.  Bacterial endospores, however, are very resistant to heat and extended exposure to much higher temperature is necessary for their destruction.  High temperature may be applied as either, a) Dry Heat b) Moist heat • Spores of Clostridium botulinum are killed in 4 to 20 min by moist heat at 120°C, whereas a 2 hours exposure to dry heat at the same temperature is required. • Spores of B. anthracis are destroyed in 2 to 15 min by moist heat at 100°C, but with dry heat 1 to 2 hours at 150°C is required to achieve the same result.
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  a. Dry heat Dryheat kills microorganisms through a process of protein oxidation rather than protein coagulation. 1. Hot Air Sterilization 2. Incineration b. Moist heat Moist heat is generally more effective than dry heat for killing microorganisms because of its ability to penetrate microbial cells. Moist heat kills microorganisms by denaturing their proteins (causes proteins and enzymes to lose their three- dimensional functional shape). It also may melt lipids in cytoplasmic membranes. 1. Pasteurization 2. Fractional Sterilization 3. Boiling Water 4. Autoclaving
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  1-Hot Air Sterilization:  Microbiological ovens employ very high dry temperatures depending on the volume : 171°C for 1 hour 160°C for 2 hours or longer 121°C for 16 hours or longer  They are generally used only for sterilizing glassware, metal instruments, and other inert materials like oils and powders that are not damaged by excessive temperature.  2. Incineration :  Incinerators are used to destroy disposable or expendable materials by burning.  We also sterilize our inoculating loops by incineration.
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  3-Pasteurization :  Pasteurizationis the mild heating of milk and other materials to kill particular spoilage organisms or pathogens. It does not, however, kill all organisms.  Milk is usually pasteurized by heating to 71.6°C for at least 15 seconds in the Flash method or 62.9°C for 30 minutes in the Holding method. 4-Fractional Sterilization :  The method involves steaming liquids and food products at 100°C on several successive days.  The first exposure kills all the vegetative cells, and in the intervals between heatings the remaining spores germinate into vegetative cells which are killed on second and third day.
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  5-Boiling water : Boiling water (100°C) will generally kill vegetative cells after about 10 minutes of exposure.  However, certain viruses, such as the hepatitis viruses, may survive exposure to boiling water for up to 30 minutes, and endospores of certain Clostridium and Bacillus species may survive even hours of boiling. 6-Autoclaving :  Autoclaving employs steam under pressure. Water normally boils at 100°C; however, when put under pressure, water boils at a higher temperature.  Pressure cooker like Apparatus.  When material to be sterilized placed under 15 pounds of pressure, the boiling point of water is raised to 121°C, a temperature sufficient to kill bacterial endospores.
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