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Chapter 9 Lecture 3 (Pasteurization- moist heat (Used for milk, ice cream,…
Chapter 9 Lecture 3
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Heat Related Methods
Heat is one of the older and more common means of microbial control. What is its effects of high temperatures:
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Cell death occurs logarithmically. When we measure the effectiveness of heat sterilization we are actually calculating the decimal reduction time.
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Boiling
Kills vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses within 10 minutes at sea level.
Boiling time is a critical factor and different elevations require different times because boiling temperature is lower at higher elevations. So because of this the atmospheric pressure is lower so you need to boil longer than 10 minutes to get same effect.
Some endospores, protozoan cysts, and some viruses (Hepatitis) can survive boiling at sea level for many minutes or even hours (20 hours)
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Autoclaving (moist heat)
True sterilization using heat requires higher temperatures than just boiling water. To achieve this, pressure is applied to boiling water to prevent the escape of heat in steam.
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Scientists have determined that a temperature of 121˚C, 15psi for 15 minutes destroys all microbes in a small volume
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Dry Heat
If we need to control the microbe population in powders and oils, we cannot sterilize them with boiling or with steam. For theses items we use dry heat, like the oven!
Hot air is effective in sterilizing because it denatures proteins and promotes the corrosion (oxidation) of metabolic and structural chemicals
In order to sterilize with dry heat, you need use higher temperatures for a longer time (dry heat penetrates (enters) more slowly)
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Filtration
Is the passage of fluid (liquid or gas) through a sieve designed to trap particles (our particles are cells or viruses) and separate them from the fluid.
Used to sterilize heat sensitive martials like ophthalmic solutions, antibiotics, vaccines, liquid vitamins, enzymes and culture media
So if a scientist is developing a new medication that needs to be injected this would be the most effective way to prepare that medicine
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Moist Heat
Commonly used to disinfect, sanitize, sterilize, pasteurize cells by denaturing proteins and destroying the cytoplasmic membranes.
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Sterility indicators
A biological indicator of sterility will use endospores of bacteria like Bacillus, which will be impregnated into tape. They use endospores because they are very hard to kill.
After autoclaving the tape is aseptically inoculate into sterile broth and if no bacterial growth appears the original material will be considered sterile.
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