Water activity in foods can be controlled lowered by

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Water activity in foods can be controlled (lowered) by: o Freezing water as crystals of pure water o Physical removal of water from food (dehydration) o Removal of some of water from food (concentration) by addition of substances that bind water in food making it unable to participate in chemical and biochemical reactions 4) ACIDS - pH determines rates of chemical and enzymatic reactions as well as survival and growth of microorganisms in foods during processing - Acidity of foods can be adjusted by addition of food grade acids or alkalis or by acids produced through microbial fermentations - pH 4.6 is a critical balue in terms of microbial growth and stability 5) SUGAR AND SALT - Decrease water binding properties in foods - At very high concentrations, may have a dehydration effect on microbial cells 6) OXYGEN - It’s the oxygen in the air or within a food that determines whether a food can support the growth of aerobic or anaerobic microorganisms o So moulds can be inhibited from growing on foods by excluding oxygen - **Removal of oxygen from low acid foods with high eater activity can pose a potential health hazard o Conditions can be created whereby anaerobic disease-causing microorganisms may be able to proliferate and produce toxins that could cause diseases - Vegetables and fish can be safely stored in oxygen-free environment only if the Clostridium botulinum spores are killed by the application of heat 7) FERMENTATION 8) CHEMICALS
9) RADIATION (ENERGY) - Ionization radiation or “food irradiation” can be used to inactivate microorganisms in food, and to destroy storage pests - Microwave treatment of food inactivates enzymes and microorganisms through high temps - Infrared radiation used to toast foods, keep foods hot and to cook foods - Ultraviolet energy is used to sterilize air and water used in food processing Module 6 Methods used in Thermal Processing 1) BLANCHING - Applied mainly to veggies and some fruit by exposing them to heated or boiling water or even culinary steam for short period of time - Designed to: o Inactivate enzymes in plant tissues so that enzymatic degradation does not occur in the interval between packaging and thermal processing or during frozen storage or in early stages of food dehydration o Wilt vegetable products to enable packaging of the products into containers so that proper fill weights can be achieved o Drive off inter- and intracellular oxygen and other gases from plant tissues so that containers are not deformed by excessively high internal pressures (due to expanding gases within the container and to permit formation of a vacuum in the container after thermal processing) 2) PASTEURIZATION - Thermal process that involves using temps at least 72 degrees for 15 seconds (high temp short time) prior to packaging - Basis is to inactivate pathogenic (disease-causing) bacteria and viruses in low acid food products such as milk - Acidic foods (pH < 4.6) mainly pasteurized to inactivate spoilage-causing microorganisms o

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