Understanding Food Chapter 7: Food Preservation
Food Spoilage Biological Changes • Yeast:A fungus (a plant that lacks chlorophyll) that is able to ferment sugars and that is used for producing food products such as bread and alcohol. • Fermentation:The conversion of carbohydrates to carbon dioxide and alcohol by yeast or bacteria.
Food Spoilage Chemical Changes • Chemical reactions or changes also contribute to food deterioration. • Enzymes play a significant role in catalyzing these reactions and can be categorized by the substance on which they act (substrate) or their mode of action. An example: • Proteases, also called proteolytic enzymes, split proteins into smaller compounds.
Food Spoilage Physical Changes • The most common physical changes occurring in foods as they spoil are evaporation, drip loss, and separation. • Dehydrate:To remove at least 95% of the water from foods by the use of high temperatures. • Freeze-dry:To remove water from food when it is in a frozen state, usually under a vacuum.
Food Preservation Methods • Drying is the food preservation process that consists of removing the food’s water, which effectively inhibits the growth of microorganisms. Like: • Sun Drying
Food Preservation Methods Commercial Drying • The most important types of commercial drying are: • Conventional: heat. • Vacuum: pulls the water out. • Osmotic: water drawn out by osmosis. • Freeze-drying: ice crystals vaporize.
Food Preservation Methods Sublimation:The process in which a solid changes directly to a vapor without passing through the liquid phase.
Food Preservation Methods • Cure:To preserve food through the use of salt and drying. Sugar, spices, or nitrates may also be added. • Fermentation • Pickling uses vinegar to preserve foods. • Edible coating:Thin layer of edible material such as natural wax, oil, petroleum-based wax, etc. that serves as a barrier to gas and moisture.
Food Preservation Methods • Carbohydrates are required for the fermentation process. • Throughout Asia, vegetables are still commonly fermented. • In North America, foods most often preserved by fermentation are cucumbers, olives, and cabbage.
Food Preservation Methods The purpose of edible coatings is fourfold: 1. To increase shelf life by acting as a barrier to moisture, oxygen, carbon dioxide, volatile aromas, and other compounds whose loss would lead to deterioration. 2. To impart improved handling characteristics, such as the ability to bend more easily without breaking. 3. To improve appearance through increased gloss and color. 4. To serve as a vehicle for added ingredients such as flavors, antioxidants, antimicrobials, etc.
Food Preservation Methods • Canning is a two-step process: • First the food is prepared by being packed into containers, which are then sealed. • Then the containers are “canned,” or heated to ensure that all microorganisms are destroyed. • Sterilization:The elimination of all microorganisms through extended boiling/heating to temperatures much higher than boiling or through the use of certain chemicals.
Pressure cooker Canner
Cold Preservation • Refrigeration slows down the biological, chemical, and physical reactions that shorten the shelf life of food. • For safety purposes, refrigerators should be kept between just above freezing to no more than 40°F (4°C). • All perishable foods should be refrigerated as soon as possible, preferably during transport, to prevent bacteria from multiplying.
Cold Preservation • Freezing makes water unavailable to microorganisms. • The chemical and physical reactions leading to deterioration are slowed by freezing. • Rancid:The breakdown of the polyunsaturated fatty acids in fats that results in disagreeable odors and flavors. • Freezer burn:White or grayish patches on frozen food caused by water evaporating into the package’s air spaces.
Heat Preservation • Pasteurization:A food preservation process that heats liquids to 160°F (71°C) for 15 seconds, or 143°F (62°C) for 30 minutes, in order to kill bacteria, yeasts, and molds.