【正文】 e and dryness E. Oxygen F. Light G. Time A. Microanisms (bacteria, yeasts and molds) More types of microanisms can spoil food than cause foodborne disease. Sources of these microanisms: soil, water, air, food itself, humans, food equipment environment. Healthy living tissue (internally) is usually sterile, hence the presence of spoilage anisms is mostly the result of contamination. Bacterial endospores are most difficult to inactivate. Heat and moisture will increase growth and activities of microanisms. Molds as pared to bacteria can generally grow at: lower pH (more acid conditions), lower moisture contents (dryer conditions), higher salt concentrations, and lower temperatures (in refrigerated foods). Molds usually only a problem with spoilage, not safety, but Aspergillus flavus and Aspergillus parasiticus produce aflatoxins which are potent hepatocarcinogens. Molds require oxygen for growth. B. Insects and rodents Insects destroy 5 to 10% of . grain crop annually (in other parts of the world it can reach 50%)。 vegetables. In nonrespiring foods in a moisturebarrier package can give up moisture, changing the relative humidity of the package headspace and with a drop of temperature, condensation in the package occurs. Excessive drying leads to undesirable texture changes and appearance. E. Oxygen 1. A very highly reactive element of the atmosphere. 2. Molds and aerobic bacteria require oxygen for growth so vacuum packaging or modifiedatmosphere packaging (MAP) works well against these spoilage anisms. F. Light 1. Visible light is a source of energy. 2. Inactivates some vitamins and causes deterioration of many food colors and flavors. 3. Opaque packaging will protect lightsensitive foods. G. Time 1. Peak time for quality is usually immediately or soon after harvest, slaughter or manufacture. 2. Exceptions are those foods aged/fermented, such as cheeses and wines. VI. Principles of food preservation A. Keep food alive as long as possible. B. If food must be killed (., for meat) clean it, cover it, and cool it as quickly as possible. ? Keeping the food alive as long as possible if often not feasible, and deterioration of perishable foods can only be delayed a short time. VII. Control of microanisms Heat Cold Drying Acid Sugar Smoke Atmospheric position Chemicals Radiation VIII. Control of enzymes and other factors A. Enzymes probably the second greatest cause for food spoilage. B. Many of same principles for food preservation apply for enzymes as for microanisms. ? For example, when a food is pasteurized, enzymes are denatured and thus rendered inactive. ? When a food is refrigerated to slow down the growth of microanisms, so is the activity of enzymes slowed down. C. However, some food enzymes may be more resistant to preservation effects than microanisms。 some enzymatic activities can be accelerated following death. Can be controlled by refrigeration or blanching. C. Heat and cold can cause deterioration of food if not controlled Excessive heat denatures proteins, breaks emulsions, dries out foods, and destroys vitamins. Uncontrolled cold will damage fruits amp。 samples are coded so that source or identity of food sample is unknown to taster. Most mon is the triangle test (a preference test): Selecting the sample that differs from two others (total of 3 samples). Usually no more than 5 samples tested at one sitting。 pressing oil from peanuts and soybeans) Liquid from a liquid (., centrifuging oil from water) Removing a gas from a liquid or solid (., pulling a vacuum) A. Hand sorting and grading still very mon (., fruits amp。 Projections: 1830: World human population reaches 1 billion 1930: 2 billion 1960: 3 billion 1975: 4 billion 1999: 6 billion [Assuming a 64year human life expectancy, of all the people born on earth since its creation, 2/3 are now alive.] 2030: 9 billion Biggest increases are expected in some of the poorest areas, such as Africa, southern Asia, and South America. Human population of Africa will double in 23 years. Population of South America will double in 29 years. Population of Europe will double in 343 years. Pr