More notes:
Food deterioration. The major causes of food deterioration are microorganisms, action of enzymes, chemical reactions, physical changes, time, and insects and/or rodents, multiple can be operating at the same time.
Microorganisms. Bacteria, molds, and yeasts.
Bacteria. Unicellular microorganisms of many forms. Some bacteria produce spores which are remarkably resistant to heat, chemicals, and other adverse conditions. Bacterial spores are far more resistant than yeast or mold spores, and more resistant to most processing conditions than natural food enzymes. All bacteria associated with foods are small, most are of the order of one to a few microns in cell length and somewhat smaller than this in diameter. (A micron is one-thousandth of a millimeter (0.001 mm) or about 0.00004 inch.) All bacteria can penetrate the smallest of openings, and many can pass through the natural pores of an egg shell once the natural bloom of the shell is worn or washed away.
Yeasts. Somewhat larger than bacteria, of the order of 20 microns in individual cell length and about half this size in diameter. Most yeasts are spherical or ellipsoidal in shape. Fresh vegetables, meat, poultry, and cheese often contain yeasts, but in these foods, bacteria outgrow the yeasts. When bacterial inhibitors are added, yeasts can dominate. Some yeasts are found in foods such as honey, molasses, sugar, and fruit. Salt-tolerant yeasts grow as films on brine food and on salted food and ham.
Molds. Larger than bacteria and yeast, they grow by a network of hair-like fibers called mycelia and send up fruiting bodies that produce mold spores referred to as conidia. The blackness of bread mold and the blue-colored veins of blue cheese are due to the conidia, while beneath the fruiting heads, the hair-like mycelia anchor the mold to the food. The mycelia are a micron or so in thickness and, like bacteria, can penetrate the smallest opening; or in the case of weakened skin or shell can digest the skin and make their own route of penetration.
Enzymes. Organic catalysts which are produced by the cells of animals, plants, or bacteria. Microorganisms possess enzymes which produce fermentation, rancidity, and putrefaction, likewise uninfected food plants and animals have their own enzyme complement. Unless these enzymes are inactivated by heat, chemicals, or other means, they continue to catalyze chemical reactions within foods. Some reactions to some levels are desirable, for example ripening of tomatoes after they are picked and natural tenderizing of beef on aging, but beyond an optimum point it becomes food deterioration.
Chemical. Examples include oxidation, color changes, reactions between a food container and its contents, and
the coagulation of proteins. A rule of chemistry states that for every 18ºF (10ºC) increase in temperature, the rate of a chemical reaction doubles. Applied to foods every such rise in temperature cuts food shelf life by half.
Physical changes. May cause food spoilage, or deteriorative changes such that the food is unsuitable to use. Examples:
Freezing. May cause destruction of emulsions and texture. Products such as salad dressing and mustard, contain a fat/oil and water mixture which does not combine without special processing or additives. When frozen the emulsion is destroyed and the fat and water separate. Fruits and vegetables will have their texture disrupted. Skins will crack, leaving the food susceptible to attack by microorganisms. The texture of canned fruits and vegetables becomes softened and mushy due.
Cold damage. Many fruits and vegetables as living systems have optimum temperature requirements. At common refrigeration temperatures of about 41ºF (5ºC), several fruits and vegetables are weakened or killed. Bananas, lemons, squash, and tomatoes are examples of products that should be held at temperatures no lower than 50ºF (10ºC) for maximum quality retention.
High Temperature. Most food should be stored between 50º-100ºF (10º-38ºC). Excessive heat can denature proteins, break emulsions, dry out foods by removing moisture, and destroy vitamins. Excessive heat in green vegetables causes cell walls and membranes to lose their integrity, acids and enzymes to be released, resulting in soft texture, off-colors and off-flavors. On muscle tissue proteins are denatured, proteins clump, and enzymes are inactivated, resulting in toughening texture, loss of waterholding capacity, cooked or caramel flavors, and development of off-colors.
Dehydration. Meat is 70 to 75 percent water. Fresh fruits and vegetables 80 to 95 percent water. When the humidity is too low in a storage area, dehydration results.
Excessive Moisture. Dried, dehydrated, and freeze-dried foods are very hygroscopic (readily taking up and retaining moisture) & if not properly packaged become lumpy or caked. A slight condensation on a food surface can become a pool for the multiplication of bacteria or the growth of mold. In a moisture-proof package, food materials such as fruits and vegetables can give off moisture from respiration and transpiration. This moisture is then trapped within the package and can support the growth of microorganisms.
Mechanical Damage. Damaged foods are more susceptible to invasion by microorganisms. Cell walls destroyed by mechanical abrasion liberates the inherent enzymes, these can begin deterioration.
Light. Can cause fading of color. Some vitamins are destroyed by light, notably riboflavin, vitamin A, and vitamin C. Milk in bottles exposed to the sun develops "sunlight" flavor due to light induced fat oxidation and changes in the protein. Sensitive foods can be protected by impervious packaging.
Potato warning. After exposure for two days or longer the skin and the flesh may develop chlorophyll and an alkaloid called solanine. The green tubers acquire a bitter, pungent taste. If eaten in quantity, they may be poisonous. Solanine is the bitter and poisonous component. Chlorophyll is tasteless and harmless.
Time. After slaughter, harvest, or manufacture there is a transitory period until the food succumbs to the above deterioration factors. The longer the time, the greater the destructive influences. Certain cheeses, sausages, wines, and other fermented foods are improved with aging up to a point, however, for the vast majority of foods, quality decreases with time, and the major goal of food handling and preservation practices is to capture and maintain freshness. Storage life is determined to a great extent by type of food, method of processing, method of packaging, and storage environment.
Insects & Rodents.
Insects are particularly destructive to cereal grains and to fruits and vegetables. When insects eat they damage the food and open it to bacteria, yeast, and mold infection. Insects are generally controlled in grain, dried fruits, and spices by fumigation with chemicals, the use of which may be prohibited in foods high in moisture because of the possible formation of toxic substances. Eggs may persist or be laid in the food after processing, as for example in flour.
Rodents. They not only consume but contaminate foods with urine and droppings may harbor several kinds of disease-causing bacteria. One rat pill, or fecal dropping, can contain several million bacteria. Even if the pill does not get into food directly, it will become dry and fall apart or be crushed. The particles then may be blown or carried into food.
Pest-proof the building. Deprive pests of food and shelter by following good housekeeping practices. Use appropriate control measures to exterminate pests.
Food is a very complex item composed of many substances, some of which are carbohydrates, proteins, fats, water, minerals, vitamins, emulsifiers, stabilizers antioxidants, and many others. It is the combination of these components which makes one food different from another. Also, each of these components is susceptible to a different form of deterioration, and the changes are subtle and complex. Realizing these facts, there are several deteriorative conditio
