Food Spoilage and Physical Factors

Food spoilage can also be caused by physical factors, such as temperature, moisture and pressure acting upon the foods. Moisture and heat can also produce hydrolytic rancidity in fats; in this case, fats are split into free fatty acids, which may cause off odors and rancid flavors in fats and oils. 

Excessive heat denatures proteins, breaks emulsions, removes moisture from food and destroys nutrients such as vitamins. However, excessive coldness, such as freezing, also discolors fruits and vegetable, changes their texture and/or cracks their outer coatings to permit contamination by organisms. 

Food under pressure will be squeezed and transformed into unnatural conformation. The compression will likely break up the surface structure, release degradative enzymes, and expose the damage food to exterior microbial contamination. 

Many health officials consider physical factors to include such things as sand, glass, wood chips, rat hair, animal urine, bird droppings, insect parts and so on. These things may not spoil the food, but they do present hazards. Some these foreign substances do lead to spoilage. 

Furthermore, insects and rodents can consume and damage stores foods and insect can lay eggs and leave larvae in the foods, causing further damage later. Such foods are no longer reliable since they contain hidden contaminants. The attacks of the by insect and rodents can also contaminate foods further with microbial infections. 

Food Spoilage and Physical Factors

Canning Processing of Acid Foods

Canning Processing of Acid Foods
Acid foods are considered to be those that have a pH of 4.5 or lower. Acid foods that are canned need not be heated at high temperatures to attain commercial sterilization. The reason for this is that bacteria, including those that form heat resistant spores, are more easily destroyed by heat when present in acid solutions. Moreover, spore forming bacteria generally will not grow in foods having pH values of 4.5 or less. There are some exceptions to this; for instance, Bacillus thermoacidurans may grow in tomato juice (maximum pH 4.5) and cause spoilage.

Acid foods are ordinarily processed by heating the cans in boiling water until all parts of the product have reached 180 – 210 degree F, and then are cooled. An exception is tomato juice, which is now often processed by flash heating to 250 degree F, holding at this temperature for 0.7 min, cooling to 200 – 210 F, filling into presterilized cans, sealing , and inverting the can so that the sterilizing effect of the heat at that pH will act upon the can cover.

Those foods that have a pH of 4.5 or less are apples and apple juice, apricots, blackberries, blueberries, boysenberries, cherries, cherry juice, a citrus fruit, and their juice, currants, gooseberry, loganberries, papaya juice, peaches, pears, pickles, pineapples in various forms and pineapples juice, plum, prune juice, raspberries, rhubarb, sauerkraut and sauerkraut juice, strawberries, tomatoes, tomato juice and youngberries.
Canning Processing of Acid Foods