Processes that cause food spoilage
Food spoilage is caused by physical, chemical, biochemical, and microbiological processes.
- Physical processes: among the most prominent of factors that cause food spoilage is the water loss that takes place when a product is directly exposed to the environment of its storage container. There is also loss of volatile components in relatively unforeseeable ways that to a great extent determine the aroma and the flavor of the product.
- Chemical processes: these occur through chemical reactions and include the oxidation of fats, which causes rancidity in products.
- Biochemical processes: these are reactions of enzymes, a typical example being the action of the enzyme polyphenol oxidase, which causes the darkening of the products.
- Microbiological processes: these are the action of microorganisms that cause spoilage.
To stop the action of these processes, storage conditions that retard spoilage are necessary. These conditions include temperature, relative humidity, air circulation, and the composition of the environment in the storage container.
Of these, temperature has the greatest impact. As the temperature decreases, all spoilage processes are diminished, resulting in the prolonged life of stored products.
As the relative humidity decreases, evaporation increases as the gradient for the transfer decreases. This, however, benefits the development of microorganisms.
The relative humidity may be higher as the temperature decreases.
However, the storage temperature has limits based on an economic analysis as well as the possible influence on the product.
When air flow increases, evaporation losses increase. This in turn creates a surface for dried products, retarding the development of microorganisms.
Refrigeration is the preservation of products at low temperature, but above their freezing temperature. In general, refrigeration falls between -1 º C and 8 º C. This achieves the nutritional and organoleptic characteristics that barely differ from those of the products at the beginning of storage. It is for this reason that consumers consider refrigerated fresh products to be healthy food.
Refrigeration prevents the growth of thermophilic microorganisms and many mesophiles.
However, achieving the expected results depends on other factors besides temperature and other conditions of storage. The shelf life of refrigerated vegetables depends on the variety, type of storage, the conditions of collection and temperature during transportation, among others. For processed foods, the shelf life depends on the type of food, degree of processing (i.e., primarily microorganisms and enzymes), hygiene of the processing, packaging and container, among others.
In the case of fruit, the respiration rate varies with temperature. In climacteric fruits, the pattern that occurs during storage is an abrupt increase of respiratory activity. These fruits include avocados, mangos and papayas. The non-climacteric fruits, such as oranges, grapefruit and pineapples, do not exhibit this pattern. The respiration of plants is similar to that of non-climacteric fruit.
When the temperature of some fruits and vegetables decreases to a certain value, undesirable changes occur which are known as chill damage.
In animal tissues, slaughter ends the supply of oxygenated blood, stopping aerobic respiration and starting anaerobic respiration. Glycogen is then converted into lactic acid, which causes a decrease in pH and initiates the process called rigor mortis. As a result of this process, muscle tissue hardens, making it inextensible.
Because this process occurs, and for the product to reach the right color and texture, it must occur during refrigeration to slow the growth of microorganisms.
Refrigeration can be used alone or in combination with other techniques, such as irradiation, modified and controlled atmospheres, and certain types of packaging, among others.
Refrigeration is widely used in the preparation of ready-to-eat meals using the concept of cooking-cooling systems.