Refrigeration or cold storage of food is a gentle method of food preservation. It has minimum adverse effects on the taste, texture, and the nutritional value of foods. It must be kept in mind, however, that refrigeration has a limited contribution towards preserving food. For most foods, we can expect refrigeration to extend the shelf-life by a few days. In many cases, refrigeration is not the sole means of preserving the food. For example, milk is first heat processed (Pasteurized), and then refrigerated. The heat treatment destroys the pathogenic microorganisms and reduces the total microbial load as well as inactivates the enzymes in the milk. Refrigeration will keep the spoilage reactions (microbial or enzymatic) to a minimum. Remember, refrigeration does not kill microorganisms or inactivate enzymes, rather it slows down their deteriorative effects.
Refrigeration temperature is a key factor in predicting the length of the storage period. For example, meat will last 6-10 days at 0° C, one day at 22° C and less than one day at 38° C. Household refrigerators are usually run at 4.7 -7°C. Commercial refrigerators are operated at a slightly lower temperature. On an average day, the room temperature is 25° C, so the longer you leave food on the kitchen counter, the sooner it will spoil. Most spoilage microorganisms prefer warmer temperatures, but there are a group of microorganisms called psychrophilic which will grow at refrigerated temperatures.
When cooling is used as a preserving technique, it is essential that the food is maintained at the proper cold temperature during manufacturing, transport, display and home storage. Signs of spoilage in refrigerated foods vary with the food product. In fruits and vegetables loss of firmness or crispness takes place. Red meat will change in color, while fish will get softer with noticeable drippage. Refrigerated food will last longer if it is cleaned and properly packaged prior to refrigeration and, of course, maintained at the proper temperature with minimum exposure to surrounding temperatures.
Since refrigeration is an energy-demanding process that must be maintained throughout the life of the product, refrigerated foods tend to cost more than non-refrigerated foods. Yet, today's consumer is buying more refrigerated foods for their fresh quality. When attempting to preserve the high quality of refrigerated foods, the consumer need only follow one key rule: keep cold food cold.