9.Cases and spoilage type due to temperature and time abuse:
9.1.Refrigeration and freezing:
Refrigeration slows down the chemical and biological processes in foods and the accompanying deterioration and the loss of quality. The storage life of fresh perishable foods such as meats, fish, fruits, and vegetables can be extended by several days by cooling, and by several weeks or months by freezing. For example, fruits and vegetables continue to respire and generate heat during storage; most foods freeze over a range of temperatures instead of a single temperature; the quality of frozen foods is greatly affected by the rate of freezing; the velocity of refrigerated air affects the rate of moisture loss from the products addition to the rate of …show more content…
It was determined that the rate of freezing has a major effect on the size of ice crystals and the quality, texture, and nutritional and sensory properties of many foods. During slow freezing, ice crystals can grow to a large size, whereas during fast freezing a large number of ice crystals start forming at once and are much smaller in size. Large ice crystals are not desirable since they can puncture the walls the cells, causing a degradation of texture and a loss of natural juices during thawing. A crust forms rapidly on the outer layer of the product and seals in the juices, aromatics, and flavoring agents. The product quality is also affected adversely by temperature fluctuations of the storage room.
The ordinary refrigeration of foods involves cooling only without any phase change. The freezing of foods, on the other hand, involves three stages: cooling to the freezing point (removing the sensible heat), freezing (removing the latent heat), and further cooling to the desired subfreezing temperature (removing the sensible heat of frozen …show more content…
Loss of quality may be seen in the frozen product, e.g. freezer burn, discoloration, mechanical damage, but in many cases the loss of quality is not noticeable until after thawing and cooking. Most of the mechanisms of quality loss are determined by storage temperature and are accelerated with time spent above the recommended value. They are also promoted by temperature fluctuations
Ice and water can damage food materials in many ways, including
1. Unfrozen water. Even below –18oC, up to 10% water can be unfrozen and take part in physical and biochemical reactions.
2. Freezing damage – the expansion of water as it turns to ice can cause structural damage to the food. This is often the cause of large voids and excessive drip loss in frozen materials after thawing. The effect can be minimised by freezing rapidly and maintaining low and consistent temperatures during frozen storage.
3. ‘Ostwald ripening’ – this is the tendency for large ice crystals to grow at the expense of smaller ice crystals. The effect is to induce freezing damage. It can be minimised by maintaining low and consistent storage
9.1.Refrigeration and freezing:
Refrigeration slows down the chemical and biological processes in foods and the accompanying deterioration and the loss of quality. The storage life of fresh perishable foods such as meats, fish, fruits, and vegetables can be extended by several days by cooling, and by several weeks or months by freezing. For example, fruits and vegetables continue to respire and generate heat during storage; most foods freeze over a range of temperatures instead of a single temperature; the quality of frozen foods is greatly affected by the rate of freezing; the velocity of refrigerated air affects the rate of moisture loss from the products addition to the rate of …show more content…
It was determined that the rate of freezing has a major effect on the size of ice crystals and the quality, texture, and nutritional and sensory properties of many foods. During slow freezing, ice crystals can grow to a large size, whereas during fast freezing a large number of ice crystals start forming at once and are much smaller in size. Large ice crystals are not desirable since they can puncture the walls the cells, causing a degradation of texture and a loss of natural juices during thawing. A crust forms rapidly on the outer layer of the product and seals in the juices, aromatics, and flavoring agents. The product quality is also affected adversely by temperature fluctuations of the storage room.
The ordinary refrigeration of foods involves cooling only without any phase change. The freezing of foods, on the other hand, involves three stages: cooling to the freezing point (removing the sensible heat), freezing (removing the latent heat), and further cooling to the desired subfreezing temperature (removing the sensible heat of frozen …show more content…
Loss of quality may be seen in the frozen product, e.g. freezer burn, discoloration, mechanical damage, but in many cases the loss of quality is not noticeable until after thawing and cooking. Most of the mechanisms of quality loss are determined by storage temperature and are accelerated with time spent above the recommended value. They are also promoted by temperature fluctuations
Ice and water can damage food materials in many ways, including
1. Unfrozen water. Even below –18oC, up to 10% water can be unfrozen and take part in physical and biochemical reactions.
2. Freezing damage – the expansion of water as it turns to ice can cause structural damage to the food. This is often the cause of large voids and excessive drip loss in frozen materials after thawing. The effect can be minimised by freezing rapidly and maintaining low and consistent temperatures during frozen storage.
3. ‘Ostwald ripening’ – this is the tendency for large ice crystals to grow at the expense of smaller ice crystals. The effect is to induce freezing damage. It can be minimised by maintaining low and consistent storage