Freezing is one of the most cost-effective ways of extending the long-term shelf life of many foods. Though other emerging technologies, such as infrared irradiation, microwaving, pulsed electric field, and ultrasound, are gaining more attention, freezing remains a dominant food preservation method.
Freezing preserves food by physically changing the state of a substance’s water content into ice by cooling it. However, even though freezing will slow down the physicochemical and biochemical reactions that influence food spoilage, it will not completely stop them. The loss in quality of frozen foods is largely dependent on the freezing process, storage temperature, the length of freezer storage time, and the thawing procedure.
Maintaining safety and quality in frozen foods is a delicate process that involves the entire frozen food cold chain: pre-treatment, processing, packaging, frozen food storage, transport, and thawing food.
How The Freezing Rate Affects Quality?
Controlling the entire freezing process is critical to achieving the best quality frozen foods. One crucial parameter is the freezing rate. In general, fast freezing produces better quality frozen food than slow freezing.
When freezing fresh vegetables and fruits, the cooling rate will determine the size of ice crystals formed and the amount of damage to the cell walls. Damaged cell walls cause food that is supposed to be crisp to be limp instead.
When freezing meat, fish, or poultry (including ground meats), water migrates out of the cells. Rapid freezing minimizes this dehydration and texture degradation. The faster the crystallization, the smaller the ice crystals will be, which will cause less damage during freezing foods.
In terms of thawed foods, the reverse is true – slow heating to room temperature allows water to diffuse back into the cells.
The detrimental effects of freezing on microorganisms may or may not be desired, depending on the type of food frozen.
When it comes to food safety, the key is maintaining a delicate balance between preserving quality while preventing microbial spoilage. The ideal storage temperature for freezing vegetables, fruit, or meat ranges from 16°F – 10°F. Microbiological spoilage can be avoided by following basic hygiene guidelines such as proper cleaning procedures, heat processing, and cutting raw materials into smaller pieces if possible.
Generally, freezing will kill between 10 and 60% of the viable microbe population, depending on the freezer temperature and frozen storage time. However, in terms of microorganisms, there is a considerable difference between their sensitivity to freezing and how quickly they can grow once the product is thawed. Special attention needs to be given here as some microbes can lead to spoilage and various food-borne illnesses, and food poisoning.
Physical Changes and Frozen Food Quality:
Specific physical changes take place when food is frozen. Among the most common, we can include:
Chemical Changes and Frozen Food Quality:
Aside from the physical changes that happen during freezing, there are also chemical changes that can affect the quality of frozen food. Among these, we can include the following:
It’s essential to recognize that a successful freezing process will only retain the already existing food quality and will not improve it. Maintaining the quality and safety of frozen food starts with pre-treatment.
The most common pre-treatments include the following:
Storage, Packaging, and Thawing:
The packaging, storage, and thawing processes also affect frozen food quality. The detrimental effects on quality and food safety are slow, gradual, cumulative, and irreversible.
It has been revealed that aluminium foil laminated packages best limit oxygen permeability, light transparency, and water vapor transmission.
Storage and distribution temperatures need to be kept at 0°F or lower to maintain quality. Every 9°F increase over 0°F increases the rate of quality loss by about 200 to 250%. The amount of food in a storage unit can affect temperature fluctuation.
Some food types, such as pork, fish, fried chicken, animal organs, and spinach, can be maintained at high-quality only for about 3 to 7 months at -4°F. In contrast, sugared fruits, beef, most vegetables, and bakery products can be maintained over one year under the same conditions.
Thawing is the final step of the freezing process and is essential to the quality and safety of frozen foods. Microbiologically safe methods of defrosting foods are to store foods in the refrigerator at temperatures below 41°F, microwave, or cook.
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