Controlled atmosphere (CA) and modified atmosphere (MA) storage are technologies for extending the shelf life of foods, especially fruits and vegetables; and for eliminating pests in stored grains and oilseeds. The most important application of CA and MA is for long-term storage of apples, but the shelf life of certain other fruits (pears, sweet cherries) and vegetables (cabbage) can also be extended by these methods. In addition, there is considerable evidence that MA can extend the shelf life of meat, fish, poultry, fresh pasta, sandwiches, eggs, and bakery products. Because grains and oilseeds are more stable than high moisture foods (e.g., fruits, vegetables, meats)
- The principle behind controlled and modified atmosphere technologies is to reduce the rate of respiration, reduce microbial growth, and retard enzymatic spoilage by changing the gaseous environment surrounding the food product. This is achieved by reducing the concentration of oxygen (O 2 ), which is required in respiration, or by adding an inhibitory gas such as carbon dioxide (CO 2 ). The balance between O 2 and CO 2 is critical, and an optimal ratio is required for each specific product.
- The difference between CA and MA storage is in the degree of control of the gaseous composition of the storage atmosphere. The CA implies a higher degree of control than MA in maintaining specific levels of O 2 , CO 2 , and other gases. Also, in MA storage the composition of the atmosphere surrounding the product is generally created and maintained by the interaction of the commodity’s respiration with the permeation of respiratory gases through the packaging material. Modified atmosphere conditions can also be established and adjusted by pulling a slight vacuum and replacing the package atmosphere with a desirable gas mixture, which can be further, adjusted through the use of O 2 , CO 2 , or ethene (C 2 H 4 ) absorbers. In CA storage facilities, both temperature and gas composition of the storage atmosphere are regulated or controlled. The gas concentration ranges encountered in CA storages are 1 to 10% O 2 , 0 to 30% CO 2 , and the balance is nitrogen (N 2 ). Air consists of approximately 78% N 2 , 21% O 2 , 0.03% CO 2 , and traces of several other gases that have no physiological significance.
Advantages of CA and MA Storage
In fresh fruits and vegetables stored under optimal CA or MA, practical quality advantages include:
- Reduction in chlorophyll breakdown, with resulting higher color stability.
- Reduction in enzymatic browning in cut produce, whenever low levels of O 2 are used.
- Increase in the storage life of the fruits.
- Improvement in texture caused by the action of CO 2 on enzymes acting on cellular membranes.
- Reduction in some physiological disorders induced by C 2 H 4 , such as scald of apples and pears and chilling injury of citrus fruits, avocado, chili
- Reduction in microbial activity especially molds.