though there has been steady progress in the United States toward approval of the process, there is still a widespread disagreement between scientific, government, and consumer groups regarding the pros and cons of using this form of energy for processing foods (21).
Two factors probably have equally contributed to this battle, namely the association in the minds of people between ionizing radiation and nuclear warfare, and the DeLaney Clause of the 1958 Food Additive Amendment to the Food, Drug and Cosmetic Law. The amendment, best known for the prohibition of a food additive that is shown to be carcinogenic in a test animal at any dose level, states that irradiation is a food additive and not a food-processing technique. It is interesting to note that the U.S. Depart-
Figure 20. Process for hard curing and drying of fish.
Figure 20. Process for hard curing and drying of fish.
ment of Agriculture has issued an extensive list of publications that show the safety and wholesomeness of irradiated foods (22).
Some confusion exists about the units used for measuring radiation doses that a product receives. This is because the original unit of measurement, the rad, was changed to kilograys (kGy); 100,000 rad (100 krad or 1 Mrad) is equivalent to 1 kGy (100,000 Gy). As shown in Table 12, the doses for processing range from 0.75-2.5 kGy for pasteurization to 30-40 kGy for sterilization. Note that specific process terminology has been suggested for the various operations. Pasteurization is radurization, sani-tization is radicidation, deinfestation is the process for destroying eggs and larvae, and sterilization is radaper-tization. Two radioisotopes, Co-60 and Ces-137, and electron-accelerator-generated electron beams meet the requirements for producing sufficient energy and intensity to penetrate food and accomplish the four basic processes.
The radurization of fresh seafood has an excellent potential for extending shelf life. Being in the low-dose range, this process should not meet the resistance that is found for the publicized high doses that accomplish sterilization, but result in some off-flavor (23). The extra week of shelf
Table 12. Dose Ranges for Food Irradiation Processes
Process Dose range
Radurization (pasteurization) Radicidation (sanitization) Destroy eggs/larvae
(deinfestation) Radappertization (sterilization)
75-250 krad 250-1,000 krad below 100 krad 3-4 Mrad
0.75-2.5 kGy 2.5-10 kGy below 1 kGy 30-40 kGy life that can be given to a fresh fish by radurization would be of economic benefit to the entire industry. The extra shelf life would eliminate product loss at the retail level and would extend the market range for delivering fresh fish.
There is every reason to believe that irradiation will eventually become an accepted and extensively used processing technique for seafood, especially seafood for the fresh market, where all parties will benefit. Perhaps during the next decade the radurization of seafoods will be commonplace. After all, 20 yr ago there was the same consternation over the use of microwave ovens, and today they are in 80% of U.S. homes.
Proper packaging of products is necessary to protect food from adverse losses and changes in weight, texture, flavor, nutritional components, and protection against contamination and physical damage. With the growing demand for high-quality seafood, the major emphasis is on packaging for fresh and frozen products. Basic types of packaging, in order of increasing ability to protect fresh or frozen food, include paper, coated paper, fiber, foil, films, laminates, and combinations.
One of the primary considerations in selecting packaging for fresh and frozen foods is the gas and water permeability of the material, usually plastic films, plastic containers, and treated paper products. There is always a balance between the cost of the package and the degree of protection given to the seafood. A very low cost uncoated cellophane has a moisture permeability that is so high that frozen and even cold fresh products are rapidly dessicated during holding. A film such as poly(vinyl chloride) (PVC) costs more but gives moisture-barrier protection that improves the overall economics of the processing and marketing chain.
The same economic analysis must be made for gas permeability, because oxygen entering the package tends to oxidize lipids and give off-flavors while some of the desirable volatile taste and odor components may be lost from the product. The fact that some films give good vapor-barrier protection but allow moisture to pass while others act in a reverse manner has encouraged the development of laminated films for food packaging. Laminates for seafood packaging often consist of polyethylene (which is cheap, is heat sealable, is usable over a wide range of temperatures, and is a good moisture barrier) and another film that has a low permeability for gas (eg, C02, 02, and N2). Examples of laminates used in frozen seafood products include polyethylene laminated with low-gas-permeability poly(vinylidene chloride) (PVDC) or saran), polyester, cellulose, aluminum, or nylon.
Packaging not only protects the food but is also an important factor in the sales appeal of the product. Packaging that shrinks film to give better evacuation of air from the package, overwraps for multiple packages and trays, overwraps to give rigidity to a package, allows see-through to the product, uses vacuum to minimize oxidation of the product, and uses gas flushing to expel further air are all popular methods of protecting processed seafoods. Pack aging materials have become quite sophisticated and the accompanying use technology has been developed to meet the requirements for economic applications, long-term storage of products (particularly frozen), and enhanced consumer appeal.
Over the last decade, the market for fresh food products has become increasingly popular. A system combining closely controlled combinations of low temperature, high humidity, and proper ventilation has allowed extensive increase of the shelf life of perishable fresh foods. This system, hypobarics, was awarded the Institute for Food Technology's Technology Industrial Achievement Award in 1979 (24). Although hypobarics is a container system rather than a package, it can be considered a package in that it is used to contain a fresh product during the plant storage and transport time required to move the product to market. Originally developed for fruit, the system was extended to all fresh food items including seafood. Although the system has not been used extensively on seafood, it has been very successful with numerous products and should certainly be mentioned as a potential use for extending the shelf life of fresh seafood.
Another important area involving packaging technology is modified-atmosphere packaging (MAP), which has been shown to increase the shelf life of many perishable foods and formulated products by reported values of from 50 to 400% (25). However, there has been considerable concern by both regulatory authorities and researchers over maintaining the safety of MAP foods as they travel through the channels of commerce. The system, consisting of modifying the gaseous environment with a package, results in various combinations of carbon dioxide, nitrogen, and oxygen. Carbon dioxide is the important factor replacing much of the oxygen and nitrogen in the air (eg, 75% C02, 15% N2, and 10% 02). Of concern is maintenance of the proper refrigeration temperatures and the gas ratios for a given product so that microbial growth does not present an undue safety hazard.
A considerable amount of research has been carried out in the MAP of seafood products (26). A significant amount of effort is being expended on developing the processor-distributor combination to improve quality and value of fresh seafoods.
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