Fish Packaging Technology

Fish has a high protein content and high water activity, so it is very susceptible to contamination by microorganisms such as spoilage bacteria and pathogens, and is prone to spoilage, resulting in food waste and economic losses. Using appropriate fish packaging technology to extend the shelf life of fish is a common concern of the entire industry. Commonly used fish packaging technologies at home and abroad include tray packaging (TP), modified atmosphere packaging (MAP), vacuum packaging (VP) and vacuum skin packaging (VSP vacuum skin packaging).

1. Tray packaging

Tray packaging is a packaging method that uses foamed polystyrene (PS) as a tray and polyvinyl chloride (PVC) or polyethylene (PE) to cover the surface of the product. It is one of the most common packaging methods for selling meat in supermarket refrigerators. This packaging is not airtight. Myoglobin (Mb) in meat can fully combine with oxygen to generate oxymyoglobin (MbO), making the meat bright red. To avoid secondary contamination, fish are usually slaughtered and vacuum packed or covered with plastic film and placed in plastic boxes, and then divided or packaged on trays when sold. 

2. Vacuum packaging

In order to meet market requirements, the use of vacuum packaging technology for fish storage has made great innovations, especially when VP is combined with refrigeration and frozen preservation technology, the shelf life of fish can be significantly extended. Vacuum packaging is a preservation method that extends the shelf life of products by sealing the packaging bag, excluding oxygen in the packaging bag, and isolating the product from the outside world. In a low-oxygen environment, the number of aerobic bacteria can be reduced, while the rate of protein degradation and fat oxidation can be slowed down. In an anaerobic environment, the physiological activity of lactic acid bacteria is enhanced, and organic acids can be produced to reduce the pH in the package, thereby further inhibiting the growth of other microorganisms. This packaging method can achieve a better preservation purpose. 

The shelf life of fish stored under vacuum conditions depends on the interaction of variables such as storage temperature and microbial conditions. By storing vacuum-packed and non-vacuum-packed carp at 3℃~15℃, it was found that the storage period of vacuum-packed carp at 3℃ was 4 to 5 days longer than that of non-vacuum-packed carp; when stored at low temperature, the content of biogenic amines measured in carp was lower and the quality of carp was better. Although vacuum packaging can inhibit the growth of most aerobic microorganisms, even if the oxygen content in the packaging is reduced to 0.8%, it still cannot inhibit the growth of some aerobic bacteria, especially the growth and reproduction of Pseudomonas. Under low temperature conditions, as the storage time increases, lactic acid bacteria will gradually replace Pseudomonas.

3. Vacuum skin packaging

As a new type of packaging method, it can prolong the storage period of meat, slow down the growth of microorganisms, and slow down the generation rate of undesirable substances during meat storage compared with ordinary vacuum packaging. The shelf life of Atlantic pomfret in vacuum skin packaging, vacuum packaging, and tray packaging is 12 days, 7 days, and 5 days respectively. Vacuum skin packaging can better maintain the sensory, biochemical and microbiological indicators of Atlantic pomfret, improve the quality under the same storage time and extend the shelf life. The shelf life of the vacuum-skin-packed mullet is 9 days at (2±2)℃. Compared with the mullet in the control group with ordinary vacuum packaging, the indicators such as volatile basic nitrogen, trimethylamine and thiobarbituric acid in the vacuum skin packaging are relatively stable. Therefore, vacuum skin packaging is more suitable for the packaging and preservation of mullet. A study compared vacuum skin packaging, ordinary vacuum packaging and MAP modified atmosphere packaging and found that vacuum skin packaging has better color stability than ordinary vacuum packaging and can achieve similar effects as modified atmosphere packaging.   

4. Modified atmosphere packaging

MAP modified atmosphere packaging is a way of preserving food by putting it into a plastic modified atmosphere box, extracting the air in the box, injecting a special single gas or mixed gas, and then sealing the package, so that the product is surrounded by special gas and isolated from the outside world. Its original principle is to exclude oxygen to limit oxidative rancidity caused by oxygen and limit the growth of microorganisms. With the development of modified atmosphere packaging, the common injected packaging gases mainly include CO2, N2, O2, and sometimes CO. One gas or multiple gases are mixed in a certain proportion to replace the original air in the product packaging. Once the package is sealed, the gas composition in the package is no longer adjusted. During the storage process, MAP modified atmosphere preservation technology is often combined with low-temperature preservation technology to inhibit the growth of microorganisms, maintain color, slow down the degradation of nutrients, and extend the shelf life. Foods packaged in modified atmosphere can usually extend the shelf life by 0.5 to 4 times, which can realize long-distance transportation of products and help maintain quality.