Rainbow trout killed vacuum.

Slaughtered fish were immersed in an 8% NaCl solution at 20°C for half an hour, fished out and dried, placed in a vacuum plastic bag and vacuumed. The rainbow trout in the vacuum bag was pre-cooled to 2° C., and then the rainbow trout was cooled down to a storage temperature between -0.8° C. and -2.0° C. in accordance with a continuous temperature change program, and the storage temperature was maintained so that the rainbow trout was realized to be stored at a super-ice temperature. The rainbow trout meat is not frozen during storage and can be stored for up to 3 days.

Other preservation methods for rainbow trout

The main preservation methods for rainbow trout are low temperature preservation, ionizing radiation preservation, gas preservation and so on. Good preservation methods need to have two aspects of the conditions: one is effective in preventing microbial reproduction and corruption, with the inhibition of enzyme biochemical reactions and air oxidation, in line with food hygiene conditions. One is suitable for the production and transportation process in a timely and effective treatment of large quantities of aquatic products in the conditions and capabilities.

Currently the most used, the best results is the low temperature preservation method, other methods in the use of conditions and the use of the effect of a number of limitations and defects.

1, low-temperature preservation

Including frozen storage and non-freezing storage at low temperatures in two aspects, generally also known as freezing and cooling. The bacteria that cause the rainbow trout to rot and deteriorate are mainly cryophilic bacteria, the minimum temperature of its growth is -7 ~ -5 ℃, the optimal temperature is 15 ~ 20 ℃. If lower than the optimal temperature, the growth of microorganisms that is inhibited; below the minimum temperature is to stop growing, most of the bacteria in 0 ℃ around the growth of the delay down.

In the low temperature range, a slight drop in temperature can significantly inhibit the growth of bacteria. In addition to the effect of low temperature, microorganisms are inhibited at freezing temperatures because the freezing of water in the fish body reduces water activity. In addition, the activity of various enzymes also decreases with the temperature drop, and is significantly inhibited at around -20℃ and almost stopped below -30℃. The chemical changes after the death of the fish, such as the rate of oxidation reaction of fats and oils are also significantly reduced with the drop in temperature.

The low-temperature preservation methods for fresh rainbow trout include ice storage, cold seawater or cold brine preservation, microfrozen preservation and frozen preservation.

2, ice storage

Widely used preservation methods. Ice melting can absorb a lot of heat to reduce the temperature of the fish body, melting water can also wash away the rainbow trout body surface attached bacteria and dirt. Fresh fish are often preserved in layers of ice using small ice cubes or flakes. The storage time varies from storage to storage, usually 1 to 2 weeks.

3, cold seawater or cold brine preservation

Fresh fish immersed in cold seawater or cold brine at a temperature of generally -1 ~ 1 ℃ for preservation, this method is mainly used in fishing boats or canning and processing plants. In the fishing boat application must first use ice or refrigeration equipment to make seawater or brine cooling. If the body of the fish immersed in cold seawater or cold brine cooled to 0 ℃ after taking out the ice preservation, the effect is better, the preservation period of about 10 ~ 20 days.

4, microfrozen freshness

To low-temperature seawater or low-temperature brine in the body of the fish circulating between the flow of microfrozen storage. Microfrozen temperature of -2 ~ -3 ℃, so that the water in the body of the fish partially frozen, preservation temperature of -3 ℃ or so. Its preservation period can range from 20 to 30 days.

The use of cold seawater or cold brine preservation and micro-frozen preservation, the effect is better than ice storage, the reason is that the temperature is lower than the ice storage, and the cooling of the fish is more solid, conducive to transportation. The disadvantage is that can cause the fish body discoloration and fish flesh salt increase; at the same time seawater or brine mixed with fish blood, mucus and other dirt is easy to produce foam and pollution.

5. Freeze storage

Also known as frozen storage, fresh rainbow trout is first frozen in a freezing device and then placed in a low-temperature cold storage. The temperature at which fresh rainbow trout begins to freeze is -0.5 to -2℃. From the beginning of freezing to -5 ℃ before and after, about 80% of the water in the muscle tissue is frozen.

The freezing of fresh rainbow trout is generally fast-frozen, that is, within 30 minutes through the 0 ~ -5 ℃ maximum ice crystal generation zone. The storage temperature after freezing is generally required to be lower than -18 ℃, can also be used -30 ℃ or even lower storage temperature.

6, gas preservation

Gas preservation method is mainly used for fruits, vegetables, meat, there is also research for rainbow trout preservation. This is also a combination of low-temperature preservation and application of preservation method. The gas used is a mixture of carbon dioxide and oxygen, sometimes mixed with nitrogen as an inert filler, used to replace the air in the low-temperature storage room or container for rainbow trout fresh storage, its quality and duration than the use of low-temperature storage alone is better and longer.

The preservation effect of gas storage on rainbow trout may be due to the fact that carbon dioxide interferes with some of the functions of the cellular enzyme system, thus inhibiting bacterial metabolism. In addition, carbon dioxide dissolved in water lowers the pH of the fish, which also helps to inhibit the growth of bacteria. The solubility of carbon dioxide increases at low temperatures, and the use of higher concentrations of carbon dioxide combined with low temperatures has a better preservation effect.

In the gas preservation, the distribution of bacterial species in the fish body by the original predominant Gram-negative bacteria into Gram-positive bacteria, thus making the fish body spoilage bacteria are inhibited, and can reduce the odor produced by corruption.