Chinese saying goes, called "Kaoshanchishan utensils" in the past, due to the limitations of technology, economy, transportation and other aspects of the mountains and the sea often only residents have the opportunity to enjoy fresh delicacies, seafood, now good life, mostly to protect the animals can not eat delicacies, seafood already become ordinary people table common dishes, but delicious seafood though, if selected properly, can easily lead to food poisoning.
Many people believe that after the frozen fish, the fish will not be bad. Refrigerator is safe, while the northern winter is a natural big refrigerator. To illustrate this problem, we need to begin at the beginning, to look after the death of the fish from getting started deterioration.
Fish spoilage
1. stiff stage
Changes in fish and meat after death is basically the same, but there is a period in the dying stages of mucus secretion. This layer of mucus mainly mucin, to resist the erosion of foreign toxic substances, which is a protective reaction of the fish itself. Fresh fish mucus is transparent and homogeneous, with a fishy smell, then with the freshness of the fish decreases gradually becomes cloudy, dirty, fishy odor disappears.
We know that rigor mortis had died, after the death of the fish will appear stiff. Fish about ten minutes to five hours will appear stiff. First stiff from scratch, by gradually back to the whole fish. This stage of the fish as hard as wood, can not be bent, shiatsu without leaving indentation, tight mouth, gills tightly together. Stiff short time tens of minutes, long up to several days. Fish stiff mainly because of the contraction caused by the fish, and fish and human contraction of muscle contraction, requires ATP decomposition intramuscular provide energy. Fish just died, fish in actin and myosin was dissolved state, so in this case the muscle is soft. When the body begins to decompose ATP, actin fibers slid muscle myosin, and condensed into a rigid actomyosin (actin and myosin fibers overlap cross), causing thickening of the muscle sarcomere shortens, so the loss of muscle stretching and become stiff. This phenomenon is similar to the living body muscle contraction, except that after the death of muscle contraction is slow, and is not reversible. So, we can use the pre-stiff and stiff of fish to determine the freshness of the fish. And may be extended by extending the freshness of the fish stiff and rigid pre-period.
Then after the death of the fish stiff factors, what does? 1) the species of fish: after the death of migratory fish stiff upper preliminary short, stiff period is and weaker activity groundfish opposite. 2) Physiological and nutritional status: food rich spring and autumn and winter season than fish bait fish scarcity season, long pre-stiff, stiff and long fat fish longer than the stiffness of thin fish. 3) Fishing and lethal conditions: after the death of the fish caught quickly, the body's glycogen consumed less than violent struggle, fatigue, stiff pre-fish died long, stiff and long term. 4) fish preservation temperature: the lower the storage temperature, the longer the pre-stiff and stiff period. Summer temperatures, the stiffness of not more than a few hours, or refrigerated as soon as possible in the winter can be maintained for several days.
When the fish muscle ATP decomposition finished, the fish began to soften. This is the beginning of a new phase.
2. autolysis phases:
After the stiff stage, the fish should start autolysis phase. Of course, after the death of the formation of actomyosin is impossible to reply, but because sarcomere Z line is disengaged, the muscles began to relax soft. At this time in the joint action of the fish itself endogenous and exogenous proteases proteinase from spoilage, and begin to break down muscle protein into the free amino acids. Gradually lose muscle tissue inherent elasticity. The protein product of decomposition is very suitable for bacterial growth and reproduction. There are some factors that are affecting autolysis. For example: cold-blooded autolysis faster than warm-blooded migratory fish faster than the average bottom crustaceans, aquatic faster than fish. PH4.5, the fish autolysis PH7, the shrimp autolysis fast. High salt state, autolyzed slow, but even the fish soaked in saturated salt water, autolysis will not stop, but slow down the speed of it. Within a certain temperature range, the temperature is low autolysis slow, high temperature and vice versa. Autolysis stage fish, it can not continue to the store. And to eat immediately. Next, enter the stage because of corruption will not continue eating.
3. Corruption stage:
Because more and more bacteria, amino acids and other nitrogenous substances as the medium will be further broken down into: ammonia, trimethylamine, indole, hydrogen sulfide, histamine and other low-level product. This makes the fish odor having corruption characteristics. This is the essential difference between corruption and metamorphic stage autolysis phase.
Under normal circumstances, in fish muscle tissue is no bacteria. The bacteria mainly in fish gills, surface and intestines. Wherein up bacteria in the intestine. When fish die, the bacteria also began to spread from these areas to the surrounding tissue. So in the case of a complete fish, intraperitoneal corruption is the earliest start, and even the appearance of corruption after some fish complete, abdominal gas was bursting corruption. Visceral corruption, increased permeability of the gallbladder, bile spills, stained green liver and adjacent organs, which is "printed guts." Therefore, as soon as possible to clear the viscera can enter mitigation of corruption. There are fish skin damage, will speed up access of corruption.
Connective tissue protein in the fish skin bacteria will break down the surface so that scale easily. Invasive bacteria break down proteins cause eye corneal opacity, eye into eye socket. The gills lose in bacterial invasion of the original bright red and become brown or gray, and odor. Bacteria enter through the gills of fish vessels, large vessels and gradually invade and cause hemolysis, the red paraspinal muscles, the so-called "red dye paravertebral" phenomenon. While the muscles on the spine off to form a separate state of flesh and blood.
Through the above understanding of all phases of fish spoilage, then for how to pick the kind of seafood will be relatively easy.
Seafood selection
First, fresh seafood is the freshest. Although this nonsense too, but gotta say. The following are mentioned as seafood is concerned for the dead.
Selection of seafood, we can go to be from the look, touch, smell, open four aspects. Began to speak from the fish.
fish
Wang: look at the overall fish must be complete and fish to maintain the inherent color and no abdominal bloating and anal prominent as well as close to the fish scales should be mucus should be with your fingers or palm holding fish the central body to observe the fish's head, torso, tail whether horizontal state, to measure the degree of stiffness and tail fins to smooth eyes bright, eye full, transparent cornea should be transparent, whether the hair around the eyes red untie gill cover gills observe whether red or reddish-brown, gill sharpness higher.
Touch: the fish have a taut feel with your fingers fish back muscles, flexibility is better, let go would soon be restored.
Wen: can smell the fish body surface, gills, muscles no foul you can also use a wooden stick pierced deep muscle, sniffing immediately after if necessary or desirable fish gills after picking up olfactory boiling water .
On: cut with scissors from the anus to the head along the white line, then cut from the anus to the dorsal lateral line to continue to cut the abdominal wall to the head, to expose all the internal organs, mainly the liver, stomach, intestine, kidney changes in and unstamped gall phenomenon, then transected spine, observe whether the next spine redness.
shrimp
The inherent color of the new shrimp shrimp have a variety of shrimp, shell clear and transparent, with the head of the prawn shrimp connection easy to fall off, there is flexion of the tail section, dense meat, the same smell. Eyes full of outstanding, allowing a slight decline. Muscle texture clear, was white jade, flexible, easy to pull off. Inherently odor smell of shrimp, no smell.
crab
Live fresh crab: flexible movement, good crawl, which can quickly turn over supine.
Dying crabs: mental fatigue, do not want to crawl, pereiopod sag or start lifting off, will not quickly turn around its supine.
Fresh crab: shell was purple, shiny, no signet, clear gill, muscle texture clear, flip handheld crab, crab no sense of movement.
Metamorphic crab: looks bleak, there signet, Crab black, brown gills. Muscle fibers are not clear, there is rancid.
Clam shell
Live clam shell: shell confinement, not easy to separate. Clear shell body fluids, muscle plump, pink was slightly yellow, no smell.
Dead clam shell: shell easily clawed, fluid turbid, dry flesh, corruption flavor.
Frozen fish after
Fish: bright-eyed, transparent cornea, the eye filled eyes bulge protrudes even slightly, flattened fins open, covered with a mucus layer on a transparent frozen flakes, natural skin color is obvious.
Dead fish: fish fins close eye not prominent. Poisoning and suffocation death frozen fish, gills and mouth open, darker skin color.
Corruption fish: no fish frozen after feature. Under suspicious circumstances, can be used as a knife or bamboo needle fish smell the odor, or a cut gills, immersed in hot water after sniffing. Spoilage of fish is inedible.
Then look at the beginning of the article the problem of frozen fish will degenerate it? The answer is: Yes. Because at low temperatures, the bacteria do not breed is not, but only slow reproduction only. Moreover, some bacteria even at low propagation speed is not slow. There are some frozen fish offal, gills not removed, the high base of the bacteria, how does corruption? There is already frozen when autolysis stage of fish, would this not corruption? Further north the city despite the low temperatures at night, but during the day was sunny, freezing temperatures is very unstable, will speed up the fish corruption. Here to remind you, the food in the refrigerator, proposes to add a note written on the frozen date, remind yourself not to leave too long of frozen food. Whether poultry meat must be noted. Food best eaten as soon as possible after thawing, do not freeze again.
62 (Author: iced tea 62)
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