Providing scientific, accurate, high quality and efficient services to all sectors of the society
Shrimp head black is not fresh? How to determine the freshness of shrimp
Shrimp is a lot of people like to eat, but what is the effectiveness of shrimp but few people know, and the shrimp during storage shrimp will be black. Shrimp head is not fresh black?
Black head shrimp is not fresh?
To understand why shrimp head black, we need to first understand a substance - tyrosinase, which is widespread in animals and plants, although different organisms in the structure of tyrosinase vary greatly, but the basic function is similar. Under the action of tyrosinase, tyrosine can gradually form quinone substances and then form black substances such as melatonin and brown melanin. The whole body of the shrimp has a tyrosinase distribution, but the head has the highest tyrosinase activity and lower abdominal and tail enzymatic activities. Therefore, the shrimp head is always the first black, then the abdomen and tail.
Shrimp black is mainly the role of enzymes, and the little relationship between microorganisms. Tyrosinase is still active even under freezing or refrigerating conditions, so blackening still occurs. Shrimp head is also the internal organs of shrimp, shrimp black hair may occur if the shrimp just eat a lot of dark algae before fishing, such as brown algae. In addition, farmed prawn undigested feed may also appear black. Therefore, shrimp head does not necessarily darken shrimp is not fresh. From this point of view, shrimp head black is not so terrible thing, need to correctly understand.
How to determine the freshness of shrimp
1, fresh shrimp body surface dry
Fresh shrimp body surface clean, feel a sense of dry hands. However, when the shrimp body is nearly metamorphosed, granulosa cells that secrete mucus under the shell disintegrate and a large amount of mucus penetrates into the body surface, feeling a sense of creaminess. If shrimp sticky hand, shrimp has been deterioration.
2, fresh shrimp color bright
Different types of shrimp, its color is also slightly different. Fresh prawn, Roche shrimp, grass shrimp green, shrimp were caught in the sea pink, bamboo shrimp, shrimp with black and white pattern slightly pink. If shrimp black hair is not fresh shrimp, the whole shrimp color is black, not bright, but also shows that has deteriorated.
3, fresh shrimp shape bending
Fresh shrimp head and tail integrity, head and tail are closely linked with the body, shrimp body quite Ting, a certain degree of flexibility and curvature. Instead of fresh shrimp, head and body, shell and meat connected loose, head and tail easy to fall off or separation, can not maintain its original curvature.
4, fresh shrimp shell to be hard
Shrimp shell to be hard, bright green light, eyes, meat firm, smell very heavy. If the shell is soft, gray and turbid, concave eye, the shell slightly separated to explain shrimp just died soon.