What happens to the sensory changes when the freshness of the fish decreases

To judge whether the fish is fresh, you just look at the gills, the gills are bright red to indicate that they are very fresh, and the gills are whitish to indicate that the fish is not fresh.

Mainly: Sensory evaluation.

Due to the simplicity of sensory inspection.

Easy. There are many applications in judging the quality of aquatic products.

Mainly used. Soon.

Sensory examination of the nose.

Different kinds. aquatic product sense.

Official test indicators and methods are not. Same. Thing.

Reason. Appraise. Price. Physical methods were used to evaluate the freshness of the slippery numbers.

There is mainly stiffness. There are two types of hard index and laser determination.

Because it can be inspected on-site.

It has been widely used in congratulatory letter fish freshness determination and to determine not.

The preservation temperature of the same species of fish at the same temperature.

Stiffness index. r

Pass the test. The degree of tail drooping of the fish body was compared with the initial value, and the obtained method for measuring the stiffness index of the fish body could accurately evaluate the freshness of the fish.

Chemistry (including biochemistry).

Appraise. Chemistry (

Biochemistry. The method is the most widely used in the evaluation of freshness of aquatic products.

It is also a relatively reliable method.

The main ones are as follows.

k-value. Fish must rely on adenosine triphosphate for muscle movement. ATP conversion provides energy.

And the fish body is contained in its body after death. at

p is broken down in the following ways. at

PADP adenosine diphosphate. One am

Plusterone. One. i

MP muscles. Licorice.

Sour. One. hx

r (muscle. Licorice. One.

hx times. Yellow.

Purine. k-value.

It is the decomposition of nucleotides.

A method for judging the freshness of the product as an index.

It is based on: ATP degradation.

Arrive. hx, etc.

6 related compounds.

Separately. Carry out.

Ration. And to get.

relative value. k-value. Be. a

TP's score. Untie. Give birth.

Thing. HXR with.

It accounts for the total number of ATP associations. of hundreds. Divide.

Compare. The k-value.

Small table. Ming production. Pinyue. New.

Fresh. k value.

for evaluation. Valence fish freshness.

chemical indicators.

The application is more accurate.

It is especially suitable for the early freshness of fish.

of the assessment. One.

Fresh fish. Target. k-value. For.

0 or less. k-value.

of the test. Quantity method. There is high. Effect.

Liquid chromatography. Law. hp

LC pole. Table.

Law. and columns. Layer. Divide.

Simple. Measure. Decide. Law.

Wait. Pole. Measured by spectroscopic method. Target. k-value with. h

PLC law has very. Good.

relevance. Pick.

Exchange the tree with anions. Fat. Column pairs.

Fish. Meat. Middle. a

TP system. Columnization. Combine.

Things. Yes. Adsorption and separation.

And then. Separately. Mensuration. No.

Same as elution. Liquid.

of sucking. Photometric calculations.

k-value. Amino nitrogen.

Amino state. Nitrogen is determined using a dual indicator.

Formaldehyde titration. Law.

Fish amino state.

Changes in nitrogen. with fish.

The meat is fresh. degree change.

Presentation. Negative phase.

Close. When the fish is new.

When the freshness does not decrease.

Amino state. Nitrogen increase. Add. Slowly.

Slow. Amino. Fish when the nitrogen increases rapidly.

of freshness. The degree is also visible.

Decline. Amino state.

Nitrogen for fish flavor.

impact. Plain as day.

With storage.

intervening. Fish.

Fleshy wind. Taste down. Fall.

The fish is tender and delicious. with terrestrial.

Compared with DU animals, fish meat contains more free amino acids, carnosine, DAO taurine and trimethyl rehoramine oxide. Most of these ammonia-containing leaching answers are substances with a refreshing umami taste. If the freshness of the fish decreases, trimethylamine oxide can be broken down into trimethylamine by the reductase enzyme of bacteria, giving off a fishy smell.

Marine fish has a high content of trimethylamine oxide, and when it is not fresh, the fishy smell is greater. Therefore, the preservation of fish is very important. Trimethylamine can react with acid, so put some vinegar when cooking to remove the fishy smell.

Not only is the amount of connective tissue in fish meat less than that of livestock and poultry meat, but it also decomposes at lower temperatures, losing its original hardness and toughness, making fish meat more tender and easy to cook. If it is cooked for too long, it will become firm and tough, and the digestibility will be reduced.

Fish contains less tryptophan but higher lysine than essential amino acids. Therefore, the combination of fish and cereals with low lysine content can make various amino acids closer to the needs of the human body in terms of quantity and proportion, so that they are easy to be fully utilized by the human body. Because the enzymes in the fish and the microorganisms carried by the fish are adapted to low temperatures, fish meat is more susceptible to spoilage than livestock and poultry meat.

Soft-shelled turtles and eels with large umami flavor have a high histidine content. If they die, the histidine in their bodies is quickly broken down into toxic histamine. Therefore, the soft-shelled turtle and eel bought back must pay attention to the freshness, and should not buy dead soft-shelled turtle and dietary fish.

Seafood: including fish, shrimp, turtles, shellfish, etc. Because they contain a large amount of unsaturated fatty acids that are easy to oxidize, the shelf life is shorter than that of livestock and poultry meat, generally up to about half a year, and it is best to eat within 4 months.

Red meat: mainly includes pork, beef, mutton, etc. The shelf life is 10-12 months. Among them, beef is more stable than pig and mutton, and lean meat is preserved longer than fatty meat.

Vegetables: Generally speaking, green leafy vegetables, melons and fruits cannot be frozen. However, a small number of vegetables, such as beans, can be frozen and kept fresh for only about 5 months.

Quick-frozen staple foods: such as dumplings, buns, glutinous rice balls, and wontons. Fillings with complex ingredients will gradually change in taste, and they are also easy to carry over flavors, so it is not advisable to freeze for too long, and it is best to eat them within a month or two.

Poultry: chicken, duck, goose, pigeon, etc. The shelf life is slightly shorter than that of red meat, at 8-10 months.

Food must be allowed to cool before freezing, and it is best not to freeze food again after thawing.

Volatile basic nitrogen (VBN) is one of the main chemical indicators to judge the freshness of fish.

Volatile basic nitrogen (TVB-N) refers to the alkaline nitrogenous substances such as ammonia and amines produced by the decomposition of proteins in animal foods due to the action of enzymes and bacteria in the process of spoilage. These substances are volatile, and the higher their content, the more amino acids are destroyed, especially methionine and tyrosine, so the nutritional value is greatly affected.

There are mainly sensory evaluations.

Due to the simplicity and ease of sensory inspection, the quality judgment of aquatic products is widely used, mainly by looking at and smelling sensory inspection. The indicators and methods of sensory testing are different for different types of aquatic products.

Physical valuation.

There are two main physical methods to evaluate freshness: stiffness index and laser measurement, which can be tested in the field and have been widely used in the determination of fish freshness and the determination of the preservation temperature of the same species of fish at different temperatures.

Stiffness index (r).

By measuring the degree of tail drooping and comparing the value at the beginning, the method obtained by measuring the stiffness index of the fish body can accurately evaluate the freshness of the fish.

Chemical (including biochemical) evaluation.

Chemical (biochemical) methods are the most widely used methods for evaluating the freshness of aquatic products, and they are also relatively reliable methods, mainly as follows

The muscle movement of k-value fish must rely on the conversion of adenosine triphosphate (ATP) to provide energy, and the ATP contained in the body of the fish after death is decomposed according to the following ways: ATP - ADP (adenosine diphosphate) - a m p (glycoside) - i m p (inosinate) - h x r (inosine) - h x (hypoxanthine) k value is a freshness judgment method based on the decomposition products of nucleotides, which is degraded to h x according to a t p and so on The relative values of the six related compounds were quantified separately.

The k value is the percentage of the solution product h x r of a t p to the total number of a t p associations, and a smaller k value indicates that the product is newer.

Fresh. The k-value is used as a chemical index to evaluate the freshness of fish, which is more accurate, and is especially suitable for the evaluation of early freshness of fish. In general, the k-value of fresh fish is below 1 0' and the method of measuring the k-value has a high-efficiency liquid chromatography.

method (h p l c ) polarography and simple column chromatography measurement, etc. The K value measured by polarography has a good correlation with the H p l C method; Anion-exchange resin columns were used to perform the ATP series compounds in fish.

Adsorption and separation, followed by the determination of the absorbance of different eluents to calculate the k-value.

Amino nitrogen. The determination of amino nitrogen is carried out by using a two-indicator formaldehyde titration method. The change of amino nitrogen was negatively correlated with the change of freshness of fish, and the increase of amino nitrogen was slower when the freshness of fish did not decrease, and the freshness of fish decreased when the amino nitrogen increased rapidly. The effect of amino nitrogen on the flavor of fish meat was obvious, and the flavor of fish decreased with the extension of storage time.

Volatile basic nitrogen (VBN) is one of the main chemical indicators to judge the freshness of fish.

K value, VBN, free amino acid nitrogen, pH value.