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What are the indexes to judge the freshness of freshwater fish?
Volatile basic nitrogen (VBN) is one of the main chemical indexes to judge the freshness of fish.

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

Extended data:

Sample handling:

Fresh (frozen) meat is peeled, degreased, boned and deboned; lean meat, fresh (frozen) seafood and aquatic products are shelled, peeled, decapitated, eviscerated and deboned; edible parts are taken, ground and stirred evenly. The finished product is directly ground and stirred.

Uniform samples such as minced meat, meat powder, floss, fish meal, floss and liquid samples can be used directly. Preserved eggs (preserved eggs), salted eggs and so on. Peel off the eggshell and egg membrane, add water according to the ratio of egg ‥ water = 2: 1, grind with a blender and stir evenly to form homogenate.

Samples of preserved eggs and salted eggs are weighed as egg homogenate 15g (when calculating the content, the mass of egg homogenate multiplied by 2/3 is the sample mass), other samples are weighed as 10g, accurate to 0.00 1g, the liquid sample is 10.0mL, and 75mL of water is added into the distillation tube.

Baidu Encyclopedia-Volatile Basic Nitrogen