Freshness of fish meal!
Freshness index of protein: VBN
The freshness of protein is determined by the level of volatile base nitrogen (VBN) and histamine.
Volatile base nitrogen - fish meal VBN within 50mg/100g freshness, more than 150mg/100g that has begun to spoil, VBN more than 150mg/100g of fish meal, generally not suitable for use.
The average histamine content of histamine-white fish meal was 28 ppm, and that of red fish meal was much higher than that of white fish meal. The average content of histamine in red fish meal was 267 ppm in steam drying, 442 ppm in direct-fire drying and 321 ppm in domestic fish meal, which was lower than that in direct-fire drying. It can be concluded that the histamine content of domestic steam fish meal is only inferior to that of imported steam fish meal, but much better than that of imported direct-fire dried red fish meal.
Freshness index of fat
The freshness of fat is generally measured by acid value, peroxide value, TBA or AOM. Feed enterprises generally use acid value (AV) to determine the freshness of fish meal fat. High acid value means serious hydrolysis of fat and poor freshness. Free fatty acids will destroy the viscoelasticity of feed. High acid value can not be used as raw material for eel feed. According to the analysis and determination, the acid value of white fish meal is within 1 mg KOH/g, shore white fish meal is 1-1.5 mg KOH/g, domestic red fish meal is 3-5 mg KOH/g, imported steam-dried red fish meal is 2.61 mg KOH/g, and direct-fire-dried red fish meal is 4-5 mg KOH/g. Therefore, white fish meal is generally used as raw material for eel and turtle feed, steam The acid value of dried imported and domestic red fish powder should be reduced to less than 1.5mgKOH/g.
Color: light yellow to light brown, excessive color indicates excessive heating, too shallow, indicating insufficient heating. The color of the whole batch of soybean meal should be basically the same.
Taste: Roasted soybean flavor, no rancidity, mildew, coking, and no smell of raw beans.
Texture: uniform fluidity, irregular fragments, powdery or granular, without excessive impurities.
Specific gravity: 0.515 - 0.65Kg/l
Soybean meal contains about 43% protein, lysine 2.5% - 3.0%, tryptophan 0.6% - 0.7%, methionine 0.5% - 0.7%, cystine 0.5% - 0.8%; carotene is less, only 0.2-0.4 mg / kg, rhodamine and riboflavin 3-6 mg / kg, nicotinic acid 15-30 mg / kg, choline 2200-2800 mg / kg. Soybean meal is lack of methionine, crude fiber is mainly from soybean skin, nitrogen-free extracts are mainly disaccharides, trisaccharides, tetrasaccharides, starch content is low, mineral content is low, calcium is less phosphorus, vitamin A, B, B2 is less. Table 2 reflects the composition comparison of soybean meal and other kinds of oil dregs.