Two. Analyze and compare the internal quality of fish meal.
1. freshness of fish meal
(1) freshness index of protein: VBN
The freshness of protein is determined by the level of volatile base nitrogen (VBN) and histamine.
A. Volatile salt-based nitrogen-fish meal VBN within 50mg/100g freshness, more than 150mg/100g that has begun to decay, VBN more than 150mg/100g of fish meal, generally not suitable for use.
B. The average histamine content of histamine-white fish meal was 28 ppm, and the histamine content of red fish meal was much higher than that of white fish meal. The average steam-dried imported fish meal was 267 ppm, the dry-dried imported fish meal was 442 ppm, and the domestic high-grade fish meal was 321 ppm, which was lower than that of imported red fish meal dried by direct-fired. Therefore, the histamine content of domestic high-grade 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.
(2) index of freshness 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 high-grade raw material for eel and turtle feed. If the acid value of imported and domestic red fish meal dried by steam is lower than 1.5mg KOH/g, the white fish meal may be partly replaced as feed for eels and turtles. Direct fire dried red fish meal is used as feed ingredient in general aquatic feed and livestock feed.
(1) evaluation of fishmeal protein quality
Fish meal is an important raw material of animal protein. It is very important to evaluate the quality of protein. Pepsin digestibility is an important basis for evaluating the quality of protein. The average imported white fish meal is about 90%, the average imported red fish meal is about 95%, and the average domestic red fish meal is about 92%, which is between the imported red fish meal and white fish meal.
(2) amino acid analysis and comparison
Protein is composed of about 20 kinds of basic acids, of which lysine, methionine, phenylalanine and other 10 are essential amino acids that fish can not synthesize. The balance of amino acid composition has great influence on protein digestibility. Different fish meal amino acid composition is different, and different breeds of fish for amino acid needs are also different, so feed enterprises have a certain preference for fish meal.
It can be seen from the above comparison that the content of methionine in white fish meal is relatively high, the essential amino acid composition is similar to the eel feed standard, and the histidine content is generally less than 1.2%, which is suitable for high-grade feed. The essential fatty acid composition of domestic red fish meal is ideal. The limited amino acid content in the feed of shrimp and eel, such as lysine, methionine and phenylalanine, is higher than that of white fish meal, and the protein nutritional value is also higher. The content of alanine, proline and glycine in red fish flour, especially domestic red fish powder, is similar to that of white fish meal. The content of aspartic acid, glutamic acid and methionine is higher than that of whitefish powder. The nutritional value of homemade steam fish meal is only inferior to that of white fish meal and super imported steam fish meal.
To sum up, the evaluation of fish meal quality depends not only on protein and other conventional nutrients and sensory indicators, but also on the freshness index, pepsin digestibility index, amino acid and fatty acid composition, otherwise one-sided conclusions will be drawn.