Fishmeal is a high-quality protein feed, but the fishmeal on the market often has adulteration, and most of the blended are cheap, non-absorbable feather powder, plant root powder, leather, etc., which greatly reduces the quality of the feed. Therefore, the quality of fishmeal must be monitored. The quality inspection method of fishmeal is described below.
First, sensory characteristics
Pure fishmeal is generally yellow-brown or yellow-brown, and there are also a small amount of white fish meal, gray fish meal and other fish species. It has a grilled fish flavor and a slightly fishy smell. The astringency of the fish paste mixed is heavier, and there is no rancidity, ammonia smell and the like, and excessive ripeness. Fishmeal is powdery, containing scales, fish bones, etc., and well-processed fishmeal has visible fish silk.
The muscle fiber of the fresh fish is sticky, so grab the fish meal with your hands and rub it with your fingers. The sticky fish powder is fresher. A fine mesh having a fineness of at least 98% can pass through a standard screen having a mesh opening width of 2.80 mm.
Second, chemical testing
1. Crude protein crude protein is a general term for nitrogenous substances in fishmeal. From the detection data and production situation of many samples, the crude protein of domestic fishmeal is generally 45% to 55%, and the crude protein of imported fishmeal is generally 60%. ~67%, too low may be caused by high impurities in fishmeal raw materials, too high may be caused by adulteration. The method for the determination of crude protein is generally carried out by a Kay-style nitrogen flask method.
2. Pepsin Digestibility Pepsin digestibility refers to the ratio between protein and crude protein digested by pepsin. For qualified fishmeal, the protease digestion rate should not be less than 85%.
Method step: accurately weigh about 1 gram of dehydrated defatted fish meal, put it into a 300 ml flask, add 150 ml of 0.2% pepsin solution preheated (42 ° C ~ 45 ° C), cover the seal, stir at 45 ° C Digestion for 16 hours (available with a constant temperature oscillator). After digestion, it was filtered with filter paper, then the undigested material on the filter paper was washed with warm water, and the undigested material was transferred to a Kay flask with a filter paper for digestion, and then the crude protein was measured in the same step, and the amount of undigested crude protein was measured. Pepsin digestibility of fishmeal = (amount of fish meal crude protein - undigested crude protein) / crude protein × 100%
In addition, the crude fat of fishmeal should generally not exceed 12%. The crude fiber of fishmeal should be almost zero, and if it is too high, it will be mixed with fibrous raw materials. Such as: raw sugar, wood chips, etc.
Third, the detection of some common adulterants
1. Test method for incorporating feather powder into fish meal Steps: Put about 1 gram of fish meal into a 500 ml flask, add 1 ml of 1.5% sulfuric acid solution, boil for 30 minutes, and add distilled water to keep boiling sulfuric acid. The concentration was allowed to stand after completion, and the residue in a small amount of bottle was placed on two slides. Observed under a microscope from 50 to 100 times.
The sulfuric acid-treated residue, if it has light-colored feather powder, is yellow in color after hydrolysis by sulfuric acid. If there is dark feather powder, the color is dark brown or black after hydrolysis by sulfuric acid. Under the microscope, the fully hydrolyzed feather powder is yellow, gray or brown translucent granules, while the incompletely hydrolyzed feather powder can see some tubes. These are dried feathers or feather tubes, mostly yellow and brown. Some are shaped like glass granules.
2. Incorporation of cottonseed cake into the fish meal. Place 20 mesh and 40 mesh sample sieves together, then take the tested fish meal into the sample sieve and shake for about 5 minutes. Observe the 40-mesh sieve residue in the middle layer and observe whether there are cotton fibers on the sieve. Most of the cotton fibers are dark yellow or brownish yellow. In addition, dark brown cotton seed shell fragments can be seen on the sieve, which can be confirmed that the fish meal is mixed with cotton seed cake.
3, fish meal mixed with urea and other nitrogen fertilizer detection method steps: take 1 gram to 2 grams of fish meal in a beaker, add distilled water 50 ml and stir well, filter with qualitative filter paper, then wash with distilled water 7 times ~ 8 times The total volume of the washing liquid is about 200 ml, and then the whole fish meal is placed on a filter paper and dried in an oven at 65 ° C for 2 hours, and the crude protein content can be measured by the Kay-style nitrogen method. For example, fishmeal is marked with 65.2% crude protein and 34.7% after water washing, indicating that the latter is spiked with a certain amount of soluble nitrogen fertilizer.
4, fish meal mixed with rapeseed cake or cotton cake test normal fish meal, its crude fiber is very low, generally 0.1% ~ 1%, coarse ash generally does not exceed 23%, when mixed with rapeseed cake or cotton cake The crude fiber is increased to more than 10%. Therefore, when the ash content is higher than 28% and the coarse fiber is higher than 2%, it indicates that there is a adulterant.
5. Inject the plant material or fine sand into the fish meal. Take a little sample and put it into a clean glass or beaker. Add 10 times of water, stir vigorously, and let stand, observe the surface float and bottom sediment. If the surface of the water floats with plant-like substances such as rice husk powder, peanut shell powder, wheat bran, etc., it indicates that there is hydrolyzed feather powder or plant matter. If there are sandstone and minerals at the bottom of the cup, it means that these substances are incorporated.
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