Fishmeal is a high-quality protein feed, but the quality of fishmeal on the market is uneven, and adulterated products occur from time to time. Most of the fishmeal is cheap and cannot be digested and absorbed by the body, which seriously affects the quality of feed. Therefore, the quality of fishmeal must be tested. Here are some common detection methods.
1. Sensory detection
1.1 Eyesight
(1) Looking at the color, high-quality fishmeal should have a fresh appearance. The color varies depending on the type of fish. Meehan fishmeal is light yellow or light brown, sardines are reddish-brown, and the transition to heat or fat is higher, and the color becomes darker.
(2) See the shape of the powder, including scales, fish bones, etc., and the well-treated fish meal can be seen in pork.
1.2 The sniffed fresh fish meal should have a roasted fish flavor and be slightly fishy. The smell of fish mixed with fish sauce should be heavier, but there should be no rancidity, ammonia odor, etc.
1.3 The hand grabs on the hand and rubs it with your fingers. The better the stickiness, the fresher the fishmeal (because the muscle fibers of the fish are sticky).
The judging method is as follows: mixing with 75% of fishmeal and 25% of starch, adding 1.-1.3 times of water to make, and then using hand-pulled viscoelasticity, it can be judged that: visco-elasticity is superior, its quality is better.
2 Physical detection
2.1 Determination of bulk density The bulk density of pure fishmeal is generally 450-660 grams per liter. If the fishmeal contains impurities or adulterants, the bulk density will change (large or small).
The test method is: Take the fish meal sample very lightly and carefully pour into a 1000 ml graduated cylinder until it reaches exactly 10000 ml scale, adjust the volume with a scraper or spoon. Pay attention to put the sample to light, and not shake and hit. The fishmeal is then poured out and weighed (three replicates are taken and averaged) and then compared to the volume of pure fishmeal.
2.2 Stereo Microscope Detection Pure fish meal includes a mixture of fish, fish bones, fish scales and fish guts. Its inspection features are:
Fish: large particles, rough surface, with a fibrous structure, yellow or brown, with a sense of transparency, broken broken tendons, seems elastic.
Fish bone: including fish bones, fish skulls, translucent or opaque pieces, different sizes and shapes, white to white, some fish bone crumbs into amber, smooth surface, fish spines slender and sharp, vertebral, careful Observe that the fishbone features a large or small tip in the fishbone pieces; the fish skull is flaky, translucent, and the front is textured, and the fish skull is stiff and inelastic. Fish scales: Flat or curly algae-shaped flakes, nearly transparent, with some concentric circular lines. Fisheye:: The surface is broken, with creamy spherical particles, translucent, dull and hard.
3 Chemical testing
3.1 Detection of Crude Protein Crude protein is a general term for nitrogenous substances contained in fishmeal, including true protein and non-protein nitrogenous substances. The latter mainly includes free amino acids, nitrates, and ammonia. The crude protein of domestic fishmeal is generally 45-55%, and the crude protein of imported fishmeal is generally 60-67%. The method of determination was performed using a Kay-type constant-nitrogen flask method. The specific procedures are omitted.
3.2 Detection of True Protein The crude protein reflects the content of all nitrogenous substances but does not reflect the true protein portion. Therefore, it is necessary to measure the true protein. The protein precipitates and precipitates with heavy metal salts under certain alkaline conditions. This precipitate is insoluble in hot water, whereas non-protein nitrogen is soluble in water. The precipitate is washed with hot water and the water-soluble nitrogenous material is washed off. The remaining precipitate was measured by the Kjeldahl method to determine the true protein content. Using the ratio of the true protein to the crude protein content, it was determined whether fishmeal contained water-soluble nonproteinaceous nitrogenous substances. test methods:
3.2.1 Pretreatment of Sample: Take 1-2 g of sample in a 200 ml beaker, add 50 ml of distilled water and boil, add 20 ml of 1% copper sulfate solution, stir while stirring, and continue stirring for one minute after adding. After standing for more than an hour or standing overnight, the precipitate is filtered through medium-speed qualitative filter paper, and the residue is repeatedly washed with hot water of 70°C or more until the filtrate is free of so2- 4 (take 5% guanidinium chloride solution 5 drops in a watch glass, A drop of 2 mol/L hydrochloric acid was added and the filtrate was dripped. No white precipitate should be observed on a black background). The filter paper and the residue are wrapped, placed in an oven, dried at 65-75°C for 2 hours, and the dried sample is placed in a flask together with the filter paper for digestion.
3.2.2 Subsequent steps The crude protein was measured and the true protein content was measured. The ratio of true protein content to crude protein content is both the true protein ratio of fishmeal. Crude protein should conform to product regulations. The true protein ratio should meet the following values: imported fishmeal should not be less than 80%, and domestic fishmeal should not be less than 75%. When the measured true protein ratio of fishmeal is less than the above value, the fishmeal is mixed with water-soluble non-soluble. Protein nitrogen material.
3.3 Determination of pepsin digestibility (in vitro digestibility) The size of pepsin digestibility indicates the quality of animal protein feed ingredients. It refers to the ratio of protein digested by pepsin to crude protein, usually expressed as a percentage. Qualified fish meal, its protease digestibility should not be less than 85%.
Method steps: Accurately weigh about 1 g of dehydrated and dehydrated fish meal, place it into a 300 ml conical flask, add 150 ml of preheated (42-45°C) 0.2% pepsin solution, cover and seal. Stir at 45°C. Digestion for 16 hours (a constant temperature oscillator is available). After digestion, it is filtered with filter paper, and then the undigested material on the filter paper is washed with warm water. The undigested material is transferred to a Kevlar flask with the filter paper for digestion. The subsequent steps are the same as the measurement of crude protein to measure the amount of undigested crude protein, and the fish meal is measured at the same time. Crude protein.
Pepsin digestibility of fishmeal = (meal of fish meal - amount of undigested crude protein) / crude protein x 100%
3.4 Determination of Amino Acids By measuring the amino acids of fishmeal, it is known that the contents of various amino acids in the fishmeal and the corresponding proportions, so that the balance of fishmeal and protein is known, the higher the amino acid content and the balance, the qualified high quality fishmeal.