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A Brief Discussion on the Common Methods for Identification of Fish Powder Adulteration

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A Brief Discussion on the Common Methods for Identification of Fish Powder Adulteration

Date of release:2017-06-06 Author: Click:

 Fishmeal is a high quality animal protein material widely used in livestock and poultry and aquatic feed. The protein content is high, the protein digestibility can reach about 90%; the amino acid composition is complete and balanced, wherein the lysine and methionine contents are high; the calcium and phosphorus content is high, the ratio is good, the utilization rate is high; the minerals, vitamins, etc. It is also very rich, in addition to a variety of unknown growth factors, good palatability, and therefore has an extremely important role in the production of aquatic feed.Adulterated doping is particularly prevalent due to its large amount of use and high market prices.

  The following describes some conventional detection methods to qualitatively determine the adulteration of fish meal. Commonly used methods include sensory identification method, microscopic identification method, near-infrared technology identification method, physical identification method, chemical identification method and amino acid component determination.

  1 sensory identification

  1.1 Observing the color

  The color is consistent without any "carrier", such as fish bones, fish fillets, fish scales, fish eyes are generally formulated fishmeal.

  1.2 smell smell

  Good fishmeal has a scent of fishy fishmeal. The adulterated fishmeal has a scent, ammonia smell, rancid taste, mixed plant flavor mixed with plant lignin raw materials, and mixed animal smell mixed with other animal-derived feed.

  1.3 taste

  The palate is the killer of fishmeal. The entrance of the good fishmeal is instant, and there is the taste of the fragrant fish fillets. The adulterated fishmeal contains no spicy, astringent, bitter, and savory flavors.

  1.4 Touch

  The thumb and index finger are lightly squid, the fishmeal is fine and smooth, and the adulterated fishmeal is coarse and has fine particles.

  1.5 burning

  The normal fishmeal induction cooker has a fishy aroma, and if it is unpleasant, smelly or aromatic, it is adulterated fishmeal.

  2 microscopic identification

  Under the microscope, the fish has large granules, rough surface, fibrous structure, yellow or yellowish brown, transparent, and shaped hooves, which are elastic; fish bones (including fish bones and fish skulls) are translucent or opaque. The blocks vary in size from white to white (some fish bones are amber), the surface is smooth, the fishbone is slender and pointed, and it looks like a vertebra. If you look closely, you can see that there is a big end or small end in the fishbone pieces. The head of the fishbone is characterized, while the fish skull is flaky, translucent, with a textured front, the fish skull is hard and inelastic; the scales are flat or curly algae-shaped sheets, nearly transparent, with some concentric lines; fish eyes , the surface is fragmented, milky spherical particles, translucent, dark and hard.Other particles or powders which are far apart from each other in the fish meal are mostly adulterants, which can be identified according to the microscopic features of the adulterated objects.

  2.1 botanical raw fishmeal adulteration

  Fishmeal mixed with soybean hull powder: Soybean skin powder is blended in fish meal, and pea skin is visible under the microscope, which is yellow or yellow lumps. The hull has concave spots, a slight curl, and a navel. It can also be seen under the microscope that white sponge-like starch floats on the surface of the block like a water droplet.

  Fish meal mixed with peanut cake: the fish cake is mixed with peanut cake, and the peanut shell and seed coat are visible under the microscope. The shell is broken, irregular, and thin and flaky. The inner layer is white sponge-like, with fiber interlacing, and the outer surface has a rib-like mesh, and the seed coat is red, pink, deep purple or brownish yellow.

  Fish meal mixed with rapeseed meal: fish meal mixed with rapeseed meal, the seed coat of rapeseed meal can be seen under the microscope, the seed coat characteristics are brown and thin, the outer surface has honeycomb mesh, the surface is shiny, and the inner surface is soft. A translucent white sheet is attached. The seed coat and seed kernel pieces of rapeseed meal are not connected together, and the seed kernel is yellow, irregular in shape and dull.

  Fish meal with cotton kernel cake: The fish meal is blended with cotton kernel cake. Under the microscope, the cotton wool fiber is attached to the outer shell and the cake particles. The cotton wool fiber is white silk, hollow, flat, curly, translucent, and Gloss, cotton husk fragments are brown or reddish brown, thicker. There are different shades of yellow or yellowish brown along its edges with a stepped surface. The cottonseed kernels are yellow or yellowish brown and contain many round flat black or reddish brown oil glands or gossypol glands.

  Fishmeal mixed with rice hull powder: rice husk powder is mixed into fish meal, and rice husk fragments are visible under the microscope. The surface of the shard is shiny and well-streaked, and the hair on the surface of the shell is visible.

  Fish-boiled fishmeal: Fish bran is blended with wheat bran, and yellow or brown, flaky bran can be seen under the microscope. The outer surface of the bran has fine wrinkles, and the inner surface is adhered with many opaque white starches.

  Fishmeal mixed with sesame cake: The fish meal is mixed with sesame cake. The sesame seed coat can be seen under the microscope. The sesame seeds are thin and have tiny round protrusions on the surface, which are black, brown or yellowish brown, depending on the variety.

  2.2 Animal raw materials, fish meal adulteration

  Fish powder mixed with leather powder: Fish powder is mixed with leather powder. Under the microscope, green, dark green and brick red blocks or filaments can be seen. Like sawdust, it is not as transparent as hydrolyzed feather powder.

  Fishmeal mixed with hydrolyzed feather meal: fish meal is mixed with hydrolyzed feather powder, and semi-transparent and irregular broken particles are visible under the microscope, and some are reflective. At the same time, the feather shaft is visible, which is like a hollow circle. Raw feathers that are not fully hydrolyzed can also be seen.

  Fish powder mixed with blood: fish powder is mixed with blood powder. The characteristics of blood powder are visible under the microscope. The blood powder has different shapes in the mirror, some edges are sharp, and some edges are rough and irregular. The color has a black-like asphalt or a bead of a blood-red crystal shell.

  Fish meal mixed with meat and bone meal: meat and bone meal is mixed into the fish meal. Yellow to dark brown particles are visible under the microscope, and the color with high fat is deep. It has a luster of oil reflection and a rough surface. Very fine, interconnected muscle fibers can be seen under the microscope. The bones are white, gray or light brownish-colored lumps, opaque or translucent, with spots and round edges. In addition, hair, hooves and the like can be seen, and the characteristics of mixed blood powder are often seen.

  Fish meal mixed with shrimp head or shrimp powder: fish head powder is mixed with shrimp head powder, and shrimp, eyeball, shrimp shell and shrimp are visible under the microscope. The shrimp shell resembles a curled mica-like sheet, which is translucent. A small amount of shrimp is tied to the shrimp shell. The shrimp eye is black spherical granules and is a more recognizable feature in shrimp head powder. Shrimp must be in the form of fragments under the microscope, long round tubular. With spiral parallel lines. The shrimp legs are broadly tubular, translucent, with or without hair.

  Fish meal mixed with crab shell powder: fish shell powder is mixed with crab shell powder, and the characteristics of crab shell can be seen under the microscope. The crab shell is a regular fragment, and the outer layer of the shell is mostly orange-red, porous, and has a honeycomb-shaped round positive spot.

  Fish meal with shell powder: The shellfish powder is mixed with fish powder. The tiny particles of the shell are visible under the microscope. The surface is smooth and the color varies greatly depending on the type of shell. Some are white or gray, and some are pink. Some of the outer surfaces of the particles have concentric or parallel textures or have darkly interlaced strands, some of which are jagged.

  Adulterated fishmeal for the purpose of increasing total nitrogen: The urea-formaldehyde polymer is a milky yellow irregular sphere which, when lightly pressed with a probe, disperses and crystallizes, and is insoluble in water.

  3 Identification of near-infrared analysis technology

  Taking fishmeal as the research object, based on near-infrared reflectance spectroscopy (NIRS) technology, the DPLS qualitative discriminant analysis model of animal and plant adulteration components in fishmeal was established, and the model was optimized by different variable screening methods. The animal and plant in fishmeal was established. The PLS quantitative analysis model of adulterated components was used to optimize the model by moving window partial least squares method and different variable screening methods. The transmission method of quantitative analysis model of adulterated components in fish meal was established. Murray et al. used the near-infrared spectroscopy technique to qualitatively and quantitatively analyze the content of meat and bone meal in fishmeal. The results show that the near-infrared technique can qualitatively distinguish whether meat and bone meal is mixed in fishmeal. Domestic related research shows that NIR technology can distinguish fake fish meal mixed with soybean meal, wheat bran, rapeseed meal and non- adulterated fish meal, and can quantitatively predict the content of adulterated products.

  4 physical identification

  4.1 Water-soluble method

  Take a small amount of the sample, put it into clean glass or burn, add 10 times of water, stir vigorously, and let stand, observe the surface floating matter and the bottom sediment. If the surface of the water is covered with feather fragments or plant-like substances such as rice husk powder, peanut shell powder, wheat bran, etc., there are sandstone and minerals at the bottom, indicating that hydrolyzed feather powder or plant-based adulterated substances are incorporated.

  4.2 Screening method

  The fishmeal samples were screened with a standard sieve having a pore size of 2.80 mm, and at least 98% of the standard fishmeal particles were passed. Otherwise, the fishmeal was mixed with fakes, and the mixed impurities were detected using sieves of different meshes.

  4.3 Odor Test Method

  The authenticity of the fish meal can be judged based on the odor generated when the sample is burned. When burning, if it smells like pure hair burning, it means animal-based adulterated substance; if you smell the aromatic smell of dried grains, it means that the fishmeal is mixed with plant matter; take 20g of sample and put it into small flask Or in a triangular flask, add 10g of soy flour, appropriate amount of water, and heat it for 15min~20min after plugging. After removing the plug, you can smell ammonia, indicating that there is urea incorporation.

  4.4 Volumetric method

  The bulk density of pure fishmeal is generally 450g/L~660g/L. If the bulk density is obviously too large or too small, it means that the fishmeal is mixed with impurities. The specific test method is: take the fishmeal sample very lightly and carefully into the 1000ml measuring cylinder until it reaches the 1000ml mark, and adjust the volume with a spatula or spoon. Be careful to put the sample in a light position and do not shake or hit it. The fish meal was then poured out and weighed (three parallel samples, averaged) and then compared to the volume of pure fishmeal.

  5 chemical detection method

  Chemical identification is divided into qualitative and quantitative.

  5.1 Qualitative identification

  5.1.1 Detection of the incorporation of plant matter into fishmeal

  All plant matter contains starch and lignin. Starch can be reacted with potassium iodide to produce a blue or blue-black compound. Lignin reacts with phloroglucin under acidic conditions to produce a red compound.Therefore, by using the above two reactions, it is possible to quickly detect whether the fishmeal is contaminated with plant matter.

  Fish powder mixed with starchy substance test: Take 1g ~ 2g of fishmeal sample in small burnt, add 10ml of water to cook for 5min, and then add two drops of I-KI solution after cooling. If there is no color reaction, it is pure fishmeal, such as The color appears blue or black and blue, indicating the presence of starch in the sample.

  Fish powder mixed with lignin test: Take 1g of fishmeal sample, place it in a test tube, soak it with a solution of phloroglucinol, place it for 5min~10min, add 2~3 drops of concentrated hydrochloric acid, observe the color, such as sample Dark red indicates that the sample contains lignin.

  5.1.2 Detection of blood meal in fish meal

  The blood meal contains iron, which decomposes hydrogen peroxide to release new ecological oxygen, oxidizes benzidine to benzidine blue, and a blue ring point appears. According to whether the ring point appears, it can be judged whether the fish meal is mixed with blood powder. Specific detection method: take a small amount of fish meal in a white porcelain dish, add a few drops of benzidine-glacial acetic acid mixture (1 g of benzidine added to 100 ml of glacial acetic acid, add 150 ml of distilled water to dilute) soaked fish powder, add 3 One drop of hydrogen peroxide solution. If the fish meal is mixed with blood powder, it will be dark green or blue-green.

  5.1.3 Detection of non-protein nitrogen compounds in fish meal

  5.1.3.1 Detection of urea formaldehyde polymer in fish meal

  The urea-formaldehyde polymer decomposes under the action of sulfuric acid to form formaldehyde, and formaldehyde reacts with chromium to form a purple compound. Protein and fat are not involved in this reaction.

  5.1.3.2 Detection of incorporation of biuret in fish meal

  The principle of this method is that biuret can be combined with Cu2+ to form a purple-red compound under alkaline environmental conditions. Detection method: Weigh 2g of the tested fish meal into 20ml distilled water, stir evenly, let stand for 10min, filter with dry filter paper, take 4ml of filtrate into the test, add 1ml NaOH solution with concentration of 6mol/L, add lml concentration to 1.5 The % CuSO4 solution was observed immediately after shaking. If the solution was purple-red, it indicated that the fish meal was doped with biuret. The darker the color, the larger the amount of incorporation.

  5.1.3.3 Detection of urea in fish meal

  The urease enzyme in raw soy flour can decompose urea to form ammonia, making the aqueous solution alkaline, and the solution is red after adding phenol red reagent. The detection method is as follows: the suspect is clipped 3 to 5 in the microscope, placed in a 15 ml colorimetric tube, and a small amount of raw soybean powder is added with about 0.2 g, 3 drops to 5 drops of phenol red indicator (1 g/L), and then Add 10ml of water, quickly cover the stopper, shake for a while, let stand for a few minutes, if the solution turns red, the sample contains urea.

  5.1.3.4 Detection of ammonium salt in fish meal

  The ammonium salt rapidly decomposes under the action of a concentrated alkali to form ammonia to make the pH test paper blue. The specific detection method is as follows: 3 pieces to 5 pieces of suspicious objects are clipped from the microscope, placed in a petri dish, and a moist pH test paper is attached to the dish, and about 3 ml of concentrated sodium hydroxide having a concentration of 30% is added to the dish. The solution is quickly covered with a petri dish. If the pH test paper turns blue immediately, the sample contains ammonium salts.

  5.1.4 Detection of the incorporation of leather powder into fishmeal

  The part of the leather powder can be changed into Cr6+ after chrome ashing, and Cr6+ can react with the homodiphenylamine urea in a strong acid solution to form a purple-red water-soluble chromium-diphenylthioindole compound. The reaction is extremely sensitive and traces of chromium can be detected. The detection method is as follows: taking 1 g to 2 g of the fish meal to be tested into a porcelain crucible, carbonizing and ashing, cooling, ash the ash with a little distilled water, adding 10 ml of (NH 4 ) 2 SO 4 to make the solution acidic, and adding a few drops of the diphenylamine group. The urea solution (0.2 g to 0.5 g of the diphenylamino urea dissolved in 100 ml of 90% ethanol), if a purple color appeared after a while, it was confirmed that the leather powder was incorporated.

  5.2 Quantitative identification

  5.2.1 Detection of crude protein

  National industry standards use crude protein content as the main indicator to measure the quality and grade of fishmeal. The crude protein should be tested first. The crude protein content was determined in accordance with the provisions of the national standard method. In general, the higher the crude protein content, the better the quality of the fish meal. But this is not the case, because the crude protein content is obtained by measuring the total nitrogen content, which does not rule out non-protein interference.

  5.2.2 Testing of true proteins

  It is important to determine the true protein content of fishmeal, which is also demonstrated in production practice. Although methods for determining true protein content have not been included in national standards, this method is currently commonly used to determine whether high nitrogen compounds are incorporated to exclude non-protein interference. According to the data, the ratio of true/crude protein content of fishmeal is roughly: imported fishmeal is greater than 80%, and domestic fishmeal is greater than 75%. The author has tested the fishmeal produced by some manufacturers, the crude protein is 55% to 60%, and the true protein is only about 10%. Such fishmeal is definitely inferior or adulterated fishmeal.

  5.2.3 Determination of pepsin digestibility

  Pepsin digestibility, which is the ratio between protein and crude protein that fish meal can be decomposed by pepsin. For qualified fish meal, the protease digestion rate should not be less than 85%. Determination of pepsin digestibility can identify whether fishmeal adulterants are high-protein and not easily absorbed, such as feather meal, leather powder, and the like. The measurement is carried out according to the national standard method. Sometimes the fishmeal sample is tested, its crude protein and true protein content are very high, but its pepsin digestibility is low, generally only 50% to 60%, or even only 30% to 40%, such fishmeal is also inferior or Adulterated fish meal.

  5.2.4 By measuring the amino acid content of fishmeal, the adulteration of fishmeal can be effectively identified.

  When using the amino acid index to judge the quality of fishmeal, it is not possible to refer only to the methionine and lysine indicators. It should be considered in combination with multiple amino acid indicators, with particular attention to serine, histidine, leucine, isoleucine and other indicators. In the actual work, the amino acid index should be combined with conventional indicators, sensory examination and microscopic examination for comprehensive judgment.

  In addition, in addition to the analysis of the above four indicators, according to the actual situation, should also analyze the coarse ash, crude fiber, total chromium, calcium, phosphorus and other indicators.

  6 Conclusion

  Select the identification method to determine the identification order. The sensory identification method is the most primitive but also the most important, the simplest and the cheapest. Other methods of identification are inseparable from its cooperation. It is the preferred method. The near-infrared NIR technology is based on a large number of physical and chemical detection, and is convenient and quick to use. The physical identification method is a method selected when the sensory identification method does not identify the result of adulterated fish meal.Chemical identification method is a method used by both sensory and physical identification methods to determine the true and false fish meal and its advantages and disadvantages. In particular, chemical quantitative identification is a necessary method to identify the quality of fishmeal. In general, in the actual testing process, the identification plan and plan should be designed according to the needs.

A Brief Discussion on the Common Methods for Identification of Fish Powder Adulteration

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