Identification of fish meal adulteration - microscopic examination and chemical method
Time：2017/7/20 19:15:50 Clicks：1563
High quality fish meal and color, yellow brown or yellow brown, powdery or granular, uniform size, surface drying and non greasy (a fatty fish meal, <12%), roast fish and slightly fishy. Carefully observed, you can see the transparent fish bones, fish bones, scales and other fish meal typical features.
Fishmeal type were observed for the yellow brown or brown, has the typical characteristics of fish, fish bones, scales, fisheye lens check identification. Fish under microscope with rough surface, fish silk fibers, like meat, color yellowish to brownish yellow; bone was translucent to opaque silver body, bone block was amber, the interspace of streamline dark wavy line, like a whip vine, from the roots along the edge extending outwards; scale transparent material flat or curved, concentric circles.
Fishmeal production, long time storage, by air oxidation and brown. Fish bone from translucent silver body to brown yellow translucent body, fish rough, fibrous structure is not clear or can not see.
Microscopic examination of adulterated fishmeal:
(1) seed coat characteristics under microscope doped rapeseed meal rapeseed meal mixed with rapeseed meal in fishmeal, the seed coat is yellowish brown to dark brown, flat, thin block, the outer surface of a honeycomb mesh, glossy surface, the inner surface is attached soft translucent white sheet. The seed coat and kernel fragments of rapeseed meal are not linked together. The seed kernel is pale yellow, irregular in shape, dull and fragile.
The typical characteristics of meal is palisade cells on the seed coat, brown pigment, 4~5 shape, cell wall, dark brown, thick wall, big cell cavity. Palisade cells are similar in shape and size, and are closely connected between cells.
(2) in the broken shell and cake particles of cotton fiber visible cottonseed meal mixed with microscopic cottonseed meal in fishmeal, white cotton fiber filament, hollow, flat, curly, translucent, shiny, cottonseed shell fragments and brown or red brown, thick and hard. Cottonseed Kernel fragments are yellow or brown, containing many round flat black or red fade oil glands or gossypol colored glands. The cottonseed hulls and the cottonseed kernels are joined together (they are pressed together, the overall color is dark, and the structure is difficult to distinguish).
(3) mixed with rice husk powder mixed with rice powder in fishmeal under microscope with glossy surface, long block is irregular, staggered texture, a grid shaped or cross stripe.
(4) mixed with wheat bran mixed with wheat bran meal under the microscope, light yellow or brown bran. There are fine wrinkles on the outer surface of wheat bran, and there are many transparent white starch granules adhered on the inner surface.
Bran, wheat bran, fine
Chemical test methods
Identification of 1, incorporation of urea in fishmeal
Microscopy: urea microscopically visible colorless / white needle like crystals, shiny.
Methods: chemical reagent: 0.1% cresol red indicator by 0.1g cresol red dissolved in 1000 ethanol mL95%.
Operation: two copies of 1.5g samples in two tubes, one of which add a little soy powder, two tubes each with distilled water 5mL, shaking it after 60-70 in constant temperature water bath 3min, 6-7 drops of cresol red indicator, adding soybean powder in deep purple red, then there is urea fish powder. Urea free tubes are yellow or brownish yellow.
(cresol red color range of 7.2-8.8, from yellow to purple red. Adding soybean powder contains urease, which can quickly decompose urea, release ammonia gas, change pH value of the solution, and then change from brown to purple after adding indicator. )
Identification of 2, fish meal incorporation of lignin or rice husk powder
Methods: chemical reagents: 20g/L benzene three phenol 95% ethanol solution. Take 20 g benzene three phenol, dissolve in 1000 mL capacity bottle, with 95% ethanol solution constant volume.
Take 1-2g samples in a test tube, add 10mL of benzene three phenol reagent, a few drops of concentrated hydrochloric acid, red particles produced for lignin, the powder is mixed with sawdust or rice husk.
Principle: benzene three phenol under acidic conditions and the lignin reaction, color reaction, generate cherry red or purple red complex. (benzene, three phenols can react with lignin in an acid environment)
Identification of 3, fish meal mixed with starch raw materials (such as starch, wheat bran, etc.)
Reagent: potassium iodide (potassium iodide 5g, 100mL dissolved in distilled water, then add 2G code)
2-3g samples in a beaker, add 2-3 times of water after heating 1min cooling after adding the reagent, if mixed with starch material is blue color. The color changes from blue to purple with the increase of the proportion of the blend.
Amylose in elemental code blue.
To test 4, fish meal mixed with calcium carbonate powder, powder, shell powder, eggshell powder available hydrochloric acid to produce carbon dioxide gas to determine carbonate.
The inspection of leather powder 5, in fishmeal
Take a little fish sample in a culture dish, add a few drops of ammonium molybdate solution (weigh 5g ammonium molybdate, 100 ml dissolved in distilled water, then adding 35 ml of concentrated nitric acid solution by immersion can), fish meal is appropriate, rest for 5~10 minutes, if not change color for leather powder, such as green for fish meal.