The determination of crude fiber has always been one of the most common test items in the laboratory. Crude fiber, which has evolved from the earliest chemical test to the later use of the instrument method-rough fiber tester, has undergone great progress. The measuring principle of the coarse fiber measuring instrument is actually the same as the previous measuring method, but it is easier to operate on the country. In addition, the crude fiber analyzer uses acid-alkali digestion. This is also the most commonly used method for crude fiber determination. In addition, crude fiber determination, in addition to the ability to study and evaluate the digestibility and nutritional value of food, also plays an important role in preventing many diseases such as heart disease and colon cancer. The following are some of the things we pay attention to in our specific experimental operations. If we can work hard, we can greatly increase the efficiency of our tests.
The national standard method uses 1.25% H2SO4 solution and filters it with linen cloth. It can be seen that there are a lot of flocculent precipitates in the filtrate. According to the principle of the method, the diluted acid is treated with starch, pectin and other substances, and the resulting residue is further diluted with alkali. Treatment, the first step of filtration has lost part of the crude fiber; after dilute alkali treatment after filtration with linen, the flocculent precipitate is still visible in the filtrate, and the second step of filtration loses some of the crude fiber, resulting in partial determination of the crude fiber content. low. The improved method adopts 200 mesh and 12 layers of nylon cloth to filter, and there is no flocculation in the filtrate after dilute acid treatment. After dilute alkali treatment, the 200 mesh 12-layer nylon cloth suction filter tube is used to draw the supernatant liquid without any loss of crude fiber during the whole process. The accuracy of the measurement results. Dilute alkali treatment after the treatment of the liquid is also very important to stand still, when the micro-boiler to remove the beaker static layered, the time can not be too short, must be stratified and then suction filter, the better. The degree of smashing of the sample also affects the measurement results of the crude fiber. The large particle size of the sample will affect the dilute acid hydrolysis of starch, pectin and other substances. The dilute alkali will dissolve and remove proteins, fats, and some hemicelluloses. If the sample particles are too small, crude fiber will be lost during filtration, resulting in a low measurement result for crude fiber. It is recommended that the sample be crushed after 80 mesh sample separation. When the sample is measured, a 500ml beaker is used to cover the watch glass for heat treatment. Because the mouth of the beaker is large, it can prevent bubble overflow when acid and alkali are added. Capping the surface dish can reduce the volatilization of acid and alkali. The reproducibility test results showed that the content of crude fiber in soybean meal was determined by filtration using 12-layer nylon fabric of 200 mesh. The repeatability of five consecutive measurements was satisfactory, with X=2.45% and RSD=2.4%.
In summary, according to the current national standard “Food Sanitation Inspection Methods • Physical and Chemical Parts (1)†(GB/T5009-2003) Determination of crude fiber in plant-based foods, the crude fiber in foods is found to have low results. In order to effectively reduce the system deviation caused by filtration, a 200-mesh 12-layer nylon cloth filtration improvement method is recommended to improve the accuracy of the determination of crude fiber in plant foods.
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