Starch is the main storage material of plants, mostly in seeds, roots and tubers. Starch is not only an important nutrient, but also has a wide range of industrial applications. Determination of the starch content in cereals is of great significance for characterizing the quality of agricultural products and for improving agricultural production techniques.
Principle
The basic principle of the determination of starch content in cereals is that starch is a polysaccharide composed of glucose residues, which is hydrolyzed into glucose by heating under acidic conditions, and then under the action of concentrated sulfuric acid, the monosaccharide is dehydrated to produce furfural compounds, and the color reaction between the onion and ketone reagent and the furfural compounds is utilized, which means that colorimetric determination can be carried out.
Operation method
Determination of starch content in cereals
Principle
The basic principle of the determination of starch content in cereals is that starch is a polysaccharide composed of glucose residues, which is hydrolyzed into glucose by heating under acidic conditions, and then under the action of concentrated sulfuric acid, the monosaccharide is dehydrated to produce furfural compounds, and the color reaction between the onion and ketone reagent and the furfural compounds is utilized, which means that colorimetric determination can be carried out.
Materials and Instruments
Material: Flour or other air-dried and pulverized samples. Move The basic procedure for the determination of starch content in grains can be divided into the following steps:1. Standard curve production: take 7 large test tubes, add reagents according to Table 52-1, shake well immediately, cover with lid, boil in boiling water bath for 10 min, remove and cool to room temperature, adjust zero with 0 tube, and compare the color at 625 nm wavelength. Take the standard glucose content as the horizontal coordinate and the absorbance value as the vertical coordinate to draw the standard curve.Table 52-1 Standard Curve Preparation and Addition Table Caveat 1. The color developing solution in the experiment is a strong acid solution, pay attention to safety in use, do not splash on your body and equipment. 2. Starch should be fully decomposed into glucose during the experiment, otherwise the experimental results will be low. 3， The starch solution must be cooled down quickly after heating to prevent the starch from aging and forming highly crystallized insoluble starch molecule micelles. For more product details, please visit Aladdin Scientific website.
Equipment: plant sample pulverizer, centrifuge, balance, spectrophotometer, thermostatic water bath, sieve (100 mesh), funnel, centrifuge tubes, etc.
Reagents:
① Concentrated H
2
SO
4
(relative density 1.84)
② Onion ketone reagent (same as experiment 52)
③80% ethanol
④4.6 mol
-④4.6 mol
HClO
4
solution and 9.2 mol - L
-1
HClO
4
solution.
2 . Sample Extraction: Weigh 50~100 mg of dried sample pulverized through a 100-mesh sieve, put it into a 15 mL graduated test tube, add 6~7 mL of 80% ethanol, and extract it for 30 min in a water bath at 80°C. Remove it and centrifuge it for 5 min (3,000 r - min 1), and collect the supernatant. Repeat the extraction twice (10 min each) and centrifuge the same way, collect the supernatant of the three times and combine them in a beaker, put it in a constant temperature water bath at 85°C, evaporate the ethanol to 2~3 mL, stir well, put it into a boiling water bath to paste for 15 min. After cooling, add 2 mL of cold 9.2 mol - L-1HClO4, stirring from time to time, after the extraction for 15 min, add the evaporated water to 10 mL, mix well, then extract for 10 min. Centrifuge for 10 min, and pour the supernatant into a 50 mL volumetric flask. Then add 2 mL of 4. 6 mol - L-1HClO4 solution to the precipitate, stir the extraction for 15 min, add water to 10 mL, mix well and centrifuge for 10 min, collect the supernatant in a volumetric flask. Then the precipitate was washed with water for 1~2 times, centrifuged, and the centrifuged solution was combined in a 50 mL volumetric flask, which was then diluted with evaporated water for starch measurement.3. Determination of samples: Take 1.0 mL of the extract of the sample to be tested into a test tube, add 5 mL of onion and ketone reagent, shake quickly, then boil it in a boiling water bath for 10 min, take out and cool it down, and then determine the absorbance value at 625 nm by zeroing with a blank, and then find out the sugar content (fJLg) from the standard curve.4 . Calculation of results:The 宀四人曰 丨 C X VTX0.9Starch content ® -")=Where a sucrose concentration from the standard curve, 卩 g - mL1 ; 卩丁一total volume of sample extract, mL;yu a volume of sample solution taken during color development, mL;m i sample weight, mg;0. 9 A coefficient of conversion from glucose to starch. Reagent Tube No. 0 1 2 3 4 5 6 Standard glucose solution/mL 0 0.1 0.2 0.4 0.6 0.8 1.0 Evaporated pomegranate water/mL 1.0 0.9 0.8 0.6 0.4 0.2 0 Sucrose concentration/(ptg・mL'1 ) 0 10 20 40 60 80 100 Onion ketone reagent/mL 5 5 5 5 5 5 5 5 5 5