Extraction and content determination of vitamin C in food.

(2, 4 - dinitrobenzene method)
(experimental purposes 1. Be familiar with the physiological function of vitamin C..2. Master the extraction and content determination of vitamin C in food..vitamin C is one of the most important vitamins in human nutrition and is an unsaturated polyhydroxy
compound
with L-sugar configuration, which belongs to the water-soluble vitamin. Vitamin C deficiency produces scurding, and therefore is also known as astraychtic acid. Vitamin C is widely distributed, and the green parts of plants and many fruits (oranges, strawberries, hawthorns, peppers, etc.) are more abundant..Vitamin C is highly reductive. Easily oxidized into dehydrogenated vitamin C. Dehydrogenated vitamin C retains the biological activity of vitamin C and is reduced to vitamin C in animal tissues such as glutathione. At pH >7.5, dehydrogenated vitamin C easily rearranges its molecular structure so that its inner ester rings crack, producing inactive dhitone guccitic acid. Vitamin C, dehydrogenated vitamin C, and dyloxone glucosaccharides are called total vitamin C..Total vitamin C in food includes both prototype and dehydrogenation. Food is old, stored for a long time and cooked and processed food, a considerable part of which becomes dehydrogenated, this form of vitamin C still has about 85% vitamin C activity, so this type of food is often measured total vitamin C. The prototype vitamin C in the sample must be oxidized into dehydrogenated vitamin C. Red , which is produced by dehydrogenated vitamin C and di ketone glucosaccharides, is directly related to the total vitamin volume due to the action of 2,4- dinitrobenzene. So theis dissolved in sulfuric acid, and then compared with the same treatment of vitamin C standard liquid color, can find out the total vitamin C content in the sample.. Equipment and
reagents 1. Equipment ,
thermostat
water bath, 72-type hydrometer, 50m1
capacity bottle
, scale
straw
, 100m1 conical bottle..2. Reagents(1) orange peel..(2) 9N sulphuric acid: 25m1 thick sulphuric acid (specific gravity 1.84) slowly added to 700m1 distilled water, cooled and diluted to 1000mI..(3) 2% 2,4-dinitrobenzene: dissolved 2g2, 4-dinitrobenzene in 100ml 4.5mol/L (9N) sulphuric acid,
filtered
. Save at 4 degrees C. It needs to be filtered again before each use and the storage time is limited to 2 weeks..(4) 85% sulphuric acid: 90m1 thick sulfuric acid (specific gravity 1.84) slowly added to 100mI water..(5) 1% herbal acid solution..(6) 10% sulfonate: said to take thiolyculfan 50g dissolved in 1%500mI grass acid, 4 degrees C preservation. The term of preservation is 2 months..(7) Activated carbon: 100g of activated carbon added 750ml 1mol/L (1N) hydrochloric acid reflow 1 to 2h, filtration, with distilled water repeatedly washed activated carbon until there is no Fe3 plus in the washing filter. Then dry the cooled rear in the oven at 110C
dry
in the receiver..(8) Standard vitamin C storage liquid: accurately named vitamin C100mg, dissolved at 1% herbal acid and fixed capacity to 100m1, 4 oC storage..(9) Standard vitamin C application liquid: accurate absorption of standard vitamin C storage liquid 1.0m1 in 100m1 capacity bottle, diluted to the scale with 1% herbal acid solution, ready to use.. Step 1.1. Sample extraction Orange peel 2g shredded place , according to 1% grass acid 10 to 15 m1,grinding 5 to 10min, the extract will be collected to 50 m1 capacity bottle, so repeated extraction 2 to 3 times, and finally add 1% astic acid to 50 m1. . 2. Oxidation, decolorization extract about 10m1 placed in a dry 100m1 conical bottle, added activated carbon 0.5g, fully shake 1min after filtration, take about 10m1 standard liquid in another dry conical bottle, add active carbon 0.5g, the same method shake, filtration. . 3. Coloring: take
test tubes
3, number, operating according to the table: reagents blank standard assay sample filter 2.5 - - 2.5 standard filter (ml) -2.5 -10% sulfide (ml) 1 1 1
. 2%2,4-dinitrobenzene (ml) 0 1.0 1.0 mixed, heated in a boiling water bath 10min removed, running water cooling, blank tube plus 2%, 2,4 - dinitrobenzene 1 ml. . 4. the dissolved tubes in the cold water bath slowly add 85% sulphuric acid 3.0m1, while shaking while cooling. After mixing, remove the test tube, at room temperature to place 10min, at 500nm wavelength for color contrast, to blank tube withering, absorbent value.
. . Note: (1) raw vegetables and fruits may produce foam when mashed, for the fixed capacity can be accurately added a few drops of glycol to remove the foam. . (2) When processing activated carbon Fe3 plus inspection method: take a little activated carbon washing filter, add a few drops of 5% potassium iron chloride, if not blue, show no Fe3 plus; or add a few drops of 1% potassium sulfate, if not red, also show no Fe3 plus. . What problems should be paid attention to when adding sulphuric acid to coloration? .