1 / 19

Determination of Vitamin C content in vegetables and fruits

Determination of Vitamin C content in vegetables and fruits. Experiment 2. Preface: Physiological Functions. Vitamin C, namely ascorbic acid, is vital for us: Electron donor with powerful antioxidant capacity Protect and even re-generate other antioxidants: Vit.E, Vit.A, GSH

danno
Télécharger la présentation

Determination of Vitamin C content in vegetables and fruits

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Determination of Vitamin C content in vegetables and fruits Experiment 2

  2. Preface:Physiological Functions • Vitamin C, namely ascorbic acid, is vital for us: • Electron donor with powerful antioxidant capacity • Protect and even re-generate other antioxidants: Vit.E, Vit.A, GSH • Facilitate gastrointestinal absorption of iron • Inhibit the synthesis of N-nitrosamine from nitrite and nitrate • Play a role in hydroxylation reactions • Detoxification • Collagen synthesis: triple helix is formed after hydroxylation of proline and lysine (proline/prolyl hydroxylase; lysine/lysyl hydroxylase) • Biosynthesis of neurotransmitters: norepinephrine from dopamine (dopamine beta hydroxylase); 5-hydroxi-tryptophan from tryptophan • Synthesis of carnitine essential for the transport of fatty acids into mitochondria for ATP generation • Promote cholesterol metabolism and excretion • Prevent scurvy: most important function

  3. Preface: Properties • Easily soluble in water, so easily lose by over-washing or with discarded cooking soup • Easily destroyed by oxidation: • Heat or prolonged cooking • Exposure to air or alkaline medium • Contact with copper or iron

  4. Determination of vitamin C Determination of total Vitamin C Determination of reduced Vitamin C Reduced De-hydrogen 85%

  5. Part 1Determination of reduced Vitamin C content(by 2,6-dichlorophenol indophenol)

  6. Principle • DCPIP (2,6-dichlorophenol indophenol) is a kind of red dye in possession of oxidizing capacity • DCPIP loses red when reduced by reduced ascorbic acid through redox reaction • DCPIP fades when reduced ascorbic acid is excessive • DCPIP displays its original red color once the reduced ascorbic acid is depleted • Therefore, the content of reduced ascorbic acid can be calculated according to the consumed DCPIP during titration • End point: light red (over 15 seconds) direct proportion Amount of consumed dye Reduced ascorbic acid content

  7. Procedure • Demarcation of DCPIP solution • Determination of sample • Calculation

  8. Determining the content of DCPIP Standard ascorbic acid solution Concentration of ascorbic acid solution Titrated by 0.001M KIO3 Concentration of dye solution Titrated by dye The result is: 1ml dye solution 0.088mg ascorbic acid T=0.088

  9. sample 1.2.2 Determining the reduced forms in sample cutting, pounding with 100ml 2% oxalic acid homogenate pentanol 100g of sample washing beaker 1% oxalic acid Diluting to graduation weighing 10g with beaker 50ml cylinder with a lid Shaking well 20ml upper clear solution white bole shaking taper bottle color fade Keeping still filtering white bole shaking 20ml 1% oxalic acid taper bottle Keeping still 5ml filtrate 5ml filtrate titrating blank light red, keeping 15sec

  10. 1.2.3 calculation T=0.06 TTT=0.062mgVC/1ml dye

  11. 2. Determination of total ascorbic acid content by 2,4-dinitrophenyl hydrazine 2.1 Principle: Reduced Vit.C De-hydrogen form 2,4-dinitrophenyl hydrazine oxidating dissolving with 85%H2SO4 red osazone making colorimetric assay There is a direct proportion between the amount of osazone and total ascorbic acid. total Vit. C

  12. 2.2 procedure • 2.2.1 Sample extracting: 4g homogenate (beaker) volumetric flask (100ml) diluting ,washing with 1% oxalic acid 1% oxalic acid diluting to graduation filtering

  13. 2.2.2 oxidation 100ml taper bottle 0.5g carbon active shaking 30sec 25ml filtrate filtering 10ml oxidated filtrate 10ml 1% oxalic acid solution mixing well

  14. 2.2.3 Formation of osazone • Getting three tubes and process as follow. • A: blank tube. B,C: sample tube. • Keeping these tubes at 37oC in water bather for 3 hours, take them out and keep at room temperature, add 0.5ml 2,4-dinitrophenyl hydrazine into tube A.

  15. 2.2.4 Dissolving of sha adding 2.5ml 85% H2SO4 slowly along the tube wall, cold water bathe, shaking • each tube taking out keeping still for 30min 490nm adjusting zero with tube A colorimetric analysis

  16. 2.2.5 Formation of standard curve standard ascorbic acid applying solution(100ug/ml) about 25ml 100ml taper bottle adding 0.5g carbon active, shaking 1 min filtering 10ml filtrate diluting with 1% oxalic acid 100ml volumetric flask final conc.: 10ug/ml

  17. Get five tubes process as follows: Doing as the same as the above described for the sample. Drawing standard curve with the light density as ordinate, and the content of ascorbic acid as abscissa.

  18. standard curve Light density calculation 0 5 10 15 20 content of ascorbic acid(ug) C:ug of standard ascorbic acid correspond to sample tube. W:g of sample in sample determination liquid

  19. Questions: • Why do we always use oxalic acid in the whole process? • The concentration of oxalic acid on making homogenate is 2%, but in other steps, it is 1%. The concentration is different ,why?

More Related