食品化学与分析(英文版)10

A at 620 nm
Use absorbances at 440 nm and then convert this to absorbance at 620 nm and subtract from the absorbance at 620 nm to determine the absorbance at 620 due to Vitamin A.
RIBOFLAVIN DETERMINATION
CH HOCH HOCH HOCH HCH N
9 10
2 OH
CH CH
3
7 6
8 5
N
1 4 2 3
O
3
N
O
6,7 Dimethyl-9-D-1-Ribitylisoalloxazine
Fluorometric Method Autoclave in 0.1 N HCl for 30 min Adjust pH to isoelectric point to precipitate proteins Filter Determination: Test Tubes 10 ml sample, + 1 ml of riboflavin standard or 1 ml H2O + 1 ml acetic acid, + 0.5 ml KMnO4 (4%) + 0.5 ml 3% H2O2 -- KMnO4 color should disappear in 10 seconds, + 20 mg powdered Na2S2O4 Calculation mg Riboflavin/ml Final Sample Solution
Tube 1 5 ml Sample 2.5 g NaCl 3 ml K3FeCN6 13 ml Isobutanol Centrifuge Tube 3 5 ml Standard (thiamin) 2.5 g NaCl 3 ml K3FeCN6 13 ml Isobutanol Centrifuge Thiamin Standard Solution = 0.2 µg/ml Calculation of B1 (µg of B1/5 ml assay sample) = (Tube 1 – Tube) / (Tube 3 - Tube 4 ) Tube 2 5 ml Sample 2.5 g NaCl 3 ml NaOH 13 ml Isobutanol Centrifuge Tube 4 5 ml Standard (thiamin) 2.5 g NaCl 3 ml NaOH 13 ml Isobutanol Centrifuge
VITAMINS
Vitamin A
H3 C
CH 3
CH 3
CH 3
CH 3 CH 2 OH
β - Carotene
CH 3 CH 3 CH 3 C H3 O xidation CH 3 C H3 H3 C C H3 CH 3 C H3
H3 C
CH 3
CH 3
C H3
O C
H
CH 3 - 2H
R etainal
Carotenoid Absorbance at 440nm
Vitamin A Absorbance at 620 nm
x x x x x
Carotenoid (µg/ml)
x x x x x
x
Vitamin A µg/cuvette (sample)
THIAMIN DETERMINATION
pyrimidine
H3 C
CH 3
CH 3
C H3 CH 2 O H Retinol (V itam in A )
CH 3
Vitamin A and β - Carotene Determination
Food KOH (Alcoholic) Saponification
3 hrs. at room temperature Ether for Extotenoids)
Total Carotenoids only at 440 nm
Vitamin A + Carotenes Carr-Price Reagent Measure at 620 nm
β-CAROTENE STANDARD ABSORBANCES AT 440 AND 620 nm
A at 440 nm
=
[F(sample) - F(blank)] x 0.1 x 0.001 F(sample + standard) - F(sample)
NIACIN
O C N OH N
O C NH 2
Niacin Determination
1. Digestion an Hydrolysis
S a m p le + C a (O H )
Thiamin Determination in Foods
5 g enriched flour 75 ml 0.1 N HCl Make volume to 100 ml Digest at 1000C for 30 min Centrifuge and filter
Oxidation of Thiamine
NIACINE STANDARD CURVE
µ g Niacin
VITAMIN C
Ascorbic Acid
CH2 OH HOCH O O -2 H +2 H HO OH O O
Dehydroascorbic Acid
CH2 OH HOCH O O
HSCH2CH2(SH)CH2OH 2,3-DIMETHYLPROPANOL Reducing agent or converting dehydroascorbic acid to ascorbic acid
Calculation for Reduced Vitamin C
F V x mg Ascorbic Acid/g = (A-B) x E X
A= B= F= V= E= X= ml of 2,6-dichloroindophenol for sample titration ml of 2,6-dichloroindophenol for blank mg of ascorbic acid equivalent to 1 ml of indophenol standard solution Initial assay solution volume Number of grams Volume sample aliquot titrated
H3C N N NH 2 CH 2 N
thiazole
S CH 2CH 2OH CH 3
K3 Fe(CN)6 Oxidation
H3C N
N
N
S
CH 2CH 2OH
N CH 3 CH 2 THIOCHROME (Fluorescent)
Excite thiochrome at 365 nm and measure the absorbance at 435 nm
Niacine Determination
1
O C OH + CNBr N
O C OH REARRANGEMENT N Br CN
-
REARRANGED RING IS OPENED DERIVATIVE
2
RERRANGED + H2 N DERIVATIVE O S OH O O C-OH R-N-CH=CH-CH=C-CH=N O S OH O
Titrimetric Method for Reduced Vitamin C
1. Extract with metaphosphoric acid (HPO3) in HOAC. 2. Titrate with 2, 6-dichloroindophenol (blue). At end point, rose pink (2, 6-dichloroindophenol in acidic condition).
2
A u to c la v e 2 H o u rs
2. PPT Protein with (NH4)2SO4 3. Centrifuge and Filter 4. Rupture of Pyridine Ring with CNBR (Cyanogen Bromide) 5. Color Formation with Sulfanilic Acid 6. Determine the Absorption at 470 nm 7. Plot the Standard Curve of Niacin vs. Concentration 8. (Straight Line of Best Fit)