The document outlines the process of quantifying polyphenols, specifically tannins from strawberries, using potassium permanganate titration with indigo carmine as an indicator. It details the procedure, including preparation of solutions, variable temperatures, and results showing the total polyphenol concentration at different temperatures. A formula for calculating the total polyphenol concentration in mg/l is provided, alongside data from the titration experiments performed at various conditions.

1. Temp on polyphenol (tannins strawberry) quantification using potassium permanganate titration (Lowenthal permanganate)
Polyphenols are antioxidants :
- found in blackberry, wines, blueberry, cranberry, grapes, cider, citrus fruits
- Tannins (TA), flavonoids, catechins, EGCG, EGC, ECG.
- quantification using potassium permanganate (titration)
- using indigo carmine indicator (blue) to green yellow
Antioxidants that can be quantified using permanganate titration
Procedure:
Potassium permanganate 0.004M (0.02N) was prepared.
0.1% (w/v) indigo carmine indicator 0.1g in 100ml acidified with H2SO4.
End point is greenish yellow.
Limitation : antioxidants like Vit C will be included
Assumption - all antioxidants esp polyphenol will be quantified.
Effect of temp (15, 45, 55, 65, 75) will be studied, using water bath.
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2. Red extract needs to be diluted down for IA study
Indicator change from blue to greenish yellow
Procedure:
Potassium permanganate 0.004M (0.02N) was prepared.
0.1% indigo carmine indicator 0.1g in 100ml acidified with H2SO4.
End point is greenish yellow.
For strawberry, 0.5 ml was added to centrifuge tube.
Tube was immersed into water bath at various temp for 10 mins.
After 10 mins, 2ml water and 200ul of indigo carmine were added. Blue sol obtained.
Titrated with 0.004M KMnO4 until end point is seen.
Ini and final vol recorded.
Blank titration was done – 2 ml water and 200ul indicator without any antioxidants
Temp/C Ini
vol
Final
vol
Vol (X)
KMnO4
Polyphenol
mg/L TA
15 7.8 9.3 1.5 1080
45 12.9 14.8 1.9 1413
55 15.4 17.1 1.7 1247
65 19.2 20.4 1.2 831
75 21.5 22.7 1.2 831
Blank (Y) 4.7 4.9 0.2 --
End point
Strawberry
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
(1.5 - 0.2) x 4.157 x 0.02 x 10000 = 1080mg/L
Formula that can be used. Click here for reference
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
4.157 – conversion factor to TA equivalents
10000 – conversion factor from % to mg/L of TA.
N – normality for KMnO4 which is 0.02N or 0.004M
X – Vol KMnO4 used
Y – Vol blank titration
TA – tannic acid
Temp on polyphenol (tannins strawberry) quantification using potassium permanganate titration (Lowenthal permanganate)

3. End point
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
(1.5 - 0.2) x 4.157 x 0.02 x 10000 = 1080mg/L
Formula that can be used. Click here for reference
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
4.157 – conversion factor to TA equivalents
10000 – conversion factor from % to mg/L of TA.
N – normality for KMnO4 which is 0.02N or 0.004M
X – Vol KMnO4 used
Y – Vol blank titration
TA – tannic acid
Red extract needs to be diluted down for IA study
Temp on polyphenol (tannins strawberry) quantification using potassium permanganate titration (Lowenthal permanganate)
Temp/C Ini
vol
Final
vol
Vol (X)
KMnO4
Polyphenol
mg/L TA
15 7.8 9.3 1.5 1080
45 12.9 14.8 1.9 1413
55 15.4 17.1 1.7 1247
65 19.2 20.4 1.2 831
75 21.5 22.7 1.2 831
Blank (Y) 4.7 4.9 0.2 --
0
0.5
1
1.5
2
15 45 55 65 75 Blank
(Y)
Vol
KMnO4
Temp/C
Temp/C vs Vol KMnO4
0
500
1000
1500
15 45 55 65 75
Polyphenol/mg/L
TA
Temp/C
Temp/C vs Polyphenol/mg/L
TA
0
500
1000
1500
0 20 40 60 80
Polyphenol/mg/L
TA
Temp/C
Temp/C vs
Polyphenol/mg/L TA
15C was removed, might be an outlier
15C was removed, might be an outlier