SOP: Colour Value in Capsicum, Red Pepper and Paprika Oleoresins
GIFSQ — Global Institute for Food Safety & Quality
Principle
The oleoresin is diluted with acetone to a defined concentration and its colour is matched visually against a potassium dichromate–cobaltous chloride blank in Nessler tubes, or its absorbance is measured spectrophotometrically at 458 nm; the colour value is calculated from the dilution used or from the absorbance multiplied by 61,000.
Apparatus required
- 100 ml volumetric flask
- 100 ml Nessler tubes
- Spectrophotometer (Beckman DU or DK) with silica or corex cell
Reagents
a. Acetone.
b. Blank solution: pipette 10 ml of 0.1 N potassium dichromate solution into a 100 ml Nessler tube, add 1 ml of 0.5 N cobaltous chloride solution (5.948 g of CoCl₂·6H₂O per 100 ml) and make up to 100 ml with distilled water.
Procedure
Visual method:
Weigh exactly 1 g of oleoresin into a 100 ml volumetric flask, make up to volume with acetone, and mix (stock solution)
↓
Dilute with acetone depending on the colour value (C.V.) as given below:
| C.V. | Dilution % | Dilution of stock solution | Approx. volume of dilute solution to be used (ml) |
|---|---|---|---|
| 100,000 | 0.01 | 1 to 100 | 8–10 |
| 50,000 | 0.02 | 1 to 50 | 8–10 |
| 40,000 | 0.02 | 1 to 50 | 10–13 |
| 30,000 | 0.02 | 1 to 50 | 15–20 |
| 20,000 | 0.04 | 2 to 50 | 10–13 |
| 10,000 | 0.10 | 5 to 50 | 8–10 |
↓
Pipette the approximate volume of dilute solution into a 100 ml Nessler tube; make up the volume almost to the mark with acetone
↓
Compare through the length of the tube with the blank; make small additions until sample and blank match
Calculation
The printed calculation expression for the visual method is illegible in the available copy of the book; the variables defined in the book are A = ml of dilute solution used and B = % of dilute solution. The procedure and the dilution table above are given as printed.
Spectrophotometric method:
Weigh 1.0 g of oleoresin into a 100 ml volumetric flask and make up to volume with acetone
↓
Dilute 1.0 ml of this solution to 100 ml with acetone in a volumetric flask (0.01% solution)
↓
Measure the absorbance in a Beckman DU or DK spectrophotometer using either a silica or corex cell at 458 nm
↓
Multiply the absorbance by 61,000 to obtain the Nesslerimeter colour value
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
EOA Specifications and Standards, EOA 239, Essential Oil Association of USA, Inc.