Food Science Experiment- Vitamin C determination Using 2,6-dichloroindophenol titrimetric method

Posted By Buddhi Katangodage

Introduction

Vitamin C is an essential nutrient in the diet,but is easily reduced or destroyed by exposure to heat and oxygen during processing, packaging, and storage of food. In food industry, the vitamin C content is determined by the 2,6-dichloroindophenol titrimetric method, for food production.

Principle

Vitamin C is determined by oxidizing it in acid medium with 2,6-Dichlorophenol indophenol to dehydroascorbic acid.

    L ascorbic acid ------> dehydroascorbic acid

Ascorbic acid reduces the indicator dye to a colorless solution. At the end point of titration excess unreduced dye is a rose-pink color in the acid solution. The titer of the dye can be determined by using a standard ascorbic acid solution. Then the ascorbic acid in the food sample can be determined by the calculation using the volume of the titration.

Reagents

• 250 ml solution of 0.1g of 2,6-Dichlorophenol indophenol
• 1000ml solution of 0.1g of ascorbic acid dissolved in 3% metaphoporic acid solution
• (Concentration of standard vitamin C solution- 0.1mg/ml)
• Fruit juice sample (orange, pineapple etc.)

Equipments

• Beakers 250ml
• Buret 50 ml
• Erlynmeyer flasks 125ml
• Funnel
• Glass rods
• Measuring cylinders 100ml,1000ml
• Pipettes
  
• Volumetric flasks 250ml, 200ml,50 ml
• Analytical balance

Methodology

1. Pipette 10ml of fruit juice and add 10ml metaphosphoric acid and fruit juice into a Erlynmeyer Flask.
2. Fill the burette with the indophenol dye solution.
3. Titrate till a faint red color persist for at least 15 seconds.
4. Calculate the vitamin C content in milligrams per 100g or 100ml of the sample according to the factor which is obtained by standard ascorbic solution.

(determinatin of the factor of standard vitamin c solution is carried out same way as the experiment)

 

Faint red color after the titration