Ah. That's why they taste bitter

 

Applications Note: 39 

Technique: Spectrophotometry 

Application Areas: Food & Drink 

l 

 

 

Determination of L-ascorbic acid in fruit juice samples 

 

Introduction 

 

Vitamin C is one of the parameters measured in the German RSK method for 

assessment of authenticity of juices.  Claims for high Vitamin C content are 

often used in labelling of juices.  Many other foods cite Vitamin C content on 

labelling.  However, during storage - especially in ambient or greater 

temperatures and in the presence of heavy metals - Vitamin C breaks down. 

 

Routine measurement of Vitamin C in foodstuffs is therefore important for 

substantiating nutritional claims and this can be conveniently accomplished by 

spectrophotometric measurement of L-ascorbic acid. 

 

 

Principle 

 

L-Ascorbic acid (L-ascorbate) and some other reducing substances reduce 

the tetrazolium salt MTT [3-(4, 5-dimethylthiazoyl-2)-2,5-diphenyltetrazolium 

bromide] in the presence of the electron carrier PMS (5-methylphenazinium 

methyl sulfate) at pH 3.5 to a formazan, which is determined by its 

absorbance at 578 nm.  This gives the total reducing substances in the 

sample.