4 replies to this topic

[qui]

Does anybody perform citric acid content analysis in fruit?

 

I'd like to share ideas and solve doubts

 

Thanks

[Konstantinos]

yes, I do, fire the question

[qui]

Thanks!!

 

Do you perform manual or automatic titration?

 

I've got a Mettler Toledo Easy pH titrator, and I'm still trying to figure out how to stablish the most accurate method.

 

My parameters are: 10 mL of juice in 30 mL of distilled water, equivalence number 3 (Citric Acis vs NaOH 0.1 M), end point pH 8.2, molecular weight 192.12 g /mol (Citric Acid) and density 1g/cm3. The results come up as % (w/v) but the bibliography shows values as % w/w, so not sure how to compare data

 

Do you reckon the parameters are correct?

[SUSHIL]

Hello qui,

  Acidity in juices is calculated as percentage citric acid (w/v)for sour fruits like lemon,orange,mango etc and for apples as malic acid and grapes as tartaric acid.

  For calculation acid factor changes in formulation.

 Factor for:

- citric acid : 0.0064 (Citrus fruit)
- malic acid : 0.0067 (Apples)
- tartaric acid : 0.0075 (Grapes)

 

1C6H8O7 + 3NaOH --> 3H2O + Na3(C6H5O7)

(citric acid +sodium hydroxide --->water + sodium citrate.

The salt created is Sodium Citrate.

3 moles of 1M NaOH are required to neutralize  1 mole of 1M Citric Acid

 3000 ml 1M NaOH is equivalent to 192.14. g citric acid.  (192.124 g/mol)

1ml 0.1M NaOH is equivalent to 0.0064g citric acid.

 

Percentage citric acid  = Titre x acid factor x 100

                                              10 (ml juice)

Percentage citric acid  =                  ml of 0 .1 NNaoH x .0064 x 100

                                                                 10 (ml juice)

 

(m/v% = g citric acid/100 mL of juice).

Normally juice acidity is calculated as w/v only.

To convert it in to w/w%  then weigh 10ml of juice on weighing balance and substitute  volume (10ml juice)to weight of 10ml juice and calculate as With weight as  (w/w% = g citric acid/100 g of juice).

example Lemon juice has   on average 4.5% to 6% citric acid.

[qui]

Thanks Sushil, very useful information.

 

For fruits as berries, because their juice is already redish, is there any indicator to carry out a manual titration??