Determination Of Proline In Orange Juice

Determination of proline in orange juice

19. November 2012

1 Introduction
The pattern of aminoacids is characteristic of different fruits, and it can be used to analytically characterize fruitproducts. Adulteration of fruit juices can be detected according to the content of aminoacid in it or the relation between the concentration of aminoacids. To evaluate a natural fruit juice we canstudy its content in proline. Proline is the aminoacid which is in a higher concentration in orange juice.
Related to the prolin concentration, there is a Prolin-quotient, which is used as a evaluationcriterion. In not-adultereted juices the Prolin-quotient is under 30.

FIG 1: Proline

2 Task
Cuantitative detremination of L-Proline in an orange juice by photometric measure.

3 Principle ofthe method
Proline reacts with Ninhydrine gibing an orange product, which we extract with acetic acid- n – butylester. Then we measure the absorption of the extract at λ = 509 nm photometrically.3.1 Reaction

FIG 2: Ninhydrine reacts with proline forming this compound which absorbs at λ = 509 nm

4 Procedure
4.1 Preparation of the calibration solutions
* Preparation of the nativesolution: We weigh 50 mg of L-Proline, put them into a 50 ml flask, and we make it up with water.
* Preparation of the standard solutions: We make 100 ml of every solution from the native solution.We make five, from 10 to 50 mg/l and we dilute them with water:
* 10 mg/l :

* 20 mg/l : (the same calculation): 2ml native solution
* 30mg/l : 3ml native solution
* 40 mg/l : 4 mlnative solution
* 50 mg/l : 5 ml native solution

4.2 Preparation of the Ninhydrin solution
We weigh 1.5 g of Ninhydrin, put them into a 50 ml flask and fill the rest withEthylenglykolmonomethylether.

4.3 Preparation of the sample
We will measure the sample in three diferent concentrations, and twice each one.
One of them will just be the juice, in my case a normal orange juice,...