**3.2 Characterization**

The amount of metallic ions present in the solutions was determined by using a conductivity meter.

#### **3.3 Determination of the chelating agent in textured soya extract**

The Biuret test is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper (II) ion forms a violet-colored complex in an alkaline solution. Several variants on the test have been develop

In order to find the chelating component in the textured soya extract, first a textured soya extract was prepared by heating to boiling point 1000 ml of deionizer water with 30 grams of textured soy for 20 minutes. 10 ml of textured soya extract is treated with an equal volume of 1% strong base (sodium or potassium hydroxide most often) followed by a few drops of aqueous copper (II) sulfate. The solution turns violet, for that reason we can affirm that proteins are present in the textured soya extract and these are the chelating agents.

A Fehling test was made too, and the Fehling reaction was positive, in which the green color characteristic of mono-saccharides was obtained. For that reason we can affirm that mono-saccharides present in the textured soya extract are present but the amount is not significant (< 3%).

### **3.4 Experimental method**

First, it was necessary to find a concentration of textured soya equivalent to an EDTA solution 5x10-4 (the maximum concentration permitted in foods). For that reason we prepared six solutions of CuSO4 with concentrations 0.05M, 0.1M, 0.15M, 0.2M, 0.25M and 0.3M. The conductivity of each one was then measured. Next, we mixed 1 ml of each CuSO4 solution with 10 ml of an EDTA solution 5x10-4 M and we measured the conductivity of each one. Several textured soya aqueous solutions were prepared by dissolving 1 grams, 2 grams, 3 grams, and 5 grams of textured soya, each one in 100 ml of water, and heating them to boiling point for 10 minutes. The fiber was then separated by filtration. Afterwards, we mixed 1 ml of each solution of CuSO4 with 10 ml of each prepared textured soya extract solution and measured the conductivity of each sample.

With the aim of studying the comparative chelating effect between textured soya extract and EDTA on some metals, we prepared five different aqueous solutions of each metal ion, Fe3+, Pb2+, Hg2+, Cd2+, Ni2+ and Cu2+ with different concentrations, with 0.01, 0.03, 0.05, 0.07 and 0.1 grams of each salt dissolved in 10 ml of deionizer water. Then we measured their conductivity. An EDTA aqueous solution of 5x10-4M was prepared. A solution of 15 grams of textured soya in 500 ml of deionizer water was heated to boiling point for 10 minutes. Afterwards, we measured the conductivity and ppm (parts of million) of each ion solution, chelant solution of textured soya extract and EDTA. In order to determine the chelating capacity of EDTA and textured soya extract, we added 0.01, 0.03, 0.05, 0.07 and 0.1 grams of each salt in 10 ml of EDTA solution, and then in the same form in 10 ml of textured soya extract solution and we measured the conductivity of each one, using a conductivity meter. All measurements were made at room temperature and at average room pressure, and pH 7.
