Electrokinetic Study of Gelatin

M.A. MASUELLI

Buenos Aires

Congreso; VII Conferencia Internacional de Proteínas y Coloides Alimentarios - CIPCA VII; 2017

VII Conferencia Internacional de Proteínas y Coloides Alimentarios - CIPCA VII

Gelatins are classified according to whether an acid or an alkali is used in the final preextraction step. If an acid solution is used as the final solvent, type-A gelatin (acid process) is obtained. In case of alkali as the final solvent, type-B gelatin (alkali process) is obtained. Type-A gelatin has a range at the isoelectric point between 9-9.4, as a milder acid process does not remove the amide nitrogen of glutamine and aspargine. If a more severe acid treatment is required, then some of the amide groups are hydrolysed and the isoelectric point are between 6 and 8. Type-B gelatin isoelectric point might be as low as 4.8-5.2, as the alkali process results in the loss of the amide groups. The electroviscous effect is a phenomenon that is manifested by an increase or decrease in viscosity by the addition of small amounts of electrolytes in solution. The electroviscous effect depends on the size of the capillary, decreases with the conductivity or the increase of the concentration of salts. In this work, the gelatin is measured from the electrokinetic point of view by means of intrinsic viscosity measurements, in order to evaluate the isoelectric point, the influence of the ionic strength and the zeta potential of these biopolymers. Gelatin B corresponds to the isoelectric point, pH 5.1, and a flexion at pH 9.1; in the case of gelatin A the isoelectric point corresponds to pH 9.2 and an flexion at pH 5. Where a flexion means a slight change in the trend of the curve. The isoelectric point is presented as the more compact form of gelatin, i.e. less drainage time, evidenced with smaller hydrodynamic radius. Both the basic or acidic flexion is due to compact forms of gelatin but not so small as to be isoelectric point. No less are the forms they take in acidic or basic, identified as linear gain widespread forms of gelatin A or B. In the neutral pH from the isoelectric points bending is the neutral form. A basic pH after the isoelectric point 9.2 shall register a new or extended basic shape. The ionic strength dependence of intrinsic viscosity is function of molecular structure and protein folding. It is well known that the conformational and rheological properties of charged biopolymer solutions are dependent not only upon electrostatic interactions between macromolecules but also upon interactions between biopolymer chains and mobile ions. Due to electrostatic interactions the intrinsic viscosity of extremely dilute solutions seems to increase infinitely with decreasing ionic concentration. Since a similar behavior can also be observed even for solutions of polyelectrolyte at low salt concentration, the primary electroviscous effect was thought as a possible explanation for the maximum, as opposed to conformation change. The best solute-solvent ratio as a function of the KCl concentration in the diluted gelatin solution is 10-3M. The data provided by the study of the electroviscous effect as a function of pH gives us a more compact shape in the isoelectric point with a hydrodynamic radii of 14.38 nm; while at acidic or basic pH a more widespread form.