Concentração de proteínas de soro do leite utilizando gel polimérico termossensível poli(N-isopropilacrilamida)

Abstract

In this work, the use of a temperature-sensitive polymer gel, Poly(N-isopropylacrylamide) for the concentration of whey proteins was studied. For the proposed study, a gel matrix was synthesized, by varying the total monomer and the crosslinking agent concentration. The gels were characterized through swelling measurements and by diferential scanning calorimetry and thermogravimetry. The gels were used to concentrate whey proteins solutions. For this concentration, the studied variables were: total monomer concentration, crosslinking agent concentration, gel mass / solution volume ratio and concentration temperature. The concentration percentage and the selectivity were determined. A simulation of the concentration process, in concentration cycles, in cross-current operation, was carried out. The gels were synthesized by chain growth free radical solution copolymerization, with monomer N-isopropylacrylamide, N,N-methylenebisacrylamide as crosslinking agent, water as solvent, ammonium persulphate and sodium metabissulfite as a redox pair initiator. A gel matrix, consisting of eleven gels, was synthesized, with different concentration of total monomer and crosslinking agent. All obtained gels showed a lower critical solution temperature behavior, with a discontinuous phase transition at around 32oC. Gels with larger concentration of total monomer and/or crosslinking agent showed a lower mass swelling ratio, at all temperatures, as a result of the predominance of the elastic contribution on the thermodynamics behavior. The gels, characterized by differential scanning calorimetry and by thermogravimetry, showed two separate degradation events, one at around 300oC and the other at around 400oC, the first one attributed to the crosslinking agent. The glass transition temperatures were determined at around 150oC, and the significant effect of the crosslinking agent in the gel structure was observed. The gel 20x5, contacted with whey proteins solution, at 5oC and at 20oC, was capable of concentrating the solution, in protein, from 10 to 33%, depending on the gel mass / solution volume ratio. The separation efficiencies, for the different studied systems, varied from around 40 to 80%. The results were discussed in the context of gels thermodynamics and through correlations between synthesis parameters and structure of the obtained gels. The 10x1 gel did not concentrate the whey proteins solution. The obatined results for the concentration of whey proteins solutions, by using temperature-sensitive polymer gel, Poly(N-isopropylacrylamide), showed that the Gel Process can indeed be used as an advantageous alternative for such separation, either from an economic or from an environmental view point.