2 nd Mercosur Congress on Chemical Engineering 4 th Mercosur Congress on Process Systems Engineering 1 Chemical and physical characterization of biopolymers extracted from Portuguese carrageenophyte seaweeds. L. Hilliou 1 * , F.D.S Larotonda 1 , P. Abreu 2 , A.M Ramos 2 , A.M Sereno 1 , M.P. Gonçalves 1 1 REQUIMTE, CEQUP – Departamento de Engenharia Química, Faculdade de Engenharia da Universidade de Porto 2 REQUIMTE, CQFB - Universidade Nova de Lisboa Abstract. In the frame of a project aiming at engineering new green edible films for food coatings and packaging, the potential use of seaweeds collected on the Portuguese coast as a source of natural thickening and gelling agents has been screened. The present study focused on two seaweeds, namely Mastocarpus stellatus and Gigartina pistillata, which are known sources of carrageenan biopolymers. The effect of seasonal harvesting and extraction parameters on the biopolymers chemical structure and yield has been studied. The elastic properties of carrageenan solutions and gels in 0.05M KCl have also been investigated. Infrared spectroscopy and proton NMR spectroscopy revealed that Mastocarpus stellatus is essentially a κ-ι hybrid carrageenan, whereas Gigartina pistillata is from the λ type. For both phycocolloids, minor seasonal variation of the chemical structure was noticed. However, for Mastocarpus stellatus, extraction parameters strongly influenced the ultimate gel strength, gel elasticity and gel melting temperature. As expected, a long alkaline pre-treatment of the seaweeds favors the substitution of the sulfate groups, which results in stronger and more elastic gels. Extraction temperatures above 95ºC, together with low pH values of the extraction water and long extraction time have a dramatic effect on the molecular weight distribution of the obtained κ-ι hybrid carrageenans. The optimal set of extraction parameters, which lead to the strongest and more elastic gel, will be presented and discussed in light of the biopolymer chemical structure. Keywords: Carrageenan, extraction and gel-setting. 1. Introduction Carrageenans are natural polysaccharides extracted from certain families of red seaweeds. Their ability to form salt or cold setting reversible gels at low concentration in water, explains the extensive use of these polyelectrolytes in the formulation of food products or pharmaceuticals. During the last few years, the total carrageenan market showed a grow rate of 3% per year (van de Velde et al., 2002). Therefore, there is an increasing industrial interest in finding new seaweed sources of carrageenan in order to supply the natural texturing agent market with a constant product quality. In the frame of a project aiming at engineering new green edible films for food coatings and packaging, the potential use of seaweeds collected on the Portuguese coast as a source of natural thickening and gelling agents has been screened. After an estimation of the availability on the northern Portuguese coast of specific seaweed families known for their polysaccharide content, two specific algae retained our attention, namely the Mastocarpus stellatus and the Gigartina pistillata. These algae can be chemically treated for the extraction of carrageenan mixtures of industrial quality, that is to say, with good enough gelling and solution thickening properties. A chemical and physical characterization of the polysaccharides extracted from Mastocarpus stellatus and Gigartina pistillata specimen has been performed. * To whom all correspondence should be addressed. Address: Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto-Portugal. E-mail: hilliou@fe.up.pt