Edible films based on sulfated polysaccharides from the seaweed Gracilaria birdiae: Physicochemical, optical and mechanical properties

Abstract

Sulfated polysaccharide (SP) was successfully extracted from rhodophyta Gracilaria birdiae cultivated in northeast Brazil. For the first time, edible SP films from G. birdiae were formulated by the casting method using an experimental design 3², in which the variables were SP concentration and glycerol concentration. A polysaccharide extraction yield of 26.4 % was obtained through hot aqueous extraction and purification by dialysis. The chemical composition indicated the quality of the SP due to the high total carbohydrate (85.1 %) and sulfate (8.1 %) contents and the absence of proteins. Structural characterization showed the presence, besides the sulfate group, of the methylated monosaccharide residues, namely 3,6-α-l-anhydrogalactose-2-O-methyl and β-d-galactose-6-O-methyl with methylation degree of 0.257. In addition, the polysaccharide chain was mainly composed of 3,6-α-l-anhydrogalactose → β-d-galactose, α-l-galactose-6-sulfate → β-d-galactose, β-d-galactose → 3,6-α-l-anhydrogalactose, and β-d-galactose → α-l-galactose-6-sulfato. SP was also considered thermostable, showing a thermal degradation pattern similar to that of galactans. Through experimental design, it was observed that the film formulation with 2 % SP and 0.2 % glycerol presented the best mechanical, physico-chemical and optical properties for application in food packaging.