Optimization of alginate extraction conditions from the brown seaweed Dictyota mertensii using a central composite design

Abstract

This work extracts alginate from Dictyota mertensii, a brown macroalga found on the north coast of northeastern Brazil. A Central Composite Design (CCD) using Response Surface Methodology (RSM) was used to optimize the process of extracting the alginate present in the brown alga Dictyota mertensii, considering the factors of time, temperature, and concentration Na2CO3. Extraction yield (η), sulfate content, intrinsic viscosity ([η]), viscosimetric molar mass (Mv), color parameters (a*, b* e L*), M/G ratio and inhibitory concentration IC50 are model response variables. The Dictyota mertensii algae has its chemical composition expressed. Response surfaces are plotted from the variables studied, a quadratic model was predicted, the influence of factors is analyzed, and response variables are subjected to analysis of variance (ANOVA) and F-test at 95 % confidence. The predicted conditions are experimentally validated. The antioxidant potential was evaluated at seven concentrations (0.2–5.0 mg/mL) based on the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The maximum extraction yield was 29.28±0.02 %, and sulfate content ranged from 3.50±0,00 % to 12.33±0.29 %. The maximum values of [η] and Mv were 5.84±0.06 dL/g and 278.00±2.66 kDa, respectively. The alginate showed a dark brown color and M/G ratio < 1, indicating that the extracted alginate provides rigid and compact gels, which allows its application in films, encapsulations, and protecting probiotics. The maximum antioxidant capacity and the IC50 were 54.93±0.27 % and 0.51±0.07 mg/mL, respectively, indicating the material obtained as a moderate natural antioxidant.