Relevance of drying treatment on the extraction of high valuable compounds from invasive brown seaweed Rugulopteryx okamurae

Abstract

The present paper is focused on the dehydration of the invasive brown seaweed Rugulopteryx okamurae comparing conventional and innovative techniques to maximize the alga potential. The optimized microwave hydrodiffusion and gravity (MHG) treatment allowed an adequate drying of the seaweed together with the recovery of antioxidant and gelling fractions. Chemical and structural profiles of the fresh and dried raw material, dehydration kinetics and the corresponding modelling, antioxidant characteristics of the gathered liquid phases or mechanical properties of the developed formulations were determined. Results indicated that MHG treatment (600 W for 5 min and 200 W for 15 min) involved a dramatic reduction in processing time (from 180 h for sunlight dehydration to 30 h for conventional oven drying and to 20 min for MHG treatment). All drying kinetics were successfully (R2 > 0.94) fitted with two-model parameters, being Page's model (R2 > 0.96) the one that provided the best fits. MHG suggested the recovery of liquid fractions with higher yields and antioxidant potential when compared with those obtained after ethanolic solid liquid extraction of conventionally dried seaweed. Slightly lower mineral content was identified in solid phases remained after MHG treatment. Alginates present in MHG liquid phases exhibited similar structural profiles to their commercial counterparts, featuring lower molecular weight distributions. It was possible to prepare alginate-based hydrogels with smoother viscoelastic properties than those commercially available, incorporated with microparticulate selected extracts after spray-drying treatment.