Advancements in ulvan valorization from Ulva rigida: Unveiling a combined approach of electric fields and subcritical water extraction

Ulvan is the sulphated polysaccharide present in the cell wall of the green seaweed Ulva sp., exhibiting some rheological and biological features. The traditional recovery of this polysaccharide has certain drawbacks, including high energy and time consumption and the use of chemicals generating dangerous residues in the environment. Green alternative processing technologies have drawn attention due to their sharp processing with a decrease in solvents, energy and environmental impact. This study aims to evaluate the effect of moderate electric fields, subcritical water extraction, combination of both and benchmark with conventional extraction, on ulvan-rich fraction recovery from Ulva rigida . The combined technology increased the extraction efficiency (9–17 %), proving to be a time-saving process by inducing the rupture of cell walls. Also, a decrease in molecular weight was observed for the treatment at 170 °C (92 kDa), and an increase in rhamnose (159 mg/g extract) and xylose (23 mg/g extract) was recorded at 150 °C. All the ulvan-rich fraction samples used in this work were considered to be weak gels and/or highly viscous liquids. According to FTIR analysis, the three different methods were capable of maintaining the intrinsic properties of the ulvan-rich fraction samples without causing structural changes. Hence, the combination of high temperature and pressure together with the passage of an electric field current, where the heating is more effective with a reduced energy consumption, is a more feasible, innovative and sustainable approach to extract seaweeds' polysaccharides. • Alternative technologies are a good option for ulvan extraction from Ulva rigida. • SWE and SWE-MEF revealed a sharp-time reduction processing in ulvan recovery. • SWE-MEF demonstrates potential to replace conventional time-consuming processes. • Intrinsic properties of ulvan extracts were not affected by different methods. • Combined approach proved to be an energy-saving and eco-friendly process.