Monitoring of the ultrasound assisted depolymerisation kinetics of fucoidans from Sargassum muticum depending on the rheology of the corresponding gels

Abstract

An ultrasound assisted hydrolysis of Sargassum muticum extracts produced under non-isothermal treatments during heating up to 170 °C was performed. Operation was made at two frequencies (37 and 80 kHz), where the composition and ABTS radical scavenging activity were analysed. Phenolic content, antioxidant capacity, sulphate and oligosaccharide content of the extracts increased with sonication time to 120 min, achieving higher values at 80 kHz. Extracts also exhibited cytotoxic against human cervical carcinoma cells (HeLa 229) at low (IC50, 0.074 mg/mL) and high frequencies (IC50, 0.304 mg/mL). All extracts displayed similar molecular weight profiles. Viscoelastic features of the alginate-based gels formulated with the hydrolysed extracts decreased with increasing sonication time and frequency. Monitoring of rheology of formulated gels and antioxidant kinetics of the corresponding soluble extracts allowed establishing exponential relationships. Overall, the obtained findings provided successful estimations (R2, 0.86–0.96) of the extracts’ antioxidant features depending on the viscoelasticity of gels.