Advanced structural characterisation of agar-based hydrogels: Rheological and small angle scattering studies

Marta Martínez-Sanz; Anna Ström; Patricia Lopez-Sanchez; Svein Halvor Knutsen; Simon Ballance; Hanne Kristine Zobel; Anna Sokolova; Elliot Paul Gilbert; Amparo López-Rubio

doi:10.1016/j.carbpol.2019.115655

Advanced structural characterisation of agar-based hydrogels: Rheological and small angle scattering studies

Carbohydr Polym. 2020 May 15:236:115655. doi: 10.1016/j.carbpol.2019.115655. Epub 2020 Feb 21.

Authors

Marta Martínez-Sanz¹, Anna Ström², Patricia Lopez-Sanchez³, Svein Halvor Knutsen⁴, Simon Ballance⁴, Hanne Kristine Zobel⁴, Anna Sokolova⁵, Elliot Paul Gilbert⁶, Amparo López-Rubio⁷

Affiliations

¹ Food Safety and Preservation Department, IATA-CSIC, Avda. Agustin Escardino 7, 46980, Paterna, Valencia, Spain. Electronic address: mmartinez@iata.csic.es.
² Dept. Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
³ Agrifood and Bioscience, RISE Research Institutes, SE 41273, Gothenburg, Sweden.
⁴ Nofima AS, Norwegian Institute of Food, Fisheries and Aquaculture Research, Ås, Norway.
⁵ Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
⁶ Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia; The Australian Institute for Bioengineering and Nanotechnology and Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Brisbane, QLD 4072, Australia.
⁷ Food Safety and Preservation Department, IATA-CSIC, Avda. Agustin Escardino 7, 46980, Paterna, Valencia, Spain.

PMID: 32172866
DOI: 10.1016/j.carbpol.2019.115655

Abstract

Agar-based extracts from Gelidium sesquipedale were generated by heat and combined heat-sonication, with and without the application of alkali pre-treatment. Pre-treatment yielded extracts with greater agar contents; however, it produced partial degradation of the agar, reducing its molecular weight. Sonication produced extracts with lower agar contents and decreased molecular weights. A gelation mechanism is proposed based on the rheological and small angle scattering characterization of the extracts. The formation of strong hydrogels upon cooling was caused by the association of agarose chains into double helices and bundles, the sizes of which depended on the agar purity and molecular weight. These different arrangements at the molecular scale consequently affected the mechanical performance of the obtained hydrogels. Heating of the hydrogels produced a gradual disruption of the bundles; weaker or smaller bundles were formed upon subsequent cooling, suggesting that the process was not completely reversible.

Keywords: Gelidium sesquipedale; Molecular weight; Rheology; SANS; SAXS; Seaweed.