Exploring the Self-Assembled Gel Behaviour of Litchi Pulp Arabinan Enriched Pectic Polysaccharides by Small and Large Amplitude Oscillatory Shear

This study elucidates the structural state of pectic polysaccharides within litchi cell walls and explores the self-assembly gelation behaviour of arabinan enriched litchi pectic polysaccharides using small and large amplitude oscillation shear methods (SAOS/LAOS). Water- (WLP), chelating agent- (CALP), sodium carbonate- (SCLP), and sodium hydroxide-soluble (SHLP) pectic polysaccharides were sequentially extracted from litchi pulp cell walls. SCLP was the fraction with the highest extracted yield (26.4%), composed by low-methoxyl pectic polysaccharides rich in neutral sugars (RG-I). SCLP demonstrated a propensity for self-assembled gel formation, as evidenced by its multi-branched structures and locally amorphous aggregates observed in AFM images. SCLP gels exhibit pseudoplastic fluid behaviour in steady shear tests, and their viscosity was dependent on concentration but not significantly affected by temperature (4-80 degrees C). Dynamic rheological measurement (SAOS) highlighted SCLP's exhibited solid-like viscoelastic behaviour (G ' > G ''), with enhanced gel strength at high concentrations. Thixotropic properties of SCLP gels increased with concentration. The temperature sweep demonstrated that the rheological behaviour of SCLP is thermally reversible. In LAOS, Lissajous curves revealed significant strain stiffening and shear thinning trends of SCLP gels, with elevated third harmonic intensity (I3/I1) correlating with the nonlinear behaviour. The occurrence of secondary loop indicates the enhanced the gel restructuring capacity at high concentration, likely due to the crosslink density provided by long arabinose side chains in SCLP. Cryogenic-scanning electron microscopy further confirmed a more regular interlinked network in high-concentration SCLP gels. These findings offer critical insights into the optimization of self-assembled pectic polysaccharide gels for use as gelling agents and thickeners in complex, real-world systems, including food.