Effect of ultrasonication on low-acetylated gellan gum gel properties

Abstract

Food product developers are constantly looking for new functional ingredients to improve or modify food textural attributes in order to meet consumers' demands. One of the ways to achieve this is to modify the functionality of existing ingredients. In this work, low-acylated (LA) gellan gum (1% w/w) was physically modified by ultrasonicating the polysaccharide solution (frequency of 20 kHz and an output of ∼30 W) at ∼50 °C (above the sol-gel transition temperature) for different durations (5, 10, 20, 30 and 40 min). The ultrasonicated LA gellan gum was characterized in terms of its molecular parameters, gel viscoelasticity and textural properties. The results obtained from multi-angle laser light scattering showed that the molar mass of gellan gum decreased from 9.7 × 105 to 2.8 × 103 g/mol as ultrasonication time increased from 0 to 40 min (50% cycle). The frequency sweeps obtained by oscillatory measurement showed minimal changes in the elastic moduli with ultrasonication time. In addition, changes in the sol-gel (39.53 ± 0.33 °C) and gel-sol transition (72.14 ± 1.42 °C) temperatures were not noticeable by ultrasonication suggesting that the number of binding sites that form the gel network were similar. However, under large deformation, the rupture stress of gellan samples obtained from uniaxial compression tests decreased markedly with ultrasonication time. In addition, the instrumental Texture Profile Analysis (TPA) indicated that the gel hardness and springiness decreased gradually with ultrasonication time. The reduction in gel strength was attributed to the reduced chain length of the gellan polymer molecules and the gel network may include dangling chains which do not contribute to elasticity.