Mechanical properties of gellan gum beads prepared with potassium or calcium ions

Biopolymer beads can be used as carrier and encapsulation system for a wide variety of materials in food, medical, pharmaceutical, cosmetics, agricultural, and environmental applications. Beads of low acyl gellan gum (0.4-1.2% w/w) were produced using extrusion technique (dripping) followed by an ionotropic gelation step with calcium or potassium chloride. In this methodology, gel formation is accomplished by cations diffusion at room temperature and, as a consequence, different structure and gel properties could be obtained. Gellan beads were subjected to uniaxial compression measurements. The force-displacement curves showed that the occurrence of structural failure under tested conditions depended on beads formulation and was only observed at polysaccharide concentration above 0.8% (w/w). Maximum force or force at failure was mainly dependent on the type (monovalent or divalent cation) and salt concentration. Moreover, at fixed salt amounts, higher values of maximum force were reached using a concentration of 1% (w/w) gellan. Young modulus, determined using Hertz approach, showed values between 445 and 840 kPa depending on polysaccharide concentration and salt type added. Mechanical properties are critical features of gel beads and can define their suitability for a specific application. Therefore, the results obtained, mainly intrinsic properties such as Young modulus, could be a tool for comparing and choosing polysaccharides for specific uses.