Development of floatable composite alginate hydrogel beads for the concentration of anthocyanins and their further characterization

Abstract

The porous nature and high surface area results in high adsorption capacity of composite hydrogel beads. This study explores three different formulations of floatable hydrogel beads using sodium alginate (SA), sodium alginate with soluble starch (SA_SS), and sodium alginate with gellan gum (SA_GG) for the adsorption of anthocyanins. Due to the anionic nature of the biopolymers, the composite hydrogel beads were employed for the concentration of positively-charged anthocyanins. The beads were synthesized by ionotropic gelation in the presence of Ca^2 + ions in a solution of acetic acid. Sodium carbonate was added to the formulation to impart floatability to the beads. The optimized proportion of sodium alginate, sodium carbonate and calcium chloride in SA beads was found to be 4.5 %, 0.96 % and 1.35 mM, respectively. For the composite SA_SS hydrogel beads, 2.39 % sodium alginate, 2.65 % soluble starch, 0.91 % sodium carbonate, and 1.72 mM calcium chloride was determined as the optimized formulation. The formulation of SA_GG was optimized at 2.31 % sodium alginate and 0.95 % gellan gum. The maximum swelling capacity (295 %) and anthocyanin loading capacity (60.57 %) was observed for SA_GG beads due to the greater negative charge (-30.42 mV). The dense and porous structure observed in SA_GG and SA_SS beads explain the higher anthocyanin loading of the composite hydrogel beads. The Langmuir adsorption isotherm was found to be the best fit (R²>0.951) for anthocyanin adsorption onto the beads. The highest thermal stability was exhibited by SA_GG beads. These anthocyanin-loaded hydrogel beads have potential applications in food matrices as a stabilizer and a carrier of natural pigments.