Evaluation of pH-responsive release behavior, antioxidant activity and cytotoxic potential of quercetin-loaded sodium alginate gellan gum hydrogel beads

A bio-based hydrogel system comprising sodium alginate (2% w/v) and gellan gum (0.5% w/v) was developed for the encapsulation and pH-responsive release of quercetin. This study explores the potential of this matrix for quercetin delivery, focusing on its physicochemical properties, antioxidant activity, and cytotoxicity. Beads were prepared by ionic gelation using calcium chloride and Tween 80. Two formulations were selected based on their encapsulation efficiency: sodium alginate–gellan gum hydrogel beads prepared with initial quercetin contents of 1% (SAGG beads A; loading capacity: 20%) and 0.5% (SAGG beads B; loading capacity: 11.1%), which exhibited encapsulation efficiency (EE) values of 84.30% and 93.26%, respectively. FTIR and XRD analyses were consistent with quercetin incorporation and reduced apparent crystallinity within the hydrogel matrix. TGA showed modified thermal behavior, and FESEM revealed spherical beads with a porous surface and internal microstructures. In vitro swelling and release studies showed quercetin release, particularly in SIF, with cumulative release after 8 h of 37.2% for SAGG beads A and 35.9% for SAGG beads B. Fresh SAGG beads A and SAGG beads B showed DPPH radical-scavenging activities of 89% and 77%, respectively, which decreased to 85% and 62% after two months of storage. In MDA-MB-231 cells, free quercetin showed the highest cytotoxicity, with an IC₅₀ of 32.7 ppm, whereas extracts from fresh and two-month-stored SAGG beads A showed apparent IC₅₀ values of 147 and 149.5 ppm, respectively, based on nominal extract concentrations. These hydrogel beads show potential as carriers for quercetin delivery and antioxidant activity retention during storage.