Electrospray alginate-Konjac glucomannan microgel as efficient colon-targeted delivery vehicle for quercetin

Colon targeted delivery of polyphenols is a promising approach in reducing the risks of colonic diseases. In this study, alginate microgels were fabricated by an electrospray method. Native Konjac glucomannan (KGM) or degraded KGM (DKGM: hydrothermal decomposition for 20 min (KMG20) or 60 min (KMG60)) were incorporated as filling material, while chitosan was added as a protective coating after microgel formation. Quercetin was encapsulated at two formulation levels to study the properties of the loaded microgels. During electrospraying, DKGM, which had lower viscosities, produced microgels with smaller average particle sizes compared to KGM, and both KGM and DKGM microgels had narrower size distribution compared to alginate-only microgels. All microgels achieved encapsulation efficient (EE) up to 100% at low quercetin formulation level (0.2% w/w), and > 75% EE at high quercetin formulation level (0.4% w/w). Loading at 125.2-191.9 mg/g freeze-dried microgel was achieved with 0.4% w/w quercetin level. FTIR confirmed the successful encapsulation of KGM/KGM20/KGM60 and quercetin into the gel matrix. Zeta potential analysis indicated that KGM/KGM20/KGM60 affected the chitosan coating and particle swelling ratio depending on quercetin loading levels. During in vitro sequential oral-gastric-intestinal digestion, KGM/DKGM retarded release compared to alginate-only microgels at low loading, but KGM and KGM20 increased release significantly at high loading. Only KGM60 maintained low release (<10%) regardless of the quercetin loading, making it a promising filling material among the tested formulations for colon-targeted delivery of quercetin.