Intragastric structuring of anionic polysaccharide kappa-carrageenan filled gels under physiological in vitro digestion conditions

• κ-Carrageenan (CAR) gels filled with sodium alginate (SA) and pectin (PEC) were made.
• CAR exerts a better in vitro intragastric structuring ability than SA and PEC.
• CAR complexation with Ca2+ reduces its structuring sensitivity to gastric chyme pH.
• CAR-Ca2+ gels filled with SA-Ca2+ or PEC-Ca2+ exert low sensitivity to in vitro ion (Na+/K+) exchange.
• Acid particulate morphology was affected by biopolymer type and counterions presence.

In the present work, sodium alginate (SA), low methoxyl pectin (PEC) and κ-carrageenan (κ-CAR) were evaluated for their intragastric structuring ability by means of light microscopy and dynamic oscillatory rheology. SA and PEC solutions, their Ca2+ complexed gel analogues as well as their binary blends with ionically or thermally set sheared κ-CAR gels, were subjected to in vitro orogastric conditions. SA and PEC – Ca2+ complexed sheared gels exerted the highest vulnerability to digestive fluid exposure due to the dialysis of egg-box dimer structures via proton-calcium exchange. Incorporation of SA and PEC systems to κ-CAR gels prevented the loss of mechanical strength of the gastric gels due to the ability of κ-CAR to undergo spontaneous gelation in the presence of Na+ and K+ ions. Binary blends of SA and PEC – Ca2+ complexed sheared gels with κ-CAR-Ca2+ gels exerted a significantly lower mechanical strength loss sensitivity against pH and counterion composition of the gastric fluids.