The gel strength and swelling in the gastrointestinal environment of pectin/κ-carrageenan gel particles based on pectins with different degrees of methylesterification

The physicochemical properties of pectin/κ-carrageenan hydrogels were studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis to reveal molecular interactions between biopolymers. It was shown an increase in hydrogen bonds in pectin/κ-carrageenan gels, the electrostatic interactions between the Ca2+ ions and COO- groups, and increased thermal stability of composite hydrogels due to the strong chemical cross-linking. The gel strength of particles based on pectins with the lower degree of methylesterification (DM) (6% and 12%) was higher than that of particles based on pectin with DM of 40%. Increasing the ratio of pectin to κ-carrageenan (P:C, 4:1) led to an increase in the gel strength. The swelling degree of particles with a higher DM of pectin was lower in the simulated gastric (SGF), intestinal (SIF) and colonic (SCF) fluids. The particles based on pectin with DM of 40% destroyed in SIF within 1 h due to the low gel strength. The swelling degree of particles with the P:C equal 3:1 and 4:1 was lower in SCF at pH 2.3 than at pH 4.0 and 7.0. The particles with the P:C equal 2:1 can be used for colonic drug delivery in ulcerative colits patients who have low intestinal pH.