Rheological study of pullulan-pectin mixtures to prepare gel beads using the drip method and evaluation as gallic acid release systems

Abstract

Pullulan (PUL) is a polysaccharide that can form gels using sodium trimetaphosphate (STMP). This gelation occurs at basic pH and has very slow kinetics, so that gel beads cannot be formed by the dripping method since PUL diffuses towards the medium before it can gel. To accelerate the gelling process and be able to obtain pullulan beads, hybrid gels were formed, mixing PUL with pectin (PEC). Then, STMP was added to gel the PUL, and Ca²⁺ was separately added to gel the PEC for comparative purposes. In both cases, the minimum concentration of gelling agent to obtain a gel was reduced by 90%. The gelation of these STMP-hybrid gels was practically instantaneous, thus allowing the production of beads by dripping the polysaccharide solution in an aqueous STMP solution. The PUL-PEC gels were characterized by FT-IR, which confirmed the junction of the PUL-PEC molecules by hydrogen bonds in the gel, as well as de-esterification of methoxyl groups and ionization of acid groups. The addition of PEC did not affect the swelling degree of the PUL gel, probably since it was governed by STMP-PUL junctions, but it increased the water holding capacity, which was related to the presence of more -OH groups to retain water by hydrogen bonds. PUL-PEC beads loaded with gallic acid were successfully prepared by the dripping method to evaluate their suitability as delivery systems for active ingredients. The release profiles show that they were systems comparable to beads formed by other biopolymers and therefore capable of adequately releasing active ingredients.