Effects of pectin molecular structure on in vitro curcumin release of calcium pectinate beads

Abstract

In an attempt to investigate the functional properties of pectin, degree of esterification (DE) of commercial high methoxyl pectin (HMP) was modified with a pectin methyl esterase (PME) isolated from papaya fruit, and modified pectin (DE 50) and commercial pectin including low methoxyl (LM) and low methoxyl amidated (LMA) pectin were prepared as encapsulating curcumin in bead. Commercial LM pectin with DE 50 and DE 5, and LMA pectin with DE 35, degree of amidation (DA) 15 and DE27, DA20 were used for experiment. Curcumin, polyphenol compound, is well-known its diverse functionalities, but its poor solubility and vulnerability to alkali, light, and oxidation prohibit its wide application in food industry. In this study, depending on different molecular structure of pectin, efficient encapsulation of curcumin was pursued, and the physicochemical properties and in vitro release of curcumin in simulated gastrointestinal tract (GIT) model were elucidated. Curcumin-loaded calcium pectinate beads were prepared by dropping 2% of pectin solution containing curcumin (250 mg) and sodium caseinate as a surfactant into 8% of CaCl2 solution. To determine a potential use as a site specific nutraceutical delivery, modified pectin (1-2%) with various levels of Ca2+ concentration (2-8%) was also used for bead preparation. After formation of the curcumin-loaded calcium pectinate beads, all beads were spheres when 2% of pectin and 8% of Ca2+ introduced except the LMP with DE 7, which had a cone aside of spherical bead surface. The beads produced from the modified pectin, the size was notably small compared to the others by entrapping at the highest dose of curcumin. Deesterification in block-wise increased Ca2+ sensitivity then induced strong gelation prohibiting the degradation of pectinate beads during digestion with the lease release of curcumin. In contrast, pectin with same DE and Mw as to PME-modified pectin has random charge distribution developing the weak gel which entrapped less curcumin and showed more than 60-fold release rate of curcumin. Generally, commercial pectin with low DE have shown the high Ca2+ sensitivity, but its small Mw due to chemical process for demethylesterification limited the functional properties. LMA pectins provided rather strong gel networks enhanced by hydrogen bonds between their amide groups. However, these amide groups might give an opened structure at high DA by distributing in block-wise manner disrupting the calcium-pectin crosslinking, which resulted in low EE and intermediate release rate of curcumin. Different matrix networks depending on molecular structure of pectins were also depicted by SEM, which also supported the explanations. This difference in entrapment ability and release rate induced by specific structure of pectin suggested a great potential for using pectin to control the release of curcumin and other lipophilic nutraceuticals in the human body.