The Effect of Concentration on the Cross-Linking and Gelling of Sodium Carbonate-Soluble Apple Pectins.

Diana Gawkowska,Justyna Cybulska,Jolanta Cieśla,Artur Zdunek

doi:10.3390/molecules24081635

Abstract

The cross-linking and gelation of low-methoxy pectins are basic processes commonly used in different industries. The aim of this research was to evaluate the cross-linking process of the sodium carbonate-soluble pectins (named DASP) extracted from apples, characterized by a low degree of methylesterification as a function of its concentration in water (CDASP). The cross-linking process was studied with a dynamic light scattering method, atomic force microscope (AFM), viscosity and pH measurements. An increase in CDASP above 0.01% resulted in a decrease in the aggregation index (AI) and the change of its sign from positive to negative. The value of AI = 0 occurred at CDASP = 0.33 ± 0.04% and indicated the formation of a pectin network. An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with AFM, which confirmed results obtained. The hydrogen bonds were involved in the cross-linking process.

Highlights

Pectins are polysaccharides characterized by a complex structure and gelling properties
An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with atomic force microscope (AFM), which confirmed results obtained
Delicious” apples, was ~59 mol % of the total uronic acids content in alcohol-insoluble residue [22]. This fraction had the highest amount of uronic acids, mainly galacturonic acid, in comparison to water- (WSP) and chelator-soluble pectin (CSP) fractions extracted, which was noted for the diluted alkali-soluble pectin (DASP) fraction from “Idared” apples [23]

Summary

Introduction

Pectins are polysaccharides characterized by a complex structure and gelling properties. Their main structural unit is the α-1,4-d-galacturonic acid (GalA) unit, which is a part of three main pectin domains: homogalacturonan (HG), rhamnogalacturonan I (RGI) and rhamnogalacturonan II (RGII) [1]. The acetyl groups may be present in this pectin domain at O-2 or/and O-3 of GalA [3,4]. They occur mainly in the hairy region of apple pectin [5,6]. Rhamnogalacturonan I and II include GalA and monosaccharides, such as arabinose, rhamnose, galactose, and, in the case of RGII, apiose, fucose, 2-O-methyl-xylose, 2-O-methyl-fucose, and others are included [7]

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