Evaluation of cation-facilitated pectin-gel properties: Cryo-SEM visualisation and rheological properties

Abstract

To provide more insight into the cation facilitated pectin-gel structure-function relationship, the microstructure of pectin-gels was explored using cryo-scanning electron microscopy (Cryo-SEM) in combination with physiochemical and rheological analysis. Pectin with different degrees of methylesterification, DM, was obtained from commercial citrus pectin (CP) and sugar beet pectin (SBP) by action of carrot pectin methylesterase. Pectin characterisation confirmed that pectin properties other than DM were unaltered and pectin from the two sources exhibited different structures. Cryo-SEM visualisation of pectin-gels prepared with different cations revealed that the network density increased with decreasing DM and increasing pH, pectin and cation-concentration. At a given DM, the more linear and less acetylated pectin (CP) exhibited a more intertwined fibrous network compared to the highly branched and more acetylated pectin (SBP). Furthermore, gel-microstructure was influenced by type of cation with Zn2+, Fe2+ and Ca2+-pectin gels showing a more intertwined network compared to Mg2+-pectin gels. Finally, rheological properties of gels complementing Cryo-SEM observations showed that as the network density increased, the gel-stiffness (G′) increased.