Influence of intrinsic and extrinsic factors on rheology of pectin–calcium gels

Pectin was selectively demethoxylated by use of NaOH or pectinmethylesterase from plant or fungal origin in order to produce a library of pectins with varying degree and pattern of methoxylation. In addition, pectin was chemically depolymerised by a heat treatment. The resulting pectin products were characterised by studying the degree and pattern of methoxylation and the extent of depolymerisation. The pattern of methoxylation was estimated quantitatively by determining the “degree of blockiness” (DB and DBabs). Pectin–calcium gels were prepared at varying concentrations of both components. Rheological properties of these gels were studied by performing small deformation oscillatory tests. Gel strengths were better explained by the pattern of methoxylation than by the degree of methoxylation. The relation between rheological properties and calcium or pectin concentration depended on the pattern of methoxylation. Depolymerisation had a detrimental effect on gel strength, especially at low calcium concentration.