Thermally induced degradation of citrus pectins during storage – Alterations in molecular structure, colour and thermal analysis

Commercial citrus pectins (17 samples from 3 different suppliers) were stored at 60 °C and 80% humidity for two weeks. Molecular parameters (galacturonan content, degree of methoxylation, intrinsic viscosity), colour and behaviour in thermal analysis (DSC and TG) were tested and the results were compared with those of model pectins prepared under laboratory conditions from a previous study. Whereas the molecular parameters and colour of both groups changed similarly, considerable differences in the thermal analysis were found not only between model pectins and commercial pectins but also between commercial samples from different suppliers. It seems that varying processing conditions between laboratory preparations and industrial processing as well as differences in industrial scale processing influence the pectin properties and their degradation during storage. mmercial citrus pectin samples were strongly demethoxylated and depolymerised, former high-methoxylated pectins with degree of methoxylation (DM) > 50% became low-methoxylated with DM < 50% and some low-methoxylated samples afterwards had a DM close to pectic acid. As a result, also their gelation properties changed markedly. For pectin producing and applying companies it might be essential to check the properties of pectins after longer storage under unfavourable conditions. As a consequence, a variation of the gelation conditions for pectins after storage might be necessary.