Influence of pectin modification on water binding properties

Water can be bound to food components and products as non-freezing, freezing-bound and free water. The interactions are crucial for any application as well as for food consumption and digestion. DSC was applied to examine the amounts of the different types of water bound to pectin, a biomacromolecule that is used as gelling and stabilising agent in many food products. One commercial high-methoxylated citrus pectin and three modified samples, prepared by acidic and alkaline demethoxylation as well as amidation, were tested. The water content of dry samples depended mainly on the molecular parameters, especially the content of hydrophilic groups at the galacturonic acid that was increased by demethoxylation and amidation, as well as on monovalent cations of the pectins. The water–pectin interactions of wetted materials were additionally influenced strongly by the availability of hydrophilic groups that depended on material properties such as amorphous or crystalline state, powder bulk and solid density and porosity as well as particle size, surface and porosity. Small amorphous porous particles, whose polar groups were rapidly available without prior softening and swelling, accelerated water uptake. Non-freezing and freezing-bound water, bound closely to the pectin molecules, depended on the number and type of polar groups. Free water, bound in micro- and macro-capillaries as well as voids within and between the pectin particles, was influenced by hydrophilic as well as hydrophobic groups of the samples. There was a strong impact of the pre-treatment during processing and modification.