Effects of extrusion-cooking on pectin-rich materials

Some by-products from the food industry contain high proportions of plant cell walls which can be used in human nutrition to produce “dietary fibre” or “functional fibre”, i.e. compounds which can be used for their water-holding/binding properties, oil-binding capacity,… or as a source of polysaccharides such as pectins which are suitable after extraction, as gelling or thickening agents. Extrusion-cooking of cell-wall rich products (e.g. wheat bran, apple pomace, citrus peels, sugar-beet pulp, pea hulls…) led to an important solubilisation of polysaccharides of various types without extensive degradation of the polymeric structure. The possibility of obtaining gelled systems directly with the extruded pectin-rich materials was demonstrated. This treatment has the advantage of avoiding the acid extraction of the pectins; it could be also used to obtain extruded products which could be used in various preparations traditionnally requiring high methoxyl pectins as gelling agents. The final products could be therefore enriched in dietary fibres and devoid of additives.