Plant cell walls consist of a variety of chemical constituents such as cellulose, humicelluloses, pertins, lignin, glycoproteins, etc. These components are strongly linked through hydrogen , covalent, ionic and hydrophobic bondings, which thus confers the self-protection capability on plants. Some processing by-products (hulls, brans, pomaces) of cereal, fruits and vegetables are very limited in further utilization due to their compact structural rigidity. In view of the fact that the plant cell walls are essentially composed of dietary fiber components , solubilization of the strong intermolecular linkage s can contribute to increasing the soluble dietary fiber content and thus diversifying the functional and physiological role of plant cell walls as dietary fiber sources. This article reviews the chemical constituents of cereals, fruits & vegetables and brown seaweeds with reference to their intermoleuclar linkages. An particular emphasis will be placed on the solubilizing phenomena of rigid plant cell walls by extrusion and the resulting change of functional properties. It is suggested that underutilized food resources, typically exemplified by various food processing by-products and surplus seaweeds, can be successfully modified toward improved functional performance by extrusion.