The significance of physico chemical properties of plant cell wall materials for the development of innovative food products

Cell wall materials (CWM) are natural constituents of fruits and vegetables. They are added in a growing extent to foods as health ingredients to create innovative products (functional food). CWM or dietary fibres, respectively, have both physiological and technological functional properties, which are considerably modified during the dietary fibre preparation, during the incorporation of the dietary fibre ingredients into foods and generally during processing. Process-dependent external stress and the influence of internal conditions induce changes of the physico-chemical properties of the food constituents (such as particle size and shape, porosity, water binding and structure-forming as well as texturization properties). These changes affect or determine the technological functional, the material and the physiological properties. To evaluate the alterations of structure and properties of plant cell walls during processing without disturbing influences CWM-water-model suspensions and cell wall preparations, carefully dried after a water-ethanol-exchange, can be used. Such model studies and investigations for the improved manufacture of dietary fibre preparations as well as dried fruit and vegetable products show that both the pre-drying treatments (addition of salt, sugar, polysaccharides and surfactants) and the drying step itself considerably influence the extent of shrinkage, cell wall stiffening as well as cell collapse and glass transition. In pre-drying treatments variations of the degree of methoxylation of the pectin component and/or cation charging can be made which cause a pre-formation of structures and/or states of matter that determine essentially the drying process. The ability of rehydration plays an important role for the application and utilization of dried CWM and dietary fibre preparations as well as of dried fruit and vegetable products. The rehydration process is achieved by the plasticizing effect of water, the temperature influence and the external stress, e.g. by stirring, and is supposed to reverse the state transitions, resulting from drying. By application in foods the rehydration of the CWM and dietary fibre preparations can contribute to the formation of texture (texturization). The texturization caused by CWM depends not only on processing and internal conditions but also essentially on the concentration, size, shape, stiffness and deformability of the particles as well as their water binding properties (amount and strength). The investigations show that improved technologies for the production of cell wall and dietary fibre preparations as well as innovative foods with selectively adjusted functional properties require a fundamental understanding of the changes in structure and properties, caused by processing. Furthermore, a well coordinated cooperation of different scientific disciplines using information technology is necessary for a successful development of innovative dietary fibre enriched products.