Vacuum impregnation for development of new dehydrated products

Vacuum impregnation (VI) of structured foods implies the partial release of gas from pores and its substitution by an external liquid. Therefore, important changes in physicochemical and structural properties take place in the food and these affect its behavior in drying operations lair-drying (AD) and/or osmotic dehydration (OD)). The adequate control of VI prior to dehydration may be used as a tool both to improve mass transfer and to develop engineered products. In order to evaluate this alternative, the effectiveness of VI as a tool in porous matrix formulation is analyzed. Likewise, its influence on some physical and transport properties of the plant tissue and the relevant changes induced in osmotic and convective drying processes are discussed, since these are probably the most interesting alternative processes to lengthen the impregnated product shelf-life. Improved yield of some dehydration processes, such as fruit candyin, when VI is applied at the beginning, is also discussed in terms of the cell network relaxation mechanism, responsible for hydrodynamic tissue impregnation. (C) 2001 Elsevier Science Ltd. All rights reserved.