Apply mass transfer analysis to product engineering.

Food engineering is associated with the operation and maintenance of food processing plants as well as research involving process design. The applications of engineering in food handling, processing, packaging and product distribution can be described in terms of unit operations. There are many different unit operations associated with the conversion of raw food materials into consumer products. The movement of foods and other materials within the processing plant requires the use of a variety of equipment and processes. And, food quality requires quantitative engineering analysis to be applied to processing and manufacturing.

Heat, mass and flow transport processes are involved in the design of products during their processing, handling and storage. The mass transfer of water and various component molecules is of particular importance in the engineering of solid and semi-solid foods. Here, the structure of the product significantly affects the kinetics of chemical, biochemical, microbiological and quality changes. The structure of a food at the molecular, nano-, micro-and macroscopic levels can be modified by applying chemical, mechanical or electrical (microwave or pulse) treatments.

A product's internal transport mechanism may control most mass transfer processes. The importance of mass transfer in product engineering is illustrated by experimental data on the transport of moisture in dehydrated food products. Greek scientists prepared food biopolymer gels and vegetable food materials in various forms to simulate the structure of food products.

The scientists determined the mass transport properties of these materials using standard techniques and computational methods. They found that mass diffusivity depends strongly on the physical structure of the product. The diffusivity of water and small solutes in food systems depends primarily on the product's porosity and pore geometry, while the effect of temperature is more important in nonporous food products.

It is possible to apply mass transfer analysis to product engineering when manufacturing food products of tailored structure, such as extruded, freeze-dried or compacted products. Mass transfer analysis is also useful when analyzing such conventional food processes as cooking, roasting, frying, extraction and freezing.

Further information. George Saravacos, National Technical University of Athens, Patision Complex, 28 Oktovriou (Patision) 42, 10682 Athens, Greece; phone: +30 210 7722017; fax: +30 210 7722028; URL: www.ntua.gr/en_index.htm.