Francesco Marra

　　Department of Industrial Engineering University of Salerno, Italy

　　Radio frequency (RF) assisted heating of foods is an established technique used in food processing such as postharvest treatment of in-shell fruits, drying of food materials and products. More recently, it has been proposed as industrial solution for continuous tempering of frozen meat blocks.

　　Freezing operation is one of the most widely used methods to preserve food products for extended shelf life. It can also be used in preservation of raw materials during transportation and storage. Before consumption or further processing activities, frozen products, such as meat, poultry and seafood, need to undergo tempering (-5°C to -2°C) or thawing procedures (-2°C to +5°C) using safe and fast methods. Thawing should be performed in a way that maintains the characteristic properties of the food product. Recommended conventional thawing methods need long processing time and, in case of thawing under running water, a considerable amount of water resource wasted. Thawing by itself is a slow process due to its constituent of various dissolved components, and takes place gradually over a range of temperature.

　　RF assisted tempering and thawing of those frozen products have great potential to reduce the quality loss encountered in slow conventional processing methods. Thanks to its rapid and volumetric heating behavior, it is also possible to achieve thawing in minutes rather than hours or days with minimized risk of product degradation. Furthermore, RF thawing can be performed in both batch and continuous modes and it can also be carried out inside the packaging materials, such as carton boxes and polyethylene bags.

　　However, the performance of this method depends on various factors, such as shape, size, composition and physical configurations of RF equipment. Furthermore, the mode of operation, either in batch or continuous, also affects the temperature distribution and heating rate in the food sample.

　　This contribution then deals with the engineering aspects of RF assisted thawing of foods, covering the analysis of transport phenomena involved in the process, the design of thawing systems (assisted by virtualization), the process configurations, the unsolved issues and the needs for further research at both industrial and academic sides.