**13. Summary and outlook**

12 The Development and Application of Microwave Heating

equipment for microwave blanching.

heating requires.

This is due mainly to the following factors:

efficiency (RodrõÂguez et al., 2003).

microwave energy for this particular application.

**11. Waste treatment under microwave irradiation** 

**9. Advantages of microwave blanching** 

these products, nor produces trans- isomers (Helmar et al., 2007).

Microwave heating involves conversion of electromagnetic energy into heat by selective absorption and dissipation. Microwave heating is attractive for heating of foods due to its origin within the material, fast temperature rise, controllable heat deposition, and easy clean-up. The very high frequencies used in microwave heating allow for rapid energy transfers and, thus, high rates of heating. These rates are a main advantage of this technique. Also, because microwaves penetrate the sample, heating is accomplished in the interior of the food. When heating rapidly, the quality of fruits and vegetables such as flavor, texture, color and vitamin content is better kept (Dorantes-Alvarez et al., 2000). However, rapid heating can also lead to problems of non-uniform heating when excessively high energy transfer rates are used (Ohlsson, 2000). It has been observed that microwave processing of chicken, beef, bacon, trout, and peanut oil does not change the fatty acid composition of

**10. Development of unique-single systems for microwave blanching** 

The most likely future for microwave food processing is in the continued development of unique single systems that overcome the limitations discussed previously. Compared to the development of traditional blanching systems, it is still a challenge to design appropriate



In the near future, it is expected that researchers interested in this matter will discover more specific effects that may be advantageous in the processing of food by microwave blanching. This would give an additional value to food products and would overcome the cost of

Many industrial activities involve the creation and subsequent disposal of waste, which represents a noticeable cost in terms of money and pollution. Moreover, sometimes waste Microwave ovens are commonplace in households and are established there as devices of everyday use. Their primary function is still the reheating of previously cooked or prepared meals. The relatively new combination of microwaves with other (e.g. conventional, infrared or air jet) heating systems should enhance their potential for a complete cooking device, that

could replace conventional ovens. Unfortunately, in industry the distribution of microwave processes is still far away from such high numbers. Only a relatively low number of microwave applications can be found in actual industrial production, compared with their indisputable high potential. These successful microwave applications range over a great spectrum of all thermal food processes. The most prominent advantages of microwave heating are the reachable acceleration and time savings and the possible volume instead of surface heating. Reasons mentioned for the failure of industrial microwave applications range from high energy costs, which have to be counterbalanced by higher product qualities, over the conservatism of the food industry and relatively low research budgets, to the lack of microwave engineering knowledge and of complete microwave heating models and their calculation facilities. The latter disadvantage has been partly overcome by the exponentially growing calculating power which makes it possible to compute more and more realistic models by numerical methods. Very important for the task of realistic calculations is the determination of dielectric properties of food substances by experiments and theoretical approaches. Nevertheless in order to estimate results of microwave heating applications and to check roughly the numerical results, knowledge of simple solutions of the one-dimensional wave propagation like the exponentially damped wave is of practical (and also educational) relevance. But still the best test for numerical calculations is experiments, which yield the real temperature distributions within the product, which is really important especially in pasteurization and sterilization applications. While more conventional temperature probe systems, like fibre optic probes, liquid crystal foils or infrared photographs only give a kind of incomplete information about the temperature distribution within the whole sample, probably magnetic resonance imaging has the potential to give very useful information about the heating patterns. Hopefully, this together with the enormous calculation and modeling power will give the microwave technique an additional boost to become more widespread in industrial food production.

The breakthrough of microwave technology in the food industry due to its high potential has been predicted many times before, but it has been delayed every time up to now. That is why we are cautious in predicting the future of microwaves in industrial use. However, we think that the potential of microwave technology in the food industry is far from being exhausted.
