**9. Conclusion**

38 The Development and Application of Microwave Heating

foods can be lost during cooking.

methods (Katz, 1994).

generated during microwave cooking. It can also be already contained in the food, *e.g.*, in a precooked meal. In any case, the release phenomenon is the same and it is the timing that may be different. If the flavour is only produced at the end of heating, losses due to volatilization will be diminished considerably. In microwave heating of a precooked product, the volatile aroma compounds are integral to its final aroma, and losses can imbalance the aroma. Aroma is defined as the volatile aroma compounds that contribute both to the orthonasal (sniffing) and retronasal (eating) smell of a food. This section will explain the theory and give examples of how aroma compounds present in microwave

The impact of microwave cooking on the formation of early Maillard products was investigated and compared with the effect of conventional cooking, using milk as a test system. Experiments were carried out at controlled temperatures of 80°C and 900C, respectively, at holding times up to 420 min. Hydroxymethylfurfural (HMF) and lactulose, which are all established indicators to estimate heat damage, were determined. The concentrations of all the heating indicators increased with increasing heating time. For example in the 90°C test series the furosine values rose from 34 mg litre-1 (0.5 h) to 94 mg litre-1 (2 h holding time) in the milk heated by microwaves and from 35 mg litre-1 (0.5 h) to 96 mg litre-1 (2 h) in the conventionally heated milk. None of the reaction products showed significant differences as between the microwave heating and conventional cooking

Flavour may be a problem in MW-cooked foods because flavour volatiles distill off, bind to proteins and other molecules or fail to develop at all. A number of methods have been developed to prevent or offset these flavor problems. Extraction process wherein substrates are mixed with MW-transparent solvent and exposed to MW which liberates target compounds from natural materials (*e.g.* spices). Selectivity can be varied by altering solvents/conditions. MW extraction in combination with liquid CO2 can be used as an alternative to supercritical fluid extraction (decaffeination of coffee, defatting of cocoa powder). A process to generate desirable aromas when a food and/or package is subjected to MW radiation. The aroma-generating material, consisting of a sugar alone or in combination with an amino acid source, and an effective amount of a MW susceptible material for

Vegetables are often cooked to increase palatability and digestibility, ascorbic acid content of MW-cooked, frozen peas was lower, retention of chlorophyll and organic acids (lactic, succinic, malic, citric……*etc*) was higher for peas cooked without water. Effects were smaller for carrots. Those cooked without water had higher flavor scores and carotene retention than those cooked with water. While MW cooking of vegetables generally results in better nutrient retention, there is no one method that produces overall superior sensory

Cooking starchy tubers gelatinizes the starch softening the texture. After a lag of 4 min, water loss during MW cooking of potatoes was rapid and linear. Starch gelatinization began at the surface and in the center, and then spread throughout the tuber cross-section after 1

conductive heat transfer sufficient to catalyze the desired chemical reactions

characteristics when considering color, flavor, texture, and moistness.

This chapter reviewed the flavours and colors appropriate for microwave foods. It discusses the types of flavor definition, the sources of natural flavours and the difference between conventional and microweave heating as well as the generation of flavour from microwave heating especially via maillard reaction. It isolates the particular effects of microwave heating on the browning reaction in flavor formation and its implications for the choice and application of flavours for microwave foods. For products that are simply seasoned and reheated, the microwave does not present significant challenges that are different from conventional heating. Microwave popcorn is an ongoing challenge to create a good flavour that will not all be volatilized during heating. Encapsulation can provide a benefit in protecting the flavour during processing and helping to retain it during the popping process. As work continues to better understand flavours, there will be new developments that will benefit microwave food products.
