Moisture microwave heating

SFME is based on the composition of microwave heating and distillation and is performed at atmospheric pressure. The composition of extracted oil varies with time, moisture content and irradiation power. The extraction... 

In addition, the coating has to resist to the conditions of storage and of preparation of the food product, for example, storage temperature, oven or microwave heating. Many ready-to-eat composite food products to which edible moisture barriers are... 

The impact of enzyme activity on the nonhydratable phospholipid content of crude soybean oil was investigated by List et al. (140). Evaluation of flakes subjected to live steam and whole beans treated by microwave heating to inactivate phospholipase D suggests that heat, moisture, and enzyme activity are important factors contributing to the formation of nonhydratable phospholipids in extracted crude oils. Approximately 8-10 minutes of microwave heating is required to completely destroy enzymatic activity. 

A halogen lamp (100 W) suffices to dry samples with low moisture contents however, a more powerful heating device is required for wet samples. Direct contact with a heating element provides good results, but introduces the risk of external contamination. Alternatives such as microwave heating can be effective for this purpose. 

FIGURE 13.7 A typical microwave heating system utilizing a conveyorized cavity applicator. A feedback system monitors the heated material and automatically adjusts the output power of the magnetron to control the final moisture. 

Material shrinkage is caused mainly by removal of moisture in a liquid phase. The moisture in a gas phase has a meaning only in a special case of very intensive microwave heating, which is not applied in common drying. 

Microwave Heating. Microwaves (wavelength of 3 to 30 cm) are used to heat foods as a result of molecular excitation of food and their penetration power. Microwave heated foods do not have a heat gradient. Foods containing high moisture and fat readily absorb microwaves and are cooked or baked. Application of microwave for both home and institutional meal preparation has increased because of its convenience and rapid heating when compared to conventional means. 

Fig. 9.2 Mechanisms of moisture transport inside unfrozen food materials during microwave heating. Adapted from Cui (2004).

A constant temperature period, which corresponds to the aforementioned constant drying rate period in which moisture is removed at the outer surface of the material and the cooling effect of vaporization remains in balance with the microwave heating. 

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