Temperature microwave-assisted drying

Moisture and temperature history relate to quality changes during microwave-assisted drying processes and have, therefore, been intensively investigated. Their... 

Temperature was found to be the most significant predictor of drying process during microwave-assisted drying, as it reflects the general drying performance rather well (Duan et al., 2010b). 

Figure 9.14 presents typical temperature curves of microwave-assisted drying for food. Here, the shape of the temperature curve of microwave-assisted freeze-drying can be seen to differ from that of the three other types of microwave-assisted drying, due to different drying mechanisms. Temperature changes are heavily dependent on the microwave power, microwave emission mode, type of dryer used, and the presence or absence of a temperature control unit. 

Three different temperature stages are observed at constant microwave power in most microwave-assisted drying processes (Clary et al., 2005 Feng et al., 1999 Ahme et al., 2007 Duan et al., 2010b) ... 

Fig. 9.14 Typical temperature curves of microwave-assisted drying for food, where 1 and 2 indicate the temperature changes in...

In order to accelerate sample preparation, new extraction methodologies such as accelerated solvent extraction (ASE) and MAE, based on the use of elevated temperature and pressure to heat the mixture sample-solvent, have been recently developed and applied for PAH extraction from meat [695] and vegetables [696-698]. Garda Falcon et al. [699] used microwave treatment with hexane to accelerate PAH extraction from freeze-dried foods. The fat extracted in this way underwent microwave assisted saponification with ethanolic KOH. Hernandez-Borges et al. [700] combined microwave-assisted hydrolysis and extraction to isolate organic pollutants from mussels, while... 

Fig. 9.9 Laboratory-scale microwave-assisted freeze-drying equipment. 1, MWFD chamber 2, Fiber-optical temperature sensor 3, Vacuum breakage valve, for MWFD 4, Sample supporting plate ...

A typical schematic diagram of microwave-assisted freeze-drying equipment is shown in Fig. 9.9. During drying, the pressure was maintained at 100 Pa by a vacuum pump, and the temperature of the cold trap (—40 to —45 °C) was sufficiently low to condense the vapor. The microwave frequency was 2450 MHz and the power could be regulated continually from 0 to 2000 W. 

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