Conclusions
Microwave drying of apples at any constant temperature cannot
balance the time, energy, and quality requirements. A high temperature
consumed short time and less energy, but resulted in poor
product quality. A low temperature resulted in good product quality,
but consumed long time and more energy. Although drying apples
at a middle drying temperature consumed intermediate time
and energy, and achieved median product quality, they still have
the potential to be improved.
Drying apples with a drying curve which followed a pre-designed
linear line could improve product quality, save time and energy
in a single process. A gradually increasing temperature (from
25 to 50 C) in the beginning and middle drying stages could
achieve a nearly linear drying curve, while real time curve control
was omitted. A 3-step temperature control (30, 40, and 50 C)
could also improve the drying effects and greatly simplify the control
system. Hence, a controlled drying curve and drying temperature
are always recommended in microwave drying practices.
Further study is recommended to investigate the microstructure
change during different drying methods and in different stages
during microwave drying.
Acknowledgement
The authors thank the financial support by NSERC (Natural Science
and Engineering Research Council of Canada).
ConclusionsMicrowave drying of apples at any constant temperature cannotbalance the time, energy, and quality requirements. A high temperatureconsumed short time and less energy, but resulted in poorproduct quality. A low temperature resulted in good product quality,but consumed long time and more energy. Although drying applesat a middle drying temperature consumed intermediate timeand energy, and achieved median product quality, they still havethe potential to be improved.Drying apples with a drying curve which followed a pre-designedlinear line could improve product quality, save time and energyin a single process. A gradually increasing temperature (from25 to 50 C) in the beginning and middle drying stages couldachieve a nearly linear drying curve, while real time curve controlwas omitted. A 3-step temperature control (30, 40, and 50 C)could also improve the drying effects and greatly simplify the controlsystem. Hence, a controlled drying curve and drying temperatureare always recommended in microwave drying practices.Further study is recommended to investigate the microstructurechange during different drying methods and in different stagesduring microwave drying.AcknowledgementThe authors thank the financial support by NSERC (Natural Scienceand Engineering Research Council of Canada).
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