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Infrared thermography assisted control for apples microwave drying

Cuccurullo, G., Giordano, L., Albanese, D., Cinquanta, L., Di Matteo, M.
Journal of food engineering 2012 v.112 no.4 pp. 319-325
air drying, apples, dried fruit, fruit quality, microwave treatment, space and time, temperature, thermography
A microwave based system was developed for drying of apple slices while on-line controlling their temperatures. An infrared thermography assisted control system allowed to realize temperature control by detecting the instantaneous maximum temperature among the samples under test instead of a chosen slice. The effectiveness of the system at hand in realizing temperature control both in space and in time was proven for three temperatures: 55, 65 and 75°C. Temperature fluctuations became larger both with time increasing and with rising temperature levels thus causing a negative impact on dried fruit quality. In fact apples slices dried at 75°C by microwave showed L∗ (lightness) and white index (WI) values significantly lower (p<0.05), when compared to the fresh samples and to the apples dried by hot air. To overcome such behaviour a mode stirrer was introduced resulting in halving the temperature spatial oscillations of sample slices.