Infrared thermography assisted control for apples microwave drying

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 bydetecting the instantaneous maximum temperature among the samples under test instead of a chosenslice. The effectiveness of the system at hand in realizing temperature control both in space and in timewas proven for three temperatures: 55, 65 and 75 C. Temperature fluctuations became larger both withtime 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 significantlylower (p < 0.05), when compared to the fresh samples and to the apples dried by hot air. Toovercome such behaviour a mode stirrer was introduced resulting in halving the temperature spatialoscillations of sample slices.