Monitoring and control of microwave drying with volatiles detection of celery stalks

A hot-air coupled microwave drying (MHD) system equipped with an online aroma detection and feedback with Portable Electronic Nose, PEN3, was developed to preserve high volatile components in celery stalk. Celery stalk slices were dried at constant temperatures of 50 °C, 60 °C, 70 °C, and 80 °C, and sensors 7 and 9 of 10 sensors in PEN3 were selected and set at stage-cooling drying. Aroma volatiles were recorded every 2 min for each of the three replicates. Fuzzy logic control and PID combined control were developed with adjustable drying temperature based on volatile changes during the drying process. Results of sensor response values and GC–MS showed that more aroma volatiles were maintained under combined control. Products dried at 50 °C had the least shrinkage ratio, and products dried at 80 °C had the highest rehydration rate and the shortest drying time. In general, the combined control kept a good balance between drying efficiency and product quality compared with other drying methods and could produce better products. Hence, the proposed control scheme based on volatile component changes can effectively preserve more volatiles and could be used to produce high-flavor and high-quality dried celery.