Study of interval infrared Airflow Drying: A case study of butternut (Cucurbita moschata)

Interval process is defined as a means of operating short-time intervals configured to allow the material to attain characteristics to match higher drying rate. The innovative Interval Infra-Red Airflow Drying (IIRAD) involves successive heating intervals (tON) of several seconds followed by tempering periods (tOFF) of a few minutes. IIRAD provides heat only when the product surface is fully rewetted. Drying of winter squash slices was performed in three cases; continuous IR-drying, IIRAD-I: tON = 5 s and tOFF = 2 min, and IIRAD-II: tON varies throughout the process with tOFF = 2 min. A higher drying rate was observed during IIRAD-I. Measured evaporating-bulb temperatures were below 21 °C with energy consumption of 0.98 and 0.77 kWh/kg of evaporated water for I-IIRAD and II-IIRAD, respectively, wherein they exceeded 66 °C and 2.19 kWh/kg of evaporated water for continuous drying. IIRAD resulted in better preservation of flavonoids and better retention of color. However, continuous IR-dried samples displayed better rehydration and higher total polyphenol content. Overall, IIRAD is shown to be a promising drying technique for heat sensitive materials in terms of efficiency, energy consumption, and preservation of key quality attributes linked to lower operating temperature, but with increased drying time. •Interval IR Airflow Drying IIRAD process has allowed increasing the drying efficiency.•IIRAD increases the drying rate thus keeping the evaporating bulb temperature below 21 °C.•IIRAD treatment reduces energy consumption until 64.8% compared to continuous IR.•Better preservation of flavonoids and color of dried squash was achieved by IIRAD.