Microwave drying kinetics and quality of Allium hirtifolium Boiss: effect of ultrasound-assisted osmotic pretreatment

Allium hirtifolium Boiss, called “Mooseer” in Iran, is a perennial herb and a rich source of vitamins, minerals, and antioxidants. Herein the effect of different pretreatments including ultrasound (US), osmotic (OD), and ultrasound-assisted osmotic (UAO) pretreatment before microwave drying on its drying characteristics was investigated to evaluate quantitative and qualitative characteristics of Allium hirtifolium Boiss drying. All pretreated samples showed lower drying time compared to untreated samples. US and UAO pretreated samples showed lower drying time compared to OD pretreated samples. Based on the fitting data of 8 common thin-layer models, the Logarithmic model was the best model to describe the microwave drying behavior of Allium hirtifolium Boiss slices. UAO pretreated samples had higher water diffusivity and the effect of ultrasound power was significant (p < 0.05) on it. The obtained values were in the range of 3.074 × 10–7 and 8.574 × 10–7 m2/s which are in the general range of diffusivity of food material. Samples subjected to OD pretreatment showed lower Total Color Difference (ΔE) and Browning Index (BI) and higher rehydration ratio compared to UAO pretreatment. Generally, compared to OD pretreatment, UAO pretreatment did not show a significant effect (p > 0.05) on the total phenolic content and vitamin C of samples. However, it had a significant effect (p > 0.05) on the antioxidant content of the samples. Consequently, UAO pretreatment can reduce the drying time while maintaining the quality of samples and contributes to energy saving. Therefore, it is recommended to use UAO pretreatment in microwave drying of Allium hirtifolium Boiss.