Mass Transfer Study on Drying of Curdlan by Hot Air Coupled with Ultrasound and Infrared Irradiation and Quality Analysis

Objective: Hot air coupled with ultrasound and infrared irradiation were used for the drying of curdlan. The drying mechanism and quality change of curdlan were explored under the multi-physical fields, so as to developing the green drying technology of curdlan. Methods: Forced convective hot air alone, ultrasound-coupled forced convective hot air, infrared irradiation alone, and infrared-coupled forced convective hot air were used to dry curdlan. A mass transfer model considering temeprature change was constructed and the quality of the dried curdlan was comprehensively assessed. Results: Under the studied forced convective hot air drying conditions, it took around 40 min to dry the curdlan, and the required drying time was reduced to 36, 26 and 22 min for ultrasound-coupled hot air drying, infrared irradiation alone drying, and infrared-coupled hot air drying, respectively. The moisture transfer model coupled with the temperature change was able to accurately predict the change of the moisture content throughout drying. Under infrared drying coupled with convective hot air, the range of moisture effective diffusivity inside curdlan was 9.79×10−9 to 9.81×10−9 m2/s, and the surface mass transfer coefficient was 4.69×10−2 kg water/(m2·s), which were higher than those of the other treatment groups, followed by those under infrared irradiation alone drying, ultrasonic-coupled hot air drying, and hot air drying alone. Moreover, the gel strength, glucose content, the distribution of chemical functional groups on surface, crystal structure and thermal stability of curdlan samples dried by different methods were all similar. Conclusion: Taking all these results into consideration, infrared drying was regarded as an efficient method for drying curdlan compared to hot air drying and ultrasound-coupled hot air drying.