Performance evaluation of the double screw conveyor in radio frequency systems: Heating uniformity and quality of granular foods |
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| Affiliation: | 1. Northwest A&F University, College of Mechanical and Electronic Engineering, Yangling, Shaanxi 712100, China;2. Department of Biological Systems Engineering, Washington State University, 213 L.J. Smith Hall, Pullman, WA 99164-6120, USA;1. College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China;2. Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA;1. College of Engineering, China Agricultural University, Beijing 100083, China;2. Chinese Academy of Agricultural Mechanization Sciences, Beijing 100083, China;3. Department of Central Research and Development, China National Machinery Industry Corporation, Beijing 100080, China;4. College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China;5. Washington State University, Department of Biological Systems Engineering, Pullman, WA 99164-6120, USA |
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| Abstract: | Non-uniform heating is a major challenge for commercial applications of radio frequency (RF) technology in the food industry. To improve the RF heating uniformity of granular foods, a double screw conveyor was designed and used to investigate effects of conveying direction, screw rotation speed, filling ratio, and electrode gap on the heating rate and uniformity of jujubes. The results showed that there was no significant (p > 0.05) difference between forward and backward conveying directions both in heating rate and uniformity, while the RF heating uniformity gradually improved with the increased screw rotation speed. RF heating rate increased gradually with the increase of filling ratio or decrease of electrode gap. Except for the significantly higher λ value found in the filling ratio of 80%, no significant (p > 0.05) changes were observed between 20 and 60%. Furthermore, the λ values also increased with decreasing electrode gap. Quality evaluation indicated that there were no significant (p > 0.05) differences in the color values, texture properties, ascorbic acid, and moisture content between control and samples treated by RF heating under the double screw conveying. Overall, the results obtained from this study demonstrate that as a simultaneous mixing and moving equipment, the screw conveying can be considered as a promising approach in improving the RF heating uniformity of granular foods for industrial applications. |
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