Drying characteristics of lotus root under microwave and hot-air combination drying

  • Joe, Sung Yong (Department of Biosystems Machinery Engineering, Chungnam National University) ;
  • So, Jun Hwi (Department of Smart Agriculture Systems, Chungnam National University) ;
  • Lee, Seung Hyun (Department of Biosystems Machinery Engineering, Chungnam National University)
  • Received : 2020.04.23
  • Accepted : 2020.07.21
  • Published : 2020.09.01


Because lotus root has a short shelf life, the quality easily deteriorates. Thus, the harvested lotus roots are processed into a variety of products. Drying is one of the simplest food preservation methods, which can increase food stability. However, the convective drying method takes a long time and requires high energy consumption. Combination drying methods have emerged to overcome the limitations of the convective drying method. This study investigated the drying characteristics of lotus root and determined the optimal drying model of lotus root depending on the microwave and hot-air combination drying conditions. The lotus root slices (5 mm in thickness and 40 mm in diameter) were dried by different drying conditions that were combined with three microwave power levels (50, 100, and 150 W) and two hot air temperatures (50 and 60℃) at a velocity of 5 m·s-1. Eight drying models were tested to evaluate the fit to the experimental drying data, and the effective moisture diffusion (Deff) values of the lotus root slices dried by combination drying were estimated. The combination drying time of the lotus root was significantly reduced with the high air temperature and microwave power. The effective moisture diffusion (Deff) of lotus root was more affected by the air temperature than microwave power intensity. Logarithmic model was most suitable to describe the drying curve of lotus root in the microwave-hot air combination drying method.


  1. Akgun NA, Doymaz I. 2005. Modelling of olive cake thin-layer drying process. Journal of Food Engineering 68:455-461.
  2. Alibas I. 2007. Microwave, air and combined microwave-air-drying parameters of pumpkin slices. LWT - Food Science and Technology 40:1445-1451.
  3. Andres A, Fito P, Heredia A, Rosa EM. 2007. Combined drying technologies for development of high-quality shelfstable mango products. Drying Technology 25:1857-1866.
  4. Chiang PY, Luo YY. 2007. Effects of pressurized cooking on the relationship between the chemical compositions and texture changes of lotus root (Nelumbo nucifera Gaertn.). Food Chemistry 105:480-484.
  5. Dong P, Kong M, Yao J, Zhang Y, Liao X, Hu X, Zhang Y. 2013. The effect of high hydrostatic pressure on the microbiological quality and physicochemical properties of lotus root during refrigerated storage. Innovative Food Science and Emerging Technologies 19:79-84.
  6. Du J, Fu Y, Wang N. 2009. Effects of aqueous chlorine dioxide treatment on browning of fresh-cut lotus root. LWT - Food Science and Technology 42:654-659.
  7. Henderson SM, Pabis S. 1961. Grain drying theory II: Temperature effects on drying coefficients. Journal of Agricultural Engineering Research 6:169-174.
  8. Jeon WP, Kim SI. 2010. An experimental study on a combined dryer using microwave and hot air heating. pp. 221-211. Korean Society for Energy, Seoul, Korea. [in Korean]
  9. Karathanos VT, Belessiotis VG. 1999. Application of a thin-layer equation to drying data of fresh and semi-dried fruits. Journal of Agricultural Engineering Research 74:355-361.
  10. Kim JS, Ryu YB, Kim MH, Hong SS, Lee MS. 2013. Drying characteristics of succinic acid using the microwave. Journal of the Korea Academia-Industrial cooperation Society 14:6023-6028. [in Korean]
  11. Lewicki PP. 2006. Design of hot air drying for better foods. Trends in Food Science and Technology 17:153-163.
  12. Liu J, Zhang M, Wang S. 2010. Processing characteristics and flavour of full lotus root powder beverage. Journal of the Science of Food and Agriculture 90:2482-2489.
  13. Madamba PS, Driscoll RH, Buckle KA. 1996. The thin-layer drying characteristics of garlic slices. Journal of Food Engineering 29:75-97.
  14. Midilli A, Kucuk H, Yapar Z. 2002. A new model for single-layer drying. Drying Technology 20:1503-1513.
  15. Moon SM, Kim HJ, Ham KS. 2003. Purification and characterization of polyphenol oxidase from lotus root (Nelumbo nucifera G.). Korean Journal of Food Science and Technology 35:791-796. [in Korean]
  16. Nijhuis HH, Torringa HM, Muresan S, Yuksel D, Leguijt C, Kloek W. 1998. Approaches to improving the quality of dried fruit and vegetables. Trends in Food Science and Technology 9:13-20.
  17. O'callaghan JR, Menzies DJ, Bailey PH. 1971. Digital simulation of agricultural drier performance. Journal of Agricultural Engineering Research 16:223-244.
  18. Page GE. 1949. Factors influencing the maximum rates of air drying shelled corn in thin layesssrs. M.S. thesis. Purdue Univ., Purdue, USA.
  19. Park HW, Han WY, Yoon WB. 2015. Effect of grain size and drying temperature on drying characteristics of soybean (Glycine max) using hot air drying. Journal of the Korean Society of Food Science and Nutrition 44:1700-1707. [in Korean]
  20. Park SH, Hyun JS, Sihn EH, Han JH. 2005. Functional evaluation of lotus root on serum lipid profile and health improvement. East Asian Soc Dietary Life 15:257-263. [in Korean]
  21. Ren G, Chen F. 1998. Drying of American ginseng (Panax quinquefolium) roots by microwave-hot air combination. Journal of Food Engineering 35:433-443.
  22. Salagnac P, Glouannec P, Lecharpentier D. 2004. Numerical modeling of heat and mass transfer in porous medium during combined hot air, infrared and microwaves drying. International Journal of Heat and Mass Transfer 47:4479-4489.
  23. Sharma GP, Prasad S. 2001. Drying of garlic (Allium sativum) cloves by microwave-hot air combination. Journal of Food Engineering 50:99-105.
  24. Therdthai N, Zhou W. 2009. Characterization of microwave vacuum drying and hot air drying of mint leaves (Mentha cordifolia Opiz ex Fresen). Journal of Food Engineering 91:482-489.
  25. Tsotsas E, Mujumdar AS. 2007. Modern drying technology volume 3: Product quality and formulation. Wiley-VCH, Weinheim, Germany.
  26. Tsuruta Y, Nagao K, Shirouchi B, Nomura S, Tsuge K, Koganemaru K, Yanagita T. 2012. Effects of lotus root (the edible rhizome of nelumbo nucifera) on the deveolopment of non-alcoholic fatty liver disease in obese diabetic db/db mice. Bioscience, Biotechnology and Biochemistry 76:462-466.
  27. Varith J, Dijkanarukkul P, Achariyaviriya A, Achariyaviriya S. 2007. Combined microwave-hot air drying of peeled longan. Journal of Food Engineering 81:459-468.
  28. Vega-Galvez A, Di Scala K, Rodriguez K, Lemus-Mondaca R, Miranda M, Lopez J, Perez-Won M. 2009. Effect of air-drying temperature on physico-chemical properties, antioxidant capacity, colour and total phenolic content of red pepper (Capsicum annuum, L. var. Hungarian). Food Chemistry 117:647-653.
  29. Wang CY, Singh RP. 1978. Use of variable equilibrium moisture content in modeling rice drying. Transactions of American Society of Agricultural Engineers 11:668-672.
  30. Wang J, Xi YS. 2005. Drying characteristics and drying quality of carrot using a two-stage microwave process. Journal of Food Engineering 68:505-511.
  31. Wang SM, Yu DJ, Song KB. 2011. Physicochemical properties of lotus (Nelumbo nucifera) root slices dehydrated with polyethylene glycol. Food Science and Biotechnology 20:1407-1411.
  32. Yagcioglu A, Degirmencioglu A, Cagatay F. 1999. Drying characteristic of laurel leaves under different conditions. pp. 565-569. In Proceedings of the 7th International Congress on Agricultural Mechanization and Energy. Faculty of Agriculture, Cukurova University, Adana, Turkey.
  33. Zhang M, Tang J, Mujumdar AS, Wang S. 2006. Trends in microwave-related drying of fruits and vegetables. Trends in Food Science and Technology 17:524-534.
  34. Zogzas N, Maroulis ZB, Marinos-Kouris D. 1996. Moisture diffusitivity data compilation in foodstuff. Drying Technology 14:2225-2253.