EFFECTS OF AIR-DRYING ON THE SHRINKAGE, SURFACE TEMPERATURES AND STRUCTURAL FEATURES OF APPLES SLABS BY MEANS OF FRACTAL ANALYSIS
Shrinkage-deformation phenomenon of apple slabs during convective drying was studied, aiming to analyse its causes. Apple slabs were dehydrated in an experimental drying tunnel using a factorial design 42. Independent variables were airflow (1, 2, 3 and 4 m/s) and drying air temperature (50, 60, 70 and 80 °C). Relative shrinkage (A/Ao) was evaluated during drying as the ratio of the projected (top view) area of slab at any time during the process (A) to the initial area (Ao) of the same slab. In five punctual measuring zones on the surface of the slab, surface temperatures (ST) and moisture contents (MC) were evaluated. ST and MC were different for each measuring zone, causing irregular dehydration. Fractal analysis was used to evaluate the non-linear (A/Ao) observed pattern and ST distribution. Fractal dimensions for (A/Ao) ratios (FDA) and ST (FDST) were 1.08-1.30 and 1.12-1.54 respectively. Temperatures of 60º and 70ºC, and airflows of 2 and 3 m/s caused the highest irregularity of shrinkage and highest FDA and FDST values. Scanning electron microscopy images for measuring zone were captured and fractal dimension of texture of images were obtained (FDSDBC) it was observed that nonlinear shrinkage was related to irregular microstructure given by FDSDBC.
A.O.A.C. (1990). Methods of Analysis (15th ed.). Association of official analytical chemist, Washington, D.C.
Barletta, H.J. and Barbosa, O.G.V. (1993). Fractal analysis to characterize ruggedness changes in tapped agglomerated food powders. Journal of Food Science 58(5),1030-1035.
Chanona, J.J., Alamilla, B.L., Farrera, R.F., Quevedo, R., Aguilera, J.M. and Gutiérrez., L.G. (2003). Description of the convective air drying of a food model by means of the fractal theory. Food Science and Technology International 9(3), 201-207.
Goldberg, A.L. (1992). Fractal mechanisms in the electrophysiology of the heart. IEEE. Engi in medicine and Biology Magazine. IEEE. Eng. Med. & Bio. 11, 47-52.
Gutierrez, G.F., Chanona, J.P. and Alamilla, L.B. (2002). A proposal of analysis of the drying phenomena by means of fractal theory. In: Engineering and Food for the 21st. Century. (J. Welti-Chanes, G.V. Barbosa-Canovas and J.M. Aguilera, eds.), Pp. 269-287.CRC press, Florida.
Hernández-Díaz, W.N., Ruiz-López, I.I., Salgado-Cervantes, M.A., Rodríguez-Jiménes, G.C. and García- Alvarado, M.A. (2008). Modeling heat and mass transfer during drying of green coffee beans using prolate spheroidal geometry. Journal of Food Engineering 86(1), 1-9.
Khraisheh, M.A., Cooper, R. and Magee, T.R.A. (1997). Shrinkage characteristics of potatoes dehydrated under combined and convective air conditions. Drying Technology 15(3-4), 1003-1022.
Kopelman, R. (1988). Fractal reaction kinetics. Science 241, 1620-1626.
Krokida, M. and Maroulis, Z.B. (1997). Effect of drying method on shrinkage and porosity. Drying Technology 15(10), 2441-2458.
Lewicki, P.P. and Jakubczyk, E. (2004). Effect of hot air temperature on mechanical properties of dried apples. Journal of Food Engineering 64(1), 307-314.
Lozano, J.E., Rotstein, E. and Urbicain, M.J. (1980). Total porosity and open pore porosity in the drying of fruits. Journal of Food Science 45(1), 1403-7.
Madamba, P.S., Driscoll, R.H. and Buckle, K.A. (1994). Shrinkage, density and porosity of garlic during drying. Journal of Food Engineering 23(3), 309-319.
Mandelbrot, B.B. (1977). The fractal geometry of nature. New York, W.H. Freeman, 30-41.
Mattea, M., Urbicain, M.J. and Rotstein, E. (1989). Computer model of shrinkage and deformation of cellular tissue during dehydration. Chemical Engineering Science 44(1), 2853-2859.
Mayor, L. and Sereno, A.M. (2004). Modelling shrinkage during convective drying of food materials: a review. Journal of Food Engineering 61(3), 373-386.
Mulet, A. (1994). Drying modelling and water diffusivity in carrots and potatoes. Journal of Food Engineering 22(1-4), 329-348.
Oliveira, L.S., Fortes, M. and Haghighl, K. (1994). Conjugate analysis of natural convective drying of biological materials. Drying Technology 12(5), 1167-1190.
Ramos, I.N., Brandao, T.R.S. and Silva, C.L. (2003). Structural changes during air drying of fruits and vegetables. Food Science Technology International 9(3), 201-206.
Rapusas, R.S., Driscoll, R.H. and Srzednicki, G.S. (1995). Bulk density and resistance to airflow of sliced onions. Journal of Food Engineering 26(1), 67-80.
Ratti, C. (1994). Shrinkage during drying of foodstuffs. Journal of Food Engineering 23(1), 91-105.
Ratti, C. and Mujumdar, A.S. (1995). Simulation of packed bed drying of foodstuffs with airflow reversal. Journal of Food Engineering 26(3), 259-271.
Sjöholm, I. and Gekas, V. (1995). Apple shrinkage upon drying. Journal of Food Engineering 25 (1), 123-130.
Sokhansanj, S. and Patil R.T. (1996) Kinetics of dehydration of green alfalfa. Drying Technology 14(5), 1197-1234.
Suzuki, K., Kubota, K., Hasegawa, T. and Osaka, H. (1976) Shrinkage in dehydration of root vegetables. Journal of Food Science 41(1), 1189-93.
Teotia, M.S. and Ramakrishna, P. (1989). Research note: Densities of melon seeds, kernels and hulls. Journal of Food Engineering 9(3), 231-236.
Wang, N. and Brennan, J.G. (1995). Changes in structure, density and porosity of potato during dehydration. Journal of Food Engineering 24(1), 61-76.
Wen-Shiung, Ch., Shang-Yuan, Y. and Chih-Ming, H. (2003). Two algorithms to estimate fractal dimension of gray-level images. Optical Engineering 42(8), 2452-2464.
Yang, Y. and Sakai, R. (2001). Drying model with shrinkage undergoing simultaneous heat and mass transfer. In: Proceedings of the 8th International Congress on Engineering and Food. Puebla, México, 2001, (J. Welti-Chanes, G.V. Barbosa-Canovas and J.M. Aguilera, eds.), Pp. 1100-1005. Technomic Publishing Co. Pennsylvania.
Zogzas, N.P., Maroulis, Z.B., Marinos-Houris, D. and Saravacos, G.D. (1994). Densities shrinkage and porosity of some vegetables during air drying. In: Drying 94, (R.V. Keey and R.B., Mujumdar, eds.), Pp. 863-870. Chapman.
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