The drying process of fruits and vegetables comprehends the ultrasonic-assisted osmotic dehydration process followed by air-drying. Total processing time can be optimized in order to reduce the drying process to a minimum, which can reduce costs and increase the overall productivity. To optimize the process, the osmotic dehydration should be used while the water loss rate of the sample is higher than the rate that would be obtained by the air-drying process. When the water loss rate in the ultrasound-assisted osmotic dehydration becomes lower than the rate that would be obtained in the air-drying process, then the sample should be transferred from the osmotic dehydration to the air-drying equipment, where the sample should stay till drying is completed (figure 12). The optimization can be carried out based on the estimated parameters for the ultrasound-assisted osmotic dehydration process and the air-drying process.
Figure 12. Illustrative scheme of the water removal rate in ultrasound-assisted osmotic dehydration and air-drying and the optimum time to change from osmotic dehydration to air-air-drying.
Table 8 shows the total processing time to achieve a final moisture content of 1.25 g of water/g of dry solids for pineapples submitted to ultrasound-assisted osmotic dehydration. In this case the use of ultrasound-assisted osmotic dehydration reduced the total drying time. In this case, the high water loss observed during the pre-treatment and the high mass of dry solids reduces the moisture content of the fruit (in dry solids basis) and the final moisture content is more rapidly achieved. The lowest total drying time for pineapples was observed
when the pre-treatment was carried out during 20 minutes using an osmotic solution of 70ºBrix, condition which reduced the total drying time in 21 minutes and the air-drying time in 41 minutes. The results for the ultrasound-assisted osmotic dehydration showed that the total drying time tend to increase with increasing sugar gain by the fruit.
Table 8. Total processing time (pre-treatment + air-drying) for pineapples to achieve a final moisture content of 1.25 g water/g dry solids
Total 10 minutes of ultrasound (35ºBrix) 20 minutes of ultrasound (35ºBrix) 30 minutes of ultrasound (35ºBrix) 10 minutes of ultrasound (70ºBrix) 20 minutes of ultrasound (70ºBrix) 30 minutes of ultrasound (70ºBrix)
473
Table 9 shows the total processing time to remove 80% of the initial water content of pineapples reducing the moisture content of the fruit by 0.67 g of water/g of fresh fruit. The use of ultrasound-assisted osmotic dehydration showed not to be a viable process to remove large quantities of water from the fruit. As presented in table 9, the ultrasound-assisted osmotic dehydration was not able to reduce the air-drying time at any of the conditions that were studied. Although this pre-treatment presents high water loss, the incorporation of sugars into the fruit increases the solid content of the fruit. High mass of dry solids reduces the moisture content of the fruit and the moisture content gradient (Fick’s law). As such, if the objective of the drying process is to reduce the initial water content in 80% (as an example) it will have to remove moisture strongly attached to the sugar incorporated into the fruit increasing the time required for drying. The results for the ultrasound-assisted osmotic dehydration showed that the total drying time increased with increasing sugar gain by the fruit.
Table 9. Total processing time (pre-treatment + air-drying) for pineapples to remove 80% of the initial water content of the fruit
Total 10 minutes of ultrasound (35ºBrix) 20 minutes of ultrasound (35ºBrix) 30 minutes of ultrasound (35ºBrix) 10 minutes of ultrasound (70ºBrix) 20 minutes of ultrasound (70ºBrix) 30 minutes of ultrasound (70ºBrix)
473
C
ONCLUSIONSThe use of ultrasound in the food industry is increasing as well as the use of ultrasound in fruit processing. Ultrasonic processes are still under development and more studies are required to fully comprehend the effects of ultrasound not only in the fruit tissue but also in some sensory characteristics such as texture, adhesiveness and other. Recent studies have shown a good potential of ultrasonic treatments.
For most fruits studied the use of ultrasound pre-treatment increased the water diffusivity of the fruit leading to faster air-drying of the fruit. This phenomenon may happen due to the process of formation of micro-channels during the application of ultrasound, phenomenon that has to be further studied to understand how the micro-channels are formed and how the cell membrane and fruit cell structure change during the process. The increase in water diffusivity at the air-drying stage makes the use of ultrasound as a pre-treatment an interesting methodology complementary to classical air-drying.
Fruits pre-treatment with ultrasonic waves presented in some cases significant loss of sugars and therefore the process can be applied to produce dried low sugar fruit that can be employed in foodstuffs with reduced calories.
A
CKNOWLEDGEMENTSThe authors thank Dr. Marisa Narciso Fernandes from Universidade Federal de São Carlos for allowing the use of the microscopy system; Dr. Maria Izabel Gallão from Universidade Federal do Ceará for the help with the preparation of the laminas.
R
EFERENCESAOAC (1990). Official methods of analysis. Washington: Association of Official Analytical Chemists.
Ahmed, F. I. K., and Russell, C. (1975). Synergism between ultrasonic waves and hydrogen peroxide in the killing of micro-organisms. Journal of Applied Bacteriology, 39, 31-40.
Allinger, H. (1975). Ultrasonic disruption. American Laboratory, 10, 75-85.
Apfel, R. E. (1981). Ultrasonics. In P. D. Edmonds (Ed.). Methods of experimental physics.
New York: Academic Press, Vol. 19, pp. 356–411.
Azoubel, P. M., and Murr, F. E. X. (2004). Mass transfer kinetics of osmotic dehydration of cherry tomato. Journal of Food Engineering, 61, 291–295.
Barbanti, D., Mastrocola, D., and Severine, C. (1994). Drying of plums. A comparison among twelve cultivars. Sciences des Aliments, 14, 61-73.
Boucher, R. M., and Lechowich, R. V. (1979). Ultrasonics: A tool to improve biocidal efficacy of sterilants or disinfectants in hospital and dental practice. Canadian Journal of Pharmacological Science, 14, 1-12.
Bustabad, O. M. (1999). Weight loss during freezing and the storage of frozen meat. Journal of Food Engineering, 41, 1–11.
Cao, H., Zhang, M., Mujumdar, A. S., Du, W. H., and Sun, J. C. (2006). Optimization of osmotic dehydration of kiwifruit. Drying Technology, 24, 89-94.
Ciccolini, L., Taillandier, P., Wilhem, A. M., Delmas, H., and Strehaiano, P. (1997). Low frequency thermosonication of Saccharomices cerevisiae suspensions: Effects of temperature and ultrasonic power. Chemical Engineering Journal, 65, 145-149.
Corzo, O., and Gómez, E. R. (2004). Optimization of osmotic dehydration of cantaloupe using desired function methodology. Journal of Food Engineering, 64, 213-219.
De Gennaro, L., Cavella, S., Romano, R., and Masi, P. (1999). The use of ultrasound in food technology I: inactivation of peroxidase by thermosonication. Journal of Food Engineering, 39, 401–407.
El-Aouar, A. A., Azoubel, P. M., and Murr, F. E. X. (2003). Drying kinetics of fresh and smotically pretreated papaya (Carica papaya L.). Journal of Food Engineering, 59, 85–
91.
Fellows, P. (2000). Food Processing Technology––Principles and Practice. Chichester, UK:
Ellis Horwood Ltd, pp. 418–440.
Fernandes, F. A. N., and Rodrigues, S. (2007). Ultrasound as pre-treatment for drying of fruits: dehydration of banana. Journal of Food Engineering, xxx.
Fernandes, F. A. N., Gallão, M. I., and Rodrigues, S. (2007). Effect of osmotic dehydration and ultrasound pre-treatment on cell structure. Proceedings of the 3rdCIGR (in CD-Rom).
Fernandes, F. A. N., Rodrigues, S., Gaspareto, O. C. P., and Oliveira, E. L. (2006).
Optimization of osmotic dehydration of papaya followed by air-drying. Food Research International, 39, 492-498.
Fernandes, F. A. N., Rodrigues, S., Gaspareto, O. C. P., and Oliveira, E. L. (2006).
Optimization of osmotic dehydration of bananas followed by air-drying. Journal of Food Engineering, 77, 188-193.
Fito, P. (1994). Modeling of vacuum osmotic dehydration of food. Journal of Food Engineering, 22, 313–328.
Fito, P. and Chiralt, A. (1997). Osmotic dehydration. An approach to the modeling of solid food-liquid operations. In Food Engineering 2000, eds. P. Fito, E. Ortega-Rodriguez and G.V. Barbosa-Canova. Chapman and Hall, New York, pp. 231-252.
Fleming, I. D., and Pegler, H. F. (1963). The determination of glucose in the presence of maltose and isomaltose by a stable specific enzymic reagent. Analyst, 88, 967-968.
Fuente-Blanco, S., Sarabia, E. R. F., Acosta-Aparicio, V. M., Blanco-Blanco, A., and Gallego-Juárez, J. A. (2006). Food drying process by power ultrasound. Ultrasonics Sonochemistry, 44, e523-e527.
Gallego-Juárez, J. A., Rodríguez-Corral, G., Gálvez-Moraleda, J.C., and Yang, T. S. (1999) A new high intensity ultrasonic technology for food dehydration. Drying Technology, 17, 597-608.
Kalichevsky, M. T., Knorr, D., and Lillford, P. J. (1995). Potential food applications of high-pressure effects on ice-water transitions. Trends in Food Science and Technology, 6, 253–258.
Karnovisky, M. J. (1965). A formaldehyde-glutaraldehyde fixative of high osmolality for use in electron microscopy. Journal of Cellular Biology, 27, 137-138.
Kuldiloke, J. (2002). Effect of ultrasound, temperature and pressure treatments on enzyme activity and quality indicators of fruit and vegetable juices. PhD thesis, Technical University of Berlin.
Li. B., Sun, D.W. (2002). Effect of power ultrasound on freezing rate during immersion freezing of potatoes. Journal of Food Engineering, 55, 277-282.
Lima, M., and Sastry, S. K. (1990). Influence of fluid rheological properties and particle location on ultrasound-assisted heat transfer between liquid and particles. Journal of Food Science, 55, 1112–1115.
López, P., and Burgos, J. (1995a). Lipoxygenase inactivation by manothermosonication:
effects of sonication physical parameters, pH, KCl, sugars, glycerol, and enzyme concentration. Journal of Agricultural and Food Chemistry, 43, 620–625.
López, P., and Burgos, J. (1995b). Peroxidase stability and reactivation after heat treatment and manothermosonication. Journal of Food Science, 60, 451–455.
López, P., Sala, F. J., Fuente, J. L., Cardon, S., Raso, J., and Burgos, J. (1994). Inactivation of peroxidase lipoxigenase and phenol oxidase by manothermosonication. Journal of Agricultural and Food Chemistry, 42, 253-256.
López, P., Vercet, A., Sánchez, A. C., and Burgos, J. (1998). Inactivation of tomato pectic enzymes by manothermosonication. Zeitschrift fur LebensmittelUntersuchung und -Forschung, 207, 249–252.
Madamba, P. S., and Lopez, R. I. (2002). Optimization of the osmotic dehydration of mango (Mangifera indica L.) slices. Drying Technology, 20, 1227-1242.
Martino, M. N., Otero, L., Sanz, P. D., and Zaritzky, N. E. (1998). Size and location of ice crystals in pork frozen by high-pressure-assisted freezing as compared to classical methods. Meat Science, 50, 303–313.
Mason, T. J. (1998). Power ultrasound in food processing - the way forward. In: Ultrasounds in Food Processing; Povey, M.J.W.; Mason, T.J. Eds.; Blackie Academic and Professional: Glasgow, pp. 104-124.
Mason, T. J., Paniwnyk, L., and Lorimer, J. P. (1996). The use of ultrasound in food technology. Ultrasonics Sonochemistry, 3, S253-S256.
Miller, G. L. (1959). Use of dinitrosalicilic acid reagent for determination of reducing sugar.
Analitical Chemistry, 31, 426-428.
Ngapo, T. M., Babare, I. H., Reynolds, J., and Mawson, R. F. (1999).Freezing rate and frozen storage effects on the ultrastructure of samples of pork. Meat Science, 53, 159–168.
Oliveira, I. M., Fernandes, F. A. N., Rodrigues, S., Sousa, P. H. M., Maia, G. A., Figueiredo, R. W. (2006). Modeling and optimization of osmotic dehydration of banana followed by air-drying. Journal of Food Processing Engineering, 29, 400-413.
Ordoñez, J. A., Sanz, B., Hernández, P. E., and López-Lorenzo, P. (1984). A note on the effect of combined ultrasonic and heat treatment on the survival of thermoduric streptococci. Journal of Applied Bacteriology, 56, 175–177.
Otero, L., Martino, M., Zaritzky, N., Solas, M., and Sanz, P. D. (2000). Preservation of microstructure in peach and mango during high pressure-shift freezing. Journal of Food Science, 65, 466–470.
Palou, E., Lopez-Malo, A., Argaiz, A., and Welti, J. (1993). Osmotic dehydration of papaya.
Effect of syrup concentration. Revista Espanola de Ciencia y Technologia de Alimentos, 33, 621–630.
Pan, Y. K., Zhao, L. J., Zhang, Y., Chen, G., and Mujumdar, A. S. (2003). Osmotic dehydration pre-treatment in drying of fruits and vegetables. Drying Technology, 21, 1104-1114.
Parjoko, Rahman, M. S., Buckle, K. A., and Perera, C.O. (1996). Osmotic dehydration kinetics of pineapple wedges using palm sugar, Lebensm.-Wiss.u.-Technol., 29, 452-459.
Park, K. J., Bin, A., Brod, F. P. R., and Park, T. H. K. B. (2002). Osmotic dehydration kinetics of pear D’anjou (Pyrus communis L.). Journal of Food Engineering, 52, 293–
298.
Peleg, M. (1988). An empirical model for the description of moisture sorption curves. Journal of Food Science, 53, 1216–1219.
Perry, R. H., Green, D. W. (1999). Perry’s Chemical Engineer’s Handbook. McGraw Hill, New York.
Prinzivalli, C., Brambilla, A., Maffi, D., Scalzo, R.L. and Torreggiani, D. (2006). Effect of osmosis time on structure, texture and pectic composition of strawberry tissue. European Food Research and Technology, 224, 119-127.
Prokharkar, S. M., Prasad, S., and Das, H. (1997). A model for osmotic concentration of bananas slices. Journal Food Science and Technology, 34, 230-232.
Raoult-Wack, A. L. (1994). Advances in osmotic dehydration. Trends in Food Science and Technology, 5, 255–260.
Raoult, A. L., Lafont, F., Rios, G., and Guilbert, S. (1989). Osmotic dehydration: Study of mass transfer in terms of engineering properties. In: A. S. Mujumdar and M. Roques (Eds.), Drying '89, Hemisphere, 487–495.
Rastogi, N. K., and Niranjan, K. (1998). Enhanced mass transfer during osmotic dehydration of high pressure treated pineapple. Journal of Food Science, 63, 508–511.
Raso, J., Condon, S., and Sala Trepat, J. (1994). Mano-thermosonication: A new method of food preservation? Food Preservation by Combined Processes. Final report, Flair Concerted Action N° 7, subgroup B, EUR 15776 EN.
Rastogi, N. K., and Raghavarao, K. S. M. S. (1997). Water and solute diffusión coefficients of carrot as a function of temperature and concentration. Journal of Food Engineering, 34, 429–440.
Rastogi, N. K., and Raghavarao, K. S. M. S. (2004). Mass transfer during osmotic dehydration of pineapple: considering Fickian diffusion in cubical configuration, Lebensm.-Wiss.u.-Technol., 37, 43-47.
Rastogi, N. K., Eshtisghi, M. N., and Knorr, D. (1999). Accelerated mass transfer during osmotic dehydration of high intensity electrical field pulse pretreated carrots. Journal of Food Science, 64, 1020–1023.
Ravivan P., Zhang, Z., and Feng, H (2005). Ultrasonication for tomato pectinmethylesterase inactivation: effect of cavitation intensity and temperature on inactivation. Journal of Food Engineering, 70, 189-196.
Rodrigues, S., and Fernandes, F. A. N. (2007a). Dehydration of melons in a ternary system followed by air-drying. Journal of Food Engineering, 80, 678-687.
Rodrigues, S., and Fernandes, F.A.N. (2007b). Use of ultrasound as pré-treatment for dehydration of melons. Drying Technology (in press).
Rooney, J. A. (1981). Ultrasonics. In P. D. Edmonds (Ed.). Methods of experimental physics.
New York: Academic Press, Vol. 19, pp. 299–353.
Sanz, B., Paklacios, P., Lopez, P., and Ordonez, J. A. (1985). Effect of ultrasonic waves on the heat resistance of Bacillus stearothermophilus spores. Federal European Microbiology Society, 18, 251–259.
Sastry, S. K., Shen, G. Q., and Blaisdell, J. L. (1989). Effect of ultrasonic vibration on fluid-to-particle convective heat transfer coefficients. Journal of Food Science, 54, 229–230.
Shi, X.Q., and Fito, P. (1994). Mass transfer in vacuum osmotic dehydration of fruits: a mathematical model approach. Lebensmittel Wissenschaft und Technologie, 27, 67-72.
Simal, S., Benedito, J., Sánchez, E. S., and Roselló, C. (1998). Use of ultrasound to increase mass transport rate during osmotic dehydration. Journal of Food Engineering, 36, 323–
336.
Spiazzi, E. A., Raggio, Z. I., Bignone, K. A., and Mascheroni, R. H. (1998). Experiments on dehydrofreezing of fruits and vegetables: mass transfer and quality factors. Advances in the Refrigeration Systems, Food Technologies and Cold Chain, International Institute of Refrigeration Proceeding Series, Vol. 6, pp. 401–408.
Suslik, K. S. (1988). Ultrasounds: its Chemical, Physical and Biological Effects. New York:
VHC Publishers.
Tarleton, E. S. (1992). The role of field-assisted techniques in solid/liquid separation.
Filtration Separation, 3, 246-253.
Tarleton, E. S., and Wakeman, R. J. (1998). Ultrasonically assisted separation process. In:
M.J.W. Povey and T.J. Mason (Eds.), Ultrasounds in Food Processing, Blackie Academic and Professional, Glasgow. pp.193-218.
Teles, U. M., Fernandes, F. A. N., Rodrigues, S., Lima, A. S., Maia, G. A., and Figueiredo, R.
W. (2006). Optimization of osmotic dehydration of melons followed by air-drying.
International Journal of Food Science and Technology, 41, 674-680.
Torreggiani, D. (1993). Osmotic dehydration in fruit and vegetables. Process and Food International, 26, 59–68.
Vercet, A., Lopez, P., and Burgos, J. (1997). Inactivation of heat-resistant lipase and protease from Pseudomonas fluorescens by manothermosonication. Journal of Dairy Science, 80, 29–36.
Vercet, A., López, P., and Burgos, J. (1999). Inactivation of heat-resistant pectinmethylesterase from orange by manothermosonication. Journal of Agricultural and Food Chemistry, 47, 432–437.
Vercet, A., Sánchez, C., Burgos, J., Montanes, L., and López-Buesa, P. (2002). The effects of manothermosonication on tomato pectic enzymes and tomato paste rheological properties. Journal of Food Engineering, 53, 273–278.
Vidal, B. C. (1977). Acid glycosaminoglycans and endochondral ossification:
microspectrophotometric evaluation and macromolecular orientation. Cell Molecular Biology, 22, 45-64.
Wan, P.J., Muanda, M.W. and Covey, J.E. (1992). Ultrasonic vs. nonultrasonic hydrogenation in a batch reactor. Journal of American Organics Chemical Society, 69, 876-879.
Zheng, L., and Sun, D.W. (2006). Innovative applications of power ultrasound during food freezing processes – a review. Food Science and Technology, 17, 16-23.
Editor: Alan P. Urwaye, pp. 137-168 © 2008 Nova Science Publishers, Inc.
Chapter 4