Osmotic treatment

The process involves placing the solid food (whole or in pieces) into solutions of high sugar or salt concentration. Le Maguer (1988), Raoult-Wack (1994), Fito and Chiralt (1997), Behsnilian and Spiess (1998), Spiess and Behsnilian (1998), Lazarides et al. (1999), and Torreggiani and Bertolo (2002) have reviewed the basic principles, modeling and control, and specific applications of osmotic dehydration on fruit and vegetables. Additionally, the most recent research advances in this field can be obtained from the European-founded network on osmotic treatments (FAIR, 1998). 

There is already much practical experience available on the osmotic treatment itself. To fulfill consumer, industrial, and environmental expectations, however, some problems remain to be solved. Osmotic treatments have been applied frequently as a low-cost processing method neglecting process optimization, but the current interest in this technique and the development of industrial applications on a large scale demand controlled processes. For successful process control and optimization, efforts have to be made in the following key areas (Figure 2). 

The state of the art and the progress in the aforementioned key areas, specifically referring to fruit and vegetables, are discussed and evaluated in this review in the light of industrial, environmental, and consumer needs. There is just a hint on osmotic treatments of fish and meat products. 

However, many other tissue parameters, such as membrane permeability, porosity, and cell size, are required for the development of models regarding all the mechanisms acting on the various components (intercellular and extracellular spaces, vacuole, etc.). For most tissues subjected to osmotic treatment, lack of data required for this modeling approach represents a hindrance to progress. 

Optimization of vacuum pulse osmotic treatment for minimally processed pineapple cylinders led to processed fruits, which exhibited a close likeness to fresh ones, without microbiological problems (Navarro and Corzo, 2001). 

Microwave-assisted (0.1 or 0.2 Wg-1) convection drying was also applied to osmotically dehydrated blueberries, leading to dried berries that were comparable to freeze-dried ones in much shorter time (Venkatachalapathy and Raghavan, 1998). Frozen blueberries were also dried in a microwave and spouted bed combined dryer (MWSB) after a pretreatment using ethyl oleate and a NaOH dipping solution followed by sucrose osmotic treatment (Feng et al., 1999). Osmotic dehydration prevented the blueberries from... 

Even though osmotic treatments have been proven to be a useful tool in fruit and vegetable cryoprotection, the changes in mechanical properties, caused by the process itself, have to be taken into account. 

The main changes induced by an osmotic treatment affecting the mechanical behavior of plant tissues are loss of cellular turgor, alteration of middle lamella (Alzamora et al., 1997), alteration of cell wall resistance, establishment of water and solute concentration profiles (Salvatori et al.,... 

The difference between the upper and the lower curves for phase composition and texture, at equal water activity, is the result of the solid gain after osmotic treatment. The higher the solid uptake, the higher the difference in texture. Compared to simple air dehydration, the combination of osmotic dehydration and air dehydration can produce a softer product at low water activity, which is more pleasant to eat by hand, or to incorporate into pastry, ice cream, cheese, yogurt (Giangiacomo et al., 1994), and so on. 

FIG. 17 Application range of salting osmotic treatment in specific fresh products. 

FIG. 18 Idealized flowchart of solution management and control system during direct osmotic treatments of plant or animal materials. 

The complexity and vastness of the scientific field that has been reviewed in this chapter bring forth, as a natural consequence, the parallel need for further in-depth studies into some key research areas. Knowledge of the process, as a unit operation, has jumped forward due to the fruitful work of the EU-FAIR Concerted Action CT96-1118 improvement of overall food quality by application of osmotic treatments in conventional and new processes and could already support the application of the technique at the industrial level as a prestep in innovative combined processes. The decisive challenge for a completely successful process control and optimization has to be focused on the following problematic aspects. 

Behsnilian, D. and Spiess, W.E.L. 1998. Improvement of overall food quality by application of osmotic treatments in conventional and new processes. In Proceedings of the 3rd Karlsruhe Nutrition Symposium, European Research towards Safer and Better Foods (V. Gaukel and W.E.L. Spiess, eds), Part 2, pp. 345-352. Druckerei Grasser, Karlsruhe, Germany. 

Collignan, A., Bohuon, P., Deumier, F., and Poligne, I. 2001. Osmotic treatment of fish and meat products. J. Food Engineer. 49, 153-162. 

Dalla Rosa, M. 1999. Osmotic treatment (OT) and problems related to the solution management. In Proceedings of 1st Seminar Osmotic Treatments for the Food Industry (A.M. Sereno, ed.), pp. 51-58. Converge Press, Porto, Portugal. 

Dalla Rosa, M., Bressa, F., Mastrocola, D., and Pittia, P. 1995. Use of osmotic treatments to improve the quality of high moisture minimally processed fruits. In Osmotic Dehydration of Fruits and Vegetables (A. Lenart and P.P. Lewicki, eds), pp. 69-87. Warsaw Agriculture Univ. Press, Warsaw, Poland. 

Di Cesare, L.F., Torreggiani, D., and Bertolo, G. 1999. Preliminary study of volatile composition of strawberry slices air dried with or without an osmotic pre-treatment. In Proceedings of the V Plenary Meeting of Concerted Action FAIR-CT96-1118, Improvement of Overall Food Quality by Application of Osmotic Treatments in Conventional and New Process , pp. 39-44. Valencia, Spain. 

Escriche, E, Chiralt, A., Moreno, J., and Serra, J.A. 2001a. Influence of osmotic treatment on the volatile profile of strawberry (Fragaria x ananassa var. Chandler). In Proceedings of the International Congress on Engineering and Food, ICEF 8 (J. Welti-Chanes, G.V. Barbosa-Canovas, and J.M. Aguilera, eds), Vol. 1, pp. 151-155. Technomic Publisher, Lancaster, PA. 

Ferrando, M. and Spiess, W.E.L. 2001. Cellular response of plant tissue during the osmotic treatment with sucrose, maltose and trehalose solutions. J. Food Engineer. 49, 115-127. 

Gianotti, A., Sacchetti, G., Guerzoni, M.E., and Dalla Rosa, M. 2001. Microbial aspects on short-time osmotic treatment of kiwifruit. J. Food Engineer. 49, 265-270. 

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