Apple osmotic dehydration

During osmotic dehydration of apple, pumpkin, and carrot in sugar solution at 30 °C, the rate of water loss was 5-10 times higher than the rate of solid gain and depended on advancement of the dewatering process (Kowalska and Lenart, 2001). Under the same dewatering conditions, pumpkin and carrot reached smaller water contents than apple (Figure 3). 

FIG. 3 Water loss (WL) and solid gain (SG) expressed on initial dry matter (idm) of strawberry (ST) slices (Brambilla et al., 2000) and apple (AP), carrot (CA), and pumpkin (PU) cubes (Kowalska and Lenart, 2001) after 60 min osmotic dehydration in a 60% (w/w) sucrose solution at 30 °C at atmospheric pressure. 

FIG. 4 Effects of varying raw material treatments prior to osmotic dehydration on moisture (MC) and solid (SC) content expressed on initial dry matter (idm). Potato slices, high hydrostatic pressure (Rastogi et al., 2001) carrot slices, PFE (Rastogi et al., 1999) bell pepper disks, PFE (Ade-Omowaye et al., 2002b) and apple slices, edible coatings (Lenart and Dabrowska, 1998). 

Another promising technique is ultrasound application during osmotic dehydration. Used on porous fruit such as apple cubes, it affects mass... 

FIG. 7 Effect of 90-min osmotic dehydration (OD) in 40% (w/w) glucose solution at 25 °C at atmospheric pressure on drying rates (M/M0 moisture content/initial moisture content) at 60 °C of infinite plate-shaped mango (Nieto et al., 2001) and apple (Nieto et al., 1998). 

Barat, J.M., Albors, A., Chiralt, A., and Fito, P. 1999. Equilibration of apple tissue in osmotic dehydration. Microstructural changes. Drying Technol. 17, 1375-1386. 

Kayamak-Ertekin, F. and Sultanglu, M. 2000. Modelling of mass transfer during osmotic dehydration of apples. J. Food Engineer. 46, 243-250. 

Krokida, M.K., Karathanos, V.T., and Maroulis, Z.B. 2000a. Effect of osmotic dehydration on color and sorption characteristics of apple and banana. Dry. Technol. 18, 937-950. 

Lenart, A. and Dabrowska, R. 1997. Osmotic dehydration of apples with polysaccharide coatings. 

Lenart, A. and Dabrowska, R. 1998. Mass transfer during osmotic dehydration of apples with pectin coatings. In Drying 98 (C.B. Akritis, D. Marinos-Kouris, and G.D. Saravacos, eds), Vol. A, pp. 903-910. Ziti Editions, Thessaloniki, Greece. 

Mavroudis, N.E., Gekas, V., and Sjoholm, I. 1998. Osmotic dehydration of apples Shrinkage phenomena and the significance of initial structure on mass transfer rates. J. Food Engineer. 38, 101-123. 

Moreira, R. and Sereno, A.M. 2001. Volumetric shrinkage of apple cylinders during osmotic dehydration. 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. 2, pp. 1351-1355. Technomic Publisher, Lancaster, PA. 

Taiwo, K.A., Angersbach, A., Ade-Omowaye, B.I.O., and Knorr, D. 2001. Effects of pretreatments on the diffusion kinetics and some quality parameters of osmotically dehydrated apple slices. 

Valdez-Fragoso, A., Welti-Chanes, J., and Giroux, F. 1998. Properties of a sucrose solution reused in osmotic dehydration of apples. Dry. Technol. 16, 1429-1445. 

Gomez Zavaglia, A., Tymczyszyn, E., De Antoni, G., and Anibal Disalvo, E. Action of trehalose on the preservation of Lactobacillus delbrueckii ssp. bulgaricus by heat and osmotic dehydration, /. Appl. Microbiol., 95, 1315, 2003. 

Another model developed [57] for solute diffusion in osmotic dehydration of apple based on solids gain divided by water content M as a function of rate constant K, time (/), and a constant A was given as M = Kt + A. A relationship was established in the form of A" = T C" where rate parameter K is related to temperature T at different sucrose concentrations C. The average activation energy of the process was 28.2 kj/mol. 

An empirical equation derived based on osmotic dehydration of apple slices could predict rate of osmosis F, that is, percentage of dehydration of any given fruit slices of specific size with time T, given the concentration of sugar (% B) and the temperature as follows [59] ... 

T.R.A. Magee, A.A. Hassaballah, and W.R. Murphy, Internal mass transfer during osmotic dehydration of apple slices in sugar solution, Irish J. Food Sci. TechnoL, 7(2) 147 (1983). 

K. Videv, S. Tanchev, R.C. Sharma, and V.K. Joshi, Effect of sugar syrup concentration and temperature on the rate of osmotic dehydration of apples, /. Food Sci. TechnoL (India), 27(5) 307 (1990). 

Lenart and Lewicki have shown that the thickness of the material shonld not exceed 10 mm [71,72]. Taking into account further processing following osmotic dehydration and use of the product, they considered a cube with a side dimension close to 10 mm as an optimal size and shape for most materials. Lewicki et al. [73-77] and Lerici et al. [78] dehydrated apples, carrots, and potatoes as cubes of 8-10 mm on a side. Flink, as well as Simal et al. [20], likewise used this shape in most of his studies [79],... 

It has been reported that immersion of some materials in CaClj solution prior to osmotic dehydration affects the properties of the product. Texture of apple was improved [84], Brining of cashew apple in NaCl solution before osmotic dehydration resulted in firmer texture of the candied product [86],... 

Solutions of sugars are mostly used to dehydrate fruits and glycerol, starch syrup, and sodium chloride are used for vegetables [62,73,91,99]. Sucrose is the most frequently used substance [17,65,100-104]. The control of pH of sucrose solution is recommended for banana slices osmotic dehydration [105]. It was also shown that control of pH of sucrose solution affects the course of osmotic dehydration of apple and carrot [106]. Addition of ascorbic acid to sugar solution is practiced to minimize browning of fruit pieces during osmotic process [72]. Sucrose can be substituted in part by lactose [15]. 

FIGURE 32.7 The effect of osmoactive substance on the course of osmotic dehydration of apples at 30°C (solid line = glucose dashed line = saccharose dotted line = starch syrnp). (From Lenart, A. and Lewicki, P.P., In IDS 89, Mujumdar, A.S. and Roques, M., eds., Hemisphere Publishing Co., New York, p. 501, 1990.)... 

---