5.1 Pretreatment
Any pretreatment (such as blanching or freezing) prior to osmotic water removal can adversely affect product quality. Immersion in a 1% citric acid solution prior to drying or osmotic dehydration prevents enzymatic browning of the fruit. The product of oleate in an alkaline or acidic solution affects the prevention of discoloration before the fruit is dried (Hussain et al, 2004; Sunkja & Ragharan, 2004). Torreggiani, (1993) reported that pretreatment or bleaching with chemicals (SO2) before fruit and vegetable drying can effectively prevent discoloration. Papaya and mango slices were immersed in 0.4% ascorbic acid solution or 0.4% ascorbic acid + 0.1% KMS solution for 30 minutes before the infiltration process to obtain an acceptable high product.
5.2 Immersion time
keeps the solution concentration constant, increasing the soaking time increases the loss of water Er, but the rate of increase is reduced. Studies on the optimization of the duration of the infiltration process have shown that material exchange occurs at a maximum rate during the first two hours of the infiltration process. Tiwari and Jalali (2004) reported that during the infiltration process, the increased duration of dehydration of mango and pineapple resulted in weight loss, but the incidence of this condition was high. Gaspartero et al. (2003) and Mauro et al. (2004) reported that when banana chips and apple slices were immersed in 70 and 50 0 Brix, respectively, the temperature of the permeate solution was soaked at 50 ° C for 3 hours to obtain the best water loss and sugar increase. Infiltrated
5.3 Temperature of the Permeate Solution
The temperature of the permeate solution significantly affects the permeability. Although this rate increases with temperature, it is limited to a maximum of 60 °C due to the high temperature destroying the cell membrane. Pokharkar and Prasad (1998) established a kinetic model for the infiltration and dehydration of banana chips and reported that the temperature of the permeate solution affects the increase in moisture and sugar during the infiltration process.
5.4 Penetrants
It is recommended to conduct studies to find out the effects of different penetrants on the osmotic dehydration process. The most commonly used penetrants are sucrose, fruit for glucose, and other penetrants include calcium chloride, monohydric alcohol and polyols such as lactose, maltodextrin, corn syrup and mixtures of these substances. Table 1 lists the effects of various penetrants.
5.5 Concentration of osmotic solution
Rahman and Lamb (1990) indicated that the increase in water loss and sugar increased linearly with increasing sugar concentration and temperature. The rate of diffusion of sugar is a function of sugar concentration and temperature. The concentration of the solution is a key factor in the osmotic dehydration process. During the study, it was found that the syrup strength was optimal in the range of 60 to 70 0 Brix (Chaudhary et al., 1993). It has also been reported that the higher the concentration, the faster the penetration rate. Torreggiani (1993) suggested that because the permeability decreases with time, it is generally not appropriate to use higher concentrations of cations during the concentration process to reduce the weight by more than 50%.
5.6 Stirring/Circulation
When the fruit is stirred in the syrup, the permeation rate will be faster because the partial dilution process is avoided and the mass transfer resistance of the surface is reduced. However, this can damage the sample. Panagiotou et al. (1998) and Tiwari (2005) observed that the agitation speed has a positive effect on the water loss during the infiltration process.
5.7 Ratio of fruit mass to osmotic solution
As the ratio of solution to sample increases, the permeability increases to some extent. However, the optimum ratio must be used, as the larger proportions present practical difficulties in processing the syrup fruit mix for processing. A ratio of 1:2 or 1:3 is optimal for practical applications (Tiwari, 2005).
