Effect Of Vacuum Impregnation Research Articles

Comparison of diffusion of fructo-oligosaccharide components during vacuum impregnation and osmotic dehydration

The osmotic behaviour of fructo-oligosaccharides was investigated during osmotic dehydration of apple cubes. The effect of vacuum impregnation on discrete diffusion coefficient (D eff) of oligomers was scrutinised. D eff were determined using the solution of Fick’s unsteady-state diffusion equation developed by Rastogi and Raghavarao. The moisture content decreases logarithmically irrespective of the type of treatment. The applied vacuum does not influence the rate of decrease of moisture content, but it reduces the water content. There are not significant differences among the D eff of oligomers. Vacuum impregnation has no effect on D eff values, which are in narrow range of the order of 10−9 m2 s−1 in the observed set of unit operation parameters. The prediction by the used model is acceptable in all cases especially in traditional osmotic dehydration, where the relative standard deviation (RSD) is less than 10%, and it also demonstrates the altered mechanism of vacuum impregnation by the increased RSD values.

Effect of vacuum impregnation on the phenolic content of Granny Smith and Stark Delicious frozen apple cvv

Effect of vacuum impregnation on the phenolic content of Granny Smith and Stark Delicious frozen apple cvv

Effect of vacuum impregnation and microwave application on structural changes which occurred during air-drying of apple

Apple slices, both vacuum impregnated (VI) with an isotonic solution and non-vacuum impregnated (NVI), were dried at 30 and 50°C air temperature, with and without microwave (MW) application (0.5W/g). MW application resulted in an increased water-soluble pectin fraction, especially in VI samples, ranging from 0.313 to 0.390 (expressed as g galacturonic acid/100g fresh sample). The MW dried slices had a harder texture when dry (water content lower than 10g water/100g sample), but softer when rehydrated (to saturation): MW application also implied a slight increase (about 2°C) of glass transition temperature (Tg) in the samples, especially in the NVI samples. In contrast to the NVI samples, in which Tg changes from about 4 to 32°C when water activity increases from 0 to 0.22, the VI ones showed a very slight water plasticization effect (mean Tg 40°C). The changes in Tg could be explained by the increase in the soluble pectin in the aqueous phase of the fruit during drying. There was no correlation between the mechanical properties and Tg.

EQUILIBRATION OF APPLE TISSUE IN OSMOTIC DEHYDRATION: MICROSTRUCTURAL CHANGES

ABSTRACT The changes in density and porosity and the microstructural development of apple tissue throughout the equilibration in osmotic treatments were analyzed for different osmotic solution concentrations. The effect of vacuum impregnation of the sample with the osmotic solution, before the osmotic treatment was also studied. Two periods were differentiated in the process. For relatively short term treatments (24–48 h) cell walls shrunk or separated from plasmalemma because of the cell water loss while compositional pseudoequilibrium was achieved. Afterwards for long term treatments, a bulk flux of osmotic solution into the fruit tissue occurred in line with the relaxation of mechanical energy accumulated in the deformed cell wall matrix. So, the true equilibrium (chemical plus mechanical), achieved when no changes either in sample composition or weight occurred, implied cell wall sphericity and sample volume recovery. However, some degree of irreversibility was observed in cell wall recovery, especially for osmotic treatments at high concentration without previous vacuum impregnation of sample.