Vacuum quality preservation

Vargas, M., Chiralt, A., Albors, A. Gonzalez-Martinez, C. (2009). Effect of chitosan-based edible coatings applied by vacuum Impregnation on quality preservation of fresh-cut carrot. Postharvest Biology and Technology, 51, 2, 263-271... 

FIGURE 1.1. Electron micrographs of liver tissue processed differently for transmission electron microscopy. (A) Processed by the conventional method. Note superior quality of ultrastructural preservation compared with that obtained with microwave heating. (B) Rapidly processed by vacuum microwave heating. The whole process from tissue fixation to resin embedding was completed in 2 hr. The quality of ultrastructural preservation is satisfactory. Magnification 6,21 Ox (B). (B) courtesy of Richard T. Giberson. 

The storage of freeze-dried carrots for 24 months in sealed cans under air and N2 and in glass containers under vacuum at room temperature was studied by Gegow [4.29]. Fifteen quality parameters were evaluated and found to be comparable to those of frozen carrots. The carotenes were only reasonably preserved under vacuum. 

Knudsen numbers signify the coexistence of both mechanisms. Fickian diffusion is significantly slower than Knudsen diffusion at the same vapor pressure gradient. Experimental measurements of water flux in the presence and absence of air in the pores have shown a two to three-fold increase on degassing. Lowering the total gas pressure in the pores decreases the frequency of water vapor-air collisions, and thereby increases the mean free path of the water molecules. However, feed pretreatment by heating or exposure to a vacuum to remove air is often counterproductive to the preservation of product quality. 

In recent years, consumer awareness of the adverse effect of high sugar and preservatives in candied fruits has resulted in a marked decrease in consumption of these products. Two approaches are being followed to reverse this trend. One is the improvement of the quality of candied fruits by using new processing techniques such as vacuum syruping or suitable packaging. The other is to develop new... 

In certain industries, single-effect evaporation cannot be used as an economy measure because of the comparatively high temperature maintained in the first effect. In the case of heat-sensitive materials such as concentrated milk products, fruit juices, and pharmaceuticals, it is often necessary to use multiple-effect vacuum evaporators and accept high operation cost in order to preserve the quality of the product. 

---