The influence of preliminary vacuum impregnation treatment on the quality of candied fruit

Manufacture of dried fruit is based on a shorter or longer process of diffusion and osmosis. In this case, an osmotic change is made between fruit and syrup, due to which fruit is gradually enriched with sugar, while the fruit juice dilutes the syrup. In this paper it is proposed to achieve the removal of air from intercellular spaces through vacuum treatment of fruit and thus to increase the diffusion rate of sucrose solution, which would penetrate in the highest amount possible and occupy a large volume in the pores of the fruit. In the first phase, the short term glazing process of fruit was followed up, without reaching an isotonic state between the plant and sucrose osmotic solution. The aim was to observe the behavior and the differences that arise between the samples impregnated under vacuum and unimpregnated ones, while maintained in osmotic solutions. The changes of mass, soluble dry substances and volume were monitored. The apple variety Golden Delicious was used for determinations. The apples were peeled off and cut in the form of cubes in order to measure volume changes. Some samples were subjected to impregnation, under vacuum of 300 mbar, with sucrose solution 65%. Both impregnated and not impregnated samples were subsequently immersed in 65% sucrose solution and kept in it, while measuring the mass, soluble dry substance and volume after 15, 45, 90, 180 and 600 min. The second phase of measurements followed the drying process up to the point of balance between fruit and sucrose solution. The measurements were made on strawberries, as this fruit is often used in such processes. The strawberries were sorted and the fruit with the same degree of ripeness and the same size was selected. The fruit was washed and the stalks were cut out. The fruit thus prepared was subjected to vacuum impregnation in the same conditions as those used in the previous survey for apples. Both impregnated and not impregnated samples were then placed in sucrose solutions. The fruit was submerged using a clock glass and kept in the solution while watching the mass and soluble dry matter every 24 hours.