Osmose process

Three processes have been worked out and extensively used. In order of their success as chemical processes they are (1) the osmose process in which the crystalliz-able materials in the molasses are separated from the non-cryscallizable by osmosis in cells with permeable diaphragms (2) the Steffens or lime process, in which the sugar is precipitated as calcium trisaccharate (3) the barium process, in which the sugar is precipitated as barium trisaccharate. 

The Royal (or Royale) process was originally developed as a method for drying timber, in which the wood is heated in oil under vacuum. The temperatures used are low (60-90 °C) compared to other thermal oil treatments, and although sufficient to lead to some curing of the oil itself, there is no direct modification of the wood as a result of this process. The oil does not penetrate the cell wall. In this process, wet timber is placed in a treatment vessel and oil is then introduced, which is heated to the desired temperature, whilst a vacuum is applied. Water is removed from the timber and the vapour is transported away by the vacuum system. When the wood has reached the desired MC, the oil is removed from the treatment vessel. After this, a vacuum is applied to removed excess oil from the wood. Some dimensional stability is imparted to the timber due to the water repellency of the oil. This treatment is marketed by Osmose as the Royale process. 

The Gesellschaft fur Electro-Osmose have devised several processes since 1912, and it is evident that practice is in advance of theory in this sphere of work, for it was not until 1914 that papers appeared which devoted attention to the theoretical side of the subject. 

Electrodialysis is the combined process of dialysis electrolysis using semipetmeable membranes ro confine the soln under treatment Dialysis is used for separating colloids from non-colloids. Electrodialysis is used for complete removal of small amts of electrolytes, usually on a lab scale Refs 1) P.H. Prausnitz J. Reitstotter, "Elektrophorese, Elektro-osmose, Elektro-dialyse in Fliissigkeiten", Steinkopf, Dresden und Leipzig (1931) 2) A. Weissberger,... 

Mowbray (U.S.P., No. 443, 105, 3rd December 1890) says that a pure cotton tissue paper less than 1/500 inch in thickness, thin as it is, takes on a glutinous or colloid surface, and thus requires some thirty minutes to enable the nitration to take place. With a thicker paper only the surface would be nitrated. He therefore uses a fibre that has been saturated with a solution of nitrate of soda, and afterwards dried slowly, claiming that the salt crystallises in the fibre, or enters by the action termed osmose, and opens up the fibre to the action of the acid. This process would only be useful when the cotton is to be nitrated at a low temperature. At a high temperature it would be unnecessary. 

The quantity and the rate of water removal depend on several variables and processing parameters. In general it has been shown that the weight loss in osmosed fruit is increased by increasing the solute concentration of the osmotic solution, immersion time, temperature, solution-to-food ratio, specific surface area of the food, and by using vacuum, stirring, and continuous reconcentration. Also, to obtain the same reduction, time tended to decrease exponentially as the temperature is increased. 

Most of fruits and vegetables are cut into pieces before they are contacted with hypertonic solution. Shape and size of the material pronouncedly affect the rate of the process. Osmosed fruits and vegetables have different forms that come from the technology and consumer requirements [62,63], Plums were dehydrated in whole or in halves [64] apples were cutinto 12 segments [65,66] or sliced into 3 mm slices [67] or 3-4 mm thick [15]. Peaches were cut into 6 or 8 segments and pears into 8 segments [65]. Carrots were cut into cubes of 5 or 10 mm [68,69], Potatoes were sliced 5 and 10 mm thick [70], or diced [20], Papaya was cut into cubes. 

It has been found that the addition of low molecular weight substances such as sodium chloride, malic acid, lactic acid, and hydrochloric acid in concentrations of l%-5% to sugars or starch syrups improves the process of osmotic dehydration. In general, they promote removal of water from the material. Calcium chloride and malic acid were added to sucrose to improve the texture of osmosed apples [130]. 

Concluding the effect of procedures and processing parameters on the rate and efficiency of osmotic dehydration it can be stated that all of them are equally important. The kind and concentration of the osmoactive substance, the weight ratio of the solution to food, the kind of osmosed material, its size and shape, temperatnre and pressure, and the pretreatment of the material prior to osmosis affect strongly not only the course of the process but also, first of all, influence the quality and organoleptic attributes of the final product. 

Concentration of substances leaching from the processed material stabilizes after few uses depending on the kind of osmosed material, and reaches the level similar to that of the osmotically processed fruits or vegetables. 

The lowest solution and food ratio is obtained when solid osmotic substance is contacted with food. Crystals of sugar or mixture of sugar and salt are mixed with food pieces in appropriate proportion and tumbled in slowly rotating cylindrical tank. The amount of osmotic substance used should be such that water removed from food pieces forms no solution in the tank. Wet but solid osmotic substance is separated from food on vibrating screen. However, some crystals stick to the food surface and can create problems in packaging or further processing of osmosed material. 

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