Food crystallization drying

Drying is often the last separation in a process. Drying refers to removal of water or other solute from solids and often follows evaporation, crystallization, or filtration. Drying is the one of the oldest methods of preservation in the food industry. Drying is often employed to reduce cost of transport, or to have material suitable for handling like in pharmaceutical or soap industries, or in some cases where moisture may cause corrosion. 

Sodium Bicarbonate. Many soda ash plants convert a portion of their production to sodium bicarbonate [144-55-8], NaHCO. Soda ash is typically dissolved, carbonated, and cooled to crystallize sodium bicarbonate. The mother Hquor is heated and recycled. The soHd bicarbonate is dried in flash or tray driers, screened, and separated into various particle size ranges. Bicarbonate markets include food, pharmaceuticals, catde feed, and fire extinguishers. U.S. demand was approximately 320,000 t in 1989 world demand was estimated at one million metric tons. 

Often, it is essential that crystals are not damaged unduly by the drying operation. And in the case of food and pharmaceutical grade materials, care should be taken to avoid contamination and powder leakage via dust formation. 

For preparing lakes, a solution of aluminium sulfate (or chloride) is mixed with sodium carbonate, forming fresh alumina Al(OH)3. The colorant is then added and adsorbed on the surface of alumina. Usually the content of colorant in the lake ranges from 10 to 40%." The product is filtered, washed with water, dried, and milled. The product is allowed to contain unreacted alumina but must not contain more than 0.5% HCl-insoluble matter and not more than 0.2 % ether-extractable matter. - Lakes are insoluble in most solvents used for pure dyes, and they have high opacity and better stability to light and heat. Lakes impart their color by dispersion of solid particles in the food. The coloring properties of lakes depend on particles, crystal structures, concentrations of dye, etc. 

Rotating cone, double cone, drum Tumbling action Blending dry, free-flowing powders, granules, crystals Pharmaceuticals, food, chemicals... 

In addition, the sublimation of ice in freeze-drying, discussed in Chapter 16, has become an important operation particularly in the biological and food industries. The various industrial applications of sublimation techniques are discussed by several authors(3,40 95 96 97), and the principles underlying vaporisation and condensation and the techniques for growing crystals from the vapour phase 99-1 are also presented in the literature. 

One of the standardized methods, electron spin resonance (ESR) technique, permits identification of food that contains a hard, dry matrix, e.g., bone. When food containing bone is irradiated, free radicals are produced and trapped in the crystal lattice of the bone, which can be detected by ESR spectroscopy [137]. Thermoluminescence of contaminating minerals for detection of radiation treatment of, e.g., spices and dried fruits can be successfully applied [138, 139]. Another standardized method that has been developed for identification of irradiated fat-containing foods is the mass-spectrometric detection of radiation-induced 2-alkylcyclobutanones after gas-chromatographic separation [140]. The... 

Sometimes there are problems in using CO2 extracts in the usual formulation because of the high concentration of vanillin. The concentration is up to 100 times higher than in alcohol extracts, where it is only 0.2%. Under certain conditions, crystalline vanillin is separated from the water phase of the extract. After drying this crystalline phase, a product with more than 90% vanillin can be produced. By mixing these vanillin crystals back with the oil-phase any desired vanillin concentration can be obtained, which makes the product very useful for the food industry. 

Even though liquid whey has been successfully commercialized in the form of alcoholic and nonalcoholic beverages, these are still a rarity in most countries. Most whey is converted to whey solids as ingredients for human food or animal feeds by traditional processes such as spray drying, roller drying, concentration to semisolid feed blocks, or production of sweetened condensed whey. Jelen (1979) reported other traditionally established processes including lactose crystallization from untreated or modified whey, production of heat-denatured whey protein concentrate, or recovery of milk fat from whey cheese in whey butter. ... 

Preservation of cell structure, food taste, and avoidance of thermal degradation are reasons for the removal of moisture from such materials by sublimation. The process is preceded by quick freezing which forms small crystals and thus minimum damage to cell walls, and is likely to destroy bacteria. Some of the materials that are being freeze dried commercially are listed in Table 19.9(b). 

Usually materials to be freeze-dried are complex mixtures of water and several other substances. When such materials are cooled below 32 F (melting point.) See Fig. I. Most food products and biologicals solidify completely at a temperature in the range of —5 to - I00°F I 15 to -73CC). Al solidification of the entire... 

Trehalose is a relatively new bulk sweetener with potential for use in soft drinks. It is a di-glucose sugar and it occurs in nature in shellfish and mushrooms, where it confers a degree of protection to plant and animal cells in conditions causing dehydration. This led to its use as a cryoprotectant in freeze-drying systems in the pharmaceutical industry. In food markets, its potential use is as a bulk sweetener. It is manufactured using the Hayashibara patented process using starch as a raw material. The process involves enzymatic conversion and crystallisation to the trehalose dehydrate crystal (LFRA, 2001). 

Meltser, V. I. and Tutova, E. G. (1987). Enhancement of drying processes of crystal-structure foods. Scientific Notes in Chemical Engineering, Technology University of Lodz, 14 Nr.356, 29-36 in Russ). 

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