Food crystallization separation, production

Crystallization is mainly used for separation as an alternative to distillation, if the involved compounds are thermally unstable (e.g., acrylic acid), have a low or practically no vapor pressure (like salts), if the boiling points are similar, or if the system forms an azeotrope. Crystallization is used for the production and purification of various organic chemicals ranging from bulk chemicals (p-xylene and naphthalene) to fine chemicals like pharmaceuticals (e.g., proteins). Further examples of industrial crystallization processes are sugar refining, salt production for the food industry, and silicon crystal wafer production. 

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. 

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. 

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... 

The fermentation uses glucose-containing organic feedstock it is aerobic and the L-glutamic acid is excreted by the cell into the surrounding liquid medium. The glutamic acid is separated from the fermentation broth by filtration the filtrate is concentrated and the acid is allowed to crystallize. MSG is manufactured on a large scale in many countries and is an additive in many food items. The worldwide production is estimated to be 800,0001. 

Because electrodialysis is a separation process that is not accompanied by phase separation, unlike evaporation and crystallization processes, it is energysaving and also suited to separating thermally unstable materials such as biomaterials, products in the food industry and similar materials from salts, acids and alkalis. 

In foods, two circumstances for controlling the formation of crystals can be distinguished (Table 13.2) those where the crystals provide an element of structure in the product and those where crystallization is a separation process. In the first case, control of the correct number, size (and distribution), shape and polymorph of crystals is required to provide the desired processing characteristics, quality (texture, flavor, etc.), appearance and/or... 

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