Flash desolventizers

Some plants divert part of their spent flake production away from a desolventi-zer-toaster to a flash desolventizer, which is designed to produce white flakes with high-protein solubility (PDI 70-90). White flakes are used as the starting material for producing protein isolates or concentrates, which contain >90% and 65% protein, respectively, and are used as food ingredients. 

Untoasted and flash-desolventized meal in which the protein is undenatured and highly soluble (>70 PDl and preferably >90 PDl) is the preferred starting material in manufacturing soy protein isolates. Under some conditions, extruded-expelled meal can be used, but the yield of soy isolate is reduced. The meal is ground in water adjusted to pH 8.0 with sodium hydroxide and centrifuged to remove insoluble fiber. The soluble fraction is acidified to pH 4.5, and the protein precipitates. The precipitated protein curd is separated from the soluble sugars by centrifuging. The protein curd may be washed, neutralized, and spray-dried. 

Of obvious concern in any DT application is the potential for overtoasting the meal and adversely affecting the water solubility of the protein, often expressed in terms of the protein dispersion index, or PDl. For certain edible flour and other applications demanding a high PDI, the DTDC process may be replaced with a flash desolventizing system. These systems, which typically use superheated solvent to evaporate volatiles present in the freshly extracted white flakes, maintain the high PDI while desolventizing the feedstock. 

High nitrogen solubihty index (NSI), soy protein for manufacture of meat analogs is prepared in flash desolventizers. Some soybean extraction plants send part of their marc through a flash desolventizer to serve the high NSI soy flour market and the balance of their marc through desolventizer/toasters to serve the animal feed soy meal market. The first flash desolventizer was commissioned by EMI Corporation (Em. Corp., Des Plaines, Illinois) in 1960 (214). 

Despite much research to demonstrate new uses, only about 3% of the available soybean meal is processed into edible flours and protein concentrates (>65% protein) and isolates (>90% protein). The flash desolventizer was developed to reduce protein denaturation and produce highly soluble protein food ingredients from soybeans (Fig. 11.17). Integrating these desolventizing systems with subsequent cooking systems produces edible protein flours with a broad spectrum of protein dispersibility characteristics. The system includes a desolventizing tube, a flake separator, a circulating... 

A relatively recent alternative to traditional flash-desolventizing systems is the down-draft desolventizer (DDD system). The DDD system incorporates a low-temperature, low-pressure desolventizer to reduce the hexane content to 2500 ppm in the first stage, followed by a high-vacuum stripper to produce white flakes with a residual... 

White flakes denote flash desolventized hexane-defatted dehulled soybean meal ... 

Mustakas, G.C. L.D. Kirk E.L. Griffin. Flash desolventizing defatted soybean meals washed with aqueous alcohols to yield a high protein product. J. Am. Oil Chem. Soc. 1962,39, 222-226. 

Vavlitis, A. E.D. Mulligan. Flash desolventizing. Proceedings of the World Conference on Oilseed Technology and Utilization T.H. Applewhite, Ed. American Oil Chemists Society Champaign, IL, 1993 pp. 286-289. 

Flash desolventizing is possible due to a very high heat and mass transfer surface of the flakes. Vavlitis and Milligan (1993) described that in the case of 0.23 mm... 

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