Major components of wheat flour include gluten and wheat starch. Gluten is the product of an interaction between water and the water-insoluble protein constituents of wheat which comprise about 80% of the protein content of flour. Wheat gluten is a common food additive and is essential in breadmaking as it provides the bread with texture. Wheat starch is used for various commercial purposes.
The many processes for the production of vital wheat gluten can be grouped generally into two types: a) those based on the Martin system in which a dough is developed prior to separation into gluten, starch and water solubles, by a doughwashing process; and b) the batter system, in which wheat flour dispersions are fractionated by centrifugal separation with decanters or hydrocyclones (Fellers, D. A. (1973) "Fractionation of wheat into major components," Chapter 4, In Industrial Uses of Cereals, Y. Pomeranz ed. Am. Assoc. Cereal Chem., St. Paul, Minn., pp. 207-228; Kempf, W., and Rohrmann (1989) "Process for the industrial production of wheat starch from whole wheat," Chapter 31, In Wheat is Unique, Y. Pomeranz, ed. Am. Assoc. Cereal Chem., St. Paul, Minn., pp. 521-540; Meuser, F., F. Althoff, and H. Huster (1989) "Developments in the extraction of starch and gluten from wheat flour and wheat kernels," Chapter 28, In Wheat is Unique, Y. Pomeranz, ed. Am. Assoc. Cereal Chem., St. Paul, Minn., pp. 479-500). The main disadvantages of the Martin dough system are the large amounts of water used (up to 10 m.sup.3 /ton of flour), the generation of heavy waste water loads (up to 5-8 m.sup.3 /ton flour) and some limited impairment of the functional properties of the resulting gluten (e.g., lower vitality, water absorption, and rate of hydration) (Sarkki, M. L. (1980) "Wheat gluten," In Cereals for Food and Beverages, G. F. Inglett and L. Munck eds. Academic Press, New York, pp. 155-169). Likewise, in some batter (slurry) systems, the total amounts of water used and waste water loads are claimed to be 3 and 2 m.sup.3 /ton flour, respectively. The practical, engineering-technological advantages and limitations of batter separation systems have been the subject of much controversy (Bart, D. J. (1989) "The engineering of a modern wheat starch process," Chapter 29, In Wheat is Unique, Y. Pomeranz ed. Am. Assoc. Cereal Chem., St. Paul, Minn., pp. 502-508; Zwisterloot, W. R. M. (1989) "Production of wheat starch and gluten: Historical review and development into a new approach," Chapter 30, In Wheat is Unique, Y. Pomeranz ed. Am. Assoc. Cereal Chem., St. Paul, Minn., pp. 509-520) and claims of batter fractionation processes using low water consumption have been challenged. The two main fractionation systems--dough and slurry--are suggested to be incompatible in that success in the batter system requires that no dough development occur during fractionation (Fellers, supra; Meuser et al., supra).
In addition to the large water requirement, waste water load, and high energy requirements, a further disadvantage of the Martin system is that the starch is admixed with pentosans that can adversely affect functional-breadmaking properties (Meuser, supra). In the batter system (unlike the dough system) it is possible to obtain a high yield of a pure, prime starch fraction of large-granule A-starch and a second fraction of B-starch in which the small granules are admixed with pentosans. There is a good market and use for both fractions if they can be separated at high resolution and yield.
A German Patent, P258 718, describes a process for the simultaneous production of wheat starch and wheat gluten. Although the process employs less water than other slurry/batter methods, fractions must be further processed to obtain useable products.
Another batter-procedure for the fractionation of wheat protein concentrate and starch from wheat flour was developed by the USDA. Accordingly, "Wheat flour is rapidly mixed in an optimum of water and them finely dispersed by additional cutting type shear that prevents gluten development. The slurry is fed to a continuous decanter-type centrifuge where prime starch is spun out and the liquid protein concentrate (PC) is decanted" (Tressler, D. K., and W. J. Sultan (1975) "Wheat protein concentrate and wheat starch," In Food Products Formulary, AVI Publ. Co., Westport, Conn., 2:11-12). This method is advantageous in that gluten vitality is not damaged. Gluten provides the material for forming gas cells in bread-making that provide the bread with texture. Gluten vitality may be lost when gluten is denatured by high temperatures or solubilized by extended exposure to warm water. A good fractionation process should retain gluten vitality.
A method for the fractionation of dough made from white wheat flour was described by Mauritzen and Stewart in 1965 (Mauritzen, C. M., and Stewart, P. R. (1965) "The ultracentrifugation of doughs made from wheat flour" Austral. J. Biol. Sci. 18:173-189). In that method, 42 gram portions of a dough were resolved into five to seven layers by ultracentrifugation at 105,000 g for 70 minutes at 30.degree. C. A layer containing 10 to 25% of the total dough had 30 to 60% of the total nitrogen and comprised up to four-fold concentrations of the original dough protein. Complete separation of protein and starch, however, could not be attained. Attempts to reproduce the results of Mauritzen and Stewart (1965) were unsuccessful (Pomeranz, Y. and O. K. Chung (1973-1974) unpublished; and Czuchajowska, Z. and Y. Pomeranz, (1990-1991) unpublished, respectively).
A simple, efficient process by which vital gluten and prime starch can be separated from wheat flour is needed. The process should employ minimal liquid and yield a light waste water load. The resulting protein concentrate should be of high quality and the starch component should have little protein contamination.