Texturized protein products are known in the art and are typically prepared by heating a mixture of protein material along with water under mechanical pressure in a cooker extruder and extruding the mixture through a die. Upon extrusion, the extrudate generally expands to form a fibrous cellular structure as it enters a medium of reduced pressure (usually atmospheric). Expansion of the extrudate results from inclusion of soluble carbohydrates which reduce the gel strength of the mixture. The extrudates are then used to form other products such as vegetable meat analogs. Extrusion methods for forming textured protein meat analogs are well known and disclosed, for example, in U.S. Pat. No. 4,099,455.
Extrusion cooking devices have long been used in the manufacture of a wide variety of edible and other products such as human and animal feeds. Generally speaking, these types of extruders include an elongated barrel together with one or more internal, helically flighted, axially rotatable extrusion screws therein. The outlet of the extruder barrel is equipped with an apertured extrusion die. In use, a material to be processed is passed into and through the extruder barrel and is subjected to increasing levels of temperature, pressure and shear. As the material emerges from the extruder die, it is fully cooked and shaped and may typically be subdivided using a rotating knife assembly. Conventional extruders of this type are described, for example, in U.S. Pat. Nos. 4,763,569, 4,118,164 and 3,117,006, which are incorporated herein by reference.
Attempts to develop processes for producing suitable meat substitutes from vegetable protein sources include extrusion cooking defatted soy flour or other vegetable proteins in order to texturize and orient the vegetable protein and produce meat extenders in the form of texturized protein products for use with hamburger or similar products. Exemplary processes of this type are taught in U.S. Pat. Nos. 3,047,395; 3,142,571; 3,488,770 and 3,870,805. Although these extrusion processes have met with a certain degree of acceptance in the art, the meat substitute products heretofore produced have possessed several characteristics which have seriously limited their use, particularly as full substitutes for meat. One of the most persistent objections to those prior products stems from the expanded, cellular, spongy nature thereof. In particular, most of these meat extenders are produced under high pressure and temperature conditions in the extrusion cooker which results in a twisted, randomly oriented meat extender. After rehydration, these extenders are characterized by a chewy structure of twisted layers lacking the appearance, mouth feel or range of utility of meat. This has for the most part limited the use of these products to the role of meat extenders in ground hamburger type meats and the like. Moreover, if too much of the prior vegetable protein product is employed in such hamburger-type meats, the extended meat becomes unacceptably spongy and exhibits a random, unappealing appearance and mouth feel.
Alternatively, the texturized protein product may be cut into smaller extrudates such as “nuggets” or powders for use as food ingredients or as functional food products.
Regardless of its form, texturized protein products must have an acceptable density, texture, and mouth feel for use as a food ingredient. Thus, conventional texturized protein products typically have a protein content of from about 40% to about 60% by weight on a moisture-free basis. Increasing the protein content of the texturized product has not been feasible because a significant fraction of carbohydrate has been deemed necessary to provide the protein extrudate with an acceptable texture and density. But in certain instances high carbohydrate functional food ingredients are undesirable to consumers wishing to reduce carbohydrate intake. Thus, a need exists for a high protein, low carbohydrate texturized protein product having an acceptable density, texture and mouth feel for use as a functional food ingredient.