Of extrusion texturized soy

TABLE I. Selected Physical and Rheological Properties of Extrusion Texturized Soy... 

Figure 3. TLMs of extrusion texturized pH-modified soy flours (I) pH 9.0 (2) pH 8.0 (3) pH 6.6 (4) pH 5.6 (5) pH 5.3 extruded at LFR (6) pH 5.3 extruded at HFR. Note that alkaline pH could increase the fihrousness of the protein matrix acidic pH produced the opposite effect. P, protein C, insoluble carbohydrate.

Figure 8. Exterior morphologies of extrusion texturized surfactant-added soy flours. Control, no surfactant added product Tolutein, yeast protein CSL SSL. Note the effect of surfactant on the diameter and surface smoothness of extrudates. (Mag. J.5X.)...

Texturization Process at Various Temperatures. Changes in soy flour components during nonextrusion texturization at various temperatures were unlike those of extrusion texturization because shearing action does not occur in nonextrusion texturization. Therefore, a higher temperature (160 C) was required to produce a puffed product. Due to lack of shearing action, nonextrusion... 

TABLE VIII. Protein Solubility and Selected Physical Properties of Extrusion Texturized Succinylated Soy Flours—... 

Figure 24. Exterior morphologies of extrusion texturized reducing or oxidizing agent-modified soy flours. Note that both reducing agents (Na>SO, and cysteine) -modified flours produced more puffed products, whereas the oidant (KIO,) modified flour showed opposite effect. (Mag. 1.5.)...

Figure 25. TLMs of extrusion texturized chemically modified soy flours (J) control (2)0.1% Na,SO, added (3) 0.2% Na,SO, added (4) 0.1% cysteine-HCl added (5) 0.2% cysteine-HCl added (6) 0.2% NotSO, and 1% SDS added (7) 0.01% KIO, added and (8) 0.05% KIO, added. Note that both NaiSOt and cysteine-HCl can increase the flbrousness of protein matrix but KIOs has the opposite effect. P, protein C, insoluble carbohydrate.

FACTORS AFFECTING EXTRUSION TEXTURIZATION PROPERTIES OF SOY FLOUR... 

The first soybean protein ingredients made commercially available for food use included full-fat and defatted soy flours and grits (3, 7, 8). These products contain ca. 46-59% protein (NX 6.25) on a moisture-free basis and are available with various heat treatments for specific end-use. Soy protein concentrates and soy protein isolates were introduced into the market about 15 years ago (3, 9, 10, II). By definition soy protein concentrates must contain no less than 70% protein (N X 6.25) and isolates no less than 90% protein (N X 6.25), all on a moisure-free basis. In the past several years there has been much activity in the commercialization of textured soy protein products intended for the extension and replacement of meat. These textured products may be obtained through fiber spinning, shred formation, extrusion, or compaction (12, 13, 14, 15). In addition, soybean milk solids and the heterogeneous proteins in soybean whey might serve as useful substrates in chemical modifications for food use. This short recitation of commercial products illustrates the type of crude protein fractions available for practical modification. Many useful functional properties have been ascribed to these new food proteins. 

The principles of extrusion were described by Mercier et al. (1989) and. the processing of proteins by Stanley (1989) and Rokey et al. (1993). Texturized Vegetable Protein and TVP are registered trademarks of the Archer Daniels Midland Company, Decatur, Illinois, and the generic terms texturized soy protein, TSP, or texturized vegetable foodprotein are used. Two types of products are made (i) extrusion-cooked meat extenders, which are made from SF or flakes or SPC and are rehydrated to 60 to 65% moisture before blending with meats or meat emulsions at levels of 20 to 30% and... 

A variety of texturized soy food proteins is available from manufacturers, including products made from SF or SPC, colored and sized to different specifications. The volatile constituents are customarily added after extrusion by one of several enrobing processes. Specifically fortified products are available for use in school-lunch and child-feeding programs and in military-feeding applications. 

Riaz, M.N. Extrusion-expelling of soybeans for texturized soy protein. Proceedings of the World Conference on Oilseed Processing and Utilization R. Wilson, Ed. AOCS Press Champaign, IL, 2001 pp. 171-175. 

Traditionally, extrusion texturization of soy protein has been used to create meat analogues. Addition of sodium hydroxide during extrusion does not aid in texturization, with worse product quality at high pH (Dahl and Villota, 1991). Precipitation within the extruder at the soy isoelectric point may be necessary for adequate texturization. Huang and colleagues (1995) at Iowa Sate University devised a process in which soy protein isolate could be extruded into textile fibers. Brittleness was offset by addition of glycerol during extrusion and by various chemical treatments post-extrusion. A similar process could be developed to produce superior meat-like fibers. 

Extrusion research is just now providing clues as to the fate of nutrients during extrusion. As nutrition science begins to unravel the importance of non-nutrient chemicals in foods, it is clear that extrusion effects on these compounds must be studied. For example, genistein and phytoestrogens in soy may help prevent cancer, yet extrusion texturization of soy might significantly reduce these compounds. 

Dahl, S.R Villota, R. Twin-screw extrusion texturization of acid and alkali denatured soy proteins. J. Food Sci. 1991,56, 1002-1007. 

Surfactants have been, reprotedly, used to prevent extensive puffing of extruded cereal products. It was found in these studies that surfactants could effectively inhibit gelatinization of cereal starch. However, effect of surfactants on protein texturization has not been reported. Two types of surfactants, sodium stearoyl-2-lactylate and calcium stearoyl-2-lactylate (at levels of 0.2 and 0.4% based on the weight of the flour), were mixed with soy flour prior to extrusion. A yeast protein (Torutein, manufactured by Amoco Inc.), claimed to be an extrusion helper although its function is not known, was added. 

High molecular weight proteins (>50,000 g/mole) are needed to form texture during extrusion of soy protein ingredients. 

Effects of Surfactants. Two types of surfactants [sodium stearoyl lactylate (SSL) and calcium stearoyl lactylate (CSL)] at two concentrations (0.2 and 0.4%) were added to soy flours to study the effect of surfactants on the texturization properties of soy flours. An extrusion helper (Tolutein, yeast cell protein) was also included at two concentrations (1 and 2%) in this study because of its behavior similar to a surfactant upon extrusion. 

Food proteins are often treated with alkali to improve their functional properties. For example, soy protein is treated with alkali and heat during extrusion to produce textured fibers for use as meat analogues and extenders which are widely marketed for human consumption (7). Several studies have shown that soy protein treated with alkali contains significant amounts of racemlzed amino acids (8-10). 

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