Protein extrudates produced

Figure IS. Protein solubilities in various buffer systems of soy extrudates produced at different temperatures ( ) pH 7.2, O.OM phosphate buffer pH 10.0, 0.0IM carbonate buffer (/ ) 1% 2-mE added phosphate buffer ( ) 1% SDS added phosphate buffer (0)1% 2-mE and 1 % 2-mE added phosphate buffer.

Denaturation and aggregation of whey proteins are affected by the pH of extrusion. When extruding WPI, alkaline conditions increase denaturation and solubility, decrease pasting properties, and produce more pronounced microstructural changes (Onwulata et ah, 2006). Denaturation in the extruder causes whey proteins to form small primary aggregates that combine to form large clusters. The clusters are then aligned by shear to form fibrous structures. 

Texturized or denatured WPl retained its native protein value, functionality, and digestibility when extruded below 50 °C changes in functionality occur at 65 °C and above. Through careful selection of extrusion conditions of temperature and moisture, TWPs with unique functionality can be produced. The degree of texturization increased with increasing temperature, but temperatures higher than 100 °C may be needed to form fibrous structures with WPl. 

The profound reason for having this many unknowns is attributed to the fact that the "technology" of extrusion texturization is well in advance of the "science". In-depth knowledge in the "science" portion of extrusion texturization will provide principles which can be used to accurately define the texturized protein product. This basic scientific knowledge should also provide data which could be used to improve operating efficiency of extruders, and serve as a basis for producing texturized protein foods, with desired characteristics for specific product applications, from a wide variety of raw ingredients. 

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.

Apparently, the energy level attained in the extruder is not high enough to form stable linkages eimong smaller molecules produced by enzymatic hydrolysis of soy proteins (Figure 7). 

M. Bonotto, USP 2413946(1947) CA 41, 2246(1947) (Non-extruding Dynamites produced by blending the usual constituents with dry vegetable protein meal, such as soybean meal)... 

Diatoms are unicellular, photosynthetic microalgae that are abundant in the world s oceans and fresh waters. It is estimated that several tens of thousands of different species exist sizes typically range from ca 5 to 400 pm, and most contain an outer wall of amorphous hydrated silica. These outer walls (named frustules ) are intricately shaped and fenestrated in species-specific (genetically inherited) patterns5,6. The intricacy of these structures in many cases exceeds our present capability for nanoscale structural control. In this respect, the diatoms resemble another group of armored unicellular microalgae, the coccolithophorids, that produce intricately structured shells of calcium carbonate. The silica wall of each diatom is formed in sections by polycondensation of silicic acid or as-yet unidentified derivatives (see below) within a membrane-enclosed silica deposition vesicle 1,7,8. In this vesicle, the silica is coated with specific proteins that act like a coat of varnish to protect the silica from dissolution (see below). The silica is then extruded through the cell membrane and cell wall (lipid- and polysaccharide-based boundary layers, respectively) to the periphery of the cell. 

Marine algae also convert Se predominantly into SeMet (Bottino et al, 1984), Se uptake is dependent on the Se/S ratio in the medium and on the chemical form supplied. Chlorella vulgaris and Chaetoceros calcitrans, for example, take up Se(IV) preferentially over Se(VI). Some of the organoselenium compounds produced by these algae are not incorporated into cellular proteins but are extruded into the culture medium (Hu et al, 1997). Chlorella also takes up SeMet and its incorporation is antagonized by Met (Shrift, 1954a,b). 

Later products employed double extrusion. The viscous mass consisting of protein continuous and carbohydrate inclusions was extruded, with some air present, in long dies. The elongational shear produced layered structures with flake-like substructure (Figure 18.8). 

It has been shown that heating soybeans reduces their protein degradability in the rumen and postpones digestion to the small intestine (98). However, the production of unavailable protein is also increased (Figure 16). The relative effects of feeding soybean meal, roasted soybeans, extruded soybeans, and raw soybeans on milk yield, protein, and fat content are shown in Table 18. Extruded soybeans gave the highest yield of 3.5% fat corrected meal (FCM) and was second to soybean meal in total protein produced. However, fat and protein contents of milk from extruded soybeans were lower than for the other treatments. 

The principle advantage of dry extruder preparation is that no expensive stacked-tray cookers or steam boiler are required, and the total capital investment for facilities under 100 tons per day in size is significantly less than for traditional full-press or solvent extraction processes. Therefore, this means of preparation is commonly applied in very small-scale plants commonly referred to as mini-mills. The primary disadvantage of dry extruder preparation is that the meal produced is higher in fat content than many poultry producers desire, and lower in bypass protein than many cattle producers desire. Thus, meal produced from a full-press mill using dry extrusion preparation generally obtains a lower price than meal produced from a traditional full-press operation. 

Socha and Satter (28) conducted a study to determine the production response of early lactation cows fed either solvent-extracted soybean meal, raw soybeans, extruded whole soybeans, or roasted soybeans with alfalfa silage as the sole forage source. They reported that dry matter intakes were lower for cows on the raw and roasted soybean treatments. Cows on the extruded soybean diet produced more milk, milk protein, and more 3.5% fat-corrected milk than cows fed the other diets. Body weight changes and body condition scores did not differ among the various treatments. 

Another protein in soybeans that is destroyed by extrusion is the trypsin inhibitor, which is produced in the pancreas. Without the action of trypsin, the animal cannot use protein, as it is trypsin that splits or hydrolyzes the protein molecule. Other less important enzyme inhibitors that are denatured by the extruder relate to fats and the carbohydrate fraction of a diet. As the heat needed to deactivate enzymes is less than that needed to prepare oilseeds for oil extraction, the effect on the amino acids is much less severe, thus making them more available to the animal or higher in digestibility. 

Moth larvae produce the polymeric material from a liquid crystalline phase to form a protective cocoon silk is extruded from the spinneret as a bave , consisting of two roughly triangular fibroin filaments ( brins ), about 20 pm across, bound together by a second protein, sericin (Figure 13). In commercial production, the chrysalid is killed before it can hatch (which would damage the thread), and a continuous filament can then be unreeled from each cocoon, giving typically 500-800 m of useable thread. 

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