Soy protein concentrates (SPC) and soy protein isolates (SPI) were produced from hexane-defatted soy white flakes and from two extruded-expelled (EE) soy protein meals with different degrees of protein denaturation. Processing characteristics, such as yield and protein content, and the key protein functional properties of the products were investigated. Both acid-and alcohol-washed SPC from the two EE meals had higher yields but lower protein contents than that from white flakes. Generally, SPC from an acid wash had much better functional properties than those from an alcohol wash. The SPI yield was highly proportional to the protein dispersibility index (PDI) of the starting material, so the EE meal with lower PDI had lower SPI recovery. The protein content in SPI prepared from EE meals was about 80%, which was lower than from white flakes. Nevertheless, SPI from EE meals showed functional properties similar to or better than those from white flakes. The low protein contents in SPC and SPI made from EE meals were mainly due to the presence of residual oil in the final products. SPI made from EE meals had higher concentration of glycinin relative to β-conglycinin than that from white flakes.Paper no. J10816 in JAOCS 81, 713-717 (July 2004). KEY WORDS:Extruding-expelling, functional property, soy protein concentrate, soy protein isolate.Soy protein products have become increasingly popular because of their low price, high nutritional quality, and versatile functional properties. Two important soybean protein products are soy protein concentrate (SPC) and soy protein isolate (SPI). SPC is defined as an edible protein product with a protein content of at least 65% on dry weight basis (1), whereas SPI is a product with at least 90% protein on dry weight basis (2). Currently, flash-desolventized solvent-extracted white flakes (typically containing 50% protein) are generally the starting materials for SPC and SPI preparation. Other soybean meals or flours besides white flakes may also be used as starting materials provided that the final products meet protein content specifications and demonstrate desired functional properties. Soybean meals produced from the extruding-expelling (EE) processing of soybeans may be used as starting materials for SPC and SPI preparation. EE is a mechanical processing technology that allows small-scale production of protein meals having a high oil content and partial recovery of oil. Extrusion, the first step of processing, provides a heat treatment that reduces trypsin inhibitors, permitting the use of the full-fat or defatted protein meals as livestock feed. The extrudate can be pressed by an expeller to partially recover the oil. The protein in the meal typically is extensively heat-denatured by extrusion. Depending on the processing conditions, EE meals with different oil contents and protein denaturation can be achieved (3). Advantages of EE technology include process simplicity, low capital investment, no need for organic solvents, and applicability to identity-preserved (IP) process...

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A series of experiments were conducted to evaluate effects of yolk contamination, shearing, and thermal treatment on foaming properties of liquid egg white. Samples obtained from industrial processing were also evaluated. Whipping and purging methods were both used to assess their effectiveness and sensitivity in evaluating foaming. A concentration as low as 0.022% (as-is basis) of yolk contamination caused significant reductions in foaming capacity and foaming speed. The neutral lipid fraction of egg yolk caused the major detrimental effect on foaming, and phospholipids fraction did not give significant foaming reduction at a concentration as high as 0.1%. High-speed and short-time shearing caused no apparent damage but longer shearing time significantly impaired foaming. Heat-induced foaming change is a function of temperature and holding time. Foaming was significantly reduced at a temperature of 55 degrees C for 10 min, whereas it did not change up to 3 min at a heating temperature of 62 to 64 degrees C. Industrial processing steps (pumping, pipe transfer, and storage) did not produce negative effects on foaming of the final products and the controlled pasteurization was actually beneficial for good foaming performance. Therefore, yolk contamination of the egg white was the major factor in reducing foaming properties of the white protein.

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Solid-state NMR determination of the depth of insertion of membrane peptides and proteins has so far utilized 1H spin diffusion and paramagnetic relaxation enhancement experiments, which are typically conducted in the liquid-crystalline phase of the lipid membrane. For membrane proteins or peptide assemblies that undergo intermediate-timescale motion in the liquid-crystalline membrane, these approaches are no longer applicable because the protein signals are broadened beyond detection. Here we show that the rigid-solid HETCOR experiment, with an additional spin diffusion period, can be used to determine the depth of proteins in gel-phase lipid membranes, where the proteins are immobilized to give high-intensity solid-state NMR spectra. Demonstration on two membrane peptides with known insertion depths shows that well-inserted peptides give rise to high lipid cross peak intensities and low water cross peaks within a modest spin diffusion mixing time, while surface-bound peptides have higher water than lipid cross peaks. Furthermore, well-inserted membrane peptides have nearly identical 1H cross sections as the lipid chains, indicating equilibration of the peptide and lipid magnetization. Using this approach, we measured the membrane topology of the α-helical fusion peptide of the paramyxovirus, PIV5, in the anionic POPC/POPG membrane, in which the fusion peptide undergoes intermediate-timescale motion at physiological temperature. The gel-phase HETCOR spectra indicate that the α-helical fusion peptide is well inserted into the POPC/POPG bilayer, spanning both leaflets. This insertion motif gives insight into the functional role of the α-helical PIV5 fusion peptide in virus-cell membrane fusion.