Flavor is a major factor that limits the use of many vegetable proteins in foods. In high quality whole cereal grains, flavor and flavor stability present little or no problem; but when some cereals are further processed into protein concentrates and isolates, objectionable flavors can arise from oxidative deteri‐oriation of unsaturated fatty esters in protein‐bound lipids. However, degermed wheat and corn flours (endosperm products) have little or no flavor. Raw legumes and oilseeds enriched with respect to lipoxygenases and other metallo‐proteins possess lipid‐derived, objectionable flavor compounds. Lipoxygenase‐mediated conversion of lipids to lipohydroperoxides and their subsequent degradation form volatile and nonvolatile constituents responsible for off‐flavors. n‐Hexanal, 3‐cis‐hexenal, n‐pentylfuran, 2(1‐pentenyl)furan, and ethyl vinyl ketone are major contributors to grassy‐beany and green flavors. Higher 2,4‐alkadienals have oxidized painty, rancid flavors sometimes noted in residual lipids. Geosmin, an oxygenated hydrocarbon, is responsible for the musty, moldy, earthy flavor of dry beans. This compound may contribute to similar flavors noted in soy and corn protein isolates. Thermally degraded phenolic acids account for some of the objectionable cooked odors of soy products that have been subjected to high temperature treatment such as retorting, autoclaving, and sterilization. Oxidized phosphatidylcholine most likely accounts for the bitter taste of soy products. Oxygenated fatty acids, including the bittertasting trihydroxy octadecenoic acids, have been identified in the bitter phosphatidylcholines isolated from soybeans. Oxidized lipids appear to be associatted with the bitter, astringent, and rancid flavors of protein isolates prepared from wet‐milled corn germ flour. Grassy‐beany, bitter flavor compounds preexist in the maturing soybean and are also generated during processing. In some legumes development of off‐flavors can be readily controlled by rapid inactivation of lipoxygenase with heat, alcohol, or acid treatment. Legume powders of acceptable flavor quality can be prepared by wet‐milling whole seeds in aqueous alcohols. Extraction of meals with hydrogen bond‐breaking solvents, such as alcohols or azeotropic mixtures of hexane and alcohol, effectively removes protein‐bound lipids to yield concentrates with greatly improved flavors. Soy protein concentrates approaching the blandness of wheat flour have been prepared by a combination of azeotrope extraction and steaming. Similar processes can also be used to greatly improve flavor scores of corn germ protein isolates. Based on our present knowledge about the identity of off‐flavor constituents and how they are derived, much progress has been made to effectively remove or modify them. These developments should result in new emerging technology that would be applicable to the manufacture of highly acceptable protein products from various vegetable sources.

A variety of published physical measurements, computational algorithms, and structural modeling methods have been used to create a molecular model of 19 kDa alpha-zein (Z19). Zetaeins are water-insoluble storage proteins found in corn protein bodies. Analyses of the protein sequence using probability algorithms, structural studies by circular dichroism, infrared spectroscopy, small-angle X-ray scattering (SAXS), light scattering, proton exchange, NMR, and optical rotatory dispersion experiments suggest that Z19 has approximately 35-60% helical character, made up of nine helical segments of about 20 amino acids with glutamine-rich "turns" or "loops". SAXS and light-scattering experiments suggest that in alcohol/water mixtures alpha-zein exists as an oblong structure with an axial ratio of approximately 6:1. Furthermore, ultracentifugation, birefringence, dielectric, and viscosity studies indicate that alpha-zein behaves as an asymmetric particle with an axial ratio of from 7:1 to 28:1. Published models of alpha-zein to date have not been consistent with the experimental data, and for this reason the structure was re-examined using molecular mechanics and dynamics simulations creating a new three-dimensional (3D) structure for Z19. From the amino acid sequence and probability algorithms this analysis suggested that alpha-zein has coiled-coil tendencies resulting in alpha-helices with about four residues per turn in the central helical sections with the nonpolar residue side chains forming a hydrophobic face inside a triple superhelix. The nine helical segments of the 19 kDa protein were modeled into three sets of three interacting coiled-coil helices with segments positioned end to end. The resulting structure lengthens with the addition of the N- and C-terminal sections, to give an axial ratio of approximately 6 or 7:1 in agreement with recent experiments. The natural carotenoid, lutein, is found to fit into the core of the triple-helical segments and help stabilize the configuration. Molecular dynamics simulations with explicit methanol/water molecules as solvent have been carried out to refine the 3D structure.

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AND SUMMARYLegumes contain unsaturated lipids that are susceptible to oxidative deterioration. Enzymic and nonenzymic deterioration of these lipids results in the development of off-flavors. The primary objective of this review is to summarize what is currently known about lipid-derived flavors of soybeans and underblanched pea seeds (Pisum sativum). Identifying the numerous volatile compounds arising from breakdown of lipid hydroperoxides coupled with organoleptic evaluation defines the flavor problem. Major contributors to the green-beaniness of soybeans were found to be 3-cis-hexenal, 2-pentyl furan, and ethyl vinyl ketone. Oxidized phosphatidylcholines cause some of the bitter taste. The interaction of lipid breakdown products 'with proteins, carbohydrates, and other constituents can affect flavor characteristics and also increase the problems of their removal from soy protein products. To prepare bland products, it will be necessary to develop processes that effectively remove bound flavor components and prevent formation of derived flavors. Solvent systems based on alcohol have been used to extract flavor principles from soybeans; aqueous alcohol treatment of the intact seed or blanching with hot water or steam inhibits formation of off-flavors in peas and soybeans. A new approach involving infusion of antioxidants into the intact seed to control lipid deterioration during processing and storage is proposed to minimize flavor formation without subsequent undesirable changes in protein which occur with alcohol treatments.

Cereal Chem. 84(3):265-270Circular dichroism studies were performed on zein to determine how the secondary and tertiary structure changes with different solvents, temperatures, or pH. Alcoholic solvent type and common denaturants such as SDS and low amounts of urea had little effect on the secondary structure of zein. Utilization of dimethylformamide or acetic acid as solvent gave changes in tertiary structure. Solutions of zein in 8M urea produced solutions with large changes in tertiary structure. The dissolution of zein in 50 mM sodium hydroxide produces a zein with large changes in secondary and tertiary structure and little loss in primary structure. Increasing the temperature of zein to 70°C in 80% ethanol-water gave reversible changes in the primary structure (20% reduction in absolute magnitude of [θ] λ at 208 and 222 nm) and tertiary structure (40% reduction in absolute magnitude of [θ] λ at 268 nm).

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Glutaraldehyde was used as a crosslinking reagent to produce electrospun zein fibers with improved physical properties and solvent resistance. Using 8% glutaraldehyde, round and ribbon fibers were produced with diameters between 1 and 70 µm. All fibers readily dissolved in acetic acid. Heating the zein/glutaraldehyde fibers at temperatures from 80 to 180 °C for different times provided various degrees of insolubility to the fibers. A model was developed relating the extent of dissolution with the amount of glutaraldehyde used and the temperature/time at which the fiber was exposed. The fibers were found to be birefringent; upon heating, the amount of α‐helix in the fiber was reduced.

Ultrafiltration followed by diafiltration (UF-DF) was evaluated for the production of protein products from partially defatted soybean meal or undefatted lupin (Lupinus albus L.2043N) meal. This study determined the effects of UF-DF on functional properties of the extracted proteins and compared the results with those of protein prepared by acid-precipitation (AP). UF-DF produced only protein concentrates (73% crude protein, dry basis, db), while AP produced protein isolates (about 90% crude protein, db). Soybean protein produced by UF-DF showed markedly higher values for solubilities up to pH 7.0, surface hydrophobicity index, emulsion activity index, and foaming capacity than did the AP soybean protein. UF-DF soy protein was also the most heat-stable among all protein samples tested. With lupin proteins, only the surface hydrophobicity and emulsion activity indices were significantly improved by using UF-DF. UF-DF generally had no adverse effects on, and in most cases even improved, the functional properties of soy protein concentrate produced by this method. UF-DF did not produce a comparable improvement in functional properties of lupin proteins as it did for soybean protein.The Clean Air Act, which limits emissions of volatile organic compounds and other hazardous air pollutants, has spurred the utilization of mechanical extraction processes in the oilseed industry (1). One such solvent-free process is extrusion-expelling (E-E), a simple and relatively inexpensive operation (2) that has produced soybean oil of such quality that only minimal refining will be required (3). The resulting meal has higher oil content than what is found in meal produced from traditional solvent extraction (2), but E-E meal is considered as a higher energy source for livestock feed (1). Because E-E does not use desolventizing and drying, the meal is also presumed to have better functional properties, which would make it possible to use E-E meal for the production of the higher-value flours, concentrates, or isolates. Heywood et al. (4) prepared low-fat soy flours from E-E meal and found them to possess good solubilities (at pH values less than and greater than 4), emulsifying and foaming properties, and water-and fat-binding capacities. No study has yet been reported on the preparation and quality of concentrates or isolates from E-E meal.The present study explores ultrafiltration (UF) as a means of producing protein concentrates or isolates from E-E soybean meal. UF is a pressure-driven membrane process that has gained wide acceptance in protein bioseparations (5). It has a broad variety of applications, but it is used mainly for concentration, desalting, clarification, and fractionation (5). Sessa (6) recently produced peroxidase and Bowman-Birk inhibitor concentrates from soybean hulls by using UF, followed by discontinuous diafiltration (DF), a membrane-based method that removes low M.W. solutes such as salts while continuously replacing the solvent lost with the permeate (5). Both peroxidase and Bowman-Birk inhibitor are valua...