Functional properties of extruded-expelled soybean flours from value-enhanced soybeans

The functional properties (protein solubility, emulsification characteristics, foaming characteristics, water- and fatbinding capacities) of extruded-expelled (EE) soy flours originating from six varieties of value-enhanced soybeans (high-sucrose, high-cysteine, low-linolenic, low-saturated FA, high-oleic, and lipoxygenase-null) and two commodity soybeans were determined. The soy flours varied in protein disperisibility index (PDI) and residual oil (RO), with PDI values ranging from 32 to 50% and RO values ranging from 7.0 to 11.7%. Protein solubility was reduced at pH values near the isoelectric region and was higher at both low and high pH. There were no significant differences for water-holding capacity, fat-binding capacity, emulsification activity, or emulsification stability. Only the high-oleic soy flour had significantly lower emulsification capacity. In general, the PDI and RO values of EE soy flours originating from value-enhanced and commodity soybeans had the greatest influence on protein functionality. The genetic modifications largely did not affect functional properties.     

Twin-screw extrusion texturization of extruded-expelled soybean flour

Texturized soy proteins (TSP) have been produced from hexane-extracted soy flours having a narrow range of characteristics. The objective of this study was to determine the influence of protein dispersibility index (PDI) and residual oil content on extrusion texturization of partially defatted soy flours produced by extruding-expelling (E-E). Ten E-E processed soy flours having residual oil contents and PDI values of 5.5–12.7% and 35.3–69.1%, respectively, were texturized using a twin-screw extruder. Water-holding capacities were greater for TSP prepared from E-E processed soy flours with lower residual oil contents. Bulk densities were significantly lower for TSP prepared from E-E processed soy flours compared with a commercial product made from hexane-extracted soy flour. The texture characteristics of extended ground beef patties containing texturized E-E processed soy flour were similar to that of 19% fat ground beef. Flavor acceptability was directly correlated (R=0.761) with residual oil content of the E-E processed soy flours. However, lower residual oil and higher PDI flours exhibited better texturization and extrudate qualities.     

Processing of lipoxygenase-free soybeans and evaluation in foods

Lipoxygenase-free soybeans were processed into flour, concentrate, and isolate and compared to normal soybeans in bread, meat patties, and a beverage, respectively. Bread made with 20% normal or lipoxygenase-free soy flour had greater (P< 0.05) beany flavor than control yeast bread. There were no differences in beany flavor scores between soy flour types, normal and lipoxygenase-free. Ground beef patties made with 5% acid-washed or ethanol-washed soy protein concentrate had greater (P<0.05) beany flavor than control ground beef patties. Ground beef patties made with ethanol-washed concentrate were scored lower in beany flavor than those made with acid-washed concentrate from normal soybeans. There were no differences in beany flavor between normal and lipoxygenase-free soy isolate in 2%-fat or no-fat beverages. Comminuted meat products made with lipoxygenase-free soy proteins, especially ethanol-washed concentrate, have potential for making soy foods with less beany flavor than foods made with normal soy.     

Effect of pro-oxidants on the occurrence of 2-pentyl pyridine in soy protein isolate

Levels of 2-pentyl pyridine in hexane-defatted soybean flours prepared from Burlison, Stressland, and Probst varieties and a variety null for lipoxygenase 1, 2, and 3 were determined using an internal standard of deuterium-labeled 2-pentyl pyridine. These defatted flours contained from 0.06 to 0.51 ppm 2-pentyl pyridine. The flours from lipoxygenase-null and Stressland varieties of soybeans contained the lowest levels. Control freeze-dried soy protein isolates (SPI) prepared from defatted-flours all contained from 0.16 to 0.18 ppm 2-pentyl pyridine. Adding pro-oxidants (FeCl₃, CuCl₂) or exposing the protein slurries to ultraviolet light during SPI processing increased the level of 2-pentyl pyridine in the protein isolates by up to 1256 percent above the control Burlison, Stressland, and Probst SPI. The CuCl₂ and/or UV treatment contributed the largest increase in each case. The same pro-oxidant and UV treatments contributed no significant increases in the level of 2-pentyl pyridine in the protein isolates from the lipoxygenase null SPI.     

Functional properties of protein ingredients prepared from high-sucrose/low-stachyose soybeans

High-sucrose/low-stachyose (HS/LS) soybeans were used to prepare ethanol-washed soy protein concentrate (EWSPC), soy protein isolate (SPI), and a new low-fiber soy protein concentrate (LFSPC) in which the protein was extracted with alkali to remove fiber and the protein extract was neutralized and freeze-dired. LFSPC prepared from HS/LS soybeans contained significantly higher ratios of β-conglycinin to glycinin (1∶1.32) than did EWSPC (1∶1.75) or SPI (1∶1.69), which may have affected functional properties. The LFSPC were also high in soluble sugars (14.7%) and low in fiber (0.3%) compared with traditional EWSPC (2.9 and 3.4%, respectively) and SPI (1.8 and 0.3%, respectively). For both normal and HS/LS soybean varieties, the LFSPC, especially when extracted at pH 7.5 as opposed to pH 8.5, had higher denaturation enthalpies than did EWSPC and SPI, indicating less denaturation had occurred. Water solubilities, surface hydrophobicities, and emulsification properties were highest for the LFSPC and lowest for EWSPC. The LFSPC also had good foaming properties and low viscosities. These desirable functional properties of the LFSPC make them unique among alternative soy protein ingredients and highly suitable for industrial applications as food additives and ingredients.     

Quality characteristics of ground beef patties extended with moist-heated and unheated seed meals

Extending ground beef with 5% peanut, soybean, pecan, or field pea meals increased cooked yields and water-retention properties of beef patties. Extended patties were more tender, requiring less force to compress than all-beef patties. Protein content was significantly increased by the addition of peanut and soybean meal to ground beef. Unheated meals produced patties with larger volumes but were poorer in aroma and flavor qualities than all-beef patties or those prepared with heated meals. Moist heat effectively improved aroma and flavor qualities of the meals without altering their binding properties.     

Effect of moisture and temperature on the phosphorus content of crude soybean oil extracted from fine flour

Analysis of total oil content in soybeans is usually done by extracting flours, whereas commercial extraction for recovery of oil is done by extracting flakes. It has recently become apparent that phosphorus content of crude soybean oil extracted from flours can vary depending on extraction temperature and flour moisture. In this study, flour moistures below 6% yielded crude oil with low phosphorus (15 ppm), but phosphorus in the oil increased rapidly to 260 ppm at 9% moisture. When temperature of the extraction was increased from 25 to 60°C, the phosphorus in extracted oil also increased for moisture contents of 6.6% and 8.3%, but not for moisture contents of 5% and 3%. In addition to the effects of extraction temperature, it was found that preheating whole soybeans at various temperatures affected phosphorus in oil from extracted flour. Preheating at 130°C caused high phosphorus content regardless of how dry the flour was, whereas preheating at 100°C or below caused phosphorus content that increased with increased moisture. The response of phosphorus content in crude oil to temperature and moisture may be useful in improving the quality of commercially extracted soy oil.     

Compositional characteristics of protein ingredients prepared from high-sucrose/low-stachyose soybeans

High-sucrose/low-stachyose (HS/LS) soybeans contained lower total concentrations of free sugars (13.3%), less stachyose (0.7%), and more galactinol (0.7%) (galactopyranosylmyo-inositol) than the control normal soybeans (14.9, 5.1, and 0.2%, respectively). A low-fiber soybean protein concentrate (LFSPC) process was developed, which is especially suited to HS/LS soybeans, by which defatted soy flour is merely extracted with alkali to remove fiber and then neutralized and dried to produce the protein-rich soluble fraction. Two different pH values (7.5 and 8.5) were used in extracting protein, and these LFSPC were compared with traditional ethanol-washed soy protein concentrate (EWSPC) and soy protein isolate (SPI) prepared from both normal and HS/LS soybeans. The LFSPC had slightly lower yields of solids and protein (∼70 and ∼81%, respectively) than conventional FWSPC (∼77 and ∼93%, respectively) but much higher than conventional SPI (∼42 and ∼70%, respectively). The LFSPC prepared from HS/LS soybeans contained significantly (P<0.05) more protein (∼66% protein content) than LFSPC prepared from normal soybeans (∼63%). Total isoflavone contents of the LFSPC (∼12 μmol/g) were significantly higher than for EWSPC (∼1.5 ìmol/g) or SPI (∼10 μmol/g). The LFSPC prepared from HS/LS soybeans contained higher sugar contents (∼15%) than either traditional EWSPC (∼2.5%) or SPI (∼1.5%); but the sums of stachyose and raffinose were only ∼1% for the LFSPC compared with ∼1% for EWSPC and 0.5% for SPI prepared from normal soybeans.     

Preparation of Glycinin and β-Conglycinin from High-Sucrose/Low-Stachyose Soybeans

A new soybean line, known as high-sucrose/low-stachyose (HS/LS) soybeans, has been developed having elevated sucrose content and reduced content of flatus-causing oligosaccharides, especially stachyose. There is also increased interest in understanding the health benefits, functional properties and potential applications for the two major storage proteins of soybeans, glycinin and β-conglycinin. We evaluated the protein fractionation behavior of a HS/LS soybean line and compared it to normal soybeans when using the three-step Wu procedure, which employs SO₂, NaCl and precipitations at pH 6.4 and 4.8 and a new two-step Deak procedure, which employs SO₂, CaCl₂ and precipitations at pH 6.4 and 4.8. Both soybean variety and fractionation procedure significantly affected fraction yields, purities and functional properties. The Wu procedure gave glycinin- and β-conglycinin-rich fractions with 100% purities and high yields of solids (15.4%) and protein (31.7%) from HS/LS soy flour, which were significantly higher than the purities and yields achieved with normal soybeans. The Deak procedure was less efficient in fractionating proteins from HS/LS soybeans than from normal soybeans, producing protein fractions from HS/LS soybeans with purities ranging from 71 to 80%. The Deak procedures yielded products with unique solubilities, surface hydrophobicities, and emulsification and foaming properties.     

Protein solubility characteristics of commercial soy protein products

Solubility characteristics of commerical soy protein products (flours, concentrates, and isolates) were determined under various conditions. From the solubility profiles at various pH values and NaCl concentrations, soy protein isolates can be divided into three groups. One group had high solubility near the pl. Another group had low solubility near the pl, but high solubility at pH 11. The third group had low solubility even at pH 11. Except for the hydrolyzed products, the protein solubilities of the soy protein products at various salt concentrations were very low. Temperature did not significantly affect the protein solubility, although a few products showed more than a 20% increase at temperatures >50°C. Soy protein concentrates and soy protein isolates showed similar solubility profiles. The proteins in all commercial products (except flours) tested were denatured, as evident from the solubility profiles in the presence of salt and the enthalpy values from DSC.     

Flaking and extrusion as mechanical treatments for enzyme-assisted aqueous extraction of oil from soybeans

Flaking and extruding dehulled soybeans were evaluated as a means of enhancing oil extraction efficiency during enzyme-assisted aqueous processing of soybeans. Cellulase, protease, and their combination were evaluated for effectiveness in achieving high oil extraction recovery from extruded flakes. Aqueous extraction of extruded full-fat soy flakes gave 68% recovery of the total available oil without using enzymes. A 0.5% wt/wt protease treatment after flaking and extruding dehulled soybeans increased oil extraction recovery to 88% of the total available oil. Flaking and extruding enhanced protease hydrolysis of proteins freeing more oil. Treating extruded flakes with cellulase, however, did not enhance oil extraction either alone or in combination with protease. Discrepancies in oil extraction recoveries were encountered when merely considering crude free fat because some oil became bound to denatured protein during extrusion and/or sample drying. Bound fat was unavailable for determination by using the hexane extraction method, but was accounted for by using the acid hydrolysis method for total oil determination. Oil extraction recovery from extruded soybean flakes was affected by oil determination methods, which was not the case for unextruded full-fat soy flour.     

Effect of processing on sphingolipid content in soybean products

Soybeans are believed to be a rich source of sphingolipids, a class of polar lipids that has received attention for their possible cancer-inhibiting activities. The effect of processing on the sphingolipid content of various soybean products has not been determined. Glucosylceramide (GlcCer), the major sphingolipid type in soybeans, was measured in several processed soybean products to illustrate which product(s) GlcCer is partitioned into during processing and where it is lost. Whole soybeans were processed into full-fat flakes, from which crude oil was extracted. Crude oil was refined by conventional methods, and defatted soy flakes were further processed into alcohol-washed and acid-washed soy protein concentrates (SPC) and soy protein isolates (SPI) by laboratory-scale methods that simulated industrial practices. GlcCer was isolated from the samples by solvent extraction, solvent partition, and TLC and was quantified by HPLC. GlcCer remained mostly within the defatted soy flakes (91%) rather than in the oil (9%) after oil extraction. Only 52, 42, and 26% of GlcCer from defatted soy flakes was recovered in the acid-washed SPC, alcohol-washed SPC, and SPI products, respectively. All protein products had a similar GlcCer concentration of about 281 nmol/g (dry wt basis). The minor quantity of GlcCer in the crude oil was almost completely removed by water degumming.     

Foaming properties of soybean protein-based plywood adhesives

A study was conducted to evaluate the potential of soy protein-based plywood glues for foam extrusion. Foaming properties were the first criterion used to screen several soy protein sources. Foaming capacities and stabilities of glue mixes containing animal blood (control) or soy products (meals, flours, concentrates, and isolates) were compared and correlated with molecular weights and surface hydrophobicity indices (S _o) in an attempt to identify structure/function relationships. The blood-based glue mix produced more foam than any of the soy-based glues. Soy flours and concentrates generally produced greater foam volumes and more stable foams than soy meal and isolates. Differences in foaming properties could not be explained by solubility profiles or S _o. However, results of gel electrophoresis indicated that soy products with poor foaming properties had extensive structure modifications or contained considerably lesser amounts of protein available for foaming reactions. Glue mixes containing the soy flours ISU-CCUR, Honeysoy 90, Nutrisoy 7B, and defatted Soyafluff and the soy concentrates Arcon F, ISU-CCUR, and Procon 2000 demonstrated the desired mixing and foaming properties for foam extrusion.     

Effect of equilibrium oil extraction on the chemical composition and sensory quality of soy flour and concentrates

Previous studies have shown that ambient-temperature equilibrium, hexane extraction of soy flour yielded the same amount of oil as was extracted from soy flakes by conventional high-temperature processing. The oil obtained at ambient temperatures contained less phospholipid than commercial crude oils obtained by traditional processing. In this study, chemical composition, flavor and odor of soy flour obtained after oil extraction by the equilibrium procedure were evaluated before and after toasting. Results were compared with those obtained for commercial untoasted food-grade soy flakes. Chemical and sensory analyses were performed on soy protein concentrates (SPC) prepared from defatted flour, defatted toasted flour and commercial defatted white food-grade flakes. SPC were made by acid and ethanol-extraction methods. Ethanol extraction of soy flour produced SPC with similar protein, lipid and sensory qualities to those obtained from commercial flakes. Acid extraction produced SPC with more lipid than was obtained by ethanol extraction. Toasted soy flour and flakes had similar sensory properties, as did the SPC prepared from them.     

Soybean protein flavor components: A review

This review on the flavor components of soybean protein products examines primarily our studies on sensory evaluation of commercial flours, concentrates and isolates; on extraction of flavor components from soybean flakes with hexane-alcohol azeotropic mixtures; on the application of proteolytic enzymes to improve flavor; and on the effect of inactivating lipoxygenase on soy beverage flavor. Evidence indicates that enzymatic reactions affect the flavor of final products. Presumably lipoxygenase is a primary culprit and linolenic acid a primary precursor when soybeans are partially processed before destroying enzymatic activity. Presented at the AOCS Meeting, Atlantic City, October 1971. ARS, USDA.     

Evaluation of the nutritive value of soybean milk prepared with microwave-treated soybeans

Aqueous soybean extracts were prepared from beans, previously treated by microwaves to almost inactivate their lipoxygenase. These soy milks thus obtained were then nutritionally evaluated. All soy milks studied showed lower protein, fat, ash and total solids contents, as compared to a control milk prepared from soy beans not processed by microwaves. The milk obtained from soybeans with 8.7% initial moisture, treated by microwaves for 240 seconds, had the best total chemical score and the highest apparent methionine availability, as well as PER. The complete inactivation of the trypsin inhibitor activity was achieved with the milk prepared from soybeans with 56.8% initial moisture, subjected to microwave treatment for 180 seconds. On the other hand, the milk obtained from soybeans with 38.8% initial moisture, processed by microwaves for 180 seconds, resulted to have the highest, in vitro, protein digestibility.     

Fate of Phytic Acid in Producing Soy Protein Ingredients

Phytic acid (myo-inositol hexaphosphate) is present in soybeans and soy protein products at 1–2% dry matter. Phytate causes poor absorption of essential electrolytes and minerals, and binds to proteins and co-precipitates with isoelectric soy protein isolates. We determined how phytic acid partitioned during different procedures to prepare soy protein ingredients. Procedure and soybean variety significantly affected phytic acid content and recovery. High-sucrose/low-stachyose (HS/LS) soybeans contained significantly (P < 0.05) less phytate than did a typical variety of commodity soybeans (IA2020). In addition, phytate was more readily extracted from the commodity soybeans than from HS/LS soybeans. Among all procedures studied, ethanol-washed soy protein concentrate had the highest phytate contents and yields in the protein products for both soybean varieties (~80 mg/g and 99%, respectively). When protein extraction was carried out at room temperature the protein products had significantly lower phytate yields (60–78%) than when extraction was at 60 °C (80–99%). The protein products obtained from normal soybeans had significantly higher phytate contents than the same products made from HS/LS soybeans. When fractionating soy proteins, the glycinin-rich fraction contained significantly less phytate than the β-conglycinin fraction except for the fractionation procedure performed at room temperature instead of 4 °C.     

Enzymatic hydrolysis of extruded-expelled soy flour and resulting functional properties

Limited hydrolysis (4% degree of hydrolysis) of extruded-expelled soy flour protein (protein dispersibility index=21) that was poor in solubility and other functional properties was evaluated at pilot-plant scale (5 kg of flour) with two endopeptidases and one exopeptidase. Some hydrolysates were merely spray-dried whereas others were jet-cooked at 104°C for 19 s before spray-drying. Solubility, emulsification capacity and stability, foaming capacity and stability, apparent viscosity, and sensory attributes were then characterized. The type of protease used and hydrothermal cooking affected functional and sensory properties. Protein solubility modestly increased with hydrolysis and jet cooking, but emulsification capacity decreased on hydrolysis and was not restored with hydrothermal cooking. Emulsion stability improved in the endopeptidase hydrolysates, but not in the exopeptidase hydrolysates. The foaming capacities of the hydrolysates for both types of enzymes were better than for the unhydrolyzed control. Highly stable foams were obtained after hydrolyzing with exopeptidase and hydrothermal cooking. Ten percent protein hydrolysate dispersions showed large losses in consistency coefficient apparent viscosity, which increased significantly with hydrothermal cooking only for the unhydrolyzed control. Difference-from-control sensory evaluation indicated that both jet-cooked and non-jet-cooked enzyme hydrolysates were different from unhydrolyzed controls.     

Effects of maturation and storage on solubility,emulsion stability and gelation properties of isolated soy proteins

Solubility, emulsion stability and gelation of isolated soy proteins and their 7S and 11S fractions from three stages of seed maturity were studied. The pH-solubility profile was similar irrespective of maturation and six-month storage. The 11S protein was more soluble in the acidic pH range than the 7S protein. Oil-in-water emulsion stability of isolated soy protein from mature soybeans was higher than that from the immature ones. This is due to the fact that there was more 7S fraction in the mature soybeans, and 7S protein was found to form a more stable emulsion than that formed from 11S protein. The result suggests that isolated soy protein from mature soybeans would serve as a better emulsifying agent. Heat-induced soy protein gels became weaker as the soybeans became more mature. This can be attributed to the higher content in the immature soybeans of 11S fraction which gives a stronger gel than 7S fraction in the protein from immature soybeans.     

Phospholipid class and FA compositions of modified soybeans processed with two extraction methods

Soybean lecithin is used as an emulsifier in food, cosmetic, and pharmaceutical industries. The proportion of individual phospholipids (PL) and their FA composition may affect the functional properties of lecithin. In this research, lecithins recovered from four modified soybeans and one commodity soybean, which were processed by extrusion-expelling and conventional solvent extraction, were analyzed for proportion of PL class and FA composition. HPLC with an ELSD analysis demonstrated that the percentage of PC in extrusion-expelled lecithin was higher than in solvent-extracted lecithin, whereas the PE content was lower. GC analysis showed that FA compositions of the PL varied with soybean type. The oil extraction method did not significantly affect FA composition. Critical micelle concentration tested with a tensiometer showed differences among the lecithins.