Characterization of extruded-expelled soybean flours

In recent years there has been widespread growth in extruding-expelling (E-E) facilities for small-scale processing of soybeans. To compete in a highly competitive market, these E-E operations are looking for ways to optimize production of their oil and meal products for values to their customers. The objective of this study was to determine the ranges of residual oil contents and protein dispersibility indices (PDI) possible with E-E processing of soybeans. We also characterized the partially defatted meal for other factors important in food and feed applications. Residual oil and PDI values ranged from 4.7 to 12.7% and 12.5 to 69.1%, respectively. E-E conditions significantly influenced residual lipase, lipoxygenase (L1–L3), and trypsin inhibitor activities. Chemical compositions were different for whole, dehulled, and reduced-moisture soybeans, with dehulled soybeans tending to produce meals having higher residual oil contents at higher PDI values. It was possible to process soybeans with different characteristics (e.g., moisture content, whole, dehulled) to produce meals and flours with wide ranges of properties, providing E-E operators with opportunities to market value-added products.     

Effect of value-enhanced texturized soy protein on the sensory and cooking properties of beef patties

Texturized soy protein (TSP) originating from varieties of value-enhanced soybeans and commodity soybeans, which were processed by extrusion-expelling, were incorporated into ground-beef patties. The soybean varieties included high-cysteine, low-linolenic, lipoxygenase-null, high-sucrose, low-saturated-fat, and high-oleic. The lower the bulk density was, the better the water-holding capacity of TSP. Neither property was affected by the protein dispersibility index or residual oil of the low-fat soy flours from which the TSP was prepared. All extruded-expelled processed flours from value-enhanced soybeans made acceptable TSP. The high-sucrose soybeans produced TSP with higher expansion and improved water-holding capacity. There were no differences in cooking properties or proximate compositions of patties for all treatments. Inside and outside colors were darker for the TSP-extended patties than for the all-beef control, and there was little difference among soybean varieties. The patties containing TSP had significantly more soy flavor and were harder than the all-beef control patties. Some TSP treatments produced more tender and less cohesive cooked patties than did the all-beef control.     

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.     

Preparation of soy protein concentrate and isolate from extruded-expelled soybean meals

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.     

Functional properties of low-fat soy flour produced by an extrusion-expelling system

Low-fat soy flour (LFSF) obtained by extrusion-expelling processing was investigated for functional properties. Flours with the following various levels of protein dispersibility indexes (PDI) and residual oil (RO) contents were investigated: “high” 67±4/10.4±1, “mid” 42±3/7.4±2, and “low” 14±5/6.5±0. The solubility of all three LFSF was minimal at pH 4.0 and increased at more alkaline and acidic pH levels. Water-holding capacity (WHC) increased with a decrease in PDI and RO content, whereas fat-binding capacity (FBC) decreased. Foaming stability increased as PDI and RO increased, with significant differences between all LFSF samples. Emulsification capacity (EC) was measured at three pH levels (5.5, 6.7, and 8.0). At each pH level, the “low” samples showed the least EC compared to the “mid” and “high” samples, with no significan difference between the “mid” and “high” samples at pH 6.7 and 8.0. Emulsification stability and activity decreased from low LFSF to high LFSF. This study showed that in general low LFSF was less functional than the other flours tested and there was no significant difference in the functionality of mid- and high-LFSF samples.     

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 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.     

Soy flour dispersibility and performance as wood adhesive

Soy flour adhesives using polyamidoamine-epichlorohydrin (PAE) resin as the curing agent are being used commercially to make bonded wood products. The original studies on the soy-PAE adhesives used purified soy protein isolate, but the much lower cost soy flour is now used commercially. We examined the performance of commercially available soy flours that have their proteins either mainly in their native (90 protein dispersibility index (PDI)) or denatured (70 and 20 PDI) states. We expected that the more native state soy proteins with their better dispersibility would provide better adhesion to wood surfaces and enhanced reaction with PAE resin. Small-scale wood bonding tests showed that neither of these effects was observed without and with a low level of PAE. In these tests, the solids content of the soy formulations had a large influence on adhesive viscosity but little influence on bond strength. Additionally, little difference was observed in any of the adhesive or viscosity properties between the soy flours having either a 0.152 or 0.075?mm (100 or 200 mesh) particle size.     

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.     

The protein quality of commercial products of texturized soybean protein and meat mixtures

The purpose of the present study was to evaluate the protein quality of eight commercial samples of texturized soybean protein (TSP) collected in the food markets of various Latin American countries. The study also included experiments designed to establish the limiting amino acids in those products, and studies to evaluate the process of texturization by extrusion cooking. Finally, experiments were also carried out to evaluate the effect of replacement of meat by TSP as well as the supplementary value of the latter to tortilla flour. The eight samples were characterized for their functional properties and protein quality. The results obtained indicate that all samples were different in density, water absorption, and nitrogen solubility. Likewise, all samples were different in their lysine, methionine and threonine content, with PER values ranging from 1.75 to 2.31. Protein quality standard value is 2.3. The amino acid supplementation studies showed a positive significant response to methionine addition, particularly in those products exhibiting low PER values. The addition of both lysine and threonine to the methionine-supplemented product, increased PER significantly. The data also demonstrated that replacement of more than 25% of meat protein by TSP protein decreased protein quality of the product, even when a TSP with an accepted protein quality value was used. This product was also found to supplement the quality of tortilla protein. Finally, it was established that the texturization process did not reduce the protein quality of soybean protein. Based on these results, it is concluded that the variability in the protein quality measured in the eight TSP samples was due to the initial quality of the soy flour texturized, which was already damaged before texturization. For this reason, it is recommended that Latin American countries establish TSP quality standards when this product is used as a protein extender for meat, and that appropriate systems be implemented for the quality control of such products.     

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.     

Functional Properties of Soy Protein Isolates Prepared from Gas-Supported Screw-Pressed Soybean Meal

White flakes (WFs) are obtained from dehulled flaked soybeans by extracting oil with hexane and flash- or downdraft-desolventizing the (defatted) flakes, and WFs are the normal feedstock used to produce soy protein ingredients. Gas-supported screw pressing (GSSP) is a new oilseed crushing technology in which traditional screw pressing is combined with injecting high-pressure CO₂, thereby producing hexane-free, low-fat, high-PDI soybean meal. The objectives of the present study were to evaluate yields, compositions, and functional properties of soy protein isolates (SPIs) produced from GSSP soybean meal and to compare these properties to those of SPIs produced from WFs. GSSP meals produced SPIs in significantly higher yields (59.7–63.1% vs. 51.6–61.1%), with greater free (0.05–0.40%) and bound fat (3.70–4.92%) contents than did WFs. There were no significant differences in protein contents of the SPI; all exceeded 90% protein content (db). SPIs prepared from GSSP meals had similar or slightly lower water-solubilities compared to SPIs prepared from WFs. SPIs prepared from GSSP meals had higher water-holding capacities and viscosities, and significantly better emulsifying and fat-binding properties compared to SPIs prepared from WFs. SPIs prepared from WFs had significantly better foaming properties compared to SPIs prepared from GSSP meals, which were attributed to the lower fat contents of SPIs prepared from WFs.     

Sensory characteristics and oxidative stability of soybean oil and flour extracted with aqueous isopropyl alcohol

Soybean flakes extracted with hexane or aqueous isopropyl alcohol (85%, 87.7% and 90.5% IPA by weight) were processed to toasted flours and the miscellas to refined soybean oils. These products were evaluated for sensory characteristics and oxidative stability. Sensory analyses of initial oils and flours indicated good quality products. Initial flavor scores of IPA-extracted oils and flours were not significantly different from those of hexane-extracted oil and flour. Flour samples aged at 49 C for 1 mo and 37 C for 3 mo were rated slightly lower in flavor score than the initial flours. Flavor scores of oils decreased after aging but remained acceptable. Oils extracted with aqueous IPA concentrations of 85% and 90.5% received significantly lower scores than oils extracted with hexane or 87.7% IPA after 8 hr of fluorescent light exposure. Oxidative stability measured by the induction of weight increases of the oils during aging was similar. Residual solvent flavors were slightly detectable in unaged IPA flours and in those aged 3 mo at 37 C.     

Soy flour in European-type bread

Effect of soy flour, soy protein concentrate, and isolate on dough and loaf properties of breads produced from flour, yeast, salt, and water with no shortening or added improvers was investigated. Wheat flour, rye flour, and mixtures of the two were included in the studies. Three wheat flours, varying in baking quality and extraction, ash content 0.65 and 0.80%, were used; 1.5, 3, and 5% soy products, flour basis, were added. Water absorption increased 3.8–4.7% at the 3% soy level and 6.1–7.3% at the 5% level of soy product addition. Dough development time and stability were increased and dough softening reduced. Dough gassing power increased ca. 7–25%. By using a shorter proofing time, more intensive mixing, and the sponge dough process, loaves only slightly smaller in volume than the control were obtained at the 3% soy level. Panel evaluations scored bread highest with 1.5 or 3% soy flour and that with 3 or 5% soy protein concentrate as lowest, but acceptable. Use of 2% lard as shortening, or 2% lard plus emulsifier, produced soy breads of excellent quality and ca. 25% higher loaf volume than controls.     

Jet cooking dramatically improves the wet strength of soy adhesives

The impact of jet cooking on shear strength of soy-and-water adhesives was investigated to understand the higher shear strength of commercial soy protein isolates compared to soy flours. Soy flour-based wood adhesives are appealing because of their bio-based content, low formaldehyde emission, and low cost, but their commercial application is limited by low wet cohesive strength. Previous researchers proposed that the process of jet cooking (steam injection with high turbulence followed by rapid cooling) was responsible for the high (~3 MPa) wet shear strength of adhesives made with commercially produced soy protein isolate, using the ASTM D 7998 test. In this work, we show that jet cooking did dramatically increase the wet strength of laboratory-produced, native-state soy protein isolate from 0.6 to 3 MPa, a strength similar to many commercial isolates. Jet cooking was far less effective at developing wet strength of soy flours, but greatly increased the viscosity of virtually all our soy materials. We hypothesize that the benefits of jet cooking are primarily a result of nonequilibrium protein aggregation states because subsequent wet autoclaving of jet cooked soy proteins dramatically decreased wet strength. The dramatic differences in adhesive properties between commercial soy protein isolates and soy flours suggests that the common practice of using results obtained with commercial isolates to predict the performance of soy flour adhesives is inappropriate.     

Effects of flour sources on acrylamide formation and oil uptake in fried batters

Food batters were formulated using flours of long-grain rice, waxy rice, wheat, or corn. Acrylamide and oil analyses were conducted for the flour and the corresponding fried batter. During frying, the formation of acrylamide ranged from 82 ng/g for the long-grain rice batter to 263 ng/g for the corn batter. Oil uptake ranged from 21.4% for the long-grain rice batter to 47.3% for the wheat batter. The incorporation of 5% pregelatinized rice flour and 1.5–3.0% milk as functional additives into the long-grain rice batter only slightly increased the acrylamide and oil contents.     

Adhesive qualities of soybean protein-based foamed plywood glues

The potential of soy protein-based plywood glues for foam extrusion was evaluated. Standard glue mixes containing the soy flours Honeysoy 90, ISU-CCUR, Nutrisoy 7B, and defatted Soyafluff, and the soy concentrates Arcon F and Procon 2000 showed excellent foaming and adhesive qualities but did not have the ability to refoam. To improve refoaming capability, the formulations were modified by increasing the quantities of soy flour or concentrate so that they provided 3.48 g protein/100 g of glue mix. This was the amount of protein contributed by animal blood when it was used as the extender in the standard formulation for foamed glue. All the modified glues containing soy flour or concentrate had good refoaming properties and adhesive strengths that were at least equal to that of the control glue. Simple cost analysis also indicated that when soy flour was used, the modified formulations were cheaper to produce than the current blood-based glue.     

Limited hydrolysis of soy proteins with endo- and exoproteases

Changes in the native state and functional properties of soy protein achieved by limited proteolysis of soy flour were investigated. Different enzyme-to-substrate ratios (E/S) were used to obtain low (3–5%) and medium (5–10%) degrees of hydrolysis (DH). Six protease preparations (three with predominately exopeptidase activities and three with predominately endopeptidase activities) were evaluated, and their effects on solubility, emulsification capacity, SDS-PAGE profiles, and denaturation enthalpies were characterized. Endoproteases (Multifect^® Neutral, Protex^? 6L, and Multifect^® P-3000) and exoproteases (Fungal Protease Concentrate, Experimental Fungal Protease #1, and Experimental Fungal Protease #2) yielded similar increases in soy protein solubility. The modifications to the soy peptide profile were similar for the three exoprotease mixtures at a 1% E/S ratio, whereas the extent of hydrolysis with Protex^? 6L was more pronounced than with the two other endoproteases (Multifect^® Neutral and Multifect^® P-3000). The emulsification capacity of protease-modified soy flour declined regardless of DH and enzyme type (exo- or endoprotease). After hydrolysis to >4% DH, denaturation enthalpies of glycinin and β-conglycinin decreased significantly, whereas hydrolysis to lower DH did not affect these values.     

Separating Oil from Aqueous Extraction Fractions of Soybean

Previous research has shown that enzyme-assisted aqueous extraction processing (EAEP) extracts 88–90% of the total soybean oil from extruded full-fat soy flakes into the aqueous media, which is distributed as cream (oil-in-water emulsion), skim, and free oil. In the present work, a simple separatory funnel procedure was effective in separating aqueous skim, cream and free oil fractions allowing mass balances and extraction and recovery efficiencies to be determined. The procedure was used to separate and compare liquid fractions extracted from full-fat soy flour and extruded full-fat soy flakes. EAEP extracted more oil from the extruded full-fat soy flakes, and yielded more free oil from the resulting cream compared to unextruded full-fat soy flour. Dry matter partitioning between fractions was similar for the two procedures. Mean oil droplet sizes in the cream and skim fractions were larger for EAEP of extruded flakes compared to non-enzymatic AEP of unextruded flour (45 vs. 20 μm for cream; 13 vs. 5 μm for skim) making the emulsions from EAEP of extruded flakes less stable. All major soy protein subunits were present in the cream fractions, as well as other fractions, from both processes. The cream could be broken using phospholipase treatments and 70–80% of total oil in the extruded full-fat flakes was recovered using EAEP and a phospholipase de-emulsification procedure.     

Enzymatic modification of soy protein concentrates by fungal and bacterial proteases

Solubility, foaming capacity and foam stability of denatured soy protein concentrate obtained from toasted flour were improved by proteolysis with fungal or bacterial proteases. Emulsifying capacity was unchanged, but emulsion stability decreased; bacterial protease highly improved oil absorption. Also, the bacterial protease was able to solubilize more protein and gave products which foamed more than those obtained with the fungal enzyme. However, the stabilizing properties of the bacterial modified soy protein concentrate at the air/water or oil/water interface were inferior. By limited hydrolysis up to degree of hydrolysis 10% most functional properties were improved without greatly reducing emulsion stability and water absorption.