Water Retention and Solubility of Soy Proteins and Corn Germ Proteins in a Model System

Response surface methodology was used to study water retention and protein solubility of soy flour (SF), concentrate (SC), and isolate (SI), and corn germ protein flour (CGPF). Water retention increased with pH (6 to 8) and incubation temperature (10–70°C), but not with increasing incubation time (10–30 min). SC had highest water retention per gTam, followed by CGPF, SF, and SI. Water retention in relation to protein content was higher in CGPF than in the three soy products. Protein solubility was significantly affected by pH and temperature of incubation. Protein solubility increased when pH (6 to 8) and incubation temperature increased (30–70°C) in all samples. SI had highest protein solubility, and CGPF had the lowest.     

COMPARATIVE STUDY OF CORN GERM AND SOY PROTEINS UTILIZATION IN COMMINUTED MEAT PRODUCTS1

Soy flour (SF), soy concentrate (SC) and corn germ protein flour (CGPF) at 3.5%, or 2% of soy isolate (SI) were incorporated in the formulations of frankfurters. There was no significant differences in proximate composition of frankfurters containing SF, SC. SI, and CGPF. Frankfurters formulated with high plant protein flour had lower cholesterol, and higher protein content than the all-meat control frankfurters. Control frankfurters had lower water holding capacity and higher cooking losses than those containing plant proteins. No significant differences (P < 0.05) were found in textural and color characteristics. Atypical aroma and flavor profiles increased in frankfurters with SF nd CGPF extension.     

Wheat Germ Protein Flour Solubility and Water Retention

The effects of pH and temperature on water retention (WR), protein solubility (PS), and total solubility (TS) of defatted wheat germ protein flour (WGPF) were studied in a model system. PS of WGPF was compared with those of corn germ protein flour (CGPF), soy flour (SF), nonfat dried milk (NFDM), and egg white powder (EWP) at 1–8%. WR increased with increase in pH from 4 to 8. Maximum WR occurred at 70°C, and slight variations were observed between 5 and 30°C. PS and TS increased with increases in pH and temperature. PS of proteins was in the order of NFDM > EWP > SF > CGPF=WGPF. The results showed the potential for usage of WGPF in comminuted meats, beef patties, breads, cakes, and cookies.     

COMPARATIVE STUDY OF SHELF-LIFE OF FRANKFURTERS CONTAINING PLANT PROTEIN ADDITIVES1

Soy flour (SF), soy concentrate (SC), soy isolate (SI) and corn germ protein flour (CGPF) were incorporated in frankfurters. The sensory analysis, chemical, and microbiological tests were conducted to investigate the effect of plant proteins on stability during vacuum-packaged storage. No significant difference in meaty aroma was found between all samples after 45 days storage. Atypical flavor and aroma of all samples, including the all-meat control increased (P < 0.05) after 45 days storage. A tendency was found of increase in atypical aroma and flavor with increase in total volatile nitrogen values and total psychrophiles during storage. Salty flavor increased with storage time in experimental samples, but juiciness decreased. Samples containing SF and SC had higher total volatile nitrogen than SI and CGPF containing samples at 2, 30 and 45 days of storage. No significant differences were found in TBA values between tested samples, except higher TBA values for SI containing samples. There was no significant difference among samples in total psychrophilic counts.     

Emulsifying Capacity and Emulsion Stability of Milk Proteins and Corn Germ Protein Flour

Comparative studies of emulsifying capacity (EC) and emulsion stability (ES) of corn germ protein flour (CGPF), nonfat dry milk (NFDM), whey protein concentrates (WPC), and sodium caseinate (SC) were carried out using response surface methodology. CGPF was an effective stabilizer of fat-protein-water emulsions. Tested proteins showed the following trend in EC and ES: SC > WPC = NFDM > CGPF. EC and ES increased with increased concentration of protein. No effect of incubation temperature on EC and ES of these proteins was detected. All protein samples showed a maximum EC at high pH (near 8.0) and 1.0% concentration under test conditions, except NFDM (about pH 7.0). Minimal pH effect on ES was found.     

Functionality of Wheat Germ Protein in Comminuted Meat Products as Compared with Corn Germ and Soy Proteins

Wheat germ protein flour (WGPF), corn germ protein flour (CGPF), and soy flour (SF) were used as additives at a level of 3.5% in comminuted meat products (CMP). Frankfurters with protein additives showed increased water-holding capacity and batter stability and decreased cooking loss. Improved viscosity and adhesiveness were observed with protein additives when the level of added water was constant. Protein additives also influenced textural and sensory properties of frankfurters. WGPF at a level of 3.5% was found similar to effects of SF and CGPF. WGPF is a potential nonmeat protein additive that can be utilized as an extender in CMP such as frankfurters and bologna.     

Fat, Soy and Carrageenan Effects on Sensory and Physical Characteristics of Ground Beef Patties

Sensory and physical characteristics of beef patties containing 20% fat, 8% fat, or 8% fat plus 20% soy protein isolate (SI), soy flour (SF), soy concentrate (SC), or a mixture (MIX) of carrageenan (0.5%), starch (0.5%), and phosphate (0.2%) were compared after 0, 4, 8, and 12 wks storage at - 18°C. MIX had higher Hunter a* values than other treatments. Cook loss was lowest for MIX and highest for all beef patties. Soy extenders decreased beefy flavor and increased off-flavor scores. Time in frozen storage increased off-flavor, rubbery texture, and TBA value, and decreased red color and Hunter b* value of ground beef patties. Quality may be lowered in frozen-stored high fat, or low-fat-soy extended beef patties.     

Foaming Properties of Selected Plant and Animal Proteins

The foaming properties of proteins are important in predicting their fnnctionality in aerated foods. In model aqueous systems, foam expansion (FE) and foam stability (FS) of commercial plant proteins, wheat germ protein flour (WGPF), corn germ protein flour (CGPF), and soy flour (SF), were compared with those of nonfat dried milk (NFDM) and egg white powder (EWP) at 1, 2, 4, 6, and 8% using one- and two-way analyses of variance. The effects of pH 4, 5, 6, 7, and 8 on FE and FS of WGPF were also measured. The highest overall FE and FS were obtained for EWP. Among plant proteins, FE and FS were maximum for CGPF and SF, respectively. FS was lowest for NFDM. Except for SF, FE and FS increased with increasing protein concentration. The FE and FS of WGPF were highest at pH 8, lowest at pH 7, and intermediate at pH 4–6.     

Single-Screw Extrusion of Defatted Soy Flour, Corn Starch and Raw Beef Blends

Effects of feed moisture, fat and corn starch levels and process temperature on physical properties of extrudates of defatted soy flour-amylose corn starch-raw beef blends were investigated using response surface methodology. Contour plots showed a convex curve of expansion ratio (ER) with moisture, concave curves of bulk density (BD) and shear-force (SF) with moisture, and concave cmves of SF with each of the four extrusion variables. Fat decreased ER and increased BD, whereas corn starch increased ER. Products with high ER and low BD and SF tended to have prominent air cells, continuous protein matrices, and smooth cell wall surfaces in scanning electron micrographs. The optimum extrusion conditions for minimal SF values, with 20% non-dehydrated beef muscle and varied amounts of defatted soy flour, were: 29.1% feed moisture; 2.96% feed fat; 22% feed corn starch; and 162°C process temperature.     

Differential Scanning Calorimetry Analysis of the Effects of Heat and Pressure on Protein Denaturation in Soy Flour Mixed with Various Types of Plasticizers

The effects of heat and pressure on protein denaturation in soy flour were explored by an experimental design that used pressure (atmospheric to 600 MPa), temperature (room to 90 °C), time (1 to 60 min), and type of aqueous plasticizer (NaCl, sucrose, betaine, and lactobionic acid (LBA)) as factors. When 50% (w/w) soy flour‐water paste was high hydrostatic pressure (HHP)‐treated for 20 min at 25 °C, the treatment at 200 MPa showed a small effect on denaturation of only the 7S soy globulin, but the treatment at 600 MPa showed a significant effect on denaturation of both the 7S and 11S soy globulins. The treatment at 60 °C showed a less‐pronounced effect on denaturation of the 11S globulin, even at 600 MPa, but that at 90 °C showed a similar extent of denaturation of the 11S globulin at 600 MPa to that at 25 °C. Chaotropic 2N NaCl, 50% sucrose‐, 50% betaine‐, or 50% LBA‐water solutions showed protective effects on protein denaturation during HHP treatment at 25 °C. Although LBA enhanced the extent of thermostability of soy protein less than did 2N NaCl, LBA exhibited better stabilization against pressure. The results from DSC analysis demonstrated that thermostable soy proteins were not always barostable.     

Influence of extrusion variables on the protein in vitro digestibility and protein solubility of extruded soy tarhana

Tarhana, supplemented with 150 g kg⁻¹ full‐fat soy flour, was extruded at different extrusion conditions (barrel temperature: 80–120°C; screw speed: 100–300 rpm; feed rate: 10–20 kg h⁻¹ ) using a twin‐screw extruder. The effect of extrusion conditions on the in vitro digestibility (PD) of the protein and protein solubility (PS) was investigated using response surface methodology. Regression equations for predicting PD and PS were developed. While the barrel temperature had a significant effect on PD (P <0.1), feed rate was the most significant variable on PS of the samples (P<0.05). Since the protein solubility should be high for the instant properties of extruded soy tarhana soup, it is suggested that soy tarhana should be extruded at low feed rates (ie high residence times) while high barrel temperatures should be achieved for the inactivation of antinutritional factors present in the soy flour. © 1999 Society of Chemical Industry     

Functionality of soymilk powder and its components in fresh soy bread

ABSTRACT:  The physicochemical changes upon addition of soymilk powder (SMP) to soy bread were investigated. Two-pound loaves of soy bread were produced with components (soluble fiber [SF], insoluble fiber [ISF], soy protein) that mimic those levels contributed by SMP. Soy flour and soy flour/SMP soy breads served as controls. The following were determined for all breads produced: physical properties (loaf volume, crust, and crumb color); chemical compositions (SF and ISF contents, protein and ash contents); and physicochemical properties (water activity, total moisture content by thermogravimetric analysis [TGA], "freezable" water [FW], "unfreezable" water [UFW] content by DSC, stiffness at 25 °C by dynamic mechanical analysis [DMA], and firmness with Instron testing machine). SMP contained significant amounts of SF aside from the ISF fraction and mostly denatured soy protein. SMP addition to soy bread formulation significantly decreased loaf volume with respect to control soy bread, which can be attributed to the ISF and SPI contents of this ingredient. Other effects of SMP were found to be lighter and yellowish crumb color, darker crust color, and increase in firmness, as well as no change in moisture content, FW and UFW contents, water activity, and stiffness parameters.     

Foaming Characteristics of Commercial Soy Protein Isolate as Influenced by Heat-Induced Aggregation

The foaming properties of commercial soy protein isolate subjected to different temperatures (20–90°C) were assessed. The results revealed that the solubility and surface hydrophobicity of a 5% (w/v) commercial soy protein isolate suspension increased with increasing temperature, which increased foaming capacity and reduced foaming stability. Commercial soy protein isolate supernatant (i.e., soluble fraction) had higher foaming capacity at low temperatures (20–50°C). A high content of commercial soy protein isolate soluble fraction increased foaming capacity but decreased foaming stability. The SDS-PAGE patterns and molecular weight distribution of commercial soy protein isolate revealed that there were soluble, large molecular weight aggregates (>400 kDa) formed mainly from A and B-11S polypeptides of commercial soy protein isolate via disulfide bonds. Additionally, some aggregates also dissociated into small polypeptides and subunits after heat treatment. Commercial soy protein isolate precipitate (i.e., insoluble fraction) had a high content of proline and cysteine, which probably contributed to the foaming stability of commercial soy protein isolate.     

Protein Solubility, Water Retention, and Fat Binding of Corn Germ Protein Flour Compared with Milk Proteins

Protein solubility (PS), water retention (WR), and fat binding (FB) of corn germ protein flour (CGPF), nonfat dry milk (NFDM), whey protein concentrate (WPC), and sodium caseinate (SC) were comparatively studied using response surface methodology. PS and WR of all samples were affected by pH except for WR of CGPF. PS and WR of all samples were not affected by incubation temperature except of WR of CGPF. Incubation temperature influenced FB of CGPF and WPC but not of NFDM and SC. Sample concentration significantly affected FB of all samples. CGPF was an effective protein source in terms of WR and FB. For FB, SC > CGPF = NFDM > WPC and for PS, WPC=NFDM=SC > CGPF.     

Development of protein-Rich Sorghum-Based Expanded Snacks Using Extrusion Technology

Sorghum is an important staple crop in semi-arid regions of Africa and India because of its drought tolerance. But low protein content and quality limit its widespread use. This project focused on developing sorghum-based extruded snacks. Results from preliminary lab-scale extrusion experiments were used to design a 2×5 factorial pilot-scale study. Two blends of sorghum flour and corn flour were prepared (6:1 and 5:2 w/w ratios) as the controls. Three different sources of protein—whey protein isolate, defatted soy flour, and mixed legume flour—were added to the sorghum/corn flour blends at 30%. A 50:50 blend of defatted soy flour and whey protein isolate was also added at 30% to the sorghum/corn flour blends. The resultant ten formulations were extruded on a pilot-scale twin-screw extruder to investigate the effects of sorghum/corn flour ratio and protein addition on product expansion, microstructure, mechanical properties, and sensory attributes. Expansion ratio of extruded product increased at the higher level of corn flour, and decreased with the incorporation of protein sources. Extrudates with defatted soy flour had a lower expansion ratio (5.3–5.4) than those with whey protein isolate (7.7–7.9), legume flour (7.1–9.9), or whey protein isolate-defatted soy flour (6.1–6.9). Extrudate microstructure, obtained by X-ray microtomography, corresponded well with expansion characteristics. Extrudates with defatted soy flour had the lowest cell diameter. Average crushing force (ranging from 40.9 to 154.87 N) was lower for extrudates with a higher level of corn flour. However, contrary to expectations, crushing force and crispness work both decreased with incorporation of protein sources. Consumer acceptability results showed that the addition of protein sources enhanced taste and overall acceptability of the extruded snacks, with the treatment sorghum/corn flour 5:2 and whey protein isolate-defatted soy flour as the protein source having significantly higher ratings than the other treatments.     

Characterization of Isoflavones in Membrane-processed Soy Protein Concentrate

ABSTRACT: Aqueous soy flour solutions (5% w/w) were treated for 3 h at 45 to 50 °C with Crystalzyme®, without enzyme at 45 to 50 °C, or blanched at 80 °C. Solutions were ultra‐ and dia‐filtered to produce membrane soy concentrates (MSC). Total isoflavones of MSCs were 3.02 mg/g, 3.12 mg/g, or 3.42 mg/g, respectively, on a dry weight basis. Membrane processing contributed to approximately 18, 15, or 8% decreases, respectively, in total isoflavones of MSCs compared with soy flour (3.71mg/g). This represents at least an 82% recovery. There was no significant difference in total isoflavone content in any MSC, however the profile of isoflavones as glucosides or aglycones changed with treatment conditions.     

Development of soy-based bread with acceptable sensory properties

Consumption of soy protein has been associated with benefits related to numerous areas of health. Due to the widespread consumption of bread, one means of contributing to the health of individuals is through the incorporation of soy protein into bread. To this end, soy flour (SF) or soy protein isolates (SPIs) in 20% and 12% substitution levels, respectively, were added to flour during bread manufacture. The developed breads were tested using a consumer panel for acceptability, using a refined white bread as a control. These data were compared to attribute intensity data collected by the trained panel to identify specific flavor and texture characteristics affecting liking. The sensory profile of the 20% SF bread was acceptable and comparable to the control bread, despite a significantly stronger beany flavor. No significant differences in sensory properties of the SF and control breads were detected by the trained panel for many sensory attributes. The SPI bread, however, had a sensory profile that was significantly more firm, dense, sour, beany, bitter, and astringent with a strong aftertaste in comparison to the wheat control bread. Consumer liking scores for the SPI bread was significantly lower than the liking of the control and the SF added bread. PRACTICAL APPLICATION: Many soy-enriched foods, while contributing positively to health, are considered unacceptable by consumers. This is due to negative sensory properties, such as beany, painty, and astringent notes, often perceived by consumers. This study provides information on the level of SF that can be included in bread in an amount that does not detract from consumer acceptability. This level also allows for a Food and Drug Administration (FDA) health claim to be made.     

Emulsifying Properties of Ethanol Soaked Soybean Flour

Soy flours prepared from soybeans soaked at 60°C for 6 hr in distilled water, 15% ethanol, or 0.1M NaHCO₃ in 15% ethanol were tested for their emulsifying capacity (EC) at pH 4.5, 6.5, and 9.0. At pH 4.5 and 6.5, there were no significant differences in EC among treatments; at pH 9.0, the EC was highest for soy flour from beans soaked in water, intermediate for flour from beans soaked in 15% ethanol, and lowest for flour from beans soaked in 0.1 M NaHCO₃ in 15% ethanol. The relationship between the amount of soluble protein and EC was inverse with EC decreasing sharply up to about 60 mg soluble protein/50 mL of flour dispersion. Photomicrographs of air incorporation during emulsion formation are presented.     

Relative Bioavailability of Dietary Iron from Three Processed Soy Products

The relative bioavailability of iron from soy flour (SF), freeze-dried soy beverage (SB) and soy concentrate (SC) was determined utilizing a hemoglobin repletion bioassay. Weanling male rats were fed a low iron depletion diet (3.5 ppm Fe) for 4 wk. For the next 2 wk groups of rats were fed repletion diets containing 0, 6, 12, or 18 ppm added iron from ferrous sulfate, SF, SB, or SC. Slope ratio analysis revealed that the relative iron bioavailabilities from SC (92%) and SF (81%) were not different from the reference standard, ferrous sulfate added to a casein-based diet, whereas that from SB (66%) was significantly less (P<0.01) than the inorganic source of iron. Analysis of results at individual iron levels suggested an iron bioavailability of SC>SF>SB.     

Formulation and Processing of a Heat Stable Calcium-fortified Soy Milk

Calcium-fortified soy milk (200 mg/100g) was formulated by adding water (85–90°C) full-fat soy flour (10%), sucrose (2.75%) and soy protein isolate (2.25%). Following homogenization, the blend was twice clarified and pasteurized at 65°C/30 min before refrigeration. Samples of the soy milk (45°C) were adjusted to pH 8 before adding calcium lactogluconate (1.55%) and varying amounts of sodium hexametaphosphate or potassium citrate. Samples with 1.25% potassium citrate the best heat stability. For successful calcium fortification, it is recommended to maintain a calcium-to-protein ratio < 38 mg/g and to use an appropriate sequestering agent at a molar ratio of 0.8/mole calcium.