Soy and corn flour precooked with microwaves and its use in the preparation of arepas]

Unhusked corn and soy grits were used as raw material, with a particle size ranging between 10 and 20 mesh (ASTM). The results obtained in this study reveal that microwave heating is effective in destroying the antinutritional factors present in soybeans. The trypsin inhibitor activity, in effect, was reduced to a 76% inactivation. The hemagglutinating titer was labile to the heating process, showing values of +8 to +3 for the full-fat soy flour and precooked soy flour, respectively. The quality of soy protein was measured by the protein efficiency ratio (PER) showing values of 2.63 for the precooked soy flour, and 2.46 to 2.21 for the precooked corn:soy blends (70:30 and 50:50). These uncooked blends present values of 1.17 and 1.04. The enriched corn:soy flour had a PER value of 1.60, in comparison to casein (PER = 2.90). The microwave heating improved the digestibility of the soy flour and blends. There were no significant differences (P less than or equal to 0.05) in relation to the functionality of the precooked flour and mixtures. The results obtained revealed that the applied process markedly improve the functional properties and nutritional value of the enriched flour, and of the "arepas" prepared from them.     

Perm-Inspired High-Performance Soy Protein Isolate and Chicken Feather Keratin-Based Wood Adhesive without External Crosslinker

Crosslinking modification can effectively improve the water resistance of soy protein isolate (SPI) adhesive, but it often depends on petroleum-based reagents, violating the concept of green environmental protection. Here, inspired by the breaking and recombination of the disulfide bond in the perm process, a high-performance wood adhesive is prepared by incorporation of SPI (modified by sodium sulfite to cleave the disulfide bonds of protein chains) and feather keratin (FK, extracted from waste chicken feathers by breaking the disulfide bond) without using any other crosslinkers. The crosslinking reaction occurs by disulfide bonds derived from the sulfhydryl group of FK and SPI. Thus the wet shear strength of the SPI/FK-20 adhesive is improved from 0.57 to 1.18 MPa, an increment of 107%. This study provides a green strategy to prepare high-performance protein-based adhesive from the waste products-chicken feathers, which will contribute to the development of the environmentally friendly wood adhesive industry.     

Physicochemical Properties of Soy Protein Adhesives Obtained by In Situ Sodium Bisulfite Modification During Acid Precipitation

Successful industrial applications of soy protein adhesives require high adhesion strength and low viscosity at high solid protein concentration. This study examined the effects of β-conglycinin (7S) and glycinin (11S) ratios on the physicochemical properties of soy protein adhesives. Soy protein adhesives with various 7S/11S ratios were extracted from soy flour slurry modified with sodium bisulfite using the acid precipitation method, which is based on the different solubilities of 7S and 11S globulins. Seven glycinin-rich soy protein fractions and six β-conglycinin-rich soy protein fractions were obtained. The external morphology of the samples changed from the viscous cohesive phase to the clay-like phase without cohesiveness. The viscous cohesive samples had good flowability and good water resistance with a wet adhesion strength of 2.0–2.8 MPa. They were stable for up to several months without phase separation at room temperature. Based on the results, we suggest that proper protein–protein interaction, hydration capacity (glycinin-rich soy protein fractions), and certain ratios of 7S and 11S (β-conglycinin rich soy protein fractions) in the soy protein sample are crucial to continuous protein phase formation. Hydrogen bonding, electrostatic forces, and hydrophobic interactions are involved in maintaining the protein viscous cohesive network, whereas disulfide bonds do not exert significant effects. This study describes a new way to investigate viscous cohesive soy protein systems with high solid protein content, thus alleviating the disadvantages of traditional methods for studying the adhesive properties of soy protein isolates, which tend to have poor water resistance, low solid contents, and short storage life.     

In Vitro Hemagglutination Activity of β-Conglycinin and Glycinin Fractions and Feeding Study of Non-Thermal Treated Soy Protein

The purpose of this study was to use non-thermal means to reduce hemagglutination activities of soy proteins and thereby improve the feeding quality of the resulting treated proteins. Two storage proteins in soybeans, β-conglycinin- and glycinin-rich fractions, were shown to have in vitro hemagglutination activity. The activity of the β-conglycinin fraction was not reduced by hydrolysis with single proteases, but the hemagglutination activity was fully eliminated by multiple enzyme treatments if it was first heated. However, the activity of glycinin fraction was not fully eliminated by either single or multiple enzyme hydrolysis. Pepsin and pancreatin hydrolysis, which was effective in eliminating hemagglutination activity of soybean agglutinin (SBA), was used to generate a feed material for in vivo evaluation of nutritional quality of soy white flake (SWF). SBA in reducing agent-treated then pepsin–pancreatin treated SWF was deactivated on analytical scale experiment, but not in the feed material. The treated SWF feed material did not improve chick growth performance compared with the raw SWF. However, chicks did not show enlargement of the pancreas or the intestines compared to the raw SWF feed, indicating deactivation of anti-nutritional factors. The trypsin inhibitors seemed to play a more important role than the hemagglutination activity of soy proteins in this nutritional test.     

Improvement of the water resistance of soybean protein-based wood adhesive by a thermo-chemical treatment approach

In order to extend the applications of wood composites and products bonded by soybean protein adhesive from interior to exterior fields of application, this study proposes a novel approach for improving the water resistance of soybean protein-based wood adhesives using thermo-chemical treatment of soybean protein. The soybean protein formed stable three-dimensional networks due to repolymerization or self-crosslinking during thermo-chemical treatment, confirmed by both increases in the water-insoluble content of the treated soybean protein and the improved hydrothermal-aged wet bond strength of the resulting soybean protein adhesive. Thermo-chemical treatment in the presence of 1 wt% sodium sulfite (which cleaves disulfide bonds) and 1 wt% sodium dodecyl sulfate (which destroys the hydrophobic interactions of proteins) released active groups buried within the globular structure of soybean protein via unfolding. This release both promoted the repolymerization of the soybean protein molecules and exposed more active sites for effective crosslinking by the post-added crosslinker EMPA. Plywood bonded by the optimal soybean protein adhesive possessed a good hydrothermal-aged bond strength of 1.22 MPa, exceeding the value required for structural use according to the JIS K6806-2003 commercial standard.     

Chemical inactivation of soybean trypsin inhibitors

Sodium metabisulfite and glutaraldehyde were used alone and in combination to inactive Kunitz trypsin inhibitor (TI) in model systems and TI in lyophilized alkaline soy meal extract. Reaction of glutaraldehyde (0.1 to 3.0%, based on total volume of the reaction mixture) with Kunitz TI (3 mg/ml buffer) at 25 C resulted in 60–75% reduction in activity. Treatment of soy meal extract containing 0.08 mg TI/mg at a concentration of 10 mg sample/ml buffer under similar reaction conditions reduced TI activity only 40%, however. A reaction temperature of 75 C had little additional effect on TI inactivation. On the other hand, sodium metabisulfite (0.05 to 1.0 mM) inactivated >96% Kunitz TI within 1 hr at 75 C and 75–94% of the TI in soy meal extract. The combination of 0.6 mM metabisulfite and 0.5% glutaraldehyde at 75 C inactivated >99% Kunitz TI, and combination of 0.6 mM metabisulfite and up to 3% glutaraldehyde inactivated 88% of TI in soy meal extract vs 91% inactivation with metabisulfite alone. Thus, metabisulfite plus glutaraldehyde inactivated Kunitz TI better than either one alone, while bisulfite alone best inactivated TI in soy meal extract. When the reactions were performed at neutral pH, protein solubility of 80% or better was retained. Presented in part at the 77th annual meeting of the American Oil Chemists’ Society, Honolulu, May 1986.     

Chemical constituents, in vitro protein digestibility, and presence of antinutritional substances in amaranth grains

The chemical composition, content of antinutritional factors, and the in vitro protein digestibility of grains of the pseudo-cereal Amaranthus were analyzed. The plants were grown in Brazil (without fertilizer), Puerto Rico (100 kg N/ha), and California (200 kg N/ha). The seed analysis gave the following values (%DM): 14.4 - 16.9 protein (N X 6.25), 4.8 - 6.8 fat, 2.5 - 3.9 ash, and 2.3 - 2.9 crude fiber. The trypsin inhibitors, phenolics and saponine contents were low, and the phytohemagglutinin activity, fairly low. The in vitro protein digestibility was 61 - 76%. Digestibility was not correlated to the analyzed proximal composition nor to the antinutritional factors. The grain composition indicates a food value equivalent to that of conventional food grains.     

Rat serum proteins and nutritional quality of full-fat soy flour: application of response surface methodology

A study was conducted to diagnose nutritional status by determining total serum proteins and electrophoretic patterns of protein reserves. Serum proteins are affected by privation of several amino acids. The purpose of the present research work was to evaluate protein quality of full-fat soy flour (FFSF) obtained from various hydrothermal processes by measuring changes in the serum proteins of Wistar rats. Response surface methodology was used as tool to determine the optimum conditions of hydrothermal process. The mean values of total serum proteins for the experimental group fed treated FFSF, were beta 0 = 5.12 +/- 0.13 g%; for the untreated FFSF group, C1 = 4.60 +/- 0.28 g%, and for the control group fed casein, C2 = 5.63 +/- 0.33 g%. All these values differ at 5% of significance (p less than or equal to 0.05). Results confirmed that treated full-fat soy flour is nutritionally superior to untreated FFSF, but not to casein.     

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.     

Evaluation of fish silage prepared by microbiological route as a proteinic supplement in diets for fattening chickens]

A bioassay in broilers was carried out during a six-week period, to evaluate, as a protein source, the quality of fish silage produced by microbiological means and to compare it with that of fish flour and soybean flour. A total of 28 broilers of the Cross by Cross strain were used, sexed and assigned at random. Additionally, the fish silage was subjected to moisture (8.1%), ash (18.4%), protein (59.5%), fat (7.55%), carbohydrates (6.47%), and pH (4.2) determinations for its inclusion in the diets formulation. The results obtained did not permit establishment of significant differences between the weight increments presented by chicks fed with fish flour, and those fed with fish silage. Nevertheless, the food conversion index of the chicks consuming the diet prepared with fish silage proved to be better that the conversion index of the diet prepared with fish and soy flours. No lesions in the organs of the animals studied were observed, and the sensory trials indicated that chicks fed with the fish silage did not present differences with those commercially acquired.     

Nutritional and stability evaluation during storage of blends extruded with sorghum

Binary sorghum:soy (70:30) and ternary sorghum:corn:soy (30:40:30) blends using high and low tannin content dehulled sorghum were extruded. The effectiveness of heat treatment was determined by protein dispersion index (PDI) and ureasic activity (delta PH), indicating that proteins were denatured and antinutritional factors reduced. The nutritional evaluation supported the fact that samples were adequately treated, giving ternary blends true digestibility (TD) and biological values (BV) similar to milk casein. Blend stabilities, expressed as peroxide index (PI), revealed a low lipid oxidation rate during the first seven months, and were acceptable up to a year of storage. Extrudates with incorporated sorghum cover protein and energy demands of the growing infant, and provide a high nutritional value and long-life product.     

Development of a pilot plant process for the preparation of a soy trypsin inhibitor concentrate

A pilot-plant procedure was developed to prepare a soy trypsin inhibitor (TI) concentrate in sufficient quantities to support a lifetime (2-yr) feeding trial in which diets containing varying amounts of TI would be fed to rats to assess the physiological effects on the pancreas and other organs. Starting with water dispersions of commercial defatted soy flour, separation of TI (MW<21,500) from non-TI protein (MW 180,000–350,000) by virtue of their MW difference was attempted using ultrafiltration techniques but was not successful. However, good separation was obtained when selective acid precipitation coupled with “salting in” of the TI with 0.1 N sodium chloride was employed. Low MW components were separated successfully by ultrafiltration using a 1,000 MW cutoff membrane. The final soy TI concentrate obtained by freeze drying exhibited a 9-fold increase in TI activity. Presented at the AOCS Annual Meeting, Dallas, May 1984.     

Biological and physiological factors in soybeans

There are limitations to which one is justified in drawing broad generalizations concerning the diverse biological and physiological effects of soy protein products. Nevertheless, there appear to be two distinct situations: (A.) Proper heat treatment exerts a beneficial effect upon the nutritive value of whole soybeans, full-fat and defatted meal. Associated with proper heating is inactivation of trypsin inhibitor and other heat-labile factors and conversion of raw refractory proteins to forms that are more readily digested. (B.) Moist heat also has a beneficial effect upon the nutritive value of soy protein isolates. However, a deficiency of certain essential nutrients and the interaction of phytic acid with protein, vitamins, and minerals during processing are the primary factors responsible for the poor nutritive value of soy isolates. Occasionally mineral deficiency symptoms do occur in animals fed soybean meal. It is a misnomer to refer to the growth-inhibiting and pancreatic hypertrophic properties as a “toxic” effect since both properties are reversible. Modern analytical techniques should be used to reinvestigate the relationship between phytic acid and availability of minerals and vitamins in soy protein isolate diets. Research also is needed to determine more accurately vitamin and mineral contents of soy protein isolates and the availability of vitamins and minerals in soy protein concentrates. Breeding soybean varieties genetically deficient in antinutritional and nonflatulent factors does not appear promising. More research is needed to determine whether fermentation and enzyme processes can be used to prepare flatulent-free soy products. Minor factors to be considered in assessing the nutritive value of soy products include a weak goitrogen present in soybeans, and a very low estrogenic activity. ARS, USDA.     

Protein–Protein Interactions in High Moisture-Extruded Meat Analogs and Heat-Induced Soy Protein Gels

Two commercial soy protein isolates were made into fibrous meat analogs by high moisture extrusion or into gels by heating and cooling, at varying concentrations and/or temperatures. Protein–protein interactions by extrusion or gelation were investigated through protein solubility studies of raw and finished products. All samples except for extrudates exhibited similar patterns of solubility in four selected extractants. Phosphate buffer (PB) extracted the least amount of protein. Addition of dithiothreitol (DTT) to PB improved protein solubility, indicating the presence of disulfide bonds. PB + Urea and PB + Urea + DTT gave the highest and almost equal amount of extractable proteins from all samples, except for the extrudates from which protein could not be extracted effectively by PB + Urea, implying that disulfide bonding was more pronounced during extrusion than gelation. The results support our hypothesis that soy protein gels and extrudates both have the same types of chemical bonds, namely covalent disulfide bonds and non-covalent interactions. It is the relative proportion of each type of bonds in their structures that differentiates the two with respect to reversibility and structure rigidity. In forming protein gels during heat-induced gelation, non-covalent bonds play a dominant role over disulfide bonds; whereas for forming the fibrous structure of protein extrudates, non-covalent bonds and covalent disulfide bonds are both important.     

Effects of soy proteins containing trypsin inhibitors in long term feeding studies in rats

Pancreatic hypertrophy that occurs in rats fed raw soy flour containing about 1200 mg tripsin inhibitor (TI)/100 g diet was reversed by switching the rats to control diets or to diets containing 30% toasted defatted soy flour. No pancreatic hypertrophy occurs in rats fed commercial, edible grade soy flours, concentrate or isolate from time of weaning to adulthood (ca. 300 days). TI content of the soy diets ranged from 178–420 mg/100 g. Except for pancreas enlargement in rats fed raw soy flour, gross and microscopic examination of pancreata revealed no abnormalities. The gross appearance of heart, kidney, spleen, and liver was normal. Soy flour, protein concentrate, and protein isolate in a formulated corn-soy diet provided optimum growth and maintained body weight only if supplemented with vitamin B-12 in long term feeding studies with rats. In the absence of such supplementation, rats fed soy diets initially grew at a rate equal to or greater than those fed a comparable corn-casein control diet; but, with continued feeding for ca. 300 days, body weight of rats fed the casein control was significantly greater than that of the soy flour-fed rats. Those fed soy isolate ceased to grow; and rats fed soy concentrate lost weight. No significant differences were found in organ weights between groups fed soy products and casein, except for increased kidney, liver, and testes weights relative to body weight with the group fed soy concentrate. Supplementation of the soy diets with vitamin B₁₂ stimulated growth to the greatest extent, calcium pantothenate or riboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the soy diets with vitamin B₁₂ stimulated growth to the greatest extent, calcium pantothenate or roboflavin had an intermediate effect, other vitamins had little or no effect; whereas a complete mineral mix was detrimental. Supplementation of the control diet was without effect. The dietary protein level in these diets was 20%, with casein or soy protein representing 75% of total protein. When fed continuously to rats from weaning to adulthood, properly processed soy protein products, when balanced with essential nutrients, can provide growth comparable to corn-casein diets.     

Effect of extrusion on the activity of anti-nutritional factors and in vitro digestibility of protein and starch in flours of Canavalia ensiformis

The effect of the extrusion (155 degrees C, 20% moisture, screw speed 75 rpm, feed speed 205 g min-1) on antinutritional factors of Canavalia ensiformis was studied. In vitro protein and starch digestibilities were assessed. The extrusion not affect protein content (23%) in the flours, but significantly (P < 0.01) decrease moisture content. The protein digestibility values were improved from 57.5 to 89.5%, these values were lower than casein (98.19%). The digestibility of starch values were improved from 37.7 to 53%. The protease inhibitors activities (trypsin and chymotrypsin) and alpha-amylase inhibitor activity were reduced by 95%. The haemagglutinating activity was eliminated as result of the high temperature employed during the extrusion process. The canavanine content in the flours were not affect by the treatment of extrusion.     

Significance of soya trypsin inhibitors in nutrition

Although recent evidence clearly indicates that trypsin inhibitors (TI) and low protein digestibility are the major factors responsible for the pancreatic hypertrophic and growth inhibitory effects of raw soybeans, there was uncertainty regarding the biological threshold level of TI at which these biological effects occur. To obtain such data, dehulled defatted flakes (10% dietary protein) containing graded levels of TI were fed to weanling rats for 4 weeks in two feeding trials. Normal pancreas weights were obtained in rats fed samples in which only 54 to 68% of the original TI of raw soya flour was inactivated. In partially toasted flakes with a nitrogen digestibility value of 77%, the average tolerance level of dietary TI activity that did not cause pancreatic hypertrophy was calculated to be 385 mg TI/100 g diet. TI tolerance level at maximum nitrogen digestibility of 85%, which did not significantly lower weight gain and reduce protein efficiencey ratios, was 260 mg TI/100 g diet. Continuous ingestion of high levels of TI (459 mg TI/100 g diet) in a 20% protein diet for 215 days did not inhibit growth nor cause pancreatic hypertrophy when compared to rats fed toasted soya flour diets. Pancreatic hypertrophy that occurs in rats fed raw soya diets containing up to about 1300 mg TI/100 g diet for 35 days was reversed by switching the rats to control diets or to 30% toasted flour. In long-term feeding studies, no pancreatic hypertrophy occurred in rats fed commercial edible-grade soya flour, concentrate, or isolate from time of weaning to adulthood (ca. 300 to 330 days). TI content of the diets ranged from 178 to 310 mg/100 g diet. Microscopic examination of the pancreas revealed no abnormalities. Gross appearances of heart, kidney, spleen and liver were normal. In long-term feeding, vitamin B-12 supplements were needed to provide optimum growth and to maintain body weight. Results of numerous chemical analyses, relatively short-term human tests and long-term animal feeding studies indicate that with proper control of manufacturing processes, soya protein products can be produced that, in mixed diets, have protein nutritional value approaching that of animal protein.     

Functional properties of hydrothermally cooked soy protein products

The effects of hydrothermal cooking on the functional properties of defatted soy flour, aqueous alcohol washed soy protein concentrate, and soy protein isolate were determined in samples that were treated at 154°C by infusing steam under pressure for 11, 19, 30, and 42 s, and then spray dried. Hydrothermal cooking increased the nitrogen solubility index (NSI) of the concentrate from 15 to 56% and altered the solubility profile from a flat profile to one more typical of native soy protein. Hydrothermal cooking also improved foaming and emulsifying properties of the concentrate. For isolate, hydrothermal cooking also improved NSI and foaming and emulsifying properties, although the improvements were less dramatic than with concentrate. NSI and emulsifying properties of the flour were improved by some processing conditions, but foaming properties were not improved by hydrothermal cooking. Dramatically increased protein solubility of concentrate and modestly improved protein solubilities of flour and isolate by hydrothermal cooking, which will also inactivate trypsin inhibitors and microorganisms, have considerable practical significance to protein ingredient manufacturers and those who use these ingredients in foods and industrial products.     

Extraction, partial characterization and nutritional aspects of proteins from Carioca 80 bean (Phaseolus vulgaris L.)

Extraction, fractionation and characterization by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of proteins from Carioca 80 beans (Phaseolus vulgaris) were performed at three pH values (2.5, 8.0 and 9.0). Extraction at pH 7.0 proved to be more efficient and, after dialysis, produced a better separation of the albumin and globulin fractions. Relative mobility of the main protein in the globulin fractions occurred between 0.30 and 0.40, and dissociation was observed when the pH was increased. The two most representative bands gave molecular weights of 35,400 and 76,900, while in regard to the trypsin inhibitor, three bands gave 28,800, 22,500 and 18,300. Pepsin and pancreatin in vitro digestibility rendered values of 33.43% and 62.63% for whole flour and for protein precipitated at pH 4.5, respectively. The content of available methionine found, of 1.36 g/16 g N, appears to be high in relation to that of other bean varieties.     

Effect of drying methods on molecular properties and functionalities of disulfide bond-cleaved soy proteins

Effects of drying methods on hydrophobicity, solubility, water hydration capacity, viscosity, and adhesive strength of soy protein isolates treated with Na₂SO₃ (disulfide bond-cleaving agent) were investigated. Treatment with 0.1 M Na₂SO₃ resulted in 28% decrease in disulfide linkages in soy proteins. While hydrophobicity and solubility increased, waterholding capacity of soy proteins decreased due to the treatment. Spray-dried product had higher hydrophobicity, solubility, water hydration capacity, and viscosity compared to freeze-dried product. Adhesive strength on wood increased due to modification; however, the drying process had no significant effect on this property. Viscosities of spray-dried product, freeze-dried product, and unmodified soy proteins were 2,200, 100, and 240 cP, respectively. Fluorescence spectra of spray-dried and freezedried products indicated a partial folding of molecules around tryptophan. High-performance liquid chromatographic elution profiles showed no significant differences in molecular sizes of unfolded molecules of spray-dried and freeze-dried proteins.