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Soy Proteins
Abstract
This chapter presents an overview of soybean proteins; it includes world soybean production, distribution, and utilization. Special emphasis has been given to important physicochemical properties of soybean proteins, examples of laboratory and industrial preparations of soybean protein ingredients, their functional properties, and applications in foods. The chapter also highlights soybean proteins composition. Most recently reported modifications on protein structure through new technologies and chemical and enzymatic reactions are presented. Health benefits of soybean proteins and their principal allergens and inhibitors are also reviewed.
... Adding value to the protein components of the meal after oil extraction is foreseen to increase the profitability of farmers and processing industries (Wang, Wu, & Bernard, 2014). For example, soy protein extracted from defatted soy meal has well established feed (Denbow, Ravindran, Kornegay, et al., 1995;Van Nhiem, Berg, Kjos, Trach, & Tuan, 2013), food (Herrero, Carmona, Cofrades, & Jiménez-Colmenero, 2008;Kasran, Cui, & Goff, 2013;Li, Yeh, & Fan, 2007;Mojica, Dia, & Mejia, 2015;Suppavorasatit, De Mejia, & Cadwallader, 2011), and nonfood uses such as biofilms (Mojica et al., 2015), plastics (Kumar, Choudhary, Mishra, Varma, & Mattiason, 2002) and adhesives (Damodaran & Zhu, 2016;Kumar et al., 2002). However, canola meal is restricted to the feed industries, mostly in the ruminant feed formulations (Newkirk, 2015). ...
... Adding value to the protein components of the meal after oil extraction is foreseen to increase the profitability of farmers and processing industries (Wang, Wu, & Bernard, 2014). For example, soy protein extracted from defatted soy meal has well established feed (Denbow, Ravindran, Kornegay, et al., 1995;Van Nhiem, Berg, Kjos, Trach, & Tuan, 2013), food (Herrero, Carmona, Cofrades, & Jiménez-Colmenero, 2008;Kasran, Cui, & Goff, 2013;Li, Yeh, & Fan, 2007;Mojica, Dia, & Mejia, 2015;Suppavorasatit, De Mejia, & Cadwallader, 2011), and nonfood uses such as biofilms (Mojica et al., 2015), plastics (Kumar, Choudhary, Mishra, Varma, & Mattiason, 2002) and adhesives (Damodaran & Zhu, 2016;Kumar et al., 2002). However, canola meal is restricted to the feed industries, mostly in the ruminant feed formulations (Newkirk, 2015). ...
Canola is second only to soy with regard to production volume, but the meal after extraction has limited value‐added applications, apart from its use as feed. Emerging interest in the meal is to develop nonfood applications such as delivery systems, adhesives, or plastics. This review critically evaluates the recent progress in research on the applications of value‐added canola protein, especially on nonfood applications such as plastics, films, packaging materials, adhesives, and drug delivery applications, and presents the perspectives on the future directions of canola protein utilization. Canola protein with suitable surface activity, gelation, interaction with other polymers, gastric and heat resistance, and biodegradability has the ability to form carriers to encapsulate, protect, and deliver bioactives/drugs. Canola‐based adhesives prepared by denaturation, chemical modification, cross‐linking, blending with synthetic resins, and nanomaterial addition show promising results in applications as adhesives. Canola protein‐based plastic films are mostly prepared by solution casting with the aid of plasticizers to improve the ductility of the protein network through increasing the mobility of protein chains; incorporation of cross‐linking agents could also increase protein–protein interactions toward the formation of stronger films. Canola proteins show wide potential for use as an encapsulant in delivery systems, as an adhesive, and as a plastic; however, further research is needed to improve the performance and to make it cost effective.
... Gels made from glycinin are harder than gels Bekhit et al. (2016) from β-conglycinin due to differences in the structure of these proteins. Glycinin is a hexamer with a molecular weight of 300-380 kDa while β-conglycinin is a glycoprotein with a molecular weight of 150-200 kDa (Mojica, Dia, & Mejía, 2015). Effects of PEF on the functional properties of soy protein isolate (SPI) reported by Li and Chen (2006) showed an increase in the degree of denaturation and aggregation and, consequently, a decrease in protein solubility (above 40 kV/cm or 432 μs), emulsifying capacity (above 30 kV/cm or 144 μs), foaming capacity (above 35 kV/cm or 432 μs), and surface hydrophobicity (above 30 kV/cm or 288 μs). ...
To assess the tangible advantages of pulsed electric fields (PEF) as alternative preservation technology, or to explore its use for improvement of functionality and healthiness of foods and ingredients or creating novel food structures, knowledge is needed regarding their impact on key food constituents such as proteins, lipids, carbohydrates, bioactive and flavor compounds, as well as on product microstructure. The successful application of the technology requires also that sensorial attributes of the PEF-treated food meet the consumer expectations and acceptance. In this chapter, studies on the impact of PEF on these key issues will be discussed, in both animal- and plant-based foods.
Breastmilk is the optimal source of nutrition for infants. However, in circumstances where breastfeeding is not possible or feasible, infant formula provides an essential alternative to fulfil the nutritional requirements of the developing infant. Traditionally, the manufacture of infant formula has involved utilisation of bovine milk as a base ingredient, formulated with other nutrients and bioactive ingredients to closely match the composition of human breastmilk. While it is the most widely available type of formula on the market, bovine-based infant formula is not suitable for all infants, and therefore alternatives such as those based on caprine milk, soy and rice protein are becoming increasingly available. This review provides a detailed examination of the composition of infant formula prepared from bovine milk, caprine milk, soy, and rice protein sources. Available literature on nutrient bio-accessibility and aspects of protein functionality relevant to infant formula is discussed.
Plant proteins constitute as one of the major sources of food proteins for the human body. In addition, they provide biological functions such as antioxidant and immunomodulation associated with naturally occurring and process-derived peptides that can alter signaling pathways promoting overall health. This chapter provides an overview on some of the plant sources of bioactive peptides. In addition, the procedures employed in the isolation, production, and purification of these bioactive peptides are discussed. Throughout the chapter, examples of plant-derived bioactive peptides and their bioactive properties are given. Discussion on the mechanistic insights as well as opportunities and challenges in the use of plant-derived peptides in human health studies are presented. Future studies answering these opportunities and challenges are needed to move forward the utilization of plant-derived peptides for the promotion of human health.
Hypercholesterolemia represents one key pathophysiological factor predisposing to increasing risk of developing cardiovascular disease worldwide. Controlling plasma cholesterol levels and other metabolic risk factors is of paramount importance to prevent the overall burden of disease emerging from cardiovascular-disease-related morbidity and mortality. Dietary cholesterol undergoes micellization and absorption in the small intestine, transport via blood, and uptake in the liver. An important amount of cholesterol originates from hepatic synthesis, and is secreted by the liver into bile together with bile acids (BA) and phospholipids, with all forming micelles and vesicles. In clinical medicine, dietary recommendations play a key role together with pharmacological interventions to counteract the adverse effects of chronic hypercholesterolemia. Bioactive compounds may also be part of initial dietary plans. Specifically, soybean contains proteins and peptides with biological activity on plasma cholesterol levels and this property makes soy proteins a functional food. Here, we discuss how soy proteins modulate lipid metabolism and reduce plasma cholesterol concentrations in humans, with potential outcomes in improving metabolic- and dyslipidemia-related conditions.
The lipoxygenases (LOX) are a family of non-heme iron-containing dioxygenases which catalyze the stereospecific insertion of molecular oxygen into arachidonic acid, leading to hydroxy derivatives as end products. In this work, we studied the behavior of seven isoflavans on 15-soybean lipoxygenases (15-sLOX), comparing them with the known inhibitors quercetin and 3, 4-dihydroxybenzoic acid. Four of the seven investigated isoflavans showed IC50 values smaller than 50 µM , being more potent than quercetin or 3, 4-dihydroxybenzoic acid. Besides a catecholic pattern, the presence of an aromatic ring B seems to confer additional activity to these compounds, a result which was rationalized by docking studies of these isoflavanss into the enzyme binding site.
The content of the antinutrient, phytic acid, of soy protein was analyzed during their extraction and purification by a series of ultrafiltration and diafiltration steps. The phosphorus content of the extracts was used as an indication of their phytic acid content and their ash content as an indication of their mineral content. The extraction of soy proteins was conducted by using a 23 factorial experimental design, pH (7.5 or 9), solvent (0.06 M KCl or water), and temperature (25 °C or 50 °C). The most promising extraction conditions were 0.06 M KCl/pH 9.0/25 °C for the lowest phosphorus to protein ratio (12.2 ± 0.1 mg P/g protein) and H2O/pH 9.0/50 °C for the combination of low phosphorus to protein ratio and the lowest ash content (13.9 ± 1.2 mg P/g protein, 9.6 ± 0.8% w/w ash content). After extraction, soy proteins were purified by sequential ultrafiltration (UF) with a volume concentration ratio (VCR) of 5 and diafiltration (DF) with volume diafiltration ratio (VD) of 4. Extracts were purified with no pH adjustment or with pH adjustment to 6.5 between the UF and the DF steps. The extraction conditions 0.06 M KCl/pH 9.0/25 °C and the purification conditions UF pH 9.0/DF pH 6.5 showed the lowest phosphorus to protein ratio (4.4 ± 0.3 mg P/g protein) and reduced membrane fouling when compared to extraction conditions with water.
Lunasin is a chemopreventive peptide present in soybean and other plant sources. The high cost involved in obtaining synthetic lunasin limits its application in chemopreventive and nutritional interventions. The objective of this study was to isolate, purify and characterise lunasin from defatted soybean flour and determine its in vitro anti-inflammatory activity using RAW 264.7 macrophages. Isolation and purification was achieved by ion-exchange chromatography, ultrafiltration and size exclusion chromatography. The identity of lunasin was established by Western blot, HPLC, MALDI-TOF and LC/MS-MS. The results showed that lunasin eluted from a DEAE anion exchange column at 0.15M NaCl, and after 1.5 void volumes from size exclusion chromatography. Fractions from both chromatographic techniques consistently showed three peptides with positive immunoreactivity against lunasin mouse monoclonal antibody corresponding to 5, 8 and 14kDa. LC/MS-MS analysis of the three immunoreactive peptides showed that 5 and 14kDa bands contained the lunasin epitope, RGDDDDDD DDD while 8kDa band showed high homology with 2S soy albumin, a lunasin precursor.This is the first report on the potential anti-inflammatory activity of lunasin. Treatment of RAW 264.7 macrophage with 100μM lunasin decreased the production of NO (92.6±0.8%) and PGE2 (10.1±4.5%), and the expression of iNOS (27.8±2.1%) and COX-2 (41.4±16.7%). We concluded that combination of ion-exchange chromatography, ultrafiltration and size exclusion chromatography represents a feasible process for the production of purified lunasin, which was also found to inhibit COX-2/PGE2 and iNOS/NO pathways. This newly discovered property of lunasin might contribute to the suppression of inflammation in vivo.
The soybean (Glycine max (L.) Merr.) is an economically important leguminous crop for feed, oil, and soyfood products. It contains about 40% protein and 20% oil in the seed and, in the international trade markets, is ranked number one in oil production (48%) among the major oil seed crops. Despite its economic importance, the genetic base of soybean cultivars is extremely narrow. The indigenous cultivars and landraces in East Asia are on the verge of extinction, because farmers are now growing high yielding soybean cultivars. The exotic germplasm, enriched with genes for abiotic and biotic stresses, has not been fully exploited by soybean breeders. Mutation breeding has improved the fatty acids of the soybeans and has produced soybeans tolerant to herbicides. By using recombinant DNA technology, Monsanto has produced stable glyphosate tolerant soybean lines known as 'Round Up Ready' soybean. DuPont is producing transgenic soybean lines with improved fatty acids content. The feasibility of developing hybrid soybeans is still an open question.Key words: soybean, Glycine spp., exotic germplasm, mutation, interspecific hybridization, biotechnology, hybrid soybeans.
The nucleotide sequence of cDNA encoding the glycinin A2Bla subunit from var. Shirotsurunoko was determined and compared with that in the case of var. Bonminori. The comparison showed six nucleotide substitutions in the coding sequence, one of which results in one amino acid replacement, and three in the 3’-noncoding region. These differences indicate the occurrence of polymorphism of the glycinin A2Bla subunit gene between the cultivars. The present data together with the previous results indicating the polymorphism of the AlaBlb subunit gene [(Utsumi et al., J. Agric. Food Chem., 35, 210 (1987)] suggest that the polymorphism is a general property of glycinin subunit genes. The expression of cDNAs encoding the A2Bla and AlaBlb subunits was examined. The results obtained in both in vivo- and in vitro-expression experiments indicate that the resultant products were readily degraded. © 1987, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.
Multilayer film composed of a soy protein isolate (SPI) inner layer and poly(lactide) (PLA) outer layers were prepared by a simple solvent casting method in order to exploit the advantageous properties of both film materials. Tensile strength and elongation at break of the multilayer film were 17.0 ± 0.3 MPa and 176.9 ± 27.9%, respectively. Especially the tensile strength of the multilayer film increased more than 5-fold compared with that of the SPI film. The mechanical properties of the multilayer film were comparable to those of low-density polyethylene (LDPE) or high-density polyethylene (HDPE) films. The lamination of PLA layers on SPI film also resulted in desirable gas barrier properties of the film with both low water vapor permeability (WVP) of PLA and low oxygen permeability (OP) of SPI. The WVP of the multilayer film [(6.66 ± 0.27) × 10-14 kg·m/m2·s·Pa] decreased 40-fold compared with that of the SPI film, and the OP of the multilayer film [(2.40 ± 0.24) × 10-18 m3·m/m2·s·Pa] decreased more than 26-fold compared with that of the PLA film. In addition, the multilayer film had adequate water resistance over short periods. All of these property improvements may be attributed to the strong adhesion between both polymers used, i.e., SPI and PLA.
The nucleotide sequence of cDNA encoding the glycinin A2B1a subunit from var. Shirotsurunoko was determined and compared with that in the case of var. Bonminori. The comparison showed six nucleotide substitutions in the coding sequence, one of which results in one amino acid replacement, and three in the 3'-noncoding region. These differences indicate the occurrence of polymorphism of the glycinin A2B1a subunit gene between the cultivars. The present data together with the previous results indicating the polymorphism of the A1aB1b subunit gene [(Utsumi et al., J. Agric. Food Chem., 35, 210 (1987)] suggest that the polymorphism is a general property of glycinin subunit genes. The expression of cDNAs encoding the A2B1a and A1aB1b subunits was examined. The results obtained in both in vivo- and in vitro-expression experiments indicate that the resultant products were readily degraded.
Glycinin and β-conglycinin have unique functionality characteristics that contribute important properties in soy foods and soy ingredients. Limited functionality data have been published for glycinin and β-conglycinin fractions produced in pilot-scale quantities. Protein extraction conditions were previously optimized for our pilot-scale fractionation process to maximize protein solubilization and subsequent product recovery. Glycinin, β-conglycinin, and intermediate (mixture of glycinin and β-conglycinin) fractions were prepared using optimized-process (OP) extraction conditions (10:1 water-to-flake ratio, 45°C) and previous conditions termed Wu process (WP) (15:1, 20°C). Viscosity, solubility, gelling, foaming, emulsification capacity, and emulsification activity and stability of the fractionated proteins, and soy protein isolate (SPI) produced from the same defatted soy white flakes were compared to evaluate functional properties of these different protein fractions. Differential scanning calorimetry, sodium dodecylsulfate-polyacrylamide gel electrophoresis, and surface hydrophobicity data were used to interpret functionality differences. OP β-conglycinin had more glycinin contamination than did the WP β-conglycinin. OP and WP solubility profiles were each similar for respective glycinin and β-conglycinin fractions. Emulsification activities and stabilities were higher for OP β-conglycinin and OP intermediate fractions compared with respective WP fractions. β-Conglycinin and SPI emulsification capacities (ECs) mirrored solubility profile, whereas glycinin ECs did not. OP glycinin had a higher foaming capacity than WP glycinin. OP and WP intermediate fraction apparent viscosities trended higher than those of other protein fractions. β-Conglycinin dispersions at pH 3 and 7 produced firm gels at 80°C, whereas glycinin dispersions formed weaker gels at 99°C and did not gel at 80°C.
Soybean, an important source of food proteins, has received increasing interest from the public because of its reported health benefits. These health benefits are attributed to its components which include isoflavones, saponins, proteins and peptides. Lunasin, Bowman-Birk inhibitor, Kunitz trypsin inhibitor and β-conglycinin are some of the biologically active peptides and proteins found in soybean. This chapter provides a comprehensive review on the biological properties and the recently used techniques in the analysis and characterization of soy bioactive peptides. Also, the basic chemistry of each of the bioactive peptides is discussed. In sum, bioactive peptides can be accurately identified and quantified using different techniques and conditions which are important in order to accurately characterize their individual biological activities.
This chapter discusses the role of urease in plant cells. Urease is important for efficient nitrogen assimilation. Considerable amounts of plant nitrogen flow through urea (urease substrate), which can be recycled only by urease action. This recapture can have significant quality impact on protein rich crops. It appears to have an important role in germination of protein poor seeds. The urease substrate urea is derived from arginine and ureides. Arginine is the richest nitrogen repository among the amino acids of seed storage proteins. On the other hand, ureides are not only significant sources of nitrogen in nucleic acid turnover but are also a predominant transport from of fixed nitrogen in soybean and other tropical legumes. Urease-negative plants accumulate substantial, nonutilizable urea in both maternal and embryonic tissue. During germination of urease-negative seeds, further urea accumulates as a dead end in nitrogen metabolism. Abundant seed ureases, such as, Sumner's jackbean urease, may play a chemical defense role. All of the ureases, both from bacteria and plants, resemble each other in primary structure and in their requirement for accessory genes.
Consumed for centuries in East Asia, soybeans have recently become popular in Western markets for the health benefits of their storage proteins, particularly due to the claim that they help reduce the risk of heart disease. This chapter investigates these storage proteins, which mainly consist of β-conglycinin and glycinin, and discusses their molecular structures, functions, relationships and subunits. The physicochemical properties and physiological functions of soy proteins as a food ingredient are examined and their nutritive value are investigated. Methods of improving soybean functionality and flavour through conventional breeding and genetic engineering are also considered.
Soybeans (Glycine max [L.] Merril) constitute about 50% of the total oilseed crops of the world. The overall production was about 11.8 million tons in 1985, and the major producers were U.S., 56%; Brazil, 18%; People's Republic of China, 10%; and Argentina, 6%. Some information about the trends in world soybean production is given in Table 1. Soybeans were brought to the U.S. aboard a clipper ship by James Meese from China in 1804, but the cultivation of soybeans only started about 1900 for fodder rather than beans. The British started crushing soybeans obtained from Manchuria at Hull in 1908. In the U.S., Pacific Oil Mills, in Seattle, Washington, did the first crushing of soybeans imported from Manchuria in 1911, and sold soybean meal for animal feeding. North Carolina was the site of one of the earliest efforts to crush locally grown soybeans at the Elizabeth City Oil & Fertilizer Co., Elizabeth City, in 1912. Windish (1981) described the efforts of pioneers in popularizing soybean cultivation. Hybrid cultivars were developed from imported cultivars during the 1940's. Since then, tremendous progress has been made and further selection and hybridization efforts have continued. Soybean meal has currently become the most important source of plant proteins in the diets of monogastric animals, especially for poultry in the U.S. The multinatio nal corporations involved in promoting poultry production all over the world using their hybrid chicks recommend similar dietary patterns relying heavily on soybean meal.
Glycerol-plasticized soy protein isolate (SPI) based films were prepared by compression with the aim to obtain environmentally friendly materials for packaging applications. Previously to the hot-pressed step, the protein was dispersed in water, the pH was fixed to values higher, lower and at the isoelectric point of SPI (pH = 4.6), and the dispersion was freeze-dried. The effect of pH on physico-chemical properties has been explained using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermo-gravimetric analysis (TGA). The changes observed by FTIR in the intensity of the bands corresponding to the amide group showed that pH affected protein–glycerol interactions. Apart from pH effect, heat and pressure also affected the grade of denaturation of SPI shown by the disappearance of the DSC peak corresponding to 7S globulin. Mechanical properties were also evaluated and related to pH and storage time. Both tensile strength and elongation at break are higher at basic pHs, when the unfolding of protein seems to be optimum in order to interact with the plasticizer. Mechanical properties remained invariable after having been stored under specific conditions for two months. Preparation of SPI-based biofilms processed at different pHs by compression is an innovative study in this field, in which the most employed technique to prepare films has been casting.
The effects of low-frequency (20 kHz) ultrasonication at varying power (200, 400 or 600 W) and time (15 or 30 min) on functional and structural properties of reconstituted soy protein isolate (SPI) dispersions were examined. Ultrasonic treatments reduced both the storage modulus and loss modulus of SPI dispersions and formed more viscous SPI dispersions (fluid character). Moreover, ultrasound treatment significantly decreased the consistency coefficients and increased the flow behaviour index of SPI dispersions. Scanning electron microscopy of lyophilized ultrasonicated SPI showed different microstructure with larger aggregates compared to non-treated SPI. No significant change was observed in the protein electrophoretic patterns by SDS-PAGE. However, free sulfhydryl content, surface hydrophobicity and protein solubility of SPI dispersions were all increased with ultrasonic treatment. Differences in solubility profiles in the presence versus absence of denaturing (0.5% sodium dodecyl sulphate and 6 M urea) and reducing (mercaptoethanol) agents suggested a decrease in non-covalent interactions of SPI in dispersion after ultrasonic treatment. Secondary structure analysis by circular dichroism indicated lower α-helix and random coil in SPI treated at lower power, in contrast to higher α-helix and lower β-sheet in SPI treated with higher power (600 W). In conclusion, under the conditions investigated in this study, ultrasonic treatment resulted in partial unfolding and reduction of intermolecular interactions as demonstrated by increases in free sulfhydryl groups and surface hydrophobicity, leading to improved solubility and fluid character of SPI dispersions, while larger aggregates of ultrasonic-treated SPI in the dry state were formed after lyophilization.
In this paper we reported the rheological and microstructural properties of a kind of novel cold, gel-like soy protein isolate (SPI) emulsions obtained by means of microfluidization. These gel-like emulsions were formed from untreated and preheated (95 °C, 15 min) SPI at a protein concentration of 6% (w/v), and various oil volume fractions (Φ; 0.2–0.6) and NaCl concentrations (0–500 mM). The rheological properties and microstructure were characterized using steady viscosity and dynamic oscillatory measurements, as well as confocal laser scanning microscopy (CLSM). The characteristics (e.g. droplet size distribution and creaming stability) of the emulsions, formed at lower protein concentrations (e.g. 0.5–4.0%), were also characterized, aiming to reveal the mechanism of the gel-like network formation. The dynamic oscillatory data indicated that both untreated and preheated SPI emulsions exhibited gel-like rheological properties, but the specific apparent viscosity (η) and storage modulus (G′) of the latter ones were much higher at a comparable Φ. Both η and G′ progressively increased upon Φ increasing, indicating enhanced inter-droplet interactions. At a given Φ value (0.3), increasing NaCl concentration progressively increased η and G′ of the preheated SPI emulsions, indicating the importance of electrostatic screening for the gel-like network formation. The CLSM analyses confirmed formation of the gel-like network, mainly composed of aggregated oil droplets, which was closely dependent on the Φ and NaCl concentration. The gel-like network was formed by bridging flocculation of oil droplets, mainly through inter-droplet hydrophobic interactions between the proteins adsorbed at the interface. These results suggested that soy proteins exhibit excellent potential to produce cold, gel-like emulsions, especially through a heat pretreatment followed by microfluidization, which might be of vital importance for the development of soy protein-based formulations, especially as carriers for heat-labile ingredients with health effects.
Soy whey protein isolate (SWPI)–fenugreek gum conjugates were prepared by Maillard type reactions in a controlled dry state condition (60 °C, 75% relative humidity for 3 days) to improve emulsification properties. SDS-PAGE electropherogram showed that conjugation formed high molecular weight products with the disappearance of 7S fraction, acidic subunits of the 11S fractions and protein band at molecular weight 21 and 24 kDa. However, the amount of protein at molecular weight 30 kDa remained unchanged. The protein solubility of SWPI–fenugreek gum conjugates improved as compared to SWPI and SWPI–fenugreek gum non-conjugated mixture especially at isoelectric point of protein when assessed in the pH range 3–8 at 22 °C. In comparison to SWPI, fenugreek gum and non-conjugated SWPI–fenugreek gum, SWPI–fenugreek gum conjugates had better emulsifying properties near the isoelectric pH of protein. Emulsification at near the isoelectric pH of protein was chosen as at this pH the proteins are prone to aggregate, which could destabilize the emulsion. Heating solutions of the conjugates prior to emulsification further improved their emulsification properties. The conjugates also showed a better emulsifying property at high salt concentration as compared to SWPI alone.
The protein concentration dependence on the rheological properties of acid-induced gels formed with unheated and heated soy protein-stabilized emulsions (UHSPE and HSPE) was investigated at different acidification temperatures. Pre-heat treatment on soy protein solutions resulted in a higher storage modulus (G′) and a shorter gelation time (tgel) of acid-induced emulsion gels. A maximum in tan δ was observed in the UHSPE gels but no maximum was detected in the HSPE gels. Increasing the acidification temperature decreased the G′ and tgel. The dependence of the G′ on the protein concentration (c) can be scaled with a power law: G′ ∼ cA. The exponent (A) increased with pre-heat treatment and acidification temperature. The experimental data.fitted the fractal scaling model (G′ ∼ φA) and the simple time- scaling model above very well for the acid-induced soy protein-stabilized HSPE gels with varying oil volume fraction. The large deformation and fracture properties were significantly affected by soy protein concentration, pre-heat treatment, acidification temperature and volume fraction of oil droplets (p < 0.05).
To strengthen the network of bio-nanocomposite hydrogels, layered montmorillonite (MMT) nanoclay was intercalated by surface-coating with soy protein (SP) before mixing with 6% w/v SP for cross-linking by microbial transglutaminase (mTGase). Dynamic rheology was performed to study variables of NaCl and mTGase concentrations, with and without 1% w/v MMT. Without mTGase, the highest storage modulus (G′) was observed at 100 mM for samples without MMT, which was twice of the highest G′ for samples with MMT, at 200 mM NaCl. With mTGase, a shorter gelation time and a stronger hydrogel were observed at a higher enzyme level. Overall, the non-gelling 6% w/v SP dispersion was transformed to a hydrogel with G′ of 1099 Pa after addition of 100 mM NaCl and 1% SP-coated MMT and treatments by 6.25 U/g-protein mTGase for 2 h and heating/cooling steps. The integration of surface-coating and mTGase cross-linking is promising to improve properties of the nanocomposite system.
To strengthen interactions in bio-nanocomposite systems, montmorillonite (MMT) was intercalated by surface-coating with soy protein before being incorporated within soy protein dispersions for cross-linking by glutaraldehyde (GA). Dynamic small strain tests were utilized as a non-destructive method to reveal the improvement of network structure in the bio-nanocomposite system. The storage modulus (G′) and loss modulus (G″) gradually increased with increasing GA concentration during isothermal treatment at 23, 60 and 90 °C. The incorporation of intercalated MMT resulted in an order of magnitude increase in the moduli. The moduli were higher at pH 5.5 than those at pH 6.5 and 10.0. At a GA concentration equal to 10 g/100 g mass of soy protein, G′ and G″ in the absence of MMT increased with an increase in temperature, while those in the presence of intercalated MMT showed the opposite trend due to restructuring of aggregated MMT. The present results confirmed that the mechanical strength of bio-nanocomposite systems can be significantly improved by first intercalating MMT with protein and subsequently cross-linking with the continuous phase protein molecules. The established chemical cross-linking method and conditions can be beneficial for preparing bio-nanocomposite materials with enhanced mechanical properties.
Soybean (Glycine max[L.] Merr.) is one of the principle field crops grown in the United States. From a crop with no significant economic value at the turn of this century, soybeans have made remarkable strides in U.S. agriculture, claiming the stature of the number two U.S. cash crop. Soybean is an important source of edible vegetable oil and protein throughout the world and is used in a multitude of food and industrial applications. Even though soybeans are a rich source of protein for livestock and humans, the nutritional quality of soybean proteins is not optimal. Some of the problems associated with soybean proteins include (1) presence of anti-nutritional factors such as trypsin inhibitor, (2) undesirable beany flavor, (3) elicitation of allergic reactions in susceptible individuals, (4) poor digestibility of soybean proteins, and (5) deficiency in sulfur-containing amino acids. As a consequence, concerted efforts are underway to improve the overall nutritive value of soybean proteins by both classical plant breeding and molecular biological approaches. This review article summarizes the current knowledge on the biochemistry and molecular biology of soybean seed storage proteins. Recent advances in the genetic improvement of amino acid composition of seed storage proteins are highlighted. The review also includes some recent achievements in modifying soybean seed composition.
The modification of soy protein isolate (SPI) with different amounts of a naturally occurring cross-linking agent (genipin, Gen) and glycerol used as plasticizer was carried out in this work. The films yielded were cast from heated and alkaline aqueous solution of SPI, glycerol and Gen and then dried in an oven. Total soluble matter, water vapor permeability and mechanical properties were improved by adding small amounts of Gen. These properties were not significantly affected (P⩾0.05) by additions exceeding 2.5% (w/w of SPI). The opacity and cross-linking degree were linearly increased with the addition of Gen, whereas the swelling ratios in water were decreased. All the films were submitted to degradation under indoor soil burial conditions and the weight loss of the films was measured at different times. This study revealed that the film biodegradation time can be controlled or modified from at least 14 to 33days. The tests performed showed the potential of Gen to improve the SPI film properties, in which the possibility of employing such new films as biodegradable food packaging was raised.
Kunitz soybean trypsin inhibitor (KSTI) is hydrolyzed during seed germination to yield amino acids needed to support initial seedling growth. The type of KSTI from Glycine max (L.) Merrill cv. Toyokomachi is KSTI-Ti-b The KSTI-Ti-b from 4-day-old post-germination cotyledons (KSTI-Ti-b) has 3 or 4 amino acid residues cleaved off at the C-terminus. This KSTI modification is important to understand the mechanism of degradation in seed reserve proteins by proteases. Protease KI also cleaves amino acid residues at the C-terminus of KSTI but it removes 5 amino acid residues. Therefore, we presumed the KSTI-Ti-b was produced by a protease other than protease KI. In this study, the protease TI responsible for cleavage of KSTI-Ti-b at the C-terminus was purified. The enzyme was estimated to have a molecular mass of 33 kDa from its mobility on SDS-PAGE gels. The N-terminal amino acid sequence of the purified protease TI corresponded to amino acids Phe-73 to Phe-92 of both thiol protease isoforms A and B from the soybean leaf, and shared 83% identity with the partial amino acid sequence of the membrane-associated cysteine protease from mung bean seedlings, a protease known to perform post-translational cleavage of C-terminal peptides of target proteins. Finally, this enzyme was shown to convert KSTI-Ti-b to KSTI-Ti-b.
Reversible and irreversible dissociations of β-conglycinin were investigated by ultracentrifugation, disc electrophoresis, and immunodiffusion methods. The protein had a protomer conformation (7S) at high ionic strength (I > 0.5) or at acidic pH (pH < 4.8) and a dimer conformation (10S) at low ionic strength (I < 0.2) in the pH region 4.8-11.0. Rapid interconversion between the protomer (trimeric structure) and the dimer (hexameric structure) was observed in the 0.2-0.5 ionic strength region. At very low ionic strength (I < 0.01), the α subunit dissociated from the protein. The dissociation was reversible but may result in the generation of multiple molecular forms (B2 to B6 conglycinins). The quaternary structures were stable at high ionic strength. Complete reversible dissociation into subunits occurred in 5 M urea (I = 0.01). Reversible dissociation into monomers (3-4S) appeared at pH 12.0 (I = 0.5). Dissociation into polypeptides (2S) at pH 2.0 and 12.0 (I = 0.01) was also reversible. Irreversible dissociation at pH 13.0 may be attributable to alkaline degradation.
The inactivation of commercial soybean lipoxygenase was studied at various temperatures using conventional and microwave heating. Conventional heating was carried out in a temperature controlled water-bath, while a custom designed microwave temperature control system was used to maintain test samples at selected temperatures either by full exposure to microwaves (microwave heating) or partial exposure by immersion in water (in a beaker) maintained at the desired temperature using the microwave oven (mixed mode). Lipoxygenase inactivation was evaluated using first-order reaction kinetics. Conventional and mixed mode heating produced somewhat similar results while the microwave mode resulted in a more rapid inactivation of the enzyme. The activation energies (Ea) were 119, 113 and 180 kJ/mol, respectively, for the conventional, mixed and microwave mode heating. Higher enzyme inactivation rates under microwave heating conditions were ascribed to possible non-thermal effects.
The formation of soluble aggregates from insoluble precipitates of commercial soy protein isolate (SPI) by means of combined homogenization and ultrasonic treatment was characterized. The heat-induced gelation of formed soluble aggregates was also investigated. The turbidity and electrophoresis analyses showed that initially insoluble precipitates of commercial SPI, most basic subunits of glycinin included, were transformed into soluble aggregates. High performance size exclusion chromatography (HPSEC) analysis confirmed the formation of soluble aggregates. Both non-covalent and covalent interactions, e.g. hydrophobic interactions, hydrogen bonds and disulfide bonds, were involved in the formation of soluble aggregates. The formation of soluble aggregates remarkably improved the heat-induced gelling ability of commercial SPI.
Profilins are pan-allergen proteins present in various plant foods and pollens. The objective was to develop a method for purification and characterisation of profilin from soy protein isolate. Furthermore, profilin was quantified in soy products and the effect of processing evaluated. Profilin was purified using poly-l-proline affinity chromatography, dialysis and ultrafiltration, and its quantification was implemented by indirect ELISA. Profilin in soymilks ranged from 4.37±0.14 to 7.24±0.30mg/g protein, while in fermented products profilin ranged from 1.67±0.02 to 5.47±0.02mg/g protein. Pasteurisation of soymilk was an ineffective method to completely eliminate profilin. Food matrix influenced thermal stability; at 100°C, β-sheet and random coil structures were altered, while the α-helices remained intact. Induced fermentation of soybean meal by Bifidobacterium lactic, Lactobacillus plantarum and Saccharomyces cerevisiae resulted in 68.3% to 72.7% reduction of soy profilin. Heat treatment, fermentation and hydrolysis effectively reduced soy profilin.
The influence of ingredients such as glucosamine, sucrose, ascorbic acid, and/or polyethylene glycol, on the release of beefy aroma components of simulated beef flavour (SBF) in the presence of soy protein isolate (SPI), were investigated. Conformational changes of SPI protein structure induced by the added ingredients were also detected. Addition of ascorbic acid alone or with polyethylene glycol resulted in reduction of disulfide bonds, increase in surface hydrophobicity and increase in unordered structure of SPI. The SPI–SBF mixtures containing ascorbic acid alone or with polyethylene glycol showed increased GC peak areas of indicator peaks, which were associated with an increase in the perceived beef characteristic attributes in descriptive analysis, as expressed by enhancement of roasted note and diminishing of soymilk-like and cereal notes. These results provide the basis for further research to elucidate strategies to maximize perception of beefy aroma in soy based products.
The swelling of soy protein filamentous hydrogels and tablets thereof and the release of riboflavin from these drug delivery devices were investigated under simulated gastrointestinal conditions in the presence or absence of digestive proteases. Microscopic examination showed riboflavin arranged into crystals dispersed randomly throughout the hydrogel and the tablet powder. Swelling experiments showed a comparable behavior of water uptake for hydrogel and tablet at pH 1.2 as well as tablet at pH 7.5, featuring a low swelling rate. Hydrogel at intestinal pH began to shrink after 1 h, which coincided with a loss its structure. Riboflavin release was faster at pH 7.5 than at pH 1.2 for both devices. Swelling was the principal mechanism of riboflavin release from tablets at pH 7.5, while drug-polymer interactions slowed this release at pH 1.2. In the presence of pepsin at pH 1.2, both devices showed slow zero-order release of riboflavin for 6 h, while both were digested completely in the presence of pancreatin at pH 7.5. These results suggest that these tabletted hydrogels and the hydrogels themselves might both be useful for transporting bioactive molecules through the gastrointestinal tract and delivering them in the small intestine. Considering their non-synthetic nature, they should be of great interest for the development of innovative functional foods.
The effects of ionic strength on heat-induced aggregation of soy protein and phase separation of different soy protein aggregates with dextran were investigated. The increase of ionic strength accelerated protein aggregation as shown by an increase in turbidity, aggregate fraction and particle size of salt-induced aggregates (SA). Adding salt (NaCl) to the aggregates formed at the ionic strength of zero (non-salt aggregates, non-SA), the increase of aggregate size was also found. Zeta potential results evidenced the charge screening effects of NaCl. The results of phase diagrams indicated that the compatibility of mixtures at higher ionic strength was lower than those at lower ionic strength, and SA was more incompatible with dextran than non-SA. The effects of the increase of aggregate size on the phase separation outweighed the ionic strength, which indicated that the depletion interaction also played an important role in the phase separation of soy protein aggregates and dextran. CLSM (Confocal Laser Scanning Microscopy) and rheological observations provided additional information of the microstructures of the mixtures.
The proportion of hexanal to total carbonyl compounds in soybean extracts was about 1–2%. When the extract was incubated in the presence of exogenous linoleic acid, the content of carbonyl compounds increased considerably. The proportion of hexanal to total carbonyl compounds derived from linoleic acid by enzymatic action was about 20%.
This review summarizes a novel hydrolytic processing of soybean proteins. Under limited hydrolytic condition, glycinin or β-conglycinin could be selectively digested in soybean proteins. The hydrolysates can be useful for an ingredient in various food applications. Selective hydrolysis may be effective for the reduction of soybean allergenicity with processing functionality.
Plant ureases have long been known for their ureolytic activities, dependent on a Ni metallocenter active site. We report here on more recently discovered novel toxic properties of ureases-properties independent of enzyme activity. Plant ureases have potent toxicity against insects that are not affected by Bt toxins. Entomotoxicity relies on an internal peptide released by insect digestive enzymes. Plant ureases are fungitoxic-in the absence of ureolytic activity - a property shared with some microbial ureases. We have found that both plant and microbial ureases also induce secretion in animal cells (and thus might be defense and pathogen factors, respectively). We suggest that in the soil, bacterial urease-induced secretion by plant roots may play a role in rhizosphere relationships. While ureases of plant, fungi, and bacteria align with greater than 50% amino acid identity, toxicity and signaling may be due to more divergent domains, such as that for the insecticidal subpeptide. These domains are potential targets for manipulation to improve plant defense against herbivores and pathogens.
Cereal Chem. 66(3):224-227 A reconstituted whole wheat bread (containing 16.3% bran plus 12.7% was included in the baking process. Addition of a high level of enzyme- shorts) with a loaf volume equal to the control was obtained by allowing active soy flour eliminated the need for the no-yeast sponge stage. Certain indigenous lipoxygenase (soaking the nonflour milling fractions) or added salts and surfactants were found to improve loaf volume. In this system, lipoxygenase (enzyme-active soy flour) to oxidize the glutathione from the compressed yeast was superior to instant dry yeast for maintaining constant germ and using optimum absorption. Because lipoxygenase requires bread quality. oxygen to function and yeast consumes oxygen, a no-yeast sponge stage Demand for whole wheat bread has increased considerably in the last few years because of its better nutritional image and an increasing preference for its organoleptic characteristics (Pomeranz 1977, Rogers and Hoseney 1982). The loaf volume of whole wheat bread is substantially smaller than that expected solely from the dilution of gluten by nonflour material (Pomeranz 1977, Rogers and Hoseney 1982). This problem makes the production of whole wheat bread with the same loaf volume as white bread more expensive because of the extra flour required (Rogers and Hoseney 1982). Lai et al (1 989a,b) studied the effect of nonflour milling fractions on breadmaking. They proposed that bran binds a relatively large amount of water and changes the appearance and the handling properties of the dough. Therefore, the gluten was not properly hydrated and developed at normal absorption levels. The use of an inappropriate absorption level results in a reduction in loaf volume (Lai et al 1 989a). Lai et al (1 989b) attributed the negative effects of shorts in breadmaking to glutathione from germ and methoxyl- hydroquinone (MHQ) types of compounds from the other shorts fractions. They also reported methods to overcome the detrimental effects of bran, shorts, and germ on bread loaf volume. The goal of this study was to develop an optimum formula and procedure to produce whole wheat bread of good quality and volume.
The effect of addition of caseinates to soy protein isolated (SPI) based films containing lipids (33% of oleic acid or 85:15 oleic acid (OA)–beeswax blend (BW)) on water vapour permeability (WVP), mechanical and optical properties was evaluated. SPI–lipids was combined with caseinates (sodium or calcium) in different SPI:caseinate ratios with the aim of improving water vapour barrier, mechanical and optical properties of SPI films containing lipids. Caseinate incorporation to SPI based films provoked an increase of elastic modulus and tensile strength at break, mainly for calcium caseinate. Both caseinates contributed to increase the water vapour barrier properties of soy protein-based films. Caseinates also provoked an increase of transparency of SPI based films and colour softening. The most effective combination was 1:1 sodium caseinate:SPI ratio, when film contains 85:15 oleic acid:beeswax ratio.
The physicochemical properties of soy proteins stabilized oil-in-water emulsions were studied after heating at two different temperatures, 75 and 95 °C. The effect of changing the order of the process (heating the solution before emulsification, or heating the emulsion) was also studied. The heating temperatures were chosen as they are known to selectively cause denaturation of the two major proteins present in the soy protein isolate: β-conglycinin and glycinin. The thermal transitions observed for soy proteins adsorbed at the interface were different from those measured in protein solutions, suggesting that some changes occur in the structure of the soy proteins upon adsorption on the oil droplet. Heating induces aggregation of the oil droplets, as shown by an increase of the particle size and the bulk viscosity of the emulsions, with a more prominent effect after heating at 95 °C. Transmission electron microscopy observations clearly demonstrate that heating induces the formation of large protein aggregates at the interface. In addition, the composition of the protein present at the interface changes depending on the order of heating and homogenization. While heating the solutions before emulsification results in all the protein subunits to be present at the interface in an aggregated form, when heating is applied after emulsification, a portion of the α and the α′ subunit of β-conglycinin as well as the acidic subunits of glycinin remain unadsorbed.
This work studies the interfacial behavior of mixed soy protein (SP) + polysaccharide (PS) systems to gain knowledge on the interactions between these biopolymers at the air–water interface under dynamic conditions at neutral pH where a limited incompatibility between macromolecules can occur. The PSs used were: hydroxypropylmethylcellulose (HPMC) as surface-active PS; lambda carrageenan (λC) and locust bean (LB) gum as non-surface-active PSs. Protein and PS concentration in the mixed systems were 2% and 0.25%, respectively. The dynamic surface pressure and rheological properties of films were evaluated with a drop tensiometer at 20∘C, pH 7 and ionic strength 0.05M.The presence of HPMC and λC greatly increased the surface pressure, surface dilatational elasticity and relative viscoelasticity on the basis of different mechanisms. HPMC competed for the interface with SP, but due to its unusual strong surface activity it could dominate the surface pressure and improve film viscoelasticity. The modification of surface pressure and rheological properties of adsorbed SP films in the presence of λC necessarily suggests the participation of λC+ contaminants at the interface. Pure λC could influence the interface by a complexation mechanism, or indirectly by a depletion mechanism in the vicinity of the interface. In addition surface-active contaminant of λC if strongly bound to the PS could bring some PS molecules at the interface.LB little affected the surface pressure and rheological properties of SP films even if surface-active contaminants were present in the commercial preparation. Differences in the interaction of λC and LB gum with the protein should be mainly ascribed to different degrees of incompatibility and to the fact that LB is not charged.
Different bran pretreatments and bran cultivars were investigated with the aim of alleviating the adverse effects caused by bran addition in brown (fiber-rich) bread. Three different bran treatments: hydration, wet heat, and wet oxidation, all hydrate bran before its addition to other breadmaking ingredients. Four different bran cultivars were investigated. All treatments improved brown bread quality significantly, resulting in larger, softer loafs. All treatments resulted in an increase in the water absorption of brown bread doughs and a decrease in potentially oxidizable substances (POS) in brans. It is suggested that prehydration treatment activates bran lipoxygenase which oxidizes POS in bran, reducing bran's contribution to brown bread dough. A further reduction of these substances is caused by a washout effect of the treatments. On average across all bran cultivars, the hydration and wet oxidation treatments improved brown bread quality significantly more than the wet heat treatment, which also reduced the bran POS significantly less than the other treatments, probably due to its rapid inactivation of lipoxygenase. The bran cultivars differed significantly in their effects on brown bread quality, suggesting that bran selection according to cultivar should be considered.