Heterogeneity of soybean seed proteins: one-dimensional electrophoretic profiles of six different solubility fractions

Characterization of structural, functional and antioxidant properties and amino acid composition of pepsin-derived glutelin-1 hydrolysate from walnut processing by-products

Glutelin-1 of defatted walnut meal protein (DWPG-1) was modified by pepsin enzymatic hydrolysis to improve its functional properties and antioxidant activities. The amino acid composition, structural characteristics, physicochemical and functional properties as well as antioxidant activities of the hydrolysate were compared with those of unmodified DWPG-1. The analysis of X-ray diffraction patterns, surface microstructure and particle size distribution indicated that enzymatic hydrolysis changed the structures of DWPG-1. Compared with the natural unhydrolyzed protein, the hydrolysate showed better physicochemical properties, such as surface hydrophobicity, solubility, emulsifying properties, foaming properties and water absorption capacity. In addition, the hydrolysate also exhibited significantly stronger antioxidant activities than DWPG-1. In conclusion, the results of this study prove that pepsin-mediated hydrolysis of walnut glutelin-1 can effectively modify the structure, function and antioxidant activity of DWPG-1, and could be used as an effective technology to produce bioactive multifunctional hydrolysates.

Pepsin-mediated hydrolysis can be used as an effective tool to improve the functional and antioxidant properties of walnut glutelin-1.

Effects of Fertigation Management on the Quality of Organic Legumes Grown in Protected Cultivation

Appropriate fertigation management plays an important role in increasing crop quality and economizing water. The objective of the study was to determine the effects of two fertigation treatments, normal (T100) and 50% sustained deficit (T50), on the physico-chemical quality of legumes. The determinations were performed on the edible parts of peas, French beans and mangetout. The trials were conducted in a protected cultivation certified organic farm. The response of legumes to the treatments varied between the cultivars tested. The fertigation treatments had a significant effect on the morphometric traits (width for mangetout and French bean; fresh weight for French bean; seed height for Pea cv. Lincoln). The total soluble solids and citric acid content have been shown to be increased by low soil water availability (T50) for mangetout. Fertigation treatments did not significantly affect the antioxidant compounds (total phenolic and ascorbic acid), minerals and protein fraction contents of legumes studied. Regarding legume health benefits, the most prominent cultivars were BC-033620 pea and French bean because of their high total phenolic (65 mg gallic acid equivalent 100 g−1 fresh weight) and ascorbic acid content (55 mg ascorbic acid 100 g−1 fresh weight), respectively. The results expand our knowledge concerning the nutraceutical quality and appropriate cultivation methods of legumes in order to make the system more sustainable and to encourage their consumption.

Extraction, composition, and functional properties of dried alfalfa (Medicago sativa L.) leaf protein

BACKGROUND

Alfalfa is considered a potential feedstock for biofuels; co-products with value-added uses would enhance process viability. This work evaluated dried alfalfa leaves for protein production and describes the functional properties of the protein.

RESULTS

Dried alfalfa leaves contained 260 g kg^-1 dry basis (DB) crude protein, with albumins being the major fraction (260 g kg^-1 of total protein). Alkali solubilization for 2 h at 50 °C, acid precipitation, dialysis, and freeze-drying produced a protein concentrate (600 g kg^-1 DB crude protein). Alfalfa leaf protein concentrate showed moderate solubility (maximum 500 g kg^-1 soluble protein from pH 5.5 to 10), excellent emulsifying properties (activity 158-219 m²  g^-1 protein, stability 17-49 min) and minimal loss of solubility during heating at pH ≥ 7.0.

CONCLUSIONS

It is technically feasible to extract protein with desirable emulsifying and heat stability properties from dried alfalfa leaves; however, the dried form may not be a practical starting material for protein production, given the difficulty of achieving high yields and high-purity protein product. © 2016 Society of Chemical Industry.

Proteomic insights into synthesis of isoflavonoids in soybean seeds

Soybean seeds are the major human dietary source of isoflavonoids, a class of plant natural products almost entirely exclusive to legumes. Isoflavonoids reduce the risk of a number of chronic human illnesses. Biosynthesis and accumulation of this class of compounds is a multigenic and complex trait, with a great deal of variability among soybean cultivars and with respect to the environment. There is a wealth of genomic, transcriptomic, and metabolomics data regarding isoflavonoid biosynthesis, but the connection between multigene families and their cognate proteins is a missing link that could provide us with a great deal of functional information. The changing proteome of the developing seed can shed light on the correlative increase in isoflavonoids, while the maternal seed coat proteome can provide the link with inherited metabolic and signaling machinery. In this effort, 'seed-filling' proteomics has revealed key secondary metabolite enzymes that quantitatively vary throughout seed development. Seed coat proteomics has revealed the existence of metabolic apparatus specific to isoflavonoid biosynthesis (isoflavonoid reductase) that could potentially influence the chemical content of this organ. The future of proteomic analysis of isoflavonoid biosynthesis should be centered on the development of quantitative, tissue-specific proteomes that emphasize low-abundance metabolic proteins to extract the whole suite of factors involved.

Fractionation, physicochemical properties, nutritional value, antioxidant activity and ACE inhibition of palm kernel expeller protein

This paper provides valuable information on the nutritional quality, functional properties, antioxidative and ACE inhibition of palm kernel expeller protein fractions.

Structural and functional analysis of various globulin proteins from soy seed

Storage proteins of soybean mostly consist of globulins, which are classified according to their sedimentation coefficient. Among 4 major types: 2S, 7S, 11S, and 15S of globulins, 7S and 11S constitute major fraction. The 11S fraction consists only of glycinin and 7S fraction majorly consists of β-conglycinin, small amounts of γ-conglycinin and basic 7S globulin (Bg7S). Glycinin exist as a hexamer while β-conglycinin as a trimer and Bg7S as a tetramer. Glycinin subunits are coded by 5 genes of a family, whereas about 15 genes are present for β-conglycinin subunits. Bg7S gene is present in four copies in soybean genome. Synthesis of all proteins takes place as a single polypeptide chain, which is cleaved after folding to yield different chains or subunits. Glycinin and β-Conglycinin are made for storage purpose. However, Bg7S has potential xylanase inhibition activity and protein kinase activity. Primary structure of Bg7S reveals 12 conserved cysteine residues involved in forming 6 disulfide bonds, which provides appreciable stability to protein. Secondary structure is predominately rich in β-sheets with few alpha helices. Bg7S shares structural similarity with various aspartic-proteases. In this review, our aim is to discuss sequence, structure, and function of various globulins present in Glycine max.

Effects of microwave irradiation on ruminal degradation and in vitro digestibility of soya-bean meal

This study was carried out to determine ruminal dry matter (DM) and crude protein (CP) degradation characteristics of untreated, 2-, 4- and 6-min microwave-treated soya-bean meal (SBM) by using nylon bags and sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS-PAGE) techniques. Nylon bags of untreated or treated SBM were suspended into the rumen of three Holstein steers from 0 to 48 h, and data were fitted to non-linear degradation characteristics to calculate effective rumen degradation (ERD). There were significant differences (P < 0·05) for DM and CP degradation parameters between untreated and microwave-treated SBM. Microwave treatments decreased the water-soluble fraction and increased the potentially degradable fraction of CP. The degradation rate of the latter fraction decreased with these treatments. As a consequence, microwave treatments decreased (P < 0·05) ERD of CP. From densitometric scanning, SBM proteins were seen to be composed of two major components; β-conglycinin and glycinin, accounting for proportionately 0·30 and 0·40 of buffer-soluble SBM proteins, respectively. Electrophoretic analysis of untreated, 2-, 4- and 6-min microwave-treated SBM protein residues revealed that two of the subunits of β-conglycinin (α -and α) were degraded completely after 2, 4, 24 and 48 h, respectively, whereas the α subunit of this protein was more resistant to degradation. In untreated SBM, the two subunits of glycinin (acidic and basic polypeptides) were degraded in the middle of the incubation period, but in microwave-treated SBM were not degraded until 48 h of incubation. In vitro digestibility of ruminally undegraded CP of untreated and treated SBM increased (P < 0·05) with increases in rumen incubation time from 8 to 24 h. In conclusion, SBM proteins appeared to be effectively protected from ruminal degradation by a 4-min microwave treatment. SDS-PAGE results indicated that ruminally undegraded protein from untreated SBM was mainly composed of the basic subunit of glycinin, whereas that from microwave-treated SBM was composed of β-conglycinin and both basic and acidic subunits of glycinin.

High-throughput peptide mass fingerprinting of soybean seed proteins: automated workflow and utility of UniGene expressed sequence tag databases for protein identification

Identification of anonymous proteins from two-dimensional (2-D) gels by peptide mass fingerprinting is one area of proteomics that can greatly benefit from a simple, automated workflow to minimize sample contamination and facilitate high-throughput sample processing. In this investigation we outline a workflow employing robotic automation at each step subsequent to 2-D gel electrophoresis. As proof-of-concept, 96 protein spots from a 2-D gel were analyzed using this approach. Whole protein (1 mg) from mature, dry soybean (Glycine max [L.] Merr.) cv. Jefferson seed was resolved by high resolution 2-D gel electrophoresis. Approximately 150 proteins were observed after staining with Coomassie Blue. The rather low number of detected proteins was due to the fact that the dynamic range of protein expression was greater than 100-fold. The most abundant proteins were seed storage proteins which in total represented over 60% of soybean seed protein. Using peptide mass fingerprinting 44 protein spots were identified. Identification of soybean proteins was greatly aided by the use of annotated, contiguous Expressed Sequence Tag (EST) databases which are available for public access (UniGene, ftp.ncbi.nih.gov/repository/UniGene/). Searches were orders of magnitude faster when compared to searches of unannotated EST databases and resulted in a higher frequency of valid, high-scoring matches. Some abundant, non seed storage proteins identified in this investigation include an isoelectric series of sucrose binding proteins, alcohol dehydrogenase and seed maturation proteins. This survey of anonymous seed proteins will serve as the basis for future comparative analysis of seed-filling in soybean as well as comparisons with other soybean varieties.

Identification of an ethanol-soluble protein as beta-amylase and its purification from soybean seeds

In the 60% ethanol extract of soybean seeds, a prominent protein band was visible after polyacrylamide gel electrophoresis, which had a molecular weight of about 55 x 10(3) M(r). This protein was purified to homogeneity by buffered ethanol extraction and preparatory gel electrophoresis. Since the N-terminus was apparently blocked, the protein was cleaved with cyanogen bromide and the largest fragment was isolated and a partial sequence determined. The sequence of the 27 N-terminal amino acid residues matched a published soybean beta-amylase peptide sequence. In addition, the purified protein had a high specific activity for beta-amylase and was not a glycoprotein. Furthermore, the partial sequence (106 nucleotides) of a cDNA clone, isolated from a soybean seed cDNA library by antibody screening, matched the cDNA sequence of soybean beta-amylase except for one base. Therefore, the ethanol-soluble protein was identified as beta-amylase. The enzyme was purified to homogeneity using a two-step purification procedure with a yield of over 50%.

Preparative anion-exchange chromatography of soybean trypsin inhibitor: the alternative of column-overload methods

The objective of preparative separation is to purify the largest amount of material in the shortest time and at a minimum cost, i.e. to maximize throughout. One of the techniques for increasing throughput is to overload the column while maintaining purity and cycle time at the same level. This principle is applied in sample displacement mode chromatography, in which the column is overloaded with sample mixture until it is completely saturated. Soybean trypsin inhibitor was purified from a crude protein extract by this technique using an analytical anion-exchange column with small particle size (20 microns). The comparison of these results, using the criterion of throughput, with those derived from a conventional scale-up, using a 40-microns preparative column, led to the conclusion that the overloaded 20 microns column gave a higher throughput than the 40-microns column.

A 23.8-kD alpha-zein with N-terminal sequence and immunological properties similar to 26.7-kD alpha-zeins

A 23.8-kD alpha-zein polypeptide, K55PC7, has been shown to be a truncated member of the 26.7-kD alpha-zein class based on its amino acid composition, N-terminal sequence, and immunological properties. This unusual polypeptide was isolated by chromatographing whole alpha-zein from inbred K55. The N-terminal sequence of K55PC7 is highly homologous to those of 4 putative 26.7-kD alpha-zeins but shows no homology to those of 10 putative alpha-zeins that belong to the 23.8-kD class. Its higher valine and lower phenylalanine contents also suggest that K55PC7 is a member of the 26.7-kD class. In addition, studies with antibodies raised to peptides corresponding to regions unique to each of the two alpha-zein classes indicate that K55PC7 has immunological similarity to 26.7-kD alpha-zeins. Peptide mapping data suggest that K55PC7 is not the putative product of the truncated 26.7-kD alpha-zein gene zA1 isolated from inbred W64A and described by Spena et al. [26]. It appears that K55PC7 occurs as a major component in inbred K55 and is a truncated version of a 26.7-kD alpha-zein, arisen either by an internal deletion or premature termination due to a nonsense mutation.

Effects of temperature on food proteins and its implications on functional properties

This article surveys the knowledge in the area of protein structure and chemistry of denaturation prior to an indepth review of the effects of heat on soy, milk, and egg proteins. It also reviews the methods available to assess denaturation of proteins. Protein denaturation is an ambiguous phenomenon and the consequences of denaturation on the functional properties of proteins is further confounded by this ambiguity. For each of the three food proteins, the known chemistry of individual proteins is reviewed followed by observations made on changes induced by heat in each protein group. Food proteins are not pure entities and purification and physicochemical characterization of various components of the food proteins have not been thoroughly investigated. Further, food is a complex milieu of water, fat, carbohydrate, vitamin, minerals, etc. along with proteins, and processing affects not only each individual component in the food but also the nature and intensity of intercomponent interactions in a food.

Crystalline ribulose bisphosphate carboxylase/oxygenase of high integrity and catalytic activity from Nicotiana tabacum

Crystalline tobacco (Nicotiana tabacum L.) ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) was prepared using a procedure which protected the enzyme from hydrolysis by endogenous proteases. Leaves were extracted in a buffered medium containing casein, leupeptin, and high concentrations of MgSO4 and NaHCO3. After filtration through ion-exchange resin to remove contaminants, the enzyme was concentrated by precipitation with polyethylene glycol and crystal formation was induced by low-salt dialysis. The crystalline enzyme had a measured specific activity of 1.7 mumol CO2 mg protein-1 min-1, and about 93% of the enzyme could be activated with Mg2+ and CO2. Crystalline enzyme prepared in the absence of casein exhibited an activity which was only one-third of this rate and only about 70% of the enzyme could be activated with Mg2+ and CO2. Casein-extracted enzyme was resolved into distinct bands corresponding to the large (55,000) and small (14,000) subunits by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The large subunit of enzyme prepared according to the latter procedure was found to be composed of five different polypeptides of slightly decreasing molecular weight. Only about one-third of the large subunits were of the 55,000 molecular weight type. No differences between the two preparations were observed in the Km (CO2) and apparent Km (ribulose bisphosphate).

[Analysis of proteins in food with electrophoretic and chromatographic methods]

The efficiency of electrophoretic methods (gel electrophoresis, isoelectric focusing, twodimensional techniques) and of chromatographic methods (size exclusion and ion exchange chromatography, reversed phase HPLC) to analyze proteins in foods is reviewed. Several selected applications are discussed in detail. The large diversity of proteins in a particular food results in a unique electrophoretic or chromatographic pattern, that can be used for identification purposes, by means of the so called indicator proteins. The adaptability and resolving power of the methods assure their extended application to many protein containing foods. The uniqueness of the patterns obtained warranties differentiations of even closely related animal or plant foods as well as mixtures of them. The methods also allow quantitative determinations of mixtures of foods. Their ease of handling and good reproducibility and reliability favours their use in routine analyses. Numerous investigations on fish, meat and derived products, non-meat proteins in meat products, milk, cheese, cereals and products made of cereals, oilseed proteins, legumes, fruits and vegetables described in the literature are here presented.

Modification of plant proteins by immobilized proteases

A potential application of plant proteins could be a replacement of animal proteins now in use in the food industry on the basis of certain specific functional properties plant proteins have. Modification of the chemical structure of selected plant proteins is needed to replace more expensive animal proteins as food ingredients that have specific functional characteristics. Structure modification may be achieved by physical, chemical, or microbiological methods, or by a combination of these. Immobilized enzyme techniques offer significant advantages for protein modification. Knowledge of the molecular properties of plant proteins is essential to understand the basis of protein functionality, to modify proteins so that they acquire desirable functional properties, and to predict potential applications of modified plant proteins. This paper reviews all the above mentioned aspects of plant protein chemistry and potential utilization.