Biopolymers Produced by Cross-linking Soybean 11S Globulin with Whey Proteins using Transglutaminase

Heterogeneity of biopolymers was determined by cross-linking acetylated-11S acidic subunits (Ac-11S) of soy protein with α-lactalbumin and β-lactoglobulin. The extent of polymerization was determined by electrophoresis and HPLC. Differential scanning calorimetry (DSC) was used to determine thermal properties of starting proteins and biopolymers. HPLC data demonstrated the absence of biopolymers from Ac-11S, acetylated α-lactalbumin and acetylated β-lactoglobulin when each was incubated separately with transglutaminase (TG). However, Ac-11S formed biopolymers with α-lactalbumin and β-lactoglobulin when TG was added. TG catalyzed the formation of heterologous and homologous biopolymers from whey protein isolate (WPI) and soybean 11S globulin (11S). Cross-linking WPI and 11S provided biopolymers with improved heat stability which may be useful to provide functionality to food products.     

大豆7S和11S球蛋白的结构和功能性质

主要介绍大豆７Ｓ和１１Ｓ球蛋白的结构和功能性质，大豆蛋白质各个成分的分子量有所不同，按超速离心分离系数可分为２Ｓ，７Ｓ１１Ｓ和１５Ｓ４个组份。７Ｓ组份占总蛋白质的３０．９％，它是由４种不同大豆蛋白民组成，１１Ｓ组份占总大豆蛋白质的４１％，而且都是单一的１１Ｓ球蛋白，１１Ｓ球蛋白的等电点为ｐＨ４．６４。     

Isolation,purification, and characterization of the globulin from wheat germ

This research optimized the extraction and purification of globulin from wheat germ and assessed the molecular weight distribution and structure properties of the globulin obtained. The results showed that the relative extraction efficiency and purity of wheat germ globulin (WGG) reached 18.0% and 89.1% under the enzymolysis conditions of 0.32‰ α-amylase, pH 6.5, and 55 °C. The maximal precipitation rate of WGG (91.3%) was obtained with pH 4.3 (acid precipitation). Additionally, the molecular weight of WGG was mainly distributed below 70 kDa. FT-IR confirmed that random coils (30.95%), β-sheet (27.02%), α-helix (26.55%), and β-turn (15.48%) were the secondary structures of WGG. Furthermore, LTQ mass spectrometry showed that WGG was rich in variety and high in complexity, which retrieved 1274 proteins belonging to 392 proteomes by inverse peptide analysis. The findings endow a great potential of preparing WGG with superior functionality for food applications.     

不同工艺条件对大豆分离蛋白7S和11S组分影响的探讨

利用碱提酸沉的工艺，通过改变温度和离子强度得到不同参数条件下的大豆分离蛋白。经过凝胶电泳分析得到蛋白质的各个条带组分图，用图像捕捉成像技术以及相关软件，分析出分离蛋白各个组分的详细情况（包括组分数、分子量和各个组分所占的百分含量）。由实验可知，分离蛋白的7S和11S组分随温度和离子强度的改变而发生变化，分析其变化规律，从而确定合适的工艺参数。     

Purification and characterisation of the 7S globulin storage protein from sesame (Sesamum indicum L.)

The 7S globulin from sesame seeds was purified by means of selective precipitation and anion-exchange chromatography on Q Sepharose Fast Flow. The 7S globulin migrated as a single band on native PAGE, which suggested homogeneity of the sample. The isolated protein was composed of at least eight polypeptide chains, ranging from 12.4 to 65.5 kDa, judged by SDS–PAGE analysis, and did not contain disulphide bonds. Furthermore, comparison of the polypeptide bands of the 7S and 11S globulins by SDS–PAGE indicated that the purified 7S globulin was free of legumin-like contaminant polypeptides and of 2S albumin. The identity of the purified polypeptides was verified by comparing the N-terminal amino acid sequences of the main polypeptide bands with the amino acid sequence deduced from a cDNA clone, which encoded the sesame 7S globulin precursor. Purification of the 7S globulin from sesame has not previously been reported.     

The subunit structure and stability of conglutin δ, a sulphurrich protein from the seeds of Lupinus angustifolius L.

The oligomeric structure and stability of conglutin δ, the 2S sulphur-rich lupin seed protein, has been studied. Molecular weights were determined by sedimentation equilibrium methods in the analytical ultracentrifuge. Conglutin δ₂ (M_r 14 000, 2S), the most abundant form, was composed of one large (?9600) and one small polypeptide chain linked by disulphide bonds. The minor oligomeric form, conglutin δ₁ (M_r 28 000, 2.8S), was a disulphide-linked dimer of conglutin δ₂. Each form was capable of reversible association and at low ionic strength (neutral pH), the conglutin δ₁ momomer associated to a homogeneous dimer (M_r 56 000, 4.1S). Calculated frictional ratios (f/f₀ ? 1.28–1.49) suggested that the three different forms were asymmetric. Spectral studies (ORD/CD) showed that conglutins δ₁ and δ₂ were rich in alpha-helix (?38%) unlike the major 7S and 11S legume seed storage proteins. The helical structure was unusually stable both to heat and chemical denaturants; below 60°C (at neutral pH) the helix remained unaffected and only partial denaturation occurred at higher temperatures. Nevertheless, complete denaturation was achieved (at 20°C) in high concentrations of guanidine hydrochloride (greater than 6.5 M). The stability was due to the presence of disulphide cross-links; with the addition of reducing agent, as little as 1 M guanidine hydrochloride (GuHCl) was sufficient for denaturation of the helical structure. Titration experiments showed a single buried tyrosine (pK 11.4) which could be exposed (pK 10.2) in 6 M GuHCl.     

Characterization of globulin from Phaseolus angularis (red bean)

Phaseolus angularis (red bean) seeds contain about 25% protein (dry basis), almost half of which is globulin. Similar to globulins from other Phaseolus species , 7S vicilin is the major fraction of red bean globulin (RBG), with 11S legumin as a minor component. The amino acid profile of RBG met or exceeded the FAO/WHO standard. Circular dichroism measurements indicate that RBG is a protein rich in α-helical and β-turn structures. RBG exhibited higher protein solubility than Supro 610, a commercial soy protein isolate, especially at acidic pHs, with minimal solubility at around pH 5.0. Compared to Supro 610, RBG had lower water hydration capacity and comparable fat binding capacity, which might be because of its lower surface hydrophobicity. RBG had higher emulsifying activity index and emulsion stability than Supro 610, but with poorer foaming properties.     

Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish

Persistent organic pollutants (POPs) encompass an array of anthropogenic organic and elemental substances and their degradation and metabolic byproducts that have been found in the tissues of exposed animals, especially POPs categorized as organohalogen contaminants (OHCs). OHCs have been of concern in the circumpolar arctic for decades. For example, as a consequence of bioaccumulation and in some cases biomagnification of legacy (e.g., chlorinated PCBs, DDTs and CHLs) and emerging (e.g., brominated flame retardants (BFRs) and in particular polybrominated diphenyl ethers (PBDEs) and perfluorinated compounds (PFCs) including perfluorooctane sulfonate (PFOS) and perfluorooctanic acid (PFOA) found in Arctic biota and humans. Of high concern are the potential biological effects of these contaminants in exposed Arctic wildlife and fish. As concluded in the last review in 2004 for the Arctic Monitoring and Assessment Program (AMAP) on the effects of POPs in Arctic wildlife, prior to 1997, biological effects data were minimal and insufficient at any level of biological organization. The present review summarizes recent studies on biological effects in relation to OHC exposure, and attempts to assess known tissue/body compartment concentration data in the context of possible threshold levels of effects to evaluate the risks. This review concentrates mainly on post-2002, new OHC effects data in Arctic wildlife and fish, and is largely based on recently available effects data for populations of several top trophic level species, including seabirds (e.g., glaucous gull (Larus hyperboreus)), polar bears (Ursus maritimus), polar (Arctic) fox (Vulpes lagopus), and Arctic charr (Salvelinus alpinus), as well as semi-captive studies on sled dogs (Canis familiaris). Regardless, there remains a dearth of data on true contaminant exposure, cause-effect relationships with respect to these contaminant exposures in Arctic wildlife and fish. Indications of exposure effects are largely based on correlations between biomarker endpoints (e.g., biochemical processes related to the immune and endocrine system, pathological changes in tissues and reproduction and development) and tissue residue levels of OHCs (e.g., PCBs, DDTs, CHLs, PBDEs and in a few cases perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonates (PFSAs)). Some exceptions include semi-field studies on comparative contaminant effects of control and exposed cohorts of captive Greenland sled dogs, and performance studies mimicking environmentally relevant PCB concentrations in Arctic charr. Recent tissue concentrations in several arctic marine mammal species and populations exceed a general threshold level of concern of 1 part-per-million (ppm), but a clear evidence of a POP/OHC-related stress in these populations remains to be confirmed. There remains minimal evidence that OHCs are having widespread effects on the health of Arctic organisms, with the possible exception of East Greenland and Svalbard polar bears and Svalbard glaucous gulls. However, the true (if any real) effects of POPs in Arctic wildlife have to be put into the context of other environmental, ecological and physiological stressors (both anthropogenic and natural) that render an overall complex picture. For instance, seasonal changes in food intake and corresponding cycles of fattening and emaciation seen in Arctic animals can modify contaminant tissue distribution and toxicokinetics (contaminant deposition, metabolism and depuration). Also, other factors, including impact of climate change (seasonal ice and temperature changes, and connection to food web changes, nutrition, etc. in exposed biota), disease, species invasion and the connection to disease resistance will impact toxicant exposure. Overall, further research and better understanding of POP/OHC impact on animal performance in Arctic biota are recommended. Regardless, it could be argued that Arctic wildlife and fish at the highest potential risk of POP/OHC exposure and mediated effects are East Greenland, Svalbard and (West and South) Hudson Bay polar bears, Alaskan and Northern Norway killer whales, several species of gulls and other seabirds from the Svalbard area, Northern Norway, East Greenland, the Kara Sea and/or the Canadian central high Arctic, East Greenland ringed seal and a few populations of Arctic charr and Greenland shark.     

Physical Properties of Soy Bean and Broad Bean 11S Globulin Gels Formed by Transglutaminase Reaction

Physical properties of transglutaminase-induced glycinin and legumin gels were compared with thermally induced gels. Results of deformation tests showed that transglutaminase-induced gels were more rigid and elastic than thermally induced gels. From creep compliance tests, all elastic moduli and viscosities except Newtonian viscosity were higher for transglutaminase-induced gels. Electron micrographs revealed that network structures of transglutaminase-induced gels were composed of larger unit particles forming more developed strands and clusters. More rigid and elastic gels were formed from glycinin as compared to legumin by both gelling methods.     

Heat-induced Gels of Rice Globulin: Comparison of Gel Properties with Soybean and Sesame Globulins

The hardness and water-holding ability of rice globulin gels were intermediate between those of gels of soybean and sesame globulins. Scanning electron micrographs showed that rice globulin gel had a rough network structure composed of small globular particles of protein aggregates. Effects of various reagents on solubilization of proteins from the three gel types were compared. Disulfide bonds and hydrophobic interactions contributed mainly to the stability of rice globulin gels. The contributions of disulfide bonds to both the formation and stability of rice globulin gels were greater than for sesame globulin gels.