Impact of incorporations of various polysaccharides on rheological and microstructural characteristics of heat-induced quinoa protein isolate gels

This study aimed to investigate the properties of heat-induced gels (85 °C for 30 min) of quinoa protein isolate (QPI) in the presence and absence of various polysaccharides including guar gum (GG), locust bean gum (LBG), and xanthan gum (XG) at pH 7. For this purpose, samples with three gum concentrations (0.05, 0.1, and 0.2 wt%) at a fixed QPI concentration (10 wt%) and a fixed ionic strength (50 mM NaCl) were studied in terms of their gelation behaviour, small and large deformation rheological properties, water holding capabilities, and microstructural characteristics. Rheological measurements revealed that all polysaccharides incorporation could improve gel strength (complex modulus, G*) and breaking stress, accelerate gel formations, and more stiffer gels were obtained at greater polysaccharide concentrations. The XG exhibited the most gel strengthening effect followed by LBG and GG. Incorporation of 0.2 wt% XG led to a 15 folds increase in G* compared to the control. Confocal laser scanning microscopy observation revealed that the polysaccharides also altered gel microstructures, with the gels containing XG showing the most compact gel structures. The findings of this study may provide useful information for the fabrication of novel QPI based food gel products with improved texture.

     

On the dual role of starch,cellulose and their dialdehydes as fillers and accelerators in the tertiary amine catalysed curing of epoxy resin

Gel time studies of epoxy resins containing varying concentrations of water, starch, cellulose, or their dialdehydes were carried out at 120°C using the tertiary amines triethylamine (TEA) and hexamethylenetetramine (HEXA) as catalysts. In the 40 parts per 100 parts of resin (phr) polysaccharide-filled epoxy-HEXA system it was found that ～50% oxidised starch or cellulose produced unexpectedly high curing rate enhancements and gel times of 13 and 22 min, respectively, were obtained. With 100% oxidised starch the gel time increased to 37 min, while with 10% oxidised cellulose the gel time obtained was 91 min. The non-oxidised starch and cellulose gave even higher gel times. Thus, there seems to be some sort of a synergistic mechanism operating when the degree of oxidation of the polysaccharide is ～50% of the glucose monomer units. The difference in the effects of TEA and HEXA on the polysaccharide-filled epoxy curing reaction is explained on the basis of the decomposition of HEXA into its constituents (formaldehyde and ammonia/ammonia derivatives) under the reaction conditions employed, the formation of intermolecular and intramolecular hemiacetal and/or various hydrated aldehyde structures, and the difference in crystallinity and rigidity of the different polysaccharides affecting the availability of hydroxyl groups.     

Polymeric collagen fibrils. An example of substrate-mediated steric obstruction of enzymic digestion.

Polymeric collagen fibrils have been reacted with fluorescein and rhodamine isothiocyanates to produce fluorescent dye-labelled fibrils, containing seven dye substituents per molecule of tropocollagen within the polymeric collagen fibrils. Two dye-labelled peptides per molecule of tropocollagen were solubilised by trypsin (EC 3.4.21.4) from the telopeptide regions and four dye-labelled peptides were located in the helical regions solubilised by bacterial collagenase (EC 3.4.24.3). The solubilisation of dye-labelled peptides from these insoluble substrates were employed to measure the kinetics of trypsin and collagenase digestion of the telopeptide and helical regions, respectively, of the insoluble polymeric collagen fibrils. These studies demonstrated an apparent excess of enzyme for the readily available substrate under conditions when it was known that a vast excess of substrate existed in the reaction mixture calculated in terms of a molecular ratio. A point of equivalence was established for both trypsin and bacterial collagenase, approximately one enzyme molecule per 870 substrate molecules. On either side of this point the quantity of products formed was controlled by either the enzyme concentration or the substrate concentration. The results can be explained in terms of the inaccessibility of tropocollagen molecules within the molecular architecture of the polymeric collagen fibrils. The external layer of tropocollagen molecules obstruct collagenolytic enzymes penetrating to, and forming enzyme-substrate complexes with, the bulk of the substrate within the interior of the fibrils.     

Observations on the different substrate behavior of tropocollagen molecules in solution and intermolecularly cross-linked tropocollagen within insoluble polymeric collagen fibrils.

Bacterial collagenase was used to compare the extent of digestion of tropocollagen monomers in solution and in reconstituted fibrils with that of tropocollagen molecules intermolecularly cross-linked within insoluble polymeric collagen fibrils obtained from mature tendons at given time-intervals. The extent of digestion of tropocollagen monomers in solution was directly proportional to the enzyme concentration (a range of enzyme substrate molar ratios 1:200 to 1:10 was used). The extent of digestion of polymeric collagen was followed by measuring the solubilization of fluorescent peptides from fluorescent-labelled insoluble polymeric collagen fibrils. The extent of digestion of tropocollagen within polymeric collagen was linear over a very small range of enzyme concentrations, when the enzyme/substrate ratio in the reaction mixture was less than 1:400 on a molecular basis. The behavior of tropocollagen in the form of reconstituted collagen fibrils, which had been matured at 37 degrees C for 8 weeks, was intermediate between the behaviour of solutions of tropocollagen and insoluble polymeric collagen fibrils. The significance of the results is discussed in terms of the structure of polymeric collagen fibrils and the protection against enzymic attack provided by tropocollagen molecules on the circumference of the fibril. The results suggest that assays of collagenase activities based on tropocollagen as substrate cannot be directly related to the ability of these enzymes to degrade mature insoluble collagen fibrils.     

A study of collagen and gelatin solutions by optical self beat spectroscopy

A study of the conformation of collagen and gelatin in aqueous solution by Optical Self Beat Spectroscopy is reported. The translational diffusion coefficient of monomeric tropocollagen was experimentally measured from the half-width of the Rayleigh scattered radiation and the value obtained is shown to be in good agreement with that calculated from hydrodynamical theory for the tropocollagen rod. The Self Beat Spectrometer was also used to investigate the factors affecting the aggregation and flexing of molecules in dilute gelatin solutions and the gel-sol transition in more concentrated gelatin solutions.     

High pressure 2H-NMR study of the order and dynamics of selectively deuterated dipalmitoyl phosphatidylcholine in multilamellar aqueous dispersions.

High pressure 2H multipulse NMR techniques were used to investigate the effects of pressure on the structure and dynamics of selectively deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) multilamellar aqueous dispersions. The samples were deuterated on both chains at positions 2, 9, or 13. The deuterium lineshapes, the spin-lattice relaxation times, T1, and the spin-spin relaxation times, T2, were measured as a function of pressure from 1 bar to 5 kbar at 50 degrees C for the three deuterated DPPC samples. This pressure range permitted us to explore the phase behavior of DPPC from the liquid-crystalline (LC) phase through various gel phases such as the Gel I (P beta), Gel II (L beta), Gel III, Gel X, and the interdigitated, Gel i, gel phase. Pressure had an ordering effect on all chain segments both in the LC phase and various high pressure gel phases as indicated by the increase in SCD bond order parameter and the first moment, M1, with pressure. Compared with the adjacent gel phases, the Gel i phase had the highest order. Also, in all gel phases the carbon-9 segment of the chains had the most restricted motions in contrast to the LC phase, where the carbon-2 segment was the most restricted. In the LC phase, T1 and T2 values for all segments decreased with pressure, indicative of the fast correlation time regime. Similarly, T1 decreased with pressure in the Gel I and the interdigitated Gel i gel phases but changed to the slow correlation time regime at the Gel i/Gel II phase transition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fractionation of pepsin-digested, denatured collagen. III. Characterization of the small fragments

The survey of the fragments obtained from pepsin-digested, denatured rat tail tendon collagen is completed. Three additional fragments could be renatured and two of them (490 A and 670 A) were located in tropocollagen by electron microscopy. Data are given on the amino acid compositions of the various fractions. Certain fragments probably originated from the associated non-collagenous material belonging to the "acidic structural proteins".     

Characterization and localization of the cell wall autolysis substrate in Pisum sativum epicotyls

The products released in cell wall autolysis from 4-day-old epicotyls of Pisum sativum elute in gel filtration chromatography (Bio Gel P.2) as two components, mono and polysaccharides, in a practically constant ratio over the time of incubation. The polysaccharides are mainly composed of arabinose and galactose, with smaller amounts of xylose and glucose, whereas the monosaccharide are almost exclusively composed of galactose. The same results were obtained when inactive cell walls were hydrolyzed by the enzymes extracted from the cell wall with LiCl. The hydrolysis of the different cell wall fractions by these enzymes shows that the autolytic substrates are preferentially located on the pectic fractions.     

AFM imaging of extracellular polymer release by marine diatom Cylindrotheca closterium (Ehrenberg) Reiman & J.C. Lewin

Extracellular polysaccharide production by marine diatoms is a significant route by which photosynthetically produced organic carbon enters the trophic web and may influence the physical environment in the sea. This study highlights the capacity of atomic force microscopy (AFM) for investigating diatom extracellular polysaccharides with a subnanometer resolution. Here we address a ubiquitous marine diatom Cylindrotheca closterium, isolated from the northern Adriatic Sea, and its extracellular polymeric substance (EPS) at a single cell level. We applied a simple procedure for AFM imaging of diatom cells on mica under ambient conditions (in air) to achieve visualization of their EPS with molecular resolution. The EPS represents a web of polysaccharide fibrils with two types of cross-linking: fibrils association forming junction zones and fibril-globule interconnections with globules connecting two or more fibrils. The fibril heights were 0.4-2.6 nm while globules height was in the range of 3-12 nm. Polymer networks of native gel samples from the Northern Adriatic and the network formed by polysaccharides extracted from the C. closterium culture share the same features regarding the fibril heights, pore openings and the mode of fibril association, proving that the macroscopic gel phase in the Northern Adriatic can be formed directly by the self-assembly of diatom released polysaccharide fibrils.     

Gel formation by fibrin oligomers without addition of monomers

Soluble fibrin oligomers were formed by reacting fibrinogen with thrombin under fine clotting conditions where the action of thrombin is the rate-determining step for polymerization, and by inhibiting the reaction shortly before gelation. Oligomeric fibrin was separated from unreacted fibrinogen and small oligomers by gel permeation chromatography. Electron microscopy revealed that the largest soluble fibrin oligomers resemble the protofibrils present in fine clots, but are somewhat shorter and entirely lack the twisted, trifunctional junctions that contribute to the elastic properties of fine clots. When thrombin was added to the soluble fibrin oligomers, polymerization resumed and clots were formed at a more rapid rate than from fibrinogen at the same concentration and resulted in a less-opaque clot under coarse clotting conditions. The results confirm a prediction of a theory for the polymerization of fibrin and provide additional evidence that the final state of a coarse fibrin clot depends on the mobility of protofibrils during its formation.     

The precipitation of toroidal collagen fibrils

The morphology of aggregates of calf-skin tropocollagen, precipitated by continuous injection into neutral phosphate buffers at 35 degrees , has been studied by electron microscopy. Although most of the collagen is precipitated as normal native fibrils, a small proportion forms closed toroidal structures having the usual native band-interband pattern. Theoretical considerations, based on elastic energies in a general microfibril model, predict that the toroids should have a simple super-helical structure, and this is not inconsistent with the observations. From the theoretical energies it was possible to estimate a crude lower limit of 3kcal./mole for the free energy of association of the tropocollagen macromolecules.     

Characterizing membrane foulants in MBR with addition of polyferric chloride to enhance phosphorus removal

The effect of polymeric ferric chloride (PFC) addition on phosphorus removal and membrane fouling were investigated in an anoxic/oxic submerged membrane bioreactor. The total phosphorus concentration in effluent averaged at 0.26 mg/L with PFC addition of 10-15 mg/L, while the rate of membrane fouling increased 1.6 times over the control MBR (without PFC addition). Three-dimensional excitation-emission matrix fluorescence spectroscopy and Gel Filtration Chromatography analysis indicated that soluble microbial byproduct-like materials and large molecules (M(W)>100 kDa) were one of the main contributors of biofouling. Fourier transform infrared spectrum confirmed that the major components of the cake layer were proteins and polysaccharides materials. Scanning electron microscopy demonstrated that membrane surfaces were covered with compact gel layer formed by organic substances and Energy Dispersive X-ray analysis indicated that ferric metals were the most important inorganic pollutants. Consequently, soluble organic substances and dose of PFC should be controlled to minimize membrane fouling.     

Thermal conformational transformations of tropocollagen. II. Viscometric and light-scattering studies

It was shown by viscometric measurements that a tropocollagen solution at low shear gradients manifests elastic features which can be connected only with the existence of a labile spatial structure which develops in time in the solution. To judge by the concentration dependence of the rate of formation of this structure, it does not represent a molecular net formed by direct contact of macromolecules. Most likely this structure is a result of stabilization of macromolecules at a certain distance from each other. The study of light scattering by tropocollagen solutions demonstrated that it does not correspond with the scattering by rigid rod-shaped units. Anomalies in the character of light scattering are probably the result of intermolecular interference produced by a spatial supermolecular structure and, in turn, indicate that this structure is to some extent regular. In the presence of salts the elastic features in the tropocollagen solution and anomalies in light scattering disappear in a narrow range of temperatures immediately before the process of denaturation which makes it possible to conclude that the supermolecular regular structure is disrupted in this temperature range.     

THP基因的重新克隆及草菇表达载体的构建

草菇 (Ｖｏｌｖａｒｉｅｌｌａｖｏｌｖａｃｅａ)是一种高温型的食用菌 ,在 4℃低温条件下 ,其菌丝自溶死亡 ,子实体发软、液化直至腐烂[1～ 3 ] 。草菇的这一特性严重地限制了草菇的生产、新鲜草菇的流通、低温冷冻保鲜和出口创汇以及草菇菌种的低温冷冻储藏。草菇是同宗结合的真菌 ,生活史复杂[4 ] ,菌丝没有锁状联合 ,杂种选择缺乏标记 ,这给草菇的杂交育种带来极大的困难[5,6] 。基因工程的发展为解决草菇不耐低温冷藏这一难题提供了可能。ＴＨＰ(ＴｈｅｒｍａｌＨｙｓｔｅｒｅｓｉｓＰｒｏｔｅｉｎ)基因—热滞后蛋白基因 ,是加拿大科学…     

The isolation, preliminary study of structure and physiological activity of water-soluble polysaccharides from squeezed berries of Snowball tree Viburnum opulus

Water-soluble polysaccharide fractions VO1-VO4 were isolated from the squeezed berries of snowball tree (Viburnum opulus) by successive extraction with water at various temperatures and pH and with aqueous solutions of ammonium oxalate. These fractions were purified by ion-exchange chromatography on DEAE cellulose, and the homogeneity of the purified polysaccharides was determined by gel filtration on Sephacryl S-500. Acidic polysaccharides close to pectins in their sugar composition were found in all the extracts (fractions VO1-1, VO2-1, VO3-2, and VO4-2). Residues of galacturonic acid, galactose, arabinose, and (to a lesser extent) rhamnose are their main constituents. Neutral polysaccharides composed mainly of galactose and mannose residues were additionally found in fractions extracted with acidified water (pH 4.0) and with aqueous ammonium oxalate solutions. Partial acidic hydrolysis and digestion with pectinase of acidic polysaccharides indicated that their carbohydrate backbone consists of alpha-1,4-linked residues of D-galacturonic acid. NMR spectra of acidic polysaccharides (fractions VO3-2 and VO3-3) confirmed this and demonstrated that their side oligosaccharide chains are composed of beta-1,4-linked galactopyranose residues and of terminal and 2,5- and 3,5-substituted residues of alpha-arabinofuranose at a Gal: Ara ratio of 3:1. Some polysaccharides from V. opulus were found to possess an immunostimulating activity: they enhance phagocytosis, in particular, the phagocytic index and the secretion of lysosomal enzymes with peritoneal macrophages. Calcium ions were found to be necessary for the appearance of the stimulating effect of acidic polysaccharides from V. opulus.     

Polyacrylamide gel electrophoresis of the capsular polysaccharides of Escherichia coli K1 and other bacteria.

Methods were developed for the polyacrylamide gel electrophoretic analysis of capsular polysaccharides of bacteria with Escherichia coli K1 as a model. Conditions were determined for the rapid and gentle extraction of the K1 polysaccharide by incubation of the bacteria in a volatile buffer and for the subsequent removal of the putative phospholipid moiety attached to the reducing end of the polysaccharide. Detection of the polysaccharides after gel electrophoresis was carried out by fluorography of samples labeled by sodium borotritiide reduction or by combined alcian blue and silver staining. The smallest components could be detected only by fluorography, owing to diffusion during staining. Components of the E. coli K1 polysialic acid capsule ranging from monomers to 80 sialic-acid-unit-containing polymers could be separated as distinct bands in a ladderlike pattern. A maximum chain length of 160 to 230 sialyl residues was estimated for the bulk of the K1 polysaccharide from the nearly linear reciprocal relationship between the logarithm of the molecular size and the distance of migration. Gel electrophoresis of capsular polysaccharides of other bacterial species revealed different electrophoretic mobilities for each polysaccharide, with a ladderlike pattern displayed by the fastest-moving components. There are many potential applications of this facile method for the determination of the sizes of molecules present in a polydisperse polysaccharide sample. When combined with the simple method for the isolation of the capsule, as in the case of the K1 capsule, it provides an efficient tool for the characterization and comparison of the capsular polysaccharides of bacteria.     

Experimental and Imaging Techniques for Examining Fibrin Clot Structures in Normal and Diseased States

Fibrin is an extracellular matrix protein that is responsible for maintaining the structural integrity of blood clots. Much research has been done on fibrin in the past years to include the investigation of synthesis, structure-function, and lysis of clots. However, there is still much unknown about the morphological and structural features of clots that ensue from patients with disease. In this research study, experimental techniques are presented that allow for the examination of morphological differences of abnormal clot structures due to diseased states such as diabetes and sickle cell anemia. Our study focuses on the preparation and evaluation of fibrin clots in order to assess morphological differences using various experimental assays and confocal microscopy. In addition, a method is also described that allows for continuous, real-time calculation of lysis rates in fibrin clots. The techniques described herein are important for researchers and clinicians seeking to elucidate comorbid thrombotic pathologies such as myocardial infarctions, ischemic heart disease, and strokes in patients with diabetes or sickle cell disease.     

A new concept of the structure of the dual electrical layer on the cell surface under the action of a high concentration electrolyte

New data are presented describing the characteristics of double electrical layers on the surfaces of cells immersed in high electrolytic solutions. Gel glycosides located at the periphery of halo-forming cells play the key role in forming these structures.