Pea,Chickpea and Lentil Protein Isolates: Physicochemical Characterization and Emulsifying Properties

This work is focused on physicochemical and emulsifying properties of pea (PP), chickpea (CP) and lentil (LP) proteins. We evaluated the molecular weight distributions, surface net charge, free sulfhydryl group (SH) and disulfide bond (SS) contents, protein solubility and thermal stability of the protein isolates. Their emulsifying properties (droplet size distribution, flocculation, coalescence and creaming) were also determined as function of pH values. The three protein isolates exhibit similar physicochemical properties, including good solubility and high thermal stability despite a high degree of denaturation. In addition, we analysed the influence of pH on stability of oil-in-water (O/W; 10 wt%/90 wt%) emulsions stabilized by the legume protein isolates. Concerning emulsifying ability and stability, the most unfavourable results for all three protein isolates relate to their isoelectric point (pI?=?4.5). A significant improvement in emulsion stability takes place as the pH value departs from the pI. Overall, this study indicates that pea, chickpea and lentil proteins have great potential as food emulsifiers.     

Interfacial and Emulsifying Properties of Quinoa Protein Concentrates

Food Biophysics - Most protein concentrates used by the food industry are derived from soybean or wheat, but a pseudocereal like quinoa is gaining interest worldwide. The aim of this study is the...     

Heat Denaturation and Emulsifying Properties of Plasma Protein

The effects of pH and NaCl on the denaturation of plasma protein during heat treatment were investigated, as well as the relationship between protein structure and emulsifying properties. When the plasma protein solution (1% w/v) was heated at 80°C, precipitation was accelerated by the presence of NaCl. The measurement of SH groups, surface hydrophobicity and CD spectrum revealed that denaturation occurs easily by heat treatment in the neutral pH region and in the presence of NaCl. The emulsifying activity index (EAI) did not change much after heat treatment at pH 3 irrespective of the presence of NaCl, but it decreased about 60% after heat treatment at pH 7 in the absence of NaCl. Gel filtration patterns indicated that a high molecular weight peak arose upon heat treatment at neutral pH. We concluded that the decrease in EAI was owing to the polymerization of serum albumin and γ-globulin, which are the main components of plasma protein, and disulfide bonds participated in this process.     

Effects of Extrusion on the Emulsifying Properties of Rumen and Soy Protein

Defatted rumen protein and soy protein concentrate were extruded in a 15.5:1 L/D single-screw extruder at the optimum conditions for their expansion (150°C and 35% moisture, and 130°C and 35% moisture, respectively). Emulsions were produced with these proteins and studied by rheology and time domain low-resolution ¹H nuclear magnetic resonance (TD-NMR). Extrusion increased storage modulus of rumen protein emulsions. The opposite was observed for soy protein. Mechanical relaxation showed the existence of three relaxing components in the emulsions whose relative contributions were changed by extrusion. Likewise, spin–spin relaxation time constants (T ₂) measured by TD-NMR also showed three major distinct populations of protons in respect to their mobility that were also altered by extrusion. Extrusion increased surface hydrophobicity of both rumen and soy protein. Solubility of rumen protein increased with extrusion whereas soy protein had its solubility decreased after processing. Extrusion promoted molecular reorganization of protein, increasing its superficial hydrophobicity, affecting its interfacial properties and improving its emulsifying behavior. The results show that extrusion can promote the use of rumen, a by-product waste from the meat industry, in human nutrition by replacing soy protein in food emulsions.     

The Formation and Disaggregation of Soy Protein Isolate Fibril: Effects of pH

To identify the effects of charged states on the formation and disaggregation of soy protein isolate (SPI) fibril, we studied the thermal aggregation behaviors of the constituent peptides of SPI fibril (CPSF) at various pH values (2–10) and investigated the structural changes of SPI fibril with increasing pH (2–11). Results showed that CPSF would assemble into diverse shapes at different pH values, among which the aggregates contained multiple β-sheet structures at pH less than 6, but these β-sheets were stacked to form fibrils only at pH 2. The damages from the increased pH to SPI fibril structure could be roughly divided into two stages, as follows: when pH was less than or equal to 6, the morphology of fibrils changed markedly due to electrostatic neutralization; at pH larger than 6, the fibrils suffered great losses in β-sheet, causing its structure to disintegrate rapidly. This study could provide theoretical reference to improve the pH stability of SPI fibril from the aspects of preparation and structural protection of the fibril.

     

Preliminary Crystallographic Analysis of a Cruciferin Protein from Seeds of Moringa oleifera

A 55 kDa cruciferin protein has been purified and characterized from seeds of Moringa oleifera plant. Protein blast of N-terminal amino-acid sequence showed 60 % sequence similarity with cruciferin from Brassica napus. The M. oleifera protein has been crystallized applying the sitting drop method using 5 % polyethylene glycol 8,000, 38.5 % 3-methyl-1,5-pentanediol and 0.1 M sodium cacodylate pH 6.5. The crystals belonged to the P6322 hexagonal space group with cell dimensions, a = b = 98.4, c = 274.3 Å. Initial diffraction data have been collected to a resolution of 6 Å.     

Physicochemical Properties of Photoconvertible Fluorescent Protein from Montastraea cavernosa

Russian Journal of Bioorganic Chemistry - Among the wide variety of currently known fluorescent probes, photoconvertible fluorescent proteins (PCFPs), which are capable to irreversibly change their...     

Effect of Counterions on Physicochemical Properties of Prazosin Salts

This study evaluated the effect of counterions on the physicochemical properties of prazosin salts. Salt forms of prazosin, namely, mesylate, besylate, tosylate, camsylate, oxalate, and maleate, were prepared and compared with the marketed anhydrous and polyhydrate forms of prazosin hydrochloride. Physicochemical characterization was performed in the order of crystallinity, hygroscopicity, solubility, and stability to select the optimal salt(s). Permeability study in Caco-2 cell lines and in vivo bioavailability study in rat model were investigated to ascertain their biopharmaceutical advantage. All salt forms were crystalline, nonhygroscopic (except the anhydrous hydrochloride salt), and had solubility in the range of 0.2 to 1.6 mg/ml. All salts were physically and chemically stable at 40°C/75% relative humidity, but degraded in UV-visible light, except the anhydrous hydrochloride salt. Prazosin mesylate was selected as the optimal salt, as it possessed higher solubility, permeability, and bioavailability, compared to the commercial hydrochloride salts. Hydrochloride salt is reported to have poor bioavailability that is partially attributed to its low solubility and extensive common-ion effect in the gastric region. Factors like hydrophilicity of the counterion, hydration state of the salt, and melting point of the salt contribute to the physicochemical properties of the salts. This study has implications in the selection of an optimal salt form for prazosin, which is suitable for further development.     

Effects of Oxidation on Water Distribution and Physicochemical Properties of Porcine Myofibrillar Protein Gel

The effects of hydroxyl radicals induced oxidation on water distribution of porcine myofibrillar protein (MP) gels were investigated using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), and relationship between MP gel properties and water distribution was analyzed with Pearson’s correlation. Results of NMR spin-spin relaxation time (T₂) and MRI suggested that, comparing with unoxidized MP gel, the population of immobile water of gel (P₂₂) decreased by 18.81 %, while that of free water (P₂₃) increased by 85.56 %, and grey scale value decreased by 18.52 %, after being oxidized with 20 mM H₂O₂, respectively. Images of scanning electron microscope (SEM) showed the highest degree of oxidation led to the most coarse and porous gel-network. Gel properties including WHC, whiteness and strength of MP gels decreased by 14.65 %, 2.83 % and 52.74 % after being oxidized with 20 mM H₂O₂ (p?<?0.05), respectively. Pearson’s correlation analysis showed oxidation, gel-properties and NMR results were highly correlated (p?<?0.05). Therefore, we hypothesized that hydroxyl radicals induced oxidation resulted in immobile water shifting to free water partly, thus reduced the abundance of water and gel properties of gels.     

Combining Effect of Microbial Transglutaminase and Bambara Groundnut Protein Isolate on Gel Properties of Surimi from Sardine (Sardinella albella)

Effects of protein isolate from bambara groundnut (BGPI) at different levels (0–6 %, w/w) in combination with microbial transglutaminase (MTGase) at different concentrations (0, 0.3 and 0.6 U g^?1surimi) on gels properties of sardine (Sardinella albella) surimi were investigated. In the absence of MTGase, the increases in breaking force and deformation of gels were obtained when BGPI at levels of 1.5–3 % was incorporated (P?<?0.05). The further increases in BGPI levels (4.5–6 %) resulted in the decrease in breaking force and deformation (P?<?0.05). When MTGase (0.3 and 0.6 U g^?1surimi) was added, the increase in breaking force and deformation were noticed, regardless of BGPI levels, and the strengthening effect was in dose-dependent manner. The increases in hardness, gumminess and chewiness were also observed when surimi gel was added with BGPI and MTGase (P?<?0.05). Water-holding capacity of gels was improved with increasing level of BGPI, and MTGase incorporated (P?<?0.05). Whiteness of gels slightly decreased with increasing BGPI levels, however the addition of MTGase had no impact on whiteness (P?>?0.05). Based on electrophoretic study, myosin heavy chain decreased with addition of MTGase, indicating the formation of cross-links. More compact structure was observed in gel added with MTGase (0.6 U g^?1surimi) and 6 % BGPI, and was accompanied by an increased gel strength.     

Effects of pH and Repellent Tactic Stimuli on Protein Methylation Levels in Escherichia coli

Intracellular pH (pH_int) and extracellular pH (pH_ext) of Escherichia coli were measured at 12-s time resolution by ³¹P-nuclear magnetic resonance: a sudden neutral-to-acid shift in pH_ext (e.g., from 7.0 to 5.6) caused a transient failure of homeostasis, with pH_int decreasing by about 0.4 unit in ca. 30 s and then returning to its original value (ca. 7.5) over a period of several minutes. Membrane proton conductance was estimated to be 20 pmol s⁻¹ cm⁻² pH unit⁻¹. Addition of the membrane-permeant weak acid benzoate at constant pH_ext also caused a lowering of pH_int; at high concentrations it generated an inverted transmembrane pH gradient (ΔpH). The buffering capacity of the cells was estimated by such experiments to be ca. 50 mM per pH unit. Effects of pH-related stimuli on the methyl-accepting chemotaxis proteins (MCPs) were examined: the steady-state methylation of MCP I was found to decrease when pH_int was lowered by weak acid addition or when pH_ext was lowered. The extent of demethylation in the latter case was too great to be explained by imperfect steady-state homeostasis; a small but reproducible undershoot in methylation level correlated with the observed short-term homeostatic failure. MCP II underwent smaller and more complex changes than MCP I, in response to pH-related stimuli. The methylation level of MCP I could not, by any condition tested, be driven below a limit of ca. 15% of the control level (unstimulated cells at pH_ext 7.0). The weak-acid concentration needed to reach that limit was dependent on pH_ext, as would be expected on the basis of ΔpH-driven concentrative effects. The potency ranking of weak acids was the same with respect to lowering pH_int, demethylating MCP I, and causing repellent behavioral responses. The data are consistent with a model whereby MCP I and hence tactic behavior are sensitive to both pH_int and pH_ext. Evidence is presented that pH_int may also have a direct (non-MCP-related) effect on motor function. Comparison of methyl-³H- and ³⁵S-labeled MCP I revealed that in both unstimulated and repellent-stimulated cells the major species did not carry methyl label, yet it had an electrophoretic mobility that indicated that it was more positively charged than the unmethylated form observed in methyltransferase mutants, and it was susceptible to base hydrolysis. This suggests that a substantial fraction of MCP I molecules is methylated or otherwise modified but neither exchanges methyl label nor undergoes reverse modification by repellent stimuli.     

Whipping and Emulsifying Properties of Soybean Products

Both whipping and emulsifying properties, the characteristic functional properties of soybean products, were investigated by using the commercial products in Japan. Whipping properties of the soybean products, expressed by foam expansion and foam stability, were found to correlate with water dispersible nitrogen, and the resultant foams were stable when the dissolved proteins were native. Thus, the native defatted soybean flour which contained native and soluble protein exhibited excellent whipping property. Emulsifying properties correlated positively with protein and negatively with fiber contents. As soybean protein isolate and soybean protein extract are rich in protein and poor in fiber contents, both of them show good emulsifying functions.     

Interfacial and Emulsifying Characteristics of Acid-treated Pea Protein

This work presents equilibrium and dynamic aspects for the adsorption at the oil–water interface of pea (Pisum sativum L.) protein isolate (PPI). Dynamic interfacial tension, γ, and surface viscoelasticity modulus, ε, were determined using pendant-drop method. Adsorption kinetics studies revealed that pea proteins adsorb faster at pH 7.0 than at acidic pH (pH 2.4). On the other hand, the measured ε is lower at pH 7.0. This is probably due to fast adsorption, leading to the formation of inhomogeneous film structures. In fact, compared with pHs above the isoelectric point (pI ~ 4.3), acidic conditions slow down the adsorption, but the modulus is increased. Pea-protein-stabilized emulsions are more stable to creaming at acidic pH and their particle-size distributions are more homogeneous in these conditions. Effect of pH on interfacial properties and on properties of oil-in-water emulsions stabilized by PPI was interpreted in terms of pea protein solubility, globulin dissociation, and oil-droplet surface electrostatic charge. We propose that at acidic conditions, adsorbed dissociated globulins form stronger and denser viscoelastic networks when adsorbed at oil–water interface. Consequently, the pH-dependence of pea-globulin-stabilized emulsions properties could be of great interest to tune barrier properties of oil/water interfacial membranes for several applications such as encapsulation and controlled release of lipophilic bioactive components within the food, medical, and pharmaceutical industries.     

Effects of Hasten Drying and Storage Conditions on Properties and Microstructure of Konjac Glucomannan-Whey Protein Isolate Blend Films

Impact of drying process and storage conditions on properties of konjac glucomannan (KGM) and whey protein isolate (WPI) blend films was investigated. Hundred grams of film solution contained 0.4 g KGM, 3.8 g WPI and 1.5 g glycerol. During drying process, air velocity was varied to produce fast drying (3 h) and slow drying (15 h) in tray dryers under 50 °C. The high air velocity resulted in a significant higher drying rate in fast drying than low air velocity in slow drying. Drying curves from both processes were well-fitted with Page model and Henderson and Pabis model (R² ≥ 0.98). Fast drying improved transparency and mechanical properties without impairing color, solubility or water vapor permeability (WVP). Fast-dried film had less surface roughness and contained larger protein clusters. It also had greater melting enthalpy of protein aggregates, implying stronger networks. For stability study, fast-dried film was stored at 4-35 °C for 24 days. Transparency decreased over time. Overall mechanical properties have improved during storage. Color, solubility and WVP did not significantly change over time at all conditions (p?>?0.05). Microstructure of aged films was relatively similar to that of the freshly prepared film. Overall, the fast-dried KGM-WPI film exhibited reasonable storage stability.     

过氧化氢对铜锌超氧化物歧化酶活性及某些理化性质的影响

用H_2O_2作用于牦牛红细胞铜锌超氧化物歧化酶。观察到酶活性随H_2O_2浓度升高及作用时间增加而下降;酶分子连接的铜和锌有所丢失;PAGE图谱中三条酶活性带成为四条酶活性带;等电点下降;680nm处表征二价铜光学性质的可见光吸收减弱;紫外吸收增加,表现为增色效应;内源性荧光减弱;在含有3.0mol/LKCl的PH3.8—5.4琥珀酸缓冲液中溶解度下降;酶对胰蛋白酶水解的敏感性增加。     

乌梅丸水提液中多糖理化性质分析及预防结肠炎的作用

目的:考察乌梅丸水提液中多糖含量,建立HPLC法分析乌梅丸多糖分子量及单糖组成方法,观察其对右旋葡聚糖硫酸钠(DSS)所致小鼠溃疡性结肠炎(UC)的预防作用,为乌梅丸临床用药及药理活性成分的研究提供依据。方法:采用水提醇沉法提取多糖;硫酸-苯酚法测定乌梅丸多糖含量;凝胶色谱法-龙智达分子量工作站测定多糖分子量;PMP柱前衍生化法HPLC分析单糖组成;DSS(3%)法建立UC小鼠模型。ICR小鼠50只随机分为5组:正常组,模型组,乌梅丸多糖2.5%,5%,10%剂量组,每组10只。造模前7天,在乌梅丸多糖治疗各组的小鼠饮水中添加乌梅丸多糖,一直给药维持至实验结束(第14天)。结果:葡萄糖在0~0.08 mg·m L-1浓度范围内呈良好的线性关系(r=0.998);右旋葡聚糖酐标准品分子量在2500~2000000 Da范围内呈良好线性关系(r=0.998);乌梅丸水提液中多糖含量为40.3%,纯化的乌梅丸多糖糖含量为91.6%;分子量范围在171343~525009 Da之间,分布系数D=1.18;其多糖的单糖组成主要为甘露糖、葡萄糖醛酸、葡萄糖、半乳糖和木糖组成,其相对含量比为1.8:1.0:19.3:32.8:4.2;乌梅丸多糖能降低结肠组织损伤程度。结论:多糖可能是乌梅丸汤剂中有效的活性成分,对小鼠UC有一定的防治作用,其理化性质分析方法简便快速,结果准确,重复性好,可作为乌梅丸多糖的质量控制方法。     

不同品种水稻秸秆的理化特性及酶解产糖的研究

本研究以不同品种水稻秸秆为原料,测定分析了三大主要组分纤维素、半纤维素和木质素含量及理化特性的差异,并分析对比了经碱预处理后酶解及直接酶解的产糖率差异。利用X-射线衍射仪测定分析了结晶度和晶粒尺寸的异同,红外光谱仪定性评估了特定基团的差异,扫描电镜观察分析了表面形态结构的差异。综合考虑理化特性和酶解产糖率结果,与a(常规水稻黄华占)相比,5种不同品种的超级杂交水稻秸秆中,b(杂交水稻Y两优1)、c(杂交水稻隆两优2010)和f(杂交水稻Y两优143)三个品种的秸秆材料比较适合作为酶解产糖的原材料。     

Effect of the Supplementation of Sulfur Amino Acids to a Diet Containing Soy Protein Isolate on Lipid Metabolism in Rats

The effect of the supplementation of sulfur amino acids to a low casein or soy protein isolate diet on tissue lipid metabolism was investigated. Supplementation of methionine to a 8% casein diet produced a fatty liver in rats, however, supplementation of methionine to a 8.8% soy protein diet (corresponding to a 8% casein diet as to sulfur amino acids content) did not produce a fatty liver. At the level of 8% or less of soy protein in the diet, the accumulation of liver lipids and serum triglyceride was observed. An amino acid mixture simulating the composition of soy protein isolate caused significant accumulation of liver lipids, but serum triglyceride was not changed. Serum cholesterol in rats fed the soy protein diet was lower than that in rats fed the casein diet, but on feeding the amino acid mixtures simulating these protein diets, there was no difference between the two groups. The small differences between soy protein isolate and casein as to lipid metabolism might be due to the small differences in the contents of sulfur amino acids or the specific nature of the soy protein or casein. The supplemental effect of methionine and cystine was also studied. About 60% of total sulfur amino acids could be substituted by cystine for maximum growth.     

Effect of Maltodextrin Dextrose Equivalent on Electrospinnability and Glycation Reaction of Blends with Pea Protein Isolate

Compared to commonly applied wet and dry heating procedures, a combination of electrospinning and heat treatment can facilitate glycation of proteins with reducing polysaccharides. This study investigates how the amount of reducing carbonyl groups (i.e. dextrose equivalent, DE) of different maltodextrins influences electrospinnability and subsequent glycation in blends with pea protein isolate (PPI). In the first step of the study, maltodextrin-PPI dispersions were electrospun. The concentrations of PPI and maltodextrin DE 2 were kept constant in the aqueous spinning dispersion. The addition of 0.05 or 0.1 g/mL maltodextrin DE 12 or 21 slightly affected the electrical conductivity and dynamic viscosity of the spinning dispersions, however, fiber production rate and morphology were dominated by the presence of maltodextrin DE 2 (0.8 g/mL). In the second step of the study, fibers were heated (60 °C, 75% rel. Humidity, 0–24 h). SDS-PAGE analysis and the measurement of free amino groups confirmed the covalent attachment of maltodextrin carbonyl groups to free amino groups of PPI. The fastest glycation and the lowest relative amount of free amino groups (49.70 ± 6.54%) after 24 h heating was measured for the fibers with the highest amount of reducing carbonyl groups. The fibers with the lowest amount of reducing carbonyl groups showed no significant (p < 0.05) decrease of free amino groups after heat treatment. The results suggest that within the boundaries of electrospinnability, the degree of glycation can be adjusted by varying the amount of reducing carbonyl groups in the fibers.