Fractionation, solubility and functional properties of wheat bran proteins as influenced by pH and/or salt concentration

The content, fractionation, solubility and functional properties of wheat bran proteins as well as the effects of pH and/or NaCl concentration on some of these functional properties were investigated. The protein content of the bran was found to be 16.80%. Albumin and glutelin are the major fractions of wheat bran proteins. The minimal protein solubility was observed at pH 5.5, the maximum at pH 11.5. The emulsifying capacity, activity and emulsion stability as well as foaming capacity and foam stability were greatly affected by pH and salt concentrations. Lower values were observed at acidic pH and high salt concentration. The least gelation concentration of wheat bran proteins was found to be 16% when the proteins were dissolved in 1.0 M NaCl. The total protein was highly viscous and dispersable with water-holding capacity of 4.20 mL H2O/g protein, oil-holding capacity of 1.70 mL oil/g protein and bulk density of 0.29 g/mL while dispensability was found to be 77.30%.     

Effects of pH and salt concentration on functional properties of rambutan (Nephelium lappaceum L.) seed albumin concentrate

Searching new protein sources is essential due to an increase in protein demand. In this study, rambutan seed albumin concentrate (RSAC) with the protein content of 80.8% was isolated from defatted rambutan seed meal. The effects of pH and sodium chloride concentration on solubility and functional properties of RSAC were investigated. RSAC had minimum solubility at pH 4. Water absorption capacity at pH 7 and oil absorption capacity of RSAC were 0.79 and 6.13 mL g^?1, respectively. Both foaming and emulsifying capacities achieved maximal levels at pH 12. In sodium chloride solution, foaming capacity and stability achieved maximal levels at the concentration of 0.6 mol L^?1, while the highest emulsifying capacity and stability were noted at the concentration of 0.2 mol L^?1. The least gelation concentration of RSAC was 100 g L^?1 and this value decreased by five times as salt concentration in the protein solution was 0.6 mol L^?1. RSAC was a potential functional ingredient in food processing.     

Emulsifying and foaming properties of transglutaminase-treated wheat gluten hydrolysate as influenced by pH,temperature and salt

Hydrolyzed wheat gluten (GH, 77–85% protein) was prepared by limited hydrolysis with chymotrypsin at 37 °C for 4 h (degree of hydrolysis=6.4%) and 15 h (degree of hydrolysis=10.3%). The effect of microbial transglutaminase (MTGase) treatment (55 °C for 1 h, or 5 °C for 18 h) on the emulsifying and foaming properties of GH was evaluated under selected food processing conditions (pH 4.0 and 6.5, 0 and 0.6 M NaCl, and temperature 20 and 5 °C). At pH 4.0 and 0 M NaCl the MTGase treatment substantially increased foaming capacity (FC) of GH compared with their respective control GH samples, as a result of enhanced peptide adsorption to the air–water interface, but FC was similar for both control and MTGase-treated GH at pH 6.5. In contrast, foam drainage stability (FS) of MTGase-treated GH decreased at pH 4.0, but increased significantly (P<0.05) at pH 6.5 when compared with their respective control GH samples. The FC and FS were affected by 0.6 M NaCl in a pH-dependent manner. The MTGase treatments increased emulsion activity index up to 15-fold at pH 6.5, while emulsion stability index was influenced by emulsion temperature and ionic strength conditions. The MTGase-induced changes in functional properties of GH were attributed to pH-dependent solubility changes, the amphiphilic nature of gluten peptides and increased electrostatic repulsion resulting from deamidation.     

Solid-solution partitioning of organic matter in soils as influenced by an increase in pH or Ca concentration

Organic matter is an important component of soil with regard to the binding of contaminants. Hence, the partitioning of organic matter influences the partitioning of soil contaminants. The partitioning of organic matter is, among other factors, influenced by the ionic composition and ionic strength of the soil solution. This study focuses on the behavior of organic matter after a change in the ionic composition of the soil solution, particularly in Ca concentration and pH. Different amounts of Ca(NO3)2 and NaOH were added to soil suspensions. The dissolved organic carbon (DOC) concentration increased with increasing pH (addition of NaOH), whereas an increase in Ca (addition of Ca(NO3)2) had the opposite effect. A stronger increase in DOC was observed if a single dose of NaOH was added, compared to a gradual addition of the same amount of NaOH. Cation binding by organic matter in the supernatant was calculated using the NICA-Donnan model. The log DOC concentration appeared to be correlated to the Donnan potential, calculated under the assumption that all DOC equals humic acid. This correlation was found for all eight neutral to acidic soils used in this study, although the slopes and elevations of the regression lines varied. The slope varied by a factor of 2 and the elevation appeared to be strongly influenced by the DOC concentration in the untreated soils, which is related to the total organic matter in the soil. Finally, we predicted the Donnan potential on the basis of an extraction of untreated soil with 0.03 M NaNO3, and the total additions of Ca(NO3)2 and NaOH. Comparison of these predictions with speciation calculations in solution showed a good correlation, indicating that a combination of one batch experiment and the presented calculation procedure can provide good estimations of DOC concentrations after addition of chemicals.     

Structural properties of stirred yoghurt as influenced by whey proteins

The effect of whey protein addition on structural properties of stirred yoghurt systems at different protein and fat content was studied using laser diffraction spectroscopy, rheology and confocal laser scanning microscopy (CLSM). The composition of heated milk systems affected micro- and macroscopic properties of yoghurt gels. Particle size increased as a function of increasing whey protein content and decreased as a function of increased fat level. Firmness (elastic modulus) and apparent viscosity of manufactured yoghurt samples increased as a function of increased interparticle interactions, mainly caused by self-aggregation of whey proteins or aggregated whey protein-coated fat globules, respectively. The resistance towards shear-induced disruption of yoghurt gels increased with an increasing proportion of casein protein in the protein mixture, whereas products with high whey protein level revealed lower resistance behaviour towards shear-forces. CLSM images illustrated that the presence of large whey protein aggregates and lower number of fat globules lead to the formation of an interrupted and coarse gel microstructure characterised by large interstitial spaces. The higher the casein fraction and/or the fat level, the less interspaced voids in the network were observed. However, it is evident that the addition of whey proteins reinforces firmness properties of low-fat yoghurts comparable to characteristics of full-fat yoghurt.     

Solubility and density of egg white proteins: Effect of pH and saline concentration

Influence of different pH values (3.0, 4.6, 6.0, 8.0 and 9.0) and salt concentrations (0.05, 0.1, 0.2, 0.35 and 0.5 mol/l) for three types of salt (NaCl, Na₂SO₄ and (NH₄)₂SO₄) on the solubility of egg white protein and density of egg white, at room temperature (25 °C) was studied. The results showed that the solubility of egg white protein was influenced by pH as well as concentration and type of salt present in the medium. Protein solubility increased with increase in pH, with higher solubility showed at pH 9.0 and lower solubility at pH 4.6. This behavior was verified for all the salts analysed. At acid pH (pH 3.0), it was observed the tendency of solubility elevation on the increase of the saline concentration, due to the salting-in effect. The density increased with increase in the salt concentration.     

芝麻蛋白提取液超滤浓缩工艺及其功能特性研究

研究超滤法浓缩芝麻蛋白提取液的工艺条件及芝麻蛋白的主要功能特性。以膜通量为评价指标,通过单因素实验,探讨了超滤压力、温度、p H和时间对芝麻蛋白提取液膜通量的影响,在此基础上通过正交实验确定超滤浓缩的最佳工艺参数。结果表明,超滤浓缩芝麻蛋白提取液的最佳工艺条件为:超滤压力为0.25MPa,提取液p H为10.0,超滤时间为15min。在此条件下获得的芝麻蛋白具有良好的功能特性,其中乳化性和乳化稳定性及发泡性能显著高于等电点沉淀法制备的芝麻蛋白(p<0.05)。本研究为芝麻蛋白的深入研究和开发利用提供一定的参考。      

草鱼盐溶蛋白溶解性的研究

采用响应面试验设计对影响盐溶蛋白溶解性的因素进行研究。结果表明,离子强度(A)为0.58,pH(B)8.16,温度(C)为32.75℃时,溶解性达到最大。离子强度和温度对溶解性的影响均显著。三因素之间的回归方程为溶解性=0.45+0.052A+0.036B-0.042C-0.014AB-0.035AC-1.425×10-3BC-0.048A2-0.075B2+0.026C,R2=0.9176。     

Characteristics and functional properties of gelatin from seabass skin as influenced by defatting

Gelatins from nondefatted and defatted seabass skins were characterised and evaluated for their functional properties in comparison with commercial fish skin gelatin. All gelatins contained α₁‐ and α₂‐chains as the predominant components and showed a high imino acid content (199–201 residues/1000 residues). All gelatins had a relative solubility greater than 90% in the wide pH ranges (1–10). Foaming properties of all gelatins increased with increasing concentrations (1–3%, w/v). Gelatin from defatted skin had higher foam expansion and stability than that extracted from nondefatted skin. Emulsion containing gelatin from defatted skin had smaller oil droplet size (d₃₂, d₄₃), compared with that having gelatin from nondefatted skin (P < 0.05). After 10 days of storage at room temperature (28–30 °C), emulsion stabilised by gelatin from defatted skin showed the higher stability as indicated by the lower increases in d₃₂ and d₄₃, and lower flocculation factor and coalescence index. Coincidentally, emulsion stabilised by gelatin from defatted skin had higher zeta potential than that containing gelatin from nondefatted skin. Thus, defatting of seabass skin directly affected characteristics and functional properties of resulting gelatin.     

Ultraviolet spectrophotometric characterization and bactericidal properties of electrolyzed oxidizing water as influenced by amperage and pH

To identify the primary component responsible in electrolyzed oxidizing (EO) water for inactivation, this study determined the concentrations of hypochlorous acid (HOCl) and hypochlorite ions (OCl-) and related those concentrations to the microbicidal activity of the water. The ultraviolet absorption spectra were used to determine the concentrations of HOCl and OCl- in EO water and the chemical equilibrium of these species with change in pH and amperage. EO water generated at higher amperage contained a higher chlorine concentration. The maximum concentration of HOCl was observed around pH 4 where the maximum log reduction (2.3 log10 CFU/ml) of Bacillus cereus F4431/73 vegetative cells also occurred. The high correlation (r = 0.95) between HOCl concentrations and bactericidal effectiveness of EO water supports HOCl's role as the primary inactivation agent. Caution should be taken with standard titrimetric methods for measurement of chlorine as they cannot differentiate the levels of HOCl present in EO water of varying pHs.     

The solubility of potato proteins from industrial potato fruit juice as influenced by pH and various additives

The effects of pH and various additives on the precipitation and (re)solubility at pH 7 of potato proteins from industrial potato fruit juice (PFJ) were studied. The use of various strong and weak acids did not result in differences in protein precipitation, which on average occurred to a maximum of 60% of total protein at pH 3. Weak acids did, however, result in precipitates with a higher resolubility at pH 7 compared with strong acids. At pH 5, addition of FeCl₃ or ZnCl₂ increased both precipitation and resolubility compared with the situation without additives. The largest increases in both precipitation and resolubility were achieved using organic solvents at pH 5 as an additive, resulting in a maximum precipitation and maximum resolubility at pH 7 of 91 and 83% of total protein respectively. The results described in this study lead to the hypothesis that precipitation and resolubilisation of potato proteins from PFJ are not determined by their isoelectric pH but by their interactions with low‐molecular‐weight components. © 2001 Society of Chemical Industry     

Mathematically modeling the repair of heat-injured Listeria monocytogenes as affected by temperature, pH, and salt concentration

Heat-injured cells of Listeria monocytogenes were inoculated into Listeria repair broth (LRB) adjusted to various pH levels (4.2, 5.0, 6.6, 8.0 and 9.6) and salt concentrations (0.5%, 2.5%, 5.0%, 7.5% and 10.0% w/v) at controlled temperatures (4, 10, 22, 37 and 43 °C) in a complete factorial manner (5³). Repair of the injured microorganisms was evaluated using selective and non-selective plating media. The Gompertz parameters, which were generated by fitting the equation with the bacterial counts, were used to calculate the repair percentage as a function of time from which the repair time was estimated. All growth curves fit the Gompertz equation well (R² ≥ 0.972). A first-order model described the repair trend closely (R² = 0.989 ± 0.011). Heat-injured Listeria could fully repair in LRB only under 63 of 125 conditions tested during 21 days of incubation. Refrigeration temperature was the most effective means to prevent the repair of heat-injured Listeria. The minimum temperature required for repair increased with an increase in NaCl concentration. The pH ranges at which the repair could occur were narrower at 4 and 10 °C than those at higher temperature. The repair was observed in media containing 10% NaCl between temperatures of 22 and 43 °C at pH 6.6.     

Characterisation and functional properties of watermelon (Citrullus lanatus) seed proteins

BACKGROUND: People in developing countries depend largely on non‐conventional protein sources to augment the availability of proteins in their diets. Watermelon seed meal is reported to contain an adequate amount of nutritional proteins that could be extracted for use as nutritional ingredients in food products. RESULTS: Osborne classification showed that globulin was the major protein (≥500 g kg ^?1) present in watermelon seed meal, followed by albumin and glutelin. Sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that the polypeptides had low molecular weights ranging from 35 to 47 kDa. Isoelectric focusing revealed that the isoelectric point of most proteins was in the acidic range 4–6. These proteins are rich in aspartic acid, glutamic acid and serine. An increase in pH (5–9) significantly (P < 0.05) decreased the denaturation enthalpy of these proteins. Among functional properties, albumin exhibited a much higher dispersibility index (810.3–869.6 g kg^?1) than globulin (227.8–245.4 g kg^?1), glutelin (182.1–187.7 g kg^?1) and prolamin (162.3–177.7 g kg^?1). Digestibility was in the ranges 760.6–910.0 and 765.5–888.5 g kg^?1 for Mateera and Sugar Baby watermelon protein fractions respectively, while surface hydrophobicity ranged from 126.4 to 173.2 and from 125.8 to 169.3 respectively. The foaming and emulsifying properties of albumin were better than those of the other proteins studied. CONCLUSION: The good nutritional and functional properties of watermelon seed meal proteins suggest their potential use in food formulations. Copyright © 2010 Society of Chemical Industry     

Manipulating interfacial behaviour and emulsifying properties of myofibrillar proteins by L-Arginine at low and high salt concentration

The present work examined the impact of L-Arginine (Arg) on the emulsifying properties, interfacial behaviour and conformational characteristics of myofibrillar proteins (MPs) at high (0.6 m ) and low (0.15 m ) salt concentration to maintain good emulsifying properties of MPs at low salt concentration. The data indicated that Arg increased the emulsifying activity index/emulsion stability index (EAI/ESI) and decreased the CI and droplet size of emulsions regardless of salt concentration. Raman spectra revealed that the α-helix content decreased from 60.30% to 51.26% at high salt concentration, and from 60.20% to 54.82% at low salt concentration in the presence of Arg. In addition, MPs treated with Arg exhibited a higher interfacial pressure and more rapidly diffusion to the oil surface. Meanwhile, Arg increased the interfacial protein loading. The results demonstrated that Arg caused the unfolding of MPs, promoting the adsorption of proteins and decreasing the interfacial tension, ultimately improving the stability of emulsions at low salt concentration.     

Sensory and functional properties of cheese: incorporation of whey proteins by pH manipulation and heat treatment

The effect of pH manipulation prior to high heat treatment on the effectiveness of whey protein denaturation in milk for cheesemaking has been studied. It has been found that the severity of heat treatment of milk required for denaturation can be reduced if the pH is altered during heating. The sensory and functional properties of cheddar-type cheese produced for high heat treated milk can be improved by manipulation of pH on heat treatment of milk.     

芝麻湿法脱皮和芝麻仁热风干燥工艺研究

对芝麻湿法脱皮和芝麻仁热风干燥工艺进行研究。以脱皮率、亮度和黄色值的综合评分为指标,通过单因素和正交试验,确定芝麻湿法脱皮最佳工艺条件为:碱液质量浓度0.9 g/mL,浸泡温度60℃,浸泡时间5 min,料液比1∶6。在最佳脱皮工艺条件下,芝麻仁品质的综合评分为154.51。此脱皮工艺结合热风干燥能够得到高品质的芝麻仁产品。     

碱与热处理对大米蛋白质结构与功能性质的影响

以大米蛋白质为原料,研究碱处理和热处理对大米蛋白质结构与功能性质的影响。研究结果发现:经不同pH处理40 min后,大米蛋白质功能性质均有一定程度改善,其中经pH 12. 0/40 min处理的大米蛋白质溶解性、乳化性与乳化稳定性、起泡性分别提高了2. 46,2. 85,1. 12,2. 51倍;同时, 100 kDa的组分含量减少,此时蛋白质分子中的α-螺旋、β-转角含量分别减少了26. 99%,10. 54%,而β-折叠、无规卷曲含量分别增加了14. 65%,20. 23%。采用50~90℃/40 min的条件对大米蛋白质进行热处理,其结构性质和溶解性、表面疏水性皆无明显变化;但乳化性与乳化稳定性、起泡性则随着热处理温度升高而提高,90℃热处理可达到最大值,分别是原大米蛋白质的2. 41,1. 09,1. 62倍。结果表明经单独碱处理、热处理后,大米蛋白质的结构发生了改变,但溶解度改善效果不明显。     

Antioxidant activity and functional properties of porcine plasma protein hydrolysate as influenced by the degree of hydrolysis

Antioxidant activity and functional properties of porcine blood plasma protein hydrolysates (PPH) prepared with Alcalase at 6.2%, 12.7% and 17.6% of degree of hydrolysis (DH) were investigated. The PPH showed stronger radical-scavenging ability and possessed stronger Cu²⁺-chelation ability and a reducing power compared to non-hydrolysed plasma protein (P < 0.05). The antioxidant activity of PPH, indicated by thiobarbituric acid-reactive substance (TBARS) values in a liposome-oxidising system, increased with increasing DH (P < 0.05). The Alcalase hydrolysis increased protein solubility from its original 68.46–81.79% (non-hydrolysed) to 82.95–94.94% (hydrolysed) over a broad pH range (3.0–8.0). However, hydrolysis decreased surface hydrophobicity and suppressed emulsifying and foaming capacity of the plasma protein. To identify antioxidant peptide, PPH was subjected to ultrafiltration, ion-exchange chromatography and reverse-phase high performance liquid chromatography (RP-HPLC), and the amino acid sequences of isolated peptides were determined by liquid chromatography/tendem mass spectrometry (LC–MS/MS). The peptide with the strongest antioxidant activity had the amino acid sequence of His-Asn-Gly-Asn. The results indicated that PPH could be used as a novel antioxidant but may be of limited utility as an emulsifying or foaming agent.     

Effect of pH and calcium concentration on some textural and functional properties of mozzarella cheese

The effects of Ca concentration and pH on the composition, microstructural, and functional properties of Mozzarella cheese were studied. Cheeses were made using a starter culture (control) or by direct acidification of the milk with lactic acid or lactic acid and glucono-delta-lactone. In each of three trials, four cheeses were produced: a control, CL, and three directly-acidified cheeses, DA1, DA2, and DA3. The cheeses were stored at 4 degrees C for 70 d. The Ca content and pH were varied by altering the pH at setting, pitching, and plasticization. The mean pH at 1 d and the Ca content (mg/g of protein) of the various cheeses were: CL, 5.42 and 27.7; DA1, 5.96 and 21.8; DA2, 5.93 and 29.6; DA3, 5.58 and 28.7. For cheeses with a high pH (i.e., approximately 5.9), reducing the Ca content from 29.6 to 21.8 mg/g of protein resulted in a significant decrease in the protein level and increases in the moisture content and mean level of nonexpressible serum (g/g of protein). Reducing the Ca concentration also resulted in a more swollen, hydrated para-casein matrix at 1 d. The decrease in Ca content in the high-pH cheeses coincided with increases in the mean stretchability and flowability of the melted cheese over the 70-d storage period. The fluidity of the melted cheese also increased when the Ca content was reduced, as reflected by a lower elastic shear modulus and a higher value for the phase angle, delta, of the melted cheese, especially after storage for <12 d. The melt time, flowability, and stretchability of the low-Ca, high-pH DA1 cheese at 1 d were similar to those for the CL cheese after storage for > or = 12 d. In contrast, the mean values for flowability and stretchability of the high-pH, high-Ca DA2 cheese over the 70-d period were significantly lower than those of the CL cheese. Reducing the pH of high-Ca cheese (27.7 to 29.6 mg/g of protein) from -5.95 to 5.58 resulted in higher flowability, stretchability, and fluidity of the melted cheese. For cheeses with similar pH and Ca concentration, the method of acidification had little effect on composition, microstructure, flowability, stretchability, and fluidity of the melted cheese.