Impact of ultrafiltration/diafiltration sequence on the production of soy protein isolate by membrane technologies

In previous studies, the advantages of combining electrodialysis using a bipolar-cationic membranes configuration to acidify a soy protein extract to pH 6 with ultrafiltration/diafiltration (UF/DF) using a 100 kDa membrane to produce a soy protein isolate with low phytic acid content and improved solubility between pH 2 and 4 was demonstrated, when compared to the production of soy protein isolates by isoelectric precipitation and by UF/DF of a soy protein extract at pH 9. However, limited work was done to establish the impact of the UF/DF sequence for the purification of the pH 6 extract. Therefore, the purpose of this work was to study the impact of four different UF/DF sequences with a total permeate volume of 1.5–1.6 times the initial volume, on membrane fouling and permeate flux, as well as on the isolate protein, ash and phytic acid contents and solubility profile. Of the investigated UF/DF sequences, the VCR 5, VD 4 sequence was shown to be the one with the most severe fouling and consequently the most severe permeate flux decline. At the same time, it was also the VCR 5, VD 4 sequence which was the most efficient in terms of ash and phytic acid removal, followed by the VCR 5, re-VCR5 sequence, the VCR 2, VD 2 sequence and the VCR 2, (re-VCR 2)X 2 sequence, respectively. It was also observed that isolate with low phytic acid content resulted in narrower protein solubility profiles around the isoelectric point and higher protein solubility for the pH range of 2 to 4.Industrial relevancePlant proteins have made up a higher proportion of the human diet in recent years. Soybeans are the most important source of plant protein ingredients accounting for some 68% of global plant protein consumption in the world. Soy protein isolate is traditionally prepared by isoelectric precipitation process. This process has high productivity, however, it results in products with poor functional properties due to protein denaturation and to the presence of phytic acid (1–3% w/w) which alters the solubility of the isolates especially for the pH below the proteins' isoelectric point. In this work, we combined electrodialysis using a bipolar-cationic membranes configuration to acidify a soy protein extract to pH 6 with ultrafiltration/diafiltration (UF/DF) using a 100 kDa membrane to produce soy protein isolates with low phytic acid content. The impact of four different UF/DF sequences on membrane fouling, permeate flux, isolate composition and solubility profile was studied. Of the investigated UF/DF sequences, the VCR 5, VD 4 sequence was shown to be the one with the most severe fouling but at the same time the most efficient in terms of ash and phytic acid removal. It was also observed that the isolate produced by the VCR 5, VD 4 sequence shows narrower protein solubility profiles around the isoelectric point and higher protein solubility for the pH range of 2 to 4 than isolates produced by alternative UF/DF sequences. This isolate could be considered as a valuable ingredient for the formulation of fruit juice beverages or power juices, considering that the pH of these liquid food products is around 3.5.     

Characterization of low-phytate soy protein isolates produced by membrane technologies

Soy protein isolates (SPI) produced by combining electro-acidification and tangential ultrafiltration/diafiltration (UF/DF) (pH 6), were compared in terms of composition and proteins solubility with isolates produced by UF/DF (pH 9) and isoelectric precipitation (pH 4.5). Mineral and phosphorus (phytic acid) removal was enhanced for the SPI pH 6. Whey-like proteins (M.W. < 66 kDa) were also found in higher concentration for the SPI produced by membrane technologies. This difference in composition resulted in improved solubility characteristics for the SPI pH 6 by as high as 25% and 60%, when compared to the SPI pH 4.5 and SPI pH 9, respectively. Improvement in solubility was most important between pH 2 and 4.5. The quantity of H⁺ ions added to the soy protein extract (SPE) and SPI to reduce the pH from 9 to 4.5, during solubility measurement, was related to the degree of proteins aggregation, as determined by size-exclusion high-performance liquid chromatography, and at a lesser extent to their phytic acid content. For the pH range of 4.5 to 2, the degree of proteins aggregation alone determines the quantity of H⁺ ions added.Industrial relevanceSoy protein production is one of the major agricultural sectors of significant importance to North America and soy proteins represent 69% of global plant protein consumption in the world. Soy protein concentrates and isolates are produced at the industrial scale by isoelectric precipitation. This process has a high productivity, however, it also generates large volumes of effluent. The final products also have significant contents of minerals and of phytic acid, the latter of which is well known to decrease the proteins and minerals adsorption in the intestine.We were the first group to combine bipolar membrane electrodialysis (BMED) and ultrafiltration (UF) (dead-end) for the production of soy protein concentrates (Mondor, Ippersiel, Lamarche & Boye, 2004). The new approach resulted in a significant decrease of the volumes of effluent due to the use of BMED to adjust the pH of the extract prior to UF and by improving the protein washing step using diafiltration (DF). It was also shown that for the pH range 6–9, minerals and phytic acid removal was improved with a decrease in pH. In this work, we present the characteristics of a soy protein isolate with a low phytic acid/protein ratio (SPI pH 6) produced by BMED and tangential flow UF/DF applying an optimal VCR5, re-VCR 5 sequence at pH 6. The SPI pH 6 shows an improved solubility by as high as 25% and 60%, when compared to an isolate produced by isoelectric precipitation at pH 4.5 and to one produced by UF/DF at pH 9, respectively. Improvement in solubility was most important between pH 2 and 4.5 indicating that this isolate could be considered as a valuable ingredient for the formulation of fruit juice beverages or power juices, considering that the pH of these liquid food products is around 3.5.     

Isolation and characterization of proteins from soymilk residue (okara)

Protein was extracted from okara at pH 9.0 and 80 °C for 30 min, giving a recovery of 53% protein. The extracted protein was isolated by isoelectric precipitation at pH 4.5, and the dried, defatted protein isolates (prepared at 25 and 80 °C) had over 80% protein.

The okara protein isolates have essential amino acid profiles similar to the FAO scoring pattern, and high in vitro protein digestibility, with methionine and cysteine as the limiting amino acids. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that okara protein isolates had a large quantity of high molecular weight components suggesting protein aggregation. Differential scanning calorimetry and hydrophobicity data suggested extensive protein unfolding in the okara products.

Okara protein isolates had lower solubility than a commercial soy protein isolate at both acidic and alkaline pH, probably due to protein aggregation. Other functional properties, including emulsifying, water and fat binding, and foaming properties, were found to be comparable to the commercial soy isolate.     

A comparative study of the functional properties of amaranth and soybean globulin isolates

The functional properties of the amaranth globulin isolate were determined and compared to those of the well studied soybean globulin isolate. Functional properties investigated included protein solubility, heat coagulation, foaming and emulsifying activity and stabilities, as well as fat binding. Overall, the amaranth globulin isolate was found to have significantly higher solubility (p ⪇ 0.05) i.e., 9 times higher, and higher heat stability (p ⪇ 0.05) in the vicinity of its isoelectric point, pH 5–6, than the corresponding soybean globulin isolate. Between pH 3–9 the amaranth globulin isolate was found to have significantly higher (p ⪇ 0.05) foaming capacities and stabilities than the soybean isolate. Maximum foaming capacity for the amaranth globulin was determined to occur around its isoelectric point. The emulsifying activity of the amaranth globulin isolate was found to be significantly higher (p ⪇ 0.05) between pH 3–9 than the corresponding soybean globulin isolate. The most substantial difference between the two isolates was that the amaranth isolate showed maximal emulsifying activity and stability at pH 7.0. Little difference was observed in the fat absorption capacities between the two prepared isolates. Nutritionally, the amaranth globulin isolate was found to be of superior quality compared to the soybean globulin isolate due to its higher content of essential amino acids. Overall, the functional properties of the amaranth globulin isolate were much better than the soybean isolate especially in the vicinity of its isoelectric point, suggesting a potential advantage if used in various thermally processed food formulations that fall within this pH range; a range where more common isolates perform very poorly.     

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3-7). The SPI formed very large (> 50 ??m) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ??-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.     

Production and Evaluation of Pea Protein Isolate

Laboratory and pilot plant processes were developed for producing pea protein isolate from field peas. Sodium proteinate and isoelectric products containing up to 90% protein were obtained by alkaline extraction and precipitation at the isoelectric point. Drying was carried out by freeze, spray and drum processes. Chemical analysis, functional properties, color and flavor of the dried isolates compared favorably with their soy counterparts. Generally, the sodium proteinates exhibited more functionality than isoelectric isolates. Drum drying decreased the nitrogen solubility index and increased water absorption. Freeze- and spray-drying resulted in isolates with the highest emulsification and water absorption values. Spray drying produced the best foaming, color and flavor properties.     

Production of guava seed protein isolates: Yield,composition and protein quality

The optimum conditions were determined for the preparation of protein isolates from ground, defatted guava seed flour. The isolates were obtained by micellisation and isoelectric precipitation techniques. The isoelectric point of guava seed protein was found to be pH 4.5 with a protein solubility of more than 85% above pH 9. Using 40–80 mesh particle size and extracting at pH 10 for 30 min, an isoelectric isolate was obtained by acidification to pH 4.5 which was 85.4% of the starting protein compared to 18.3% for micellisation protein obtained by twofold dilution with cold distilled water of 5% NaCl protein extract. The isolates were easily digested by the pepsin-pancreatin enzyme system and were comparable to casein. The amino acid composition showed that guava seed flour and isolates were deficient in sulphur-containing amino acids and in lysine, but contained the other essential amino acids in adequate levels. The micellisation isolate had higher fat absorption and emulsion stability than the isoelectric isolate, while other functional properties were almost similar.     

Functional properties of raw and heat processed cashew nut (Anacardium occidentale, L.) kernel protein isolates

The functional properties viz. solubility, water and oil absorption, emulsifying and foaming capacities of the protein isolates prepared from raw and heat processed cashew nut kernels were evaluated. Protein solubility vs. pH profile showed the isoelectric point at pH 5 for both isolates. The isolate prepared from raw cashew nuts showed superior solubility at and above isoelectric point pH. The water and oil absorption capacities of the proteins were slightly improved by heat treatment of cashew nut kernels. The emulsifying capacity of the isolates showed solubility dependent behavior and was better for raw cashew nut protein isolate at pH 5 and above. However, heat treated cashew nut protein isolate presented better foaming capacity at pH 7 and 8 but both isolates showed extremely low foam stability as compared to that of egg albumin.     

Protein Isolates from Bambara Groundnut (Voandzeia Subterranean L.): Chemical Characterization and Functional Properties

The physicochemical, functional, and thermal properties of protein isolates obtained from two varieties of Bambara groundnut were evaluated. Proteins were isolated using alkaline extraction (isoelectric precipitation [IEP]) and micellisation techniques. IEP recorded a higher protein yield (56.3–58.2 g/100 g) than the micellised protein (MP) (14.2 – 15.6 g/100 g). A similar trend was observed for the protein content of the isolates. The isolates contained a high level of lysine, arginine, and glutamic acid compared to soy protein. Minimum solubility of the flours of the two varieties occured at pH 5. MP isolates exhibited higher solubility than the corresponding isoelectric (IEP) isolates over all pH values. The micellised protein recorded superior functional characteristics than the isoelectric isolates. The micellised isolates also showed a significantly higher (P < 0.05) foam capacity and stability, oil and water absorption properties than the isoelectric isolate. The MP of both varieties also recorded significantly higher emulsifying properties-+ than their isoelectric protein isolates. The micellised protein also had better gelation properties than the isoelectric isolate. Micellised and isoelectric isolates did not reveal major differences in the electrophoretic patterns; both isolates had three major bands at 35.0, 43.0, and 112.0 kDa. The bands in the isoelectric protein isolate however, were well defined compared with the micellised isolate. All Bambara isolates were not dissociated by 1,4-Dithiothreitol (DTT) suggesting that they do not contain subunits linked by a disulphide bond. This suggests that 7S vicilin may be the major storage protein in Bambara groundnut isolates. Differential scanning calorimetry studies (DSC) of the two varieties of bambara groundnut proteins indicated that the thermograms of the micellised isolates have a higher denaturation temperature Td (97.9–108.4°C) than their corresponding isoelectric isolates (89.5–90.6°C).     

Functional properties of protein hydrolysates from pea (Pisum sativum,L) seeds

The aim of this study was to investigate the effects of partial enzymatic hydrolysis on functional properties of two different pea protein isolates obtained from two pea genotypes, Maja and L1. Papain and commercial protease (Streptomyces griseus protease) were used for protein modification. Solubility, emulsifying and foaming properties were estimated at four different pH values (3.0, 5.0, 7.0 and 8.0). Papain increased solubility of L1 pea protein isolate at pH 3.0, 5.0 and 8.0, emulsifying properties and foaming capacity at all pH values. Otherwise, papain increased solubility of Maja pea protein isolate only at pH 8.0. This pea protein isolate modified with both enzymes formed emulsions with improved stability at lower pH (3.0, 5.0). The commercial protease‐prepared pea protein isolates showed generally low solubility and different emulsifying and foaming properties. Proper selection of enzyme, conditions of hydrolysis and genotypes could result in production of pea protein isolates with desirable functional properties.     

Functional Properties of Chinese Rapeseed Protein Isolates

A membrane-based protein isolation process developed in our laboratory produced two protein isolates from CH₃OH/NH₃/H₂O-hexane-extracted Chinese rapeseed meal. Both contained ～99% protein (NX6.25), and they were essentially free of glucosinolates or their breakdown products (<2,2 μmol/g). Their functional properties were evaluated and compared with a commercial soybean protein isolate. The precipitated isolate gave high values for all properties except nitrogen solubility index (NSI) while the soluble isolate showed excellent NSI and fat absorption but poor emulsification characteristics. They both had good foaming properties. The two Chinese rapeseed protein isolates complemented each other and were comparable to soybean protein isolate in most functions.     

EFFECT OF PROCESSING METHOD AND pH OF PRECIPITATION ON THE YIELDS AND FUNCTIONAL PROPERTIES OF PROTEIN ISOLATES FROM GLANDLESS COTTONSEED

SUMMARY— Glandless cottonseed meals were prepared under controlled conditions in a pilot plant by three different processing methods. These meals along with a glandless cottonseed meal produced at a commercial oil mill were used as source meals for protein isolates. Two protein fractions differing in composition and characteristics were isolated from each type meal using a two-step, two-solvent isolation procedure developed at the USDA Southern Utilization R & D Div. yields of each isolate precipitated at three different pH levels were determined on the pilot plant meals. Isolate yields from the commercial meal were determined near the respective isoelectric points of the two fractions. Functional properties including whippability, heat gelation, solubility and foaming properties, were measured on all isolates. Variation in measured values due to meal processing method and precipitation pH was statistically assessed in some instances. Meal processing method was found to significantly affect the yield of Isolate I, the minor isolate. pH of precipitation was found to significantly affect the yield of Isolate II, the major isolate. Also, it was shown that the pH-solubility profiles of both Isolates I and II could be altered by changing the pH at which they were precipitated. The functional properties of isolates from meals processed without heat were superior to those of isolates from heated meals. Data collected indicated the need for a new practice in evaluating the extent of denaturation of cottonseed protein products. The present practice of determining nitrogen solubility at one point was shown to be inadequate.     

Influence of pH Shift on Functional Properties of Protein Isolated of Tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) Muscles and of Soy Protein Isolate

The physicofunctional and chemical properties of acid-aided protein isolate (AcPi), alkaline-aided protein isolate (AlPi) and soy protein isolate (SPI) prepared from tilapia muscle and defatted soy flour as a function of pH and/or NaCl concentration were investigated. Both acid- and alkali-aided processes lead to significant recoveries (P < 0.05) of proteins with substantial reduction of lipids in AlPi (0.81%) and AcPi (0.96%), the lowest for SPI (0.336%) facilitated by the processing method and sample used. There is greater lipid reduction at alkali pH, effective removal of impurities such as bones and scales, indicated by percentage ash (AcPi, 4.53%; AlPi, 3.75% and SPI, 3.51%). No major difference noted in sodium dodecyl sulphate polyacrylamide gel electrophoresis protein bands (14.4–97.4 kDa) possibly representing partial hydrolysis of myosin. Solubility was the highest at pH 3.0 and 11.0 and the lowest at isoelectric point with foam capacity showing similarity at varying pH. The addition of NaCl improved foam stability, possibly due to the increased solubility and surface activity of the soluble protein. On the whole, AcPi, AlPi and SPI manifested lower solubility and foamability at pH 4.0 and 5.0. AlPi exhibited appreciable levels of solubility, emulsion capacity, oil-holding capacity, viscosity and whiteness, whereas SPI had appreciable water-holding capacity. AcPi, AlPi and SPI have excellent relevance for product development based on their functionality.     

Foaming Characteristics of Commercial Soy Protein Isolate as Influenced by Heat-Induced Aggregation

The foaming properties of commercial soy protein isolate subjected to different temperatures (20–90°C) were assessed. The results revealed that the solubility and surface hydrophobicity of a 5% (w/v) commercial soy protein isolate suspension increased with increasing temperature, which increased foaming capacity and reduced foaming stability. Commercial soy protein isolate supernatant (i.e., soluble fraction) had higher foaming capacity at low temperatures (20–50°C). A high content of commercial soy protein isolate soluble fraction increased foaming capacity but decreased foaming stability. The SDS-PAGE patterns and molecular weight distribution of commercial soy protein isolate revealed that there were soluble, large molecular weight aggregates (>400 kDa) formed mainly from A and B-11S polypeptides of commercial soy protein isolate via disulfide bonds. Additionally, some aggregates also dissociated into small polypeptides and subunits after heat treatment. Commercial soy protein isolate precipitate (i.e., insoluble fraction) had a high content of proline and cysteine, which probably contributed to the foaming stability of commercial soy protein isolate.     

沙米麸皮和外胚乳分离蛋白的理化及功能性质

利用碱提-等电点沉淀技术分别从沙米麸皮和去皮沙米中提取出沙米麸皮分离蛋白(B-pro)和外胚乳分离蛋白(S-pro),研究这两种蛋白的理化及功能性质。结果表明,沙米麸皮中蛋白以球蛋白为主,而去皮沙米中以清蛋白为主。B-pro和S-pro纯度分别为94.33%、91.80%(m_d),S-pro颜色更白。两种蛋白均含有丰富的必需氨基酸,且S-pro中Lys含量较高。B-pro和S-pro的功能性质随pH值的变化均符合植物蛋白的一般规律,总体而言,不同pH值条件下S-pro的功能性均优于B-pro。与大豆分离蛋白和鸡蛋蛋白相比,B-pro和S-pro的持油能力及发泡性较好,而溶解性、持水力及乳化性较弱。     

酱油渣中蛋白的乳化特性研究

对比分析了酱油渣中蛋白(SRP)、糖基化大豆分离蛋白(GSP)和大豆分离蛋白(SPI)的ξ-电位、疏水性以及乳化活性和乳化稳定性。发现SRP的总糖和蛋白含量比为1∶1.4,其中含有大量的糖蛋白;SRP疏水性是SPI的2.5倍。SRP等电点接近pH=3.5,在酸性环境下溶解性较好。在酸性、高盐环境下SRP乳化能力高于GSP和SPI,在pH=5时,SRP的乳化活性(EAI)是SPI的8.1倍,在NaCl浓度为0.3mol/L时,SRP的EAI是SPI的1.77倍。     

Succinylation of Cottonseed Flour: Effect on the Functional Properties of Protein Isolates Prepared from Modified Flour

Succinylated cottonseed protein isolates (40% and 54% modification of amino groups of control isolate) were prepared under pilot scale processing conditions. Partial succinylation of cottonseed flour increased the yield of protein isolate in isoelectric precipitation (pH 4.5). The succinylated isolates were more water soluble, less heat-coagulable in water, and lighter in color as compared to conventional isolates. They also showed improved functional properties including higher oil absorption, emulsion capacity, gel strength, water hydration, water retention, and viscosity. Bulk density was decreased and resulted in fluffy isolates.     

马来酸酐酰化改性对大豆分离蛋白功能性质的影响

研究马来酸酐酰化改性对大豆分离蛋白功能性质的影响。结果表明:随着马来酸酐用量的增大,大豆分离蛋白的酰化度增大,等电点降低;随着酰化度的增大,大豆分离蛋白构象松散,色氨酸残基的微环境趋向于暴露于水的状态,亲水性增强;经马来酸酐酰化改性后,大豆分离蛋白的溶解性、发泡性、乳化性及乳化稳定性均显著提升,但泡沫稳定性有所下降。研究表明,马来酸酐酰化改性大豆分离蛋白是一种非常有前景的功能性食品添加剂。     

A Study of Film Formation by Soy Protein Isolate

Film formation of soy protein at an oil water boundary has been evaluated for the pH range 1 – 10. Definite films were seen at all pH values below that of the isoelectric point of the protein and up to pH 6.5. Beyond 7.4 increasing solubility of the protein limits observable film formation. The technique described shows that the lipophillic behavior of soy protein is active over a pH range which includes most food systems and all meat emulsions.     

Emulsifying properties of canola and flaxseed protein isolates produced by isoelectric precipitation and salt extraction

The emulsifying (emulsion capacity, EC; emulsion activity/stability indices, EAI–ESI and creaming stability, CS) and physicochemical properties (surface charge/hydrophobicity, protein solubility, interfacial tension, and droplet size) of chickpea (ChPI), faba bean (FbPI), lentil (LPI), and pea (PPI) protein isolates produced by isoelectric precipitation and salt extraction were investigated relative to each other and a soy protein isolate (SPI). Both the legume source and method of isolate production showed significant effects on the emulsifying and physicochemical properties of the proteins tested. All legume proteins carried a net negative charge at neutral pH, and had surface hydrophobicity values ranging between 53.0 and 84.8 (H₀-ANS), with PPI showing the highest value. Isoelectric precipitation resulted in isolates with higher surface charge and solubility compared to those produced via salt extraction. The EC values ranged between 476 and 542 g oil/g protein with LPI showing the highest capacity. Isoelectric-precipitated ChPI and LPI had relatively high surface charges (~−22.3 mV) and formed emulsions with smaller droplet sizes (~ 1.6 μm), they also displayed high EAI (~ 46.2 m²/g), ESI (~ 84.9 min) and CS (98.6%) results, which were comparable to the SPI.