Comparative study of potato protein concentrates extracted using ammonium sulfate and isoelectric precipitation

In this study, effects of NaCl concentrations (0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 M) and pH (3.0, 5.0, 7.0, and 8.0) on the physico-chemical and functional properties of potato protein concentrates extracted from potato fruit juice (PFJ) using ammonium sulfate precipitation (ASP) and isoelectric precipitation (IEP) were investigated. The total polyphenol content of potato protein concentrates extracted by IEP (IEPP) was 2.5 times of that of potato protein concentrates extracted by ASP (ASPP), which resulted in the color of IEPP darker than that of ASPP. More protein fractions (74, 62, and 35 kDa) were found in IEPP compared to ASPP. ASPP exhibited higher solubility than IEPP. The emulsifying properties of ASPP and IEPP increased along with the increasing NaCl concentration. ASPP and IEPP showed the lowest emulsifying properties and foaming ability at pH 5.0. While the foaming stability of ASPP and IEPP achieved the maximum and minimum at pH 5.0, respectively. Two endothermic peaks were observed in ASPP at pH 3.0, 8.0, and higher NaCl concentration (≥0.6 M), while more than two endothermic peaks were observed in IEPP at all NaCl concentrations (0.2–1.0 M) and pH values (3.0, 5.0, 7.0, and 8.0). The glutamic acid concentration of ASPP and aspartic acid concentration of IEPP were the highest, while histidine was the lowest according to the amino acid profile of both ASPP and IEPP. In terms of an essential amino acid index with respect to a reference protein of FAO/WHO, the nutritional values of IEPP were higher than those of ASPP.     

苦杏仁蛋白的功能特性

采用稀盐溶液浸提及等电点盐析相结合的方法提取制备苦杏仁蛋白,研究pH值、NaCl浓度、蛋白质量浓度和温度等因素对苦杏仁蛋白功能特性(溶解性、持水性、吸油性、乳化性及乳化稳定性、起泡性及起泡稳定性)的影响。结果表明：在等电点pI附近时,苦杏仁蛋白的溶解性、持水性、乳化性及乳化稳定性、起泡性最差;在较低NaCl浓度范围内(0～0.8mol/L)提高NaCl浓度可促进蛋白溶解性、乳化性及乳化稳定性、起泡性及起泡稳定性的提高,而较高的NaCl浓度对蛋白功能特性提高具有抑制作用;当蛋白质量浓度达到一定水平时(3～4g/100mL),蛋白功能特性(乳化性及乳化稳定性、起泡性及起泡稳定性)提高趋于平缓;在适宜的温度范围内,提高温度可有效提高苦杏仁蛋白各项功能特性,但当温度继续上升,各项功能特性持续降低。     

Isolation and characterization of protein isolated from defatted cashew nut shell: Influence of pH and NaCl on solubility and functional properties

This work reports the isolation of protein from defatted cashew nut shell (CNS), with the crude protein product containing 91.07% protein. Under its natural conditions, the solubility of this protein isolate is comparable (74.02%) to that of mustard green meal protein. The solubility of the protein isolate decreases with decreasing pH, with the minimum solubility observed at its isoelectric point (pH 3). The water holding capacity, oil holding capacity, foaming capacity, foam stability, emulsifying capacity and emulsion stability were found to be 2.56 cm³ H₂O/g protein, 4.28 cm³ oil/g protein, 76.88%, 70.98%, 62.0% and 79.0%, respectively. The profiles of these functional properties were determined with varying pH values and NaCl concentrations, and improved properties were observed in the alkaline pH range and in the presence of NaCl. Electrophoretic analysis showed that the high molecular weight protein globulin was the major protein in the protein isolate.     

Effect of acetylation and succinylation on solubility profile, water absorption capacity, oil absorption capacity and emulsifying properties of mucuna bean (Mucuna pruriens) protein concentrate

Mucuna protein concentrate was acylated with succinic and acetic anhydride. The effects of acylation on solubility, water absorption capacity, oil absorption capacity and emulsifying properties were investigated. The pH-dependent solubility profile of unmodified mucuna protein concentrate (U-mpc) showed a decrease in solubility with decrease in pH and resolubilisation at pH values acidic to isoelectric pH (pH 4). Apart from pH 2, both acetylated mucuna protein concentrates (A-mpc) and succinylated mucuna protein concentrate (S-mpc) had improved solubility over the unmodified derivative. Acylation increased the water absorption capacity (WAC) at all levels of ionic strength (0.1-1.0 M). WAC of the protein samples increased with increase in ionic strength up to 0.2 M after which a decline occurred with increase in ionic strength from 0.4-1.0 M. When protein solutions were prepared in salts of various ions, increase in WAC followed the Hofmeister series in the order: NaSCN < NaClO4 < NaI < NaBr < NaCl < Na2SO. Acetylation improved the oil absorption capacity while the lipophilic tendency reduced the following succinylation. Emulsifying capacity increased with increase in concentration up to 2, 4 and 5% w/v for U-mpc, A-mpc and S-mpc, respectively, after which an increase in concentration reduced the emulsifying capacity. Both acetylation and succinylation significantly (P < 0.05) improved the emulsifying capacity at pH 4-10. Initial increase in ionic strength up to 0.4 M for U-mpc and 0.4 M for A-mpc and S-mpc increased the emulsion capacity progressively. Further increase in ionic strength reduced emulsion capacity (EC). Contrary to the effect of various salts on WAC, increase in EC generally follows the series Na2SO4 < NaCl < NaBr < NaI < NaClO4 < NaSCN. At all levels of ionic strength studied, S-mpc had a better emulsifying activity (EA) than both A-mpc and U-mpc. EA and emulsifying stability (ES) were pH-dependent. Maximum EA and ES were recorded at pH 10. ES of protein derivatives were higher than those of U-mpc in the range of pH 4-10 but lower at pH 2. Studies revealed that both A-mpc and S-mpc had better ES and EA than the unmodified derivative when protein solutions were prepared in salts of various anions.     

红松种子水溶性蛋白乳化性及起泡性研究

以红松种子为原料,制备红松种子水溶性蛋白,研究了pH、蛋白质量浓度、NaCl浓度对红松种子水溶性蛋白起泡性和泡沫稳定性以及乳化性和乳化稳定性的影响.结果表明:蛋白的起泡性和乳化性随蛋白质量浓度的增加而增大;pH的变化对起泡性和乳化性的影响也较大,等电点处红松种子水溶性蛋白的起泡性和乳化性最差,pH 11时起泡性和乳化性均较好;NaCl浓度对泡沫稳定性影响不大,对乳化稳定性影响较大.     

马铃薯淀粉废水蛋白的功能特性

以碱提酸沉法制备的马铃薯淀粉废水蛋白为原料,分别考察了pH值、NaCl浓度和温度对蛋白功能特性（溶解性、持水能力、乳化性及乳化稳定性、起泡性及泡沫稳定性）的影响。结果表明,pH值、NaCl浓度和温度对蛋白的功能特性产生不同程度的影响。在等电点（pH 4.0）时,马铃薯蛋白表现出最低的溶解性、持水性、乳化性、乳化稳定性及起泡性,而泡沫稳定性最好。在较低NaCl浓度（＜0.2 mol/L）时,蛋白溶解性、持水能力、乳化性和乳化稳定性随NaCl浓度的增加而提高,而高浓度的NaCl（＞0.2 mol/L）对上述性质具有抑制作用;蛋白的起泡性和泡沫稳定性在NaCl浓度为0.4 mol/L时具有最大值。在4～80 ℃范围内,蛋白质的各项功能性质随温度的升高均呈现先增加后降低的趋势,且溶解性、持水性、乳化稳定性、起泡性及泡沫稳定性在40 ℃时最佳,乳化性在60 ℃最佳。     

Solubility properties of barley flour,protein isolates and hydrolysates

Protein solubility properties of barley flours (BF), barley protein isolates (BPI) and barley protein hydrolysates (BPH) were determined as a function of pH and NaCI concentration. BPIs were produced from both hulled (BPI-1 and BPI-3) and hull-less (BPI-2 and BPI-4) barley flours. Sodium metabisulphite (BPI-1 and BPI-2) or L-cysteine (BPI-3 and BPI-4) were included in the extraction procedure. BPI-4 was hydrolyzed with Alcalase in order to produce hydrolysates of 3% (BPH-1) and 6% (BPH-2) degree of hydrolysis. Electrophoretic properties of BFs, BPIs and BPHs were examined by SDS-PAGE. The results showed that solubility properties were affected by the changes of pH and ionic strength of the medium in all samples. The solubility properties of barley proteins were especially higher in the strong acidic and basic pH regions. Solubilities of BPI-1 and BPI-2 in distilled water were lower than those of BPI-3 and BPI-4. The lowest solubility was observed around the isoelectric points of BFs and BPIs. SDS-PAGE provided significant information about the monitoring of limited protein hydrolysis that produced large quantities of low molecular weight barley protein fragments with the Alcalase treatment. The solubility properties of BPHs around the isoelectric point were increased as a result of the limited hydrolysis.     

桑叶蛋白的功能特性研究

采用超声波辅助提取结合盐酸沉析法提取桑叶蛋白,研究pH值、离子强度、蔗糖质量浓度和温度对桑叶蛋白功能特性的影响。结果表明：远离其等电点时,桑叶蛋白具有良好的持水性、溶解度、乳化性及乳化稳定性、起泡性;桑叶蛋白的持水性、溶解度和起泡性与NaCl浓度(0～1.0mol/L)呈正相关,而过高的离子强度(NaCl浓度高于0.6～0.8mol/L)会使桑叶蛋白的乳化性和乳化稳定性下降;蔗糖的加入会增加桑叶蛋白的持水性,但会降低其溶解度和起泡性,对桑叶蛋白的乳化性和乳化稳定性影响不大;桑叶蛋白的吸油性和起泡性与温度(4～80℃)呈正相关,持水性、溶解度、乳化性及乳化稳定性于60℃时最好。     

Solubility, Emulsifying, and Foaming Properties of Rice Bran Protein Concentrates

Rice bran protein concentrates were prepared from full-fat and defatted raw rice bran. Selected functional properties, viz. nitrogen solubility, emulsification properties, and foaming properties were measured over the pH range 2.0 to 10.5 and in three dispersion media including water, 0.1M NaCl (low salt) and 1.0M NaCl (high salt). Below and above the isoelectric pH (4.5) the nitrogen solubility increased. Higher pH enhanced the nitrogen solubility and, thereby, considerably improved the functional properties. In higher salt concentration, nitrogen solubility was reduced which also altered the properties of emulsification and foaming. Multiple regression analysis showed that pH was the primary determinant of nitrogen solubility, emulsification and foaming properties. Multiple regression models including pH, salt concentration and nitrogen solubility as independent variables were found to be more accurate in predicting other functional properties.     

美藤果蛋白的功能性质研究

以美藤果饼为原料,采用碱提酸沉法制备美藤果蛋白,研究pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白功能性质的影响。结果表明:当pH为5时,美藤果蛋白的溶解度、乳化性能和起泡性均最小;随着温度的升高,美藤果蛋白的溶解度、持水性、持油性呈先增大后减小的趋势;加入适量NaCl可增大美藤果蛋白的溶解度、乳化性能和起泡性能;加入蔗糖使美藤果蛋白的起泡性降低,而加入适量的蔗糖可增大美藤果蛋白的乳化性能。pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白的功能性质有一定影响,可通过改变上述条件以获得良好加工性质的美藤果蛋白产品。     

Comparative studies on the functional properties of various protein concentrate preparations of peanut protein

The effect of different preparations on the functional properties of peanut protein concentrates was studied. Peanut protein concentrates were isolated from defatted peanut flour by isoelectric precipitation, alcohol precipitation, isoelectric precipitation combined with alcohol precipitation, alkali solution with isoelectric precipitation and their functional properties (protein solubility, water holding/oil binding capacity, emulsifying capacity and stability, foaming capacity and rheology) were evaluated. The results showed that the protein solubility, foaming capacity and stability of protein prepared by alkali solution with isoelectric precipitation were the best of all the peanut protein products. But the protein prepared by alcohol precipitation had better water holding/oil binding capacity, which was significantly different from other protein products. The emulsifying stability of protein concentrate prepared by different methods was significantly lower than that of defatted protein flour. The protein prepared by isoelectric precipitation and isoelectric precipitation combined with alcohol precipitation had better gel properties which indicated that they were a potential food ingredient.     

Effect of pH and NaCl/CaCl2 on the solubility and emulsifying properties of sweet potato protein

BACKGROUND: The effects of NaCl and CaCl₂ on the solubility and emulsifying properties, namely emulsifying activity index (EAI) and emulsion stability index (ESI) of sweet potato proteins (SPPs) at pH 1–10, were investigated. RESULTS: At lower NaCl (0.1 mol L^?1) and CaCl₂ (0.05 mol L^?1) concentrations, the solubility profiles of the SPPs were very similar to those in distilled water, and the lowest solubility occurred at pH 4. Increased NaCl and CaCl₂ concentration resulted in lower SPP solubility in most of the pH studied (P < 0.05). At pH < 3, NaCl improved the EAI of SPP while at pH > 7 it reduced the EAI of the SPP (P < 0.05). Moreover, addition of NaCl also resulted in reduction of ESI of the SPP in most of the pH studied (P < 0.05). On the other hand, the presence of 0.2 mol L^?1 CaCl₂ rendered the EAI and ESI of the SPPs independent of the influence of pH. CONCLUSION: The present studies show that pH and salts modified the emulsifying properties of the SPPs, and CaCl₂ at a certain concentration could be used to improve the emulsifying properties of the protein. Copyright © 2008 Society of Chemical Industry     

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.     

荞麦蛋白的功能特性研究

采用碱萃取酸沉析法提取制备了荞麦蛋白，并较为系统地研究了蛋白质浓度、温度、pH值、氯化钠和蔗糖对荞麦蛋白的三种功能特性（溶解性质、乳化特性和泡沫特性）的影响。结果表明，本实验条件下制备的荞麦蛋白具有优良的溶解性质，其乳化性质与对照样品大豆分离蛋白相当，但泡沫特性较差。     

Functional properties of protein concentrates and isolates produced from cashew (Anacardium occidentale L.) nut

Protein isolates and concentrates were obtained from defatted cashew nut powder by two methods: alkaline extraction-isoelectric precipitation (IP) and alkaline extraction-methanol precipitation (MP). The functional properties of cashew nut protein isolates, concentrates and powder were significantly different (p < 0.05). Cashew nut protein isolate (CNPI) had higher water and oil absorption capacities (2.20 ml/g and 4.42 ml/g, respectively), emulsifying stability index (447%), foam capacity and stability (45% and 55%, respectively), and least gelation capacity (13.5%) than cashew nut protein concentrate (CNPC), which was also higher than that of defatted cashew nut powder (DCNP). However, emulsifying activity index (12.45%) and bulk density (0.31) of CNPI were lower than that of CNPC, which were also lower than that of DCNP. The water solubility of CNPI (95%) and CNPC (95%) was not significantly different (p > 0.05) among the samples, but was significantly different (p < 0.05) from that of DCNP (75%). The CNPI, CNPC and DCNP showed decreasing solubility with decreasing pH, with the minimum solubility being observed at a pH range of 4.0–4.5, confirming the isoelectric point of cashew proteins. However, higher water solubility, emulsifying activity, and foaming property were observed at an alkaline pH than at an acidic pH in all samples.     

Solubility and functional properties of sesame seed proteins as influenced by pH and/or salt concentration

The protein content, solubility and functional properties of a total protein isolate prepared from sesame seeds (Kenana 1 cultivar) as a function of pH and/or NaCl concentration were investigated. The protein content of the seed was found to be 47.70%. The minimum protein solubility was at pH 5 and the maximum was at pH 3. The emulsifying capacity, activity and emulsion stability as well as foaming capacity and foam stability were greatly affected by pH levels and salt concentrations. Lower values were observed at acidic pH and high salt concentration. The protein isolate was highly viscous and dispersable at pH 9 with water holding capacity of 2.10 ml H₂O/g protein, oil holding capacity of 1.50 ml oil/g protein and bulk density of 0.71 gm/ml.     

Functionality of native and denatured cashew nut kernel protein isolates at isoelectric pH as a function of salt concentration

The reduced solubility of proteins near the isoelectric pH limits their use in food formulations whose pH lies in the range 5.0–6.0 because of poor functionality. In the present study, the effect of salt on the functionality of native and denatured cashew nut kernel protein isolates at the isoelectric pH was investigated. Both isolates showed improvement in their functional properties, but the improvement was greater for the denatured protein isolate. The solubilities of denatured and native protein isolates at the isoelectric pH increased from 26.4 g l^?1 and 64 g l^?1, respectively, without salt to maxima of 363 and 308 g l^?1, respectively, at 0.75 M salt concentration. The water binding capacity of the isolates increased with increase in NaCl concentration from 1.70 ml g^?1 to 1.77, 1.82, 1.92 and 2.2 ml g^?1 for denatured protein isolate and from 1.45 ml g^?1 to 1.65, 1.69, 1.82 and 1.97 ml g^?1 for native protein isolate at 0.25, 0.50, 0.75 and 1.0 M salt concentrations, respectively. When the properties of the isolates in 0.75 M NaCl solutions were compared with those in salt‐free water there were 15% and 116% increases in emulsifying capacity, 40‐fold and 45‐fold increases in emulsifying activity and 4.6‐fold and 40‐fold increases in emulsion stability for native and denatured protein isolates, respectively, whilst the corresponding foaming capacities increased from 4 to 5.5 and 0 to 8.9 ml g^?1 protein. Statistically, no difference in the foaming capacity of either of the isolates was observed above 0.5 M NaCl. The foam stability also exhibited similar behaviour. Copyright © 2004 Society of Chemical Industry     

Functional properties of plant proteins. Part 2. Selected physicochemical properties of native and denatured protein isolates from faba beans,soybeans, and sunflower seed

Functional properties — as solubility, water and oil adsorption, emulsifying capacity, emulsion activity and stability — of protein isolates from faba beans, soybeans and sunflower seed depending on the isolation process were determined. Proteins isolated under mild conditions, it means by precipitation using dialysis or dilution of salt extracts with water, show the highest solubility, characterized by a sharp minimum of solubility at a rather narrow range of pH. An incubation of the precipitated proteins at low pH (pH 2) results in a decrease of the solubility on the alcaline and acidic part of the solubility profile. On the contrary to the decreased solubility, the proteins denatured by acid show an increased water adsorption capacity. Depending on the kind of protein and the conditions of preparation these values can reach the manifold ones of the control. Smaller increases of oil adsorption in acid-denatured proteins were found, too. The emulsion activity and stability were not or only slightly influenced, but the emulsifying capacity was strongly decreased by the denaturation procedure. The emulsifying capacity was influenced by the solubility of the protein, but a strong correlation does not exist. The high water adsorption of Promine D can be reached by the other plant proteins after denaturation. The sunflower protein showed the highest emulsifying capacity. Increasing the pH from the isoelectric range to 7 improves all studied functional properties.     

Foaming properties of barley protein isolates and hydrolysates

Foaming properties of the barley protein isolates (BPI) and barley protein hydrolysates (BPH) were investigated by using gas sparging method. BPIs were produced from hulled (BPI-1) and hull-less (BPI-2) barley flours by extracting with 70% (v/v) ethyl alcohol. BPI-2 was hydrolyzed with Subtilisin enzyme using pH-stat technique in order to produce hydrolysates at 3% (BPH-1) and 6% (BPH-2) degree of hydrolysis. Barley flour, BPI-1 and the pellets and supernatants obtained from centrifugation of BPI-1 were examined by SDS-PAGE. The foaming properties of BPIs and BPHs were determined as a function of pH and protein concentration. The results showed that foaming properties were affected by the changes in pH of the medium in isolates and hydrolysates. Foaming properties of isolates were improved below and above the isoelectric pH. The lowest values were observed at pH 6, which is close to the isoelectric pH of BPIs. The protein hydrolysates displayed improved foam stability at basic pH values, while stability was very low at acidic pH values. Generally, at all pH values in both isolates, the highest foam volumes and stability were observed for 1% (w/v) protein concentrations.     

Characterisation and functional properties of proteins of some Indian chickpea (Cicer arietinum) cultivars

BACKGROUND: Chickpea (Cicer arietinum L.) proteins have received attention during recent years owing to their higher biological values and better functional ingredients than oilseed proteins. In this study the composition, fractionation, electrophoretic behaviour and functional properties of five chickpea protein concentrates were determined. RESULTS: The chickpea proteins contained 15.9–54.8 g kg^?1 albumin, 48.9–154.1 g kg^?1 globulin, 39.2–76.5 g kg^?1 glutelin and traces of prolamin. Electrophoresis of the various fractions revealed that albumin and globulin were made up of sub‐units of different molecular weights ranging from 7 to 96 kDa. Water and oil absorption of the protein concentrates varied from 1.15 to 2.75 g g^?1 and from 2.60 to 5.65 g g^?1 respectively. Foaming capacity and foam stability of the protein concentrates were good and improved with the addition of salt (10 g L^?1 NaCl) or sugar (100 g L^?1 sucrose) at both isoelectric and neutral pH. Emulsifying capacity and emulsion stability of the protein concentrates were good and excellent respectively. CONCLUSION: Protein concentrates prepared from chickpeas have potential use in food formulations owing to their good emulsifying/foaming and water/oil‐binding capacities. Copyright © 2008 Society of Chemical Industry