The influence of genotypic variation in protein composition on emulsifying properties of soy proteins

This study describes the relationship between the emulsifying properties of soybean proteins and their composition, i.e., glycinin (11S) and β-conglycinin (7S). Twelve investigated soybean genotypes showed significant differences in storage protein composition. The β-conglycinin concentration positively correlated with extractable soluble protein content, which was positively correlated with protein extractability. These data suggest that the level of β-conglycinin has a positive influence on protein extractability. The emulsion activity index (EAI) was strongly and positively correlated with the 11S∶7S ratio and strongly and negatively correlated with the concentration of β-conglycinin. The emulsion stability index (ESI) showed a moderate positive correlation with the monomeric form of glycinin and a strong positive correlation with the ratio of the monomeric to dimeric form of glycinin. No association was evident between ESI and EAI. Also, no relationship was found between ESI or EAI and extractability. Based on these data, it appears that the 11S∶7S ratio strongly reflects the ability of soybean proteins to form emulsions, whereas the ratio of the two different forms of glycinin may be crucial factors for the stability of soybean protein emulsions. Thus, understanding the relationship between protein composition and functionality could be useful for further improvement of functional behavior of soy proteins in food systems.     

Functional properties of pea (Pisum sativum, L.) protein isolates modified with chymosin

In this paper, the effects of limited hydrolysis on functional properties, as well as on protein composition of laboratory-prepared pea protein isolates, were investigated. Pea protein isolates were hydrolyzed for either 15, 30 and 60 min with recombined chymosin (Maxiren). The effect of enzymatic action on solubility, emulsifying and foaming properties at different pH values (3.0; 5.0; 7.0 and 8.0) was monitored. Chymosin can be a very useful agent for improvement of functional properties of isolates. Action of this enzyme caused a low degree of hydrolysis (3.9-4.7%), but improved significantly functional properties of pea protein isolates (PPI), especially at lower pH values (3.0-5.0). At these pH values all hydrolysates had better solubility, emulsifying activity and foaming stability, while longer-treated samples (60 min) formed more stable emulsions at higher pH values (7.0, 8.0) than initial isolates. Also, regardless of pH value, all hydrolysates showed improved foaming ability. A moderate positive correlation between solubility and emulsifying activity index (EAI) (0.74) and negative correlation between solubility and foam stability (-0.60) as well as between foam stability (FS) and EAI (-0.77) were observed. Detected enhancement in functional properties was a result of partial hydrolysis of insoluble protein complexes.     

Effects of Tween 20 and Transglutaminase Modifications on the Functional Properties of Peanut Proteins

The effects of Tween 20 on the emulsification and gelation properties of peanut protein isolates (PPI) were investigated. The functional properties of different peanut protein products, including PPI, Tween 20-assisted aqueous extraction peanut proteins (TPP), and their transglutaminase-modified products (TG-TPP), were then compared. The results indicate that the addition of Tween 20 to the PPI resulted in higher emulsifying activity index (EAI) and emulsion stability index (ESI) values than PPI without Tween 20; however, the emulsions produced by the PPI–Tween 20 mixtures were easier to destabilize during storage. As the amount of Tween 20 was increased, both the surface hydrophobicity and gel strength of the PPI–Tween mixtures significantly decreased. TPP (containing approximately 11% Tween 20) exhibited significantly different functional properties from PPI. Compared with PPI, TPP had higher EAI and ESI values but a weaker heat-induced gelation ability. The protein solubility of TPP was markedly higher than that of PPI. Modification of TPP with transglutaminase (TGase) significantly enhanced their gelation and oil-binding properties but reduced the protein solubility and ESI value. The remarkable improvement in the gelation ability of TG-TPP was mainly attributed to the formation of high-molecular-weight protein aggregates and their conformational changes.     

Preparation and characterisation of protein hydrolysates from Indian defatted rice bran meal

Rice bran meal is a very good source of protein along with other micronutrients. Rice bran meal has been utilized to produce protein isolates and respective protein hydrolysates for potential application in various food products. De-oiled rice bran meal, available from Indian rice bran oil extraction plants, was initially screened by passing through an 80-mesh sieve (yield about 70%). A fraction (yield-30%) rich in fibre and silica was initially discarded from the meal. The protein content of the through fraction increased from 20.8% to 24.1% whereas silica content reduced from 3.1% to 0.4%. Rice bran protein isolate (RPI) was prepared by alkaline extraction followed by acidic precipitation at isoelectric point. This protein isolate was hydrolysed by papain at pH 8.0 and at 37 degrees C for 10, 20, 30, 45 and 60 minutes. The peptides produced by partial hydrolysis had been evaluated by determining protein solubility, emulsion activity index (EAI), emulsion stability index (ESI), foam capacity and foam stability (FS). All protein hydrolysates showed better functional properties than the original protein isolate. These improved functional properties of rice bran protein hydrolysates would make it useful for various application especially in food, pharmaceutical and related industries.     

Functional properties and protein concentrate of Pigeon pea (Cajanus cajan (I.) Millsp) flour

The objective of this investigation was to study the functional properties of Pigeon pea (Cajanus cajan (L.) Millsp) flour and protein concentrate. The solubility of both samples were superior than 70% at pH above 6.7 and below 3.5. The water and oil absorption were 1.2 and 1.07 ml/g of sample and 0.87 and 1.73 ml/g of flour and protein concentrate samples, respectively. The minimum concentration of flour and protein concentrate needed for gelation was 20% and 12%, respectively. The emulsifying capacity of flour and concentrate was 129.35 g and 191.66 g oil/g of protein and the emulsion stability 87.50 and 97.97%, respectively, after 780 minutes. The foam capacity and stability of flour foam were 36.0% and 18.61, while of the concentrate were 44.70% and 78.97% after 90 minutes. These properties indicate that the flour as well as the concentrate could have application in various food systems.     

Hydrophobicity, solubility, and emulsifying properties of soy protein peptides prepared by papain modification and ultrafiltration

Peptide size control is important for obtaining desirable functional properties so that these peptides can be better utilized. Proteolytic enzymatic modification of soy protein isolates (SPI), followed by ultrafiltration, is an effective way to fractionate these proteins into peptides with controlled molecular size. SPI was predenatured by mild alkali at pH 10 and heated at 50°C for 1 h prior to partial hydrolysis by papain at pH 7.0 and 38°C for 10, 30, and 60 min (PMSPI10, PMSPI30, and PMSPI60). The hydrolysate PMSPI60 was further fractionated by ultrafiltration with a stirred cell and disc membranes (100-, 50-, and 20-kDa molecular weight cut-off) into one retentate (R100) and three permeates (P100, P50, and P20). Molecular weight distribution, surface hydrophobicity (S ₀), protein solubility (PS), emulsifying activity index (EAI), and emulsion stability index (ESI) of the control SPI (without added papain), hydrolysates, and ultrafiltrates were investigated. Significant increases (P<0.001) in S ₀, PS, EAI, and ESI were observed in the hydrolysates. Peptides in the permeates had higher PS and EAI but lower S ₀ than the peptides in the retentate and hydrolysate. Soy protein peptides that were prepared from SPI by papain modification and ultrafiltration had lower molecular weight, higher solubility, and higher emulsifying properties. They could find use in products that require these properties, especially in the cosmetic and health food industries.     

Extraction,Composition and Functional Properties of Pennycress (Thlaspi arvense L.) Press Cake Protein

This study compared two methods for extracting the protein in pennycress (Thlaspi arvense L.) press cake and determined the composition and functional properties of the protein products. Proteins in pennycress press cake were extracted by using the conventional alkali‐solubilization–acid‐precipitation (AP) method or saline‐based (SE) procedure (0.1 M NaCl at 50 °C). The extraction method has a major influence on the purity and functional properties of press cake protein products. AP had a lower protein yield (23 %) but much higher purity (90 % crude protein) compared with SE (45 % yield, 67 % crude protein). AP protein isolate had high foam capacity (120 ml), high foam stability (96 % foam volume retention) and high emulsion stability (24–35 min), and it was resistant to heat denaturation (3 % loss of solubility at pH 2 and pH 10). On the other hand, SE protein concentrate showed remarkably high solubility (>76 %) between pH 2 and 10 and exceptional emulsifying activity (226–412 m²/g protein), but was more susceptible to heat denaturation at pH 7 and pH 10 (65–78 % loss of solubility). These results strongly demonstrate that higher purity pennycress press cake protein can be produced by either saline extraction or acid precipitation and have functional properties that are desirable for non‐food uses.     

Improved Solubility and Emulsification of Wet-Milled Corn Germ Protein Recovered by Ultrafiltration–Diafiltration

This study evaluated Ultrafiltration–Diafiltration (UFDF) as a means to improve the extractability of wet-milled corn germ protein and determined its effects on the functional properties of the recovered protein product. Wet germ and dried germ proteins were extracted by using 0.1 M NaCl at 50 °C. Major steps in the method were stirring, centrifugation, UFDF and freeze-drying. For dried germ, the UFDF method showed marginal increase in protein extraction efficiency, while that of wet germ remained similar to what we observed for the baseline method (saline extraction with dialysis instead of UFDF). UFDF protein extracts from both germ samples were significantly more soluble than extracts recovered by the baseline method and showed atypical solubility profiles; i.e., the amount of soluble protein was essentially unchanged under acidic, neutral, and alkaline pH. UFDF-dried germ protein was markedly more soluble than UFDF-wet germ protein (80 vs 50 % soluble protein, respectively) between pH 2 and pH 10. Both of these UFDF-germ proteins also had emulsifying capacities and water-holding capacities that were superior to those of proteins extracted by the baseline method, but this favorable effect by UFDF was not observed for emulsion stability, foaming properties, and heat stability.     

Enzymatic modification of soy protein concentrates by fungal and bacterial proteases

Solubility, foaming capacity and foam stability of denatured soy protein concentrate obtained from toasted flour were improved by proteolysis with fungal or bacterial proteases. Emulsifying capacity was unchanged, but emulsion stability decreased; bacterial protease highly improved oil absorption. Also, the bacterial protease was able to solubilize more protein and gave products which foamed more than those obtained with the fungal enzyme. However, the stabilizing properties of the bacterial modified soy protein concentrate at the air/water or oil/water interface were inferior. By limited hydrolysis up to degree of hydrolysis 10% most functional properties were improved without greatly reducing emulsion stability and water absorption.     

Partially hydrolyzed rapeseed protein isolates with improved functional properties

Limited rapeseed protein hydrolysates ranging from 3.1 to 7.7% hydrolysis were produced from isoelectric-precipitated protein isolate. Water absorption, oil absorption, whippability, foam capacity and stability, emulsifying activity, and emulsion stability of the hydrolysates were determined. All protein hydrolysates showed better functional properties than the original protein isolate. Foam and emulsion stability decreased as the degree of hydrolysis increased. The hydrolysate with the lowest degree of hydrolysis showed the best functional properties. These improved functional properties make rapeseed protein hydrolysates a useful product to be used in foods such as breads, cakes, ice creams, meat products, desserts, and salad dressings.     

Toxic Compound, Anti-Nutritional Factors and Functional Properties of Protein Isolated from Detoxified Jatropha curcas Seed Cake

Jatropha curcas is a multipurpose tree, which has potential as an alternative source for biodiesel. All of its parts can also be used for human food, animal feed, fertilizer, fuel and traditional medicine. J. curcas seed cake is a low-value by-product obtained from biodiesel production. The seed cake, however, has a high amount of protein, with the presence of a main toxic compound: phorbol esters as well as anti-nutritional factors: trypsin inhibitors, phytic acid, lectin and saponin. The objective of this work was to detoxify J. curcas seed cake and study the toxin, anti-nutritional factors and also functional properties of the protein isolated from the detoxified seed cake. The yield of protein isolate was approximately 70.9%. The protein isolate was obtained without a detectable level of phorbol esters. The solubility of the protein isolate was maximal at pH 12.0 and minimal at pH 4.0. The water and oil binding capacities of the protein isolate were 1.76 g water/g protein and 1.07 mL oil/g protein, respectively. The foam capacity and stability, including emulsion activity and stability of protein isolate, had higher values in a range of basic pHs, while foam and emulsion stabilities decreased with increasing time. The results suggest that the detoxified J. curcas seed cake has potential to be exploited as a novel source of functional protein for food applications.     

Influence of pH and salt concentration on protein solubility,emulsifying and foaming properties of sesame protein concentrate

The effects of pH and NaCl concentration on protein solubility, emulsification, and foamability of sesame protein concentrate from dehulled seeds were investigated. The protein content of the concentrate was 70.7%. Protein solubility, emulsion, and foaming capacities varied with pH and ionic strength. Protein solubility, which was least at pH 4, (2.1%) ranged from 6.6% at pH 2 to 13.1% at pH 10. The solubility increased with increase in ionic strength, ranging from 9.8% at 0.0 M to 16.1% at 1.0 M concentration. The emulsion capacity ranged from 6.2 mL oil/g sample at pH 2 to 19.4 mL oil/g sample at pH 10. The emulsion capacity increased from 11.5 mL oil/g sample at 0.0 M to 20.9 mL oil/g sample at 1.0 M salt concentration. Stability of the emulsion increased with increase in NaCl concentration, ranging from 42% at 0.0 M concentration to 70% at 1.0 M concentration, but 0.5 M NaCl produced the most stable foam after 120 min of whipping while the least stable was at 1.0 M.     

Evaluation of Variation in Protein Composition on Solubility,Emulsifying and Gelling Properties of Soybean Genotypes Synthesizing β' Subunit

The effects of subunit composition of two major proteins of soybean: glycinin (11S) and β‐conglycinin (7S) in nine different genotypes, on solubility and emulsifying and gelling properties at different pH (3, 5, 6, and 8) were examined. High‐protein genotypes (more than 40%) contained low amounts of the β′ subunit. The main factors influencing solubility at pH 6 were the content of α′, α (r = 0.89 and r = 0.91 at P < 0.05, respectively) and β′ subunit contents (r = ?0.71 at P < 0.05) of β‐conglycinin, while at pH 3 acidic subunits in glycinin had a positive correlation with solubility (r = 0.69 at P < 0.05). Emulsion activity at pH 6 was higher for genotypes synthesizing β′ subunit (r = 0.57 at P < 0.05). Genotypes synthesizing higher amounts of α′ and α subunit had higher emulsion stability at pH 6 (r = 0.85 and r = 0.92 at P < 0.05, respectively) and pH 8 (r = 0.91 and r = 0.97 at P < 0.05, respectively). The rheological measurements showed that genotypes with 11S/7S ratio higher than 2.2 formed gels with enhanced storage moduli. This influence was largely due to the high content of SH groups in glycinin acidic polypeptides resulting in stabilization of gels via disulfide bonding. Gels prepared from genotypes containing higher amounts of β′ subunit of β‐conglycinin exhibited reduced elastic properties. Genotypes showing better solubility also had higher emulsion stability, but formed weaker gels and had lower emulsion activity near neutral pH.     

Functional properties of a protein product from Caryodendron orinocense (Barinas nut)

The functional properties of Caryodendron orinocense protein product were investigated and compared with those of soybean (Glycina maxima). The product protein content was 24.47 g/100 g (Nx6.25). Solubility increased at both sides of the isoelectric point (pH 4.0) and with increased NaCl concentration up to 0.5M. Compared with soybean flour (50% protein), the protein product exhibited higher water and oil absorption, but lower emulsifying activity, emulsion stability, foaming capacity, and foam stability, the last one increase at higher pH. Emulsifying activity, foaming capacity, and foam stability were ionic strength dependent. C. orinocense protein product increased its emulsifying activity steadily from 0.05M to 0.75M NaCl, while it remained almost constant for soybean flour. Foaming capacity increased drastically at pH 10. The minimum time and concentration to form a gel was 20% in 4 min and 10% in 8 min for the Caryodendron protein product and soybean flour, respectively. The bulk density was 0.5056+/-0.0041 g/mL.     

Potential Relationships Between Fatty Acid Compositions and Phytochemicals of Selected Low Linolenic Soybeans Grown in Maryland

Eight soybean genotypes grown in Maryland were analyzed for total phenolic content, antioxidant capacity, isoflavone composition, lutein content, tocopherol composition, and fatty acid profile. The soybean samples consisted of seven low α-linolenic (18:3n-3) genotypes and 1 standard genotype for comparison. 18:3n-3 levels were positively correlated with palmitic acid (16:0) content, and negatively correlated with oleic acid (18:1n-9) concentration. Daidzein and genistein concentrations were positively correlated with 18:3n-3 levels. α-Tocopherol, γ-tocopherol, and total tocopherol contents were negatively correlated with that for 18:3n-3. Two of the reduced 18:3n-3 genotypes contained significantly higher lutein levels than the non-modified genotype. All genotypes contained similar antioxidant capacity to the non-modified genotype. There were not significant differences among genotypes in relative 2,2-diphenyl-1-picrylhydrazyl (DPPH·) scavenging capacity or oxygen radical absorbing capacity. No correlation was observed between 18:3n-3 and antioxidant capacity. The results of this study show that the Maryland-grown low 18:3n-3 soybeans are sources of phytochemicals and antioxidants with potential health benefits. Specific genotypes may be selected for food production to obtain the most desirable combination of nutritional, nutraceutical, and chemical properties. The reduction in 18:3n-3 may also influence the levels of other fatty acids and antioxidant compounds in soybeans.     

Toxic Compound,Anti-Nutritional Factors and Functional Properties of Protein Isolated from Detoxified Jatropha curcas Seed Cake

Jatropha curcas is a multipurpose tree, which has potential as an alternative source for biodiesel. All of its parts can also be used for human food, animal feed, fertilizer, fuel and traditional medicine. J. curcas seed cake is a low-value by-product obtained from biodiesel production. The seed cake, however, has a high amount of protein, with the presence of a main toxic compound: phorbol esters as well as anti-nutritional factors: trypsin inhibitors, phytic acid, lectin and saponin. The objective of this work was to detoxify J. curcas seed cake and study the toxin, anti-nutritional factors and also functional properties of the protein isolated from the detoxified seed cake. The yield of protein isolate was approximately 70.9%. The protein isolate was obtained without a detectable level of phorbol esters. The solubility of the protein isolate was maximal at pH 12.0 and minimal at pH 4.0. The water and oil binding capacities of the protein isolate were 1.76 g water/g protein and 1.07 mL oil/g protein, respectively. The foam capacity and stability, including emulsion activity and stability of protein isolate, had higher values in a range of basic pHs, while foam and emulsion stabilities decreased with increasing time. The results suggest that the detoxified J. curcas seed cake has potential to be exploited as a novel source of functional protein for food applications.     

Effect of dehulling methods and desolventizing temperatures on proximate composition and some functional properties of sesame (Sesamum indicum L.) seed flour

Sesame seeds were dehulled mechanically and in 10% sodium chloride solution before oil extraction and drying to obtain the flour. The effect of these dehulling methods on the proximate composition, oil and water absorption, emulsification, and foaming properties of the flour was investigated. The effect of desolventizing temperatures (80, 90, and 100°C) on these properties was also investigated. Protein contents of seeds, dehulled mechanically (MDSF) and in 10% NaCl solution (SDSF), were 58.5 and 52.1%, respectively. Carbohydrate and ash contents of both flours also varied. The oil and water absorption capacities of the flours were 268 and 252% for MDSF and 370 and 410% for SDSF, respectively. The emulsion capacity of the MDSF sample was slightly lower (20.0 mL oil/g sample) but more stable than the SDSF sample, whose value was 20.4 mL oil/g sample. The foam capacity of MDSF was, however, higher (48.5%) but less stable than SDSF (33.7%). An increase in desolventizing temperatures of the meal led to increases in oil and water absorption capacities of the flours. Foam and emulsion capacities, on the other hand, decreased with increase in temperature. Desolventizing temperatures had no effect on the stability of the formed emulsion but had a decreasing effect on the stability of the foam.     

Functional properties of protein extracted from flaked,defatted, whole corn by ethanol/alkali during sequential extraction processing

Functional properties (solubility, foaming capacity and stability, emulsifying capacity, emulsion stability, heat coagulability, heat gelation and film formation) of protein extracted by 45% ethanol/55% 0.1 M NaOH from flaked, defatted, undergermed corn during the Sequential Extraction Process (SEP) were evaluated and compared with those of a laboratory-prepared soy protein concentrate. SEP is a new approach to corn fractionation that recycles the ethanol produced from the fermentation of cornstarch to unstream steps of protein extraction and the simultaneous extraction of corn oil and dehydration of the ethanol. Freeze-dried corn protein extracts contained at least 80% crude protein (dry basis), which is indicative of protein concentrates. SEP protein concentrates had solubilities in water of greater than 80% at pH values of 7 or above and were significantly more soluble than the soy protein concentrate at pH above 3. SEP corn proteins also showed better heat stabilities and greater emulsifying capacities and emulsion stabilities. Dilute dispersions (0.1%) of corn protein produced substantial but less stable foams. Corn proteins produced films similar to zein and soy protein films but were unable to form heat-induced gels. These results indicate that SEP produces a protein concentrate with functional properties suitable for food and industrial uses. Paper presented at the session on New Processes: Extractions and Purifications II, 83rd Annual Meeting of the AOCS, Toronto, May 10–14, 1992.     

Effects of Conjugation between Proteins and Polysaccharides on the Physical Properties of Emulsion-Based Edible Films

The effects of conjugation between protein (soybean or peanut protein isolates) and polysaccharides (dextran or gum acacia) with different glycation time (0–32 hours) on the physical properties of emulsion-based edible films containing beeswax as dispersed phase were studied. Both the reaction time and type of polymers significantly (P < 0.05) affected the emulsifying properties of conjugates. Pearson's correlation analysis showed that the emulsifying activity index (EAI), emulsifying stability index (ESI), and droplet size of emulsions were in strong correlation with the physical properties of films, such as whiteness index, transparency, water vapor permeability, surface hydrophobicity, thermal stability, and mechanical properties. Furthermore, even though glycation could significantly (P < 0.05) affect intermolecular interactions between polymers in films, there was no strong correlation between the intermolecular interactions and the physical properties of films. Therefore, the emulsifying properties of conjugates are essential for preparing emulsion-based edible films.     

极端酸碱pH偏移改善白果蛋白溶解性和乳化性

以白果种子为原料提取蛋白,研究其分离蛋白经历极端酸性(pH 2.0、3.0、4.0)和极端碱性(pH 10.0、11.0、12.0)偏移处理2h后、再将pH恢复至中性后的溶解性和乳化性。基于0.5mol/LNaCl溶液体系,采用物理化学分析、光谱技术及电泳技术等手段表征白果分离蛋白的水化性质、分子组分和结构修饰以及蛋白分子聚集行为和乳化特性,探讨以上极端酸碱pH偏移对蛋白结构和功能性的影响。结果表明,极端酸碱偏移处理致使蛋白疏水性、巯基含量和内源性荧光强度均提高,促进蛋白分子展开、重排和疏水基团的暴露,形成由二硫键调节的分子聚集;显著提高蛋白溶解度(特别是pH10.0处理,溶解度从未处理组的13.42%增加到31.91%)和最高约为未处理组2倍的蛋白乳化活性,但降低蛋白乳化稳定性。