Functional Properties of the Great Northern Bean (Phaseolus vulgaris L.) Proteins: Sorption, Buffer, Ultraviolet, Dielectric, and Adhesive Properties

Several functional properties of the Great Northern bean (Phuseolus vulguris L.) proteins were investigated. Sorption isotherms of the bean flour, albumins, globulins, protein concentrates, and protein isolates had similar patterns at corresponding temperatures. The bean flour registered higher equilibrium moisture content than albumins, globulins, protein concentrates, and protein isolates at corresponding temperature and equilibrium relative humidity. Buffer capacity of the bean proteins in the pH range 4–8 was modest. Modification (succinylation and oxidation) improved oil absorption capacity of the bean proteins. Water absorption capacity of the bean flour and protein isolates increased on modification. Modification of the bean proteins decreased the yellowness and increased the redness. About 1–2 KV/mm thickness potential difference was necessary for the passage of electrical current through these proteins. Globulins registered the highest stickiness (92N) among the samples investigated.     

Comparative studies on the physicochemical properties of soy protein isolate-maltodextrin and soy protein isolate-gum acacia conjugate prepared through Maillard reaction

Dry-heated Maillard reaction was applied in the preparation of protein–polysaccharide conjugates. Reaction mixtures containing soy protein isolate (SPI) and maltodextrin (1:1 weight ratio) were dry-heated at 60 °C and 79% relative humidity for three days. The mixtures of SPI and gum acacia (GA) were dry-heated at the same condition for one week. The conjugate of SPI–MD showed lower levels of free amino groups and higher degree of graft, which indicated that reaction between SPI and MD developed much faster than reaction between SPI and GA. The solubility of SPI at isoelectric point was improved remarkably after grafting with MD or GA. The grafted SPI showed significantly higher levels of emulsifying properties than SPI and the emulsifying properties of SPI–GA conjugate were much better than SPI–MD. Decreases of lysine and arginine contents after the graft reaction indicated that these two amino acid residues attended the covalent linkage between SPI and MD or GA. The graft reaction reduced surface hydrophobicity and fluorescence emission maximum value because of a shielding effect of the polysaccharide chain bound to proteins. The results of secondary structure suggested that grafted SPI had decreased the levels of α-helix, β-sheet and β-turn and increased unordered coils level.     

Emulsifying properties of proteins extracted from Australian canola meal

Canola protein albumin fraction, globulin fraction, and canola protein isolate (CPI) were compared to commercial soy protein isolate (SPI) in terms of their emulsifying properties at various pH values. The globulin fraction had higher emulsifying capacity (EC), higher emulsifying activity index (EAI), and the droplet size of emulsions it stabilized was consistently smaller irrespective of pH compared to albumin fraction or CPI. In comparison to SPI, globulin fractions also had higher EC at all pH values tested, higher EAI at acidic pH, and smaller or comparable average emulsion droplet size at both pH 4 and 7. The stability of canola protein based emulsions were comparable to those of SPI based emulsions at most pH values (except the emulsion stabilized by the CPI at pH 4), with no significant (p > 0.05) changes in droplet size during storage for up to 7 days at room temperature. These emulsions, however, experienced separation into the emulsion and serum phases after 24 h storage at room temperature with the exception of CPI- and SPI-stabilized emulsions at pH 9. This study demonstrates the comparable emulsifying properties (forming or stabilizing) of some canola proteins to commercially available SPI, suggesting the potential use of canola proteins in food applications.     

Effects of different oils on the properties of soy protein isolate emulsions and gels

The emulsion properties, protein adsorption and visco-elastic properties of heat-treated soy protein isolate (SPI) emulsions containing sunflower oil, soy oil and palm stearin were studied at neutral pH. The rheological properties, textural profile and fat adsorption capacity of subsequently induced glucono-δ-lactone (GDL) gels were investigated. At neutral pH the palm stearin emulsions showed higher stability than the sunflower and soy oil emulsions. The former also showed higher protein adsorption, emulsifying activity index and visco-elastic properties than the latter, indicating a higher denaturation degree for SPI at the oil/water interface of palm stearin emulsions at neutral pH. Acidified SPI-palm stearin emulsion gels were significantly harder than the soy and sunflower oil versions as well as the control (SPI without oil), whereas gels containing the two liquid oils were softer than the control. SPI-palm stearin gels also had higher fat adsorption capacity than SPI-sunflower oil/soy oil emulsion gels.     

Influence of sugars on the characteristics of glucono-δ-lactone-induced soy protein isolate gels

The effects of the reducing sugars (glucose and lactose) and the non-reducing sugar (sucrose), heated in combination with soy protein isolate (SPI) at neutral pH, on the physicochemical and rheological properties of SPI were determined. After formation of gels induced by glucono-δ-lactone (GDL), the textural profile and physicochemical bonds of the non-heated and heated SPI gels were investigated. The gelation of SPI was induced in three stages of processing that is similar to some tofu-making procedures. First, SPI was heated in the presence of sugars at neutral pH above the denaturation temperature of SPI; then gelation was induced by GDL at iso-electric pH and finally the acidic gels were heat treated again. Heat treatment with glucose at neutral pH resulted in SPI with higher glycation degree than with lactose, whereas SPI heat treated in the presence of sucrose was not glycated. GDL-induced gels of SPI glycated with glucose was more soluble in water than gels of SPI reacted with lactose, which in turn was more soluble than the control and gels of SPI heated in the presence of sucrose. This indicates a change in the net charge of proteins caused by the glycation reaction. Glucose and lactose had a protective effect on protein denaturation at neutral pH, albeit less than sucrose, resulting in GDL-induced gels with increased water holding capacity and reduced gel hardness than sucrose. Chemical analysis indicated that disulphide bonds were involved in maintaining the structure of the gels, and solubility profiles of gels in different buffers indicate that other types of covalent bonds besides disulphide bonds were formed in gels of glycated SPI, resulting in reduced gel elasticity.     

Effect of soy protein substitution for sodium caseinate on the transglutaminate-induced cold and thermal gelation of myofibrillar protein

The influence of soy protein isolate (SPI) substitution for sodium caseinate (SC) on the properties of cold-set (4 °C) and heat-induced gels of pork myofibrillar protein (MP) incubated with microbial transglutaminase (TG) was investigated. The strength of cold-set MP–SC gels (formed in 0.45 M, NaCl, 50 mM phosphate buffer, pH 6.25) increased with time of TG incubation, but those gels with more than 66% SPI substituted for SC had a >26% reduced strength (P < 0.05). Upon cooking, both incubated and non-incubated protein sols were quickly transformed into highly elastic gels, showing up to 6000 Pa in storage modulus (G′) at the final temperature (72 °C). However, no differences (P < 0.05) in G′ were observed between heated samples with SPI and SC. Myosin heavy chain, casein and soy proteins gradually disappeared with TG incubation, contributing to MP gel network formation. Both cold-set and heat-induced gels had a compact protein matrix, attributable to protein cross-linking by TG.     

加工工艺对荞麦蛋白功能特性的影响

探讨了加工工艺对荞麦蛋白(BWP)功能特性的影响。pH＜5．0和 pH＞6．0时,喷雾干燥制备的荞麦蛋白(SBWP)的溶解度高于商品大豆分离蛋白(SPI)(P＜0．05)。pH＜7．0时,超声协助提取荞麦蛋白(U- BWP)的溶解度较搅拌提取荞麦蛋白(M-BWP)和脱脂、超声协助提取荞麦蛋白(DU-BWP)好；pH＞7．0时,结果相反。总体来说,BWP 持油能力较 SPI 强,且冷冻干燥制备的荞麦蛋白(F-BWP)的持水、持油能力强于 S-BWP (P＜0．05)。BWP 的乳化活性与其溶解度呈正相关。pH 4．0～5．0时,BWP 的乳化活性指数(EAI)最小而乳化稳定性(ES)最高。脱脂处理明显提高了 BWP 的 EAI 和 ES。     

Preparation and characterisation of glyceollin‐enriched soya bean protein using solid‐state fermentation

Glyceollins, stress‐induced phytoalexins from parent soya bean isoflavones, were elicited with Aspergillus oryzae. This solid‐state fermentation facilitated the conversion of isoflavone glycosides into aglycones and glyceollins, which could mainly enrich in soya bean protein isolate (SPI) during protein preparation due to protein–polyphenol interactions. Glyceollin‐enriched SPI exhibited less flavour volatiles, higher solubility, lower whiteness and higher antioxidant activity than unfermented SPI. Fermented SPI was more easily to be digested during in vitro pepsin–trypsin digestion. This may be attributed to partial degradation of protein, especially α′ and α subunits of β‐conglycinin and acidic subunit of glycinin. The antioxidant activity of digestive products derived from fermented SPI was obviously enhanced with increasing digestion time due to simultaneous release of antioxidant peptides and glyceollins involved in the interior of protein molecule. These results suggest an effective technique for producing a nutrient‐enhanced SPI as novel functional ingredients applied in food industry.     

Protein extraction optimisation,characterisation, and functionalities of protein isolate from bitter melon (Momordica charantia) seed

Bitter melon seeds are a rich source of protein. Optimum conditions for protein extraction from the seeds, determined using a response surface design, were at a pH 9.0 and 1.3 M NaCl. Soy protein isolate (SPI) was included for comparison. Surface hydrophobicity of bitter melon seed protein isolate (BMSPI) (690) was significantly higher than that of SPI (399). Electrophoretograms of BMSPI showed bands at 40 and 55 kDa, and at 22, 25, and 35 kDa in non-reducing and reducing buffers, respectively. BMSPI had most of the essential amino acids and hence could be considered as a high quality protein. BMSPI had a single denaturation temperature (113.1 °C) while SPI had two denaturation temperatures (78.0 and 94.8 °C). The proteins exhibited U-shaped curves with solubilities ranging from 62.0% to 67.5% for BMSPI and 86.7% to 90.1% for SPI at pH ? 7.0. BMSPI had lower emulsifying activity (0.36 vs. 0.73), foaming capacity (39.6 vs. 61.0 ml), and foaming stability (21.5 vs. 25.5 min) than had SPI.     

Optimization of trypsin-assisted extraction,physico-chemical characterization,nutritional qualities and functionalities of palm kernel cake protein

The extraction of palm kernel cake protein (PKCP) was enhanced by trypsin-assisted assay. From the Response Surface Methodology (RSM) generated model, the optimum conditions were using trypsin at concentration 1.36 g/100 g, reacted on palm kernel cake (PKC) slurry (1.1 g/100 mL) at 50 °C and pH 9.5. The trypsin extracted protein yield (61.99 ± 0.74 g/100 g) was significantly (P < 0.05) higher than the alkaline (pH 9.5) method (10.21 ± 0.24 g/100 g). Surface hydrophobicity of PKCP (159.36) was significantly (P < 0.05) higher than soy protein isolate (SPI) (51.51). PKCP had a lower denatured temperature (66.88 °C) than SPI (101.41 °C). The electrophoretograms of PKCP showed 3 bands at 2.20, 3.51 and 4.28 kDa, compared to SPI which had 22 bands with molecular weight ranging from 2.00 to 82.79 kDa. Except lysine, the essential amino acids of PKCP met the suggested requirements of FAO/WHO for 2–5 year old infants. The in-vitro digestibility, essential amino acids/total amino acids (E/T) value, biological value and computed-protein efficiency ratio (C-PER) value for PKCP were significantly (P < 0.05) higher than that of SPI. PKCP also showed better solubility (30.12–97.79 vs. 9.15–69.78 g/100 g) emulsifying activity (143.25 vs. 32.57 m²/g); but lower emulsifying stability (37.83 vs. 43.08%), foaming capacity (22.5 vs. 100.0 ml/100 ml) and foam stability (3.70 vs. 19.20 ml) than the SPI.     

不同凝固剂对大豆分离蛋白分子间作用力及蛋白质二级结构的影响

为探究盐类凝固剂和酸类凝固剂在诱导大豆蛋白凝固过程中对分子间作用力和蛋白质二级结构的影响,本文以大豆分离蛋白（SPI）为研究对象,分析了不同凝固剂对大豆蛋白凝固过程中pH、表面疏水作用力、游离巯基（SH）、Zeta电位、α-螺旋、β-折叠、β-转角和无规卷曲的变化规律。结果表明:盐类凝固剂和酸类凝固剂均能降低SPI溶液的pH,其终点pH分别为6.08~6.14和5.25~5.58。与仅热处理的SPI溶液相比,加入凝固剂会导致SPI溶液中蛋白质表面疏水作用力和游离SH含量的增加,Zeta电位降低。在加入凝固剂后的0~45 min内,SPI的表面疏水作用力呈现先增加后降低的趋势,游离SH含量逐渐降低;酸浆处理的SPI溶液Zeta电位显著高于其他凝固剂（P<0.05）,为9.19~9.90 mV。此外,盐类凝固剂会导致SPI的α-螺旋和β-转角转变为β-折叠,酸类凝固剂则会破坏SPI中β-折叠。特别地,添加酸浆的SPI的α-螺旋比例介于乳酸和盐类凝固剂之间,而β-转角比例介于乳酸和醋酸之间。     

Effect of processing parameters on the properties of transglutaminase-treated soy protein isolate films

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g^− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g^− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties.Industrial relevanceThe development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.     

单宁酸对鸢乌贼肌原纤维蛋白膜性能的影响

采用葡聚糖接枝的肌原纤维蛋白,以及酸、碱提取等电点沉淀方法提取的鸢乌贼（Symplectoteuthis oualaniensis）蛋白为原料,分别制得酸提、碱提、糖基化肌原纤维蛋白膜,研究不同浓度的单宁酸对蛋白膜物理性能的影响。结果表明：接枝反应后肌原纤维蛋白中自由氨基含量明显降低。成膜液中的自由氨基和巯基的含量随单宁酸添加量增大而显著降低（P＜0.05）。3 种蛋白膜中,糖基化蛋白膜含水量最低,同时具有较高的水溶性和机械强度。在碱性环境下由于单宁酸氧化交联导致蛋白膜颜色明显变深,表面粗糙度增大。此外,单宁酸的引入使得蛋白膜的拉伸强度增加,而断裂伸长率降低。其中,添加1%的单宁酸的糖基化蛋白具有较高的膜拉伸强度和断裂伸长率,分别为1.26 MPa和118%,同时具有较低的水蒸气透过率。此研究对鸢乌贼蛋白用于可食用包装膜的制备以及延长食品货架期具有重要意义。     

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.     

Edible films made from membrane processed soy protein concentrates

Edible films were prepared from membrane processed soy protein concentrate (MSC) at various film forming solution pHs, and their mechanical, barrier, and physical properties were compared with soy protein isolate (SPI) films. As the film solution pH increased from 7 to 10, the resulted MSC films were more transparent, yellowish, and had lower oxygen permeabilities. However, tensile strength (TS), modulus of elasticity (ME) and water vapor permeabilities of MSC films were not affected by film solution pHs. The values of MSC films prepared at pH 7 were not significantly (P>0.05) different from those of SPI films prepared at alkaline solutions (pH 8-10). The uniform TS and ME values of MSC film over the wide film solution pH ranges were attributed to the higher solubility of MSC at pH 7. For the films formed at neutral film solutions (pH 7.0), MSC films showed significantly (P<0.05) higher elongation value, film solubility, and transparency compared to SPI films.     

Preparation and characterisation of soya milk enriched with isoflavone aglycone fermented by lactic acid bacteria combined with hydrothermal cooking pretreatment

A fermented soya milk (FSM) enriched with isoflavone aglycone (FSM‐SPIA) was prepared from heated soya protein isolate (SPI)‐isoflavone complex. After 48 h of fermentation, FSM‐SPIA contained higher contents of living bacteria, free amino acids and aglycone compared with the FSM of SPI (FSM‐SPI) and the FSM of SPI‐isoflavone complex (FSM‐Mix). In the in‐vitro digestion experiment, FSM‐SPIA showed higher antioxidant capacity and isoflavones (ISO) bioavailability than FSM‐SPI and FSM‐Mix. This was likely due to the soya milk containing a higher level of amino acid, peptides and the presence of soya bean isoflavone. The improved protein digestibility, the interaction and binding ability between proteins and ISO may affect the properties of the protein and the fermented products. The FSM enriched with isoflavone aglycone can be used as a functional fermented drink, as well as an auxiliary food for menopausal women during a specific pathological period.     

Comparing the heat stability of soya protein and milk whey protein emulsions

The heat stability of emulsions stabilized by WPC or SPI or mixtures of the two are compared by following the change in oil droplet number during heating, and applying kinetic rate equations to calculate the rate constant (k) for destabilization. SPI emulsions were found to be unstable to heat at pH around the pI, whilst being stable at pH further from the pI. This is related to the pH dependent solubility of soy proteins. This determined that a pH close to the pI (pH 4.5) be used for further studies so as to give a heat labile emulsion. Both WPC and SPI emulsions showed a weak dependence of k on protein concentration at pH 4.5, and an increasing k as the temperature increased. Arrhenius plots for emulsions made with WPC were bilinear, whilst those for SPI followed a single straight line. The change in slope of the Arrhenius plots for the WPC emulsions occurred around 70 °C, lower than would be expected from the denaturation temperature of β-lactoglobulin, the protein that dominates the thermal behaviour of WPC. The activation energies for WPC and SPI emulsions calculated from the slopes of the Arrhenius plots are slightly lower for WPC and considerably lower for SPI than the equivalent values in the literature for these proteins in solution. This, and the apparent lower denaturation temperature of β-lactoglobulin in emulsions, we explain by hypothesizing that the WPC and SPI proteins are already partially denatured by surface adsorption when they are heated, and thus require less energy to denature, and unfold at lower temperatures than native non-adsorbed proteins.     

紫苏分离蛋白功能性研究

为了开发紫苏蛋白在食品工业中的应用,以大豆分离蛋白为对照,研究紫苏分离蛋白的功能特性。结果表明：紫苏分离蛋白的溶解性与大豆分离蛋白的溶解性随pH值变化的趋势基本一致,但在等电点时紫苏分离蛋白的溶解性高于大豆分离蛋白。在pH7.0时,紫苏分离蛋白的持水性、起泡性及泡沫稳定性、乳化性和凝胶性均不及大豆分离蛋白。但紫苏分离蛋白的吸油性仅稍小于大豆分离蛋白,此外,在紫苏分离蛋白的蛋白质质量浓度为3g/100mL以后,其乳化稳定性与大豆分离蛋白的乳化稳定性基本相当。紫苏分离蛋白在食品加工中作为一种蛋白质强化剂具有一定潜力。     

Effect of pH on Formation, Proximate Composition and Rehydration Capacity of Winged Bean and Soybean Protein-Lipid Film

The effect of various pHs on winged bean and soybean protein-lipid films formation, proximate composition and rehydration capacity were studied. Film can only form within a specific range of pH. Films prepared at high pHs (7.5, 9.0, 10.0 and 11.0) contained higher proportions of proteins, ash and carbohydrate but lower proportion of fat than those at pH 6.7, 2.5 and 2.0. Winged bean and soybean films were found to have different pattern of rehydration, however both tended to absorb more water at high pH. With regard to film formation efficiency, nutritional value (higher protein content) and rehydration capacity, soybean film is better than winged bean film.     

PROCESSING AND QUALITY EVALUATION OF SOURSOP (ANNONA MURICATA L) NECTAR

Soursop (Annona muricata L) nectar was processed from pasteurized unstored or pasteurized frozen pulp. Nectars of pH 3.6–3.7 with 0.1% xanthan gum were produced from either 6° or 8° Brix pulp and increased to 13° or 15° Brix by addition of sucrose. The effect of storage (4C or 30C for 12 weeks) was investigated on nectar pH, titratable acidity (TA), browning, consistency, microbes and sensory attribute. At 8 weeks of storage, consistency was similar in all nectars, except for thinning of nectar from pasteurized, unstored pulp (8°–15° Brix) stored at 4C for 12 weeks. Nectars produced from frozen pulp had significantly (p < 0.01) lower pH and higher TA than nectars from unstored pulp. Browning increased in all products except nectar produced from unstored 8° Brix pulp adjusted to 15° Brix and then stored at 4C. This nectar was most highly ranked and had an overall rating of being liked moderately to liked very much after 12 weeks of storage. Microbial growth occurred in all nectars between 8–12 weeks of storage.