鲤鱼鱼肉蛋白酶水解物抗氧化性及功能特性

采用碱性蛋白酶对鲤鱼鱼肉蛋白进行酶解,制备不同水解度的水解物。测定水解物的抗氧化活性以及不同pH值条件下水解物的功能特性。结果表明:随着水解度的逐渐升高,水解物的抑制脂质氧化能力、D PP H自由基清除能力、还原能力以及金属离子(Cu2+和Fe2+)螯合能力逐渐增加(P<0.05);同时,水解物的溶解性、乳化性和起泡性都在pH值为4.0(等电点)时达到最低,而后溶解性和乳化性随着pH值升高而增大(P<0.05),而起泡性随着pH值的升高先上升后又下降。因此,鲤鱼鱼肉蛋白碱性蛋白酶水解物可以提高蛋白质的抗氧化活性和溶解性,但是较高的水解度会在一定程度上降低其乳化性和起泡性。     

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.     

Relationship of hydrophobicity and solubility with some functional properties of cowpea (Vigna unguiculata) protein isolate

The relationship of hydrophobicity and solubility with some functional properties of cowpea protein isolate was determined. Cowpea protein isolate was prepared by alkali extraction followed by precipitation at pH 4.5. The precipitated proteins were then neutralized to pH 7. Heating of the protein isolate to 100°C for 10 min followed by cooling to room temperature resulted in a significant (P ≦ 0.05) decrease in aromatic hydrophobicity (ARH) when compared to the native protein isolate. The inclusion of sodium dodecyl sulfate (SDS) during heating gave a significant (P ≦ 0-05) 1.7-fold increase while inclusion of mercaptoethanol (ME) gave a significant (P ≦ 0.05) 2.5-fold increase in ARH of the cooled protein solution. Protein solubility (PS), foam expansion (FE) and emulsification activity index (EAI) of the isolate generally increased significantly (P ≦ 0.05) upon heating or treatment with urea or SDS or a combination of SDS and ME. Backward stepwise multiple regression was used to obtain equations for predicting emulsifying and foaming properties of the protein isolate from solubility and hydrophobicity parameters. PS, ARH and aliphatic hydrophobicity (ALH) were important in predicting foam stability and emulsion stability, while PS and ALH were important for predicting FE. ALH alone was important for predicting EAI.     

Effects of limited enzymatic hydrolysis with trypsin on the functional properties of hemp (Cannabis sativa L.) protein isolate

Effects of limited enzymatic hydrolysis induced by trypsin on the physicochemical and functional properties of hemp (Cannabis sativa L.) protein isolate (HPI) were investigated. The enzymatic hydrolysis was confirmed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC). SEC and differential scanning calorimetry (DSC) analyses confirmed the presence of aggregates in the corresponding hydrolysates (with the degree of hydrolysis of 2.3–6.7%). Functional properties, including protein solubility (PS), thermal properties, emulsifying and foaming properties, and water holding and fat adsorption capacities (WHC and FAC) were evaluated. The PS was remarkably improved by the limited enzymatic hydrolysis at all tested pH values. However, the enzymatic hydrolysis led to the marked decreases in emulsifying activity index, foaming capacity and foam stability, WHC and FAC. These decreases were to a great extent related to the presence of aggregates in the hydrolysates.     

Formation and emulsification properties of self-assembled potato protein microgel particles under different pH conditions

This study evaluated the formation of potato protein microgel particles (PPM) formed by heating a protein solution at pH 2–8 in order to improve emulsifying potential of commercial potato protein (PP). The physicochemical properties (particle diameter, ζ-potential and contact angle), structural characteristics and emulsifying capacity of PPM were investigated. The results indicated that preparation pH of PPM had significantly influenced the emulsification properties. The PPM samples prepared near the isoelectric point of PP (pI ~ 4.5) had low ζ-potential, high particle size, lower emulsifying activity index (EAI) and emulsifying stability index (ESI). Meanwhile, compared to PP, PPM prepared at pH (pH = 2, pH = 6–8) stay away from isoelectric point had higher EAI and ESI, evidenced by the appropriate ζ-potential and contact angel. In conclusion, PPM prepared at specific pH (pH = 6) would enhance the emulsifying properties of potato protein, the findings would broaden the application of potato protein in the food industry.     

A comparative study of physicochemical and conformational properties in three vicilins from Phaseolus legumes: Implications for the structure–function relationship

The polypeptide constituents, physicochemical and conformational properties of three vicilins from kidney, red and mung beans, fractionated using combined acid extraction and ion-exchange chromatographic techniques, were characterized and compared. The tested physicochemical and conformational properties included amino acid composition, surface charge and hydrophobicity, protein solubility (PS; as a function of pH), emulsifying activity index (EAI) and emulsion stability index (ESI), as well as secondary, tertiary and/or quaternary conformations. The amino acid composition (especially relative acidic/basic charged amino acid ratio, and the percentage of polar uncharged amino acids) was an intrinsic physicochemical parameter that largely determined other physicochemical and conformational properties. The PS and EAI (and ESI) of these vicilins at various pH values were associated with each other, and both were closely related to their surface charge and/or hydrophobicity. Far-UV CD spectral analyses indicated that these vicilins exhibited similar secondary structure compositions at pH deviating from the isoelectric point (about pH 4.5). However, their tertiary and/or quaternary conformations, as determined by differential scanning calorimetry, intrinsic fluorescence and near-UV CD spectroscopy, remarkably varied. At pH 7.0 or 9.0, there were close relationships between the EAI and the flexibility in quaternary conformation, and between the ESI and the flexibility in tertiary conformation. This is the first observation to elucidate the importance of tertiary and/or quaternary conformations for the emulsifying properties of legume vicilins. Additionally, an underlying mechanism of the emulsification process for the vicilins (trimeric form) with excellent emulsifying properties was proposed.     

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。     

中国毛虾酶解产物的功能性质研究

研究了木瓜蛋白酶酶解中国毛虾产物的功能特性。对毛虾酶解产物的溶解性、乳化性、乳化稳定性、起泡性、泡沫稳定性和粘度等功能性质进行了研究,并与虾粉的功能特性进行了对比。结果表明:毛虾酶解产物的蛋白质含量高达85.5%,比虾粉提高17.5%;酶解产物的溶解度、乳化性和起泡性明显高于虾粉;酶解产物的乳化稳定性、泡沫稳定性和粘度略低于虾粉。毛虾酶解产物作为一种潜在的功能性配料,在食品工业中具有一定的应用前景。     

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.     

牙鲆鱼、多宝鱼肌原纤维蛋白性质比较

鱼类肌肉蛋白的组成与性质决定了其加工特性和产品特性。以牙鲆鱼和多宝鱼为研究对象,用SDS-PAGE分析二者肌肉蛋白的组成形式,采用差示扫描量热法(DSC)、动态流变仪研究二者肌原纤维蛋白的热变特性、流变特性,以及乳化性和起泡性等蛋白功能特性,并对以上性质进行比较。SDS-PAGE电泳结果显示牙鲆鱼肌浆蛋白在20.1~44.3 kDa间,较多宝鱼肌浆蛋白多两条特异条带,而牙鲆鱼肌原纤维蛋白在97.2~66.4 kDa处较多宝鱼多一条特异条带。DSC研究显示牙鲆鱼肌原纤维蛋白变性温度为39.98℃,高于多宝鱼的37.86℃,流变分析中,牙鲆鱼、多宝鱼肌原纤维蛋白损耗模量G″在30~40℃间均有流变特性转折点。二种鱼类肌原纤维蛋白的功能特性随着蛋白浓度的升高而降低。乳化性结果显示,低浓度时牙鲆鱼肌原纤维蛋白乳化活性高于多宝鱼。起泡性研究显示,低浓度牙鲆鱼肌原纤维蛋白起泡性低于多宝鱼,中与高浓度时高于多宝鱼。同时随着浓度的升高,多宝鱼起泡性趋于稳定。研究结果表明,牙鲆鱼及多宝鱼的蛋白组成二者肌原纤维蛋白流变特性-乳化特性以及起泡性等功能特性均有一定差异。     

Functional properties of protein preparations from amaranth seeds in model system

The gross chemical composition and functional properties (solubility, emulsifying and foaming properties) of different amaranth protein preparations were studied in model systems and were compared to those of casein and soy protein isolates. Preparations of alkaline-soluble total protein, albumin, globulin, and glutelin-like alkaline-soluble residual protein were produced from two different types of defatted amaranth meals by extraction and fractionation. Although similarity can be shown between protein patterns of legumes (including soy) and amaranth, the emulsifying and foaming properties of amaranth protein preparations are relatively poor in comparison to the reference proteins, except foaming properties of albumin preparations. Nevertheless, taking in mind that these properties depend on interactions with other food components and textural requirements of individual food products, the amaranth protein preparations may be treated as potential protein sources and food ingredients.     

Effects of Acylation on the Functional Properties and In Vitro Trypsin Digestibility of Red Kidney Bean (Phaseolus vulgaris L.) Protein Isolate

ABSTRACT:  The effects of succinylation and acetylation on some functional properties and the  in vitro  trypsin digestibility of kidney bean protein isolate (KPI) were investigated. The extent of succinylation or acetylation progressively increased from 0% to 96% to 97%, as the anhydride-to-protein ratio increased from 0 to 1 g/g. Polyacrylamide gel electrophoresis (PAGE) and zeta potential analyses indicated that acylation, especially succinylation, considerably increased the net charge and hydrodynamic radius of the proteins in KPI, especially vicilin. Acylation treatment at various anhydride-to-protein ratios (0.05 to 1 g/g) remarkably improved the protein solubility (PS) and emulsifying activity index (EAI) at neutral pH, but the improvement by succinylation was much better than that by acetylation. Succinylation resulted in a marked decrease in mechanical moduli of heat-induced gels of KPI, while the mechanical moduli were, on the contrary, increased by acetylation. Additionally,  in vitro  trypsin digestibility was improved by the acylation in an anhydride-type and level-dependent manner. The results suggest that the functional properties of KPI could be modulated by the chemical acylation treatment, using succinic or acetic anhydride at appropriate anhydride-to-protein ratios.     

苏尼特羊宰后成熟过程中肌原纤维蛋白特性与肉品质的变化分析

以6 月龄苏尼特羊股二头肌为材料,测定其宰后成熟过程中（0～3 d）的肉品质、肌原纤维蛋白功能特性和蛋白降解相关指标,旨在探究肌原纤维蛋白对宰后肉品质的影响,并确定苏尼特羊合适的宰后成熟时间。结果表明,4 项肉品质指标（pH值、色泽、剪切力和蒸煮损失率）中,pH值、蒸煮损失率和剪切力在成熟2 d时达到最优值,并与成熟3 d时无明显差异;肌原纤维蛋白的3 种功能特性,即水合特性（溶解度、疏水性）、凝胶特性（凝胶保水性、凝胶硬度）和乳化特性（乳化活性指数（emulsifying activity index,EAI）、乳化稳定性指数（emulsifying stability index,ESI））在成熟1 d时较差,在成熟2 d时有所回升,随后趋于稳定;肌原纤维蛋白降解相关指标,即肌原纤维小片化指数（myofibril fragmentation index,MFI）和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳结果均表明在成熟2 d后蛋白降解程度较小,趋于稳定;相关性分析中,MFI、溶解度、疏水性、EAI、ESI和凝胶保水性与各项肉品质指标间都呈现一定的相关关系。综上所述,苏尼特羊宰后成熟过程中,肌原纤维蛋白的降解与功能特性变化对肉品质有较大影响,并且各主要指标指示在宰后2 d时已基本成熟。     

Preparation and characterisation of surface‐active pectin from soya hulls by phosphate‐assisted subcritical water combined with ultrasonic treatment

Surface‐active pectin was efficiently extracted from soya hull using phosphate‐assisted subcritical water combined with ultrasonic treatment (PASW‐UT). The physicochemical and functional properties of soya hull pectin (PSHP) were evaluated. Compared to pectin prepared by traditional acid extraction (ASHP), the yield and purity of PSHP were significantly increased, as well as PSHP also contained more protein moiety and displayed better emulsifying and foaming properties. However, the emulsifying and foaming properties of protein‐depleted soya bean hull pectin (PDSHP) were markedly decreased as compared to PSHP, which was supported by data of dynamic interfacial tension of pectins, suggesting that the emulsifying and foaming capacity of PSHP should be mainly ascribed to the existence of more extensin, as evidenced by the results of hydroxyproline content. In further comparison with commercial sugar beet pectin (SBP), the PSHP exhibited similar emulsifying properties with SBP over the pH range of 2–6. Moreover, the foam ability and stability were even higher than those of SBP, especially at pH 4.0. These findings suggest that PASW‐UT could be used as an effective strategy to prepare novel surface‐active pectin from soya hull.     

Functional properties of bovine blood plasma intended for use as a functional ingredient in human food

With the aim of using bovine blood as functional ingredient in food processing, as an emulsifier or fat replacer, a study of some functional properties of blood plasma was made. The effect of pH (3.0–8.0), tryptic hydrolysis and NaCl addition (0.034 mol/L) on the solubility, hydrophobicity and emulsifying properties of bovine blood plasma were studied. The results showed that the hydrophobicity and emulsifying activity index (EAI) of bovine blood plasma reached a maximum at pH 3.0 and 7.0, respectively, while the other parameters stayed nearly constant with pH change. Tryptic hydrolysis improved hydrophobicity at certain hydrolysis times, reduced solubility and emulsifying capacity (EC) and showed no effect on EAI and emulsion stability (ES). The influence of NaCl tested at pH 5.0 and 6.0 was only positive for plasma EAI at pH 5.0 and significantly reduced solubility, hydrophobicity and EC at pH 5.0 and 6.0. For ES, NaCl addition did not produce any modification.     

全蛋液pH值对其功能性质的影响

对全蛋液pH值对其蛋白溶解度、起泡性、乳化性、凝胶强度等功能性质的影响进行了研究。结果表明:在pH 6.5～9.0内,随着全蛋液样品pH值升高,全蛋液的蛋白溶解度、乳化稳定性和凝胶强度逐渐提高,而全蛋液乳化活力逐渐下降;在pH 7.0～7.5内,全蛋液具有较好的起泡力和泡沫稳定性,pH值过高或过低时全蛋液起泡性都会下降;在实际应用中可以根据对全蛋液各种功能性质的不同要求选择适当pH值的全蛋液。     

Polypeptide profile and functional properties of defatted meals and protein isolates of canola seeds

Laboratory‐defatted meals from four types of canola seeds were analysed for protein profile by reducing and non‐reducing forms of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE). In the absence of a reducing agent (2‐mercaptoethanol), four major polypeptide bands (16, 18, 30 and 53 kDa) were prominent in similar ratios in all varieties. In the presence of mercaptoethanol, significant reductions in intensity of the major bands occurred, suggesting that the major polypeptides contained smaller units which were held together by disulphide bonds. Meals from Brassica napus seeds had higher protein solubilities than meals from Brassica rapa seeds. Meals with higher protein solubility values also had higher foaming capacity (FC) values. Generally, the acid‐precipitated (pH 4.0) protein isolates (APPIs) had higher FC values than the calcium‐precipitated isolates (CPPIs). On the other hand, the CPPIs formed emulsions with higher values of emulsifying activity index (EAI) when compared to the APPIs. The results indicate that variations in functional properties of protein isolates and meals between the four seed types were probably due to differences in protein conformation in aqueous solutions rather than differences in polypeptide composition. © 2001 Society of Chemical Industry     

Functional and structural properties and in vitro digestibility of acylated hemp (Cannabis sativa L.) protein isolates

The effects of succinylation and acetylation on some functional, structural properties and in vitro trypsin digestibility of hemp protein isolate (HPI) were investigated. The extent of acylation gradually increased from 0 to 60–70%, with the anhydride‐to‐protein ratio increasing from 0 to 1.0 g g^?1. Size exclusion chromatography showed that succinylation led to formation of more soluble protein aggregate than acetylation, especially at anhydride levels higher than 0.1 g g^?1. Succinylation led to gradual increase in protein solubility (PS) from 30 to 85–90%, while in the acetylation case, the PS was improved only at low anhydride levels, increasing from 30 to about 50% with anhydride‐to‐protein ratio increasing from 0 to 0.2 g g^?1. At neutral pH, the emulsifying activity indexes (EAI) of HPI was 22.1 m² g^?1, and the EAI linearly and significantly increased with the extent of acylation. The EAIs of succinylated and acetylated HPI (1.0 g g^?1) were 119.0 and 54.4 m² g^?1, respectively. Differential scanning calorimetry (DSC) and intrinsic fluorescence spectrum analyses indicated gradual structural unfolding of proteins, or exposure of hydrophobic clusters to the solvent, especially at higher anhydride levels. Additionally, the in vitro trypsin digestibility was significantly improved by the succinylation. The results indicated that the chemical acylation treatment (especially succinylation) could be applied to modify some selected functional properties of hemp proteins, especially PS and emulsifying ability.     

微波处理对大豆分离蛋白-磷脂复合体系功能特性的影响

研究不同微波功率处理对大豆分离蛋白-磷脂复合体系起泡性、乳化性、凝胶性等功能特性的影响,对大豆分离蛋白-磷脂复合体系分别进行了起泡活性、泡沫稳定性、乳化活性、乳化稳定性、絮凝指数、乳层析指数、持水性及质构性的测定并通过扫描电子微镜技术对凝胶的微观结构变化进行观察。结果发现：随着微波功率的增加,复合体系的起泡性质、乳化性质、凝胶性质均基本呈现先升高后降低的趋势。其中,当微波功率为900 W时,复合体系的起泡性质和乳化性质均表现最佳;当微波功率为1 100 W时,复合体系的凝胶性质较对照组有明显提高,这表明微波处理会促进大豆分离蛋白与磷脂通过相互作用在水油界面上形成较稳定的界面膜,且蛋白适宜的结构改变可以提高复合体系的凝胶特性。     

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