Effect of pH and Pepsin Limited Hydrolysis on the Structure and Functional Properties of Soybean Protein Hydrolysates

Effects of limited enzymatic hydrolysis with pepsin on the functional properties and structure characteristics of soybean proteins were investigated. Hydrolysates with different incubation time (10 to 900 min) were prepared. Results showed that SPI hydrolyzed for 60 min exhibited the best emulsibility and the ability of resisting freezing/thawing. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis proved that pepsin can degrade glycinin but had little effect on the α’ subunit of β‐conglycinin. The structure unfolding reached the largest extent after incubation for 60 min and the soluble and flexible aggregates were formed. After 120 min, glycinin was degraded totally and β‐conglycinin formed insoluble aggregates. Moreover, 2 methods were applied for the deactivation of pepsin to obtain final hydrolysates at pH 2.0 and 7.0, respectively. The structure analysis revealed that the unfolding extent and structure characteristic were different in these 2 conditions. When adjusting the pH value from 2.0 to 7.0, the unfolding protein molecular would reaggregate again at pH 7.0 due to the charge neutralization, and the hydrodynamic diameter and λ_max absorbance decreased compared to pH 2.0. Moreover, some of the insoluble aggregates formed at pH 2.0 became soluble at pH 7.0, because of the salt‐in phenomenon.     

冷冻及解冻处理对肌原纤维蛋白理化性质的影响

研究不同的冻结温度（-18 ℃和-50 ℃）和解冻方式（微波解冻、空气解冻及4 ℃解冻）对猪肉肌原纤维蛋白含量和理化特性的影响。结果表明,在不同冻结温度与解冻方式下,肌原纤维蛋白的含量、溶解性、乳化活性、乳化稳定性、起泡性及起泡稳定性均降低,表面疏水性增加。其中,采用-18 ℃冻结,微波解冻处理的肌原纤维蛋白与对照组相比,其溶解性、乳化性、乳化稳定性、起泡性及起泡稳定性分别降低了38.7%、16.5%、28.3%、39.6%和17.3%;采用-50 ℃冻结,4 ℃解冻的蛋白其含量（6.32%）、溶解性（22.05%）、乳化性（7.89 m2/g）、乳化稳定性（32%）、起泡性（30.95%）及起泡稳定性（62.25%）与其他处理对应的各指标相比,理化特性均保持较好。不同的冷冻和解冻条件下,肌原纤维蛋白各指标之间的变化相互关联。     

胰蛋白酶水解对荞麦蛋白功能特性的影响

研究胰蛋白酶水解及热处理对荞麦蛋白功能特性的影响。结果表明：随水解度的增大,蛋白质溶解性增大,表面疏水度降低,乳化性及乳化稳定性升高,起泡能力及泡沫稳定性下降。热处理使荞麦蛋白溶解性上升,表面疏水度增大,乳化性及乳化稳定性下降,起泡能力上升,并且加热处理可抑制由于水解度下降导致的泡沫稳定性降低的趋势。     

高压均质对菜籽蛋白功能性质和酶解效果的影响

为了了解高压均质技术对菜籽蛋白的影响,采用不同压力(306、0、901、201、50 MPa)对菜籽蛋白溶液进行均质处理,并分析了处理前后菜籽蛋白功能性质和水解度的变化。结果表明:高压均质可提高菜籽蛋白的溶解度、乳化性、起泡性和泡沫稳定性等功能性质,且随着均质压力的升高其乳化性、起泡性和泡沫稳定性均增强;同时高压均质对蛋白质的氮溶指数、乳化稳定性也有显著的影响;此外,高压均质对菜籽蛋白的酶解也起到了促进作用,且随着压力的增大作用效果越明显。     

Functional properties of whey proteins as affected by dynamic high-pressure treatment

An ultra high-pressure homogenizer was used to treat whey protein isolate solutions (3%, w/w). The treated solutions (up to 300 MPa) were characterised for both physico-chemical properties (particle size distribution, surface hydrophobicity and structural conformation) and functional properties (solubility, foaming stability and interfacial rheology). Dynamic high-pressure treatment did not affect the conformation of the proteins (determined by micro-calorimetry, size-exclusion chromatography and electrophoretic technique). This treatment dissociated large protein aggregates leading to unmasking of the buried hydrophobic groups without affecting protein solubility. Interactions may then occur between these groups that enhance the viscoelasticity of air-water interfaces (assessed by drop tensiometry) and improve foam stability (evaluated by sparging method). Dynamic high-pressure-treated whey proteins showed better foaming and stabilising properties.     

酸性条件下高压均质对大豆蛋白结构与功能特性的影响

通过还原电泳、粒度分布以及内源荧光扫描光谱等手段研究了酸性条件(pH3.0)下高压均质处理对大豆蛋白结构的影响,并测定了改性样品功能特性的变化。结果表明,酸性条件下高压均质对大豆蛋白亚基组成影响较小。随着均质压力的上升,改性样品的粒径呈现先增大后下降的趋势,在40MPa时达到最大值,为94.33nm;而内源扫描最大吸收波长λmax也呈现先增大后下降的过程,表明大豆蛋白结构先展开后聚集,在20MPa时,其λmax为336.0nm,展开程度达到最大。功能特性方面,均值压力为20MPa时能有效改善大豆蛋白的溶解性;其乳浊液的粒径随着均质压力的增大而不断下降。     

高压均质对大豆分离蛋白功能性质的影响

为了了解高压均质技术对大豆分离蛋白（SPI）功能性质的影响,采用不同的均质压力、均质次数和料液比对大豆分离蛋白溶液进行了高压均质处理,并分析处理前后SPI功能性质的变化.结果表明：高压均质可在一定程度上提高SPI的溶解性、乳化活性及其稳定性和起泡性及泡沫稳定性.均质压力在0～70 MPa的范围内升高时,SPI的溶解性、乳化稳定性、起泡性和泡沫稳定性得到了相应的改善,而乳化活性在压力为40 MPa时达到最高;均质次数由1次向3次增加时,SPI的乳化稳定性、起泡性及泡沫稳定性得到了提高,而溶解性和乳化活性则降低;均质物料料液比在1∶16～1∶8 （g∶mL）的范围内逐步增大时,SPI的各项功能性质均有不同程度的提高,并在料液比为1∶8时达到了最高值.     

Effect of ascorbic acid on the foaming and gelling of globular proteins

Foam expansion and foam stability of plasma and egg albumen proteins were enhanced in the presence of increasing concentrations of ascorbic acid (0.1–1.0%). BSA showed the greatest improvement in foaming properties following treatment with ascorbic acid, whilst foaming properties of egg albumen were improved to a limited extent. A combination of partial acid hydrolysis and treatment with 1% ascorbic acid was required to dramatically improve the foaming properties of bovine blood plasma. In the presence of sucrose, foam expansion of both native and ascorbic acid-treated blood plasma was decreased. In contrast the foam expansion of ascorbic acid-treated egg albumen was greater although this effect decreased slightly on incubation. the gelation of ascorbic acid treated proteins increased with increasing temperatures over 80–90°C, particularly for BSA and blood plasma, and with increasing concentrations of ascorbic acid. Ascorbic acid-treated proteins exhibited enhanced surface and exposed hydrophobicity and reduced numbers of sulphydryl groups indicating the involvement of these factors in foam and gel formation.     

超声波处理对蜂王浆蛋白功能和结构的影响

探讨不同功率的超声波处理(20 kHz,200、400、600 W)对蜂王浆蛋白溶解性、乳化性、起泡性、水解度以及表面疏水性的影响。同时,通过对王浆蛋白二级结构、三级结构和微观结构的分析,探讨超声波处理改善蜂王浆蛋白功能特性的机制。结果表明,与未处理组相比较,蜂王浆蛋白经过400 W处理后,其溶解度增加10.90%,乳化活性增加67.18%,乳化稳定性增加15.87%,起泡性增加60.00%,起泡稳定性增加118.75%,水解度增加83.33%,表面疏水性增加18.65%。蛋白质的二、三级结构分析显示,该处理条件可以诱导蛋白质发生去折叠化。微观结构分析显示,蛋白质经400 W处理后,其表面较为粗糙,碎片化程度增加。这些结果表明,超声波处理所诱导的蛋白质构象的变化,是其功能特性得以改善的主要原因。     

响应面法优化元宝枫籽粕酶解工艺及多肽功能特性研究

本文以元宝枫籽粕为原料,采用碱性蛋白酶法对元宝枫籽粕进行酶解,以酶解时间、加酶量、pH、酶解温度、料液比为考察因素,酶解多肽得率为评价指标,在单因素实验的基础上,根据Box-Behnken中心组合实验设计对元宝枫籽粕碱性蛋白酶酶解多肽制备工艺进行优化,并对优化工艺获得的酶解多肽进行了氨基酸组成、吸水性、吸油性、起泡性质、乳化性质和表面疏水性等功能特性表征。结果表明:最优的酶解制备工艺为:酶解时间3.3 h,pH为10,加酶量为3%,酶解温度为55 ℃。在最优制备工艺条件下元宝枫籽粕碱性蛋白酶酶解多肽得率为40.13%±0.15%。氨基酸组成分析表明酶解多肽所含八种必需氨基酸量高达20.3%,远高于国际粮农组织所建议成人所需必需氨基酸量。此外,酶解多肽的吸油性（4.553 g/g）高于大豆蛋白（2.61 g/g）,其表面疏水性（1365.3）与大豆7S球蛋白的表面疏水性相似,乳化性和乳化稳定性略低于大豆分离蛋白。本研究所获得的元宝枫籽粕碱性蛋白酶酶解多肽具有较好的功能特性,这也表明它可作为一种潜在的功能成分应用于食品中,为元宝枫籽粕的新应用开发提供数据和理论支撑。     

高压均质对大豆蛋白乳液性质影响的研究进展

大豆蛋白作为一种高分子蛋白质,具有良好双亲性和表面活性,可通过在油水界面形成粘弹性蛋白层的方式在乳液中起到乳化作用,从而提高乳液体系的稳定性。高压均质技术是一种通过静高压和均质阀产生的综合效应从而改变蛋白质的结构和加工特性的新型非热加工技术,可以制备纳米级的大豆蛋白乳液。本文聚焦大豆蛋白乳液,阐述了高压均质制备大豆蛋白乳液的过程以及均质条件的影响,分析总结了高压均质处理对大豆蛋白乳液结构（粒径、ζ-电位、空间结构）和功能特性（流变特性、乳化性能和凝胶性能）影响的国内外研究进展及作用机理。最后,针对目前研究进展对高压均质在大豆蛋白乳液的加工应用做出展望,以期为大豆蛋白乳液的研究提供一定的帮助。     

酸解均质制备纳米豆渣纤维素工艺

以富含纤维素的豆渣为原料,采用酸水解辅以均质法制备纳米纤维素,研究HCl浓度、水解时间、水解温度、液料比4个因素对豆渣水解率和纤维素粒度的影响,通过正交试验确定制备豆渣纳米纤维素的最佳工艺条件。结果表明： 最佳工艺条件为HCl溶液浓度3mol/L、水解温度100℃、水解时间120min、液料比45:1(mL/g)、均质压力30MPa;通过激光粒度分析和扫描电镜分析,纳米豆渣纤维素呈微球状,粒度为50～100nm。盐酸水解辅以高压均质工艺处理能有效制得纳米大豆纤维素。     

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.     

Screening of Proteolytic Enzymes to Enhance Foaming of Whey Protein Isolates

Whey protein isolate (WPI) was modified to enhance foaming characteristics by controlled hydrolysis using proteolytic enzymes. Alcalase, acid fungal protease, chymotrypsin, pepsin and trypsin were used to hydrolyze 5% rehydrated WPI. Decree of hydrolvsis was estimated by freezing point depression and terminated at 2.5 to 3% by heating or pH adjustment. Controls were treated under similar conditions but without enzymes. Hydrolysates were separated into permeate and retentate by ultrafiltration and concentrated by reverse osmosis before freeze drying. Foam capacity, stability and surface tension of hydrolysates were measured. Permeate from Alcalase exhibited the best foaming characteristics, comparable to egg white.     

酶解处理对扁桃仁蛋白质起泡特性影响及其应用研究

扁桃仁营养丰富,是一种优质的坚果蛋白资源.为拓宽扁桃仁的应用领域,以扁桃仁分离蛋白质为研究对象,以其起泡能力和泡沫稳定性为观测指标,探讨生物酶解处理对其起泡特性的影响.结果表明:扁桃仁分离蛋白质经胃蛋白酶酶解处理后,其酶解产物的粒径减少,表面疏水性增加,分子质量(10～25 kDa)与电位值(-20.06)均减小,即胃蛋白酶酶解处理显著改善了扁桃仁分离蛋白质的起泡性和泡沫稳定性.在此基础上,将酶解180 min的扁桃仁分离蛋白质水解物(al-mond protein isolate hydrolysates,APIH180)作为发泡剂应用到蛋糕中,结果发现,当APIH180添加量为20％时,蛋糕的外观、口感与全蛋蛋糕相比,均有所提升;APIH180添加量超过40％的蛋糕品质明显下降,即APIH180添加量为20％ ～40％时可以起到良好的发泡效果,且改善了蛋糕的品质.本研究旨在拓展扁桃仁蛋白质的开发利用思路,进而丰富植物基蛋白质资源应用的理论与技术.     

Germination‐Assisted Enzymatic Hydrolysis Can Improve the Quality of Soybean Protein

This study aimed to investigate the effects of combined germination and Alcalase hydrolysis on the quality of soybean protein. Protein profiles, water solubility, foaming and emulsifying properties, thixotropic properties, and in vitro protein digestibility (IVPD) were tested, the chemical score (CS), essential amino acid index (EAAI), and protein efficiency ratio (PER) of soybean protein were also defined. The combined treatment of germination and Alcalase hydrolysis remarkably improved the solubility, emulsification activity index, emulsion stability index, and foaming capacity of soybean protein. Notably, a decrease in foaming stability was detected. The electrophoretic profile showed a weak breakdown of soybean protein during germination. However, a strong breakdown of protein was observed after the hydrolysis with Alcalase. The combined treatment also decreased the CS and EAAI of soybean protein, but only by 18%. Meanwhile, the IVPD and PER of soybean protein were significantly improved. Moreover, the protein of the germinated and hydrolyzed soybean flour demonstrated better swallowing properties. These findings indicated that the combined treatment of germination and enzymatic hydrolysis can improve the quality of soybean protein.     

Effect of Partial Proteolysis and Succinylation on Functionality of Corn Germ Protein Isolate

Corn germ protein isolate (CGPI) was partially hydrolyzed with trypsin and pepsin and succinylated at three levels. Various functional and electrophoretic properties of the native and modified protein were determined. Water absorption and foaming properties of CGPI were Improved by partial hydrolysis with trypsin; emulsifying capacity and nitrogen solubility were reduced; oil absorption was increased only slightly. CGPI pepsin hydrolyzate has decreased oil absorption, nitrogen solubility and emulsifying capacity but improved foaming properties; water absorption was unchanged. Treatment of CGPI with succinic anhydride improved water and oil absorption, nitrogen solubility and foaming capacity but decreased emulsifying capacity; foam stability was unchanged. Succinylation retarded electropohoretic mobility while hydrolysis altered band intensities.     

Simple pH treatment as an effective tool to improve the functional properties of ovomucin

Ovomucin has been considered to contribute a lot to the excellent functional properties of egg white. This work focused on investigating the effects of pH and protein concentration on foaming and emulsifying properties of ovomucin to evaluate the proper use of this egg protein as a functional food ingredient, and to clarify its contribution to the functional properties of egg white under different pH conditions. Protein solubility and surface hydrophobicity were measured through the pH ranged from 2.3 to 11.0. Alkali treatment gave ovomucin improved emulsification properties, which were correlated well with the surface hydrophobicity (r ≥ 0.89, P < 0.01). Although ovomucin showed lower foaming capacity in acid and neutral solution, enhanced foaming stability was observed with weak acid-treated ovomucin (pH 5 to 6) compared to native ovomucin. These results demonstrated that acid and alkali treatment, which leads to partial unfolding of ovomucin can improve functional properties of ovomucin, with the greatest improvement for emulsification properties being from the alkali treatment and for foaming stability being from weak acid treatment. These results are helpful to produce unfolding ovomucin suitable for wide range of applications in food industry, and to provide useful information on the proper use of egg white in different food systems. PRACTICAL APPLICATION: Ovomucin plays a critical functional role in egg white products. However, it is typically insoluble in distilled water or common salt solutions, which has thus limited its commercial applications. Alkaline treatment resulted in gradual increase in solubility, which markedly enhanced the emulsifying properties, on the other hand foaming stability of ovomucin can be promoted by weak acid treatment. The results of this work help to produce unfolding ovomucin suitable for wide range of applications in food industry, and to provide useful information on the proper use of egg white in different food systems.     

Functional properties of limited hydrolysed cross‐linked casein–gelatin composites

A casein–gelatin composite was prepared by cross‐linking of caseinate and bovine gelatin with a microbial transglutaminase, and the impact of limited proteolysis by trypsin on some functional properties of the composite was investigated in the present work. Two hydrolysed composites were prepared with degree of hydrolysis (DH) of 1 and 2% and analysed by SDS‐PAGE to reflect polypeptide profiles. Some functional properties of the two hydrolysed composites were evaluated, among which solubility, digestibility in vitro, surface hydrophobicity and emulsifying properties showed dependence on the DH. Limited proteolysis of the composite improved its solubility in pH 3–10, especially when the DH was 2%. Compared to the composite, the hydrolysed composites showed an increased emulsifying activity index (about 357–408%), emulsion stability index (about 23–28%) and digestibility in vitro (about 65–80% for pepsin, whereas 2–3% for pepsin–trypsin hydrolysis), together with a decreased surface hydrophobicity (about 55–62%) and oil absorption capacity (about 20–23%). The applied proteolysis also led to the aqueous dispersions of the two hydrolysed composites much lower apparent viscosity, storage and loss modulus.     

Enhancement of Functional Properties of Rice Bran Proteins by High Pressure Treatment and Their Correlation with Surface Hydrophobicity

Changes in functional properties of rice bran proteins as influenced by high-pressure (HP) treatment (100–500 MPa, 10 min) were studied. Properties evaluated were protein solubility, water absorption capacity, oil absorption capacity, foaming capacity, foam stability, emulsifying activity, emulsion stability, least gelation concentration, and surface hydrophobicity. HP treatment at 100 and 200 MPa significantly improved the solubility and oil absorption capacity, while water absorption and foaming capacities increased further reaching the maximum at 500 MPa. Compared with the untreated control sample, the emulsifying activity and foam stability of treated samples were significantly higher and least gelation concentration was lower, but none of them showed any specific trend with pressure level. Emulsion stability and surface hydrophobicity increased with the pressure level until 400 MPa and decreased slightly at 500 MPa. Pearson correlation coefficients clearly showed that surface hydrophobicity was positively correlated with water absorption capacity, foaming capacity, emulsifying activity index, and emulsion stability index, but negatively correlated with least gelation concentration. The pressure treated rice bran protein possessed good functional properties for use as a food ingredient in the formulations.