Walnuts (Juglans regia L): proximate composition,protein solubility,protein amino acid composition and protein in vitro digestibility

Walnuts contained 16.66% protein and 66.90% lipids on a dry weight basis. Non‐protein nitrogen values ranged from 6.24 to 8.45% of the total nitrogen when the trichloroacetic acid concentration was varied within the range 0.25–1.0 M . Albumin, globulin, prolamin and glutelin respectively accounted for 6.81, 17.57, 5.33 and 70.11% of the total walnut proteins. Walnut proteins were minimally soluble at pH 4.0. The majority of total walnut protein polypeptides had estimated molecular weights in the range 12 000–67 000. The Stokes radius of the major protein in walnuts (glutelin fraction) was 66.44 ± 1.39 Å. Lysine was the first limiting essential amino acid in total walnut proteins as well as in the globulin and glutelin fractions. Leucine and methionine plus cysteine were the second limiting essential amino acids respectively for the prolamin and albumin fractions. Hydrophobic and acidic amino acids dominated the amino acid composition in all protein fractions. Native and heat‐denatured walnut glutelins were easily hydrolysed by trypsin, chymotrypsin and pepsin in vitro. © 2000 Society of Chemical Industry     

宰后高温诱导制备类PSE兔肉

研究了类苍白、松软、表面汁液渗出（pale soft exudative,PSE）兔肉的制备方法,以保证PSE兔肉科学研究用实验材料品质的一致性。以新鲜的兔背最长肌和后腿肉为实验材料,参照猪、家禽PSE肉的制备方法,研究37 ℃水浴条件下兔背最长肌和腿肌肉感官品质、pH值、色泽、失水率、弹性、肌原纤维蛋白溶解度及弹性储能模量（G′）的变化。结果表明：随着处理时间的延长,兔背肌和腿肌的感官品质下降;pH值、a*值、弹性、蛋白质的溶解度及凝胶G′值均显著下降（P＜0.05）;L*值和失水率显著增加（P＜0.05）。水浴2 h时,兔背肌肉的极限pH＜5.74,L*＞63.40,汁液损失率＞25.36%;3 h时,兔腿肌肉的极限pH＜5.84,L*＞56.82,汁液损失率＞17.85%。在37 ℃保温2 h,兔背肌肉表现出了PSE肉的特征;在37 ℃保温3 h,兔腿肌肉表现出了PSE肉的特征。     

Determination of changes in protein conformation caused by pH and temperature

Protein denaturation has a major impact on meat quality parameters such as water holding capacity, tenderness and color. Specific information about structural changes of the individual muscle proteins post-mortem could help understand the factors affecting meat quality. An aromatic dye, 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid (bisANS) that binds to the hydrophobic patches of proteins was used to monitor changes in the conformation of individual sarcoplasmic proteins caused by pH. The bisANS reagent was covalently linked to the proteins with UV-light and the proteins were separated and identified using gel electrophoresis and mass spectrometry. The results showed that the sarcoplasmic proteins creatine kinase M, aldolase A and lactate dehydrogenase showed increased hydrophobicity whereas carbonic anhydrase III showed decreased hydrophobicity with increasing pH. Temperature only had a marked effect on the results at around 40 °C, there being no change between 25 and 35 °C.     

pH值对米糠清蛋白和球蛋白的结构、溶解性及表面疏水性的影响

为解决米糠蛋白提取率低、产品功能性质不佳的问题,以达到增加米糠蛋白利用率的目的。本实验基于蛋白质化学理论和谱学分析技术等探究pH值对米糠清蛋白和球蛋白结构、溶解性及表面疏水性的影响。结果表明：随着pH值的增加,米糠清蛋白、球蛋白的流体动力学直径分布均呈降低趋势,Zeta电位绝对值均呈增大的趋势;米糠清蛋白中α-螺旋结构的含量逐渐增大,而β-折叠结构含量则逐渐减小,无规卷曲结构含量逐渐增大;米糠清蛋白和球蛋白的色氨酸残基趋近于“暴露”态。因此,碱性条件下,米糠球蛋白保留了大部分二级结构、亚基解离诱导的蛋白质三级结构解折叠是其表面疏水性小幅提高的主要原因;米糠清蛋白的二级结构单元的无序性转变、亚基解离诱导的蛋白结构解折叠,是其表面疏水性增大的原因;亚基解离成小粒径以及碱性条件赋予米糠蛋白电荷,是米糠清蛋白及球蛋白溶解性增加的重要原因。     

高压均质处理对不同浓度肌原纤维蛋白水悬液理化特性及蛋白结构的影响

以鸡肉中的肌原纤维蛋白(Myofibrillar proteins,MP)为对象,研究103 MPa压力条件下高压均质(High pressure homogenization,HPH)对不同浓度(5、10、15 mg/mL)MP水悬液理化性质和蛋白结构的影响。结果表明:HPH可以显著提高不同浓度MP在水中的溶解性(P<0.05),改善MP水悬液的分散性、流变性等理化特性,破坏蛋白结构。随着MP浓度增加,MP水悬液溶解度下降、稳定性变差(P<0.05);高浓度的MP在HPH处理过程中可能会发生蛋白聚集,导致水悬液中蛋白粒径增大,表观粘度变大,流动性降低;MP水悬液二、三级结构改变,表面疏水性降低,巯基含量上升,α-螺旋增加,β-折叠下降,从而影响其溶解性;其中5 mg/mL的MP水悬液经过HPH处理后溶解性较好,溶解度达到88.39%,在4 ℃条件下放置9 d后仍然能保持79.08%的溶解度。本研究为食品行业中肉蛋白的深加工提供了参考依据。     

Optimization of lentil protein extraction and the influence of process pH on protein structure and functionality

Response surface methodology was used to optimize alkaline extraction of protein from lentil flour to maximize both protein content and yield. Solid/solvent ratio and pH were the significant factors that determined protein extraction efficiency. At the optimized condition of pH 9.0 and solid/solvent ratio of 1:10 (g:mL), a yield of 14.5 g of protein extract/100 g of flour was obtained with a protein content of 82 g/100 g at (22 °C) after 1 h of extraction. The impact of extraction pH on the molecular structures and functionalities of lentil protein was investigated. Increasing the extraction pH to 10 caused partial protein hydrolysis and unfolding as suggested by size exclusion high performance liquid chromatography and Fourier transform infrared spectroscopy analysis, leading to improved protein solubility and gelling property. Environmental pH influenced protein solubility and surface charge, and subsequently the gelling and foaming properties. The foaming capacity was especially strong, comparable to whey and egg proteins.     

猪腿纤维蛋白的热致胶凝与功能性质(英文)

本实验探讨了蛋白浓度和 pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重以及热致胶凝性质的影响。在 0.6mol/L、pH6.0 的 NaCl 溶液中,纤维蛋白的胶凝性最强,凝胶强度随着蛋白浓度的增加而增加。然而,蛋白浓度的增加对蒸煮失重和蛋白质溶解度产生不利影响。猪腿纤维蛋白在 4℃贮存一段时间后,其溶解度有所增加。实验结果表明:pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重和粘弹性都有一定的影响。在 pH6.0 时,蛋白的凝胶强度最大,而在 pH7.0 时,蛋白溶解度最大,蒸煮失重最小。     

pH值对柞蚕蛹粉凝胶特性及蛋白质热聚集行为的影响

柞蚕蛹富含优质蛋白质,是一种具有很高开发利用价值的食品原料。采用质构仪、流变仪和激光扫描共聚焦显微镜等分析不同pH值对柞蚕蛹粉凝胶特性及蛋白质分子热聚集行为的影响。结果表明:pH值为7时形成的柞蚕蛹粉凝胶网络较为连续和均匀,凝胶保水性最高(51.67%±0.79%,P<0.05);pH值为9时的柞蚕蛹粉有最低的临界凝胶质量分数(8%)、最高的凝胶硬度(41.67N±3.37N,P<0.05)和弹性(2.81mm±0.07mm,P<0.05)。柞蚕蛹粉凝胶的储能模量与蛋白质的溶解度呈显著正相关(R=0.92,P<0.05),而与蛋白质的凝固率(R=-0.52)和表面疏水性(R=-0.77)呈显著负相关(P<0.05)。pH 值为9时,蛋白质溶解度最高(62.13%±0.63%,P<0.05),表面疏水性最低(70.06μg±9.32μg, P<0.05),形成了更多的小尺寸热聚集物并增强了凝胶基质;而在pH值为5时,蛋白质溶解度最低(28.96%±1.13%,P<0.05),表面疏水性最高(195.66μg±1.30μg,P<0.05),促使更多的大尺寸热聚集物形成并无序堆叠而削弱凝胶基质。研究旨在通过调节pH值控制柞蚕蛹粉中蛋白质的热聚集行为,进而获得理想质地和保水性的柞蚕蛹粉凝胶。     

藜麦蛋白及肽的研究进展

藜麦是一种无麸质谷物,蛋白质含量较高,无限制性氨基酸的存在,氨基酸构成比例合理。藜麦蛋白与牛乳酪蛋白的氨基酸模式相当,是一种优质蛋白质来源。文章综述了藜麦蛋白及肽的理化特性、加工功能特性、提取与制备方法及生物活性。     

超声辅助pH值偏移对苦荞蛋白结构和功能特性的影响

探讨pH偏移联合超声处理对苦荞蛋白结构及功能特性影响的结果表明：通过超声辅助及pH偏移处理,苦荞蛋白的游离巯基含量显著增加（P<0.05）,这可能是由于蛋白质去折叠导致内部巯基暴露,或蛋白质中二硫键断裂而生成新的巯基所致。在超声时间为20 min,功率为300 W时,苦荞蛋白表现出最高的表面疏水性,表明蛋白质在改性过程中经历了重组,导致疏水相互作用下形成的蛋白聚集体被破坏,蛋白粒径减小,进而暴露更多内部的疏水基团。此外,经超声辅助pH偏移处理显著提升了苦荞蛋白的溶解度,尤其在碱性pH条件下,溶解度从63.85%显著提升至103.48%。该处理也导致了苦荞蛋白粒径的显著下降（P<0.05）,以及绝对电位和乳化活性的显著增强（P<0.05）。综上所述,超声辅助pH偏移处理不仅有效改善了苦荞蛋白的结构特性,还显著提升了其功能特性,为苦荞蛋白在食品工业中的应用开辟了新的前景。     

Effect of phytate on the in-vitro solubility of Al+, Ca2+, Hg2+ and Pb2+ as a function of pH at 37°C

The effect of phytate on the solubility of Al³⁺ and Pb^{2 +} has been investigated in vitro at 37°C across the pH ranges 3–7 (Pb²⁺) and 2–5 (Al³⁺). For both ions minimum solubility was found when the initial metal ion: phytate ratio was in the range 5:1–3:1 across the whole pH range. For Al³⁺ the solubility rose sharply either side of these ratios whereas for Pb^{2 +} solubility rose only slowly as the metal ion: phytate ratio was reduced. Hg²⁺ was totally soluble under all conditions tested. At pH 7 Ca²⁺ solubility was found to be at a minimum when the initial Ca : phytate ratio was 5 :1 irrespective of the initial Ca²⁺ concentration.     

大豆蛋白溶解性研究

该文概述大豆蛋白溶解特性及其与一般物质溶解差异,介绍提高大豆蛋白溶解性改性方法及研究现状,对比不同改性增溶方法优、缺点,并提出今后大豆蛋白改性研究方向。     

动态超高压均质对花生蛋白溶解性和乳化性的影响

以花生蛋白为原料,研究了动态超高压均质技术对花生蛋白溶液的溶解性和乳化性的影响。结果显示,花生蛋白溶液经动态超高压均质处理后,溶解性有显著提高,乳化性也有所提高。