Electrochemical sensor for hazardous food colourant quinoline yellow based on carbon nanotube-modified electrode

A novel electrochemical method using multi-wall carbon nanotube (MWNT) film-modified electrode was developed for the detection of quinoline yellow. In pH 8 phosphate buffer, an irreversible oxidation peak at 0.71 V was observed for quinoline yellow. Compared with the unmodified electrode, the MWNT film-modified electrode greatly increases the oxidation peak current of quinoline yellow, showing notable enhancement effect. The effects of pH value, amount of MWNT, accumulation potential and time were studied on the oxidation peak current of quinoline yellow. The linear range is from 0.75 to 20 mg L⁻¹, and the limit of detection is 0.5 mg L⁻¹. It was applied to the detection of quinoline yellow in commercial soft drinks, and the results consisted with the value that obtained by high-performance liquid chromatography.     

Multispectroscopic studies on the interaction of 2-tert-butylhydroquinone (TBHQ), a food additive,with bovine serum albumin

The interaction of 2-tert-butylhydroquinone (TBHQ) and bovine serum albumin (BSA) was investigated by spectrophotometry, spectrofluorimetry, circular dichroism (CD) and FT-IR techniques. The experimental results indicated that the quenching mechanism of BSA by TBHQ was a static procedure. Various binding parameters were evaluated. The negative value of ΔH, positive value of ΔS and the negative value of ΔG indicated that hydrophobic and hydrogen bonding interactions play major roles in the binding of TBHQ and BSA. Based on Forster’s theory of non-radiation energy transfer, the binding distance, r, between the donor (BSA) and acceptor (TBHQ) was evaluated. The results of CD, UV–vis and FT-IR spectroscopy showed that the binding of TBHQ to BSA induced conformational changes in BSA.     

Multispectroscopic studies on the interaction of maltol,a food additive,with bovine serum albumin

The interaction between maltol, a food additive, and bovine serum albumin (BSA) under simulated physiological conditions was investigated by fluorescence, UV–Vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. The results suggested that the fluorescence quenching of BSA by maltol was a static procedure forming a maltol–BSA complex. The positive values of enthalpy change and entropy change indicated that hydrophobic interactions played a predominant role in the interaction of maltol with BSA. The competitive experiments of site markers revealed that the binding of maltol to BSA mainly took place in subdomain IIA (Sudlow site I). The binding distance between maltol and BSA was 3.01 nm based on the Förster theory of non-radioactive energy transfer. Moreover, the results of UV–Vis, synchronous fluorescence, CD and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of maltol.     

Mechanistic and conformational studies on the interaction of food dye amaranth with human serum albumin by multispectroscopic methods

The mechanism of interaction between food dye amaranth and human serum albumin (HSA) in physiological buffer (pH 7.4) was investigated by fluorescence, UV–vis absorption, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopy. Results obtained from analysis of fluorescence spectra indicated that amaranth had a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The negative value of enthalpy change and positive value of entropy change elucidated that the binding of amaranth to HSA was driven mainly by hydrophobic and hydrogen bonding interactions. The surface hydrophobicity of HSA increased after binding with amaranth. The binding distance between HSA and amaranth was estimated to be 3.03 nm and subdomain IIA (Sudlow site I) was the primary binding site for amaranth on HSA. The results of CD and FT-IR spectra showed that binding of amaranth to HSA induced conformational changes of HSA.     

光谱法研究绿原酸和牛血清白蛋白的相互作用

为了解绿原酸和牛血清白蛋白的相互作用,在模拟动物生理条件下,采用荧光光谱和紫外-可见吸收光谱结合Stern-Volmer方程、double-reciprocal方程和热力学公式来研究绿原酸与牛血清白蛋白相互作用特征。结果表明:绿原酸和牛血清白蛋白在298K和310K两个温度下的结合常数分别为1.869×105L·mol-1和1.574×105L·mol-1;结合位点分别为1.18和1.16;且热力学参数ΔH0、ΔS0、ΔG0;结合距离小于7nm。因此,绿原酸对牛血清白蛋白有较强的荧光静态猝灭作用,符合静态猝灭过程,结合力为疏水作用。     

Effects of pulsed electric field treatment on a bovine serum albumin–dextran model system,a means of promoting the Maillard reaction

Effects of pulsed electric field treatment on browning intensity, antioxidant activity, protein patterns and chemical structure of the bovine serum albumin–dextran copolymer were investigated. Results showed Maillard reaction between bovine serum albumin and dextran was significantly accelerated when the electric field intensity was higher than 10 kV/cm, which was proved by changes in A₂₉₄, browning, antioxidant activity and electrophoresis tests. At the same time, pronounced changes of chemical structure were found by circular dichroism test. The α-helix, β-sheet, β-turns and random coil were changed from approximately 42.6%, 1.9%, 17.5% and 33.9% to 14.5%, 33.0%, 21.2% and 30.2%, respectively, after treatment at 20 kV/cm for 7.35 ms. All data indicated that pulsed electric field was a means to promote Maillard-based copolymerisation.     

山梨酸钾与牛血清白蛋白相互作用的研究

在模拟动物体生理条件下,用荧光光谱、三维荧光光谱、同步荧光光谱、紫外-可见吸收光谱法等研究了在不同温度下,山梨酸钾(PSS)与牛血清白蛋白(BSA)结合反应的光谱行为。试验发现,PSS对BSA有较强的荧光猝灭作用。用Stern-Volmer和Lineweaver-Burk方程及热力学方程分别处理试验数据,发现BSA与PSS发生反应生成了新的复合物,属于静态荧光猝灭,得到了它们相互作用的生成常数KLB(8.421×103L.mol-1)、热力学参数(ΔHθ=-3.595kJ.mol-1,ΔSθ=63.26 J.K-1,ΔGθ=-22.73kJ.mol-1)和结合位点数(0.970)等。位点竞争实验结果显示PSS与BSA的作用位置主要在BSA的SiteI(sub-dom ain IIA)位。证明二者主要靠静电作用力结合,同时用三维荧光光谱及同步荧光光谱法探讨了PSS对BSA构象的影响,为研究PSS的毒性和生物学效应提供了重要信息。     

Study of the interaction of deoxynivalenol with human serum albumin by spectroscopic technique and molecular modelling

The mechanism of interaction between deoxynivalenol (DON) and human serum albumin (HSA) was studied using spectroscopic methods including fluorescence spectra, UV-VIS, Fourier transform infrared (FT-IR) and circular dichroism (CD). The quenching mechanism was investigated in terms of the association constants, number of binding sites and basic thermodynamic parameters. The distance between the HSA donor and the acceptor DON was 2.80?nm as derived from fluorescence resonance energy transfer. The secondary structure compositions of free HSA and its DON complexes were estimated by the FT-IR spectra. Alteration of the secondary protein structure in the presence of DON was confirmed by UV-VIS and CD spectroscopy. Molecular modelling revealed that a DON–protein complex was stabilised by hydrophobic forces and hydrogen bonding. It was potentially useful for elucidating the toxigenicity of DON when combined with biomolecular function effect, transmembrane transport, toxicological testing and the other experiments.     

Determination of brilliant blue FCF in the presence and absence of erythrosine and quinoline yellow food colours by cathodic stripping voltammetry

A study of the voltammetric behaviour of the food colours brilliant blue FCF (C.I. 42090), erythrosine (C.I. 45430) and quinoline yellow (C.I. 47005) in the pH range 2-10 have been carried out by cathodic stripping voltammetry. At pH 4.5 (acetate buffer) with an accumulation potential of 0V and accumulation time of 30s, the voltammograms presented well-defined reduction peaks at potential - 0.76V for brilliant blue FCF, - 0.85V for quinoline yellow and - 0.54V for erythrosine. Linear calibration graphs were obtained from 8 to 80 μg l^-1 brilliant blue, from 4 to 43 μg l^-1 quinoline yellow and from 10 to 70 μg l^-1 erythrosine. The method has been successfully applied to identify and quantify binary mixtures of these dyes and applied for determining brilliant blue FCF in commercial food products.     

Impact of sorbitol on the thermostability and heat-induced gelation of bovine serum albumin

The influence of sorbitol (0–40 wt.%) on the thermal denaturation and gelation of bovine serum albumin (BSA, pH 7.0) in aqueous solution has been studied. The effect of sorbitol on heat denaturation of 0.5 wt.% BSA solutions was measured using ultrasensitive differential scanning calorimetry. The unfolding process was irreversible and was characterized by the thermal denaturation temperature (T_m). As the sorbitol concentration increased from 0 to 40 wt.%, T_m increased from 73.0 to 80.9 °C. The rise in T_m was attributed to the increased thermal stability of the globular state of BSA relative to its native state. The dynamic shear rheology of 4 wt.% BSA solutions containing 200 mM NaCl was monitored as they were heated from 30 to 90 °C at 1.5 °C min⁻¹, held at 90 °C for 120 min, and then cooled back to 30 °C at −1.5 °C min⁻¹. Sorbitol increased the protein gelation temperature (ΔT_gel +10 °C for 40 wt.% sorbitol), decreased the isothermal gelation rate at 90 °C, but increased the final shear modulus of the gels cooled to 30 °C. The impact of sorbitol on gel characteristics was attributed to its ability to increase protein thermal stability, increase the attractive force between proteins and decrease the protein–protein collision frequency.     

荧光光谱法结合分子对接探究pH对姜黄素与牛血清白蛋白结合的影响

目的 采用荧光光谱法结合分子对接探究姜黄素(curcumin,CUR)与牛血清白蛋白(bovine serum albumin,B SA)在不同pH条件下相互作用。方法 通过荧光光谱法计算结合常数和热力学参数分析CUR对BSA荧光猝灭作用和机制;采用位点Marker和分子对接分析结合位点。结果 CUR与BSA结合形成了复合物,产生内源性荧光猝灭作用,属于静态猝灭。不同pH条件下的结合作用力不同,但结合位点数目均为1。由同步荧光可知,色氨酸残基附近疏水性增强,说明与CUR结合后BSA构象出现了收缩,结合位点靠近色氨酸。位点Marker实验证明pH影响CUR与BSA结合位点,分子对接结果表明, pH 7.4时CUR与BSA的结合位点位于Sudlow’s site I附近。结论 本研究表明pH影响CUR与BSA的结合反应,为CUR的活性保护及蛋白基递送载体研究提供理论支持。     

纤维素金属螯合亲和膜的制备及其对牛血清白蛋白的吸附研究

以纤维素分析滤纸为载体、环氧氯丙烷(EPI)为交联活化剂、亚氨基二乙酸(IDA)为配基、铜离子为金属螯合离子,可制得Cu2 -IDA型固定化金属螯合膜。实验表明,滤纸先用4mol／L的NaOH浸润45min,再在75℃水浴中活化反应45min,所得亲和膜环氧基密度可达3.97μmol／cm2。最佳配基偶联反应条件为:25mgIDA／cm2膜、60℃、15h时可获得对Cu2 最大螯合量。牛血清白蛋白(BSA)等温吸附线基本符合Langmuir形式,经曲线拟合得最大吸附量为59.52mg/g干膜。     

Spectroscopic investigation on the interaction of 3,7-dihydroxyflavone with different isomers of human serum albumin

The interaction mechanism of 3,7-dihydroxyflavone (3,7-diHF) and human serum albumin (HSA) was investigated by fluorescence quenching, fluorescence enhancement, steady-state and time-resolved fluorescence emission and UV-vis absorption spectrometry. The binding site of 3,7-diHF on protein was determined by investigating the spectroscopic properties of 3,7-diHF-HSA complex at pH 7.4 and pH 3.5 individually, and confirmed by the site marker competitive experiments. The binding parameters of 3,7-diHF-HSA complex were estimated by fluorescence quenching experiments, and the data were in good agreement with the results obtained from fluorescence enhancement measurements. A remarkable increase in the fluorescence anisotropy values suggested that 3,7-diHF bound at a motional restricted pocket on HSA. The results indicated that 3,7-diHF, in anionic form, was bound within the hydrophobic pockets of the subdomain IIA of HSA (site I), and stabilised mainly by electrostatic force and ionic interactions. The binding mode of drug-protein was discussed based on above experimental results.     

Effect of luteolin on xanthine oxidase: Inhibition kinetics and interaction mechanism merging with docking simulation

Xanthine oxidase (XO) catalyses hypoxanthine and xanthine to uric acid in human metabolism. Overproduction of uric acid will lead to hyperuricemia and finally cause gout and other diseases. Luteolin is one of the major components of celery and green peppers, its inhibitory activity on XO and their interaction mechanism were evaluated by multispectroscopic methods, coupled with molecular simulation. It was found that luteolin reversibly inhibited XO in a competitive manner with inhibition constant (K_i) value of (2.38 ± 0.05) × 10⁻⁶ mol l⁻¹. Luteolin could bind to XO at a single binding site and the binding was driven mainly by hydrophobic interactions. Analysis of synchronous fluorescence and circular dichroism spectra demonstrated that the microenvironment and secondary structure of XO were altered upon interaction with luteolin. The molecular docking results revealed luteolin actually interacted with the primary amino acid residues located within the active site pocket of XO.     

牛血清蛋白的超滤提取工艺研究

采用超滤技术提取牛血中的血清蛋白,主要研究了超滤液温度、超滤压力、超滤液pH和超滤时间对牛血清蛋白提取时膜通量、提取率和得率的影响。实验结果表明,超滤技术可应用于牛血清蛋白的提取,其最佳提取工艺参数为超滤液温度30℃,超滤压力0.1MPa,超滤液pH6.5,超滤时间20min,在此提取工艺参数条件下提取牛血清蛋白时,膜通量达54.58L/m2.h,牛血清蛋白提取率达98.13%,得率达24.09g/L。     

Spectroscopic studies on the interaction of sodium benzoate,a food preservative,with calf thymus DNA

The interaction between sodium benzoate (SB) and calf thymus DNA in simulated physiological buffer (pH 7.4) using acridine orange (AO) dye as a fluorescence probe, was investigated by UV–Vis absorption, fluorescence and circular dichroism (CD) spectroscopy along with DNA melting studies and viscosity measurements. An expanded UV–Vis spectral data matrix was resolved by multivariate curve resolution-alternating least squares (MCR−ALS) approach. The equilibrium concentration profiles and the pure spectra for SB, DNA and DNA–SB complex from the high overlapping composite response were simultaneously obtained. The results indicated that SB could bind to DNA, and hydrophobic interactions and hydrogen bonds played a vital role in the binding process. Moreover, SB was able to quench the fluorescence of DNA−AO complex through a static procedure. The quenching observed was indicative of an intercalative mode of interaction between SB and DNA, which was supported by melting studies, viscosity measurements and CD analysis.     

Preparation of size-controlled bovine serum albumin (BSA) nanoparticles by a modified desolvation method

The size effect of nanomaterials is of major interest, since it may affect their bioavailability and toxicity. In this study, bovine serum albumin (BSA) nanoparticles were prepared using a modified desolvation method. Bare BSA nanoparticles and calcium (Ca)-loaded BSA nanoparticles were fabricated at the targeted sizes, 100, 400, and 800 nm. The mean diameters of the prepared BSA nanoparticles were 125, 393, and 713 nm; those of the Ca-BSA nanoparticles were 260, 353, and 919 nm. The surface-area-to-volume-ratios of the prepared BSA nanoparticles were 4.82, 1.53, and 1.03 nm⁻¹; those of the Ca-BSA nanoparticles were 2.34, 1.72, and 0.90 nm⁻¹. The size and the surface-area-to-volume-ratio of the BSA nanoparticles were controlled by adjusting BSA concentration, pH, and NaCl content, which affected the coagulation of the BSA molecules. The surface-area-to-volume-ratio is a more useful parameter than the mean diameter of particles for comparing effectiveness of nanoparticles.     

The influence of flavonoids on the binding of pantoprazole to bovine serum albumin by spectroscopic methods: With the viewpoint of food/drug interference

The interaction of pantoprazole to bovine serum albumin (BSA) has been investigated with and without four popular 5,7,3',4'-hydroxy-substituted flavonoids, quercetin, luteolin, taxifolin and (+)-catechin. The presence of flavonoids decreased binding constants of pantoprazole with BSA from 39.7% to 93.8%, which depended on flavonoid structures. Analysis of infrared spectroscopy (IR) and circular dichroism (CD) showed the binding of pantoprazole to BSA caused apparent change in secondary structure of BSA. The calculated values of spatial-distance indicated the existence of quercetin, luteolin and taxifolin may compete with pantoprazole binding to BSA, while the existence of (+)-catechin possibly formed ternary pantoprazole-BSA-(+)-catechin complex. However, all the fluorescence quenching was initiated by static quenching procedure irrespective of the absence or presence of flavonoids, while van der Waals force and hydrogen bonds played major roles for pantoprazole-BSA association. All above results may have relevant consequence in rationalising the interferences of common food to gastric ulcer treatments.