Cholesterol In Food Samples Research Articles

Radix Pueraria Flavonoids Assisted Green Synthesis of Reduced Gold Nanoparticles: Application for Electrochemical Nonenzymatic Detection of Cholesterol in Food Samples.

Using radix pueraria flavonoids (RPFs) as a reducing and stabilizing agent, we report a simple, cost-effective, and ecologically friendly green synthesis technique for gold nanoparticles (AuNPs) in the present study. Ultraviolet-visible (UV) spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) investigations were used to characterize the AuNPs. The results demonstrated that the produced AuNPs were nearly spherical and that their particle sizes had a mean diameter of 4.85 ± 0.75 nm. The "Green" AuNPs, exhibiting remarkable peroxidase-like activity and Michaelis-Menten kinetics with high affinity for H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), were effectively applied to the fabrication of a sensitive nonenzymatic enhanced electrochemical sensor for the detection of cholesterol (Cho). Under optimum circumstances, it was possible to establish two linear ranges of 1-100 and 250-5000 μmol/L with a detection limit of 0.259 μmol/L (signal/noise ratio (S/N) = 3). The suggested sensor was utilized with satisfactory findings to determine the amount of Cho in food samples.

Development of a novel biosensor based on a conducting polymer

A new type of amperometric cholesterol biosensor was fabricated to improve the biosensor characteristics such as sensitivity and reliability. For this purpose, a novel immobilization matrix 2-(4-fluorophenyl)-4,7-di(thiophene-2-yl)-1H-benzo[d]imidazole (BIPF) was electrochemically deposited on a graphite electrode and used as a matrix for the immobilization of cholesterol oxidase (ChOx). Due to strong π-π stacking of aromatic groups in the structures of polymer backbone and enzyme molecule, one can easily achieve a sensitive and reliable biosensor without using any membrane or covalent bond formation between the enzyme molecules and polymer surface. Moreover, through pendant fluorine group of the polymer, H-bond formation between with enzyme molecules and polymer was generated. Cholesterol was used as the substrate and amperometric response was measured in correlation with cholesterol amount, at -0.7 V vs. Ag/AgCl in phosphate buffer (pH 7.0). Consequently, optimum conditions for this constructed biosensor were determined. K(M)app, I(max), LOD and sensitivity values were investigated and calculated as 4.0 nM, 2.27 µA, 0.404 µM and 1.47 mA/mM cm(2), respectively. A novel and accurate cholesterol biosensor was developed for the determination of total cholesterol in food samples.

A sepiolite modified conducting polymer based biosensor

A conducting polymer modified with sepiolite was utilized in the construction of a highly sensitive and fast amperometric cholesterol biosensor. In this study a monomer; (10,13-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)dibenzo[a,c]phenazine (PHED)) was synthesized and then its polymer was coated on a graphite electrode by electropolymerization to obtain a matrix for enzyme immobilization. Cholesterol oxidase was immobilized onto polymer coated electrode by adsorption technique. Sepiolite was introduced for a successful immobilization of the cholesterol oxidase. Immobilized enzyme kinetic parameters (KMapp, Imax) were evaluated by Michaelis-Menten kinetics and calculated as 0.031mM and 6.06μA, respectively. LOD and sensitivity were estimated as 0.36μM and 1.64mA/mMcm2. Characterization of designed biosensor was done to examine the effect of various factors such as enzyme amount, optimum pH and shelf-life. A novel accurate and inexpensive cholesterol biosensor was developed for the determination of total cholesterol in food samples.

Determination of cholesterol in food samples using dispersive liquid–liquid microextraction followed by HPLC–UV

A fast, simple, and sensitive sample preparation procedure based on dispersive liquid–liquid microextraction (DLLME) is proposed for the determination of cholesterol in food samples using isocratic reverse phase high performance liquid chromatography (RP-HPLC) and UV detection. The influence of several important parameters on extraction efficiency of cholesterol was evaluated. Under optimized conditions, a linear relationship was obtained between the peak area and the concentration of cholesterol in the range of 0.03–10 μg l −1. The detection and quantification limits were 0.01 and 0.03 μg l −1, respectively. Intra-day and inter-day precisions for the analysis of cholesterol were in the range of 1.0–3.1%. The applicability of the proposed method was demonstrated by analyzing cholesterol in milk, egg yolk and olive oil.

Development of cholesterol biosensor based on immobilized cholesterol esterase and cholesterol oxidase on oxygen electrode for the determination of total cholesterol in food samples

The development of a cholesterol biosensor by co-immobilization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOX) on oxygen electrode is described. The electrode consists of gold cathode and Ag/AgCl anode. The enzymes were immobilized by cross-linking with glutaraldehyde and Bovine Serum Albumin (BSA). The immobilized enzymatic membrane was attached to the tip of the electrode by a push cap system. The optimum pH and temperature of the sensor was determined, these are 6 and 25 °C respectively. The developed sensor was calibrated from 1–75 mg/dl of cholesterol palmiate and found linear in the range of 2–50 mg/dL. The calibration curve was drawn with V i (ppm/min)(initial velocity) vs different concentrations of cholesterol palmiate (mg/dL). The application of the sensor to determine the total cholesterol in different real food samples such as egg, meat was investigated. The immobilized enzymatic layer can be reused over 30 times and the stability of the enzymatic layer was studied up to 9 weeks.

Development of organic phase amperometric biosensor for measuring cholesterol in food samples

Previous works on organic phase enzyme electrodes (OPEE) applied methods that worked mostly under stirred conditions. The aim of our present work was to develop a flow-through measuring set-up for determination of cholesterol content in organic media. For determination of free cholesterol content cholesterol oxidase (COD) was used, while for measuring the total cholesterol content a bi-enzyme cell containing immobilised cholesterol esterase (CE) and cholesterol oxidase was developed. Enzyme immobilisation took place on a natural protein membrane, by a glutaraldehyde cross-linking method, in a thin-layer enzyme cell made from Teflon. The enzyme cell was connected into a stopped-flow injection system (SFIA), with a flow-through amperometric detector. The parameters of biochemical and electrochemical reactions were measured. The effect on amperometric detection of different organic salts as electron mediator or conducting salts was studied. The optimal concentration of (TBATS) was 2.4 mg L−1 while for (FMCA) an optimal concentration was found at 0.4 mg L−1. The minimum amount of water, necessary for enzymatic activity in the organic phase, was also determined. Changing the concentration of toluene in acetonitrile carrier solution, the peaks increased definitely in the range 10–40% toluene. Since CE and COD were immobilised together in the enzyme cell, the conversion rate was found to be about 0.7–0.8 when the toluene content was higher then 30%. The linear measuring range for cholesterol oleate and cholesterol was 0.1–0.5 mM. Total cholesterol content of lard, butter and pasta samples were determined. It is concluded that an organic phase bi-enzyme cell may be suitable for cholesterol determination in food.

Graphite-teflon composite bienzyme electrodes for the determination of cholesterol in reversed micelles. Application to food samples.

A bienzyme amperometric composite biosensor for the determination of free and total cholesterol in food samples is reported. Cholesterol oxidase and horseradish peroxidase, together with potassium ferrocyanide as a mediator, are incorporated into a graphite-70% Teflon matrix. The compatibility of this biosensor design with predominantly nonaqueous media allows the use of reversed micelles as working medium. The reversed micelles are formed with ethyl acetate as continuous phase (in which cholesterol is soluble), a 4% final concentration of 0.05 mol L(-1) phosphate buffer solution, pH 7.4, as dispersed phase, and 0.1 mol L(-1) AOT as emulsifying agent. Studies on the repeatability of the amperometric response obtained at +0.10 V, with and without regeneration of the electrode surface by polishing, on the useful lifetime of one single biosensor and on the reproducibility in the fabrication of different pellets illustrate the robustness of the biosensor design. Determination of free and total cholesterol in food samples such as butter, lard, and egg yoke was carried out, and the obtained results were advantageously compared with those provided by using a commercial Boehringer test kit.

Supercritical fluid extraction and chromatography of cholesterol in food samples

A method based on supercritical fluid chromatography is presented which can be used for the determination of cholesterol in certain foods. The method involves the extraction with supercritical carbon dioxide and analysis of the extracts using capillary column with supercritical carbon dioxide as mobile phase and flame ionization detection. Quantification is achieved using cholesteryl chloroacetate as an internal standard.