Tyramine reduction by tyrosine decarboxylase inhibitor in <Emphasis Type="Italic">Enterococcus faecium</Emphasis> for tyramine controlled <Emphasis Type="Italic">cheonggukjang</Emphasis>

This study was carried out to find a method to control tyrosine decarboxylase activity (TDC) of a strain of Enterococcus faecium capable of producing high levels of tyramine. To select a TDC inhibitor, enzyme assay was first performed using purified TDC enzyme and 0.1% of TDC inhibiting chemicals. When 0.23% of nicotinic acid was added, tyramine content (363 ug/mL) was lower than that of the control group (873 ug/mL). At the same time, bacterial growth was decreased 1 log cycle from 8.62 to 7.56 log CFU/mL. TDC expression level in E. faecium was measured by using RT-qPCR. Lower expression level (below 0.7) was observed after the addition of 0.23% nicotinic acid (in vitro). When cheonggukjang was manufactured with addition of nicotinic acid, tyramine contents were decreased from 698.67 to 117.27 mg/kg when the concentration of nicotinic acid added was increased from 0.10 to 0.30%. These results suggest that nicotinic acid could be used as an agent (TDC inhibitor) to reduce tyramine content in cheonggukjang.     

Construction of an amperometric polyphenol biosensor based on PVA membrane

A method is described for construction of an amperometric biosensor for determination of polyphenolic content using polyvinyl alcohol membrane bound polyphenol oxidase mounted on a gold coated Ag wire as a working electrode, a silver/silver chloride (Ag/AgCl) reference electrode and Pt wire as auxiliary electrode. The biosensor showed optimum response within 30 s, when operated at 30 °C. A linear relationship was obtained between L-DOPA concentration (0.5–20 μM) and current (μA). Limit of detection of the method was 0.5 μM. The biosensor measured polyphenols in tea leaves, alcoholic beverages and water. The enzyme electrode was used 280 times over 6 months, when stored at 4 °C. The biosensor is better than earlier membrane based biosensors in terms of detection limit (0.5 μM) and stability (6 months).     

Formation of tyramine byLactobacillus curvatus LTH 972

The effect of food-related environmental factors on the formation of tyramine byLactobacillus curvatus LTH 972 was investigated in liquid culture supplemented with tyrosine. The highest concentrations of tyramine (up to 201 mg/l) were formed at 30 °C, pH 5.2 and at a water activity (a_w) of 0.97. At lower temperatures and at higher pH- and a_w values the reaction slowed down but was still clearly detectable. Glucose, nitrate and nitrite had no effect at concentrations applied in sausage fermentations. The strain was able to form tyramine from tyrosine-containing di- and tripeptides in phosphate buffer. Therefore, in proteinaceous substrates an increased formation of tyramine cannot be excluded when ongoing proteolysis creates precursors, as is the case in the presence of proteolytic micro-organisms.     

Arsenic in rice and diets of children

Levels of arsenic in Australian and imported rice (n = 36) were evaluated using inductively coupled plasma mass spectrometry (ICP-MS) for total arsenic and a hyphenated high-performance liquid chromatography ICP-MS system for arsenic species. The study also assessed the daily intake of total As from diets of healthy children (n = 15), collected over three consecutive days. A wide variation of total As levels (range: <0.05–0.42 mg/kg) in Australian and imported rice was found. The mean level of total As (0.24 ± 0.09 mg/kg, n = 10) in the Australian rice was relatively higher than imported rice from other countries (0.09 ± 0.04 mg/kg, n = 26). The mean level (0.25 ± 0.08 mg/kg, n = 7) of dimethylarsenic acid was considerably higher than that of inorganic As (III) (0.07 ± 0.03 mg/kg, n = 7) in the Australian rice. Children’s daily intakes of total As varied widely, ranging from 1.7 to 31.2 (11.5 ± 8.9 µg/day), which was comparable to other countries.     

Healthy aspect of low‐cholesterol ghee on modulation of lipid profile of rats

Low‐cholesterol ghee (LCG) feeding did not show any significant increase in total plasma cholesterol level from day 0 (56.8 ± 6.8 mg/dL) to day 90 (59.5 ± 0.8 mg/dL). Plasma HDL cholesterol (HDL) levels increased by 59.9%, whereas LDL cholesterol (LDL) showed a reduction of 74.8%. Total plasma triacylglycerol (mg/dL) did not show any significant change within or between groups. Relative contribution of lipoprotein fraction HDL was 69% vs 47% in control. Atherogenic Index was low (0.47 ± 0.05) vs 1.03 ± 0.2 in the control. Deposition of cholesterol in arteries and liver was also less (0.423 mg/g tissue) than in control (0.648 mg/g tissue). Feeding LCG improved the lipid profile of rats.     

An improved determination method for tyramine in foods using ultra-high performance liquid chromatography with benzylamine as internal standard

Tyramine has been considered a biological hazard for foods and beverages. In this study, an ultra-high pressure liquid chromatography (UPLC) with benzylamine as an internal standard in dansyl chloride pre-column derivatisation was developed to determine tyramine in various foods. Different from other tyramine determination methods usually without an internal standard in the pre-column derivatisation, benzylamine which chemical structure is similar to tyramine was selected as an internal standard. The limits of detection and quantification of this method were 0.05 and 0.25 mg L⁻¹, respectively, while the relative standard deviations of repeatability and reproducibility were 2.1% and 3.1%, respectively. The sensitivity and reliability of this method were also evaluated by determining tyramine in common liquid, pasty and solid foods. The recoveries of tyramine in these foods were between 87.3% and 96.8% by using this method. Overall, it is a fast, inexpensive, reliable and sensitive method to measure tyramine in different food products.     

Short communication: Analytical method and amount of preservative added to milk samples may alter milk urea nitrogen measurements

Milk urea N (MUN) is used by dairy nutritionists and producers to monitor dietary protein intake and is indicative of N utilization in lactating dairy cows. Two experiments were conducted to explore discrepancies in MUN results provided by 3 milk processing laboratories using different methods. An additional experiment was conducted to evaluate the effect of 2-bromo-2-nitropropane-1, 3-diol (bronopol) on MUN analysis. In experiment 1, 10 replicates of bulk tank milk samples, collected from the Pennsylvania State University's Dairy Center over 5 consecutive days, were sent to 3 milk processing laboratories in Pennsylvania. Average MUN differed between laboratory A (14.9 ± 0.40 mg/dL; analyzed on MilkoScan 4000; Foss, Hillerød, Denmark), laboratory B (6.5 ± 0.17 mg/dL; MilkoScan FT + 6000), and laboratory C (7.4 ± 0.36 mg/dL; MilkoScan 6000). In experiment 2, milk samples were spiked with urea at 0 (7.3 to 15.0 mg/dL, depending on the laboratory analyzing the samples), 17.2, 34.2, and 51.5 mg/dL of milk. Two 35-mL samples from each urea level were sent to the 3 laboratories used in experiment 1. Average analyzed MUN was greater than predicted (calculated for each laboratory based on the control; 0 mg of added urea): for laboratory A (23.2 vs. 21.0 mg/dL), laboratory B (18.0 vs. 13.3 mg/dL), and laboratory C (20.6 vs. 15.2 mg/dL). In experiment 3, replicated milk samples were preserved with 0 to 1.35 mg of bronopol/mL of milk and submitted to one milk processing laboratory that analyzed MUN using 2 different methods. Milk samples with increasing amounts of bronopol ranged in MUN concentration from 7.7 to 11.9 mg/dL and from 9.0 to 9.3 mg/dL when analyzed on MilkoScan 4000 or CL 10 (EuroChem, Moscow, Russia), respectively. In conclusion, measured MUN concentrations varied due to analytical procedure used by milk processing laboratories and were affected by the amount of bronopol used to preserve milk sample, when milk was analyzed using a mid-infrared analyzer. Thus, it is important to maintain consistency in milk sample preservation and analysis to ensure precision of MUN results.     

Effects of NaCl, lactose and availability of oxygen on tyramine production by the Enterococcus durans CCDM 53

Combined effects of concentration of lactose (5?g/L), NaCl (20?g/L) and aero/anaerobiosis on production of tyramine by Enterococcus durans CCDM 53 were subjected to a study. The influence of the above factors and temperature of cultivation (10?±?1?°C) was monitored under conditions applied in real technological processes of cheese production; the enterococci act as non-starter lactic acid bacteria. Production of tyramine by E. durans CCDM 53 was mainly influenced by both concentration of NaCl in cultivation medium and presence/absence of oxygen in the environment. The highest production of tyramine occurred during cultivation under anaerobic conditions in the presence of the highest (20?g/L) applied concentration of NaCl and lactose (5?g/L). In the media with equal concentrations of NaCl and lactose, the concentrations of tyramine grew higher under anaerobic conditions than in aerobic environment. Regarding cultivation media with various levels of NaCl and lactose, higher production of tyramine was always found in the anaerobic environment.     

Amperometric Determination of Quercetin in Some Foods by Magnetic Core/Shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@ZnO Nanoparticles Modified Glassy Carbon Electrode

In this paper, Fe₃O₄@ZnO core/shell magnetic nanoparticles (MNPs) have been synthesized by a simple method, to modify carbon paste/glassy carbon electrode and improve its efficiency for determination of quercetin. The synthesized MNPs were characterized by X-ray powder diffraction (XRD), transmission electronic microscope (TEM), and scanning electronic microscope (SEM). SEM and TEM results show that the prepared Fe₃O₄@ZnO MNPs are made of the spherical shape particles with an average size of about 15 nm. The electrochemical behavior of quercetin at the surface of modified electrode was investigated. Under the optimal conditions, a linearity range of quercetin was 7.9?×?10^?7 to 6.1?×?10^?5 mol/L (0.24–18.44 mg/L) with detection limit (S/N?=?3) and sensitivity of 0.16 μmol/L (0.048 mg/L) and 0.04 μA/μM, respectively. The validated method was applied successfully for determination of quercetin in some foods and human breast milk.     

Screening selected strains of probiotic lactic acid bacteria for their ability to produce biogenic amines (histamine and tyramine)

The aim of this study was to investigate the production of biogenic amines (BA), histamine and tyramine by some probiotic lactic acid bacteria (LAB). Fifteen strains representing six LAB species were screened qualitatively by growing them in a decarboxylase medium. Quantitative analysis was carried out by HPLC analysis with direct derivatization of acid extracts. Lactobacillus casei (TISTR 389) and Lactobacillus delbrueckii subsp. bulgaricus (TISTR 895) were found to produce BA. The highest levels of histamine (1820.9 ± 3.5 mg L^?1) and tyramine (5486.99 ± 47.6 mg L^?1) formation were observed for the TISTR 389 strain, while TISTR 895 produced only histamine (459.1 ± 0.63 mg L^?1) in the decarboxylase broth. Biogenic amine potential was not observed for the Lactobacillus acidophilus, Lactobacillus lactis subsp. lactis, Lactococcus lactis subsp. lactis, and Lactobacillus plantarum strains studied. This study confirmed that BA formation is strain dependent and not related to the species. Therefore, careful screening for amino acid decarboxylase activity is recommended before selecting LAB as appropriate starter or probiotic strains in food and dairy industry.     

Effect of butyrate on passive transfer of immunity in dairy calves

The objectives of this study were to determine the effects of supplemental butyrate on (1) Ig production in dams and (2) Ig absorption in their calves. Twenty dry dams fed a close-up total mixed ration were assigned to either a control treatment (CTRL-D) or a butyrate treatment where the close-up total mixed ration was supplemented with butyrate at 1% of dry matter intake (wt/wt; BUT-D). At calving, calves were assigned to 1 of 2 treatments: a control group fed colostrum replacer only (CTRL-C) and a butyrate group fed colostrum replacer with supplemental butyrate at 2.5% (wt/vol; BUT-C). Serum IgG, glucose, and β-hydroxybutyrate were measured weekly in both dams and calves. Additionally, calves were weighed weekly to determine average daily gain. In dams, serum IgG concentration was not different between CTRL-D and BUT-D (1,785 ± 117 vs. 1,736 ± 137 mg/dL, respectively), nor was there a change in Ig levels in the colostrum between control and butyrate groups. Serum total protein did not differ between CTRL-D and BUT-D dams. Dam dry matter intake did not differ between CTRL-D and BUT-D but did decrease 1 wk before parturition. Compared with CTRL-C calves, BUT-C calves had significantly decreased serum IgG concentration at 24 h (2,110 ± 124 vs. 1,400 ± 115 mg/dL), wk 1 (1,397 ± 121 vs. 866 ± 115 mg/dL), and wk 2 (1,310 ± 121 vs. 797 ± 115 mg/dL). Additionally, apparent efficiency of absorption was lower for the BUT-C group compared with the CTRL-C group (35.3 ± 2.1 vs. 25.9 ± 2.0). Differences in serum Ig concentrations between the CTRL-C and BUT-C groups did not affect average daily gain (0.59 ± 0.05 vs. 0.48 ± 0.05 kg/d, respectively), serum glucose concentrations, or serum β-hydroxybutyrate concentrations. These data demonstrate that butyrate inclusion in colostrum negatively affects IgG absorption in newborn calves, whereas calf body weight gains were unaffected.     

A Rapid Size-Exclusion Solid-Phase Extraction Step for Enhanced Sensitivity in Multi-Allergen Determination in Dark Chocolate and Biscuits by Liquid Chromatography–Tandem Mass Spectrometry

Enhanced sensitivity for the simultaneous determination of five nut allergens in biscuit and in dark chocolate complex matrices was obtained by introduction of a rapid size-exclusion solid-phase extraction-based step before liquid chromatography–electrospray ionization-tandem mass spectrometry (LC-ESI-MS²) analysis. A very fast and efficient separation (<12 min) of marker peptides with selected reaction monitoring detection was obtained. Limits of detection in the 0.1–1.3 mg nut/kg and 5–15 mg nut/kg ranges for biscuit and dark chocolate samples as well as high recoveries (84(±6)–106(±4)% for biscuits and 98(±5)–108(±6)% for dark chocolate) proved the excellent capabilities of the exploited sample treatment method combined with the LC-MS² analysis. Good precision in terms of intra- and inter-day repeatability was calculated, being always lower than 19 % (n?=?75). Linearity was demonstrated up to four and three orders of magnitude for biscuit and dark chocolate, respectively. Finally, the validated method was successfully applied to the investigation of hidden nut trace allergens in commercially available biscuits and chocolates of different brands aiming to ascertain possible discrepancies between allergen content and food allergen labelling.     

Lipid-modifying activity of curcuminoids: A systematic review and meta-analysis of randomized controlled trials

Objective: The aim of this systematic review and meta-analysis was to determine and clarify the impact of curcuminoids on serum lipid levels. Methods: Randomized controlled trials (RCTs) investigating the effects of curcuminoids on plasma lipids were searched in PubMed-Medline, Scopus, Web of Science databases (from inception to April 3^rd, 2017). A random-effects model and generic inverse variance method were used for quantitative data synthesis. Sensitivity analysis was conducted using the leave-one-out method. A weighted random-effects meta-regression was performed to evaluate the impact of potential confounders on lipid concentrations. Results: A meta-analysis of 20 RCTs with 1427 participants suggested a significant decrease in plasma concentrations of triglycerides (WMD: ?21.36 mg/dL, 95% CI: ?32.18, ?10.53, p < 0.001), and an elevation in plasma HDL-C levels (WMD: 1.42 mg/dL, 95% CI: 0.03, 2.81, p = 0.046), while plasma levels of LDL-C (WMD: ?5.82 mg/dL, 95% CI: ?15.80, 4.16, p = 0.253) and total cholesterol (WMD: ?9.57 mg/dL, 95% CI: ?20.89, 1.75, p = 0.098) were not altered. The effects of curcuminoids on lipids were not found to be dependent on the duration of supplementation. Conclusion: This meta-analysis has shown that curcuminoid therapy significantly reduces plasma triglycerides and increases HDL-C levels.     

酪胺分子印迹聚合物的制备及识别特性研究

利用分子印迹技术制备用于酪胺快速检测的分子印迹聚合物.以酪胺为模版分子,甲基丙烯酸(MAA)为功能单体,偶氮二异丁腈(AIBN)为引发剂,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,在乙腈中沉淀聚合制备了酪胺分子印迹聚合物微球.通过紫外光谱法对酪胺与MAA的相互作用进行了分析,结果表明在研究的浓度范围内主客体主要存在形式为1个酪胺分子与1个MAA分子发生作用.对聚合物吸附动力学进行了初步研究,通过静态平衡吸附实验研究了聚合物微球对模板分子的结合能力,印迹聚合物微球在8h后逐渐达到吸附平衡.利用Langmuir数学模型对吸附特性进行了分析,Scatchard图显示印迹聚合物的最大吸附量Bmax=325.0μmol/g和解吸常数KD=0.577mmol/L.同时印迹聚合物的吸附选择性较好.此方法合成的印迹聚合物微球对酪胺有较好的结合性能,可应用于酪胺的分离检测.     

Effects of quercetin supplementation on lipid profile: A systematic review and meta-analysis of randomized controlled trials

Background: In spite of promising experimental findings, randomized controlled trials (RCTs) have yielded mixed results on the impact of quercetin supplementation on plasma lipid levels.

Aim: The present study aimed to quantify the effects of quercetin on plasma lipids using a meta-analysis of RCTs.

Methods: A systematic literature search of Medline was conducted for RCTs that investigated the efficacy of quercetin supplementation on plasma lipids comprising total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated for net changes in lipid concentrations using a random-effects model. Meta-regression analysis was conducted to assess the effect of quercetin dose and duration of supplementation as moderators on the calculated effect measures.

Results: Five RCTs totaling 442 subjects (221 in the quercetin and 221 in the control group) fulfilled the eligibility criteria and selected for analyses. Combined estimate of effect size for the impact of quercetin on plasma LDL-C (WMD: 1.43 mg/dL, 95% CI: ?0.92–3.78, p = 0.23), HDL-C (WMD: 0.26 mg/dL, 95% CI: ?0.74–1.25, p = 0.61) and triglycerides (WMD: ?9.42 mg/dL, 95% CI: ?27.80–8.96, p = 0.32) was not statistically significant. However, a borderline significant but clinically non-relevant increase in total cholesterol was observed (WMD: 3.13 mg/dL, 95% CI: ?0.01–6.27, p = 0.05). When the analysis was confined to the subgroups of studies with quercetin doses ≥500 mg/day and follow-up of ≥ 4 weeks, a significant increase in total cholesterol (WMD: 3.57 mg/dL, 95% CI: 0.21–6.92, p = 0.04) and a decline in triglycerides (WMD: ?24.54 mg/dL, 95% CI: ?33.09 to ?15.99, p < 0.00001) was observed, but LDL-C and HDL-C concentrations remained unchanged (p > 0.05). Changes in plasma triglycerides, but not other indices of lipid profile, were significantly associated with quercetin dose (slope: ?0.057; 95% CI: ?0.103 to ?0.010; p = 0.02) and duration of supplementation (slope: ?5.314; 95% CI: ?9.482 to ?1.147; p = 0.01).

Conclusion: Available evidence from RCTs does not suggest any clinically relevant effect of quercetin supplementation on plasma lipids, apart from a significant reduction of triglycerides at doses above 50 mg/day.     

Caffeine Content of Retail Market Coffee in Portugal

How much caffeine does one ingest when drinking a simple cup of coffee in Portugal? The study presented herein tried to answer this question through the assessment of caffeine content of commercially available espresso coffee samples, both caffeinated and decaffeinated, using a high-performance liquid chromatography assay. Caffeine was rapidly separated from the sample matrix using a RP-18 column (250?×?4 mm i.d., 5 μm). The flow rate was 1.0 mL/min and the mobile phase consisted of water acidified with 5% of orthophosphoric acid/methanol (35:65, v/v). Caffeine was detected directly at 273 nm. The assay was validated for linearity, lower limit of quantification and limit of detection, precision, accuracy, and stability. Seventeen different brands of caffeinated coffee and six of decaffeinated coffee were analyzed. As for capsule coffee, eight caffeinated and two decaffeinated blends were analyzed. The caffeine content of caffeinated coffee varied from 53.8?±?5.9 to 141.3?±?5.3 mg/cup, whereas for caffeinated capsule coffee caffeine concentrations ranged from 45.0?±?5.3 to 60.8?±?6.2 mg/cup. As for decaffeinated coffee, caffeine concentrations ranged from 0.96?±?0.04 to 3.9?±?0.1 mg/cup and for decaffeinated capsule coffee from 0.93?±?0.04 to 1.2?±?0.1 mg/cup.     

The effect of high-polyphenol extra virgin olive oil on cardiovascular risk factors: A systematic review and meta-analysis

Abstract

The polyphenol fraction of extra-virgin olive oil may be partly responsible for its cardioprotective effects. The aim of this systematic review and meta-analysis was to evaluate the effect of high versus low polyphenol olive oil on cardiovascular disease (CVD) risk factors in clinical trials. In accordance with PRISMA guidelines, CINAHL, PubMed, Embase and Cochrane databases were systematically searched for relevant studies. Randomized controlled trials that investigated markers of CVD risk (e.g. outcomes related to cholesterol, inflammation, oxidative stress) were included. Risk of bias was assessed using the Jadad scale. A meta-analysis was conducted using clinical trial data with available CVD risk outcomes. Twenty-six studies were included. Compared to low polyphenol olive oil, high polyphenol olive oil significantly improved measures of malondialdehyde (MD: ?0.07µmol/L [95%CI: ?0.12, ?0.02µmol/L]; I²: 88%; p?=?0.004), oxidized LDL (SMD: ?0.44 [95%CI: ?0.78, ?0.10µmol/L]; I²: 41%; P?=?0.01), total cholesterol (MD 4.5 mg/dL [95%CI: ?6.54, ?2.39 mg/dL]; p<0.0001) and HDL cholesterol (MD 2.37 mg/dL [95%CI: 0.41, 5.04 mg/dL]; p?=?0.02). Subgroup analyses and individual studies reported additional improvements in inflammatory markers and blood pressure. Most studies were rated as having low-to-moderate risk of bias. High polyphenol oils confer some CVD-risk reduction benefits; however, further studies with longer duration and in non-Mediterranean populations are required.     

Hypolipidaemic effects of synbiotic yoghurt in rabbits

The hypolipidaemic effects of synbiotic yoghurt prepared using Lactobacillus acidophilus, fructooligosaccharide (FOS) and isomaltooligosaccharide (IMOS) were assessed through biological study. Hyperlipidaemia‐induced rabbits were fed on a diet containing different levels of synbiotic yoghurt, and the blood of the animals was analysed for lipid profile on a weekly basis. There were significant reductions in total cholesterol (124.00 ± 7.10 mg/dL), triglycerides (155.00 ± 8.88 mg/dL), low‐density lipoprotein levels (13.27 ± 0.76 mg/dL) and very low‐density lipoprotein levels (57.04 ± 3.27 mg/dL), whereas high‐density lipoprotein levels (53.70 ± 0.35 mg/dL) were increased. On the basis of these results, it was concluded that the synbiotic yoghurt possessed a significant hypolipidaemic potential.     

In Vitro Assay of Iron in Fortified Rice Analogues

A simple in vitro assay for the determination of soluble iron in fortified rice analogue/natural rice blends is described. The soluble iron, measured as an indicator of iron bioavailability, is quantified by FerroZine? colorimetry of the supernatant obtained after simulated gastric (pepsin) and intestinal (pancreatin) digestions. Method suitability was defined by assessments of linearity (R ² average=0.9999±0.0001, and low standard residual average=+0.6±0.9 %; n=17), precision (day-to-day RSD values [n=3 days] ranged from 5.3 % to 75 % for concentrations from 0.017 to 0.585 mg per 100 g of fortified rice analogue/natural rice blend), accuracy (spike recovery=97.5±0.4 %, n=4, spiking level=0.2 to 0.8 mg/l; and linear response of the digest plot [R ²=1.0000] vs. the standard solution plot [R ²=1.0000]), and selectivity (absence of interference from Ca, Mg, Mn, and Zn; reagent blank correction for minimal bias by Cu). The assay provides for a reliable quantification of the soluble iron in fortified rice analogue/natural rice blends. The assay is regarded not as a substitute for in vivo determination of iron absorption, but instead as a tool for identifying formulation, extrusion, and storage issues that are worthy of formal in vivo study. In this connection, application of the assay to fortified rice analogue/natural rice blends and to experimental rice flour preparations has identified potential agents of iron absorption enhancement (e.g., NaFeEDTA at only 2 % of total iron), and of iron absorption inhibition (zinc).     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Multi-Walled Carbon Nanotubes-Chitosan for the Determination of Beef Freshness

In this study, the glucose biosensor was developed for the determination of the beef meat freshness based on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and chitosan (Chi). Glucose oxidase (GOx) was immobilized onto the MWCNTs-Chi/GCE surface by cross-linking the enzyme through glutaraldehyde with bovine serum albumin (BSA). Glutaraldehyde solution (0.25%, w/w) was also added to prevent enzyme release. The properties of the developed biosensor were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) using [Fe (CN)₆]^3?/4?as the supporting electrolyte. The influence of various parameters was investigated, and 0.1 mol L^?1 PBS with pH = 6.4 was chosen as the optimal supporting electrolyte for this experiment. The linear relationship between the current and the concentration of glucose was obtained from 0.2 to 1.2 mmol L^?1, with a detection limit of 0.05 mM at a signal-to-noise ratio of 3 and displayed good linearity (R ² = 0.9902), while the biosensor showed a rapid response to glucose. In addition, the developed glucose biosensor was applied in the determination of glucose in beef as an indicator of beef freshness compared to the total volatile basic nitrogen (TVB-N) method. The glucose level was decreased with increasing beef storage time.