基于硅溶胶-凝胶化学修饰电极直接测定酱油中的曲酸

研究了曲酸在硅溶胶-凝胶化学修饰电极上的电化学行为,建立了测定酱油中曲酸的简易方法。在实验条件下,曲酸测定的线性范围为2×10-5～7×10-4mol/L,相关系数为0.9993,检测下限为1×10-5mol/L,连续测定8次1×10-4mol/L曲酸的相对标准偏差为0.9%。溶胶-凝胶化学修饰电极集分离与测定与一体,方法简单方便,可应用于酱油中曲酸含量的直接测定,避免了样品的前处理过程。     

Electrochemical determination of Sudan I using montmorillonite calcium modified carbon paste electrode

In the current work, a sensitive, rapid and convenient electrochemical method was developed for the determination of Sudan I utilizing the excellent properties of montmorillonite calcium (MMT-Ca). Compared with the unmodified carbon paste electrode (CPE), MMT-Ca modified CPE not only significantly enhances the oxidation peak current of Sudan I but also lowers the oxidation overpotential, suggesting that the MMT-Ca modified CPE can remarkably improve the determining sensitivity of Sudan I. The experimental conditions such as determining medium, the content of MMT-Ca and accumulation time were optimized for the determination of Sudan I. The oxidation peak current is proportional to the concentration of Sudan I over the range from 0.05 mg L⁻¹ (2.01 × 10⁻⁷ mol L⁻¹) to 1.0 mg L⁻¹ (4.03 × 10⁻⁶ mol L⁻¹), and the limit of detection is 0.02 mg L⁻¹ (8.06 × 10⁻⁸ mol L⁻¹) for 2-min accumulation. Finally this newly-proposed sensing method was successfully employed to detect Sudan I in practical samples and good recovery was achieved.     

邻苯二甲酸二壬酯修饰电极对抗坏血酸的氧化作用及测定

用邻苯二甲酸二壬酯修饰玻碳电极。研究了修饰电极在0、1mol/LKCl底液中维生素C的氧化作用。抗坏血酸在0.08g～0.72g/L具有良好的线性关系,线性方程为C=0.1689ipc-0.0294（g/L）r=0.9995。此电极对维生素C的选择性大大提高,可以用于测定饮料中维生素C。      

利用3-噻吩丙二酸修饰玻碳电极检测粮油中残留苯嗪草酮

利用电化学聚合法制备3–噻吩丙二酸修饰玻碳电极,应用循环伏安法研究苯嗪草酮在3–TPA修饰玻碳电极上电化学行为,考察pH值、富集时间、扫描速率及扫描范围等条件对该修饰电极检测苯嗪草酮影响。在最佳条件下,利用差分脉冲伏安法得出苯嗪草酮浓度在9.77×10–7~6.25×10–5mol/L范围内呈良好线性关系,相关系数r=0.9998,检测限为9.77×10–7mol/L。面粉、米粉和花生油样品加标回收率分别为99.2%、100.1%、93.9%,相对标准偏差为0.17%、0.25%、0.49%。     

Determination of sodium in processed foodstuffs using a bis(12-crown-4) derivative-based poly(vinyl chloride) membrane electrode

A poly(vinyl chloride) matrix membrane sodium selective electrode based on bis[(12-crown-4)ylmethyl] 2-dodecyl-2-methylmalonate ((12-crown-4)yl = 1,4,7,10-tetraoxacyclododecyl) was utilised for the determination of sodium in various foodstuffs such as soup stocks, instant noodle stocks and milk powders. Good agreement was obtained between the proposed electrode and flame photometric methods. Also, the electrode exhibits minimum interference from potassium, calcium, magnesium, iron(III), copper(II) and glucose, and from the synthetic colours tested.     

Indirect determination of ascorbic acid (vitamin C) by spectrophotometric method

A novel spectrophotometric method is described. The procedure involves the use of Cu (II) as vitamin C oxidant. After completion of oxidation reaction, excess of Cu (II) is determined by complexation with alizarin red s (ARS). Thiocyanate ion is used as stabilising agent for Cu (I) which is the product of oxidation reaction. This method is used for determination of vitamin C in fruits and pharmaceutical products. Linearity was found to be perfect in the range 3.5 × 10^?6–4.8 × 10^?5 m (0.6–8.2 ppm). The detection limit and relative standard deviation of method are 2.0 × 10^?6 m (0.35 ppm) and 1.03%, respectively. The proposed method is simple, safe, inexpensive and rapid.     

Quantitative determination of fatty acid compositions in micro-encapsulated fish-oil supplements using Fourier transform infrared (FTIR) spectroscopy

The research describes a rapid method for the determination of fatty acid (FA) contents in a micro-encapsulated fish-oil (μEFO) supplement by using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic technique and partial least square regression (PLSR) analysis. Using the ATR-FTIR technique, the μEFO powder samples can be directly analysed without any pre-treatment required, and our developed PLSR strategic approach based on the acquired spectral data led to production of a good linear calibration with R(2)=0.99. In addition, the subsequent predictions acquired from an independent validation set for the target FA compositions (i.e., total oil, total omega-3 fatty acids, EPA and DHA) were highly accurate when compared to the actual values obtained from standard GC-based technique, with plots between predicted versus actual values resulting in excellent linear fitting (R(2)≥0.96) in all cases. The study therefore demonstrated not only the substantial advantage of the ATR-FTIR technique in terms of rapidness and cost effectiveness, but also its potential application as a rapid, potentially automated, online monitoring technique for the routine analysis of FA composition in industrial processes when used together with the multivariate data analysis modelling.     

Study of the effect of using different levels of tahinah (sesame butter) on the protein digestibility‐corrected amino acid score (PDCAAS) of chickpea dip

This study was conducted to investigate the effect of using different proportions of tahinah (0–25%) on the protein digestibility‐corrected amino acid score (PDCAAS) of chickpea dip and to evaluate this parameter when chickpea dip is consumed with wheat bread. Protein quality was evaluated using the methods of amino acid score and true protein digestibility in weanling Sprague–Dawley rats. The levels of tahinah that provided the best true protein digestibility and protein digestibility‐corrected amino acid score were 20 and 25%. Values of true protein digestibility were significantly higher (P ≤ 0.05) than for the other types of chickpea dip (0.87 and 0.88 respectively). The consumption of wheat bread with chickpea dip led to a marked improvement in the true protein digestibility of the protein mixture (0.90); however, the protein digestibility‐corrected amino acid score did not change in the same manner owing to the relatively low amino acid score. It can be concluded that the addition of tahinah to chickpea led to an increase in the protein digestibility‐corrected amino acid score of chickpea dip (based on laboratory rat requirements for essential amino acids) and that the consumption of chickpea dip with bread led to an improvement in the protein digestibility of chickpea dip but not in the protein digestibility‐corrected amino acid score. © 2002 Society of Chemical Industry     

高效液相色谱法快速测定食品中胭脂红酸(胭脂虫红)

目的 建立高效液相色谱法快速测定含蛋白和脂肪的食品中胭脂红酸（胭脂虫红）的分析方法。方法 采用2.0 mol/L HCl溶液,90 ℃水浴下酸解30 min,利用混合型强阴离子固相萃取小柱净化, 2%磷酸甲醇洗脱液注入高效液相色谱仪,由ZORBAX SB-C18 (150 mm×4.6 mm, 5 μm)快速分离后进入紫外检测器（494 nm和276 nm）进行测定。结果 含乳饮料、酸奶、调制乳粉、调制炼乳、熟肉制品、火锅底料食品中胭脂红酸（胭脂虫红）在0.1~5.0 μg/mL的范围内, 线性关系良好(r2≥0.999), 平均回收率在87.4%~95.1%之间, 相对标准偏差(relative standard deviations, RSDs)低于10%, 检出限(limits of detection, LODs)为0.3 mg/kg, 定量限(limits of quantitative, LOQs)为1.0 mg/kg。结论 此方法前处理准确性好、灵敏度高, 可实现含蛋白和脂肪食品基质中胭脂红酸（胭脂虫红）的快速测定。     

An amperometric sensor based on Prussian blue and poly(o-phenylenediamine) modified glassy carbon electrode for the determination of hydrogen peroxide in beverages

An amperometric sensor based on Prussian blue (PB) and poly(o-phenylenediamine) (POPD) modified glassy carbon electrode (GCE) was developed for the determination of hydrogen peroxide (H₂O₂). The PB film was electrodeposited onto the GCE surface by amperometry, while the POPD film was formed on the top of PB layer by cyclic voltammetry. It was found that the POPD film remarkably improved the stability and selectivity of PB-based sensor. Under the optimised conditions, the developed electrode demonstrated a wide linear range from 0.1 μM to 0.12 mM with the detection limit of 0.05 μM. Furthermore, the developed electrode was applied for the amperometric determination of H₂O₂ in 10 different commercial beverages. The pretreatment of the beverage samples was the adjustment of pH value. Experimental results showed that the proposed electrode could be a useful tool to detect H₂O₂ in aseptically packaged beverages.     

Sensor-containing microspheres of chitosan crosslinked with 8-hydroxyquinoline-5-sulphonic acid for determination of Cu(II) in instant coffee

A novel carbon paste electrode containing chitosan microspheres for the determination of Cu(II) in instant coffee by anodic stripping voltammetry was developed. Chitosan was crosslinked with the chelating agent 8-hydroxyquinoline-5-sulphonic acid and glutaraldehyde. The microspheres of the crosslinked chitosan biopolymer were obtained by the spray drying technique and employed in the construction of the sensor. In acetate buffer solution (0.1 mol L⁻¹, pH 6.0), the calibration curve obtained was linear for concentrations of 5.0 × 10⁻⁷ to 1.4 × 10⁻⁵ mol L⁻¹ (r = 0.9990); the detection limit was 5.5 × 10⁻⁸ mol L⁻¹. The relative standard deviation (n = 8) was lower than 3.0% for solutions containing 6.0 × 10⁻⁶, 5.0 × 10⁻⁵ and 1.5 × 10⁻⁴ mol L⁻¹ of Cu(II). The method was successfully employed for determination of Cu(II) in instant coffee and the results obtained showed good agreement when compared with those using electrothermal atomic absorption spectrometry.     

Study of volatile organic acids in freeze-dried Cheonggukjang formed during fermentation using SPME and stable-isotope dilution assay (SIDA)

Volatile organic acids in freeze-dried Cheonggukjang were quantified using a stable-isotope dilution assay (SIDA) according to the fermentation period. Five organic acids, acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, and 3-methylbutanoic acid, were identified using solid-phase microextraction (SPME) in conjunction with gas chromatography–mass spectrometry (GC–MS). The contents of volatile organic acids in Cheonggukjang were highly dependent on the fermentation period and they increased during fermentation. Moreover, the branched-chained organic acids (namely 2-methylpropanoic acid and 3-methylbutanoic acid) were formed earlier and were present at much higher contents than the corresponding straight-chained organic acids during Cheonggukjang fermentation.     

Characterisation of an acidic peroxidase from papaya (Carica papaya L. cv Tainung No. 2) latex and its application in the determination of micromolar hydrogen peroxide in milk

An acidic peroxidase isoform, POD-A, with a molecular mass of 69.4 kDa and an isoelectric point of 3.5 was purified from papaya latex. Using o-phenylenediamine (OPD) as a hydrogen donor (citrate–phosphate as pH buffer), the optimum pH for the function of POD-A was 4.6, and the optimum temperature was 50 °C. The peroxidase activity of POD-A toward hydrogen donors was both pH- and concentration-dependent. Under optimal conditions, POD-A catalysed the oxidation of OPD at higher rates than pyrogallol, catechol, quercetin and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The chemical modification reagents N-bromosuccinimide and sodium azide significantly inhibited POD-A activity. The results of kinetic studies indicated that POD-A followed a ping-pong mechanism and had a K_m value of 2.8 mM for OPD. Using CPC silica-immobilised POD-A for the determination of micromolar H₂O₂ in milk, the lower limit of determination was 0.1 μM, and the recoveries of added H₂O₂ were 96–109%.