Simple determination of main organic acids in grape juice and wine by using capillary zone electrophoresis with direct UV detection

An accurate, simple and rapid capillary zone electrophoresis (CZE) method with direct UV detection has been set up for the determination of main organic acids in grape juice and wine. The determination of tartaric, malic, and citric acids in grape juices and tartaric, malic, succinic, acetic, lactic and citric acids in wines can be achieved in less than 3 min with only a simple dilution and filtration treatment of the sample. Validation parameters of the method as detection and quantification limits, linearity, precision (intraday and interday analysis) and recovery were also studied in grape juice, white wine, rose wine and red wine, separately. The proposed method decreases the analysis times of the previous reported CZE methods and allows the rapid control of the grape maturity, the winemaking processes and the detection of wine alterations and/or illnesses.     

A robust capillary electrophoresis method for the determination of organic acids in wines

A robust capillary electrophoresis (CE) method for the determination of the six main organic acids in wines is described. The CE method is based on the use of 2,6- pyridinedicarboxylic acid (PDC) as background electrolyte (BGE) for the indirect UV detection of tartaric, malic, citric, succinic, acetic and lactic acids. Ethylenediaminetetracarboxylic acid (EDTA) was added to the BGE to eliminate interferences from trace metals on the determination of citric acid. Problems related to linearity reported in the literature using the same BGE were shown to be the result of the sample pH being lower than that of the buffer. Although this could be overcome simply by adjusting the pH of the sample, electrokinetic injection was found to be a better alternative, improving at the same time the sensitivity of the determination. Linearity over the range 100–5,000 mg/l (ppm) for all acids was achieved, requiring only 80× dilution of standards and samples prior to injection. Within day repeatabilitys (n=7) of migration times (RSD%<0.15) and peak areas (RSD%<5) as determined for a wine sample were found to be excellent. The method was applied to 20 South African wine samples, and the results are compared to data obtained by ion-exclusion liquid chromatography. Succinic acid was consistently overestimated using the latter technique, while for the other acids good agreement between the methods was noted.     

The simultaneous separation and determination of five organic acids in food by capillary electrophoresis

The simultaneous separation of quinic acid, anisic acid, salicylic acid, benzoic acid and sorbic acid was performed by capillary electrophoresis with 20 mmol L⁻¹ NaOH–20 mmol L⁻¹ H₃BO₃ (pH 8.8) as the background electrolyte. The choices of the background electrolytes and the applied voltage were optimized. The effects of tetrabutylammonium bromide and sodium dodecylsulfate on the separation were investigated in detail. Under the optimum condition, the linearity, reproducibility and detection limit of five organic acids were shown, respectively. As an application of the method proposed, 10 samples of soy sauce and vinegar were analysed to determine benzoic acid and sorbic acid. The procedure described provides the advantages of good selectivity, rapid speed and simplicity for the separation and determination of organic acids.     

A rapid quantitative determination of phenolic acids in Brassica oleracea by capillary zone electrophoresis

A simple and rapid capillary zone electrophoresis method to quantitatively determine the phenolic acid contents in brassica vegetables is described. Phenolic compounds were extracted from broccoli, broccolini, Brussels sprouts, cabbage and cauliflower and the main hydroxycinnamic acids (sinapic, ferulic, p-coumaric and caffeic acids) were isolated by solid phase extraction with C18 cartridges. Using an optimised method, the four analytes were separated in less than 7 min in a 50 μm × 60 cm capillary with a 15 mM borate buffer (pH = 9.13) and a separation voltage of 30 kV at 30 °C. A linear relationship was observed for the method (r = 0.9997–0.9999) with detection limits ranging from 1.1 to 2.3 mg/kg of vegetables for the analytes. This method demonstrated good reproducibility with coefficients of variation of less than 5% for peak area and less than 1% for migration time (n = 7). The method was successfully applied to quantitatively determine the phenolic acid contents in a range of brassica vegetables and the results were in good agreement when compared to those from high performance liquid chromatography analysis.     

A review of the analytical methods to determine organic acids in grape juices and wines

The determination of low molecular weight organic acids in grape juices and wines is important because of their influence in organoleptic properties (flavour, colour and aroma) and in the stability and microbiologic control of these beverages. The analysis of these acids allows to check the process of maturation of grapes and to control the evolution of the acidity of wines during the several stages of their elaboration process (alcoholic fermentation, malolactic fermentation, aging process, etc).

In this work, a comprehensive review of the analytical methods developed for the determination of short-chain organic acids in grape juices and wines has been shown. This review included non-enzymatic spectrophotometric, enzymatic, chromatographic and electrophoretic methods. Details of the chromatographic and electrophoretic conditions of these methods have been collected in tables.     

饮料中六种金属阳离子的毛细管电泳分析

应用毛细管区带电泳(CZE)法测定了饮料中的6种金属阳离子。采用8mmol/L咪唑作为背景电解质,8mmol/La-羟基乙酸作为选择性改性剂,在pH4.0,分离电压为25kV,柱温为22℃的电泳条件下,采用间接紫外检测(214nm),在6min内分离测定了饮料中的K 、Na 、Ca2 、Mg2 、Sr2 、Zn2 等6种金属阳离子。方法快速、简便、灵敏度高、重现性好、测定成本低。     

Simultaneous quantification of the main organic acids and carbohydrates involved in tomato flavour using capillary zone electrophoresis

A capillary zone electrophoresis (CZE) procedure for the simultaneous determination of the major organic acids (oxalate, malate and citrate) and carbohydrates (fructose, glucose and sucrose) in Lycopersicon fruits is reported. Comparison of this method with routine HPLC methods indicates that the CZE method offers several attractive features (speed, resolution, sensitivity and cost) which significantly improve the determination of these compounds. Detection limits were better than 1.6 µg ml^?1 for organic acids and from 13 to 24 µg ml^?1 for carbohydrates; repeatabilities were better than 2.1% for migration times and between 1.4 and 7.3% for peak areas. The proposed protocol is very useful to characterise large series of tomato samples not only in breeding programmes but also in systematic and routine analysis in the tomato industry. © 2002 Society of Chemical Industry     

Determination of biogenic amines in beers and brewing-process samples by capillary electrophoresis coupled to laser-induced fluorescence detection

We have developed a sensitive capillary electrophoretic method for the simultaneous determination of 10 biogenic amine which usually appears in beer samples, using laser induced-fluorescence. Sample amines were first derivatized and filtered and then separated with an uncoated capillary tubing in the presence of 50 mM sodium borate and 20% acetone at pH 9.3 at 30 kV. It was possible to analyze biogenic amines in brewing-process samples and in beer samples in less than 30 min, obtaining detection limits between 0.3 μg l⁻¹ for ethylamine and 11.9 μg l⁻¹ for 1,6-hexanodiamine.     

Fast method to determine furosine in breakfast cereals by capillary zone electrophoresis

Furosine is a well-know marker of the extent of the thermal treatment applied to foodstuffs. A fast, reproducible and accurate capillary zone electrophoresis (CZE) method to analyse furosine focused on complex matrices, such as cocoa-added breakfast cereals, is presented. A representative group of 17 commercial cocoa-added breakfast cereals were determined by the reference method (HPLC) and by CZE. In addition, eight ready-to-eat breakfast cereals were tested to point out the application of the procedure to a simpler matrix. Data from both methodologies are compared by F-test and unpaired Student's t-test, showing no significant differences among them and an adequate correlation between methods was found (r ²=0.9852; p=0.000). The CZE method provides a valuable analytical tool for determination of furosine in cocoa-added breakfast cereals and is suitable for routine analysis where presence of highly retained material could limit the resolution and shelf-life of the analytical columns applied for HPLC. The analysis is carried out in 3 min. The stability of the migration time and the good correlation between HPLC–CZE results support the effectiveness of the method.     

Monoalkyl carbonates in carbonated alcoholic beverages

The presence of monoethyl carbonate (MEC) in beer and sparkling wine is demonstrated for the first time, as well as the formation of this species in drinks prepared with a distilled beverage and a carbonated soft drink. A capillary electrophoresis (CE) equipment with two capacitively coupled contactless conductivity detector (C⁴D) was used to identify and quantify this species. The concentrations of MEC in samples of lager beer and rum and cola drink were, respectively, 1.2 and 4.1 mmol/l, which agree with the levels of ethanol and CO₂ available in these products. Previous results about the kinetics of the reaction suggest that only a small amount of MEC should be formed after the ingredients of a drink are mixed. However, in all three cases (whisky and club soda; rum with cola; gin and tonic water), MEC was quickly formed, which was attributed to the low pH of the drinks.     

Application of capillary electrophoresis to determine metal cations,anions, organic acids,and carbohydrates in some Pinot Noir red wines

Capillary electrophoresis was used for determination of inorganic alkali and alkali earth metal cations, inorganic anions, anions of organic acids, and carbohydrates in six Pinot Noir grape red wines. Spectrum analysis was applied to evaluate the possible chemical differences between the wines from different geographic origin. In addition, sensory evaluation was used to reveal differences between wines from the end user point of view. Both chemical analyses and the sensory evaluation revealed clear differences among the wine samples. The total concentrations of inorganic ions, carboxylate anions, and carbohydrates varied 1.9–3.1 g L⁻¹, 4.3–5.5 g L⁻¹, and 1.5–7.5 g L⁻¹, respectively. Although the grape was same in all samples, the results show considerable variations in chemical composition, the red wine from Tasmanian being the most different among samples.     

Protein haze formation in wines revisited. The stabilising effect of organic acids

The effect on the wine protein haze potential of five organic acids commonly encountered in wines (l(+)-tartaric, l(−)-malic, citric, succinic and gluconic acids) was assessed. All five acids, tested at 20 mM, reduced dramatically the haze potential of proteins, either in wine or dissolved in water, throughout the range of pH values typical of wines (i.e., from 2.8 through 3.8). Subtle differences among the acid effects did not correlate with the number of their carboxyl groups, but were attributed to electrostatic interactions that depend upon the acid pK_a values, the protein pI values and the medium pH. These results invalidate or question the validity of all experiments on wine proteins involving wine model solutions containing organic acids. Overall, the results obtained in the present work clearly indicate that organic acids with a common occurrence in wines exhibit a stabilising effect upon the haze potential of the wine proteins.     

毛细管区带电泳-间接紫外检测法测定饮用水中5种阴离子

目的建立毛细管区带电泳-间接紫外检测法测定饮用水中5种阴离子的新方法。方法样品无需滤膜过滤可直接进样。用未涂覆熔融石英毛细管(75μm×80 cm,有效长度为70 cm)作为分离柱。以20 mmol/L邻苯二甲酸、100 mmol/L二乙醇胺和0.5 mmol/L十六烷基三甲基溴化铵为分离缓冲体系。结果 Cl~-、NO_3~-、SO_4~(2-)、F~-和H_2PO_4~-这5种阴离子的校正峰面积与质量浓度分别在0.5～100.0、0.2～20.0、0.5～100.0、0.2～4.0和0.2～5.0 mg/L范围内呈线性相关,相关系数分别为0.998 8、0.999 9、0.999 7、0.999 7、0.999 8。检出限均为0.05 mg/L,定量限均为0.15 mg/L,方法精密度均小于5%(n=6)。低、中和高质量浓度加标回收率在81.6%～108.6%之间,相对标准偏差在0.6%～3.7%之间(n=6)。用本法分析了7份饮用水样品,并与离子色谱法的结果相比较,除矿泉水中Cl~-结果偏低外,其余基本吻合。结论本方法简单,所用试剂环保,为饮用水中5种阴离子的常规检测提供了一种新方法,但不适合测定水样中低浓度的Cl~-。     

Rapid simultaneous determination of organic acids,free amino acids,and lactose in cheese by capillary electrophoresis

A capillary electrophoresis (CE) method for the simultaneous separation of 11 metabolically important organic acids (oxalic, formic, citric, succinic, orotic, uric, acetic, pyruvic, propionic, lactic, and butyric), 10 amino acids (Asp, Glu, Tyr, Gly, Ala, Ser, Leu, Phe, Lys, and Trp), and lactose has been optimized, validated, and tested in dairy products. Repeatability and linearity were calculated for each compound, with detection limit values as low as 0.2 x 10(-2) mM for citric acid and Gly. The method was applied to analyze yogurt and different varieties of commercial cheeses. This method yielded specific CE patterns for different varieties of cheese. Also, it has been shown to be sensitive enough to measure small changes in composition of some of those compounds in fresh cheese stored under accelerated ripening conditions for 2 d at 32 degrees C (e.g., from 1728.3 +/- 45.0 to 1166.7 +/- 4.5 mg/100 g of DM in the case of lactose, or from 23.5 +/- 0.6 to 76.8 +/- 16.7 mg/100 g of DM in the case of acetic acid).     

Capillary zone electrophoresis for gliadin separation: applications in a spelt breeding program

Gliadins of 27 European spelt [Triticum aestivum ssp. spelta (L.) Thell.] cultivars (cvs) were separated by capillary zone electrophoresis (CZE). A great amount of diversity was found within the CZE gliadin patterns of these cvs; however, only 15 had unique patterns, whereas 2 triples and 3 pairs were identical, i.e., differences were within the uncertainty of the method and environmental effects. Two of these identical pairs were attributed to mislabeling: affected were one of the two Swiss spelt cvs 'Ostar' and 'Sertel', and the German spelt cv 'Steiners Roter Tiroler'. The German cv 'Franckenkorn' showed considerable similarity with the Belgian cv 'Rouquin'. CZE gliadin patterns of 12 modern German bread wheat cvs were distinctly different from those of spelt cvs selected from old land varieties like the Swiss cv 'Oberkulmer Rotkorn'. In the gliadin patterns of 11 spelt cvs, bread wheat elements were found. 7 of the 24 cvs not mislabeled are known to be progeny of wheat/spelt crosses, 4 cvs are described as pure spelt, and the pedigrees of 13 are unknown. Wheat elements were spotted in only 4 of the 7 wheat/spelt crosses and in none of the 4 pure spelt cvs. The results suggest that crossing spelt with modern wheat may be, but is not necessarily, reflected in the gliadin pattern.

毛细管区带电泳测定酪蛋白磷酸肽方法的研究

用毛细管区带电泳(CZE)对酪蛋白磷酸肽(CPP)进行了分离和测定。研究出的适宜电泳操作条件为:工作电压30KV、柱温25℃、毛细管长度50cm、内径70μm、进样量5sec(气压进样)、紫外检测波长200nm、缓冲液pH值9.2测定不同N/P样品的CPP含量分别为42.2％、50.0％、51.0％。     

高效液相色谱法测定葡萄酒的有机酸及乙酸

采用高效液相色谱法同时测定葡萄酒中的有机酸和乙酸。根据色谱柱的特点优化了分离条件，根据葡萄酒的特性进行了相应的预处理，得出了分离良好的色谱图，各组分相对标准偏差（n=5）为1．5％－3．3％，平均回收率为93．9％－98．5％，达到了分析方法的要求。     

Comparison between capillary electrophoresis and HPLC-FL for ochratoxin A quantification in wine

A capillary electrophoresis method with DAD detection has been developed and validated for ochratoxin A (OTA) determination in wine and compared with a previously validated HPLC-FL method. Although the use of UV detection has originated a high value for the quantification limit and, therefore, this method can not be used yet in the determination of OTA in wine in real samples, the analytical performance of the CE-DAD method is fully satisfactory. The more important advantage of CE is the use of the economical and ecological aqueous borate buffer in the separation process. A good correlation of the results has been obtained when 27 fortified wine samples were analyzed by CE-DAD and HPLC-FL. This work demonstrates that the CE technique is a valuable alternative to HPLC-FL analysis of OTA in wine if fluorescence detection is available.     

Determination of reducing sugars in selected beverages by capillary electrophoresis

 A method for the analysis of reducing sugar enantiomers in beverages using capillary zone electrophoresis is presented. Based on previous results, a resolution of all aldo-hexoses, -pentoses, -tetroses and trioses is achieved. Additional separation of uronic acids, deoxy and amino sugars in different buffer systems is demonstrated. Derivatives of sugar enantiomers change their migration order if derivatized with the phenylethylamine enantiomer. Thus, the use of a chiral derivatizing agent leads to simpler peak validation and opens new opportunities for the development of new applications. Screening of pharmaceutical drugs or food for rare sugar enantiomers with a detection limit of 25 fmol (5 μM) is feasible. Adaptation of the general method to wine, juice and instant coffee is demonstrated. The aldose, uronic acid and deoxy aldose enantiomer composition of the presented beverages is obtained in a single run. Received: 20 April 1998 / Revised version: 15 June 1998     

毛细管电泳测定蘑菇中多种水溶性维生素

建立了毛细管电泳法分析蘑菇粉中水溶性维生素的方法,并研究缓冲溶液、工作电压等因素对维生素测定的影响.样品进行测定时,先过C18柱,可以对样品中的维生素起到纯化和富集的作用.电泳条件为20kV,在 20mmol/L pH8.72硼砂-硼酸缓冲液,10min内实现了蘑菇粉中多种水溶性维生素(VB 1、VB2、VB6、VC和VPP)的有效分离,具有良好的稳定性、精密度、线性关系等.