Determination of flavonoids and ascorbic acid in grapefruit peel and juice by capillary electrophoresis with electrochemical detection

Grapefruit (Citrus paradisi Mact. (Rutaceae)) has been known for its accumulation of flavonoids and ascorbic acid. These contents are important because of their nutritional and antioxidant properties. Five flavonoids (hesperidin, naringin, hesperedin, narigenin and rutin) and ascorbic acid were separated and determined in grapefruit juice by capillary electrophoresis with electrochemistry detection (CE-ED). Two flavonoids (hesperidin, naringin) and ascorbic acid were found in extract of grapefruit peel with the same method. And the distribution comparision of the ingredients between juice and peel was discussed. The effects of several CE parameters on the resolution were studied systematically. Under the optimum conditions, the analytes could be well separated within 25 min in a 60 mmol L⁻¹ borate buffer (pH 9.0). The response was linear over four orders of magnitude with detection limits (S/N = 3) ranging from 1.4 × 10⁻⁷ to 1.0 × 10⁻⁶ g ml⁻¹ for the analytes. The method has been successfully applied for the analysis of grapefruit with satisfactory results.     

Determination of ascorbic acid levels in food samples by using an ionic liquid-carbon nanotube composite electrode

A novel carbon composite electrode consisted of ionic liquid n-octylpyridinum hexafluorophosphate (OPFP) and single-walled carbon nanotube (SWCNT) was fabricated and investigated. This electrode combined the advantages of ionic liquid and SWCNT together with the "bulk" composite electrode. Compared with other composite electrodes using graphite or paraffin oil, the ionic liquid-SWCNT (IL-SWCNT) composite electrode exhibited remarkable increase in the electron transfer rate for electroactive compound and significant decrease in the overpotential for ascorbic acid oxidation reaction. Based on the greatly enhanced electrocatalytic activity for the oxidation of ascorbic acid, a wide linear detection range from 3.0 μM to 4.2 mM with a low detection limit of 1.0 μM was obtained. Furthermore, the IL-SWCNT electrode was applied to determine ascorbic acid levels in real food samples. Experimental results showed that the proposed electrode could be used as an effective and sensitive sensor for direct detection of ascorbic acid.     

毛细柱气相色谱法测定饮料中的山梨酸、苯甲酸

探讨了采用毛细柱气相色谱法测定饮料中作为防腐剂的山梨酸、苯甲酸，此方法可使各组分得到良好分离，分析时间短，准确度高，山梨酸、苯甲酸测定的检出限为0．1mg／kg，相对标准偏差小于3％，样品加标回收率为89％～99％。     

HPLC-UV determination of total vitamin C in a wide range of fortified food products

A HPLC method for the quantification of total ascorbic acid (AA) and isoacorbic acid (isoAA) in fortified food products, premixes and duomixes has been developed. The method is based on the acidic extraction of AA in the presence of reducing agent Tris [2-carboxyethyl] phosphine (TCEP), which maintained AA in its reduced form. The separation was performed on a C₁₈ column with a sodium acetate eluent (pH = 5.4) containing TCEP and decylamine as ion pairing agent. The limit of detection was estimated at 0.1 mg/100 g and the recoveries were between 93% to 105% when spiking various food products with different amounts of AA. The intra-assay coefficient of variation value was 4.6% (n = 8) for infant formula and 0.8% (n = 9) for the premixes. The relative standard deviation reproducibility values obtained by 9 different laboratories ranged between 2.0% and 8.0% (n = 10). Application of the method to the analysis of 25 fortified food products, different premixes and duomixes revealed similar results to those found by the AOAC official titrimetry method.     

高压液相色谱法同时测定食品中抗坏血酸与异抗坏血酸的含量

目的 建立食品中同时测定抗坏血酸和异抗坏血酸含量的高压液相色谱检测方法。方法 用乙腈?0.1%磷酸水溶液(90∶10, v/v)作流动相和提取液, 以Venusil HILIC色谱柱(250 mm?4.6 mm, 5 ?m, 100 ?)分离抗坏血酸和异抗坏血酸。结果 抗坏血酸的平均回收率为96.61%, 异抗坏血酸的平均回收率为96.53%,异抗坏血酸和抗坏血酸最低检出浓度分别为0.35 ?g/mL和0.42 ?g/mL。结论 该方法准确、灵敏、精密度高, 适用于食品中抗坏血酸与异抗坏血酸的测定。     

Determination of ascorbic acid in vegetables and fruits by differential pulse polarography

A method for the determination of ascorbic acid in vegetables and fruits using differential pulse polarography has been developed. The extraction medium recommended is a mixture of oxalic acid (1%), trichloroacetic acid (2%) and sodium sulphate (1%), and simple filtration is used to remove the residue. An acetate buffer (2M) is recommended to keep the pH at 4.5. The polarograms were recorded using a modulation amplitude of 50mV, a scan rate of 2mVs^?1, and a drop time of 1 s. The precision of the procedure was found to be 1.4% at the 1 mg litre^?1 level of ascorbic acid. The calibration graph was linear in the range of 0–20 mg litre ^?1 of ascorbic acid with a slope of 0.48μA mg litre^?1. Most common anions and cations did not interfere, however, Fe³⁺ and EDTA interfered, and Br^? and I^? seriously interfered with the determination. The method was applied to determine the ascorbic acid content of a number of vegetables and fruits using the standard-addition calibration.     

Determination of preservatives in some food products by capillary isotachophoresis

In the food and especially preserving industry several chemical preservatives are used by which the storage life of foods is prolonged. Each preservative must fulfill hygienic and health demands. For the chemical preservatives there are determined the highest allowable quantities for concrete kinds of semiproducts and ready-made products, as well. The most used preservatives in our country are: formic acid, benzoic acid, sorbic acid, sulphur dioxide, acetic acid. Several methods were developed for the determination of the individual preservatives. Some methods do not enable the simultaneous determination of several preservatives. The chromatographic methods remove these lacks and some authors used in the determination of preservatives especially high performance liquid chromatography, as well [1, 2].     

Determination of pantothenic acid in food by capillary isotachophoresis

Pantothenic acid (vitamin B₅) has been quantified in non-fortified and fortified milk-based samples and fortified cornflakes samples by column-coupling capillary isotachophoresis. The leading electrolyte was 10 mmol/l hydrochloric acid including 0.1% polyvinylpyrrolidone adjusted with histidine to pH 6.0. The terminating electrolyte was 5 mmol/l 4-morpholineethanesulfonic acid adjusted with Tris(hydroxymethyl)aminomethane to pH 6.2. The driving current was 350 wA in the preseparation capillary. The driving current was initially 50 wA in the analytical capillary. During detection, the current was reduced to 40 wA. Linearity was observed from 0.50 to 12.0 mg/l with a coefficient of determination (r²) of 0.999. The limit of quantification was calculated to be 1.6 mg/kg. Sample preparation consisted of deproteination with acetic acid followed by centrifugation and filtration. The minimal sample pretreatment and relatively low running costs make isotachophoresis a good alternative to existing methods.     

Determination of ascorbic and dehydroascorbic acid in lean and fatty fish species by high-performance liquid chromatography with fluorometric detection

Ascorbic acid (AA) and dehydroascorbic acid (DHAA) were analysed in fish muscle by high performance liquid chromatography (HPLC) coupled with fluorescence determination using 4,5-dimethyl-o-phenilenediamine (DMPD) as a derivative agent. The use of the DMPD in combination with isobutanol extraction eliminated many matrix interferences and increased significantly the specificity and sensitivity of the method. A strong pH dependence in the derivatization reaction was also demonstrated. Satisfactory results in terms of sensitivity, stability and reproducibility were obtained. The analyses demonstrated that the relative ratio of AA and DHAA in post-mortem fish muscle differs among fish species and seems to be related with the susceptibility to oxidation.     

Determination of phytic acid in feeds and faeces of pigs and poultry by capillary isotachophoresis

A method for phytic acid determination in the feeds and faeces of pigs and poultry has been developed on the basis of capillary isotachophoresis. Phytic acid was extracted by 0.95 M HCl and separated from interfering compounds by iron precipitation. Complete formation of ferric phytate required 7 mol FeCl₃ mol⁻¹ phytic acid. Residual Fe³⁺ was estimated colorimetrically by the tiron reagent, and ferric phytate was dissolved in 1.5 M NaOH at 9 mol NaOH mol⁻¹ Fe precipitated. Analyses were carried out using an electrolyte system with Cl⁻ as the leading anion, bis‐tris‐propane, and 2‐morpholinoethanesulphonic acid as the terminating anion. The recovery of phytic acid (added to hen faeces) using this procedure was 962 ± 24 g kg⁻¹. The limit of determination of phytic acid was 0.3 µmol ml⁻¹ extract. The amount of phytic acid in feeds ranged from 8.3 to 10.8 g kg⁻¹ on a dry matter basis. Phytic acid P represented 112 g kg⁻¹ total P in faeces of young pigs (40–60 kg) fed a feed with supplemental phytase (490 U kg⁻¹), 153 g kg⁻¹ total P in faeces of finishing pigs and 185 g kg⁻¹ total P in faeces of non‐lactating sows. Excreta of laying hens contained 23.7 g phytic acid kg⁻¹ dry matter (362 g kg⁻¹ total P). The isotachophoretic method is sufficiently simple and reproducible to be used for routine analyses of feeds and faeces. © 2000 Society of Chemical Industry     

UPC~2快速测定葡萄酒中抗坏血酸和异抗坏血酸含量研究

建立了超高效合相色谱法(Ultra Performance Convergence Chromatography,UPC2)分离和测定葡萄酒中抗坏血酸和异抗坏血酸的方法。超高效合相色谱(UPC2)技术集合超临界流体色谱(Supercritical Fluid Chromatography,SFC)和超高效液相色谱(Ultra Performance Liquid Chromatography,UPLCTM)的技术优点,流动相CO2为主体,0.1%磷酸甲醇为助溶剂。选用Waters BEH色谱柱,流速1.5 m L/min,检测波长为245 nm,方法检出限为2.0 mg/kg,定量限为6.0 mg/kg,线性范围为2.5~80.0 mg/L;加标回收率范围为93.2%~105.9%;相对标准偏差RSD为4.5%~9.8%,该方法操作便捷、检测速度快、准确性高、重复性好、节约成本,能够满足葡萄酒中抗坏血酸和异抗坏血酸的检测。      

Absorption of folic acid and ascorbic acid from nutrient comparable beverages

One hundred percent fruit juices can help consumers increase the nutrient content of the diet since these beverages can be naturally rich in micronutrients. Micronutrient-fortified low-calorie beverages are an important alternative to those wishing to minimize their calorie intakes. However, little is known about the bioavailability of nutrients from fortified beverages relative to 100% fruit juices. The present study examined the bioavailability of ascorbic acid (AA) and folic acid (FA) in 100% orange juice (OJ) and a low-calorie beverage fortified with these nutrients. In a within-subjects, cross-over design, 12 adult men consumed a 591 mL serving of OJ, a low-calorie beverage fortified with AA and FA, and 1% low fat milk. Participants were aged 20 to 35 y, with body mass indexes between 20 and 30 kg/m(2). Blood plasma concentrations of AA and serum concentrations of FA were assayed by serial blood draws, made at 30 min intervals for 4.5 h. Blood plasma concentration of AA was significantly greater after ingestion of the fortified beverage compared to after OJ ingestion. However, the bioavailability of AA did not significantly differ from that of OJ. Analyses of FA indicated no significant difference between fortified beverage and OJ. Consumption of both vitamin containing beverages led to higher concentrations of AA and FA than the milk control. This study showed that similar levels of AA and FA bioavailability can be attained through ingestion of 100% OJ and a fortified beverage.     

Determination of nitrates in vegetables by capillary isotachophoresis

The presented paper deals with the determination of nitrates by capillary isotachophoresis. The determination was tested on vegetable samples bought in the shop and the market hall. High nitrates concentration in vegetable is mainly due to excessive nitrogen content in the soil system, thus deteriorating the nutritional and hygienic values of products and complicating the processing and storage. Hence, increased attention is paid to nitrates not only by medical staffs, especially by hygienists, but also by farmers, nutritionists and, to a certain degree, also by consumers. At present, various analytical methods are used to determine nitrates in biological material, such as the spectrophotographic and potentiometric methods. Nitrates may also be estimated by polarography, atomic absorption spectrophotometry, gas chromatography, high performance liquid chromatography and capillary isotachophoresis (ITP) [1–3].     

A screening method for the determination of ascorbic acid in fruit juices and soft drinks

A simple and rapid liquid chromatographic method based on a new stationary phase Teknokroma, Tr-010065 Mediterranea sea₁₈ (15 cm × 0.4 cm, id 3 μm), to determine ascorbic acid in beverages is reported. With the proposed method the samples were analysed by direct injection without a previous treatment. The total analysis time does not exceed 6 min. The method showed a good repeatability (RSD < 2%: n = 6) and an excellent sensitivity (LOD = 0.01 mg/l). Seventeen samples were analysed, including fruit juices, soft drinks and isotonic beverages. Ascorbic acid contents ranged from 6.6 to 840 mg/l. The ascorbic acid stability in some beverages during their shelf-life was also evaluated. Degradation of about 54% was observed in a tea drink.     

Using capillary isotachophoresis for the determination of biogenic amines and D‐isocitric acid in food products

This paper presents results achieved in the determination of biogenic amines in various food products and quality evaluation of some commercial orange juices by capillary isotachophoresis. The highest amount of histamine was determined in frankfurters (146.75 mg·kg^–1); the content of tyramine was either under detection limit of method or it was present in very low concentrations. The highest amount of cadaverine was determined in Kari?ka cheese (666.36 mg·kg^–1). The limit of determination was 1.59 mg·kg^–1 for histamine and 1.25 mg·kg^–1 for tyramine. The recovery of method ranged from 95.4 to 104.9%. Surprisingly it was found that many organge juice samples did not reach required values according to the Code of Practice. The lowest ratio of citric to D ‐isocitric acids was found in Happy day juice (44.1). Limit of determination was 1.62 mg·dm^–3 for citric acid and 2.00 mg·dm^–3 for D ‐isocitric acid. The recovery of the method ranged from 89 to 96.5%.     

Aminocarminic acid in E120-labelled food additives and beverages

An analytical method was developed for investigating aminocarminic acid occurrence in E120-labelled red-coloured-beverages and in E120 additives, with the aim of controlling the purity of the carmine additive in countries where the use of aminocarminic acid is forbidden. The carminic acid and the aminocarminic acid were separated by high-performance liquid chromatography–photodiode array–tandem mass spectrography (HPLC-PDA-MS/MS). The method was statistically validated. The regression lines, ranging from 10 to 100?mg/L, showed r^2?>?0.9996. Recoveries from 97% to 101% were obtained for the fortification level of 50?mg/L; the relative standard deviations did not exceed 3%. The LODs were below 2?mg/L, whereas the LOQs did not exceed 4?mg/L. The method was successfully applied to 27 samples of commercial E120-labelled red-coloured beverages and E120 additives, collected in Italy during quality control investigations conducted by the Ministry. The results demonstrated that more than 50% of the samples contained aminocarminic acid, evidencing the alarming illicit use of this semi-synthetic carmine acid derivative.     

采用褪色光度法测定维生素C

在硫酸介质中,利用维生素C（L-VC）对高锰酸钾的褪色效应建立了褪色光度法测定维生素C的方法。在最大吸收波长为526nm,表观摩尔吸收系数为6.71×103L·mol-1·cm-1时,维生素C浓度在0～20μg/ml范围内与溶液的褪色程度（△A）服从比尔定律,最小检出限为0.91mg/L,相对标准偏差为0.54%～0.96%,回收率为92.5%～101.8%。     

Effect of pasteurisation on ascorbic acid,dehydroascorbic acid,tocopherols and fatty acids in pooled mature human milk

Ascorbic and dehydroascorbic acids (vitamin C), tocopherols (vitamin E) and unsaturated fatty acids are heat-sensitive and therefore, their concentrations in human milk could be affected by pasteurisation. Here we determined the concentrations of ascorbic acid plus dehydroascorbic acid, ascorbic acid alone, and α- and γ-tocopherols, and the percentages of fatty acids in samples of human milk after pasteurisation by a slow (62.5 °C, 30 min) or fast heating (100 °C, 5 min) procedure. Both methods led to a significant decrease in the concentrations of ascorbic acid plus dehydroascorbic acid (12% and 29%), ascorbic acid (26% and 41%), α-tocopherol (17% and 34%) and γ-tocopherol (13% and 32%), respectively. However, milk fatty acids, including the polyunsaturated long-chain fatty acids, were unaffected by the two methods. On the basis of these observations, we recommend that human milk be treated using a slow pasteurisation. In addition, we propose ascorbic acid as a marker of the degree of heat treatment.     

Maintaining the quality of sugarcane juice with blanching and ascorbic acid

The physicochemical changes in fresh sugarcane juice stored at 10 °C were studied by determining juice yield, color, reducing sugar, titratable acidity, viscosity, pH, polyphenol oxidase (PPO), sucrose neutral invertase (SNI) and total microbial count. Results showed that blanching of stems before squeezing effectively prevented degreening and/or browning, and reduced activities of PPO and SNI in fresh sugarcane juice. Added ascorbic acid delayed the increase of reducing sugar, titratable acidity, viscosity and total microbial count, and also prevented degreening and/or browning with reduced PPO and SNI activities in fresh sugarcane juice during storage. Addition of 0.1% ascorbic acid seemed to be more effective than blanching of sugarcane stems, and was able to maintain the quality of fresh sugarcane juice for up to 5 days at 10 °C. Deterioration of fresh sugarcane juice was demonstrated as a rapid increase of titratable acidity and viscosity with a obvious browning.     

Curcumin antifungal and antioxidant activities are increased in the presence of ascorbic acid

The objective of this study was to evaluate the antifungal and antioxidant activities of curcumin, ascorbic acid and the mixture of these two compounds. For the antifungal assay, the minimum inhibitory concentrations (MIC) were determined using Candida strains (ATCC and clinical isolates). Curcumin alone inhibited growth of Candida albicans yeast cells, whereas ascorbic acid did not present effects. However, when the mixture of ascorbic acid and curcumin was assayed to determine the association of the two compounds, the curcumin MIC decreased 5- to 10-fold. In the antioxidant assays, the sum of the alone activities of curcumin and ascorbic acid were lower than the activity of the two-compound mixture. This study highlights the importance of the association between two common antioxidants in foods, to improve the antifungal and antioxidant activities of curcumin (in vitro), and can be applied to Candida spp. infection and diseases associated with oxidative stress.