High resolution gas chromatographic method for determination of Robusta coffee in commercial blends

The unsaponifiable lipid fractions extracted from Arabica and Robusta coffee samples were analyzed by high resolution gas chromatography (HRGC) in a polar column with a thermally stable stationary phase (TAP, Chrompack). Certain characteristic ratios among diterpenic alcohols were found to permit measurement of the amount of Robusta blended with Arabica coffee, given a minimum content of 5–10%. Determination does not appear to be influenced by geographic origin of produce or even by decaffeination.     

Influence of the surfactant bromide of cetyltrimetyl ammonium in the determination of chlorogenic acid in instant coffee and mate tea samples

In this study, two quantitative differential-pulse polarography (DPP) and square-wave voltammetry (SWV) methods were developed to determine total chlorogenic acid (CGA). Studies on this compound involve its reduction at a hanging mercury drop electrode in micellar media—a simple, fast, reliable, and sensitive method. The use of surfactant cationic cetyltrimethylammonium bromide (CTAB) was pivotal to the development of these methods, allowing for satisfactory changes in CGA reduction. The supporting electrolyte which provided the best-defined CGA determination was 0.04-mol L⁻¹ phosphate buffer at pH 6.0 in the presence of CTAB. Based on this use and under optimized conditions, the two new DPP and SWV methods for CGA analysis had detection limits of 2.36 × 10⁻⁷ and 1.34 × 10⁻⁹ mol L⁻¹, respectively, for a pure standard. Analysis of the standard in the presence of treated instant coffee and mate tea samples allowed for good average recovery rates, ranging from 97.06% to 105.90%.     

Salting-out gradients in centrifugal partition chromatography for the isolation of chlorogenic acids from green coffee beans

In addition to sample solubility constraints, the use of polarity gradients in normal-phase centrifugal partition chromatography (CPC) for the purification of complex mixtures is also limited by the instability of biphasic systems as a consequence of dramatic changes in the settling times along the gradient, leading in many cases to column bleeding when working under maximum efficiency conditions. In this paper an electrostriction approach is proposed as a strategy in reversed-phase CPC to fractionate intermediate polarity extracts in a single run by bringing its components into the “sweet spot” in a controlled fashion through a stepwise reduction of salt concentration in the aqueous mobile phase. The salting-out gradient method was successfully tested with the separation of the major chlorogenic acids (CGAs, hydroxycinnamoylquinic acids) present in green coffee beans (5-caffeoylquinic acid (5-CQA), 5-feruloylquinic acid (5-FQA) and 3,5-dicaffeoylquinic acid (3,5-diCQA)) using ethyl acetate-hexane as the stationary phase and an ionic gradient of LiCl (5.0, 2.5 and 0.1 M) as the mobile phase in one case and (NH₄)₂SO₄/KNO₃ (3.0 and 1.5 M/1.5 M) in another. Regioisomers of each chlorogenic acid obtained by base-catalyzed isomerisation were also separated by CPC using isocratic elution. The best resolution for both FQAs and diCQAs was achieved with a chloroform–n-butanol–0.01 M pH 2.5 phosphate buffer (84:16:100; v/v) system, while CQAs were best isolated using chloroform–n-butanol–0.01 M pH 2.5 phosphate buffer/5.0 M LiCl (82:18:100; v/v).     

水中汞量的酶法测定

提出用酶催化动力学光度法测定汞，是基于乳酸脱氢酶催化丙酮酸和还原型烟酰胺腺嘌呤二核苷酸的反应，汞离子对于酶催化的抑制作用原理，通过测定还原型烟酰胺腺嘌呤二核苷酸吸光度的变化率得出其酶促反应速度，对应于汞而制得标准曲线。检出限为0、18μg／L。讨论了pH值和共存离子对测定的影响。     

High resolution gas chromatographic determination of diterpenic alcohols and sterols in coffee lipids

Summary The composition of the unsaponifiable fraction of coffee lipids extracted before and after roasting was determined in two coffee types (Arabica and Robusta) of different geographic origin. Component identification was performed by gas chromatography-mass spectrometry. Large amounts of diterpene mono- and di-alcohols were found in both varieties; cafestol, kahweol and 16-O-methylcafestol were identified. Other components that were partly generated during roasting were also identified; these compounds seem to arise from the dehydration of cafestol and dehydrocafestol.     

High resolution gas chromatographic determination of diterpenic alcohols and sterols in coffee lipids

Summary The composition of the unsaponifiable fraction of coffee lipids extracted before and after roasting was determined in two coffee types (Arabica and Robusta) of different geographic origin. Component identification was performed by gas chromatography-mass spectrometry. Large amounts of diterpene mono-and di-alcohols were found in both varieties; cafestol, kahweol and 16-O-methylcafestol were identified. Other components that were partly generated during roasting were also identified; these compounds seem to arise from the dehydration of cafestol and dehydrocafestol.     

Rapid determination of sucrose in chocolate mass using near infrared spectroscopy

This paper reports the results of a rapid method to determine sucrose in chocolate mass using near infrared spectroscopy (NIRS). We applied a broad-based calibration approach, which consists in putting together in one single calibration samples of various types of chocolate mass. This approach increases the concentration range for one or more compositional parameters, improves the model performance and requires just one calibration model for several recipes. The data were modelled using partial least squares (PLS) and multiple linear regression (MLR). The MLR models were developed using a variable selection based on the coefficient regression of PLS and genetic algorithm (GA). High correlation coefficients (0.998, 0.997, 0.998 for PLS, MLR and GA-MLR, respectively) and low prediction errors confirms the good predictability of the models. The results show that NIR can be used as rapid method to determine sucrose in chocolate mass in chocolate factories.     

酶法测定乳酸

利用乳酸在氧化型烟酰胺腺嘌呤二核苷酸（NAD）存在的条件下,由乳酸脱氢酶（L-LDH）催化生成丙酮酸和还原型烟酰胺腺嘌呤二核苷酸（NADH）。通过测定NADH吸光度的变化率可得出乳酸的酶促反应速度,并制得标准曲线。样品中的乳酸可由标准曲线求得。讨论了试剂用量、pH、温度和共存离子对测定的影响。     

Ion chromatographic determination of some organic acids, chloride and phosphate in coffee and tea

An ion chromatographic method for the simultaneous determination of organic acids and inorganic ions is described. Acetic, malic, ascorbic, citric, malic and succinic acids, chloride and phosphate were determined in coffee and tea samples. The separation is performed on an anion-exchange column operated at 40 °C within 25 min by an isocratic elution with 0.6 mM aqueous potassium hydrogenphthalate (pH 4.0) solution containing 4% (v/v) acetonitrile as eluent and determination by conductivity detection. The method does not need a special sample treatment and was successfully applied to the analysis of black, green and oolong tea samples. Also, green and roasted coffee samples from the varieties arabica and robusta were analyzed.     

Simultaneous determination of glucose and sucrose by a glucose-sensing enzyme electrode combined with an invertase-attached cell

Glucose and sucrose are simultaneously determined by using a glucose-sensing enzyme electrode combined with a cell that contains immobilized invertase. The electrode current changes linearly with time for several minutes from ca. 1 min after the addition of a glucose-sucrose mixture. The concentration of sucrose (60 μM-6 mM) is determined from the rate of current change in the linear region, and that of glucose (5 μM-1 mM) is determined by extrapolating the straight current-time line to t=0.45 min and by measuring the intercept on the vertical (current) axis at t=0.45 min. The relative standard deviations are 1.8% for glucose and 3.7% for sucrose (n=10). More than 20 food samples can be analysed in 1 h.     

Spectrophotometric determination of lead in vegetables with dibromo-p-methyl-carboxysulfonazo

A new highly sensitive and selective chromogenic reagent dibromo-p-methyl-carboxysulfonazo (DBMCSA) was synthesized and studied for the spectrophotometric determination of lead in detail. In 0.25 M phosphoric acid medium, which greatly increases the selectivity, lead reacts with DBMCSA to form a 1:2 blue complex, having a sensitive absorption peak at 648 nm. Under the optimal conditions, Beer's law is obeyed over the range from 0 to 0.8 μg ml⁻¹ Pb(II) and the apparent molar absorptivity is 1.04×10⁵ l mol⁻¹ cm⁻¹. The detection limit and the variation coefficient were found to be 2.14 ng ml⁻¹ and 1.0%, respectively. It is found that, except for Ca(II) and Ba(II), all foreign ions studied do not interfere with determination. The interference caused by Ca(II) and Ba(II) can be easily eliminated by prior extraction with potassium iodide-methylisobutylketone. The method has been applied to the determination of lead in vegetables with satisfactory results.     

反相高效液相色谱法同时测定咖啡豆中的6种酚酸类化合物

建立了同时测定咖啡豆中6种酚酸类化合物(咖啡酸、3-咖啡酰奎尼酸、4-咖啡酰奎尼酸、5-咖啡酰奎尼酸、3,5-二咖啡酰奎尼酸、4,5-二咖啡酰奎尼酸)的反相高效液相色谱测定方法。采用Kromasil C18柱(200 mm×4.6 mm, 5 μm),以乙腈和0.1%甲酸水溶液为流动相进行梯度洗脱,二极管阵列检测器检测,45 min内可对6种目标物进行同时检测,且各化合物都能达到基线分离。经测定,样品中6种酚酸类化合物的加标回收率为90.76%～104.73%,相对标准偏差为0.7%～3.9%。该法简便、快速、灵敏度高,适用于咖啡豆中6种酚酸类化合物的同时分析以及咖啡豆原料与制品的质量控制和综合评价。     

Enzymatic—spectrophotometric determination of phytic acid with phytase from Aspergillus ficuum

A method to determine phytic acid in the range 3–60 μM based on the spectrophotometric determination of inorganic phosphate with vanadate and molybdate, after liberation by enzymatic hydrolysis of phytic acid with phytase from Aspergillus ficuum at pH 2.5 and 37 °C is reported. The method has been applied successfully to determine phytic acid in wheat flour and in a pharmaceutical product.     

Selective determination of caffeine and trigonelline in aqueous extract of green coffee beans by FT-MIR-ATR spectroscopy

A non-destructive, fast, simple and reliable Fourier transform mid-infrared attenuated total reflectance spectroscopy (FT-MIR-ATR) method for the selective determination of caffeine and trigonelline in the aqueous extract of green coffee beans was developed and validated. The calibration curves were linear in the range 2000 − 7000 mg/L for caffeine and trigonelline with R² ≥ 0.9997. The limits of detection (LOD) were 140 and 100 mg/L and the limits of quantification (LOQ) were 470 and 330 mg/L for caffeine and trigonelline, respectively. The precision (% RSD) was 3.0% and 4.3% for caffeine and trigonelline, respectively. The developed method was applied to 20 samples of green coffee beans to determine the two alkaloids. The amount of caffeine and trigonelline in the green coffee beans were found in the range 0.84 − 1.15% (w/w) and 0.83 − 1.13% (w/w), respectively. The accuracy of the developed analytical method was evaluated by spiking standard caffeine and trigonelline to green coffee beans and the average recoveries were 93 ± 5% and 98 ± 4%, respectively. Therefore, the developed FT-MIR-ATR methods can be used for direct determination of the two alkaloids in the green coffee beans.     

Evaluation of a fluorometric-enzymatic method based on 3alpha-hydroxysteroid dehydrogenase for the mycotoxin zearalenone determination in corn

A new method for the fluorometric determination of zearalenone (ZEN) based on its reaction with βNADH in the presence of the enzyme 3α-hydroxysteroid dehydrogenase (3α-HSD) is described. The procedure is based on the change in fluorescence intensity that takes place during the enzymatic reaction (excitation at 340 nm and emission at 454 nm). The optimum reaction conditions and the analytical characteristics were studied; linear response range (1-10 mg l⁻¹) and reproducibility (8 mg l⁻¹, 2.7%, n=7). Moreover, a mathematical model explaining the analytical signal is proposed. The method has been applied to zearalenone determination in a spiked corn sample.     

酶催化动力学光度法测定锌

近年来酶法在分析测定方面的研究非常活跃,酶法测定锌已有报道,基本为终点测定法。本文中的研究是基于LDH催化下列反应：丙酮酸＋NADH=乳酸＋NAD^＋（氧化型烟酰胺腺嘌呤二核苷酸）,锌离子的存在对酶催化反应具有抑制作用,反应速度的变化率与锌离子的浓度呈相关关系,从而可测定试样中的锌离子含量。本方法不需要底物转变完全,与终点测定法相比,可减少测定时间并节省酶量。     

Detection of adulterations in processed coffee with cereals and coffee husks using capillary zone electrophoresis

The proposed method for the identification of adulteration was based on the controlled acid hydrolysis of xylan and starch present in some vegetable adulterants, followed by the analysis of the resulting xylose and glucose, which are the monosaccharides that compose, respectively, the two polysaccharides. The acid hydrolysis with HCl increases the ionic strength of the sample, which impairs the electrophoretic separation. Thus, a neutralization step based on anion exchange resin was necessary. The best separations were obtained in NaOH 80 mmol/L, CTAB 0.5 mmol/L, and methanol 30% v/v. Because of the high value of pH, monosaccharides are separated as anionic species in such running electrolyte. The LOQ for both monosaccharides was 0.2 g for 100 g of dry matter, which conforms to the tolerable limits.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

Simultaneous determination of tartrazine and sunset yellow in cosmetic products by first-derivative spectrophotometry

A spectrophotometric method for the simultaneous determination of Tartrazine (TT) and Sunset Yellow (SY) in cosmetic products has been developed. An extraction process was carried out using methylene chloride and the colouring matters were measured in the aqueous phase formed, the other components of the sample remaining in the organic phase. The applicable concentration ranges were 0.5–10 ug/ml TT and 0.5–12 g/ml SY. The detection limits were 26 and 11 ng/ml and the relative standard deviations were 1.0 and 0.9% for TT and SY, respectively. The method was applied to the determination of both compounds in cosmetics.     

Kinetic of catalytic sucrose esterification in aqueous media

The process of sucrose esterification in the presence of a homogeneous catalyst was developed directing the reaction to the production of weakly substituted esters. Esterification of sucrose was processed with octanoyl chloride in a discontinuous reactor, in presence of 4-dimethylaminopyridine as catalyst. The process was operated in a time interval ranging from 0 to 80 min, at temperatures from 288 to 303 K, pH=10 and at atmospheric pressure. The following conversion levels were obtained: octanoyl chloride 11-84%, primary monoester production of 9-67%, secondary monoesters of 1.3-17%. Activation energies ranging from 158 l to 300 kJ/mol characterized the stages of the process, among them the stage of formation of the DMAP/RCOCl complex (162.43 kJ/mol). The increase in primary monoesters yield due to the temperature rise, leads to an increase in the rate of the direct reaction as well as in the speed of secondary monoester conversion to primary monoesters, quantifying a selectivity in primary isomers in the following positions sequence: 6> 1" > 6".