A kinetic study of the reactions of (+)‐catechin with aldehydes derived from toasted oak

The reactions between (+)‐catechin and representative oak wood furanic (furfuraldehyde, 5‐hydroxymethylfurfuraldehyde and 5‐methylfurfuraldehyde) and phenolic (vanillin and syringaldehyde) aldehydes in a wine‐like model solution were studied and the corresponding condensation kinetics at pH 3.0 and 3.5 were compared. A comparative study on the reactivity of these two representative families of aldehydes towards (+)‐catechin showed a large difference between them. When incubated separately with (+)‐catechin at both pH values, the reactions were faster with furanic aldehydes than with phenolic aldehydes. In mixtures containing (+)‐catechin and individual aldehydes, new compounds were identified by high‐performance liquid chromatography (HPLC)/UV–visible detection, some of which were characterised by liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI‐MS). The increase in solution absorbance with time was closely linked to these new products. Copyright © 2007 Society of Chemical Industry     

基于Fe3O4@Au模拟酶智能手机比色法检测牛奶中尿酸的研究

目的 利用Fe3O4@Au的过氧化物模拟酶活性构建检测牛奶中过量尿酸的智能手机比色传感器。方法 通过单因素正交实验获取模拟酶比色和智能手机比色的最佳检测条件, 利用紫外分光光度法和智能手机比色法测定不同浓度的尿酸溶液, 同时评估体系的灵敏度、抗干扰性和稳定性。结果 Fe3O4@Au最优催化体系为反应温度60℃, 反应时间50 min及Fe3O4@Au添加量0.015 g。智能手机比色体系最优相机分辨率为12 MP, 光圈f值为4.00 mm, 感光度(photosensibility, ISO)值为800及快门速度为0.002 s; 基于智能手机比色法检测尿酸最优条件下, 尿酸浓度在0.075~7.500 mmol/L范围内显现出良好的线性关系, 工作曲线为Y1=?47.362X1+494.35 (r2=0.9918), 检出限为0.043 μmol/L。在实际样品检测中, 加标回收率在96.90%~112.81%之间, 相对标准偏差均低于4.00%。结论 基于Fe3O4@Au模拟酶活性建立的智能手机比色检测体系, 具有极高的灵敏度, 良好的抗干扰性和稳定性, 该研究成果将为尿酸等食品成分的分析检测提供一条新的渠道。     

Colorimetric assay for determination of trimethylamine-nitrogen (TMA-N) in fish by combining headspace-single-drop microextraction and microvolume UV–vis spectrophotometry

In this work, headspace-single-drop microextraction has been used in combination with microvolume UV–vis spectrophotometry to enhance the determination of trimethylamine-nitrogen (TMA-N) in fish samples. TMA-N is often used for monitoring fish freshness, but due to the low analytical sensitivity usually achieved, its determination must be performed after certain time of storage in some fish species. The proposed methodology, based on the extraction and subsequent complexation of volatile TMA-N onto a picric acid-containing xylene microdrop exposed to the headspace, involves an important improvement of sensitivity (detection limit 6 × 10⁻⁴ mg TMA-N per 100 g of fish), a miniaturization of the AOAC Official Method (971.14) and a simple approach for routine labs. This method is well suited to determination of TMA-N in different species of frozen and fresh fish samples from markets and to study the evolution of TMA-N concentration in farmed turbot at the earliest stages of deterioration.     

The development of a suitable manufacturing process for ‘Benifuuki’ green tea beverage with anti‐allergic effects

Epigallocatechin‐3‐O‐(3‐O‐methyl) gallate (EGCG3″Me) has been reported to inhibit type I allergy better than epigallocatechin gallate (EGCG), a major catechin in tea leaves (Camellia sinensis L). We examined the effects of extraction and sterilization on the catechin content and histamine release from mast cells, as a representative reaction of early phase allergy, in the manufacture of ‘Benifuuki’ green tea beverage. Among various varieties of tea, the cultivar ‘Benifuuki’ contains approximately 2% of EGCG3″Me. Ester‐type catechins and their epimers increased with the increased extraction temperature of the tea. A tea infusion, extracted at 90 °C, strongly inhibited histamine release from mast cells. Furthermore, sterilization affected the catechin content in the manufactured green tea beverage. Sterilization at high temperature promoted the isomerization of catechins and the sterilized green tea beverage had a strong inhibitory effect. When EGCG3″Me, EGCG, epicatechin‐3‐O‐gallate (ECG) and their epimers, GCG3″Me (gallocatechin‐3‐O‐(3‐O‐methyl) gallate), GCG (gallocatechin‐3‐O‐gallate) and CG (catechin‐3‐O‐gallate) were compared, the anti‐allergic effect of GCG3″Me was strongest, and the order of activity was GCG3″Me > EGCG3″Me > GCG > EGCG. We consequently suggest that it was necessary to extract components from tea at the highest temperature possible, and to pasteurize under retort conditions (118.1 °C, 20 min), to manufacture functional green tea beverage with an anti‐allergic action. Copyright © 2005 Society of Chemical Industry     

Thermodynamic characteristics of copigmentation reaction of acylated anthocyanin isolated from blue flowers of Scutellaria baicalensis Georgi with copigments

Anthocyanin extracts are increasingly used as food colorants. So far, anthocyanins have not been broadly used in foods and beverages, since they are not as stable as synthetic dyes. Copigmentation between anthocyanins and copigments is the main colour‐stabilizing mechanism. The process of copigmentation between isolated acylated anthocyanin and rutin, QSA or baicalin has been observed using UV–vis spectrophotometry. The thermodynamic parameters were correlated to the structure and position of the substituents in the interacting molecules. The acylated anthocyanin was isolated from cultivars of Scutellaria baicalensis Georgi flowers and purified by column chromatography by our own method and has been identified by ¹H‐/¹³C‐NMR spectroscopy and electrospray mass spectrometry as delphinidin‐3‐O‐(6‐O‐malonyl)‐β‐D ‐glucopyranosyl‐5‐O‐β‐D ‐glucopyranoside. Copyright © 2004 Society of Chemical Industry     

Screening method for identification of adulterate and fake tequilas by using UV–VIS spectroscopy and chemometrics

Based on UV–VIS spectroscopy and chemometric techniques, a screening method is presented with which the studied brands of white and rested tequila can be differentiated among them and on the other hand, adulterate and fake tequilas can be distinguished from the corresponding genuine brands. Eighty bottles of tequila (39 white type and 41 rested type) were studied and purchased at liquor stores; special care was taken to get different batches. Through the use of support vector machine (SVM), principal component analysis (PCA) and linear discriminant analysis (LDA) the studied tequilas were differentiated and classified into 8 sets: 4 sets of white and 4 of rested tequilas; each set corresponded to a specific tequila brand. Seven additional samples with similar labeling than the 80 samples were used to validate the method and it was found that each sample was located within the ellipse of confidence of the corresponding tequila brand. Furthermore, 14 adulterated samples were generated from 2 bottles of tequila, one white and one rested, and they could be distinguishable from the genuine tequila, i.e., they were outside of the corresponding ellipse of confidence. In addition, the screening method here presented was employed to analyze rested tequilas that were purchased on the street market, i.e., fake tequilas, with the same label than 3 of the used brands in this work. These samples were discriminated from the corresponding genuine tequila brand. The results suggested that the reported method could play an important role when a quick, trustworthy and feasible result on site is needed since the test of the spirit takes minutes, affording robustness, reliability and in addition, a skilled worker is not required necessarily to apply the method.     

Survey on the content of vitisin A and hydroxyphenyl-pyranoanthocyanins in Tempranillo wines

Little is known about the content and development of pyranoanthocyanins, pigments mainly formed during red wine ageing, in commercial wines. Some of the major pyranoanthocyanins in a wide selection of 1–10 years-old Spanish Tempranillo wines and also in a 29 years wide-vertical series of Tempranillo wines from an individual cellar have been determined. Great variability in pyranoanthocyanin concentrations was found (range, mg/l): vitisin A, 0–10.76; pinotin A, 0–4.26; and malvidin 3-glucoside-4-vinylphenol, 0.03–1.37. Vitisin A and malvidin 3-glucoside-4-vinylphenol were already present in 1–2 years-old wines, whereas pinotin A was only detectable in a few of the 1 and 2 years-old wines. Vitisin A tended to decrease with wine age, while hydroxyphenyl-pyranoanthocyanins showed the reverse trend. However, the aforementioned trends were interrupted by various temporary maxima, most likely due to some “refreshment” of the oldest wines (i.e., addition of young wine), as suggested by unexpected high concentrations of malvidin 3-glucoside, in contrast to the results found in the wine vertical series. The effects of addition of young wine on aged wine pyranoanthocyanin concentrations were confirmed by wine refreshment experiments.     

Discrimination of Chinese rice wines of different geographical origins by UV–vis spectroscopy and chemometrics

Discrimination of Chinese rice wines from four geographical origins (‘Zhejiang’, ‘Jiangsu’, ‘Shanghai’ and “Fujian”) in China was investigated according to their UV–vis spectra. The UV–vis absorption spectra of 112 samples in the wavelength range of 190–800 nm were collected. Then the absorption data was subjected to principal component analysis to reveal differences between samples and the potential possibility of using multivariate methods to distinguish differences. Classification models were developed by soft independent modelling of class analogy, linear discriminate analysis (LDA), discriminant partial least squares and support vector machine. Seven mathematical pre‐treatments were applied to improve the performance of the multivariate classification models. Among the seven pre‐treatments, standard normal transformation (SNV) was superior to the other six methods. The results showed that, compared with other models, SNV‐treated LDA models achieved better performances with an average correct classification rate of 98.96% in the training set and 100% in the testing set. The results demonstrate that UV spectroscopy combined with chemometric data analysis, as a rapid method to classify Chinese rice wines according to their geographical origins, is feasible. Copyright © 2015 The Institute of Brewing & Distilling     

A comparative study on the determination of lactic acid in silage juice by colorimetric,high-performance liquid chromatography and enzymatic methods

The determination of lactic acid in the silage juice of artichokes with different additives (formid acid, molasses and NaCl) by the colorimetric method and its comparision with the high-performance liquid chromatography and enzymatic methods was investigated. The lactic acid content of the artichoke with molasses (62.1 g kg⁻¹) was higher than that of those with formic acid, or NaCl and without any additive (39.3, 33.0 and 43.2 g kg⁻¹, respectively). However, this effect was not significant (P > 0.05). There were significant differences on the method of measuring lactic acid of the artichoke silages (P < 0.001). The use of the enzymatic method resulted in a higher (75.6 g kg⁻¹) lactic acid content than when the colorimetric or HPLC methods were employed (with results of 42.0 and 28.9 g kg⁻¹, respectively). However, the levels of lactic acid in silage juices found using the colorimetric and HPLC methods were not different, and recovery percentages, by using the colorimetric method, were satisfactory (103.78%), when the detection limit at maximum level (30 µg ml⁻¹) was not exceeded. © 1999 Society of Chemical Industry     

Simultaneous Analysis of Nε‐(Carboxymethyl)Lysine and Nε‐(Carboxyethyl)Lysine in Foods by Ultra‐Performance Liquid Chromatography‐Mass Spectrometry with Derivatization by 9‐Fluorenylmethyl Chloroformate

Isotope dilution ultra‐performance liquid chromatography–electrospray tandem mass spectrometry with derivatization by 9‐fluorenylmethyl chloroformate was successfully applied to quantify N^ε‐(carboxymethyl)lysine (CML) and N^ε‐(carboxyethyl)lysine (CEL) in processed foods. We demonstrate that this analytical method is well validated for the determination of CML and CEL contents in processed foods. Relative standard deviations (RSD) indicate repeatability (RSD < 6% for CML and CEL) and reproducibility (RSD < 6% for CML and < 7% for CEL) in this method. Percent recovery is also good. We obtain recoveries of 102% to 112% for CML and 86% to 114% for CEL. CML levels detected in the samples vary from 2.29 to 480 mg/kg food, whereas CEL is detected in significantly lower concentrations ranging from 0.56 to 107 mg/kg food. These data could help consumers make better food choices by monitoring intake of advanced glycation end‐products, which may pose a risk to human health.     

Characterisation of odour‐active compounds in lupin flour

BACKGROUND: Lupin ingredients are promising alternatives to soybean products owing to their similarly high protein content. Lupin flour exhibits a green and bean‐like off‐flavour in higher amounts. The aim of this study was to characterise and identify the main odour‐active compounds in lupin flour. RESULTS: The orthonasal aroma of lupin flour was evaluated by means of aroma profile analysis and was found to be characterised by grassy‐green, metallic, fatty, fruity, hay‐like, cheese‐like, and meat‐like odour qualities. Volatile compounds of lupin flour of Lupinus angustifolius cv. Boregine were extracted with dichloromethane and isolated by solvent‐assisted flavour evaporation. Aroma extract dilution analysis (AEDA) was carried out with the obtained extract. In total, 50 odorants were detected by high‐resolution gas chromatography–olfactometry. AEDA revealed 26 odour‐active compounds with flavour dilution factors higher or equal to 32. The substances were unequivocally identified by their odour characteristics, their retention indices and their mass spectra using one‐dimensional or two‐dimensional gas chromatography–mass spectrometry, respectively. CONCLUSION: A series of unsaturated and saturated aldehydes, ketones, carboxylic acids, alkyl‐methoxypyrazines and terpenes were identified for the first time as odour‐active contributors to the aroma of lupin flour. Copyright © 2009 Society of Chemical Industry     

Common aroma‐active components of propolis from 23 regions of China

BACKGROUND: The study of propolis odorants by gas chromatography–olfactometry–mass spectrometry has rarely been put into practice until now. This study aimed to investigate the common odorants of 23 samples of Chinese propolis and analyse the relationship between the principal components and the regions where the samples had been obtained. RESULTS: By using dynamic headspace sampling, gas chromatography–olfactometry–mass spectrometry and two internal standards, the principal aroma‐active components of 23 propolis samples were analysed qualitatively and quantitatively. The common aroma‐active components were compared with each other by principal component analysis from concentration, odour activity value (OAV) and sensory evaluation score. The components with high OAVs were acetic acid, 2‐phenylethyl acetate, and naphthalene, in decreasing order, which approximated the sensory evaluation scores. On the discrete‐point map the first three principal components seemed to be grouped into three patterns, while four samples were outliers. CONCLUSION: The concentrations of aroma‐active components were closely related to the regions from a discrete‐point map by the first three principal components. It was confirmed that components with high concentrations did not always play important roles in odour contribution, for odour level was linked with their threshold. OAVs could reflect the level of odour exactly according to the approximate result from the comparison between OAVs and sensory evaluation scores. Copyright © 2010 Society of Chemical Industry     

Solid‐phase extraction and spectrophotometric determination of Allura Red (E129) in foodstuff,soft drink,syrup and energy drink samples: a comparison study

Amberlite XAD‐7 and XAD‐8 resins were used as adsorbents for preconcentration and determination of Allura Red (AR) food dye in aqueous medium. The effects of pH, sample volume, sample and eluent flow rates on the extraction of AR were optimised. The determination of dye was performed at 506.0 nm using spectrophotometry. Interference effects of matrix ions and some dyes were also investigated under optimised conditions. The methods permitted low detection limits which were 1.2 and 0.6 μg L^?1 for XAD‐7 and XAD‐8, respectively. Adsorption behaviours were investigated by adsorption isotherms and zero charge pH experiments. Validations of the method were performed by determination of AR contents in some foodstuffs. AR contents of liquid samples were found between 58 and 440 μg mL^?1. AR concentrations of solid samples were between 416 and 432 μg g^?1. The XAD‐7 and XAD‐8 resins presented a fast and reliable potential to determine AR dye in real samples.