A simple method for concentrating volatile flavor compounds in aqueous systems using RP-HPLC

Summary Volatile flavor compounds in aqueous model systems, distillates of coffee extract and juices such as apple, tomato, pineapple and grape were adsorbed on an ODS column during HPLC and monitoring absorption at 280nm. The adsorbed volatile compounds were eluted with a small volume of ethanol. Volatile compounds in the eluates were concentrated 22 to 100 times those in the distillates. Recovery of compounds was 50–90%. Breakthrough of specific compounds such as -valerolactone, furfuryl acetate and t-2-hexenal in the model systems and several compounds in the juice distillates was detected by capillary GC. Pattern similarity calculated between the GC profiles of a juice distillate and the corresponding eluate gave a qualitative comparison. This novel and versatile method utilizing conventional RP-HPLC may be widely applicable for concentrating volatiles in aqueous systems, at levels from ppm to ppb.     

Development of direct microwave desorption/gas chromatography mass spectrometry system for rapid analysis of volatile components in medicinal plants

A new direct microwave desorption–gas chromatography‐mass spectrometry method was developed for the analysis of the essential oils of medicinal plants. A homemade direct microwave desorption system was fabricated and used for the desorption of volatile components of medicinal herbs. The desorbed volatiles are transferred directly into the gas chromatography injector for analysis in a one‐step process. Approximately 0.3 g of the herb was needed for the desorption of samples in 60 s. In this study, more than 53 volatile compounds were identified and quantified for Echinophora platyloba DC as model herb sample. The results were found to be in good agreement with the conventional hydrodistillation extraction data. The described results show that direct microwave desorption is fast, simple, and easy to automate and requires only a small amount of sample. The results indicate that essential oil components valuable for varietal identification and characteristic of each variety analyzed when direct microwave desorption–gas chromatography‐mass spectrometry was used for analysis.     

Differentiation of the volatile profile of microbiologically contaminated canned tomatoes by dynamic headspace extraction followed by gas chromatography-mass spectrometry analysis

The aromatic profile of microbiologically contaminated canned tomatoes was analyzed by the dynamic headspace extraction technique coupled with gas chromatography-mass spectrometry. Canned tomatoes contaminated with Escherichia coli, Saccharomyces cerevisiae and Aspergillus carbonarius were analyzed after 2 and 7 days. About 100 volatiles were detected, among which alcohols, aldehydes and ketones were the most abundant compounds. Gas chromatographic peak areas were used for statistical purposes. First, principal component analysis was carried out in order to visualize data trends and clusters. Then, linear discriminant analysis was performed in order to detect the set of volatile compounds ables to differentiate groups of analyzed samples. Five volatile compounds, i.e. ethanol, β-myrcene, o-methyl styrene, 6-methyl-5-hepten-2-ol and 1-octanol, were found to be able to better discriminate between uncontaminated and contaminated samples. Prediction ability of the calculated model was estimated to be 100% by the “leave-one-out” cross-validation. An electronic nose device was then used to analyze the same contaminated and not contaminated canned tomato samples. Preliminary results were compared with those obtained by dynamic headspace gas chromatography-mass spectrometry, showing a good agreement.     

SPME Analysis of Potential Attractants for Palm Weevils

Abstract

Solid-phase microextraction was applied for the analysis of a mixture of potential attractants for palm weevils, constituted by seven organic compounds. Various fibers, coated with different sorbent phases, were used in this study and the best results were obtained with the polydimethylsiloxane (PDMS)/divinylbenzene (DVB) and the Carboxen/PDMS fibers. A waiting time of 5 min before sampling was adequate for sample homogenisation and a sampling time of 30 min was used to obtain good extraction efficiencies. A complete desorption of the analytes into the injection port of the gas chromatograph was achieved with an injection time of 1 min. The detection limit of the method ranged from 0.29 to 156 ng/ml for the different components of the mixture, with a lower detection limit for the compounds with higher affinity for the fiber coating. This method was used in the analysis of volatiles released from a diffuser filled with the attractant mixture.     

Analysis of the volatile components of cheddar cheese by direct thermal desorption-GC x GC-TOF/MS

Volatile compounds were isolated from Cheddar cheese using direct thermal desorption (DTD) and analysed using comprehensive 2-D GC (GC x GC) coupled with TOF MS (TOF/MS). In total 12 aldehydes, 13 acids, 13 ketones, 5 alcohols, 3 hydrocarbons and 9 miscellaneous compounds were identified at desorption temperatures of 100, 150, 200 and 250 degrees C using mature Cheddar cheese. A temperature of 150 degrees C was found to be optimum for the DTD of volatiles from mature Cheddar cheese. The major components were acetic acid, butanoic acid, 3-hydroxy-2-butanone and 2,3-butanediol. A DTD temperature of 150 degrees C was used to observe the effect of maturation (mild, medium or mature) on the volatiles of Cheddar cheese. The major components of the volatiles of mild, medium and mature Cheddar cheese were almost the same. However, their percentage compositions were found to change with the stage of maturity. DTD is simple, fast and requires only a small amount of sample (approximately 10 mg) and works well with comprehensive GC x GC-TOF/MS. Comprehensive GC also separated a number of components which remained overlapped on the single column, such as octane and hexanal.     

Direct osmotic concentration of tomato juice in tubular membrane – module configuration. II. The effect of using clarified tomato juice on the process performance

A study was carried out by using a new tubular direct osmosis module, constructed by PCI UK and equipped with a novel AFC99 membrane 400 μm thick, to investigate the effect of clarifying tomato juice on the rate of direct osmotic concentration. Under virtually the same operating conditions five respective clarifications of juice were tried including full, unclarified, tomato juice. The process performance was calculated in terms of permeation flux. In all the experimental runs the osmotic medium was sodium chloride brine (initial concentration approx. 23% NaCl). A remarkable increase of permeation flux (over 100%) was observed shifting from unclarified to the clarified tomato juice. Clarification was carried out by passing the juice through 35 μm mesh and also by using membranes of molecular weight cut-off 200 000, 100 000 and 25 000 Daltons (Da), respectively, in order to obtain the juice ultrafiltrates. It is also worth mentioning that the flux value obtained with 25 000 Daltons (Da) ultrafiltrate appeared to be considerably higher than values reported in experiments carried out by other researchers, where unclarified juice was used, despite the disadvantage of a far thicker membrane being used in the present investigation. This specific finding discloses great potential in using a combined low temperature and pressure ultrafiltration and direct osmosis process to produce tomato concentrates.     

固相微萃取-气相色谱-质谱联用结合嗅觉检测法鉴定血橙汁中的香气活性化合物

采用固相微萃取-气相色谱-质谱法(SPME-GC-MS)和嗅觉检测法对血橙汁中的挥发性物质进行分析,确定了血橙汁中的香气活性化合物。采用二乙烯基苯/碳分子筛/聚二甲基硅氧烷共聚物(DVB/CAR/PDMS)萃取头在40 ℃条件下顶空萃取40 min。通过气相色谱-质谱联用结合保留指数,在所萃取的血橙汁的挥发性化合物中共鉴定出46种化合物。通过嗅觉检测法检测出34种具有气味的化合物,其中23种被定性。结果表明,对血橙汁香气起主要贡献的化合物是丁酸乙酯、辛醛、γ-松油烯、芳樟醇、4-乙酰基-1-甲基环己烯、癸醛、(-)-香芹酮、乙酸香叶酯、巴伦西亚桔烯以及保留指数分别为1020,1143,1169和小于800的4个未知化合物,这些香气强度较高的化合物的总相对含量为7.22%。     

Rapid determination of C6-aldehydes in tomato plant emission by gas chromatography-mass spectrometry and solid-phase microextraction with on-fiber derivatization

A simple, rapid, sensitive, and solvent-free method was developed for determination of plant-signalling compounds, the three C6-aldehydes hexanal, (Z)-3-hexenal, and (E)-2-hexenal, in tomato plant emission by gas chromatography-mass spectrometry (GC-MS) and solid-phase microextraction (SPME) with on-fiber derivatization. In this method, O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) in aqueous solution was first headspace adsorbed onto a 65 microm poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber at 25 degrees C for 5 min, and then the fiber with adsorbed PFBHA was used for headspace extraction of tomato plant emission at 25 degrees C for 6 min. Finally, the resulting oximes adsorbed on the fiber were desorbed and analyzed by GC-MS. Extraction conditions and method validation were studied. The proposed method had low detection limit values for the three aldehydes from 0.1 to 0.5 ng/L and good precision (RSD less than 10%). In this work, the method was applied to investigation of tomato plant defense response to Helicoverpa armigera.     

Headspace methods for volatile components of grapefruit juice

Summary Static headspace, dynamic headspace (DHS) and strip/trap methods were evaluated with grapefruit juice volatiles and an aqueous model system of selected grapefruit volatile flavour components, to select the best method for the isolation of volatile components for subsequent GC analysis.Recoveries were calculated for these methods in the concentration range 0.01–10gml^–1 and compared. Analyte trapping followed by thermal desorption was performed with Tenax TA traps which gave good results in terms of very low blanks. DHS analysis gave the best results in terms of recovery efficiency and, if adequately combined with a simultaneous steam distillation/solvent extraction method, is the most suitable for the qualitative and quantitative investigation of grapefruit juice volatiles, and it might be extended to other fruit juices or liquid foods.     

Exploring the Volatiles Released from Roots of Wild and Domesticated Tomato Plants under Insect Attack

Plants produce volatile organic compounds that are important in communication and defense. While studies have largely focused on volatiles emitted from aboveground plant parts upon exposure to biotic or abiotic stresses, volatile emissions from roots upon aboveground stress are less studied. Here, we investigated if tomato plants under insect herbivore attack exhibited a different root volatilome than non-stressed plants, and whether this was influenced by the plant’s genetic background. To this end, we analyzed one domesticated and one wild tomato species, i.e., Solanum lycopersicum cv Moneymaker and Solanum pimpinellifolium, respectively, exposed to leaf herbivory by the insect Spodoptera exigua. Root volatiles were trapped with two sorbent materials, HiSorb and PDMS, at 24 h after exposure to insect stress. Our results revealed that differences in root volatilome were species-, stress-, and material-dependent. Upon leaf herbivory, the domesticated and wild tomato species showed different root volatile profiles. The wild species presented the largest change in root volatile compounds with an overall reduction in monoterpene emission under stress. Similarly, the domesticated species presented a slight reduction in monoterpene emission and an increased production of fatty-acid-derived volatiles under stress. Volatile profiles differed between the two sorbent materials, and both were required to obtain a more comprehensive characterization of the root volatilome. Collectively, these results provide a strong basis to further unravel the impact of herbivory stress on systemic volatile emissions.     

Rapid determination of volatile compounds in grapes by HS-SPME coupled with GC-MS

Volatile compounds of grapes are responsible of varietal aroma. At the moment, methods used for analysis of these compounds are solvent-based, time-consuming and generally require large amounts of sample. In order to obtain an appropriate technique to study grape volatile compounds, HS-SPME method has been developed. The optimal sampling conditions were: 70 °C for 20 min with a 65-μm PDMS/DVB fibre. Sixteen volatile compounds have been quantified in pulp and skins of Muscat grapes. Terpenes, mainly linalool, geraniol and nerol, have been the volatiles present in the highest concentration, since these compounds contribute, to a larger extent, to the aroma of Muscat grapes and wines. So the proposed technique can be used for the characterisation of grape varieties or cultivars and for the determination of the aromatic maturity of grapes.     

Free Amino Acids and Volatile Aroma Compounds in Watermelon Rind,Flesh, and Three Rind-Flesh Juices

Watermelon rind is treated as agricultural waste, causing biomass loss and environmental issues. This study aimed to identify free amino acids and volatiles in watermelon rind, flesh, and rind-flesh juice blends with ratios of 10%, 20%, and 30%. Among the 16 free amino acids quantified, watermelon rind alone contained higher total amino acids (165 mg/100 g fresh weight) compared to flesh alone (146 mg/100 g). The rind had significantly higher (1.5×) and dominant amounts of citrulline and arginine (61.4 and 53.8 mg/100 g, respectively) than flesh. The rind, however, contained significantly lower amounts of essential amino acids. Volatile analysis showed that watermelon rind total volatiles (peak area) comprised only 15% of the flesh volatiles. Of the 126 volatiles identified, the rind alone contained 77 compounds; 56 of these presented in all five samples. Aldehydes and alcohols were most prevalent, accounting for >80% of the total volatiles in all samples. Nine-carbon aldehyde and alcohol compounds dominated both the flesh and rind, though the rind lacked the diversity of other aldehydes, alcohols, ketones, terpenes, terpenoids, esters and lactones that were more abundant in the watermelon flesh. Watermelon rind was characterized by the major aroma compounds above their thresholds, including 17 aldehydes and six unsaturated nine-carbon alcohols. This study demonstrated the potential for rind as a food or beverage supplement due to its key features such as concentrated citrulline and arginine, relatively low odor intensity, and valuable volatiles associated with fresh, green, cucumber-like aromas.     

Rapid determination of methyl salicylate, a plant-signaling compound, in tomato leaves by direct sample introduction and thermal desorption followed by GC-MS

Many plants infested by herbivores or viruses can rapidly produce and accumulate a plant-signaling compound, methyl salicylate (MeSA), in their leaves to activate disease resistance. In the present work, a simple, rapid, and sensitive method was developed for the determination of MeSA in tomato leaves by direct sample introduction and thermal desorption followed by GC-MS. Results show that the proposed method has a low detection limit (0.08 ng mg(-1)) and good precision (RSD = 8.9%). The present method was applied to the investigation of tomato plant defense response to tobacco mosaic virus (TMV) by rapid analysis of volatile compounds in plant leaves. It was found that tomato plants can produce large amounts of MeSA as a defense response to TMV. This indicates that MeSA may be a plant-signaling compound in tomato plant defense response to TMV.     

Dynamic headspace enrichment system for CGC analysis of volatiles released by plants

The aim of the present study is to develop a method for following the changes in the chemical composition of volatile substances released by plants. Dynamic headspace enrichment, followed by on-line thermal desorption and cryotrapping was coupled with capillary gas chromatography. The technique was optimized by adjusting the sampling and desorption parameters and by designing a special condensing device to avoid the transfer of excessive amounts of water into the analytical column. Details are given for the characterization of volatiles compounds released by mosses.     

吹扫/捕集-热脱附气质联用法对荷叶挥发油成分的对比分析

采用同时蒸馏萃取提取得到荷叶挥发油, 通过吹扫/捕集-热脱附法(P&T-TD)对上述提取物中挥发性成分进行富集, 以气质联用(GC/MS)进行定性检测, 同时与直接进样GC/MS法分析的成分进行比较. 两种方法成功分离分析出有机酸、酯、醛、醇、酚、烷烃、芳香烃、烯烃以及含氮、硫、氧杂原子的化合物等共计84种成分, 其中P&T-TD GC/MS鉴定出63种有机化合物, GC/MS鉴定出41种有机化合物, 有20种成分共同检出. 对比分析表明: P&T-TD GC/MS的吹扫/捕集-热脱附过程能富集各种组分, 相比GC/MS分析, 可以鉴定出微量成分及更多挥发性和半挥发性成分, 在精油等挥发性成分的分析检测中使用优势明显.     

Determination of endosulfan isomers and endosulfan sulfate in tomato juice by matrix solid-phase dispersion and gas chromatography

A rapid method based on matrix solid-phase dispersion was developed for the determination of endosulfan isomers and endosulfan sulfate in commercial tomato juice. After the optimisation of different parameters such as the type of adsorbent, the extraction solvent, and the extraction assistance by sonication, the recoveries obtained ranged from 81 to 100% with relative standard deviations equal to or lower than 10%. The analysis of samples was accomplished using gas chromatography with electron-capture detection and the identity of endosulfan residues was confirmed by gas chromatography-mass spectrometry with selected ion monitoring. The detection limit for these compounds, calculated as three times the background noise, was 1 microg/kg. The proposed method was applied to the analysis of these compounds in commercial juice samples and levels of endosulfan between 1 and 5 microg/kg were detected in some samples.     

Characterization of the Influence of Thermal Sterilization on the Volatiles in Flat Peach Juice

This study characterized the effect of thermal sterilization on the volatiles in flat peach juice. In three independent trials, juice samples prepared with flat peaches from Shihezi, Xinjiang, China were divided into groups sterilized at 65, 75, and 85°C for 30?min. The chemical compositions were identified by gas chromatography–mass spectrometry combined with headspace solid-phase microextraction and analyzed by hierarchical clustering and principal component analysis. Fourteen volatiles (seven esters, four alcohols, two aldehydes, and one ketone) were identified as characteristic in fresh peach juice. Esters of thermally treated samples were significantly decreased by threefold (P?相似文献   

A preliminary study of plant aroma profile characteristics by a combination sampling method coupled with GC-MS

Plant aroma profile characteristic is an important bio-information. In this study, a sampling method in combination with headspace solid phase microextraction (HSSPME), simultaneous distillation extraction (SDE) and steam distillation (SD), followed by gas chromatography-mass spectrometry (GC-MS) detection, was used to study the aroma profile characteristics of the fresh and stale samples of common tomato, cherry tomato, durian and longan, and of the different samples of Chinese mango and Allium varieties. The typical aroma volatiles of these samples were isolated and identified according to the different degrees of certainty. The different samples showed different aroma profile characteristics when principal component analysis (PCA) was conducted to analyze the data of the aroma profile chromatograms. Then the crucial aroma volatiles contributing greatly to the clustering differences of the aroma profile characteristics of the fresh and stale common tomato, cherry tomato, durian and longan were identified by common model strategy. These compounds are potential bio-markers of plant metabolism, but further study is needed. Continuous investigations for the aroma profile characteristics of common tomato during storage and chive during growth were conducted to distill the potential bio-information from the plant metabolism processes. The saturated hexanal of common tomato increased during storage, whereas the unsaturated hexenal reduced. The accumulating trends of volatile sulfides were observed during chive growth. The preliminary results related with the corresponding bio-information could provide helpful clues to the study of plant's secondary metabolism process and benefit quality control.     

PVC photo-oxidative degradation: Identification of volatiles

Volatile products present in poly(vinyl chloride), PVC, after outdoor weathering have been compared with volatiles from laboratory, UV exposed PVC surfaces. Compounds both present in the photo-degraded polymer surface layer and directly emitted from the polymer were measured in the laboratory experiments. The hydrocarbons, oxygenated compounds and chloro-organic species were measured and identified by capillary gas chromatography with a mass spectrometer detector.     

The ability of spectrum autocorrelation models to predict the lycopene concentration in foods through visible spectroscopic data

We developed a novel computerized approach based on lag-k autocorrelation coefficients (LCCs) and linear models (LMs) to estimate the concentration of lycopene in foods by the spectroscopy. The LCCs were calculated using the data obtained using whole visible scans from 400 to 600 nm (vide supra) of lycopene standards and food samples (ketchup, tomato juice and tomato sauce). The chaotic parameter (CP) was then transferred into a LM to estimate the concentration of lycopene compound. The integrated LCC/visible spectroscopy method developed can be considered as a satisfactory analytical technique able to estimate lycopene concentration in food samples in a fast accurate way, with a mean prediction error lower than 5.7% and a mean correlation coefficient higher than 0.957.