Volatile sampling by headspace techniques

Aroma determination in alcoholic beverages: Green MS-based sample preparation approaches

Aroma determination in alcoholic beverages has become a hot research topic due to the ongoing effort to obtain quality products, especially in a globalized market. Consumer satisfaction is mainly achieved by balancing several aroma compounds, which are mixtures of numerous volatile molecules enclosed in challenging matrices. Thus, sample preparation strategies for quality control and product development are required. They involve several steps including copious amounts of hazardous solvents or time-consuming procedures. This is bucking the trend of the ever-increasing pressure to reduce the environmental impact of analytical chemistry processes. Hence, the evolution of sample preparation procedures has directed towards miniaturized techniques to decrease or avoid the use of hazardous solvents and integrating sampling, extraction, and enrichment of the targeted analytes in fewer steps. Mass spectrometry coupled to gas or liquid chromatography is particularly well suited to address the complexity of these matrices. This review surveys advancements of green miniaturized techniques coupled to mass spectrometry applied on all categories of odor-active molecules in the most consumed alcoholic beverages: beer, wine, and spirits. The targeted literature consider progresses over the past 20 years.

Chromatographic Methods and Sample Pretreatment Techniques for Aldehydes, Biogenic Amine, and Carboxylic Acids in Food Samples

This review paper critically examines the current state of research concerning the analysis and derivatization of aldehyde, aromatic hydrocarbons and carboxylic acids components in foods and drinks samples, with a specific focus on the application of Chromatographic techniques. These diverse components, as vital contributors to the sensory attributes of food, necessitate accurate and sensitive analytical methods for their identification and quantification, which is crucial for ensuring food safety and compliance with regulatory standards. In this paper, High-Performance Liquid Chromatography (HPLC) and Gas Chromatographic (GC) methods for the separation, identification, and quantification of aldehydes in complex food matrices were reviewed. In addition, the review explores derivatization strategies employed to enhance the detectability and stability of aldehydes during chromatographic analysis. Derivatization methods, when applied judiciously, improve separation efficiency and increase detection sensitivity, thereby ensuring a more accurate and reliable quantification of aldehyde aromatic hydrocarbons and carboxylic acids species in food samples. Furthermore, methodological aspects encompassing sample preparation, chromatographic separation, and derivatization techniques are discussed. Validation was carried out in term of limit of detections are highlighted as crucial elements in achieving accurate quantification of compounds content. The discussion presented by emphasizing the significance of the combined HPLC and GC chromatography methods, along with derivatization strategies, in advancing the analytical capabilities within the realm of food science.

Development of a Novel HS-GC/MS Method Using the Total Ion Spectra Combined with Machine Learning for the Intelligent and Automatic Evaluation of Food-Grade Paraffin Wax Odor Level

The intensity of the odor in food-grade paraffin waxes is a pivotal quality characteristic, with odor panel ratings currently serving as the primary criterion for its assessment. This study presents an innovative method for assessing odor intensity in food-grade paraffin waxes, employing headspace gas chromatography with mass spectrometry (HS/GC-MS) and integrating total ion spectra with advanced machine learning (ML) algorithms for enhanced detection and quantification. Optimization was conducted using Box-Behnken design and response surface methodology, ensuring precision with coefficients of variance below 9%. Analytical techniques, including hierarchical cluster analysis (HCA) and principal component analysis (PCA), efficiently categorized samples by odor intensity. The Gaussian support vector machine (SVM), random forest, partial least squares regression, and support vector regression (SVR) algorithms were evaluated for their efficacy in odor grade classification and quantification. Gaussian SVM emerged as superior in classification tasks, achieving 100% accuracy, while Gaussian SVR excelled in quantifying odor levels, with a coefficient of determination (R2) of 0.9667 and a root mean square error (RMSE) of 6.789. This approach offers a fast, reliable, robust, objective, and reproducible alternative to the current ASTM sensory panel assessments, leveraging the analytical capabilities of HS-GC/MS and the predictive power of ML for quality control in the petrochemical sector's food-grade paraffin waxes.

From inspection to analysis: A combined approach to identifying counterfeit whiskeys using HS-GC-FID and bottle integrity

Counterfeiting of alcoholic beverages, particularly high-value spirits such as whiskey, presents significant challenges for regulators, manufacturers, and consumers. In this study, we introduce and validate a novel application of headspace extraction (HS) followed by gas chromatography with flame ionization detection (GC-FID) for the quantitative determination of ethanol content in 42 suspected counterfeit brazilian samples of whiskeys. This method, in conjunction with visual inspection of material inconsistencies, offers a combined approach to identify potential cases of fraud. The HS-GC-FID findings revealed that only 19% of the analyzed samples had ethanol content in the limits declared on the label, emphasizing the role of ethanol content as a chemical marker for suspected beverage fraud.

Analyzing Alkyl Bromide Genotoxic Impurities in Febuxostat Based on Static Headspace Sampling and GC-ECD

Herein, a sensitive and selective gas chromatography-electron capture detector (GC-ECD) method was developed and validated for the quantification of trace levels of five bromo-containing genotoxic impurities in Febuxostat active pharmaceutical ingredient (API) after headspace sampling (HS). Multivariate experimental designs for the optimization of static headspace parameters were conducted in two stages using fractional factorial design (FFD) and central composite design (CCD). The optimum headspace conditions were 5 min of extraction time and a 120 °C extraction temperature. Baseline separation on the analytes against halogenated solvents was carried out using an Agilent DB-624 (30 m × 0.32 mm I.D., 1.8 μm film thickness) stationary phase under isothermal conditions. The method was validated according to ICH guidelines in terms of specificity, linearity, the limits of detection and quantification, precision and accuracy. The linearity was assessed in the range of 5-150% with respect to the specification limit. The achieved LOD and LOQ values ranged between 0.003 and 0.009 and 0.01 and 0.03 μg mL-1, respectively. The accuracy of the method (expressed as relative recovery) was in the range of 81.5-118.2%, while the precision (repeatability, inter-day) was less than 9.9% in all cases. The validated analytical protocol has been successfully applied to the determination of the impurities in various Febuxostat API batch samples.

Automated, cryogen-free headspace-trap with gas chromatography-mass spectrometry analysis of ethylene oxide and 2-chloroethanol as residual fumigants in foods

Ethylene oxide (EtO), although banned for use, is still being detected in foodstuffs that have been fumigated to eradicate pests during storage and transport. Residual levels over the European Union's (EU) maximum residue limit (MRL) pose severe health concerns. Recent detection of EtO and its by-product 2-chloroethanol (2-CE) at alarming levels have led to product recalls throughout the EU. Here, a simple, automated headspace (HS)-trap method for the simultaneous determination of EtO and its derivative 2-CE by gas chromatography-mass spectrometry (GC-MS) at the required MRL of ≤ 0.05 mg/kg has been implemented. Syringe-based HS combined with backflushed trapping technology provided enrichment of multiple extractions from the same sample vial (known as multi-step enrichment or MSE®) to increase sensitivity for EtO and 2-CE analysis by GC-MS using single-ion-monitoring (SIM) mode. Method detection limits (MDLs) of 0.00059 mg/kg and 0.00219 mg/kg for EtO and 2-CE, respectively, were obtained without the need for manual handling, solvent extraction or derivatization methods. Recoveries were shown to average (n = 5) at 98% and 107% for EtO and 2-CE, respectively, and the reproducibility was <10% for both compounds.

Assessment of greenhouse emissions of the green bean through the static enclosure technique

Urban green installations are extensively promoted to increase sustainable and accessible food production and simultaneously improve the environmental performance and liveability of city buildings. In addition to the multiple benefits of plant retrofitting, these installations may lead to a consistent increase in biogenic volatile organic compounds (BVOCs) in the urban environment, especially indoors. Accordingly, health concerns could limit the implementation of building-integrated agriculture. In a building-integrated rooftop greenhouse (i-RTG), throughout the whole hydroponic cycle, green bean emissions were dynamically collected in a static enclosure. Four representative BVOCs, α-pinene (monoterpene), β-caryophyllene (sesquiterpene), linalool (oxygenated monoterpene) and cis-3-hexenol (LOX derivate), were investigated in the samples collected from two equivalent sections of a static enclosure, one empty and one occupied by the i-RTG plants, to estimate the volatile emission factor (EF). Throughout the season, extremely variable BVOC levels between 0.04 and 5.36 ppb were found with occasional but not significant (P > 0.05) variations between the two sections. The highest emission rates were observed during plant vegetative development, with EFs equivalent to 78.97, 75.85 and 51.34 ng g^-1 h^-1 for cis-3-hexenol, α-pinene, and linalool, respectively; at plant maturity, all volatiles were either close to the LLOQ (lowest limit of quantitation) or not detected. Consistent with previous studies significant relationships (r ≥ 0.92; P < 0.05) were individuated within volatiles and temperature and relative humidity of the sections. However, correlations were all negative and were mainly attributed to the relevant effect of the enclosure on the final sampling conditions. Overall, levels found were at least 15 folds lower than the given Risk and LCI values of the EU-LCI protocol for indoor environments, suggesting low BVOC exposure in the i-RTG. Statistical outcomes demonstrated the applicability of the static enclosure technique for fast BVOC emissions survey inside green retrofitted spaces. However, providing high sampling performance over entire BVOCs collection is recommended to reduce sampling error and incorrect estimation of the emissions.

Balanced extraction of volatile and semi-volatile compounds by dynamic linked position unity solid-phase microextraction

Although the compound profiles in extracts are linked to the solid-phase microextraction (SPME) position (headspace or liquid), a theoretical interpretation of this scenario has not yet been provided. In this study, the dynamic linked position unity (DLPU)-SPME is proposed as a method that allows balanced extraction of volatile and semi-volatile compounds. Furthermore, the pH, temperature, and salt were confirmed as the key factors affecting the extraction efficiency of DLPU-SPME. Theoretical calculations indicated that K_fs⁰K_fs is a key factor directly indicating the SPME extraction position (K_fs⁰K_fs > 1, headspace; K_fs⁰K_fs = 1, any position; K_fs⁰K_fs < 1, in liquid), while the target analytes determined that V_hK_hs+V_sV_eK_fhK_hs regulates the effect of the extraction position on the extracted amount. The proposed DLPU-SPME method containing both extraction positions (i.e., headspace and liquid) can simultaneously extract volatile and semi-volatile compounds, thus avoiding extraction bias.

Dynamic headspace solid-phase extraction at room temperature: a theoretical model, method, and application for propofol analysis

Herein, a simple dynamic headspace solid-phase extraction (DHS-SPE) process at room temperature was used for a material that is sensitive to increase in the temperature. A proposed method was implemented to rapidly extract propofol (PF) from a complex matrix before fluorescence spectroscopy analysis, within a short sampling time without involving a hot plate or stirrer. A mini diaphragm pump was used to circulate the headspace gas. As the headspace gas flows over the sample solution surface, bubbles form and release analytes from the liquid into the headspace. During the extraction process, the headspace gas passes through the coated metal foam as a sorbent that is placed in a homemade glass vessel and analytes are trapped from the gas phase. A theoretical model of DHS-SPE based on the consecutive first-order process is proposed in this study. A mathematical solution for the dynamic process of mass transfer was obtained by correlating the variation in analyte concentration in the headspace and adsorber with the pump speed and amount of analyte extracted to the solid phase. Using electrochemically Nafion-doped polypyrrole (PPy-Naf) film on nickel foam as the solid-phase coupled to fluorescence detection, a linear dynamic range over the concentration range of 100-500 nM with a detection limit of 15 nM was obtained. This method was applied successfully for PF determination in human serum sample matrices without the interference of co-administered drugs, such as cisatracurium, which have significant emission spectrum overlap. The developed method can lead to a new idea for sample pretreatment, which is compatible with many analytical techniques and has been successfully combined with fluorescence spectroscopy in this work. This format of sampling simplifies the transfer of analytes from complex matrices to the headspace for the extraction and preconcentration process, eliminating the heating step and the need for expensive equipment.

Sampling Volatile Organic Compound Emissions from Consumer Products: A Review

Volatile organic compounds (VOCs) are common constituents of many consumer products. Although many VOCs are generally considered harmless at low concentrations, some compound classes represent substances of concern in relation to human (inhalation) exposure and can elicit adverse health effects, especially when concentrations build up, such as in indoor settings. Determining VOC emissions from consumer products, such as toys, utensils or decorative articles, is of utmost importance to enable the assessment of inhalation exposure under real-world scenarios with respect to consumer safety. Due to the diverse sizes and shapes of such products, as well as their differing uses, a one-size-fits-all approach for measuring VOC emissions is not possible, thus, sampling procedures must be chosen carefully to best suit the sample under investigation. This review outlines the different sampling approaches for characterizing VOC emissions from consumer products, including headspace and emission test chamber methods. The advantages and disadvantages of each sampling technique are discussed in relation to their time and cost efficiency, as well as their suitability to realistically assess VOC inhalation exposures.

Bioprospecting of Essential Oil-Bearing Plants: Rapid Screening of Volatile Organic Compounds Using Headspace Bubble-in-Drop Single-Drop Microextraction for Gas Chromatography Analysis

Essential oils are vital constituents of oil-bearing plants. However, their screening still demands harvesting of the plant for laboratory analysis. We report herein a simple, rapid and robust headspace bubble-in-drop microextraction screening technique (BID-SPME) requiring only small amounts of plant material. The optimised method uses 0.5 g of the crushed plant leaves sample obtained in a 2 mL capped chromatography vial, heated to 55 °C and sampled with 2 µL heptadecane in a Hamilton gastight syringe equilibrated for 15 min exposed to the headspace volume. The method was applied to three plants, Pinus radiata, Tagetes minuta and Artemisia afra, which are known for their essential oil content. The method was able to extract at least 80% of the oil constituents in such abundance that they could be easily annotated using the gas chromatography-mass spectrometry (GC-MS) mass spectral libraries. The major volatile organic compounds (VOCs) detected included tagetone, terpinen-4-ol, ocimenone, caryophyllene, dihydrotagetone, terpinolene and artemisia ketone, just to mention a few, at different concentrations in different plants. Importantly, these annotated VOCs were also reported in other studies in the same and even different plants, extracted using normal steam distillation and importantly those reported in the literature for different extraction techniques.

Volatile organic compounds in aquatic ecosystems - Detection, origin, significance and applications

Volatile organic compounds (VOCs) include a broad range of compounds. Their production influences a large number of processes, having direct and secondary effects on different fields, such as climate change, economy and ecology. Although our planet is primarily covered with water (~70% of the globe surface), the information on aquatic VOCs, compared to the data available for the terrestrial environments, is still limited. Regardless of the difficulty in collecting and analysing data, because of their extreme complexity, diversification and important spatial-temporal emission variation, it was demonstrated that aquatic organisms are able to produce a variety of bioactive compounds. This production happens in response to abiotic and biotic stresses, evidencing the fundamental role of these metabolites, both in terms of composition and amount, in providing important ecological information and possible non-invasive tools to monitor different biological systems. The study of these compounds is an important and productive task with possible and interesting impacts in future practical applications in different fields. This review aims to summarize the knowledge on the aquatic VOCs, the recent advances in understanding their diverse roles and ecological impacts, the generally used methodology for their sampling and analysis, and their enormous potential as non-invasive, non-destructive and financeable affordable real-time biomonitoring tool, both in natural habitats and in controlled industrial situations. Finally, the possible future technical applications, highlighting their economic and social potential, such as the possibility to use VOCs as valuable alternative source of chemicals and as biocontrol and bioregulation agents, are emphasized.

Exploring chemical diversity in Glycine max cultivars: A multivariate approach in the search for bioactive compounds against Spodoptera cosmioides

Soybean crop is regulated by abiotic and biotic stresses with great potential in reducing grain yield and quality. The selection of resistant cultivars is a promising approach for mitigating these damages. We evaluated the chemical profile of Glycine max leaves from different cultivars in order to explore their defense mechanisms against Spodoptera cosmioides caterpillars. We optimized solid-liquid extraction techniques using ultrasound bath and static headspace extraction. Additionally, we developed an approach based on liquid and gas chromatography for analyzing the chemical profile of G. max cultivars. The principal component analysis allowed the classification of transgenic cultivars, which are classified as susceptible to S. cosmioides, from those obtained by genetic improvement and resistant to the insect. Differences were observed in the abundance of phenolic glycosides, lipids, aldehydes, and alcohols. More specifically, S. cosmioides resistant cultivars presented molecules related to the jasmonic and salicylic acid pathways. Such data can contribute to a molecular understanding of phenotypic diversity in soybean cultivars, from plant quality to resistance mechanisms and adaptation, to environmental stress and herbivory.

Traceability of VOCs in tire inner liner by chromatography-mass spectrometry

Many parts of the vehicle cabin generate volatile organic compounds (VOCs), and some are hazardous and/or odorous to humans. In this study, VOCs in the inner liner of automobile spare tire, including raw rubbers and resins, were detected by gas chromatography-mass spectrometry (GC-MS) coupled with an extracting method of static headspace sampling (SHS). The results demonstrated that the sources of VOCs can be traced back to raw rubbers and resins: alkylphenol resins can release a large amount of 2,4,4-trimethyl-1-pentene and 2,2,4,6,6-pentamethyl-3-heptene; chlorobutyl rubber (CIIR) contained 3-methyl-pentane, and methyl-cyclopentane, and these VOCs are odorous. When alkylphenol resin and natural rubber (NR) with low VOCs were used to replace the corresponding resin and NR in the initial formulation, the total volatile organic compounds (TVOCs) in the inner liner could be reduced. We expected that the information gained from this work could provide a basic reference for the manufacture of environmental-friendly tire products.

Chromatographic fingerprint application possibilities in food authentication

The aim of the study was to compare the effectiveness of the use of low-peak chromatographic fingerprints for the differentiation of various food products. Three groups of unprocessed products (mushrooms, hazelnuts and tomatoes), food preparations (bread, dried herbs and tomato juice) and alcoholic beverages (vodka and two types of blended whiskey) were examined. A commercial electronic nose based on ultrafast gas chromatography (acquisition time 90 s) with a flame ionization detector was used for the research. Static headspace was used as a green procedure to extract volatile compounds without modifying the food matrix. Individual extraction conditions were used for each product group. Similarities and differences between profiles were analyzed by simple Principal Components Analysis. The similarity rating was determined using the Euclidean distances. Global model was built for recognition chromatographic fingerprints of food samples. The best recognition results were 100% and 89% for tomato juices, spices, separate champignon elements and hazelnuts. On the other hand, the worst recognition results were 56% and 77% for breads and strong alcoholic beverages.

Behavior Matters-Future Need for Insect Studies on Odor-Mediated Host Plant Recognition with the Aim of Making Use of Allelochemicals for Plant Protection

Allelochemicals, chemical cues that, among other things, mediate insect-plant interactions, such as host plant recognition, have attracted notable interest as tools for ecological control of pest insects. Advances have recently been made in methods for sampling and analyzing volatile compounds and technology for tracking insects in their natural habitat. However, progress in odor-mediated behavioral bioassays of insects has been relatively slow. This perspective highlights this odor-mediated insect behavior, particularly in a natural setting and considering the whole behavioral sequence involved in the host location, which is the key to understanding the mechanisms underlying host plant recognition. There is thus a need to focus on elaborate behavioral bioassays in future studies, particularly if the goal is to use allelochemicals in pest control. Future directions for research are discussed.

Non-Targeted Screening Approaches for Profiling of Volatile Organic Compounds Based on Gas Chromatography-Ion Mobility Spectroscopy (GC-IMS) and Machine Learning

Due to its high sensitivity and resolving power, gas chromatography-ion mobility spectrometry (GC-IMS) is a powerful technique for the separation and sensitive detection of volatile organic compounds. It is a robust and easy-to-handle technique, which has recently gained attention for non-targeted screening (NTS) approaches. In this article, the general working principles of GC-IMS are presented. Next, the workflow for NTS using GC-IMS is described, including data acquisition, data processing and model building, model interpretation and complementary data analysis. A detailed overview of recent studies for NTS using GC-IMS is included, including several examples which have demonstrated GC-IMS to be an effective technique for various classification and quantification tasks. Lastly, a comparison of targeted and non-targeted strategies using GC-IMS are provided, highlighting the potential of GC-IMS in combination with NTS.

Multivariate optimization of dual-sorbent dynamic headspace extraction of volatiles in wine analysis

The main critical point of newly developed miniaturized sample preparation techniques is a limited extraction capacity. Dynamic headspace extraction offers increased volume of sorbent which is commonly used in environmental analysis. Application of two sorbents (Carbopack B/Carbopack X and Tenax® TA) at different extraction temperatures allows enhancing a range of volatile organic compounds available for analysis. Such approach was applied in our research for quantification of volatile organic compounds in botrytized wines with gas chromatography. The central composite design was included to analysis simultaneous effects of incubation time, incubation temperature, purge volume and purge flow. In attempt to properly assess results, the data evaluation involved Pareto charts, surface response methodology and principal component analysis. Multivariate experimental design revealed statistical significance of purge volume and quadratic terms of incubation time and temperature, for response of volatiles. The quantification method with 0.2-2.0 µg/L LOD and 0.5-5.0 µg/L LOQ values, was developed under simultaneously optimized experimental conditions such as a 54 °C incubation temperature, a 20.18 min incubation time, a 344.3 mL purge volume and a 16.0 mL/min purge flow. The increased levels of linalool oxide, ethyl phenylacetate, γ-hexalactone and α-terpineol were observed in the samples, that correlated with botrytized wine technology.

Ethylbenzene and toluene interactions with biochar from municipal solid waste in single and dual systems

The present study investigated adsorptive removal of toluene and ethylbenzene from the aqueous media via using biochar derived from municipal solid waste (termed "MSW-BC") in a single and binary contaminant system at 25-45 °C. The adsorption was evaluated at different pH (3-10), experimental time (up to 24 h), and initial adsorbate concentrations (10-600 μg/L) in single and binary contaminant system. A fixed-bed column experiment was also conducted using MSW-BC (0.25%) and influent concentration of toluene and ethylbenzene (4 mg/L) at 2 mL/min of flow rate. The adsorption of toluene and ethylbenzene on the MSW-BC was mildly dependent on the pH, and the peak adsorption ability (44-47 μg/g) was recorded at a baseline pH of ~8 in mono and dual contaminant system. Langmuir and Hill are the models that match the isotherm results in a single contaminant environment for both toluene (R² of 0.97 and 0.99, respectively) and ethylbenzene (R² of 0.99 and 0.99, respectively) adsorption. In the binary system, the isotherm models matched in the order of Langmuir > Hill > Freundlich for toluene, whereas Hill > Freundlich > Langmuir for ethylbenzene. The adsorption in the batch experiment was likely to take place via cooperative and multilayer adsorption onto MSW-BC involving hydrophobic, π- π and n- π attractions, specific interaction such as hydrogen-π and cation-π interactions, and van der Waals interactions. The thermodynamic results indicate exothermic adsorption occurred by physical attractions between toluene and ethylbenzene, and MSW-BC. The breakthrough behavior of toluene and ethylbenzene was successfully described with Yoon-Nelson and Thomas models. The data demonstrate that the low-cost adsorbent derived from the municipal solid waste can be utilized to remove toluene and ethylbenzene in landfill leachate.

Rapid and sensitive analysis of benzyl isothiocyanate in peel, pulp, and seeds of Carica papaya Linn. by headspace gas chromatography-mass spectrometry

A rapid and sensitive headspace gas chromatography-mass spectrometry (HS-GC–MS) method was established for the determination of benzyl isothiocyanate (BITC) in the peel, pulp, and seeds of Carica papaya Linn. Tween 80 solution with a concentration of 0.002% (w/v) was chosen as a headspace medium for solving the poor solubility of BITC in water without using organic solvents and ensuring high headspace efficiencies. Extraction parameters had been evaluated and optimized by using an orthogonal design with an OA9(34) table. Optimal headspace conditions were obtained when vials were equilibrated at 80 °C for 20 min at a stirring speed of 375 rpm. The calibration curve obtained by using GC–MS was linear in a concentration range of 10–320 ng/mL. The recoveries of peel, pulp, and seeds ranged from 97.3 to 100.6% with RSDs less than 3.0%. The method is simple, rapid, sensitive, and environmentally friendly. It is suitable for analyzing BITC in papaya fruit and is expected to have important application potential in the extraction of water-insoluble volatile components in foods, plants, medicines, and other samples.

Role of lactic acid bacteria in flavor development in traditional Chinese fermented foods: A review

Traditional Chinese fermented foods are favored by consumers due to their unique flavor, texture and nutritional values. A large number of microorganisms participate in the process of fermentation, especially lactic acid bacteria (LAB), which are present in almost all fermented foods and contribute to flavor development. The formation process of flavor is complex and involves the biochemical conversion of various food components. It is very important to fully understand the conversion process to direct the flavor formation in foods. A comprehensive link between the LAB community and the flavor formation in traditional Chinese fermented foods is reviewed. The main mechanisms involved in the flavor formation dominated by LAB are carbohydrate metabolism, proteolysis and amino acid catabolism, and lipolysis and fatty acid metabolism. This review highlights some useful novel approaches for flavor enhancement, including the application of functional starter cultures and metabolic engineering, which may provide significant advances toward improving the flavor of fermented foods for a promising market.

On sample preparation methods for fermented beverage VOCs profiling by GCxGC-TOFMS

INTRODUCTION

Aromas and tastes have crucial influences on the quality of fermented beverages. The determination of aromatic compounds requires global non-targeted profiling of the volatile organic compounds (VOCs) in the beverages. However, experimental VOC profiling result depends on the chosen VOC collection method.

OBJECTIVES

This study aims to observe the impact of using different sample preparation techniques [dynamic headspace (DHS), vortex-assisted liquid-liquid microextraction (VALLME), multiple stir bar sorptive extraction (mSBSE), solid phase extraction (SPE), and solid phase micro-extraction (SPME)] to figure out the most suitable sample preparation protocol for profiling the VOCs from fermented beverages.

METHODS

Five common sample preparation methods were studied with beer, cider, red wine, and white wine samples. After the sample preparation, collected VOCs were analyzed by two-dimensional gas chromatography coupled with time of flight mass spectrometry (GCxGC-TOFMS).

RESULTS

GCxGC oven parameters can be optimized with the Box-Behnken surface response model and response measure on peak dispersion. Due to the unavoidable column and detector saturation during metabolomic analysis, errors may happen during mass spectrum construction. Profiling results obtained with different sample preparation methods show considerable variance. Common findings occupy a small fraction of total annotated VOCs. For known fermentative aromas, best coverage can be reached by using SPME together with SPE for beer, and VALLME for wine and cider.

CONCLUSIONS

GCxGC-TOFMS is a promising tool for non-targeted profiling on VOCs from fermented beverages. However, a proper data processing protocol is lacking for metabolomic analysis. Each sample preparation method has a specific profiling spectrum on VOC profiling. The coverage of the VOC metabolome can be improved by combining complementary methods.

Optimization of Ethanol Detection by Automatic Headspace Method for Cellulose Insulation Aging of Oil-immersed Transformers

The method using ethanol to evaluate the cellulose insulation aging condition of oil-immersed transformers has been proposed. At present, the dominating method for detecting ethanol in insulating oil is to use headspace–gas-chromatography–mass-spectrometry (HS-GC-MS). However, the problem of quantitative inaccuracy will be sometimes encountered in the actual detection process due to improper instrument parameter setting and improper manual operation. In this study, as an aging marker, ethanol in transformer insulating oil was separated by using VF-624 ms capillary column. The effects of gas-chromatography–mass-spectrometry (GC-MS) optimization conditions, headspace equilibrium temperature, headspace equilibrium time and standard solution preparation method on the determination of ethanol content in oil were discussed, and optimized measures were proposed. The experimental results showed that the measurement can be more accurate under the headspace temperature of 80 °C and the headspace time of 40 min, and relative standard deviation percentage (RSD%) could reach to 4.62% under this condition. It was also pointed out that, for the preparation of standard solution, the method which controlled the sampling volume of anhydrous ethanol by microliter syringe could make the peak area of ethanol chromatogram have a better linear relationship with the standard curve. Under the similar linear range, the goodness of fitting curve without diluting process could be as high as 0.9993, while the method of preparing the stock solution and diluting stepwise to obtain the fitting curve only had a goodness of 0.9910. The method was validated by standard addition recovery test, and the recovery values obtained were between 90.3% and 95.8%. The optimized method is of great significance for the measurement of ethanol dissolved in insulating oil.

Metabolomic study of volatile compounds emitted by lavender grown under open-field conditions: a potential approach to investigate the yellow decline disease

INTRODUCTION

Fine lavender and lavandin are perfume and medicinal plants originate from the South of France and are widely cultivated for their essential oils. Recently, cultivated plants suffered from a severe decline in France, due to the propagation of the yellow decline disease. This disease is caused by the stolbur phytoplasma, a bacterium transmitted by a sap-sucking insect, the planthopper.

OBJECTIVES

In order to understand the complex relationships between host plant, pest, pathogen and environment responsible for the yellow decline of lavender, we use a metabolomic approach to highlight changes in chemical emissions from asymptomatic ("healthy") and symptomatic ("infected") plants.

METHODS

Volatile compounds produced by fine lavender and lavandin were collected in the field using a dynamic headspace extraction approach. Afterwards, compounds trapped on Tenax adsorbent were thermodesorbed and analysed using an automated thermal desorption-gas chromatography-mass spectrometry (ATD-GC-MS). Multivariate statistical analyses was performed using principal component analysis and partial least square discriminant analyses.

RESULTS

The untargeted screening of volatiles allowed the separation of asymptomatic and symptomatic plants according to their emissions. The approach was sufficiently accurate so as to separate the emissions according to the different stages of infection. Twelve compounds were found to be deregulated metabolites of yellow disease infection, common to fine lavender (variety 7713) and lavandin (variety abrial).

CONCLUSION

The metabolomic approach allowed for the effective identification of chemical variations between infected and healthy plants in a complex field environment.

Multiple headspace sampling coupled to a programmed temperature vaporizer to improve sensitivity in headspace-gas chromatography. Determination of aldehydes

The improvement of sensitivity in headspace (HS) sampling of not very volatile analytes constitutes a challenge that has usually been approached through coupling with additional techniques. Here we propose a new methodology for increasing sensitivity through a multistep approach. This proof of concept is based on direct coupling of a headspace sampler with a programmed temperature vaporizer (PTV) and a gas chromatograph (GC), with mass spectrometry (MS) detection. Analytes are extracted from the same vial in a stepwise procedure, splitting the headspace generation time of conventional HS into four periods and using the PTV to cryogenically trap the analytes during the successive HS samplings. Solvent vent mode is mandatory in order to retain the analytes, purging the gas solvent at an adequate initial low temperature and flash-heating the PTV liner in a quick ramp (720 °C/min), once the HS samplings are finished. Linear aldehydes, from pentanal to decanal, possible biomarkers of several diseases have been selected as model compounds. This multiple HS method has been compared with conventional HS, and it has been validated in terms of linearity, limits of detection, repeatability, reproducibility and accuracy. The limits of detection (LOD) ranged from 0.004 to 0.159 µg/L. Enrichment factors (EF) in relation to the conventional HS method ranged from 3.0 to 6.7, except for pentanal (EF: 0.8), which is too volatile and polar to be trapped in the PTV with the multiple HS methodology. Similar enrichment factors were obtained in a urine sample.

Dissolved Gas Analysis Equipment for Online Monitoring of Transformer Oil: A Review

Power transformers are the most important assets of electric power substations. The reliability in the operation of electric power transmission and distribution is due to the correct operation and maintenance of power transformers. The parameters that are most used to assess the health status of power transformers are dissolved gas analysis (DGA), oil quality analysis (OQA) and content of furfuraldehydes (FFA) in oil. The parameter that currently allows for simple online monitoring in an energized transformer is the DGA. Although most of the DGA continues to be done in the laboratory, the trend is online DGA monitoring, since it allows for detection or diagnosis of the faults throughout the life of the power transformers. This study presents a review of the main DGA monitors, single- or multi-gas, their most important specifications, accuracy, repeatability and measurement range, the types of installation, valve or closed loop, and number of analogue inputs and outputs. This review shows the differences between the main existing DGA monitors and aims to help in the selection of the most suitable DGA monitoring approach according to the needs of each case.

Novel sample preparation approaches in gas chromatographic analysis: Promising ideas

The development of sample preparation procedures is still a dynamic process despite a number of already proposed techniques. The main challenge in this research field is to fully replace classical procedures like liquid-liquid extraction and solid-phase extraction in gas chromatographic analysis. Some progress has been already achieved for the last 20 years when miniaturized techniques were incorporated in ISO standards. The current review is focused on novel approaches in sample treatment that appeared since 2010. It includes research studies describing non-conventional instrumental design available to inspire future progress in the field. A combination of a few extraction principles and supporting with additional treatment are the main core suggested for improvement of sample preparation efficiency. This requires good compatibility of extraction media, assessment of multiple experimental parameters, and potential automatization possibilities.

Simultaneous determination of aromatic and chlorinated compounds in urine of exposed workers by dynamic headspace and gas chromatography coupled to mass spectrometry (dHS-GC-MS)

Mixed exposure to chemical products is a topical issue for occupational health and often includes exposure to volatile organic compounds (VOCs). As very few methods are available for evaluating these mixed exposures, the aim of this work was to develop a simple biomonitoring method to assess simultaneous occupational exposures to chlorinated and aromatic VOCs by analyzing the unmetabolized fraction of the VOCs in the urine of workers. Volatile organic compounds were analyzed using dynamic headspace gas chromatography coupled to mass spectrometry (dHS-GC-MS), and 11 unmetabolized urinary VOCs were measured into headspace phase, without any time-consuming pretreatment. Simultaneously, a standardized collection protocol was designed to avoid VOC losses or the contamination of urinary samples. The calibration samples were real urines, spiked with known amounts of the VOC mixtures studied. Test investigations were performed on potentially exposed workers in three factories in order to assess the effectiveness of both the collection protocol and analytical method. A satisfactory level of sensitivity was achieved, with limits of quantification (LOQ) between 10 and 15 ng/L obtained for all VOCs (except for styrene at 50 ng/L). Calibration curves were linear in the 0-20 μg/L range tested, with R² correlation coefficients of 0.991 to 0.998. At the lowest concentration tested (0.08 μg/L), within-day precision varied from 2.1 to 5.5% and between-day precision ranged from 2.7 to 8.5%. Sample stability at -20 °C required that urinary samples be analyzed within 3 months. Even though the urinary concentrations of VOCs used in the plants were mostly quite low, significant differences between post-shift and pre-shift were observed. In conclusion, a fast, sensitive, specific and easy-to-use method has been developed for extracting VOCs from human urine using dHS-GC-MS. The method described has proven to be reliable for assessing current occupational exposure to chlorinated and aromatic VOCs in France.

Dynamic headspace analysis using online measurements: Modeling of average and initial concentration

Dynamic headspace sampling is an important technique for the analysis of consumer products, the study of biological samples and environmental water analyses. This paper shows the influence of experimental conditions, such as the sampling time, sampling flow rate, headspace volume, liquid volume and Henry coefficient on the measured average concentration values. A corresponding closed expression as function of these variables is introduced in order to quantify the deviation of the initial headspace concentration. The proposed bi-exponential function embeds different current existing models for recovery calculation in dynamic sampling analyses in one single expression. A fully automated and user-friendly Excel^® file to investigate or to model the dynamic headspace sampling results is added to everyone's easy use.

Aroma Profile Analyses of Filamentous Fungi Cultivated on Solid Substrates

Filamentous fungi have been used since centuries in the production of food by means of solid substrate fermentation (SSF). The most applied SSF involving fungi is the cultivation of mushrooms, e.g., on tree stumps or sawdust, for human consumption. However, filamentous fungi are also key players during manufacturing of several processed foods, like mold cheese, tempeh, soy sauce, and sake. In addition to their nutritive values, these foods are widely consumed due to their pleasant flavors. Based on the potentials of filamentous fungi to grow on solid substrates and to produce valuable aroma compounds, in recent decades, several studies concentrated on the production of aroma compounds with SSF, turning cheap agricultural wastes into valuable flavors. In this review, we focus on the presentation of common analytical methods for volatile substances and highlight various applications of SSF of filamentous fungi dealing with the production of aroma compounds. Graphical Abstract.

Identification of VOCs from natural rubber by different headspace techniques coupled using GC-MS

Different extraction procedures were evaluated to assess their potential for measuring volatile organic compounds (VOCs) from raw rubber materials. Four headspace sampling techniques (SHS, DHS, HS-SPME and µ-CTE) were studied. Each method was firstly optimised to ensure their reliability in performance. Passive sampling was also compared as a rapid identification of background VOCs. 352 VOCs were identified, 71 from passive sampling and 281 from active headspace sampling, with 62 not previously reported (hexanenitrile, octanone, decanal, indole, aniline, anisole, alpha-pinene as well as pentanol and butanol). The volatiles belonged to a broad range of chemical classes (ketones, aldehydes, aromatics, acids, alkanes, alcohol and cyclic) with their thermal effects (lower boiling points) greatly affecting their abundance at a higher temperature. Micro-chamber (µ-CTE) was found to be the most suitability for routine assessments due to its operational efficiency (rapidity, simplicity and repeatability), identifying 115 compounds from both temperatures (30 °C and 60 °C). Whereas, HS-SPME a widely applied headspace technique, only identified 75 compounds and DHS identified 74 VOCs and SHS only 17 VOCs. Regardless of the extraction technique, the highest extraction efficiency corresponded to aromatics and acids, and the lowest compound extraction were aldehyde and hydrocarbon. The interaction between techniques and temperature for all chemical groups were evaluated using two-way ANOVA (p-value is 0.000197) explaining the highly significant interactions between factors.

Lab-In-Syringe automation of stirring-assisted room-temperature headspace extraction coupled online to gas chromatography with flame ionization detection for determination of benzene, toluene, ethylbenzene, and xylenes in surface waters

Online coupling of Lab-In-Syringe automated headspace extraction to gas chromatography has been studied. The developed methodology was successfully applied to surface water analysis using benzene, toluene, ethylbenzene, and xylenes as model analytes. The extraction system consisted of an automatic syringe pump with a 5 mL syringe into which all solutions and air for headspace formation were aspirated. The syringe piston featured a longitudinal channel, which allowed connecting the syringe void directly to a gas chromatograph with flame ionization detector via a transfer capillary. Gas injection was achieved via opening a computer-controlled pinch valve and compressing the headspace, upon which separation was initialized. Extractions were performed at room temperature; yet sensitivity comparable to previous work was obtained by high headspace to sample ratio V_HS/V_Sample of 1.6:1 and injection of about 77% of the headspace. Assistance by in-syringe magnetic stirring yielded an about threefold increase in extraction efficiency. Interferences were compensated by using chlorobenzene as an internal standard. Syringe cleaning and extraction lasting over 10 min was carried out in parallel to the chromatographic run enabling a time of analysis of <19 min. Excellent peak area repeatabilities with RSD of <4% when omitting and <2% RSD when using internal standard corrections on 100 μg L^-1 level were achieved. An average recovery of 97.7% and limit of detection of 1-2 μg L^-1 were obtained in analyses of surface water.

Radiolysis products and degradation mechanism studies on tri-isoamyl phosphate (TiAP)

As an alternate extractant for spent fuel reprocessing, the radiolysis properties of TiAP should be systematically studied to evaluate the feasibility of using it in engineering scale. In this paper, the irradiation stability of TiAP was investigated by using the concept of radiolysis ratio and G value. It is found the extent of radiolysis would be increased with the increasing of absorbed doses, but decreased with the increasing of pre-equilibrium aqueous HNO3concentration. Furthermore, the radiolysis products were analyzed qualitatively and quantitatively with gas, liquid and ion chromatograph, based on which the possible radiolysis mechanism of TiAP was also concluded.