Development of a Method for the Quantitation of Three Thiols in Beer, Hop, and Wort Samples by Stir Bar Sorptive Extraction with in Situ Derivatization and Thermal Desorption-Gas Chromatography-Tandem Mass Spectrometry

Comparison of polyfunctional thiol, element, and total essential oil contents in 32 hop varieties from different countries

Volatile thiol 3-mercaptohexan-1-ol (3MH) and particularly 4-mercapto-4-methylpentan-2-one (4MMP) are highly potent flavour compounds in hops. For the determination, a simple and robust stable isotope dilution LC-MS/MS method was developed and applied to 32 hop varieties worldwide from harvest years 2019 and 2020. Limit of detection, precision, and recovery were 0.15 μg/kg, 10%, and 97-108%, respectively. Levels of 3MH and 4MMP ranged from 1.9 to 79.2 μg/kg and from undetectable to 37.1 μg/kg, respectively. Citra, Mosaic, and Strata were rich in both thiols. ICP analyses revealed, that variation of potassium content between the two harvest years was inversely correlated with that of manganese and rubidium (|r| ≥ 0.89) among 12 US varieties excluding Citra and Mosaic. Total essential oil content (0.34-2.7 mL/100 g) was inversely correlated with calcium content (|r| ≥ 0.65). Greatly varying thiol levels depending on variety, region and harvest year might lead to differing flavour results in beer.

Application of Sorbent-Based Extraction Techniques in Food Analysis

This review presents an outline of the application of the most popular sorbent-based methods in food analysis. Solid-phase extraction (SPE) is discussed based on the analyses of lipids, mycotoxins, pesticide residues, processing contaminants and flavor compounds, whereas solid-phase microextraction (SPME) is discussed having volatile and flavor compounds but also processing contaminants in mind. Apart from these two most popular methods, other techniques, such as stir bar sorptive extraction (SBSE), molecularly imprinted polymers (MIPs), high-capacity sorbent extraction (HCSE), and needle-trap devices (NTD), are outlined. Additionally, novel forms of sorbent-based extraction methods such as thin-film solid-phase microextraction (TF-SPME) are presented. The utility and challenges related to these techniques are discussed in this review. Finally, the directions and need for future studies are addressed.

Online monitoring of higher alcohols and esters throughout beer fermentation by commercial Saccharomyces cerevisiae and Saccharomyces pastorianus yeast

Higher alcohols and esters are among the predominant classes of volatile organic compounds (VOCs) that influence the quality of beer. The concentrations of these compounds are determined through a specific yeast strain selection and fermentation conditions. The effect of yeast strains on the formation of higher alcohols and esters throughout fermentations (at 20°C) was investigated. Flavour-relevant esters (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl octanoate) and higher alcohols (isoamyl alcohol, isobutyl alcohol and phenylethyl alcohol) were monitored throughout the fermentation using proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) coupled with an automated sampling system for continuous measurements. Compound identification was confirmed by analysis of samples using gas chromatography-mass spectrometry (GC-MS). Results demonstrated the specific time points where variation in higher alcohol and ester generation between yeast strains occurred. In particular, the concentrations of isoamyl acetate, ethyl octanoate and isoamyl alcohol between yeast strains were significantly different over the first 2 days of fermentation; whereas, after Day 3, no significant differences were observed. The two Saccharomyces pastorianus strains produced comparable concentrations of the key higher alcohols and esters. However, the key higher alcohol and ester concentrations varied greatly between the two S. cerevisiae strains. The use of PTR-ToF-MS to rapidly measure multiple yeast strains provides new insights on fermentation for brewers to modify the sensory profile and optimise quality.

Pulsed-post column derivatization coupled to green liquid chromatography for the determination of glutathione and cysteine based on thioacrylates formation

In the present work, we developed a method for the determination of thiols (cysteine and glutathione) in yeast samples under the new concept of Pulsed-post column derivatization (Pulsed-PCD). For the chromatographic separation of the analytes, 100% aqueous mobile phase was used and the eluted compounds reacted on-line with the injected pulses (100 μL) of the derivatizing reagent (ethyl propiolate + Britton-Robinson buffer). Spectrophotometric detection of the derivatives was carried out at 285 nm. The Pulsed-PCD configuration, the selection of the analytical column and the pulsed-PCD reaction conditions were investigated. The method was validated for the determination of endogenous content of the analytes in dry and fresh yeasts, with LODs of 3.0 μmol L^-1. The percent recovery ranged between 85.2 and 114.4% in all cases and the results were compared with a corroborative method based on classical PCD. The analytical greenness of the proposed method was evaluated using two tools; Analytical Eco-Scale and Green Analytical Procedure Index (GAPI). The greenness score of the HPLC-Pulsed-PCD method (score = 77) was compared with that of the corroborative HILIC-PCD method (score = 71) and was found to be greener in terms of the amount of chemicals used and the produced wastes.

Roles of sulfur-containing compounds in fermented beverages with 2-furfurylthiol as a case example

Aroma is a critical component of the flavor and quality of beverages. Among the volatile chemicals responsible for fragrance perception, sulfur compounds are unique odorants due to their extremely low odor threshold. Although trace amounts of sulfur compounds can enhance the flavor profile of beverages, they can lead to off-odors. Sulfur compounds can be formed via Maillard reaction and microbial metabolism, imparting coffee aroma and altering the flavor of beverages. In order to increase the understanding of sulfur compounds in the field of food flavor, 2-furfurylthiol (FFT) was chosen as a representative to discuss the current status of their generation, sensory impact, enrichment, analytical methods, formation mechanisms, aroma deterioration, and aroma regulation. FFT is comprehensively reviewed, and the main beverages of interest are typically baijiu, beer, wine, and coffee. Challenges and recommendations for FFT are also discussed, including analytical methods and mechanisms of formation, interactions between FFT and other compounds, and the development of specific materials to extend the duration of aroma after release.

Investigation into mousy off-flavor in wine using gas chromatography-mass spectrometry with stir bar sorptive extraction

Three major compounds, 2-acetyl-1-pyrroline (APY), 2-acetyltetrahydropyridine (ATHP) and 2-ethyltetrahydropyridine (ETHP), have been identified as responsible for the mousy off-flavor in wines, although to date quantification data reported in the literature are limited. A simple method for simultaneous quantitation, by SBSE-GC-MS, of these N-heterocyclic compounds was developed. Both previously reported tautomers of ATHP, 2-acetyl-1,4,5,6-tetrahydropyridine and 2-acetyl-3,4,5,6-tetrahydropyridine were identified. The limits of detection and quantification of the method were determined in white, rosé and red wines and are lower than previously published concentrations in spoiled wine. ETHP was detected in almost all wines produced with limited use of SO₂. ATHP was detected in almost all wines suspected of mousiness whereas APY was only detected in few cases. This method will provide a support for further studies aimed at understanding the phenomena that influence the occurrence of mousy off-flavor and the oenological parameters that modulate its expression.

Organosulfur in food samples: Recent updates on sampling, pretreatment and determination technologies

Organosulfur compounds (OSCs), mainly found in garlic, are the main biologically active substances for their pharmacological effects, including lowering of blood pressure and cholesterol, anti-cancer effect, liver protection, and anti-inflammatory. Efficient and sensitive pretreatment and determination methods of OSCs in different food matrices are of great significance. This review provides a comprehensive summary about the pretreatment and determination methods for OSCs in different food samples since 2010. Commonly used pretreatment methods, such as liquid-liquid extraction, microwave-assisted extraction, pressurized liquid extraction, liquid-liquid microextraction, solid phase extraction, dispersive solid phase extraction, solid-phase microextraction, and so on, have been summarized and overviewed in this paper. In particular, we discussed and compared various analysis methods including high performance liquid chromatography coupled with different detectors, gas chromatography-based methods, and few other methods. Finally, we tried to highlight the applicability, advantages and disadvantages of different pretreatment and analysis methods, and identified future prospects in this field.

Derivatization Strategies in Flavor Analysis: An Overview over the Wine and Beer Scenario

Wine and beer are the most appreciated and consumed beverages in the world. This success is mainly due to their characteristic taste, smell, and aroma, which can delight consumer’s palates. These olfactory characteristics are produced from specific classes of volatile compounds called “volatile odor-active compounds” linked to different factors such as age and production. Given the vast market of drinking beverages, the characterization of these odor compounds is increasingly important. However, the chemical complexity of these beverages has led the scientific community to develop several analytical techniques for extracting and quantifying these molecules. Even though the recent “green-oriented” trend is directed towards direct preparation-free procedures, for some class of analytes a conventional step like derivatization is unavoidable. This review is a snapshot of the most used derivatization strategies developed in the last 15 years for VOAs’ determination in wine and beer, the most consumed fermented beverages worldwide and among the most complex ones. A comprehensive overview is provided for every method, whereas pros and cons are critically analyzed and discussed. Emphasis was given to miniaturized methods which are more consistent with the principles of “green analytical chemistry”.

Qualitative Screening of Volatile Thiols in Wine by Selective Silver Ion Solid-Phase Extraction with Heart-Cutting Multidimensional Gas Chromatography Mass Spectrometry/Olfactometry

The chemical analysis of odorous volatile thiols is intrinsically challenging. Substantial progress has been made in quantitative analysis of targeted thiols at ultra-trace concentrations (ng/L), but lesser analytical attention has been given to the qualitative screening of unknown thiols. This work presents a solid-phase extraction (SPE) method using a silver ion (Ag⁺)-based sorbent to isolate volatile thiols from red wine. This proposed Ag⁺ SPE method was effective (recovery: 87-101% for four non-furan thiols and 35-49% for two furan thiols), simple, safe, and greatly reduced artifacts, testifying to its suitability as the sample preparation protocol for a qualitative screening experiment. Separation and detection were conducted using heart-cutting multidimensional gas chromatography coupled to mass spectrometry/olfactometry (H/C MDGC-MS/O). Key parameters including H/C width, main host oven temperature, and cryogenic trapping temperature were investigated for optimal instrument performance. The developed Ag⁺ SPE H/C MDGC-MS/O strategy was readily applicable for qualitative screening of odorous volatile thiols in wine, as demonstrated by two case studies.

Identification of 2-furanmethanethiol contributing to roast aroma in honkaku shochu and awamori

Honkaku shochu and awamori are traditional Japanese spirits. 2-Furanmethanethiol (2FM), a volatile thiol, was identified as a roast aroma compound in honkaku shochu and awamori. The detection threshold of 2FM in 25% (v/v) ethanol water solutions was determined as 1.6 ng/L. The odor activity values, calculated using the detection threshold suggested that 2FM affects the quality of honkaku shochu and awamori. The odor activity values of 2FM were higher in barley shochu distilled at atmospheric pressure than in sweet potato shochu, rice shochu and awamori; therefore, 2FM is considered to contribute to the characteristics of barley shochu.

Effect of "Late Harvest" of Hops (Humulus lupulus L.) on the Contents of Volatile Thiols in Furano Beauty, Furano Magical, and Cascade Varieties

In recent years, many hop varieties with unique aromas, so-called "flavor hops", have been bred and grown. Here, we investigated the effect of late-harvested hops using three flavor hop varieties; Furano Beauty, Furano Magical, and Cascade. The sample hops were harvested at different days after flowering (DAF): DAF 45 (normal harvest), DAF 65, DAF 75, and DAF 85. We measured the volatile thiols in sample cones. The results indicated that 4-methyl-4-sulfanylpentane-2-one contents showed almost no change or a slightly decrease with a delay in harvest, whereas 3-sulfanyl-4-methylpentan-1-ol (3S4MP) content in late-harvested samples increased several fold in comparison with normal-harvested samples. Additionally, 3S4MP contents in the beers brewed with DAF 65 samples were several times higher than those using DAF 45 ones. From these results, we propose a new method to control 3S4MP content in hop cones by changing its harvest date.

Aroma Profiles of Dry-Hopped Ciders Produced with Citra, Galaxy, and Mosaic Hops

Cider quality and consumer acceptance are greatly influenced by its aroma. With the continued expansion of the craft cider industry, cider producers are employing techniques such as dry hopping to develop unique flavor profiles. Few studies, however, have explored the VOCs of dry-hopped cider. Herein, we monitor the development of VOCs from pressed apple juice, through fermentation and dry hopping by HS–SPME–GC–MS, to elucidate when and how aroma compounds arise in cider production. In all, 89 VOCs were detected, spanning eight classes of organic compounds. Racking events decreased ester concentrations by 10 ± 1%, but resting on the lees allowed these pleasant, fruity aromas to be reestablished. Dry hopping was conducted with three types of hops (Citra, Galaxy, and Mosaic). The varied development of terpenes and esters between hop varieties supports the use of this technique to diversify the aroma profiles of ciders. Herein, we report that both the variety of hops and the timing of key processing steps including racking and hop addition significantly alter the identity and concentration of aroma-important VOCs in dry-hopped cider.

Untargeted flavor profiling of lager beers by stir bar sorptive extraction -capillary gas chromatography - time-of-flight mass spectrometry: High analytical performance with a green touch

Beer is one of the most popular beverages in the world and its complex flavor is widely appreciated. Beer flavor profiling is important for brewers to optimize beer production and to guarantee odor quality and taste stability of the final products. This is especially the case for pale lager beers that represent the beer type with the largest worldwide production volume. In this study, the combination of stir bar sorptive extraction (SBSE) with capillary gas chromatography (GC) hyphenated to time-of-flight mass spectrometry (TOFMS) was used to perform a detailed aroma profiling of lager beer samples originating from Belgium, The Netherlands, and France. A generic SBSE method was applied resulting in a very broad extraction coverage of odor solutes, while the extraction process is miniaturized, unattended and solventless, meeting green analytical chemistry requirements. Using GC-TOFMS analysis operated in untargeted mode, MS deconvolution and statistical data analysis, with principal component and hierarchical clustering analysis, it was possible to clearly differentiate brands and origins of the beer samples and to identify marker compounds for flavor profiling of these closely related beer samples. An extended database of beer aroma compounds was created. The developed method can be applied in beer quality optimization and quality control in routine laboratories.

Analysis of Hop-Derived Thiols in Beer Using On-Fiber Derivatization in Combination with HS-SPME and GC-MS/MS

The quantitation of the hop varietal thiols 4-mercapto-4-methyl-2-pentanone (4MMP), 3-mercapto-1-hexanol (3MH), and 3-mercaptohexylacetate (3MHA) from beer is challenging. This primarily relates to their low concentration (ng/L levels) and their reactivity. Published assays for thiol quantitation from beer include complex and/or time-consuming sample preparation procedures involving manual handling and use reagents that are harmful because they contain mercury. To facilitate thiol analysis from beer, the current article is concerned with the implementation of an automated headspace solid-phase microextraction (HS-SPME) on-fiber derivatization (OFD) approach using 2,3,4,5,6-pentafluorobenzyl bromide followed by gas chromatography-tandem mass spectrometry (GC-MS/MS). Optimization of HS-SPME and MRM conditions was based on a central composite design approach. The final OFD-HS-SPME-GC-MS/MS method yielded limits of quantitation below the sensory thresholds of 4MMP, 3MH, and 3MHA. Method validation and application on beers brewed with German, Australian, and US hops, as well as with added fruits displayed excellent method performance.

Extraction Techniques and Analytical Methods for Characterization of Active Compounds in Origanum Species

Phytochemical research based on ethnopharmacology is gaining interest in industries such as functional food, nutraceuticals, cosmetics and pharmaceutical industries. Plants and plant extracts are a rich source of bioactive secondary metabolites. These compounds are often involved in plant protection against biotic or abiotic stresses. The exploitation of available technologies should be oriented and intensified to extend and enhance the continued usefulness of the plants as renewable sources of chemicals, especially medicinal compounds. This current contribution is focused on extraction and analytical techniques for their isolation from the oregano species, their characterization and their potential antioxidative, as well as their antimicrobial, antifungal and anticarcinogenic properties. The work is structured rendering to the different steps involved in the research; starting with extraction and sample preparation, followed by discussing the analytical techniques employed for the isolation and identification of compound/s responsible for the biological activity and methods and techniques for biological activity assessment.

Analysis of Potent Odour-Active Volatile Thiols in Foods and Beverages with a Focus on Wine

Certain volatile thiols are some of the most potent odour-active molecules that are found in nature. Thiols play significant roles in the aroma qualities of a range of foods and beverages, including wine, with extremely low odour detection thresholds (nanogram per litre range). A fundamental understanding of their formation, fate, and impact essentially depends on the development of suitable analytical methods. The analysis of volatile thiols in foods and beverages is a challenging task when considering (1) the complexity of food and beverage matrices and (2) that thiols are highly reactive, low molecular-weight volatiles that are generally present at trace to ultra-trace concentrations. For the past three decades, the analytical evaluation of volatile thiols has been intensively performed in various foods and beverages, and many novel techniques related to derivatisation, isolation, separation, and detection have been developed, particularly by wine researchers. This review aims to provide an up-to-date overview of the major analytical methodologies that are proposed for potent volatile thiol analysis in wine, foods, and other beverages. The analytical challenges for thiol analysis in foods and beverages are outlined, and the main analytical methods and recent advances in methodology are summarised and evaluated for their strengths and limitations. The key analytical aspects reviewed include derivatisation and sample preparation techniques, chromatographic separation, mass spectrometric detection, matrix effects, and quantitative analysis. In addition, future perspectives on volatile thiol research are also suggested.

Hop Compounds: Extraction Techniques, Chemical Analyses, Antioxidative, Antimicrobial, and Anticarcinogenic Effects

Hop plants comprise a variety of natural compounds greatly differing in their structure and properties. A wide range of methods have been developed for their isolation and chemical analysis, as well as for determining their antioxidative, antimicrobial, and antigenotoxic potentials. This contribution provides an overview of extraction and fractionation techniques of the most important hop compounds known for their health-promoting features. Although hops remain the principal ingredient for providing the taste, stability, and antimicrobial protection of beer, they have found applications in the pharmaceutical and other food industries as well. This review focuses on numerous health-promoting effects of hops raging from antioxidative, sedative, and anti-inflammatory potentials, over anticarcinogenic features to estrogenic activity. Therefore, hops should be exploited for the prevention and even healing of several prevalent diseases like cardiovascular disorders and various cancer types. New ideas for future studies on hops are finally presented: computational investigations of chemical reactivities of hop compounds, nanoencapsulation, and synergistic effects leading to a higher bioavailability of biologically active substances as well as the application of waste hop biomass from breweries for the production of high-added-value products in accordance with the biorefinery concept.

Measuring Thiols in Single Cultivar South African Red Wines Using 4,4-Dithiodipyridine (DTDP) Derivatization and Ultraperformance Convergence Chromatography-Tandem Mass Spectrometry

Wine varietal thiols are important contributors to wine aroma. The chemical nature of thiols makes them difficult to measure due to low concentrations, high sensitivity to oxidation, and low ionization. Methods for the measurement of thiols usually consist of multiple steps of sample preparation followed by instrumental measurement. Studies have collected large datasets of thiols in white wine but not in red wine, due to the lack of availability of suitable methods. In this study, for the first time, convergence chromatography was used to measure thiols in red wine at ultratrace levels with improved sensitivity compared to previous methods. Performance parameters (selectivity, linearity, limits of detection, precision, accuracy) were tested to demonstrate the suitability of the method for the proposed application. Red wine thiols were measured in South African Pinotage, Shiraz, and Cabernet Sauvignon wines (n = 16 each). Cultivar differentiation using the thiol profile was demonstrated.

Recent Developments of Stir Bar Sorptive Extraction for Food Applications: Extension to Polar Solutes

Stir bar sorptive extraction (SBSE) is a miniaturized and solvent-less sample preparation method for extraction and concentration of organic compounds from aqueous samples. The method is based on sorptive extraction, whereby the solutes are extracted into a polymer, such as polydimethylsiloxane (PDMS), coated on a stir bar. Using an apolar PDMS coating, SBSE provides high recoveries for apolar solutes; however, SBSE recoveries for polar solutes are low. Although several more polar coatings for SBSE were developed, these extraction phases are mostly not compatible with thermal desorption (TD) and/or have inferior performance characteristics related to robustness, bleeding, stability, etc. compared to PDMS. In this perspective, two recently introduced SBSE approaches are described that can be used to extend the applicability of a PDMS coating to more polar solutes: (1) SBSE with freeze concentration [ice concentration linked with extractive stirrer (ICECLES)], which is based on the concentration of analytes by gradually reducing the phase ratio (sample/extraction phase), and (2) SBSE using a solvent-swollen PDMS [solvent-assisted SBSE (SA-SBSE)], which is based on a combination of polarity modification and volume increase by PDMS phase swelling using certain types of solvents while maintaining the original characteristics of the PDMS phase.

Evaluation of PTR-ToF-MS as a tool to track the behavior of hop-derived compounds during the fermentation of beer

Hop-derived volatile organic compounds (VOCs) play an important role in the flavor and aroma of beer, despite making up a small percentage of the overall profile. To understand the changes happening during fermentation, proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) was applied for the first time in brewing science to directly measure the changes in hop-derived VOCs during the fermentation of four different worts containing one of two aroma hops in combination with one of two yeast biotypes. PTR-ToF-MS successfully detected and tracked mass-to-charge ratios (m/z) arising from interactions between the different yeast strains and the hop cultivars. Differences were observed in the dynamic VOC profiles between different beer treatments for m/z such as m/z 145.121 (ethyl hexanoate) and m/z 173.153 (isoamyl isovalerate or ethyl octanoate). The ability to monitor changes in VOCs during fermentation provides valuable information on the priority of production and transformation reactions by yeast.

Quantitation of 4-Methyl-4-sulfanylpentan-2-one (4MSP) in Hops by a Stable Isotope Dilution Assay in Combination with GC×GC-TOFMS: Method Development and Application To Study the Influence of Variety, Provenance, Harvest Year, and Processing on 4MSP Concentrations

A stable isotope dilution assay was developed for quantitation of 4-methyl-4-sulfanylpentan-2-one (4MSP) in hops. The approach included the use of 4-(¹³C)methyl-4-sulfanyl(1,3,5-¹³C₃)pentan-2-one as internal standard, selective isolation of hop thiols by mercurated agarose, and GC×GC-TOFMS analysis. Application of the method to 53 different hop samples revealed 4MSP concentrations between <1 and 114 μg/kg. Notably high concentrations were associated with United States varieties such as Citra, Eureka, Simcoe, and Apollo, whereas 4MSP was absent from traditional German and English varieties. Further experiments showed that besides the variety, also harvest year and storage vitally influenced 4MSP concentrations, whereas the impact of provenance was less pronounced. Hop processing such as drying and pelletizing had only a minor impact on 4MSP concentrations. Like the majority of other hop volatiles, 4MSP is predominantly located in the lupulin glands.

Determination of Six Pyrazole Fungicides in Grape Wine by Solid-Phase Extraction and Gas Chromatography-Tandem Mass Spectrometry

A gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed for the first simultaneous identification and quantification of six pyrazole fungicides (furametpyr, rabenzazole, fluxapyroxad, penflufen, bixafen, and isopyrazam) in grape wine samples. The grape wine samples were first diluted with water, then purified by solid-phase extraction, and finally examined by GC-MS/MS in multiple reaction monitoring (MRM) mode. Matrix-matched calibration curves were used to correct the matrix effects. The limits of quantification (LOQs), calculated as 10 times the standard deviation, were 0.2-0.8 μg kg(-1) for the six pyrazole fungicides. The average recoveries were in the range of 74.3-94.5%, with relative standard deviations (RSDs) below 5.8%, measured at three concentration levels. The proposed method is suitable for the simultaneous determination of six pyrazole fungicides in grape wine samples.