Key odorants in peated malt whisky and its differentiation from other whisky types using profiling of flavor and volatile compounds

Removal of Cu (II) by ion exchange resin and its re-utilization of the residual solution from the distilled Lycium barbarum wine

In order to re-utilize the residual from the distillation of the Chinese wolfberry wine and reduce the environmental pollution, the residual is firstly filtered by the ceramic membrane of 50 nm, then the Cu (II) has transferred from the distillation is removed using the ion exchange resin, and the treated solution is recombined with the distilled liquor to make the Chinese wolfberry brandy and the comparison has conducted on the physicochemical properties, antioxidant activity and flavor compounds between the recombined brandy and the finished brandy. The results indicate that the Cu (II) was effectively removed by ceramic membrane combined with the D401 resin. Compared with finished brandy, the recombined brandy contains high contents of polysaccharides, phenols and flavonoids, thus contributing to the improvement of antioxidant capacity. The gas chromatography-ion mobility spectrometry (GC-IMS) reveals that 25 volatile compounds like esters and alcohols have identified in the brandy samples, and the differences are significant between the recombined and the finished brandy. In summary, the distilled residual from the Chinese wolfberry wine might be re-used after the appropriate treatment so as to reduce the discharge and environmental pollution.

Co-culture fermentation by Saccharomycopsis fibuligera and lactic acid bacteria improves bioactivity and aroma profile of wheat bran and the bran-containing Chinese steamed bread

Co-culture fermentation with yeast and lactic acid bacteria (LAB) exhibits advantages in improving the bioactivity and flavor of wheat bran compared to single-culture fermentation, showing application potentials in bran-containing Chinese steamed bread (CSB). To explore the effects of combination of yeast and different LAB on the bioactivity and flavor of fermented wheat bran, this study analyzed the physicochemical properties, phytate degradation capacity, antioxidant activities, and aroma profile of wheat bran treated with co-culture fermentation by Saccharomycopsis fibuligera and eight different species of LAB. Further, the phenolic acid composition, antioxidant activities, texture properties, aroma profile, and sensory quality of CSB containing fermented wheat bran were evaluated. The results revealed that co-culture fermentation brought about three types of volatile characteristics for wheat bran, including ester-feature, alcohol and acid-feature, and phenol-feature, and the representative strain combinations for these characteristics were S. fibuligera with Limosilactobacillus fermentum, Pediococcus pentosaceus, and Latilactobacillus curvatus, respectively. Co-culture fermentation by S. fibuligera and L. fermentum for 36 h promoted acidification with a phytate degradation rate reaching 51.70 %, and improved the production of volatile ethyl esters with a relative content of 58.47 % in wheat bran. Wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus for 36 h had high relative content of 4-ethylguaiacol at 52.81 %, and exhibited strong antioxidant activities, with ABTS•+ and DPPH• scavenging rates at 65.87 % and 69.41 %, respectively, and ferric reducing antioxidant power (FRAP) at 37.91 μmol/g. In addition, CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. fermentum showed a large specific volume, soft texture, and pleasant aroma, and received high sensory scores. CSB containing wheat bran treated with co-culture fermentation by S. fibuligera and L. curvatus, with high contents of 4-ethylguaiacol, 4-vinylguaiacol, ferulic acid, vanillin, syringaldehyde, and protocatechualdehyde, demonstrated strong antioxidant activities. This study is beneficial to the comprehensive utilization of wheat bran resources and provides novel insights into the enhancement of functions and quality for CSB.

Distribution and Sensory Impact of (2E,4E,6Z)-nonatrienal and Trans-4,5-epoxy-(E)-2-decenal in Wines and Spirits

This study reports the distribution of (2E,4E,6Z)-nonatrienal (1) and trans-4,5-epoxy-(E)-2-decenal (2) in wines and spirits. We validated a quantification method using solid-phase extraction (SPE) and negative chemical ionization (NCI, NH3) gas chromatography-mass spectrometry (GC-MS) analysis. Both were identified for the first time in wines and spirits from different grape varieties and raw materials. Their olfactory detection thresholds (ODTs) were 16 and 60 ng/L, respectively. Analysis of 66 wines showed that the highest levels of (1) (441.3 ng/L) and (2) (386.5 ng/L) were found in red and white wines, respectively. At these levels, they modify the balance of the fruity expression of red (fresh to cooked fruits) and white (vegetal/green hazelnut nuance) wines. Similar quantitative and sensory analyses were conducted in spirits. With ODT estimated at 500 and 400 ng/L and concentrations ranging from trace amounts to 1.1 and 2.4 μg/L respectively, (1) and (2) can contribute directly to the aroma of spirits.

A review on flavor of Baijiu and other world-renowned distilled liquors

The flavor characteristics of distilled liquors significantly affect consumer acceptance and adoption. Therefore, odorants that contribute to sensory properties have received more attention. The odorants depend on the operating parameters, such as raw materials and ingredients, manufacturing process and maturing circumstances. This review summarized the odorants in the Baijiu and other world-renowned distilled liquors. Especially, the contribution of the odorants to the dominant aroma attributes is given more attention. The variations in the constituents and contents of odorants among the liquors are discussed comprehensively. In general, further research is still needed on the interaction mechanism between the odorants and sensory properties of distilled liquors.

Recent advances in whiskey analysis for authentication, discrimination, and quality control

In order to safeguard authentic whiskey products from fraudulent or counterfeit practices, high throughput solutions that provide robust, rapid, and reliable solutions are required. The implementation of some analytical strategies is quite challenging or costly in routine analysis. Qualitative screening of whiskey products has been explored, but due to the nonspecificity of the chemical compounds, a more quantitative confirmatory technique is required to validate the result of the whiskey analysis. Hence, combining analytical and chemometric methods has been fundamental in whiskey sample differentiation and classification. A comprehensive update on the most relevant and current analytical techniques, including spectroscopic, chromatographic, and novel technologies employed within the last 5 years in whiskey analysis for authentication, discrimination, and quality control, are presented. Furthermore, the technical challenges in employing these analytical techniques, future trends, and perspectives are emphasized.

Quick insights into whisky - investigating rapid and efficient methods for sensory evaluation and chemical analysis

The evaluation of aroma properties of beverages, both analytically as well as with human sensory studies, is a challenging task and most often related to time- and cost-intensive analyses. Whisky is a spirit offering a wide variety of aroma impressions caused by a complex mixture of aroma active compounds. In the present study, methods for the efficient evaluation of aroma characteristics are evaluated for 16 whisky samples of different origins (Scotch and American). Rate all that apply (RATA) was applied as a rapid method for the sensory evaluation of whiskies. Sensory evaluation of the samples led to the determination of eight significant aroma attributes: caramel-/cream caramel-/toffee-like, vanilla-like, (canned) peach-like, phenolic, smoky, fruity, flowery and (fermented) apple-/cider-like. Chemical analysis was conducted by stir bar sorptive extraction (SBSE) coupled to gas chromatography-mass spectrometry in combination with an in-house data processing tool for semi-automated analyte detection. Through chemical analysis of the whisky samples and automated compound detection, we report over 200 mostly aroma-active volatiles. To test both approaches for their potential for sample classification, a simple classification problem (Scotch vs. American) was applied. Linear discriminant analysis (LDA) indicates both that sensory evaluation by RATA (97.86%) and the applied analytical procedure (96.94%) are suitable for the distinction between the two whisky types. In both approaches, potential markers were determined for the classification. These investigations build a solid foundation for the implementation of a versatile platform facilitating rapid and efficient aroma evaluation in various foodstuffs and beverages.

Chinese Baijiu and Whisky: Research Reservoirs for Flavor and Functional Food

Baijiu is a traditional spirit with high reputation in the Chinese community, and whisky, on the other hand, is a renowned spirit in Western culture, with both contributing a major proportion to the consumption and revenue in the global spirit market. Interestingly, starting with similar raw materials, such as grains, diverse production methods lead to different organoleptic profiles. In addition, such enormous attention they attract renders them as a crucial part in food and the related industry. Therefore, great efforts are made in improving product quality and optimizing production processes, such as flavor enhancement, facility development, and deep utilization of byproducts. Given the huge impacts and great involvements of these spirits in the general food industry, research focusing on either spirit is of referential significance for other relevant fields. With the aim of facilitating such collaboration, this review discusses the current research status, in a comparative manner, of both spirits in respect to key production processes-oriented sensory and flavor analysis, deep utilization of byproducts, and spirit-derived functional food investigations. Finally, the internal correlations based on the abovementioned criteria are identified, with research prospects proposed.

The multi-faceted food odorant 4-methylphenol selectively activates evolutionary conserved receptor OR9Q2

4-Methylphenol is a food-related odor-active volatile with a high recognition factor, due to its horse stable-like, fecal odor quality. Its ambivalent hedonic impact as key aroma compound, malodor, and semiochemical has spurred the search for its cognate, chemosensory odorant receptors across species. A human odorant receptor for the highly characteristic 4-methylphenol has been elusive. Here, we identified and characterized human receptor OR9Q2 to be tuned to purified 4-methylphenol, but not to its contaminant isomer 3-methylphenol. This highly selective function of OR9Q2 complements an exclusive phenol detection gap in the ancient, most broadly tuned human odorant receptor OR2W1. Moreover, a 4-methylphenol function is evolutionary conserved in phylogenetically related OR9Q2 orthologs from chimpanzee, mouse, and cow. Notably, the cow receptor outperformed human OR9Q2 10-fold in signal strength, consonant with previous reports of 4-methylphenol as a bovine pheromone. Our results suggest OR9Q2 as best sensor for the key food odorant, malodor, and semiochemical 4-methylphenol.

Can Volatiles Fingerprints be an Alternative to Isotope Ratio Mass Spectrometry in the Botanical Origin Determination of Spirits?

Mass spectrometry based quasi-electronic nose using solid-phase microextraction to introduce volatiles directly to mass spectrometer without chromatographic separation (HS-SPME-MS) was used to discriminate 45 raw spirits produced from C3 (potato, rye, wheat) and C4 (corn, sorghum) plants. The samples were also subjected to isotope ratio mass spectrometry (IRMS), which unequivocally distinguished C3 from C4 samples; however, no clear differentiation was observed for C3 samples. On the contrary, HS-SPME-MS, which uses unresolved volatile compounds "fingerprints" in a form of ions of a given m/z range and various intensities provided excellent sample classification and prediction after OPLS-DA data processing verified also by the artificial neural network (ANN).

Multi-objective evaluation of freshly distilled brandy: Characterisation and distribution patterns of key odour-active compounds

The characterisation and distribution patterns of key odour-active compounds in head, heart1, heart2, tail, and stillage cuts of freshly distilled brandy were investigated by gas chromatography–olfactometry-mass spectrometry coupled with aroma extract dilution analysis (AEDA) and chemometrics analysis. Results from AEDA showed that there were 50, 61, 48, 25, and 18 odour-active compounds in the head, heart1, heart2, tail, and stillage cuts, respectively. Besides, 19, 22, 11, 5, and 4 quantified compounds with odour activity values ≥ 1, respectively, were considered to be potential contributors to the aroma profile of different distillation cuts. Especially, the chemometrics analysis illustrated the heart1 fraction was characterized by 3-methylbutanol, ethyl hexanoate, 1-hexanol, ethyl octanoate, benzaldehyde, ethyl decanoate, and 2-phenylethyl acetate; (E)-hex-3-en-1-ol, (Z)-hex-3-en-1-ol, and 2-phenylethyl acetate greatly contributed to the characteristics of the heart2 cut. Furthermore, different volatile compounds with a variety of boiling points and solubilities followed diverse distillation rules during the second distillation. Our findings may provide a rational basis for concentrating more pleasant aroma components contributing to brandy.

Exploring the volatile profile of whiskey samples using solid-phase microextraction Arrow and comprehensive two-dimensional gas chromatography-mass spectrometry

We present a novel sample preparation method for the extraction and preconcentration of volatile organic compounds from whiskey samples prior to their determination by comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS). Sample preparation of the volatile compounds, important for the organoleptic characteristics of different whiskeys and their acceptance and liking by the consumers, is based on the use of the solid-phase microextraction (SPME) Arrow. After optimization, the proposed method was compared with conventional SPME regarding the analysis of different types of whiskey (i.e., Irish whiskey, single malt Scotch whiskey and blended Scotch whiskey) and was shown to exhibit an up to a factor of six higher sensitivity and better repeatability by a factor of up to five, depending on the compound class. A total of 167 volatile organic compounds, including terpenes, alcohols, esters, carboxylic acids, ketones, were tentatively-identified using the SPME Arrow technique, while a significantly lower number of compounds (126) were determined by means of conventional SPME. SPME Arrow combined with GC × GC-MS was demonstrated to be a powerful analytical tool for the exploration of the volatile profile of complex samples, allowing to identify differences in important flavour compounds for the three different types of whiskey investigated.

The periodic table of fermented foods: limitations and opportunities

Fermentation is one of the oldest methods of food processing and accounts for a substantial proportion of human foods, including not only staple foods such as bread, cereal porridges or fermented legumes but also fermented vegetables, meats, fish and dairy, alcoholic beverages as well as coffee, cocoa and condiments such as vinegar, soy sauce and fish sauces. Adding the regional varieties to these diverse product categories makes for an almost immeasurable diversity of fermented foods. The periodic table of fermented foods aims to map this diversity on the 118 entries of the periodic table of chemical elements. While the table fails to represent the diversity of fermented foods, it represents major fermentation substrates, product categories, fermentation processes and fermentation organisms. This communication not only addresses limitations of the graphical display on a "periodic table of fermented foods", but also identifies opportunities that relate to questions that are facilitated by this graphical presentation: on the origin and purpose of food fermentation, which fermented foods represent "indigenous" foods, differences and similarities in the assembly of microbial communities in different fermentations, differences in the global preferences for food fermentation, the link between microbial diversity, fermentation time and product properties, and opportunities of using traditional food fermentations as template for development of new products. KEY POINTS: • Fermented foods are produced in an almost immeasurable diversity. • Fermented foods were mapped on a periodic table of fermented foods. • This table facilitates identification of communalities and differences of products.

Integrated data analysis making use of the total information from gas chromatography and high-resolution time-of-flight mass spectrometry to identify qualitative differences between two whisky samples

RATIONALE

Analysis of complex mixtures with gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC/HRTOFMS) can produce a large amount of data. A new software program was recently reported that integrates all of the available mass spectrometric information from GC/HRTOFMS analysis into a concise report. New capabilities have now been added to the software to incorporate retention index data and to identify differences between two samples.

METHODS

Two Scotch whisky samples were sampled by solid-phase microextraction (SPME) and analyzed by GC/HRTOFMS. One of the two whisky samples (Sample B) was identical to the other sample (Sample A) except for an additional 6-months storage in sherry casks. Both electron ionization (EI) and chemical ionization (CI) data were obtained using a new GC/TOFMS system (JEOL AccuTOF GC-Alpha) with enhanced resolving power and mass accuracy. Statistical analysis of replicate measurements of the whisky samples was carried out with a new software program (msFineAnalysis version 3.2) to identify and assign differences between the samples.

RESULTS

There were 124 peaks detected in the two whiskies. Thirteen compounds were detected with a relative peak area greater than 0.05% that were present in greater amounts in the whisky that had been stored in sherry casks for an additional 6 months. Ten of these compounds were identified by the software with high confidence, two were identified as isomers with close retention indices, and one was identified interactively.

CONCLUSIONS

The software identified small differences between the two samples that resulted from sherry cask aging. Because all of the information available from the hard and soft ionization analyses for each compound is summarized in a concise integrated report, the operator can rapidly determine the level of confidence for each assignment and inspect the information for compounds that are not present in the database.

PLS-R Calibration Models for Wine Spirit Volatile Phenols Prediction by Near-Infrared Spectroscopy

Near-infrared spectroscopic (NIR) technique was used, for the first time, to predict volatile phenols content, namely guaiacol, 4-methyl-guaiacol, eugenol, syringol, 4-methyl-syringol and 4-allyl-syringol, of aged wine spirits (AWS). This study aimed to develop calibration models for the volatile phenol’s quantification in AWS, by NIR, faster and without sample preparation. Partial least square regression (PLS-R) models were developed with NIR spectra in the near-IR region (12,500–4000 cm⁻¹) and those obtained from GC-FID quantification after liquid-liquid extraction. In the PLS-R developed method, cross-validation with 50% of the samples along a validation test set with 50% of the remaining samples. The final calibration was performed with 100% of the data. PLS-R models with a good accuracy were obtained for guaiacol (r² = 96.34; RPD = 5.23), 4-methyl-guaiacol (r² = 96.1; RPD = 5.07), eugenol (r² = 96.06; RPD = 5.04), syringol (r² = 97.32; RPD = 6.11), 4-methyl-syringol (r² = 95.79; RPD = 4.88) and 4-allyl-syringol (r² = 95.97; RPD = 4.98). These results reveal that NIR is a valuable technique for the quality control of wine spirits and to predict the volatile phenols content, which contributes to the sensory quality of the spirit beverages.

Spent Grain from Malt Whisky: Assessment of the Phenolic Compounds

In order to extract antioxidant phenolic compounds from spent grain (SG) two extraction methods were studied: the ultrasound-assisted method (US) and the Ultra-Turrax method (high stirring rate) (UT). Liquid to solid ratios, solvent concentration, time, and temperature/stirring rate were optimized. Spent grain extracts were analyzed for their total phenol content (TPC) (0.62 to 1.76 mg GAE/g SG DW for Ultra-Turrax pretreatment, and 0.57 to 2.11 mg GAE/g SG DW for ultrasound-assisted pretreatment), total flavonoid content (TFC) (0.6 to 1.67 mg QE/g SG DW for UT, and 0.5 to 1.63 mg QE/g SG DW for US), and antioxidant activity was measured using 2,2-diphenyl-2-picrylhydrazyl (DPPH) free radical (25.88% to 79.58% for UT, and 27.49% to 78.30% for UT). TPC was greater at a high stirring rate and high exposure time up to a certain extent for the Ultra-Turrax method, and at a high temperature for the ultrasound-assisted method. P-coumaric acid (20.4 ± 1.72 mg/100 SG DW for UT, and 14.0 ± 1.14 mg/100 SG DW for US) accounted for the majority of the phenolic found compounds, followed by rosmarinic (6.5 ± 0.96 mg/100 SG DW for UT, and 4.0 ± 0.76 mg/100 SG DW for US), chlorogenic (5.4 ± 1.1 mg/100 SG DW for UT, and non-detectable for US), and vanillic acids (3.1 ± 0.8 mg/100 SG DW for UT, and 10.0 ± 1.03 mg/100 SG DW for US) were found in lower quantities. Protocatechuic (0.7 ± 0.05 mg/100 SG DW for UT, and non-detectable for US), 4-hydroxy benzoic (1.1 ± 0.06 mg/100 SG DW for UT, and non-detectable for US), and caffeic acids (0.7 ± 0.03 mg/100 SG DW for UT, and non-detectable for US) were present in very small amounts. Ultrasound-assisted and Ultra-Turrax pretreatments were demonstrated to be efficient methods to recover these value-added compounds.

The Impact of Terroir on the Flavour of Single Malt Whisk(e)y New Make Spirit

The impact of barley variety and its geographical growth location (environment) on the flavour of new make spirit was investigated to determine if "terroir" can be applied in the production of single malt whisk(e)y. New make spirits were produced at laboratory scale under controlled conditions from two different barley varieties (Olympus and Laureate) grown at two distinct environments (Athy, Co Kildare and Bunclody, Co Wexford) in Ireland over two consecutive seasons (2017 and 2018). The spirit samples were analysed by gas chromatography mass spectrometry olfactometry and descriptive sensory analysis. Forty-two volatiles were detected with eight deemed as very influential and fifteen deemed as influential to the aroma of new make spirit. Sensory attributes were influenced by barley variety, environment, and the interactions thereof over both seasons, with environment and the interaction of variety x environment having a greater impact than variety alone. Chemometric analysis of the olfactometry and sensory data found that both environment and season had a greater impact on the aromatic sensory perception of the new make spirits than variety alone. Therefore, this study clearly demonstrates a "terroir" impact on the flavour of new make spirit and highlights its potential importance especially in relation to single malt whisk(e)y.

Validation of a mass spectrometry method to identify and quantify ellagitannins in oak wood and cognac during aging in oak barrels

Ellagitannins are the main extractible phenolic compounds in oak wood; the monomers vescalagin and castalagin, lyxose/xylose-bearing monomers grandinin and roburin E, dimers roburins A and D and lyxose/xylose-bearing dimers roburins B and C are the principal ones. These compounds are responsible for the high durability of wood and may contribute to the organoleptic quality of wines and spirits (color, astringency, bitterness). Despite their importance, their presence and forms in distilled spirits are not well known. The aim of this work was therefore to develop and validate a method to identify and quantify oak wood ellagitannins in Cognac using high liquid chromatography-triple quadrupole (LC-QQQ) analysis. The method was validated using vescalagin as the standard and by studying sensitivity, linearity in working range, intraday repeatability, and intraday precision in order to quantify individual ellagitannins in this complex matrix.

A full-scale study of high-rate anaerobic bioreactors for whiskey distillery wastewater treatment with size fractionation and metagenomic analysis of granular sludge

Two full-scale high-rate bioreactors, i.e. external circulation sludge bed (ECSB) and expanded granular sludge bed (EGSB), were monitored for three years. Their performances for treating wastewater in a whiskey distillery were compared in terms of COD, pH, alkalinity and VFA. Even though feed flowrate highly fluctuated, COD removals of ECSB and EGSB were both excellent (95.7 ± 1.3% and 94.8 ± 3.0%, respectively). The influent and effluent characteristics of ECSB reactor were profiled and urea and urethane were also detected. High-strength properties of raw spent wash were exhibited in TOC, soluble COD and BOD5,20°C of 13500, 37750, and 1950 mg·L-1, respectively and characterized by GC-MS. Anaerobic granular sludge sampled from different heights of ECSB reactor were fractionated for demonstrating vertical size distributions. Moreover, major species found by next-generation sequencing technique were archaea, i.e. Methanosaeta and Methanolinea, while major bacteria were Bacteroidetes with minor Nitrospiraceae. This metagenomic analysis provided an insight of anaerobic microbial consortium.