Characterization of Key Aroma Compounds in Pellets of Different Hop Varieties (Humulus lupulus L.) by Means of the Sensomics Approach

The insights into sour flavor and organic acids in alcoholic beverages

Alcoholic beverages have developed unique flavors over millennia, with sourness playing a vital role in their sensory perception and quality. Organic acids, as crucial flavor compounds, significantly impact flavor. This paper reviews the sensory attribute of sour flavor and key organic acids in alcoholic beverages. Regarding sour flavor, research methods include both static and dynamic sensory approaches and summarize the interaction of sour flavor with aroma, taste, and mouthfeel. In addition, this review focuses on identifying key organic acids, including sample extraction, chromatography, olfactometry/taste, and mass spectrometry. The key organic acids in alcoholic beverages, such as wine, Baijiu, beer, and Huangjiu, and their primary regulatory methods are discussed. Finally, future avenues for the exploration of sour flavor and organic acids by coupling machine learning, database, sensory interactions and electroencephalography are suggested. This systematic review aims to enhance understanding and serve as a reference for further in-depth studies on alcoholic beverages.

Characterization of the key aroma compounds in different varieties of hops by application of the Sensomics approach

Aroma is a crucial indicator of hop quality. This study analyzed the differences in aroma compound composition among six hop varieties from three regions: North America, Europe, and Asia. Descriptive analysis and sensomic approaches including gas chromatography-olfactometry/aroma extract dilution analysis, odour activity value calculation and aroma recombination were used for the detailed characterization and comparative analysis of hop aroma. A total of 55 aroma-active compounds were identified. Among them, linalool, geraniol, β-myrcene, 2-undecanone, and methyl decanoate contributed significantly to hop aroma. Orthogonal partial least squares discriminant analysis revealed that, except for the SAAZ and XinYuan hops with some similarities in their aroma composition, the remaining hops exhibited unique aroma characteristics. A total of 16 compounds, including methyl 5-methylhexanoate and (E)-β-farnesene, were identified as differentiating aroma compounds in the six hop samples. This study enriches the knowledge on hop flavour with different origins and provides valuable insights into its application.

Unlocking Flavor Potential Using Microbial β-Glucosidases in Food Processing

Aroma is among of the most important criteria that indicate the quality of food and beverage products. Aroma compounds can be found as free molecules or glycosides. Notably, a significant portion of aroma precursors accumulates in numerous food products as nonvolatile and flavorless glycoconjugates, termed glycosidic aroma precursors. When subjected to enzymatic hydrolysis, these seemingly inert, nonvolatile glycosides undergo transformation into fragrant volatiles or volatiles that can generate odor-active compounds during food processing. In this context, microbial β-glucosidases play a pivotal role in enhancing or compromising the development of flavors during food and beverage processing. β-glucosidases derived from bacteria and yeast can be utilized to modulate the concentration of particular aroma and taste compounds, such as bitterness, which can be decreased through hydrolysis by glycosidases. Furthermore, oral microbiota can influence flavor perception by releasing volatile compounds that can enhance or alter the perception of food products. In this review, considering the glycosidic flavor precursors present in diverse food and beverage products, we underscore the significance of glycosidases with various origins. Subsequently, we delve into emerging insights regarding the release of aroma within the human oral cavity due to the activity of oral microbial glycosidases.

Flavor perception and health benefits of tea

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Recovery of flavor compounds from vanilla bagasse by hydrolysis and their identification through UPLC-MSE

Vanilla is a globally treasured commodity, and the consequences of its unstable value affect social, environmental, economic, and academic ambits. The extensive range of aroma molecules found in cured vanilla beans is crucial to the complexity of this natural condiment and knowledge about their recovery is of the essence. Many strategies aim on reproducing the chemical intricacies of vanilla flavor, such as biotransformation and de novo biosynthesis. Few studies, however, aim at the exhaustion of the cured pods, of which the bagasse, after the traditional ethanolic extraction, might still bear a highly valued flavor composition. An untargeted liquid chromatography coupled with mass spectrometry (LC-MS^E) approach was applied to elucidate if sequential alkaline-acidic hydrolysis was effective in extracting flavor related molecules and chemical classes from the hydro-ethanolic fraction. Important vanilla flavor related compounds present in the hydro-ethanolic fraction were further extracted from the residue through alkaline hydrolysis, such as vanillin, vanillic acid, 3-methoxybenzaldehyde, 4-vinylphenol, heptanoic acid, and protocatechuic acid. Acid hydrolysis was effective on further extracting features from classes such as phenols, prenol lipids, and organooxygen compounds, though representative molecules remain unknown. Finally, sequential alkaline-acidic hydrolysis rendered natural vanilla's ethanolic extraction residues as an interesting supplier of its own products, which could be used as a food additive, and many other applications.

The hops (Humulus lupulus) genome contains a mid-sized terpene synthase family that shows wide functional and allelic diversity

BACKGROUND

Hops (Humulus lupulus L.) are a dioecious climbing perennial, with the dried mature "cones" (strobili) of the pistillate/female inflorescences being widely used as both a bittering agent and to enhance the flavour of beer. The glandular trichomes of the bract and bracteole flowering structures of the cones produce an abundance of secondary metabolites, such as terpenoids, bitter acids and prenylated phenolics depending on plant genetics, developmental stage and environment. More knowledge is required on the functional and allelic diversity of terpene synthase (TPS) genes responsible for the biosynthesis of volatile terpenes to assist in flavour-directed hop breeding.

RESULTS

Major volatile terpene compounds were identified using gas chromatography-mass spectrometry (GC-MS) in the ripe cones of twenty-one hop cultivars grown in New Zealand. All cultivars produced the monoterpene β-myrcene and the sesquiterpenes α-humulene and β-caryophyllene, but the quantities varied broadly. Other terpenes were found in large quantities in only a smaller subset of cultivars, e.g. β-farnesene (in seven cultivars) and α-pinene (in four). In four contrasting cultivars (Wakatu™, Wai-iti™, Nelson Sauvin™, and 'Nugget'), terpene production during cone development was investigated in detail, with concentrations of some of the major terpenes increasing up to 1000-fold during development and reaching maximal levels from 50-60 days after flowering. Utilising the published H. lupulus genome, 87 putative full-length and partial terpene synthase genes were identified. Alleles corresponding to seven TPS genes were amplified from ripe cone cDNA from multiple cultivars and subsequently functionally characterised by transient expression in planta. Alleles of the previously characterised HlSTS1 produced humulene/caryophyllene as the major terpenes. HlRLS alleles produced (R)-(-)-linalool, whilst alleles of two sesquiterpene synthase genes, HlAFS1 and HlAFS2 produced α-farnesene. Alleles of HlMTS1, HlMTS2 and HlTPS1 were inactive in all the hop cultivars studied.

CONCLUSIONS

Alleles of four TPS genes were identified and shown to produce key aroma volatiles in ripe hop cones. Multiple expressed but inactive TPS alleles were also identified, suggesting that extensive loss-of-function has occurred during domestication and breeding of hops. Our results can be used to develop hop cultivars with novel/improved terpene profiles using marker-assisted breeding strategies to select for, or against, specific TPS alleles.

Effect of Hop Varieties and Forms in the Hopping Process on Non-Alcoholic Beer Quality

The aim of this study was to determine how the hopping technique affects the quality of non-alcoholic beer (NAB). A series of NABs were brewed and tested for basic physicochemical characteristics, profiles of selected volatile compounds, and microbial contamination. The brewing process yielded 13 experimental groups of beers, all of which had an ethanol content of <0.5%v/v. Among the batches brewed with ‘Marynka’ hops, the pellet form was found to provide the highest concentrations of hop-derived volatile compounds, whereas in the ‘Magnum’ groups, the extracts and whole hops proved superior. Humulene and caryophyllene were the primary volatiles in terms of quantity. All the brews were contamination-free—no microbes other than yeast cells were detected. Their microbiological purity was also supported by an assay of beer-defect indicators (volatile compounds), which only showed low levels of acetaldehyde, 1-propanol, 2-methylbutanol, and 3-methylbutanol. The hopping technique deployed was found not to affect the physicochemical parameters of NABs, but did have a significant impact on their volatile compound profile.

Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques

Tea is among the most consumed nonalcoholic beverages worldwide. Understanding tea flavor, in terms of both sensory aspects and chemical properties, is essential for manufacturers and consumers to maintain high quality of tea products and to correctly distinguish acceptable or unacceptable products. This article gives a comprehensive review on the aroma and off-flavor characteristics associated with 184 odorants. Although many efforts have been made toward the characterization of flavor compounds in different types of tea, modern flavor analytical techniques that affect the results of flavor analysis have not been compared and summarized systematically up to now. Thus, the overview mainly provides the instrumental flavor analytical techniques for both aroma and taste of tea (i.e., extraction and enrichment, qualitative, quantitative, and chemometric approaches) as well as descriptive sensory analytical methodologies for tea, which is helpful for tea flavor researchers. Flavor developments of tea evolved toward time-saving, portability, real-time monitoring, and visualization are also prospected to get a deeper insight into the influences of different processing techniques on the formation and changes of flavor compounds, especially desired flavor compounds and off-flavor substances present at (ultra)trace amounts in tea and tea products.

Metabolomics identify landscape of food sensory properties

Sensory evaluation is a key component of food production strategy. The classical food sensory evaluation method is time-consuming, laborious, costly, and highly subjective. Since flavor (taste and smell), texture, and mouthfeel are all related to the chemical properties of food, there has been a growing interest in how they affect the senses of food. In the past decades, emerging metabolomics has received much attention in the field of sensory evaluation, because it not only offers a broad picture of chemical composition for sensory properties but also revealed their changes and functions in food proceeding. This article reviewed food chemicals regarding the flavor, smell, and texture of foods, and discussed the advantages and limitations of applying metabolomics approaches to sensory evaluation, including GC-MS, LC-MS, and NMR. Taken together, this review gives a comprehensive, critical overview of the current state, future challenges, and trends in metabolomics on food sensory properties.

An efficient, fast, and green procedure to quantify α- and β-acids and xanthohumol in hops and their derived products

The main precursors of bitter principles of beer are α-acids, followed by β-acids. Determination of their content in hop cones and their derivatives is an essential part of brewing. HPLC-UV is the preferred technique when a more precise quantification of some specific bitter acids are required. However, current methods do not allow the proper quantification of all the six major α- and β-acids; furthermore, these multi-step methods generate considerable volumes of chemical waste. In this work, a new UHPLC-UV protocol was developed and compared side-by-side with reference, considering traditional and sustainability parameters. Baseline separations were achieved for the six major bitter acids and xanthohumol, while a greener and faster sample preparation procedure was developed. The new validated procedure could be adopted for quality control of hops and their derivative products with enhanced sample throughput and with a potential gain in the safety of the analyst.

Performance of alternative drying techniques on hop (Humulus lupulus L.) aroma quality: An HS-SPME-GC-MS-O and chemometrics combined approach

Economically feasible and effective hop drying strategies are urgently needed to respond to the increasing number of microbrewers in US. In this study, hops were dried by dehydrator-drying (52 °C), oven-drying (52 °C) and freeze-drying (25 °C) until the final moisture content reached 8-10%. Headspace solid-phase microextraction-gas chromatography-mass spectrometry-olfactometry (HS-SPME-GC-MS-O) was employed to analyze the aroma profiles in all dried hops. Methyl octanoate, β-myrcene, trans-α-bergamotene, linalool and geraniol were perceived as high-intensity aromas in all samples. Generally, dehydrator-dried hops contained the highest contents of aroma compounds among all groups, showing an increase of 5-23% and 6-37% when compared to freeze- and oven-dried hops, respectively. Principal component and hierarchical cluster analyses also revealed aroma content differences from three drying methods. Dehydrator drying at 52 °C was therefore considered as an alternative and promising drying approach for smaller-scale hop processing, which can largely benefit regional producers and local craft breweries.

Comparative investigation on aroma profiles of five different mint (Mentha) species using a combined sensory, spectroscopic and chemometric study

Mint is a widely used aromatic plant, and the aroma varies among different species. The aroma of five mint species, Mentha citrata L. (MC), Mentha piperita L. (MPI), Mentha spicata L. (MSP), Mentha persicaria L. (MPE), and Mentha suaveolens L. (MSU), were comparatively studied on the sensorial and molecular level. Quantitative descriptive analysis revealed that MC presented a pronounced lemon-like note, MSU is dominated by citrus and floral aromas, MPI has a prominent minty flavor, MSP and MPE have a similar scent, both of which are flavored with a spearmint-like note. Forty-one odorants with odor activity values (OAVs) ≥1 were characterized. Principal component analysis and orthogonal partial least squares discrimination analysis based on OAVs indicated that α-citral, menthofuran, isomenthone, menthol, carvone, and linalool were potential odor-active markers for five mint species discrimination. This study herein will provide guidance for mint resources utilization and also aid mint breeding with better flavor.

Aroma characterization of regional Cascade and Chinook hops (Humulus lupulus L.)

Aroma compounds in Cascade and Chinook hops harvested from multiple Virginia locations were identified by gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and aroma extract dilution analysis (AEDA). Selected aroma compounds were quantitated by combination of stable isotope dilution analysis (SIDA) and standard addition method (SAM). A total of 33 aroma-active compounds were detected in five samples with β-myrcene, methyl octanoate, geraniol and linalool being the predominant compounds based on their high flavor dilution (FD) factors and odor activity values (OAVs). L-Calamenene and germacrene B was the major characteristic component unique to Cascade and Chinook variety, respectively. Principal component analysis (PCA) showed distinctive aroma profiles for all samples except for Blacksburg and Petersburg Cascade. Hierarchical cluster analysis (HCA) reflected the higher contents of most aroma-active compounds in Meadowview Cascade and Chinook when compared to their counterparts. The significant variations suggested the potential influences of environmental factors and agronomic practices on hop aroma quality.

Optimized Supercritical CO2 Extraction Enhances the Recovery of Valuable Lipophilic Antioxidants and Other Constituents from Dual-Purpose Hop (Humulus lupulus L.) Variety Ella

The article presents the optimization of supercritical CO₂ extraction (SFE-CO₂) parameters using response surface methodology (RSM) with central composite design (CCD) in order to produce single variety hop (cv. Ella) extracts with high yield and strong in vitro antioxidant properties. Optimized SFE-CO₂ (37 MPa, 43 °C, 80 min) yielded 26.3 g/100 g pellets of lipophilic fraction. This extract was rich in biologically active α- and β-bitter acids (522.8 and 345.0 mg/g extract, respectively), and exerted 1481 mg TE/g extract in vitro oxygen radical absorbance capacity (ORAC). Up to ~3-fold higher extraction yield, antioxidant recovery (389.8 mg TE/g pellets) and exhaustive bitter acid extraction (228.4 mg/g pellets) were achieved under the significantly shorter time compared to the commercially used one-stage SFE-CO₂ at 10–15 MPa and 40 °C. Total carotenoid and chlorophyll content was negligible, amounting to <0.04% of the total extract mass. Fruity, herbal, spicy and woody odor of extracts could be attributed to the major identified volatiles, namely β-pinene, β-myrcene, β-humulene, α-humulene, α-selinene and methyl-4-decenoate. Rich in valuable bioactive constituents and flavor compounds, cv. Ella hop SFE-CO₂ extracts could find multipurpose applications in food, pharmaceutical, nutraceutical and cosmetics industries.

Hop-induced formation of ethyl esters in dry-hopped beer

Abstract

Fruity smelling esters play an important role for the aroma of hops and beer and they have been characterized as key aroma compounds in different hop varieties. Studies on the transfer of hop-derived compounds into beer during dry-hopping showed calculated transfer rates of different ethyl esters far above 100%, leading to the assumption that these esters must be newly formed. To investigate this formation, dry-hopping was imitated in water to eliminate the influence of the beer matrix on the formation of these odorants. Thereby, the formation of ethyl esters of 2-methylbutanoic acid, 3-methylbutanoic acid, and methylpropanoic acid, induced by the addition of hops, was shown. Different approaches inhibiting enzyme activities and experiments with different hop extracts might lead to the assumption that enzymes are involved in the formation of these esters, beside possible transesterification.

Graphical abstract

Dry-Hopping to Modify the Aroma of Alcohol-Free Beer on a Molecular Level-Loss and Transfer of Odor-Active Compounds

There are mainly two options for the dealcoholization of beer: evaporation of ethanol by heat treatment, whereby desired aroma-active compounds are also removed, and stopped fermentation that leads to beers still containing high amounts of unfermented sugar in parallel with lower amounts of aroma-active fermentation products. Thus, dry-hopping could be an opportunity to compensate for these aroma deficiencies. Therefore, following the sensomics approach, odorants were characterized in dry-hopped (Hallertauer Mandarina Bavaria, Hallertauer Cascade, or Hallertauer Mittelfrüh) top- and bottom-fermented alcohol-free beers either after thermal dealcoholization or stopped fermentation. Twenty-three odorants were quantitated via stable isotope dilution analysis, and odor activity values (OAVs; ratio of concentration to odor threshold) were calculated. Thermally dealcoholized samples showed high losses (up to 100%) of key odorants like 3-methyl-1-butanol or 3-methylbutyl acetate. During stopped fermentation, aroma compounds like ethyl butanoate or 2-phenylethanol were formed in relevant concentrations, leading to OAVs ≥ 1, but the amounts were significantly lower compared to beers with normal alcohol contents. For hop-derived odorants (linalool, geraniol, myrcene, and esters), transfer rates between 20 and 90% were found, leading to OAVs ≥ 1 in beer. Furthermore, hop addition apparently induced the formation of ethyl esters of hop-derived monocarboxylic acids.

Identification of key odorants in complex mixtures occurring in nature

Covering: up to 2019Soon after the birth of gas chromatography, mass spectrometry and olfactometry were used as detectors, which allowed impressive development to be achieved in the area of odorant determinations. Since the mid-80s, structured methods of gas chromatography-olfactometry have appeared, allowing the determination of which odor constituents play a key role in materials. Progressively, numerous strategies have been proposed for sample preparation from raw materials, the representativeness evaluation of extracts, the identification of odor constituents, their quantification, and subsequently, the recombination of the key odorants to mimic the initial odor. However, the multiplicity of options at each stage of the analysis leads to a confusing landscape in this field, and thus, the present review aims at critically presenting the available options. For each step, the most frequently used alternatives are described, together with their strengths and weaknesses based on theoretical and experimental justifications according to the literature. These techniques are exemplified by many applications in the literature on aromas, fragrances and essential oils, with the initial focus on wine odorants, followed by a short overview on the molecular diversity of key odorants, which illustrates most of the facets and complexities of odor studies, including the issues raised by odorant interactions such as synergies.

Co-fermentation Involving Saccharomyces cerevisiae and Lactobacillus Species Tolerant to Brewing-Related Stress Factors for Controlled and Rapid Production of Sour Beer

Increasing popularity of sour beer urges the development of novel solutions for controlled fermentations both for fast acidification and consistency in product flavor and quality. One possible approach is the use of Saccharomyces cerevisiae in co-fermentation with Lactobacillus species, which produce lactic acid as a major end-product of carbohydrate catabolism. The ability of lactobacilli to ferment beer is determined by their capacity to sustain brewing-related stresses, including hop iso-α acids, low pH and ethanol. Here, we evaluated the tolerance of Lactobacillus brevis BSO464 and Lactobacillus buchneri CD034 to beer conditions and different fermentation strategies as well as their use in the brewing process in mixed fermentation with a brewer's yeast, S. cerevisiae US-05. Results were compared with those obtained with a commercial Lactobacillus plantarum (WildBrewTM Sour Pitch), a strain commonly used for kettle souring. In pure cultures, the three strains showed varying susceptibility to stresses, with L. brevis being the most resistant and L. plantarum displaying the lowest stress tolerance. When in co-fermentation with S. cerevisiae, both L. plantarum and L. brevis were able to generate sour beer in as little as 21 days, and their presence positively influenced the composition of flavor-active compounds. Both sour beers were sensorially different from each other and from a reference beer fermented by S. cerevisiae alone. While the beer produced with L. plantarum had an increased intensity in fruity odor and dried fruit odor, the L. brevis beer had a higher total flavor intensity, acidic taste and astringency. Remarkably, the beer generated with L. brevis was perceived as comparable to a commercial sour beer in multiple sensory attributes. Taken together, this study demonstrates the feasibility of using L. brevis BSO464 and L. plantarum in co-fermentation with S. cerevisiae for controlled sour beer production with shortened production time.