Effect of yeast strain on aroma compounds in Cabernet franc icewines

Comprehensive Analysis of Physicochemical Properties and Volatile Compounds in Different Strawberry Wines under Various Pre-Treatments

Pre-fermentation treatment has an important impact on the color, aroma, taste, and other characteristics of fruit wine. To discover suitable pre-treatment techniques and conditions that yield strawberry wine of excellent quality, the influences of juice fermentation, pulp maceration, thermovinification, and enzymatic hydrolysis pre-treatments on the basic chemical composition, color, antioxidant capacity, and volatile organic compounds in strawberry wines were investigated. The results showed that the color, antioxidant properties, and volatile aroma of strawberry wines fermented with juice were different from those with pulp. Strawberry wines fermented from juice after 50 °C maceration had more desirable qualities, such as less methanol content (72.43 ± 2.14 mg/L) compared with pulp-fermented wines (88.16 ± 7.52 mg/L) and enzymatic maceration wines (136.72 ± 11.5 mg/L); higher total phenolic content (21.78%) and total flavonoid content (13.02%); enhanced DPPH (17.36%) and ABTS (27.55%) free radical scavenging activities; richer essential terpenoids and fatty acid ethyl esters, such as linalool (11.28%), ethyl hexanoate (14.41%), ethyl octanoate (17.12%), ethyl decanoate (32.49%), and ethyl 9-decenoate (60.64%); pleasant floral and fruity notes compared with juice-fermented wines macerated at normal temperatures; and a lighter color. Overall, juice thermovinification at 50 °C is a potential pre-treatment technique to enhance the nutrition and aroma of strawberry wine.

Effects of high power pulsed microwave on the enhanced color and flavor of aged blueberry wine

A new method of high-power pulsed microwave (HPPM) was applied to accelerate the aging of blueberry wine. The color changes of blueberry wines during aging were investigated through Chemical Wine Age and CIE-LAB measurement. Results showed that the blueberry wines treated by HPPM at low frequencies (50 and 100 Hz) exhibited improved color characteristics with L* value reaching 47.04 at 100 Hz, an increased maturity of wine body, and a shortened chemical wine age from 90 days to 75 days. Moreover, the aroma changes determined by GC-MS showed that HPPM accelerated the formation of esters in blueberry wine, which were increased by 18.44% and 56.97% respectively under the conditions of 50 and 150 Hz. The formation of acid substances was reduced compared with the original wine, with contents of acetic acid, caproic acid, and octanoic acid of 29.46 µg/mL, 15.60 µg/mL, 17.74 µg/mL, respectively, displaying an enhanced wine flavor.

Food yeasts: occurrence, functions, and stress tolerance in the brewing of fermented foods

With the rapid development of systems biology technology, there is a deeper understanding of the molecular biological mechanisms and physiological characteristics of microorganisms. Yeasts are widely used in the food industry with their excellent fermentation performances. While due to the complex environments of food production, yeasts have to suffer from various stress factors. Thus, elucidating the stress mechanisms of food yeasts and proposing potential strategies to improve tolerance have been widely concerned. This review summarized the recent signs of progress in the variety, functions, and stress tolerance of food yeasts. Firstly, the main food yeasts occurred in fermented foods, and the taxonomy levels are demonstrated. Then, the main functions of yeasts including aroma enhancer, safety performance enhancer, and fermentation period reducer are discussed. Finally, the stress response mechanisms of yeasts and the strategies to improve the stress tolerance of cells are reviewed. Based on sorting out these related recent researches systematically, we hope that this review can provide help and approaches to further exert the functions of food yeasts and improve food production efficiency.

Re-Rolling Treatment in the Fermentation Process Improves the Aroma Quality of Black Tea

Aroma is a vital factor influencing tea quality and value. It is a challenge to produce a kind of black tea with a floral/fruity aroma, good taste, and without a green/grassy odor simultaneously using small- and medium-leaf tea species. In this study, the effect of re-rolling treatment on the aroma quality of small-leaf Congou black tea was investigated using the methods of the equivalent quantification of aroma and gas chromatography-mass spectrometry (GC-MS). Sensory evaluation showed that re-rolling treatment improved the aroma quality of Congou black tea by conferring upon it floral and fruity scents. In total, 179 volatile compounds were identified using GC-MS, of which 97 volatiles showed statistical differences (Tukey s-b(K), p < 0.05). Re-rolling treatment significantly reduced the levels of alcoholic fatty acid-derived volatiles (FADVs) and volatile terpenoid (VTs), but increased the levels of aldehydic and ester FADVs, most amino acid-derived volatiles (AADVs), carotenoid-derived volatiles (CDVs), alkene VTs, and some other important volatile compounds. Based on the odor characteristics and fold changes of differential volatile compounds, hexanoic acid, hexyl formate, cis-3-hexenyl hexanoate, (Z)-3-hexenyl benzoate, hexyl hexanoate, phenylacetaldehyde, benzyl alcohol, β-ionone, α-ionone, dihydroactinidiolide, ipsenone, β-farnesene, β-octalactone, melonal, etc., were considered as the potential key odorants responsible for the floral and fruity scents of re-rolled black tea. In summary, this study provides a novel and simple processing technology to improve the aroma quality of small-leaf Congou black tea, and the results are beneficial to enriching tea aroma chemistry.

Monitoring the Aroma Compound Profiles in the Microbial Fermentation of Seaweeds and Their Effects on Sensory Perception

Seaweeds have a variety of biological activities, and their aromatic characteristics could play an important role in consumer acceptance. Here, changes in aroma compounds were monitored during microbial fermentation, and those most likely to affect sensory perception were identified. Ulva sp. and Laminaria sp. were fermented and generally recognized as safe microorganisms, and the profile of volatile compounds in the fermented seaweeds was investigated using headspace solid-phase microextraction with gas chromatography–mass spectrometry. Volatile compounds, including ketones, aldehydes, alcohols, and acids, were identified during seaweed fermentation. Compared with lactic acid bacteria fermentation, Bacillus subtilis fermentation could enhance the total ketone amount in seaweeds. Saccharomyces cerevisiae fermentation could also enhance the alcohol content in seaweeds. Principal component analysis of volatile compounds revealed that fermenting seaweeds with B. subtilis or S. cerevisiae could reduce aldehyde contents and boost ketone and alcohol contents, respectively, as expected. The odor of the fermented seaweeds was described by using GC–olfactometry, and B. subtilis and S. cerevisiae fermentations could enhance pleasant odors and reduce unpleasant odors. These results can support the capability of fermentation to improve the aromatic profile of seaweeds.

Use of Mixed Cultures for the Production of Grape–Plum Low-Alcohol Fermented Beverages

This work presents the attempt to develop a production technology for grape–plum low-alcohol beverages and enhance their chemical composition and flavor complexity through the non-Saccharomyces species. Saccharomyces cerevisiae (SC) pure cultures were used as reference beverages. Pure cultures of Lachancea thermotolerans (LT) and co-inoculated Lachancea thermotolerans with Saccharomyces cerevisiae (MIX) were included for grape–plum must fermentation at a pilot scale. The process involves two steps: a primary alcoholic fermentation in stainless steel tanks (F1) and a secondary fermentation in a bottle after dextrose syrup addition (F2). The chemical compositions of all beverages obtained in F1 and F2 were studied. Compared to SC, must inoculated with L. thermotolerans (LT and MIX) required four more days to complete the fermentation of sugars during F1. SC fermentation tended to have slightly higher pH and titratable acidity values and lower concentrations of total phenols. Final levels of aromatic precursor nitrogen and sulfur amino nitrogen were obtained more in SC than in LT and MIX. SC treatment had higher final levels of histidine, phenylalanine, isoleucine, lysine, methionine, threonine, valine, and cysteine. Related to individual amino acids, SC treatment had higher final levels of histidine, phenylalanine, isoleucine, lysine, methionine, threonine, valine, and cysteine. Analysis of the volatile composition showed that, compared with SC, MIX had the highest percentage of higher alcohols (3-methyl-1-butanol and 2-methyl-1-butanol) and acetates (isoamyl acetate and isobutyl acetate) which are associated with fruity and banana aromas. A decreasing trend in volatile fatty acids was observed in LT and MIX compared to SC. LT application, both in pure and mixed culture, significantly modified the values of the percentage of 5 of the 10 ethyl ester compounds analyzed. Finally, the sensory analysis showed that there were no significant differences, even though the non-Saccharomyces had a higher percentage of volatile metabolites. The results have shown that through this process an innovative and high-quality product was obtained: a low-alcohol beverage made from grapes and plums, which could be developed at an industrial level due to the increasing interest of consumers in this type of product.

Saturated Linear Aliphatic γ- and δ-Lactones in Wine: A Review

Saturated linear aliphatic lactones are widespread aroma compounds in wine, linked to stone fruit, dried red fruit, and coconut descriptors. Despite their ubiquity, bioproduction pathways associated with these compounds in wine are unclear, but higher concentrations have been linked to many common vitivinicultural practices, including grape variety, microbiological influence, oak- and bottle-aging, and wine styles such as late harvest, noble rot, and icewine. Development of analytical techniques has enabled increasingly accurate quantification of lactones in wine, shedding more light on their potential origins. This review provides an in-depth summary of the research into linear aliphatic lactones over the past 50 years and provides direction for possible future research to elucidate the biogenesis of these compounds and better estimate their impact on wine aroma.

Impact of Two Commercial S. cerevisiae Strains on the Aroma Profiles of Different Regional Musts

The present research is aimed at investigating the potential of two commercial Saccharomyces cerevisiae strains (EC1118 and AWRI796) to generate wine-specific volatile molecule fingerprinting in relation to the initial must applied. To eliminate the effects of all the process variables and obtain more reliable results, comparative fermentations on interlaboratory scale of five different regional red grape musts were carried out by five different research units (RUs). For this purpose, the two S. cerevisiae strains were inoculated separately at the same level and under the same operating conditions. The wines were analyzed by means of SPME-GC/MS. Quali-quantitative multivariate approaches (two-way joining, MANOVA and PCA) were used to explain the contribution of strain, must, and their interaction to the final wine volatile fingerprinting. Our results showed that the five wines analyzed for volatile compounds, although characterized by a specific aromatic profile, were mainly affected by the grape used, in interaction with the inoculated Saccharomyces strain. In particular, the AWRI796 strain generally exerted a greater influence on the aromatic component resulting in a higher level of alcohols and esters. This study highlighted that the variable strain could have a different weight, with some musts experiencing a different trend depending on the strain (i.e., Negroamaro or Magliocco musts).

Evaluation of Four Indigenous Non-Saccharomyces Yeasts Isolated from the Shangri-La Wine Region (China) for Their Fermentation Performances and Aroma Compositions in Synthetic Grape Juice Fermentation

This study investigated the fermentation performances and aroma compositions of synthetic grape juice that was fermented by four indigenous non-Saccharomyces yeast isolates that were obtained from the Shangri-La wine region (China): Meyerozyma guilliermondii (AD-58), Saccharomycopsis vini (BZL-28), Saturnispora diversa (BZL-11), and Wickerhamomyces anomalus (DR-110), in comparison to those of Saccharomyces cerevisiae (EC1118). The four indigenous non-Saccharomyces yeasts showed a lower fermentative capacity and a lower conversion rate of sugar to alcohol, but a higher yield of volatile acidity. W. anomalus (DR-110) had a greater ability to produce numerous esters and short-chain fatty acids and the representative flavors of its fermented medium were fruity and fatty. Sac. vini (BZL-28), interestingly, exhibited great capacity in the formation of many monoterpenes, particularly (Z)-β-ocimene, E-β-ocimene, linalool, citral, and geraniol and its fermented medium was characterized by a strong fruity (citrus-like) and floral flavor. M. guilliermondii (AD-58) and Sat. diversa (BZL-11) only mildly affected the aroma profiles of their resultant fermented media, since the concentrations of most of the volatiles that were produced by these two isolates were much lower than their sensory thresholds. The four indigenous non-Saccharomyces yeasts exhibited distinctive fermentation performances and aroma production behaviors. In particularly, W. anomalus (DR-110) and Sac. vini (BZL-28) have shown good potential in enhancing the aromas and complexity of wine.

Semibiocatalytic Approach toward Regioisomerically Enriched Ethyl Dimethylpyrazines Important in Flavor Industries

Alkylpyrazines are important heterocyclic compounds used as flavorants in food and beverage industries. In this study, a regioselective semibiocatalytic process was developed to synthesize 2-ethyl-3,5-dimethylpyrazine (235-EDMP) over its 3-ethyl-2,5-dimethyl pyrazine (325-EDMP) isomer and vice versa. We initially explored how sterics could direct the coupling orientations between diamines and diketones to access 235- or 325-EDMP selectively. Also, the physical parameters of the reaction conditions were changed, such as reduced temperature, the order-of-addition of the reactants, and supplementation with chiral zeolites to template the orientation of the coupling partners to direct the reaction regiochemistry. Each reaction trial resulted in 50:50 mixtures of the EDMP isomers. An alternative approach was explored to control the regioselectivity of the reactions; α-hydroxy ketones replaced the diketones as the electrophilic coupling reactant used in previous trial experiments. The hydroxy ketone reactants were made biocatalytically with pyruvate decarboxylase. The coupling reaction between 2-hydroxypentan-3-one and propane-1,2-diamine resulted in the desired 235-EDMP at >70% (∼77 mg) relative to 325-EDMP in the mixture. The 3-hydroxypentan-2-one congener was biocatalyzed and reacted with propane-1,2-diamine as a proof of principle to synthesize 325-EDMP (∼60% relative abundance, ∼73 mg) over 235-EDMP. These results suggested a mechanism that was directed by the hydroxy ketone electrophilicity and the sterics at the diamine nucleophilic centers.

New Ciders Made by an Exhaustion Method: An Option to Val-Orise Subproducts from the Making of Ice Ciders

Cryo-extraction (pressing of frozen apples), is one of the two freeze-enrichment systems allowed for the making of ice juices. Its ciders are often described as more complex and aromatic, however, the production yield is quite low. The Exhaustion method associated with the previous one proposes the valorisation of the discarded apple juice fractions for the making of new ciders. Three types of apple juices and three species of yeasts (S. bayanus, C6; S. cerevisiae, Levuline-CHP, and T. delbrueckii, Biodiva-TD291) have been used to evaluate the Exhaustion method. The ciders obtained were analysed for chemical and volatile composition as well as sensory characteristics. The yield (%) of the Exhaustion process ranged between 24 and 37%. The yeasts promoted the fermentation at different rates, providing ciders with alcoholic degrees between 9 and 12 (%v/v), and low volatile acidities. The yeast strain significantly influenced most of the parameters analysed, whereas the raw apple juice influenced the perception of the attributes fruity, apple and butter. Although the ciders produced by Exhaustion presented significantly lower concentrations of all the volatile compounds analysed than the corresponding ice ciders obtained by Cryo-extraction, the S. bayanus C6 and T. delbrueckii TD291 gave highly valued ciders from the sensory point of view.

Different Wines from Different Yeasts? "Saccharomyces cerevisiae Intraspecies Differentiation by Metabolomic Signature and Sensory Patterns in Wine"

Alcoholic fermentation is known to be a key stage in the winemaking process that directly impacts the composition and quality of the final product. Twelve wines were obtained from fermentations of Chardonnay must made with twelve different commercial wine yeast strains of Saccharomyces cerevisiae. In our study, FT-ICR-MS, GC-MS, and sensory analysis were combined with multivariate analysis. Ultra-high-resolution mass spectrometry (uHRMS) was able to highlight hundreds of metabolites specific to each strain from the same species, although they are characterized by the same technological performances. Furthermore, the significant involvement of nitrogen metabolism in this differentiation was considered. The modulation of primary metabolism was also noted at the volatilome and sensory levels. Sensory analysis allowed us to classify wines into three groups based on descriptors associated with white wine. Thirty-five of the volatile compounds analyzed, including esters, medium-chain fatty acids, superior alcohols, and terpenes discriminate and give details about differences between wines. Therefore, phenotypic differences within the same species revealed metabolic differences that resulted in the diversity of the volatile fraction that participates in the palette of the sensory pattern. This original combination of metabolomics with the volatilome and sensory approaches provides an integrative vision of the characteristics of a given strain. Metabolomics shine the new light on intraspecific discrimination in the Saccharomyces cerevisiae species.

Chemical and Sensory Characterization of Vidal Icewines Fermented with Different Yeast Strains

The aim of this study is to comprehensively investigate the aroma composition and sensory attributes of Vidal icewine fermented with four yeast strains (ST, K1, EC1118, and R2). A total of 485 kinds of volatile components were identified by comprehensive two-dimensional gas chromatography-time of flight mass spectrometry, among which 347 kinds of volatile compounds were the same in four kinds of sample. The heat map was conducted with 156 volatile compounds, which have aroma contributions, and the analysis results identified the characteristics of the aroma composition of icewine fermented with different yeasts. Quantitative descriptive analysis was performed with a trained panel to obtain the sensory profiles. The aroma attributes of honey and nut of the icewine fermented by R2 were much higher than others. Partial least squares discriminant analysis further provided 40 compounds that were mainly responsible for the differences of the aroma characteristics of the icewines fermented by four yeasts. This study provides more data on the current status of Vidal icewines by main commercial yeasts.

Aroma of Icewine: A Review on How Environmental, Viticultural, and Oenological Factors Affect the Aroma of Icewine

The aroma of a wine is mostly driven by not only the factors in the vineyard, such as the grape variety and harvest time, but also the fermentation process. Icewine is a unique, intensely sweet wine made from late harvested grapes that have frozen naturally on the vine. Different from normal table wines, the grapes used in icewine naturally undergo a dehydration process and freeze-thaw cycles, and the must for icewine making has to be pressed from frozen grapes. This pressing process leaves water behind as ice crystals and allows the grape juice to be concentrated with more sugars, acids, and other dissolved solids, resulting in a slower than normal fermentation. These special procedures can lead to a unique aroma characteristic of icewine. This review delves into recent advances in chemical compounds related to icewine aroma characteristics and addresses how changes in these aroma characteristics and composition are influenced by environmental, viticultural, and oenological factors in the vineyard and winery. Deficiencies in previous studies and future trends related to the flavor science of icewine were also briefly addressed.

Influence of Harvest Date and Grape Variety on Sensory Attributes and Aroma Compounds in Experimental Icewines of Ukraine

Icewine is a sweet dessert wine whose sensory and chemical attributes are caused by technology peculiarities including the special climatic conditions and acceptable grape varieties. This study aimed to evaluate the sensory characteristics and aromatic compounds in experimental icewines produced from the grape varieties Rkatsiteli, Telti kuruk, Marselan, and Moldova that had been picked in the Odessa region at temperatures of at least minus 7 °C during the 2015 (H1) and 2016 (H2) harvests. Sensory attributes were determined by trained experts, and descriptors for icewines were chosen by consensus. A total of 33 aromatic compounds including 12 that exceeded the threshold were identified using chromatographic analysis. Rkatsiteli icewine obtained from H1 was characterized by the highest concentration of geraniol, 1-octanol, and 2-phenyl acetate, influencing the pronounced citrus and sweet fruit aromas in sensory profiles. The highest concentrations of ethyl hexanoate and ethyl octanoate associated with aromas of dried fruits were detected in Moldova and Marselan icewines made from H2. No 1-hexanol and benzyl alcohol were found in Rkatsiteli and Telti kuruk icewines. Only Moldova and Marselan icewines had γ-nonalactone and benzaldehyde, respectively. Sensory parameters and the quantity of aromatic compounds of Ukrainian experimental icewines depended on harvest date and grape varieties.

Yeast population dynamics during spontaneous fermentation of icewine and selection of indigenous Saccharomyces cerevisiae strains for the winemaking in Qilian, China

BACKGROUND

Icewine produced in China is becoming popular, but there is only limited knowledge available on the yeast population that occurs during fermentation and also on the selection of indigenous Saccharomyces cerevisiae strains for its production. In this work, we first investigated yeast species and the evolution of yeast population in spontaneous fermentations of icewine produced in the Qilian region of China and then analyzed the biodiversity and important enological properties of S. cerevisiae isolates.

RESULTS

Seven species of five genera including S. cerevisiae, S. uvarum, Torulaspora delbrueckii, Hanseniaspora uvarum, Lachancea thermotolerans, Metschnikowia aff. fructicola and H. osmophila were identified by the colony morphology on Wallerstein Laboratory Nutrient medium and sequence analysis of the 26S rRNA gene D1/D2 domain. Saccharomyces cerevisiae, H. uvarum and L. thermotolerans were the dominant species, representing almost 87% of the total yeast isolates. Microvinification with seven preselected S. cerevisiae strains were performed on Vidal. All selected strains could complete fermentations, and the enochemical parameters were within the acceptable ranges of the wine industry. W5B3 produced higher amounts of ethyl hexanoate and ethyl octanoate than other strains. R3A10 was a low volatile acid producer and the corresponding icewine presented the highest values on some odorants including β-damascenone, 1-octen-3-ol, ethyl 2-methylbutyrate, and isoamyl alcohol. Vidal icewines fermented with R3A10, R3A16 and W5B3 were well accepted by the judges because of superior sensory quality.

CONCLUSION

Three indigenous strains (R3A10, R3A16 and W5B3) could be used as starters and could potentially improve the regional character of the icewine in Qilian. © 2020 Society of Chemical Industry.

Determination of selected terpenic substances in grapes and wine of the cultivar Pálava

The presented study is focused on the determination of the content of terpenic substances in grapes and subsequently produced a wine of Czech variety Pálava (the Czech Republic, wine region Morava), which is a protected landscape with long-term tradition and culture. The aim of this study was the analysis of the aromatic profile of the cultivar Pálava, which was fermented by the original yeast strains from the Moravian wine region. Larger amounts of flavoring substances occur in grapes as bound flavoring substances, most often in the form of glycosides. One of the basic groups of aromatic substances is monoterpenes. The content of twelve free and bound terpenic substances was measured by the GC-MS method, namely linalool, ho-trineol, α-terpeniol, β-citronellol, nerol, geraniol, furan linalool oxide 1, furan linalool oxide 2, nerol oxide, epoxylinalol 1, epoxylinalol 2 and 2,6-dimethyl-3,7-octadiene-2,6-diol. The results were statistically compared by using a simple descriptive statistical method and ANOVA method. We noted a difference between the content of free and bound terpenes was very significant (p ≤0.05). We found that using uncommercial yeasts could have an effect on the content of the volatile and terpenic compounds in wines. An important finding was that in fresh berry extracts there was a higher proportion of bound terpenes than free terpenes. The results have shown that the production technology of wine and the fermentation process has a clear impact on the content of the substances.

Comprehensive investigation of lactones and furanones in icewines and dry wines using gas chromatography-triple quadrupole mass spectrometry

A number of lactones and furanones associated with pleasant odorants play a vital role in grape and wine aroma profiles. However, they are usually present at trace levels and are particularly challenging to measure. In this work, an optimized method based on solid-phase extraction (SPE) coupled with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS/MS) was developed for simultaneous determination of 14 lactones and 3 furanones. The validation was carried out using different types of wine as matrices, and satisfactory linearity, sensitivity, trueness and precision were confirmed. Furaneol and sotolon showed significantly lower limits of detection (LODs) in three real wines compared to model wine due to the matrix effect. Furthermore, the method was successfully applied to investigate the concentration range of lactones and furanones in several icewines, dry red and white wines. Icewines contained higher concentrations of most lactones and furanones compared with dry red and white wines. Partial least squares-discriminate analysis (PLS-DA) also indicated that γ-hexa-, γ-octa-, γ-nona-, γ-deca-, δ-hexa-, and δ-decalactone, as well as 5,6-dihydro-6-pentyl-2H-pyran-2-one (C10 massoia lactone), sotolon and homofuraneol contributed greatly to the discrimination between icewines and dry wines. Moreover, the calculation of odor activity value (OAV) suggested that γ-octa-, γ-nona-, and γ-decalactone, as well as furaneol and homofuraneol contributed greatest to the aroma of icewines.

Aromatic Potential of Bordeaux Grape Cultivars: Identification and Assays on 4-Oxononanoic Acid, a γ-Nonalactone Precursor

γ-Nonalactone has been demonstrated to be a chemical marker of dried/cooked fruit nuances detected in must and wine, but little is known about its formation pathways. Therefore, on the basis of the literature, we hypothesized 4-oxononanoic acid as a potential precursor. Using dichloromethane extraction followed by gas chromatography coupled to negative chemical ionization mass spectrometry, this keto acid was identified and quantified in Merlot and Cabernet Sauvignon musts. Its concentration ranged from traces to 60 μg/L. The biotransformation of 4-oxononanoic acid into γ-nonalactone by Saccharomyces cerevisiae during alcoholic fermentation was demonstrated using labeled d₆-4-oxononanoic acid. Additional experiments shed light on the 4-oxononanoic acid role as a γ-nonalactone precursor and revealed that this biotransformation was (R)-enantioselective. Sensory and distribution studies of the enantiomers revealed that the detection threshold of R and S forms were 66 and 35 μg/L and the average ratio of R/S in grape and wine was 94:6 and 65:35.

Aromatic, olfactometric and consumer description of sweet ciders obtained by cryo-extraction

Nine ciders obtained by cryo-extraction were analysed for chemical, olfactometric and sensory characteristics. Three types of ice apple juices and three autochthonous yeast strains were evaluated. The quantitative volatile profile is mainly influenced by the apple juice. Regarding the olfactometric profiles of the ice ciders, 23 odorants not previously found in Spanish still ciders, and described as sweet, spicy, fruity and floral were observed. Among these, it is worth mentioning 5 high-boiling point compounds found in an olfactometric zone where heavy, phenolic odours predominate in still ciders. The sensory descriptions obtained by Check-All-That-Apply classified the ice ciders mainly by their sweet taste and smoothness, these attributes being the most influential in the assessment of the overall quality of the ciders. The most highly valued ciders were described as the sweetest, most fruity ones, in agreement with their having the highest values for the ratio between total sugars and total acidity.

Saccharomyces bayanus Enhances Volatile Profile of Apple Brandies

Qualitative and quantitative profiles of volatiles in alcoholic beverages depend mainly on the quality of raw materials, yeasts used for fermentation, and processing technique. Saccharomyces bayanus is a yeast species which is not commonly used for the production of alcoholic beverages, but it is able to produce volatiles that add desirable aroma. Since there is little information regarding the application of that microorganism for the production of apple brandies and how it affects volatile profile of finished products, we decided to address that issue. The aim of the study was to determine the impact of S. bayanus on the profile of volatile compounds and sensory properties of apple spirits obtained from three apple cultivars (Topaz, Rubin, and Elise) in comparison to spirits obtained from fermentation carried out spontaneously or with Saccharomyces cerevisiae. Obtained brandies were analysed using gas chromatography-flame ionization detector (GC-FID), solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and sensorially. In our study, brandies produced from musts fermented by S. bayanus demonstrated the highest concentration of ethyl esters and increased concentrations of isoamyl acetate, 2-phenylethyl acetate, ethyl palmitate and hexanol. Moreover, our results support the hypothesis that non-Saccharomyces yeasts which are present during spontaneous fermentation and demonstrate higher β-glucosidase activities enhance aroma of alcoholic beverages through releasing aroma compounds from glycosidic forms, e.g., α-phellandrene, (E)-β-fanesene, (Z,E)-α-farnesene, α-farnesene, and farnesol. Considering results obtained in sensory analysis, we proved that S. bayanus is suitable for the production of apple brandies, improving their flavour. Brandies obtained from musts fermented by S. bayanus obtained the highest average range for "overall note" parameter in sensory analysis.

Assessment of chemical composition and sensorial properties of ciders fermented with different non-Saccharomyces yeasts in pure and mixed fermentations

This work presents the attempt to enhance the flavor complexity of cider fermented by different non-Saccharomyces species. Pichia kluyveri and Hanseniaspora vineae pure cultures were used as reference ciders. Mixed cultures between all 4 species gave 5 fermentations, where Hanseniaspora uvarum or Torulaspora quercuum were included for apple juice fermentation. Chemical composition and sensorial properties of all ciders were studied. The results indicated that the growth of P. kluyveri and H. vineae were interreacted and also affected by H. uvarum and T. quercuum. H. vineae was more capable of consuming sugar than P. kluyveri. Ciders from the single culture fermentation with P. kluyveri (Pk), as well as from mixed fermentation with P. kluyveri and H. uvarum (Pk-Hu), had high residual sugar, sugar/acid ratio, and glucose-fructose consumption ratio. Large shifts in the consumption and production of organic acids and polyphenols among all ciders were observed. The calculation of the relative odor activity value (rOAV) showed that 17 volatile compounds had an rOAV >1 in at least one sample, and acetate esters and ethyl esters were the groups with the highest number of volatile compounds of importance to the cider aroma. Among these 17 compounds, 3-methylbutyl acetate, 2-methylbutyl acetate, ethyl hexanoate, ethyl octanoate, and β-damascenone exhibited high rOAVs in some ciders and might contribute fruity, floral, and sweet features to the cider aroma. Besides, the tropical fruity aroma from 3-methylbutyl acetate was only perceived in Pk and Pk-Hu. The partial least squares regression (PLSR) analysis revealed that acetate esters contributed positively to the roasted and cooked odor of all ciders. This is the first study evaluating simultaneous fermentation of two non-Saccharomyces yeasts to produce cider, which provides new insights into cider production.

The effects of apple variety, ripening stage, and yeast strain on the volatile composition of apple cider

This work examined the degree of influence of apple variety, apple ripening stage, and yeast strain on the volatile composition of apple cider. Four apple varieties grown in Estonia were selected for the study – Antei, Melba, Kulikovskoye, and Orlovski Sinap. The must from the apples at various stages of ripening (unripe, ripe, overripe) underwent alcoholic fermentation using commercially available yeast strains. Gas chromatography - mass spectrometry was employed to assess the differences in volatile composition between the samples. Out of the variables analyzed in this work, apple variety turned out to be the primary attribute influencing the quality and aroma properties of apple cider. The effect of yeast strain and the maturity of the fruit was variety-specific where the volatile profiles of ciders made with Melba variety were the least influenced by the ripening stage of apples and yeast strains used for the fermentation.

Characterization and differentiation of key odor-active compounds of 'Beibinghong' icewine and dry wine by gas chromatography-olfactometry and aroma reconstitution

Freezing-thawing events contribute to the unique aroma profile of icewines. Differences in key odor-active volatile compounds between 'Beibinghong' (Vitis amurensis × V. vinifera) icewines and dry wines were investigated by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Acceptable agreement between the olfactometric and quantitative results was obtained. 'Beibinghong' icewine was characterized by high concentrations of volatile phenols, lactones, (E)-β-damascenone, and phenylacetaldehyde, which were associated with on-vine freezing-thawing events in grape. Low concentrations of higher alcohol acetates and ethyl esters of fatty acids were attributed to hyperosmotic stress during fermentation. The overall aroma of icewine could be mimicked by reconstitution containing 44 identified volatiles. Partial least squares regression analysis demonstrated that the concentrations of these volatile compounds determined the distinct sensory profiles of icewines, which have higher intensities of honey/sweet, smoky, caramel, dried fruit, apricot/peach, and floral aromas, and lower intensities of fresh fruity and herbaceous notes in comparison with dry wines.

Identification of Key Aroma Compounds in Type I Sourdough-Based Chinese Steamed Bread: Application of Untargeted Metabolomics Analysisp

Untargeted metabolomics is a valuable tool to analyze metabolite profiles or aroma fingerprints of different food products. However, less attention has been paid to determining the aroma characteristics of Chinese steamed breads (CSBs) by using this approach. The aim of this work was to evaluate the key aroma compounds and their potential generation pathway in Chinese steamed bread produced with type I sourdough by a metabolomics approach. Based on the aroma characteristics analysis, CSBs produced with type I sourdough and baker’s yeast were clearly distinguishable by principal component analysis (PCA) scores plot. A total of 13 compounds in sourdough-based steamed breads were given the status of discriminant markers through the untargeted metabolomics analysis. According to the odor activity values (OAVs) of discriminant aroma markers, ethyl acetate (fruity), ethyl lactate (caramel-like), hexyl acetate (fruity), (E)-2-nonenal (fatty) and 2-pentylfuran (fruity) were validated as the key volatile compounds in the breads produced with type I sourdough as compared to the baker’s yeast leavened steamed bread. The metabolite analysis in proofed dough indicated that esters are mainly generated by the reaction between acid and alcohol during steaming, and aldehydes are derived from the oxidation of palmitoleic acid and linoleic acid during proofing and steaming.

Use of Indigenous Hanseniaspora vineae and Metschnikowia pulcherrima Co-fermentation With Saccharomyces cerevisiae to Improve the Aroma Diversity of Vidal Blanc Icewine

Using novel non-Saccharomyces strains is regarded as an effective way to improve the aroma diversity of wines to meet the expectations of consumers. The non-Saccharomyces Hanseniaspora vineae and Metschnikowia pulcherrima have good aromatic properties useful for the production of table wine. However, no detailed information is available on their performances in icewine fermentation. In this study, simultaneous and sequential fermentation trials of indigenous M. pulcherrima CVE-MP20 or H. vineae CVE-HV11 with S. cerevisiae (SC45) were performed in 50-L fermenters of Vidal icewine, respectively. The results showed that SC45 cofermented with different non-Saccharomyces strains could generate a distinct aroma quality of icewine compared with four S. cerevisiae strain monocultures as evidenced by principal component analysis (PCA). Mixed fermentation of MP20/SC45 produced higher contents of acetate esters and β-damascenone with lower C₆ alcohols relative to SC45 monoculture. Interestingly, HV11/SC45 generated the highest amounts of C₆ alcohols [(Z)-3-hexen-1-ol and (E)-3-hexen-1-ol], higher alcohols (isobutanol, isopentanol, and 2-phenylethanol), acetate esters (2-phenethyl acetate and isoamyl acetate), cis-rose oxide, β-damascenone, and phenylacetaldehyde. Compared with simultaneous inoculation, sequential inoculation could achieve higher aroma diversity and produce higher intensity of fruity, flowery, and sweet attributes of icewine as assessed by calculating the odor activity values (OAVs). Our results verified the desired enological characteristics of H. vineae strain in icewine fermentation and also demonstrated that using indigenous non-Saccharomyces and Saccharomyces strains is a feasible way to improve aroma diversity of icewine products, which could provide an alternative way to meet the requirement of wine consumers for diversified aromatic quality.

Chemical and sensory characterisation of sweet wines obtained by different techniques

Little is known about the chemical and sensory characteristics of natural sweet wines obtained by different grape dehydration processes. The main aim of this work is to characterise several natural sweet wines, in order to understand the influence of grape dehydration on the chemical and sensory profile of those wines. First, conventional oenological parameters and low molecular weight phenolic compounds have been determined. Next, sensory descriptive analysis was performed on individual samples based on citation frequencies for aroma attributes and conventional intensity scores for taste and mouth-feel properties. Low molecular weight phenolic compounds and acidity were found in a lower concentration in most wines from off-vine dried grapes. Late harvest wine presented higher amounts of phenolics. White wines showed higher sensory and chemical acidity. Most wines obtained from off-vine and on-vine grape dehydration presented common notes of dry fruits and raisins as aroma properties. Chemical and sensory analyses performed in this study were able to define sweet wines. No significant differences have been found in chemical and sensory profiles of sweet wines according to dehydration processes of the grapes. Late harvest wine and white wines were differentiated from other wines through chemical and sensory analysis.

Predominant yeasts in Chinese traditional sourdough and their influence on aroma formation in Chinese steamed bread

A total of 105 yeast isolates was obtained from 15 sourdough samples collected from different regions in China and subjected to random amplified polymorphic DNA (RAPD) analysis. Six species were identified including Pichia membranifaciens, which has not previously been reported in Chinese sourdoughs. Different species of yeast were used in single-culture fermentation to make Chinese steamed bread (CSB). The volatiles of the CSB were captured by solid-phase microextraction method, separated and identified by gas chromatography-mass spectrometry. In total, 41 volatile compounds were found in all the steamed breads. All CSBs showed a similar volatile profile; however, significant differences in the quantity of some volatile compounds were seen among the CSB fermented by different yeast species. A partial least squares discriminant analysis showed that the CSBs could be separated by their characteristic volatile profiles. The study suggested that the aromatic properties of CSB are determined by the yeast used.

Monitoring volatile compounds production throughout fermentation by Saccharomyces and non-Saccharomyces strains using headspace sorptive extraction

Currently, there is a growing interest in the use of non-Saccharomyces yeast to enhance the aromatic quality of wine, with pure or mixed cultures, as well as sequential inoculation. Volatile components of wines were closely related to their sensory quality. Hence, to study the evolution of volatile compounds during fermentation was of great interest. For this, sampling methods that did not alter the volume of fermentation media were the most suitable. This work reports the usefulness of headspace sorptive extraction as non-invasive method to monitor the changes in volatile compounds during fermentation. This method allowed monitoring of 141 compounds throughout the process of fermentation by Saccharomyces cerevisiae and Lachancea thermotolerans strains. Both strains showed a similar ability to ferment a must with high sugar content. The S. cerevisiae strain produced higher amount of volatile compounds especially esters that constitutes fruity aroma than L. thermotorelans.