Tropical Fruit Aroma Research Articles

The impact of simultaneous inoculation with Torulaspora delbrueckii and Hanseniaspora uvarum combined with Saccharomyces cerevisiae on chemical and sensory quality of Sauvignon blanc wines.

Non-Saccharomyces yeasts have great potential in improving wine quality, showing personality characteristics, and highlighting the terroir of wine. In this study, we evaluated the impact of simultaneous inoculation with the non-Saccharomyces yeasts Torulaspora delbrueckii or (and) Hanseniaspora uvarum in combination with Saccharomyces cerevisiae (EC1118 or VL3) on the aromatic compounds and sensory quality of Sauvignon blanc wines. The growth of yeast groups in the alcoholic fermentation process was tracked using fluorescence in situ hybridization. The presence of non-Saccharomyces yeast notably impacted the distribution of S. cerevisiae and was related to the species of yeast. The co-fermentation of H. uvarum and S. cerevisiae improved the content of total esters, especially acetate esters. Simultaneous inoculation of T. delbrueckii or (and) H. uvarum significantly increased the content of total terpenes, especially linalool. Similar results were found for some higher alcohols and organic acids. Sensory evaluation showed that the wines mixed fermentation with H. uvarum had significantly tropical fruit aroma characteristics. Citrus and mineral notes, typical aroma characteristics of Sauvignon blanc wine, were enhanced by mixed fermentation strategies with T. delbrueckii or (and) H. uvarum and different S. cerevisiae. Hence, co-fermentation by T. delbrueckii or H. uvarum combined with S. cerevisiae could significantly improve the sensory quality of Sauvignon blanc wine.

Understanding the relationship between tropical fruit aroma, acceptance, and emotional response in chardonnay wines

Tropical fruit aromas are prominent in many white wines. The purpose of this work was to determine if winemaking practices could impact the tropical fruit aromas in the Chardonnay wines and how those aroma differences influenced wine consumers acceptance and emotional responses. Four treatments were tested at varying fermentation temperature gradients and skin contact times: control fermentation at 13 °C with no skin contact (Control), fermentation at 13 °C with 18 h of skin contact (SC), fermentation temperature gradient by time (20 °C for 4 days then reduced to 13 °C) with no skin contact (FG), fermentation temperature gradient by time with 18 h of skin contact (SCFG). Acceptance, using a 7-point hedonic scale, showed there was not a significant difference between treatments. Emotional response, using a 5-point Rate-All-That-Apply (RATA) scale, showed significant differences for ‘calm’ and ‘disgusted’ emotions. Check-all-that-apply (CATA) for aroma descriptors showed that Control is described using aromas of passionfruit, lychee, and pome fruit; SC had aromas of grapefruit and floral; FG was described as having melon, lychee, and pineapple aromas; and SCFG was described with aromas of lemon/lime, mango, and guava. Positive emotions were associated with fruity aromas in the wines, although no difference in acceptance was found. Winemaking treatments impacted the aroma profile of chardonnay wine, with tropical aromas evoking positive emotions in consumers. The relationship between specific aromas and consumers emotion responses can be an important tool to understand the factors behind a wine’s success or lack thereof. Moreover, it can help with the creation of new wine products.

Revealing the sensory impact of different levels and combinations of esters and volatile thiols in Chardonnay wines

The assessment of different aroma families on tropical fruit aroma perception is still not well understood. This study aimed to investigate the effect of esters and volatile thiols on tropical fruit aroma perception in white wines. Four levels of thiols (none, low, medium and high) and three levels of esters (none, low, medium) were added to a dearomatized white wine base in a full factorial design. Check-All-That-Apply (CATA) was used to determine the aroma descriptors that most differentiated the wines followed by Sensory Descriptive Analysis (SDA) to evaluate the intensity of those significant aroma attributes. More than 78% of the total variance was described in the first two dimensions when using Canonical Variate Analysis. Tropical fruit aromas were associated with wines containing different levels of esters and ester-thiol combinations. Volatile thiols alone imparted an earthy aroma and were grouped with the control wine. The different ester-thiol combinations altered the tropical fruit aroma quality in the wines from citrus to passionfruit, pineapple and guava. Understanding the cause of tropical fruit aroma allows for targeted processing to achieve the desired wine sensory quality.

Fertilize or Supplement: The Impact of Nitrogen on Vine Productivity and Wine Sensory Properties in Chardonnay

The impact of nitrogen (N) fertilization in the vineyard on vine productivity, fermentation, and wine sensory properties was compared to that of winery N addition on enological characters in Chardonnay between 2016 and 2018. Five treatments, including no vineyard or winery N addition (No N), addition of diammonium phosphate in the winery (+DAP), addition of organic N in the winery (+Org N), and addition of N to the vineyard soil (Soil N), or to foliage (Foliar N) were evaluated. The Foliar N treatment was evaluated in 2017 and 2018 only, while the other treatments were assessed in all years. Soil N increased leaf and petiole N status in all years and increased canopy growth and yield in years two and three. Foliar N had only a minor influence on leaf or petiole N status and did not alter vine growth or yield. Both Soil N and Foliar N elevated juice yeast assimilable nitrogen (YAN), although the extent of increase was greater for Soil N. Addition of DAP in the winery boosted juice YAN similar to the Soil N treatment, and addition of organic N was similar to the Foliar N musts. Fermentations proceeded more quickly in Soil N musts than in No N musts, with the Foliar N, +DAP, and +Org N treatments intermediate between Soil N and No N treatments. Wine sensory analysis revealed that Soil N wines were most distinct, with greater tropical fruit aromas. These findings show that while winery N additions provide similar fermentation kinetics to vineyard N fertilization in Chardonnay, they may not produce a wine with similar sensory characteristics.

Characterization of Unmalted Barley Treated with Aspergillus oryzae

Koji is a complex of substrate and the filamentous fungus Aspergillus oryzae. It is used for saccharification in fermented foods and beverages. Its role in co-fermentations is known, but its application in beer brewing contexts is unclear. The goal of this study was to determine what effect A. oryzae has on the characteristics of unmalted barley in brewing contexts, if it might bypass traditional malting, and what sensory attributes a koji beer might exhibit. Koji barley was prepared with pearled barley and a red rice koji strain and compared to untreated pearled barley and malted barley control groups. The total production time of koji barley was nine days and the process consumed 4 ± 2 L water per kg of grain. Coarse grind extract in koji barley was three times greater than pearled barley while approximately ten percent less than malted barley. Diastatic power was over three times greater in malted barley versus koji barley, while no significant difference (p < 0.05) was found between koji barley and untreated pearled barley. Koji barley congress wort exhibited three times more glucose but less than half the maltose content of malted barley wort. Analysis of wort organic acids showed increased concentrations of citric, succinic, and kojic acid in koji barley versus pearled barley. Qualitative sensory analysis of fermented koji barley wort identified moderate tropical, citrus, and sour flavors as well as green apple and tropical fruit aromas. The results demonstrated that koji barley shows characteristics similar to specialty malts and may favor hazy, fruited, and sour beer styles.

Analysis, occurrence, and potential sensory significance of tropical fruit aroma thiols, 3-mercaptohexanol and 4-methyl-4-mercapto-2-pentanone, in Chinese Baijiu

Fruity notes are important to the flavor of Baijiu (Chinese Liquor) and are considered to originate from ester compounds; however, little is known about the other chemicals that contribute to the fruity aroma. In this study, the sensory impacts of two tropical fruit aroma thiols, 3-mercaptohexanol (3MH) and 4-methyl-4-mercapto-2-pentanone (4MP), in Chinese Light-, Strong- and Soy sauce flavor type Baijiu were systemically subjected to a sensory evaluation, qualitative and quantitative analysis, and multivariate statistical analyses. The flavor dilution factors of 3MH and 4MP were 9–729. The contents of 3MH and 4MP were the highest (p < 0.001) in Strong- and Soy sauce aroma-type Baijiu, respectively. According to their odor activity values (OAVs), 3MH (OAV: 1–22) and 4MP (OAV: 1–9) are important to the aroma of Baijiu. Notably, 4MP was identified for the first time in Baijiu, and the multivariate statistical analysis demonstrated that 3MH and 4MP could be used to differentiate Baijiu.

Use of grape seeds to reduce haze formation in white wines

Grape pathogenesis-related (PR) proteins in white wine can induce haze and hinder the sale of the product. Bentonite is used to remove proteins and “heat-stabilise” wine however it is non-selective and can reduce wine quality. Grape seed powder (GSP) has previously been shown to remove PR proteins and reduce haze formation on a lab scale, however the effect on wine sensory properties was unknown and crucial to the evaluation of GSP as a bentonite alternative. Semillon (SEM) and Sauvignon Blanc (SAB) juices (20L in triplicate) were treated with GSP at two doses, Low (7.5 g/L) and High (15 g/L), prior to fermentation. GSP treatment reduced the concentration of wine PR proteins by up to 57% and 37% for SEM and SAB, respectively, and reduced the amount of haze formed in a heat test by up to 75% and 80%, respectively. Sensory analysis conducted by a trained panel showed that for both wine types the high GSP treatments were rated deeper in colour and higher in bitterness than the bentonite controls, with the low GSP treatment having a similar but less pronounced effect on these attributes. The GSP-treated SAB wine showed greater tropical fruit aroma, and pungency, compared to the bentonite control. Use of GSP can reduce the amount of bentonite needed to stabilize wines and may provide a sustainable and effective alternative to bentonite, notably for textural white wine styles.

First synthesis of 3-S-glutathionylhexanal-d8 and its bisulfite adduct

3-Sulfanylhexan-1-ol (3SH) is an impact odorant of white wines, imparting tropical fruit aromas. A reliable synthetic pathway to 3-S-glutathionylhexanal (glut-3SH-al), a precursor to 3SH that has not been intensively studied, was developed starting from 1-butanol. Application of this synthesis to 1-butanol-d10, conserved eight deuteriums, producing glut-3SH-al-d8, which can be used as an internal standard for future work on the occurrence and evolution of glut-3SH-al in wine systems. Additionally, both glut-3SH-SO3 and glut-3SH-SO3-d8 were synthesised from the corresponding aldehyde, enabling further study of the role of these bisulfite adducts in 3SH biogenesis.

Characteristic fruit wine production via reciprocal selection of juice and non-Saccharomyces species

This study examines the effect of juices and non-Saccharomyces yeasts on physicochemical properties and sensory quality for fruit wines. Here, fruit wines produced from six kinds of fruit juices and eight non-Saccharomyces yeasts were evaluated, and the results show significant phenotypic diversity within these yeasts for wine fermentation on a range of substrates. Substantial variations in indicators such as total acid, sugar content and organic acid content were observed, which were caused by selection of both yeasts and juice types. These differences in characteristics had an impact on consumer preference. Considering overall acceptance by the panelists, correspondence analysis showed that Pichia kluyveri X31-10 (Pk31) was the most suitable strain for apple juice fermentation, and Fuji apple juice was the best substrate for this fermentation. A partial least-squares regression model of aroma characteristics against aroma components revealed that acetate esters were the primary contributors to tropical fruit aroma notes of ciders from Pk31. Additionally, 1-butanol, 3-methyl-, acetate; acetic acid, hexyl ester; and acetic acid, pentyl ester have been implicated as characteristic volatiles associated with Pk31.

Additions of Glutathione or Specific Glutathione-rich Dry inactivated Yeast Preparation (DYP) to Sauvignon blanc Must: Effect on Wine Chemical and Sensory Composition

Although the addition of pure glutathione (GSH) is not allowed under current regulations, the concentration of this compound can be increased in wine through the addition of glutathione-enriched dry yeast preparations (DYP). These preparations have been observed to have antioxidant properties and could thus influence wine aroma and sensory characteristics. The main aim of this study was to investigate the effect of DYP and GSH juice additions on the sensory and chemical composition of Sauvignon blanc wine. Four juice additions were performed and compared against a control treatment: 5.5 mg/L of GSH; 0.4 g/L of DYP; 80 mg/L of GSH; 0.4 g/L of DYP plus 80 mg/L of GSH. After three months of bottling, the volatile and sensorial composition was investigated. The addition of DYP preparations to must increased the concentration of certain wine volatile compounds, with increased attributes of riper tropical fruit aromas, which was not always observed with the GSH additions. The addition of DYP influenced the concentrations of some volatile compounds, which modified the white wine aroma. The release of compounds other than GSH by the yeast products is proposed as the reason for these changes. The results observed in this study can assist winemakers to modify the aroma profile of Sauvignon blanc wines.

Characterisation of Thiol-releasing and Lower Volatile Acidityforming Intra-genus Hybrid Yeast Strains for Sauvignon blanc Wine

A single Saccharomyces cerevisiae wine yeast strain produces a range of aroma and flavour metabolites (e.g. volatile thiols), as well as unfavourable metabolites (e.g. volatile acidity [VA]) during the alcoholic fermentation of white wine, especially Sauvignon blanc. The former contributes to the organoleptic quality of the final wine. Previous research showed that yeast derived enzymes (proteins) are involved in the release of wine quality enhancing or reducing metabolites during fermentation. Small-scale winemaking trials were initiated to evaluate protein expression and metabolite release of tropical fruit aroma wine producing S. cerevisiae hybrid yeasts. Commercial ‘thiol-releasing’ wine yeasts (TRWY) were included in winemaking trials as references. Improved hybrids were identified which showed enhanced thiol-releasing, specifically 3-mercaptohexanol (3MH), and lower VA formation during the production of Sauvignon blanc wines compared to some commercial TRWY references. It is noteworthy that the hybrid NH 56 produced wines with the second highest 3MH levels after hybrid NH 84, and lowest acetic acid of all strains included in this study. This yeast was also the only strain to have down-regulated proteins linked to amino acid biosynthesis, pentose phosphate pathway, glycolysis and fructose and galactose metabolism during the lag phase. Furthermore, differences in protein expression were reflected in the variation of metabolite release by different strains, thereby confirming that enzymes (proteins) are the final effectors for metabolite release.

English

Wine yeasts (Saccharomyces cerevisiae) vary in their ability to develop the full aroma potential of Sauvignon blanc wine due to an inability to release volatile thiols. Subsequently, the use of ‘thiol-releasing’ wine yeasts (TRWY) has increased in popularity. However, anecdotal evidence suggests that some commercially available TRWY intermittently exhibit undesirable characteristics for example, volatile acidity (VA) formation. Therefore, a trial was undertaken to select and evaluate S. cerevisiae hybrids for the production of Sauvignon blanc wine with enhanced fruity and tropical aromas, but low VA. Hybrids were characterised by clamped homogeneous electrical field (CHEF) DNA karyotyping and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) biotyping, and subsequently trialled against top commercial TRWY that is, Zymaflore VL3 and Zymaflore X5 (Laffort Oenologie), and Fermicru 4F9 (DSM Oenology) in laboratory-scale Sauvignon blanc vinifications during 2013. Most hybrids produced wines with VA levels significantly lower than those produced with Zymaflore VL3, Zymaflore X5 and Fermicru 4F9. Low VA forming hybrids also produced wines with tropical wine aroma notes. Wines produced by Fermicru 4F9 had the lowest acetic acid (the main volatile acid) of the commercial TRWY in this study. However, some hybrid yeasts produced wines with less acetic acid on average than wines produced by Fermicru 4F9. Overall, hybrids NH 6, NH 48, NH 56, NH 88 and NH 145 produced wines with enhanced tropical fruity aroma, but lower VA compared to wines produced by commercial TRWY. Key words: Hybrid yeasts, CHEF, MALDI-TOF/TOF MS biotyping, Sauvignon blanc, tropical fruit aroma, volatile acidity.

Impact of Mechanical Harvesting and Optical Berry Sorting on Grape and Wine Composition

The impact of mechanical harvesting, optical berry sorting, and their possible synergistic effect on grape and wine composition was investigated. Pinot noir grapes from the Russian River Valley American Viticultural Area were harvested by hand, by a standard bow-rod mechanical harvester, or by a mechanical harvester with a Selectiv’ Process on-board. For each harvest method, half of the grapes were unsorted and half were optically sorted at the winery. The grapes, wines at bottling, and wines after three months of bottle aging were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC), ultraviolet-visible spectroscopy (UV-vis), and headspace solid-phase microextraction (HS-SPME) gas chromatography mass spectrometry (GC-MS) for color expression and phenolic and aroma profiling. The machine-harvested grapes had higher levels of β-damascenone, linalool, β-myrcene, and α-terpinene, potentially caused by glycosidic hydrolysis triggered by berry damage during harvest or from induced synthesis as a wounding response. In general, differences in wine composition attributable to harvest method were diminished or eliminated by optical sorting. The machine harvester with the Selectiv’ Process on-board led to wines with the most phenolics, although these differences may have been decreased or eliminated had the grapes been crushed before fermentation as the wines were produced by whole-berry fermentation. Descriptive sensory analysis conducted on wines three months after bottling determined that the wines made from hand-harvested fruit had significantly greater tropical fruit aroma, while wines made from optically sorted treatments had less hue saturation. With only two significant differences among the 18 aroma, taste, and mouthfeel attributes tested, it was concluded that all treatments led to wines of similar character.

Yeast genes required for conversion of grape precursors to varietal thiols in wine.

Three varietal thiols are important for the tropical fruit aromas of Sauvignon blanc: 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexanol (3MH) and its acetylated derivative 3-mercaptohexyl acetate (3MHA). These thiols are produced by yeast during fermentation from precursors in grape juice. Here we identify genes in Saccharomyces cerevisiae that are required for the transport and cleavage of two thiol precursors: cysteine-4MMP and glutathione-3MH. A full-length copy of IRC7 is absolutely required for the cleavage of both precursors in the tested strains; the deleted form of the enzyme found in most yeast strains is incapable of converting these compounds into detectable thiols. By using strains that overexpress full-length IRC7, we further show that the glutathione transporter OPT1 and the transpeptidase CIS2 are also required for conversion of glut-3MH to its varietal thiol. No transporter for cys-4MMP was identified: a strain deleted for all nine known cysteine transport genes was still capable of converting cys-4MMP to its varietal thiol, and was also able to take up cysteine at high concentrations. Based on these results, we conclude that cysteine and glutathione precursors make a relatively minor contribution to 3MH production from most grape juices.

Chemo-enzymatic synthesis of α-terpineol thioacetate and thiol derivatives and their use as flavouring compounds.

Reaction of (R,S)-α-terpineol with thioacetic acid in food-grade n-hexane resulted into two α-terpineol thioacetate derivatives with the same molecular weight. After 5 h of reaction time, (R,S)-α-terpineol was completely transformed and the mixture analysed by different chromatographic techniques. The aroma character of the α-terpineol thioacetates was described as exotic, sweet, blackcurrant, roasted and sulphury. Of eight lipases and two esterases assayed, only non-immobilized pig liver esterase (PLE) hydrolysed α-terpineol thioacetates into the corresponding α-terpineol thiols. When reactions were performed in 0.2 m phosphate buffer at pH 8.0 and 30 °C with non-immobilized PLE, α-terpineol thiols were produced in an optimal yield of 88% after 24 h of reaction time. The aroma character of α-terpineol thiols was described as green, exotic and fresh grapefruit. Flavouring powders were prepared by freeze-drying the α-terpineol thioacetates and α-terpineol thiols in the presence of maltodextrine. Preliminary applications showed that these flavouring preparations could be used to improve the flavour quality of lighter cooked notes and tropical fruit aromas.

Characterisation of free and glycosidically bound aroma compounds of La Mancha Verdejo white wines

The aroma of Verdejo La Mancha white wines was studied by instrumental and sensory analysis across five consecutive vintages to determine their typicity and quality. Free and glycosidically-bound aroma compounds were isolated by solid phase extraction (SPE) to later be analysed using gas chromatography–mass spectrometry (GC/MS). Seventy-four (74) free aroma compounds and thirty-six (36) bound aroma compounds were identified and quantified in La Mancha Verdejo wines oven this five year period. Based on the result, Verdejo white wines presents a complex chemical profile with a wealth of aromas in its aromatic composition. The sensory profile of Verdejo wines was evaluated by experienced wine-tasters and was characterised by fresh, citric, green apple, fruity and tropical fruit aroma descriptors. This study shows the first complete aromatic characterisation of La Mancha Verdejo white wines, also the data suggest that these wines present a great aromatic potential.

Preparation and Odour Properties of (S)-3-Mercapto-1-Heptyl Acetate

Synthesis of ( S)-3-mercapto-1-heptyl acetate was achieved in four steps. Sharpless asymmetric epoxidation of ( E)-2-heptenol yielded (2 R,3 R)-2,3-epoxy-1-heptanol, which was treated with thiourea in the presence of Ti(OPri)4 to give (2 S,3 S)-2,3-epithio-1-heptanol, reduction of which followed by acetylation afforded ( S)-3-mercapto-1-heptyl acetate in 91% ee. The optically active product possessed a tropical fruit aroma reminiscent of mango and passion fruit, with berry, ester-like, sweet, and pepper-like aspects.

Influence of Sulfur Dioxide Additions at Harvest on Polyphenols, C6-Compounds, and Varietal Thiols in Sauvignon blanc

The varietal thiols 3-mercaptohexanol (3MH), derived from odorless precursors in the grape juice, and 3-mercaptohexyl acetate (3MHA), arising from 3MH during fermentation, are prominent compounds responsible for tropical fruit aromas in Sauvignon blanc wines. Machine-harvested grapes were sourced from three different locations in Marlborough, New Zealand. Different concentrations of sulfur dioxide (0, 30, 60, 120, and 300 mg/kg) were added to the grapes and juice in the field, followed by transport to the University of Auckland, pressing, and fermentation in triplicate 750 mL bottles using EC1118 yeast at 15°C. Juices transported without SO2 or with a low SO2 addition were more oxidized and contained lower concentrations of most polyphenols. The juices fermented at a similar rate, with a delay in the onset of fermentation of up to a day with the 120 mg/kg SO2 juices, but around 12 days for the 300 mg/kg SO2 additions. In the more oxidized juices, there were higher concentrations of C6-alcohols in the finished wines but lower concentrations of the corresponding acetate esters. With each set the highest concentrations of 3MH and 3MHA were found in wines produced from the juices with a 120 mg/kg addition of SO2 at harvest. Conversely, wines made from juices that were transported with low SO2 additions had much lower concentrations of the varietal thiols.

Influence of Grape-Harvesting Steps on Varietal Thiol Aromas in Sauvignon blanc Wines

The intense tropical fruit aroma of Sauvignon blanc wines has been associated with the varietal thiols 3-mercaptohexanol (3MH), derived from odorless precursors in the grape, and 3-mercaptohexyl acetate (3MHA), arising from 3MH during fermentation. Grapes and juice were sourced from five locations in Marlborough, New Zealand, taking hand-picked grapes and samples at four stages during the mechanical harvesting process and pressing, which were then fermented in replicated 750 mL bottles. With each set of juices, the highest concentrations of Cys-3MH and Glut-3MH were found in the juices pressed to 1 bar, but these juices produced wines with lower 3MH and 3MHA concentrations. With three of the juices, there was an increase in varietal thiol content for wines made from juices that had been machine harvested compared to the hand-picked samples, which matched earlier findings of lower 3MH and 3MHA levels in wines made from hand-picked grapes. Juices that were more oxidized, and which showed a higher absorbance at 420 nm, were found to produce wines with lower 3MH and 3MHA concentrations.

Gas chromatography–mass spectrometry determination of 3-mercaptohexan-1-ol and 3-mercaptohexyl acetate in wine: A comparison of headspace solid phase microextraction and solid phase extraction methods

A gas chromatography–mass spectrometry method was established using headspace solid phase microextraction (HS-SPME) as the sampling procedure to analyse 3-mercaptohexan-1-ol (3-MH) and 3-mercaptohexyl acetate (3-MHA), two molecules with a tropical fruit aroma, in wine at trace level. This method offers important advantages, as it neither requires time-consuming sample preparation nor uses dangerous organic compounds, thus making control of wine aroma easier and suitable for routine analysis. As a comparison, a solid phase extraction (SPE) method, already described elsewhere for aroma analysis, was applied to quantify these analytes, extending this exhaustive enrichment to two important thiols. Detection limits for both the approaches were close to the sensory threshold value, resulting lower for the HS-SPME procedure and suitable for requirements in the oenological field. The application of the two proposed methods to 52 wines of different varieties gave similar results.