Determination of ortho- and retronasal detection thresholds for 2-isopropyl-3-methoxypyrazine in wine

ABSTRACT:  2-isopropyl-3-methoxypyrazine (IPMP) is a grape-derived component of wine flavor in some wine varieties as well as the causal compound of the off-flavor known as ladybug taint (LBT), which occurs when Harmonia axyridis beetles are incorporated with the grapes during juice and wine processing. The main objective of this study was to obtain robust estimates of the orthonasal (ON) and retronasal (RN) detection thresholds (DTs) for IPMP in wines of differing styles. The ASTM E679 ascending forced choice method of limits was used to determine DTs for 47 individuals in 3 different wines—Chardonnay, Gewürztraminer, and a red wine blend of Baco Noir and Marechel Foch. The group best estimate thresholds (BETs) obtained for IPMP (ng/L) were Chardonnay, ON: 0.32; Gewürztraminer, ON: 1.56, RN: 1.15, and red wine blend, ON: 1.03, RN: 2.29. A large variation in individual DTs was observed. Familiarity with LBT was inversely correlated with DTs for Gewürztraminer, and no difference in thresholds was observed between winemakers and nonwinemakers. We conclude that the human DT for IPMP is extremely low and influenced significantly by wine style and evaluation mode. We recommend against the reporting of single-threshold values for wine flavor compounds, and encourage the determination of consumer rejection thresholds for IPMP in wine.     

Inhibition and inactivation evaluation of exogenous glycosidases in wines using p‐nitrophenylglycosides

BACKGROUND: Glycosidases are often used to improve the aroma of wines via hydrolysis of glycosidic precursors. The aim of this work was to develop a method to test activity and stability of these enzymes in wine environments using p‐nitrophenylglycosides, avoiding interference by colored substances. RESULTS: The proposed procedure for determination of glycosidase activity in wines involves quantification of the hydrolysis product p‐nitrophenol by HPLC. The method was applied to compare the inhibition of some commercial glycosidases by red and white wines. It was found that inhibition of a β‐D ‐glucosidase by ethanol, glucose and gluconolactone was smaller than that produced by wine. This enzyme was also inhibited by wine fractions rich in phenolic compounds and glycosides. When glycoside fractions were first hydrolyzed, their inhibition was strongly reduced. The stability of glycosidases in red wines was tested, showing a destabilizing effect of β‐glucosidases that was stronger than in white wine. CONCLUSION: The method developed allows measurement of glycosidase activity on p‐nitrophenylglycosides in the presence of colored wine compounds. Comparison of relative glycosidase activity in wines to that in buffer solution under the same conditions can assist in the selection of appropriate aroma‐enhancing enzymes. Copyright © 2009 Society of Chemical Industry     

Yeast strain affects 3‐isopropyl‐2‐methoxypyrazine concentration and sensory profile in Cabernet Sauvignon wine

Background and Aims: 3‐Isopropyl‐2‐methoxypyrazine (IPMP) is both a grape‐ and insect‐derived trace compound found in wine that can contribute green characters. There has been renewed interest in examining how wine IPMP concentrations can be modulated due to recent concerns regarding ladybug taint – an off‐flavour from IPMP extracted from Harmonia axyridis (Pallas) (multicoloured Asian lady beetle). This study sought to determine the influence of commercial Saccharomyces yeast strains on IPMP concentration in Cabernet Sauvignon wines and to describe their sensory impact. Methods and Results: Rehydrated juice from Cabernet Sauvignon concentrate was spiked with 30 ng/L IPMP and fermented in triplicate by yeast strains Lalvin BM45, Lalvin EC1118, Lalvin ICV‐D21 or Lalvin ICV‐D80. IPMP concentration was determined using headspace solid‐phase micro‐extraction coupled with gas chromatography mass spectrometry (HS‐SPME‐GC‐MS), and was unchanged from juice levels in wine fermented by EC1118, Lalvin D21 and Lalvin D80 but increased by 11 ng/L (29%) in wine fermented by Lalvin BM45. Yeast strains differed in their sensory impact on wine made from IPMP‐spiked juice for five aroma and four flavour attributes. Conclusions: HS‐SPME‐GC‐MS allows for sensitive measurement of IPMP that, for the first time, has demonstrated the capacity for wine yeast to affect IPMP concentration. Yeast strains demonstrate varying ability to mask green or ladybug taint characters in wine. Significance of the Study: This information should be useful in guiding selection of yeast strains for juices of high IPMP concentration, including those that are multicoloured Asian lady beetle‐affected, under‐ripe or from varieties with high methoxypyrazine loads such as Cabernet Sauvignon.     

Sensory and chemical characteristics of trans‐resveratrol‐fortified wine

Background and Aims: trans‐Resveratrol (tR) is a grape‐derived polyphenolic that is believed to confer considerable health benefits to humans. Its concentration in wine, however, is highly variable, and thus direct fortification of wine with tR has been proposed to create a high‐value, health‐promoting wine product. This study determines the sensory and chemical characteristics of tR fortified white and red wine. Methods and Results: Riesling and Cabernet Sauvignon wines were enriched with 20 mg/L and 200 mg/L tR. Basic chemical and sensory indicators of wine quality, trans‐ and cis‐resveratrol concentrations, and antioxidant capacity were assessed at bottling and at 6, 18, 31, 44 and 58 weeks post‐bottling. tR concentrations in bottled wine remained relatively stable throughout the 58‐week period of this study. In addition, tR‐enriched wines had a significantly higher antioxidant capacity compared with control wine, and Cabernet Sauvignon fortified at both tR concentrations had greater colour intensity. Basic chemical indicators of wine quality were not affected by tR fortification, and sensory changes were minimal, with higher bitterness intensity in Riesling fortified at 200 mg/L tR the most consistent finding. Conclusions: tR is relatively stable in wine during bottle aging, and tR enrichment up to 200 mg/L results in minimal change to wine quality, particularly with red wine. Significance of Study: This is the first study to investigate the chemical and sensory characteristics of tR‐enriched wines. Results indicate that these products may have considerable potential for the functional food market.     

Determination of Chloroanisoles and Chlorophenols in Cork and Wine by using HS‐SPME and GC‐ECD Detection

Cork taint is an off‐flavor problem in wine, the main reason being the presence of 2,4,6‐trichloroanisole (TCA) in the cork stopper. In addition to the TCA, the presence of other chloroanisole and chlorophenol family compounds (the perception limits of which are very low) can also result in, or contribute to, cork taint problem. In this study, the levels of 2,4‐dichloroanisole (DCA), 2,4,6‐trichloroanisole (TCA), 2,3,4,6‐tetrachloroanisole (TeCA), pentachloroanisole (PCA), 2,4,6‐trichlorophenol (TCP), 2,3,4,6‐tetrachlorophenol (TeCP) and penthaclorophenol (PCP) were assayed in cork stoppers (natural, agglomerated and colmate) and in red wine samples from different wineries in Turkey using HS‐SPME and GC‐ECD detection. The performance parameters for all chloroanisole and chlorophenol compounds were as follows: recovery 92.48–102.53%, R 0.992‐0.996. The LOQ values were DCA (8.4 ng/L), TCA (0.8 ng/L), TeCa (0.6 ng/L), PCP (0.8 ng/L), TCP (0.8 ng/L), TeCP (1.2 ng/L), and PCP (1.1 ng/L) respectively. In cork stoppers, the amounts of 2,4,6 TCA ranged between 5.4–130.6 ng/g. The 2,3,4,6 TeCA ranged between 1.12‐8.2 ng/g and the PCA ranged between nd (not detected)‐11.01 ng/g. In the wine samples, 2,4,6 TCA ranged between 1.42–70.2 ng/L. The 2,3,4,6 TeCA ranged between nd‐15.1 ng/L and the PCA ranged from nd‐5.16 ng/L. The results indicated that there was a significant correlation between the TCA in wines and the TCA in cork stoppers.     

Consumer rejection threshold of ethyl phenylacetate and phenylacetic acid,compounds responsible for the sweet‐like off odour in wines made from sour rotten grapes

Backgrounds and Aims: This study aimed to determine a consumer rejection threshold (CRT) for ethyl phenylacetate (EPhA) and phenylacetic acid (PhAA) in wine. These compounds have recently been reported to be responsible for sweet‐like, honey off odours in wine made from sour rotten grapes. Methods and Results: Non‐expert wine consumers (n = 35) received pairs of samples comprising a control wine against a spiked wine with an ascending concentration of the target compounds and were asked to indicate which sample they preferred. Results estimated a conjoint CRT for EPhA and PhAA of 140 and 700 µg/L, respectively. Wines spiked with a EPhA and PhAA concentration around the CRT evoked intense ‘dried fruit’ aromas that led to a decrease of the general aroma quality; these wines are significantly rejected by consumers. Conclusions: The measured CRT provides an initial estimation of the risk concentration for EPhA and PhAA in red wine, as they represent a ‘taint’ for regular wine consumers. Significance of the Study: These data allow wine producers to predict if a given wine will be disliked by consumers or to help guide ‘blending away’ of such wines.     

Flavonol composition of Australian red and white wines determined by high‐performance liquid chromatography

Background and Aims: Flavonols are present in Vitis vinifera L. wine grapes as glycosides and are found in wines in both their glycosidic and aglycone forms. Flavonols and their glycosides are important components in wine because of their impact on colour, taste and health properties. An assessment of the flavonols and flavonol glycosides present in a wide selection of Australian red and white wines (n = 121 and 44, respectively) was undertaken. Methods and Results: Analyses were performed using HPLC, with compound identification being aided by HPLC‐MS. In the red wines, quercetin and myricetin dominated the flavonol profile, and quercetin‐3‐glucuronide was by far the most abundant glycoside present. White wines had considerably lower levels of flavonols and their glycosides, in most cases, being below the detection limit of the HPLC method. Conclusions: There appeared to be no correlation between the flavonol profile and wine variety or region in either white or red wines. Contrary to literature reports of rutin in wine, rutin was not found in any of the wines we analysed, and spiking experiments showed rutin rapidly degraded to the aglycone quercetin. Furthermore, changes in elution order for some quercetin glycoside standards were observed depending upon the acid used in the mobile phase. Significance of the Study: This is the first time the flavonol contents of an extensive cross section of Australian wines have been reported. The concentrations are consistent with those reported in wines from other countries. In light of the instability of rutin in wine, critical review should be given to reports discussing its presence.     

Retronasal Odor of Dried Bonito Stock Induces Umami Taste and Improves the Palatability of Saltiness

A traditional Japanese umami‐rich stock, dried bonito stock, was reported to improve the palatability of a low‐salt diet due to its characteristic aroma. Two pathways are available for the presentation of odors: the orthonasal and retronasal pathways. Aroma is perceived through the orthonasal pathway. In contrast, retronasal application of odors is thought to evoke different sensations from the orthonasal pathway, which is typically perceived as taste and modifies taste. Therefore, the effect of retronasal odor on salt‐reduction might be different from that of aroma, that is, orthonasal odor. Thus, the effects of the retronasal odor of dried bonito stock on the enhancement and improvement of palatability upon salt reduction were examined using sensory evaluation. Moreover, the contributions to flavor expression and palatability of dried bonito stock were also investigated. Although the retronasal odor of dried bonito did not enhance saltiness, it improved the palatability of saltiness. In the presence of no tastants except 0.68% NaCl, a content 15% less than that of Japanese traditional soup, the retronasal odor of dried bonito generated umami, enhanced the suitability for dried bonito stock, and increased palatability. This indicates that the retronasal odor of dried bonito stock could improve the palatability of a salt‐reduced diet. These findings can be applied to the development of new seasonings for improving the palatability of salt‐reduced foods.     

FLAVOR AND AROMA ATTRIBUTES OF RIESLING WINES PRODUCED BY FREEZE CONCENTRATION AND MICROWAVE VACUUM DEHYDRATION

This article describes the production of sweet dessert wines produced using late‐harvest freeze concentration, wine produced from fresh grapes frozen using refrigeration and wine produced from grapes partially dried using microwave vacuum dehydration. The objective was to compare the aroma and flavor attributes of the wines to determine the effect of each method of juice concentration. The replicated wine samples were evaluated by 12 experienced judges, and the wines were analyzed using solid‐phase microextraction. The microextraction detected 28 compounds; however, levels of concentration of these compounds were below published aroma thresholds. Although all the wines were judged as acceptable sweet dessert wines, the judges detected significant differences. The wine made from the dehydrated grapes exhibited lower fresh fruit aroma, higher fusel oils and oxidation, and flavor notes including citrus/grapefruit and acidity were lower.     

Effect of Maceration Time on Free and Bound Volatiles of Red Wines from cv. Karaoğlan (Vitis vinifera L.) Grapes Grown in Arapgir,Turkey

Skin maceration is an essential winemaking technique that affects sensory properties and aroma of red wines. The aim of this study was to investigate aroma profiles of red wines made from cv. Karao?lan, a grape variety grown in Arapgir (Malatya, Turkey) and the effect of maceration time (5, 10, and 15 d) on free and bound aroma compounds and sensory properties. Three maceration times were applied in durations of 5, 10, and 15 d. Free and glycosidically bound aroma compounds were analyzed using gas chromatography‐mass spectrometry (GC‐MS) in Karao?lan wines, and the effect of different maceration times on aroma composition were evaluated. Results indicate that extended maceration time significantly influenced the aroma composition of wines both qualitatively and quantitatively. A total of 59 free and 22 bound aroma compounds were identified in the final wines. The maximum of free aroma content was achieved with 5 d of maceration, while 15 d of maceration gave the highest amount of glycosidically bound aroma compounds. From sensorial point of view, the wine produced with 10 d of maceration had the best panel score compared to wines with 5 and 15 d of maceration. This is the first study referring to the composition of aroma compounds of red wines made from cv. Karao?lan. It was concluded that this cultivar resulted in a good quality wine in terms of bound and free aroma compounds. This information of vinification practices that influence the chemical properties of wine is useful for grape growers and winemakers.     

The role of olfaction in the elaboration and use of the Chardonnay wine concept

The existence of a Chardonnay wine concept was explored in two experiments. In the first experiment, 28 Chardonnay wine experts assessed in terms of a score the degree of representativeness of 48 white wines according to their own Chardonnay wine concept. The samples were 29 wines made from Chardonnay grapes and 19 wines made from other grape varieties (Aligoté, Melon de Bourgogne, Sylvaner, Sauvignon blanc, Chenin, Marsanne and Pinot blanc). Two assessment conditions were conducted: orthonasal and global (orthonasal plus retronasal and mouthfeel perceptions). Globally, scores were higher for Chardonnay wines than for non-Chardonnay ones and the consensus among experts demonstrated the existence of a shared Chardonnay wine sensory concept. The global evaluation led to a better discrimination between Chardonnay and non-Chardonnay wines, indicating that the sensory concept includes olfactive as well as taste and mouthfeel sensations. In the second experiment, the perceptive similarities of a subset of 18 wines (nine among the less representative and nine among the most representative) were studied. Twenty consumers freely sorted the wines according to odour similarity. Results were analysed by means of multidimensional scaling. Except for an extreme wine exhibiting very low representativeness, no clear separation of wines according to a Chardonnay wine concept was observed on the MDS space. However, a regression analysis showed significant correlations between representativeness scores and the first and third dimensions of the MDS space. This suggests that the Chardonnay wine concept is an experts' construct, elaborated by specific weighing of sensory features, partially based on perceptive similarities.     

Determination of γ‐aminobutyric acid in Chinese rice wines and its evolution during fermentation

γ‐Aminobutyric acid (GABA) is a functional amino acid that is widely present in Chinese rice wine. In this study, high‐performance liquid chromatography coupled with ultraviolet detection (HPLC‐UV) was established for the determination of γ‐aminobutyric acid in 22 Chinese rice wines collected from the Shaoxing region of China. Furthermore, the evolution of GABA was studied in Chinese rice wine during primary and post‐fermentation process. Results showed that the HPLC method was reliable with good linearity, accuracy, precision and stability. Additionally, the GABA content varied significantly in the 22 Chinese rice wines, and the content was much higher in wine samples with long aging periods. Regarding the evolution of GABA in Chinese rice wine during the brewing process, the level slowly increased during primary fermentation. A decrease in GABA was observed in the wine at the early stage of the post‐fermentation process. However, a marked increase on the GABA content occurred in wine at the late stage of post‐fermentation. The findings from this study are that HPLC can be successfully applied to determine GABA in Shaoxing brewed rice wines, and further provide useful information on quality control of such wines. Copyright © 2017 The Institute of Brewing & Distilling     

Volatile aroma compounds in wines from Chinese wild/hybrid species

The volatile aroma compounds in wines produced from Chinese wild/hybrid species were investigated in comparison to wines from European grapes. Volatiles were extracted by headspace solid‐phase micro‐extraction and identified by gas‐chromatography/mass‐spectrometry. The identification of analyte was performed by a combination of the linear retention index approach with the comparison of the obtained mass spectra. A total of 98 peaks were tentatively assigned as wine aroma components, and 15 odorants can be found at concentrations above their odor threshold among the odor activity values (OAVs) of 46 compounds evaluated in all of the wines. The “OAVs’ aroma wheels” showed that the classes of aromatic series are first fruity, next herbaceous and roasty and no spicy and caramelized notes. Via principal component analysis, all the grape germplasm studied could be divided into four groups: “Jingsheng‐1,” “Cabernet Gernischt,” “Beibinghong,” and others, which exhibited distinctive aroma features, respectively. Practical applications Chinese wild grape species have many desirable properties for wine grape breeding such as possessing strong resistant genes to fungal diseases and cold condition, especially after hybridization with European grapes. As an emerging wine country, wines from Chinese wild/hybrid species have achieved much success in the last few years. The chemical content and biological properties have been studied extensively in many but there are a few studies in our knowledge about the wine tastes of these species. In this paper, the key odorants in wines produced from the Chinese grape species of V. amurensis Rupr., V. davidii Foex., and V. quinquangularis Rehd. and its hybrids were characterized in comparison to wines produced from European grapes (V. vinifera). The findings will help to the further understanding of the key aroma components in the different Chinese grapevine germplasm, and make further efforts to enrich the wine types in the marketplace.