Plant and microbial glycoside hydrolases: Volatile release from glycosidic aroma precursors

Following a brief look at the structure and occurrence of glycosidic flavour precursors in plants and fruits, attention is given to mechanisms of enzymatic hydrolysis, the properties of relevant glycosidases, as well as endogenous and exogenous glycosidases affecting flavour release in plants, in fruit juice processing and in winemaking. The constraints for technological applications and future prospects are discussed.     

A rapid method for quantifying aroma precursors: Application to grape extract,musts and wines made from several varieties

This paper reports on a quick and simple method for reliably quantifying aroma precursors in grape extract, musts and wines of different grape varieties. The method, which is intended mainly for use by wineries and analytical laboratories, is based on isolation of terpenyl-β-d-glycosides through selective retention on a C₁₈ reversed-phase column, followed by hydrolysis to liberate terpenes, yielding an equimolar proportion of free aglycons and glucose. Sugar was measured using an enzyme analysis kit. Aroma precursors were quantified using this method, in a range of crushed grapes, musts and wines produced in the Castilla La Mancha region. The method was also applied on a larger scale in a wine analytical laboratory, to chart the behavior of terpenyl glycosides during the final stages of ripening of grapes from different viticulture Spanish regions.     

Volatile aroma and sensory analysis of black raspberry wines fermented by different yeast strains

Robus coreanus Miquel is a small berry fruit used for Korean black raspberry (KBR) wine‐making. Twelve different yeast strains were investigated by laboratory‐scale fermentation to develop a wine with a high flavour quality. Volatile aroma compounds from the wines were analysed using headspace–solid phase microextraction–gas chromatography–mass spectrometry and sensory evaluation was performed to evaluate the flavour characteristics. The volatile aroma compounds that mostly contributed to the flavour of KBR wines were those related to fruity (esters) and floral (terpenes) aromas. Fifteen out of the 67 identified volatile compounds showed higher odour activity values than other compounds in the wines, and these compounds were considered as important contributors to the final aromas of the wine. Additionally, the KBR wine fermented by the M1 yeast strain had the highest sensory preference because of higher fruity and floral aroma characters compared with other wines. In addition to the M1 strain, the other yeast strains that produced favourable sensory characteristics included Enoferm CSM, Uvaferm VRB, Lalvin ICV GRE, Lalvin ICV Opale and LevureSeche Active. Of these strains, the M1 strain produced a particularly excellent black raspberry wine, and thus could be applied for further large‐scale production of black raspberry wines. It is also expected that this work will expedite research on the production of high‐quality black raspberry wines with beneficial physicochemical properties, functionality and good sensory characteristics. Copyright © 2015 The Institute of Brewing & Distilling     

Influence of some prefermentative treatments on aroma composition and sensory evaluation of white Godello wines

The influence of the static settling time and the addition of ammonium salts on basic parameters, aroma composition and tasting of white Godello wines have been studied. The statistical analysis showed a significant influence of those treatments on several analytical parameters. The static settling time proved to be very influential on total acidity, free sulphur dioxide, esters, terpenols and fatty acids, while the addition of ammonium salts showed a significant effect on higher alcohols and ethyl lactate. According to the odour active value (OAV), 14 out of 47 studied volatile components had OAV >1 in all the analysed wines, while six volatile components showed OAV >1 only for some of them. Ethyl octanoate, isoamyl acetate and ethyl hexanoate showed the highest OAV values. During the tasting session, the two studied factors became relevant, being better valued the wine made with must containing higher limpidity and with the addition of diammonium hydrogen phosphate.     

Impact of chemical profile on sensory evaluation of tropical red wines

This study evaluated the correlation between the chemical composition of red wines and the sensory perception of the products. The visual, gustatory and flavour attributes of eight samples of tropical red wines were characterised by semi-trained panellists using the check-all-that-apply methodology. Titratable and volatile acidity, pH, contents of ethanol, total polyphenols and anthocyanins, and the chromatic parameters of the red wine samples were determined. The analysis of the correlations between visual attributes and sensory perception indicated that the evaluation of the wine colour attributes can predict other sensory characteristics related to aromas and flavours. This enabled the wine tasters to distinguish subtle variations in the visual attributes of the product. The results of this study indicated that panellists who underwent short-term training can sensorially perceive the influence of physicochemical variables on wine quality. Additionally, the correlation analysis enabled the identification of production adjustments and the understanding of the consumer perception of a complex product.     

The influence of malolactic fermentation and Oenococcus oeni strain on glycosidic aroma precursors and related volatile compounds of red wine

Free and glycosidically bound volatile compounds of red wine were measured after malolactic fermentation (MLF) with four different commercial starter cultures of Oenococcus oeni. MLF resulted in a significant decrease in the concentration of total glycosides, expressed as phenol‐free glycosyl glucose. Gas chromatographic analyses of wine enzyme hydrolysates showed that the extent of hydrolysis of glycosides during MLF was dependent on both bacterial strain and chemical structure of the substrate. The highest decrease was observed for glycosidic precursors of primary terpene alcohols. Glycoside‐related aroma compounds such as linalool, farnesol, and β‐damascenone were increased after MLF with all the bacterial strains tested. Two of the strains were also able to release significant amounts of vinylphenols during MLF. Copyright © 2006 Society of Chemical Industry     

Stability, antioxidant activity and phenolic composition of commercial and reverse osmosis obtained dealcoholised wines

The purpose of this work is to evaluate the phenolic profile and the antioxidant activity of commercial dealcoholised wines and monitor the stability of their composition over time. This work also aims to test the influence of reverse osmosis (RO) process on phenolic compounds and on the antioxidant activity (AA) of dealcoholised wine.AA was measured by ORAC, DPPH and FRAP assays. Phenolic compounds were determined by LC-DAD.In the commercial dealcoholised wines, AA fell by between 33% and 54% and the concentration of phenolic compounds decreased significantly after 30 days of storage. However, RO process did not significantly affect any phenolic acids, regardless of their chemical structure (benzoic acids, cinnamic acids) and alcoholic degree. The AA and phenolic compounds of these products were monitored for seven months. No significant changes were observed. RO process therefore makes it possible to obtain a healthy, low-alcohol (<2% v/v) product with bioactive compounds that are stable in the product and are similar to those found in the original wine.     

Effect of storage temperature on the chemical composition and sensory profile of Sauvignon Blanc wines

Background and Aims: Most white wines lose fresh and fruity characteristics, associated with volatile esters, during ageing in the bottle. A higher storage temperature accelerates these changes. The aim of this study was to examine the influence of storage temperature on the chemical and sensory properties of Sauvignon Blanc wines. Methods and Results: Three commercially bottled Sauvignon Blanc wines from the 2008 and 2009 vintages were stored at 5, 10, 18°C and at room temperature for 12 months. Wines stored at warmer temperatures (18°C and room temperature) contained lower concentrations of acetate esters, including the prominent varietal thiol 3MHA, and ethyl esters of fatty acids, than the wines stored at cooler temperatures (5 and 10°C). A warmer temperature accelerated the rate of ester hydrolysis. Conversely, the concentrations of ethyl esters of branched acids were higher in wines stored at the warmer temperatures. The sensory profile of the wines was assessed after 12 months for the two 2008 wines and after 8 months for the 2009 wine. The wines stored at cooler temperatures were characterised by higher fruity and fresh vegetal aromas, whereas the wines stored at warmer temperatures exhibited the opposite sensory profile, with dominant woody/smoky/oaky, buttery, flinty and canned asparagus notes. Conclusions: These results indicate that temperature‐dependent hydrolysis processes are critical for Sauvignon Blanc aroma stability during the first year in the bottle. Significance of the Study: Cool storage temperature conditions can significantly increase the shelf‐life of Sauvignon Blanc wines by preserving their fruity and fresh green characters.     

Differences in the phenolic composition and sensory profile between red wines aged in oak barrels and wines aged with oak chips

The aim of this study was to evaluate the similarities or differences in the phenolic composition and the sensory characteristics between wines traditionally aged in new French and American barrels for different periods of time, and wines aged for 30 days with different kinds (different geographical origin al toasting degree) of oak chips. This study was carried out with two grape varieties, Mencía and Tinta del País, and in two consecutive vintages. The results obtained indicated that it was not possible to obtain wines aged with chips with sensory characteristics similar to those aged for a long time in new barrels, independently. However, the results showed that the use of oak chips could be a good alternative for elaborating young wines with slight olfactory and gustative wood notes quite similar to wines aged in new barrels for short periods of time (about three months).     

Impact of starter cultures and fermentation techniques on the volatile aroma and sensory profile of chocolate

The sensory quality of chocolate is widely determined by the qualitative and quantitative composition of volatile compounds resulting from microbial metabolism during fermentation, and Maillard reactions taking place during drying, roasting and conching. The influence of applying mixed starter cultures on the formation of flavour precursors, composition of volatile aroma compounds and sensory profile was investigated in cocoa inoculated with cultures encompassing a highly aromatic strain of Pichia kluyveri or a pectinolytic strain of Kluyveromyces marxianus, and compared to commercially fermented heap and tray cocoa. Although only minor differences in the concentration of free amino acids and reducing sugars was measured, identification and quantification by dynamic headspace gas chromatography–mass spectrometry (HS/GC–MS) revealed pronounced differences in the composition of volatiles in roasted cocoa liquors and finished chocolates. 19 of the 56 volatile compounds identified in the chocolates were found in significantly higher amounts in the tray fermented sample, whilst significantly higher amounts of 2-methoxyphenol was measured in the two inoculated chocolates. The P. kluyveri inoculated chocolate was characterized by a significantly higher concentration of phenylacetaldehyde and the K. marxianus inoculated chocolate by significantly higher amounts of benzyl alcohol, phenethyl alcohol, benzyl acetate and phenethyl acetate compared to a spontaneously fermented control. Sensory profiling described the heap and tray fermented chocolates as sweet with cocoa and caramel flavours, whilst the inoculated chocolates were characterized as fruity, acid and bitter with berry, yoghurt and balsamic flavours. The choice of fermentation technique had the greatest overall impact on the volatile aroma and sensory profile, but whilst the application of starter cultures did affect the volatile aroma profile, differences were too small to significantly change consumer perception of the chocolates as compared to a spontaneously fermented control.     

Evolution of the aroma composition of wines supplemented with grape flavour precursors from different varietals during accelerated wine ageing

The wines obtained by fermentation of a model medium supplemented with flavour precursors from different grape varieties (Muscat, Chardonnay, Grenache, Tempranillo, Merlot, Cabernet Sauvignon, Verdejo, and Syrah) were submitted to an accelerated ageing at 50 °C for 9 weeks simulating maturation in the bottle. The volatile compounds coming from grape flavour precursors were extracted by SPE and determined by GC–MS at the end of the alcoholic fermentation and after 1, 3, and 9 weeks of ageing. In general, the biggest changes were observed in the first week of accelerated ageing, most compounds showing a significant increase and a further steady decrease in their concentrations. Unexpectedly, Riesling acetal, 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), and trans-1-(2,3,6-trimethylphenyl)buta-1,3-diene (TPB) also followed this trend. However, vanillin derivatives, furan linalool oxides, 3-oxo-β-ionone, actinidols, 4-ethylphenol, and guaiacol showed a continuous increase during the ageing process. Syrah and Muscat were the most different varieties after fermentation and also at the end of the process. Differences between the rest of the varieties increased during the accelerated ageing, and, in most cases, differences were in accordance with those observed after acid and enzymatic hydrolysis of the grape precursor extracts.     

Volatile aroma components of Australian port wines

The volatile aroma compositions of a blended port wine, having an equivalent age of 20 years, and a 100-year-old port wine were examined by gas chromatography and gas chromatography-mass spectrometry. The compounds identified were products of yeast fermentation, acetalisation, esterification and oxidation reactions occurring during storage, carbohydrate degradation (of residual grape sugar and wood hemi-celluloses) and wood extraction. High concentrations of ethyl lactate, diethyl succinate and diethyl malate were found relative to quantities present in young wine. 1-Ethoxy-1-(3-methylbutoxy)ethane, 1-ethoxy-1-(2-methylbutoxy)ethane, 1,1-diethoxypropan-2-one, cis-5-hydroxy-2-methyl-1,3-dioxane and cis-4-hydroxymethyl-2-methyl-1,3-dioxolane were identified. The presence of these and other acetals demonstrated that carbonyl compounds were also present. Carbonyl compounds are likely to contribute to the ‘rancio’ flavour of these port wines. Carbohydrate-derived compounds found included furfural, 2-acetylfuran, 5-methylfurfural, ethyl laevulinate, ethyl furoate and 5-ethoxymethyl furfural. Oak lactone, which is a wood extractive, was also identified and is likely to contribute to the woody aroma distinguishable in these port wines.     

模糊综合评价法在肉味香基感官评价中的应用

以自制水解液、氨基酸和还原糖为原料,经美拉德反应得到具有肉味特征的香基料,以模糊数学综合评价作为评判标准。单因素实验结果表明,半胱氨酸添加量、葡萄糖和木糖比例及大豆蛋白液的添加量是影响产物特征的关键因素,采用正交实验L9(33)确定最佳配比为,半胱氨酸添加量为2.5%,葡萄糖和木糖比为1:3,大豆蛋白液添加量为30%,得到产物的感官评分为4.965。