Identification of substances responsible for the ‘sawdust’ aroma in oak wood

The unpleasant ‘sawdust’ odour sometimes found in wines aged in new barrels was studied by gas chromatography olfactory detection and mass spectrometry. A particular aromatic zone has several chromatographic peaks, corresponding to certain characteristic odours which can be detected by smelling the gas effluent. These include the subtle rancid, weedy odour of ‘sawdust’. Various carbonyl components have been identified in this particular zone. These include (E)-2-nonenal, 3-octen-1-one, (E)-2-octenal and 1-decanal. These molecules are the primary cause of disagreeable oak wood odours. By measuring (E)-2-nonenal in wines, after derivation by O-(2,3,4,5-pentafluobenzyl)-hydroxilamine (PFBOA), it was possible to correlate the concentration of this unsaturated aldehyde with the intensity of the ‘sawdust’ character noted in tasting. The possible explanations for the presence of these carbonyl compounds are debatable. The carbonyl content varied from one wood sample to another. However, controling the toasting of the wood, both in the laboratory and in the cooperage, produced a major reduction in the extractable (E)-2-nonenal content and eradicated the ‘sawdust’ character of the wine. © 1998 SCI.     

Fast aroma profiling to detect invert sugar adulteration with zNose™

Rapid aroma profiling of food products is a potential technique for at‐line food quality evaluation. In this work the potential of zNose^?, a surface acoustic wave‐based sensor, was tested for honey quality assessment. Buckwheat honey was purposely adulterated with different levels of beet and cane invert sugar, and its aroma profile was measured after different periods of headspace equilibration. PCA using the relative peak areas as well as the full zNose^? spectra resulted in a clear separation between honey, and beet and cane invert sugar adulterants in the mixtures. PLS models were developed for quantitative estimation of adulterants using the entire spectra as well as the relative peak areas. Better predictions were obtained with the PLS models based on spectra than with those based on relative peak areas. A correlation of validation of 0.98 was obtained between predicted and measured percentage of adulteration. This model was also successfully validated with an external set of honey mixtures, resulting in an average deviation of 3% adulteration between the predicted and reference values. Copyright © 2004 Society of Chemical Industry     

Multivariate analysis of maturity stages,including quality and aroma,in ‘Royal Glory’ peaches and ‘Big Top’ nectarines

Ethylene production, quality attributes and aroma compounds were analysed to determine the maturity evolution of ‘Big Top’ nectarines and ‘Royal Glory’ peaches at harvest dates ranging from 89 to 116 days after full bloom (DAFB) for nectarines and from 85 to 112 DAFB for peaches. These cultivars are highly coloured even in the early stages of maturity. However, the two cultivars had different patterns of ethylene production, this being slower in nectarines than in peaches. Principal component analysis (PCA) was used to provide partial visualisation of the complete data set in a reduced dimension plot. Separation of the two cultivars can be shown by means of a two‐dimensional plot of the samples. Although only some aroma compounds are slightly correlated with quality parameters, when aroma volatiles were included in the PCA, the aroma compound set allowed both cultivars to be classified into three stages of maturity: immature, intermediate and fully mature. Compounds such as propanol, hexyl acetate, 2‐methylpropyl acetate, limonene, butanol, (Z)‐3‐hexenyl acetate, buthyl acetate, linalool, ethanol, propyl acetate and ethyl acetate are the most important volatiles for ‘Big Top’ nectarines. It is suggested that the presence of these compounds can be used to indicate when the fruit should be harvested. The presence of γ‐decalactone, δ‐octalactone, γ‐octalactone, ethyl butyrate, hexanal and (E)‐2‐hexenol can be used to indicate the harvesting maturity stage for ‘Royal Glory’ peaches. The optimum maturity date for harvest would be 105–107 DAFB for ‘Big Top’ nectarines and 93–95 DAFB for ‘Royal Glory’ peaches. © 2002 Society of Chemical Industry     

Effect of Different Indigenous Yeast β‐Glucosidases on the Liberation of Bound Aroma Compounds

This study investigated β‐D‐glucosidase activity in the indigenous wine yeast present on grape berries in Yantai in Shandong Province, China. Yeast population profiles from the Yantai production area in China were examined. Among the ten species identified by RFLP analysis of the 5.8S rRNA gene, four exhibited higher β‐glucosidase activity, namely, Hanseniaspora uvarum, Trichosporon asahii, Pichia fermentans and Saccharomyces cerevisiae. The β‐glucosidases from the four representative strains were chosen to hydrolyse the glycosidic precursors of Cabernet Sauvignon. After enzymatic hydrolysis, 31 compounds were identified and quantified, including terpenes, C₁₃‐noriso‐prenoid, C₆ compounds, alcohols, aldehydes and volatile phenols. Results showed that different strains exhibited different hydrolytic abilities on the bound aroma precursors. The main variables included C₆ compounds, terpenes and alcohols. The concentration of the 14 compounds showed significant differences between enzymatic treatments, with 11 treated using the β‐glucosidase of the F6 strain (T. asahii). These findings may have some applicative value for utilizing the strains or their β‐glucosidases, which are able to complement and optimize wine quality.     

‘新红星’和‘长富2号’果实贮藏期间香气成分的变化

采用顶空固相微萃取技术和气相色谱-质谱联用研究‘新红星’和‘长富2号’苹果果实不同贮藏期间香气成分的组成及含量变化。结果表明:‘新红星’和‘长富2号’成熟果实中分别检测出50、49种挥发性成分,共有的香气成分38种,其中30种为酯类物质,乙酸酯类物质相对含量分别占香气物质总量的70.81%和52.60%,对成熟期苹果果实香气的形成发挥重要作用。常温(15~25℃)贮藏过程中,‘新红星’和‘长富2号’果实中酯类物质含量呈先升后降的趋势,贮藏20 d时达到最高值,分别占2个品种香气物质总量的97.94%和95.83%。贮藏期间乙酯类物质相对含量明显增加,其中丁酸乙酯、2-甲基丁酸乙酯、丙酸乙酯、乙酸乙酯、己酸乙酯等上升幅度较大,对‘新红星’和‘长富2号’苹果贮藏期间特有香气的形成起重要作用。     

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     

Purification,characterisation and application of α‐l‐rhamnosidase from Penicillium citrinum MTCC‐8897

An α‐l ‐rhamnosidase secreted by Penicillium citrinum MTCC‐8897 has been purified to homogeneity from the culture filtrate of the fungal strain using ammonium sulphate precipitation and cation‐exchange chromatography on carboxymethyl cellulose. The sodium dodecyl sulphate/polyacrylamide gel electrophoresis analysis of the purified enzyme gave a single protein band corresponding to the molecular mass 51.0 kDa. The native polyacrylamide gel electrophoresis also gave a single protein band confirming the enzyme purity. The K_m and V_max values of the enzyme for p‐nitrophenyl α‐l ‐rhamnopyranoside were 0.36 mm and 22.54 μmole min^?1 mg^?1, respectively, and k_cat value was 17.1 s^?1 giving k_cat/K_m value of 4.75 × 10⁴ m ^?1 s^?1. The pH and temperature optima of the enzyme were 7.0 and 60 °C, respectively. The purified enzyme liberated l ‐rhamnose from naringin, rutin, hesperidin and wine, indicating that it has biotechnological application potential for the preparation of l ‐rhamnose and other pharmaceutically important compounds from natural glycosides containing terminal α‐l ‐rhamnose and also in the enhancement of wine aroma.     

1,3‐Dimethoxybenzene,a newly identified component of port wine

1,3‐Dimethoxybenzene was identified by GC–O, GC–MS and Kovats indices (polar Supelcowax, 1709; non‐polar Rtx‐5MS, 1158) as a new volatile component of port wine. Sensory evaluation described this compound as having a sweet medicinal odour with hazelnut, resinous and woody notes. Respective threshold limits in model wine and port wine were 21 and 47 µg l^?1. Quantitative analysis by GC–MS, using a selected characteristic ion (m/z 138), indicated that young port wines from the 1998 vintage contained up to 3 µg l^?1 whereas ports from the 1999 vintage contained up to 20 µg l^?1. © 2002 Society of Chemical Industry     

Study of the aroma compounds of rose apple (<Emphasis Type="Italic">Syzygium jambos</Emphasis> Alston) fruit from Brazil

Volatiles of the headspace and total aqueous extract from the rose apple fruit were investigated by gas chromatography (GC)–flame ionization detection, GC–mass spectrometry and GC–olfactometry/aroma extract dilution analysis O/AEDA). The headspace fraction was rich in low boiling compounds, while medium and high volatility components predominated in the total aqueous extract. GC–O/AEDA revealed that hexanal, 3-penten-2-one, hexanol, (Z)-3-hexen-1-ol, linalool, isovaleric acid, benzyl alcohol, 2-phenylethylalcohol and (E)-cinnamaldehyde were potent odorants contributing to the headspace aroma. Thus, they might be related to the first odour impression of the fruit. Other potent volatiles, such as caproic and phenylacetic acids, methyl-(E)-cinnamate and (E)-cinnamyl alcohol were identified in the total aqueous extract, only. These results indicated that some volatiles, with medium and high boiling points, might also contribute to the overall rose apple flavour. Besides them, volatiles with lower odour potency, such as 7-octen-4-ol, acetic acid, 2-octen-1-ol and cinnamic acid, could have some additional effect for the overall fruit aroma.     

Comparative aroma profiles using supercritical carbon dioxide and Likens–Nickerson extraction from a commercial brand of Basmati rice

A comparative evaluation of the extraction of the aroma constituents of a popular commercial brand of Basmati rice using Likens–Nickerson extraction and supercritical fluid extraction (SFE) with carbon dioxide was carried out. SFE at 50 °C and 120 bar for 2 h provided appreciable extraction of the volatile constituents of the rice as compared with Likens–Nickerson extraction. The advantages of smaller sample size, shorter time of extraction and negligible possibility of artefacts with the SFE technique merit its use for recovery of aroma volatiles from Basmati rice. Copyright © 2003 Society of Chemical Industry     

Hydrolysis of grape monoterpenyl glycosides by Candida molischiana and Candida wickerhamii β-glucosidases

The exocellular β-glucosidases of Candida molischiana and Candida wickerhamii are able to hydrolyse geranyl, neryl, citronellyl, linalyl and α-terpinyl-β-D -glucopyranosides. The nature of the aglycone residue greatly affects the rate of hydrolysis. Glucosides with a tertiary alcohol as aglycone residue are more slowly hydrolysed than those with a primary alcohol. The β-glucosidase from C molischiana is also able to hydrolse α-L-arabinofuranosides. This results in the release of monoterpenols from a glycoside extract from grape juice.     

‘爱甘水’梨果实生长发育过程中香气成分的变化分析

采用固相微萃取法提取‘爱甘水’梨果实生长发育过程的香气成分,经气相色谱-质谱联用技术分析花后不同时期‘爱甘水’梨果实的香气成分。结果表明,‘爱甘水’梨果实香气成分主要为酯类、醛类和醇类。其中,酯类物质含量在果实生长发育过程中逐渐升高,从0.41%增加到57.05%;醛类物质含量在果实生长发育过程呈现先增后降的变化规律,最大值为31.86%;而醇类物质含量在果实生长发育过程呈现“M”形的变化规律,最高达到18.28%。此外,还检测出己醛、2-己烯醛、己酸乙酯、苯甲酸乙酯、丁酸乙酯、戊酸乙酯、辛酸乙酯、丁酸-2-乙基丙酯、十九烷为成熟‘爱甘水’梨果实的特征香气成分。     

单丛茶香气物质基础分析

采用茶叶感官审评及气相色谱-质谱等技术手段对香气成分进行检测,并结合多种统计分析方法,系统研究单丛茶香气化学品质的物质基础。结果表明：单丛茶最主要挥发性物质为吲哚、脱氢芳樟醇、芳樟醇、茉莉内酯、臧红花醛和β-环柠檬醛,其他重要挥发性物质为橙花叔醇、苯乙腈和α,4-二甲基-3-环己烯-1-乙醛等。在单丛茶挥发性组分中,以花果香为主的醇类化合物含量最多,含氮化合物含量次之。在相关分析与聚类分析中,银花香和桂花香表现较为独特。蜜香型和花香型单丛茶在主成分分析和正交偏最小二乘法判别分析结果中有较好分属区域,所建正交偏最小二乘法判别分析模型适用性和检验效果良好。该研究结果可为单丛茶的香气品质评价和提高产品质量提供科学依据。     

Effects of Different β‐D‐Glycosidases on Bound Aroma Compounds in Muscat Grape Determined by HS‐SPME and GC‐MS

Important “floral” aromas naturally occur in grapes predominantly as flavourless glycoconjugate precursors. Since these aroma compounds can be released by hydrolysis, different glycosidase enzymes can potentially contribute different aromas to wines. In this paper, we first established a procedure for profiling the free and bound volatile compounds in grape using GC‐MS combined with headspace solid‐phase microextraction (HS‐SPME). Comparison of the free and bound aroma compounds revealed that non‐volatile glycosides, known as aroma precursors, occur in high concentrations in musts. Among all compounds identified, 11 were fully quantified according to established standard calibration curves, while others were semi‐quantified. Using three different glycosidase enzymes, a total of 38 bound volatile compounds were identified in Muscat grape, including terpenes, higher alcohols, C‐6 compounds, and phenols, among others. The different enzymes had significant effects on the varietal aroma. Principal component analysis indicated that the characteristic aroma hydrolyzed by the commercial enzyme AR2000 was clearly different from that produced by other enzymes.     

Comparative Studies on Volatile Components of Non-Fragrant and Fragrant Rices

Volatile compounds (70 in all) were identified in cooked fragrant and non-fragrant rice. The most important compounds were alkanals, alk-2-enals, alka-2,4-dienals, 2-pentylfuran, 2-acetyl-1-pyrroline and 2-phenylethanol, but many other compounds were identified that contributed to the total aroma profile. Non-fragrant rice (Pelde) contained much more n-hexanal, (E)-2-heptenal, 1-octen-3-ol, n-nonanal, (E)-2-octenal, (E)-2,(E)-4-decadienal, 2-pentylfuran, 4-vinylguaiacol and 4-vinylphenol, than the fragrant rices (Basmati, Jasmine, Goolarah, YRF9). Jasmine and Goolarah had much more indole, Goolarah and YRF9 had higher amounts of 2-acetyl-1-pyrroline compared with those of Pelde, whilst Basmati had the highest amount of 2-phenylethanol and the lowest content of n-hexanal among all the rice types examined. Results of the sensory evaluation showed that YRF9 and Goolarah had the highest pandan-like aroma whilst Basmati had the highest popcorn-like aroma.