Occurrence of polyfunctional thiols in fresh lager beers

Polyfunctional thiols are known to have a strong impact on the overall aroma of many fermented foods. Surprisingly, very little data is available on their occurrence in beer. A specific extraction with p-hydroxymercuribenzoic acid was performed on four different fresh light-protected lager beers. gas chromatography-olfactometry, gas chromatography-mass spectrometry, and gas chromatography-pulsed-flame photometer detector analyses of the extracts revealed the presence of more than 10 polyfunctional thiols. All of them were absent from wort, suggesting a key role of the H(2)S excreted by yeasts. 3-Methyl-2-buten-1-thiol, 2-mercapto-3-methylbutanol, 3-mercapto-3-methylbutanol seem to be created from hop allylic alcohols via four different mechanisms: nucleophilic substitution, addition-elimination, and radical anti-Markovnikov or electrophilic Markovnikov additions. 1,4 Addition of hydrogen sulfide to wort alpha,beta-unsaturated aldehydes or ketones may explain the synthesis of 1-mercapto-3-pentanol, 3-mercaptohexanol, and 4-mercapto-4-methyl-2-pentanone through fermentation. Finally, 2-mercaptoethanol, 3-mercaptopropanol, and their corresponding acetates may derive from Ehrlich degradation of sulfur amino acids, while 2-methyl-3-furanthiol should be logically issued from Maillard reactions.     

Occurrence of Odorant Polyfunctional Thiols in Beers Hopped with Different Cultivars. First Evidence of an S-Cysteine Conjugate in Hop ( Humulus lupulus L.)

Forty-one thiols, mainly β-sulfanylalkyl acetates, β-sulfanylalkyl alcohols, and β-sulfanylalkyl carbonyls, were recently evidenced in hop. In a beer hopped with the Tomahawk cultivar, most of them were found at higher levels than expected. The aim of the present work was to investigate the polyfunctional thiols in beers hopped with different varieties. A few thiols proved not to come only from hop (mainly 2-sulfanylethyl acetate, μg/L levels, and 1-sulfanylpentan-3-one and 1-sulfanylpentan-3-ol, ng/L levels, internal standard (IST) equivalents). The thiol profile of Saaz-hopped beer proved similar to that of the reference beer produced without hop. A high level of 3-sulfanyloctan-1-ol emerged as an indicator of the use of Tomahawk hop (140 ng/L, IST equivalents; FD (flavor dilution) = 65536). In both Cascade- and Tomahawk-hopped beers, 3-sulfanylhexan-1-ol and 3-sulfanylheptan-1-ol were smelled at high flavor dilutions, although only for the latter, significant amounts of the unreduced 3-sulfanylheptanal were found in hop. As already claimed for hop authentication, 3-sulfanyl-4-methylpentan-1-ol remains a good marker of Nelson Sauvin-hopped beers (548 ng/L, IST equivalents; FD = 65536), together with 4-sulfanyl-4-methylpentan-2-one (128 ng/L, FD = 4096). As illustrated by the huge production occurring during fermentation, accurate prediction of hop varietal impact requires quantitating thiol adducts in hop. S-3-(1-Hydroxyhexyl)cysteine was evidenced here for the first time in Cascade hop.     

Identification based on quantitative measurements and aroma recombination of the character impact odorants in a Bavarian Pilsner-type beer

Application of aroma extract dilution analysis on the volatiles isolated from a Bavarian Pilsner-type beer revealed 40 odor-active constituents in the flavor dilution (FD) factor range of 16-2048, among which ethyl octanoate, (E)-beta-damascenone, 2- and 3-methylbutanoic acid, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone showed the highest FD factor of 2048. After quantitation of the 26 odorants showing FD factors > or =128 by stable isotope dilution analysis and determination of their odor thresholds in water, odor acitivity values (OAVs) were calculated. The results indicated ethanol, (E)-beta-damascenone, (R)-linalool, acetaldehyde, and ethyl butanoate with the highest OAVs, followed by ethyl 2-methylpropanoate and ethyl 4-methylpentanoate, which was previously unknown in beer. Finally, the overall aroma of the beer could be mimicked for the first time by recombining 22 reference odorants in the same concentrations as they occurred in the beer using ethanol/water as the matrix.     

Volatile Profiles of 13 Foxtail Millet Commercial Cultivars (Setaria italica Beauv.) from China

The volatile components from 13 commercially valuable foxtail millets from China were investigated by means of gas chromatography–mass spectrometry combined with simultaneous distillation extraction. A total of 52 volatile compounds were identified in all of the samples: 19 aldehydes, 5 alcohols, 10 ketones, 9 hydrocarbons, 6 benzene derivatives, and 3 others. Here, 23 common constituents were found in all samples. Aldehydes were the predominant volatile components in various cultivars. The importance of each volatile was assessed on the basis of odor thresholds and odor activity values (OAVs). Here, 35 volatile compounds were described using aroma character, and 24 volatile compounds were found to be odor‐active compounds. Another 11 common constituents were found in all samples. The components with the highest OAVs in most cultivars were (E )‐2‐nonenal and (E,E )‐2,4‐decadienal. Most of the other aldehydes also had high OAVs. Some of the ketones, alcohols, benzene derivatives, and other compounds were found to contain an odor‐active compound in several cultivars of foxtail millet. Principal component analysis was employed to evaluate the differences among cultivars. The results demonstrated that the volatile profile based on the OAVs of aroma compounds enabled good differentiation of most cultivars.     

Olfactory perception of cysteine-S-conjugates from fruits and vegetables

Volatile sulfur compounds have a low odor threshold, and their presence at microgram per kilogram levels in fruits and vegetables influences odor quality. Sensory analysis demonstrates that naturally occurring, odorless cysteine- S-conjugates such as S-( R/ S)-3-(1-hexanol)- l-cysteine in wine, S-(1-propyl)- l-cysteine in onion, and S-(( R/ S)-2-heptyl)- l-cysteine in bell pepper are transformed into volatile thiols in the mouth by microflora. The time delay in smelling these volatile thiols was 20-30 s, and persistent perception of their odor occurred for 3 min. The cysteine- S-conjugates are transformed in free thiol by anaerobes. The mouth acts as a reactor, adding another dimension to odor perception, and saliva modulates flavors by trapping free thiols.     

Occurrence of odorant polyfunctional thiols in the Super Alpha Tomahawk hop cultivar. Comparison with the thiol-rich Nelson Sauvin bitter variety

Tomahawk hop (Humulus lupulus) is a recently developed Super Alpha cultivar (14-18% α-acids w/w), already widely used by brewers to impart bitterness and a citrus-like aroma to beer. By comparison with two bitter varieties (Nelson Sauvin and Nugget) and two aromatic ones (Cascade and Saaz), the Tomahawk cultivar showed a very particular terpenoid profile, rich in both α- and β-selinenes (>600 mg/kg IST equiv in total), methyl geranate (>40 mg/kg IST equiv), and geraniol (>200 mg/kg). Tomahawk also proved to contain a wide variety of odorant polyfunctional thiols. The major β-sulfanyl acetate, 3-sulfanyl-2-ethylpropyl acetate, newly identified here, was found at similar levels in the famous Sauvignon-like Nelson Sauvin and Tomahawk varieties (15-44 μg/kg IST equiv). On the other hand, lower levels of total β-sulfanyl alcohols were measured in Tomahawk, although 3-sulfanylhexan-1-ol was found at a similar level and the 3-sulfanyl-4-methylpentan-1-ol previously claimed to be specific to the Nelson Sauvin variety was also evidenced in the Super Alpha cultivar (9-13 μg/kg IST equiv). As revealed by boiling and fermentation, Tomahawk hop also contains very interesting bound polyfunctional thiols that should be investigated for better use by brewers.     

电子鼻结合HS-SPME-GC-MS分析辐照对甲鱼预制菜挥发性风味成分的影响

为了探究辐照对甲鱼预制菜挥发性风味成分的影响,采用0、4.7、7.1、9.9 kGy剂量⁶⁰Co-γ射线辐照处理甲鱼预制菜,通过感官评定并利用电子鼻结合顶空固相微萃取-气相色谱-质谱联用技术(HS-SPME-GC-MS)分析辐照前后挥发性风味成分的变化。结果表明,5 kGy以内剂量辐照对甲鱼预制菜的感官品质无明显影响,高于5 kGy会影响其气味和滋味,进而可能产生异味。辐照对甲鱼预制菜特征气味引起的差异主要表现在传感器响应值较高的芳香成分和有机硫化物、氮氧化合物、甲烷、醇类和醛酮类物质,利用主成分分析(PCA)和线性判别分析(LDA)能够有效区分经不同剂量辐照处理的甲鱼预制菜。4.7 kGy组与对照组气味差异较小,7.1、9.9 kGy组与对照组差异相对较大。不同剂量辐照后甲鱼预制菜挥发性成分的种类增加,醛类、酸类相对含量降低,烃类、芳香族类、酮类、酯类相对含量升高,醇类、含氮含硫及杂环类相对含量先降低后升高。相对气味活度值(ROAV)分析结果表明,壬醛、癸醛、辛醛、己醛、庚醛、1-辛烯-3-醇和2-戊基呋喃是甲鱼预制菜的关键风味成分,苯甲醛、苯乙醛、(E,E)-2, 4-癸二烯醛对其风味具有重要修饰作用。辐照后辛醛、己醛、1-辛烯-3-醇对甲鱼预制菜总体风味的贡献率降低,庚醛、2-戊基呋喃的贡献率先降低后增加,苯乙醛的贡献率增加并成为关键风味成分。因此,建议采用不超过5 kGy剂量的⁶⁰Co-γ射线辐照处理甲鱼预制菜,在杀菌的同时最大限度保持其原有风味。本研究结果为辐照技术在甲鱼预制菜杀菌保鲜中的应用提供了科学依据。     

基于电子鼻和分光测色仪技术的茶树叶片氮营养诊断

【目的】利用电子鼻和分光测色仪建立一套快速检测茶树叶片氮含量的无损伤检测方法。【方法】供试样品为茶树顶芽向下第3~4片无损伤叶片。在预实验中优化了气体收集瓶体积、顶空预热温度和顶空时间等参数。采用电子鼻自带Winmuster软件将经过优化后的传感器响应特征值进行主成分分析(principal component analysis,PCA)、线性判别法分析(linear discriminant analysis,LDA)和负荷加载分析(loadings analysis,LA),筛选出灵敏性最好的传感器。同时用分光色差仪对茶树叶片色度值进行测定。样品的测量部位是叶肉区,每组20次重复。色度值主要包括L (表示黑白或者亮暗)、a (表示红绿)、b (表示黄蓝)值。采用Origin 8.0软件对测色仪L、a、b值分别进行一元线性回归分析。利用SPSS 16.0软件采用LSD法进行单因素方差分析(one-way Anova),并进行t检验。对分光测色仪中色差指标进行筛选,以获得相关系数最高的参数。采用凯氏定氮法测定茶叶总氮含量。正式试验第二步是以不同氮含量下的电子鼻和分光测色检测数据为基础,分别建立气味、颜色、气味结合颜色的3种氮含量预测模型,并进行比较分析。【结果】通过预备试验,建立了气体收集器体积为50 mL、顶空预热温度为30℃、顶空时间为30 min的电子鼻检测体系。正式试验第一步确定了以对氮氧化合物灵敏(S2),对甲烷灵敏(S6),对无机硫化物灵敏(S7),对醇类、醛类、酮类物质灵敏(S8),对有机硫化物灵敏(S9)的传感器为主要传感器。根据L、a、b表色系统,b值与叶片缺氮程度呈线性相关。正式试验第二步利用气味、颜色、气味结合颜色建立的3个氮含量预测模型都具有可行性,其中气味结合颜色建立的预测模型准确率最高,达到90%。【结论】用气味结合颜色的预测模型预测茶树叶片氮含量准确度较高,可在实际工作中进行运用。     

Multivariate modeling of aging in bottled lager beer by principal component analysis and multiple regression methods

Data collected from the sensory test score evaluation of bottled lager beer, together with the chemical components related to aging, including carbonyl compounds, higher alcohols, unsaturated fatty acid, organic acids, alpha-amino acids, dissolved oxygen, and staling evaluation indices, including lag time of electron spin resonance (ESR) curve, 1,1'-diphenyl-2-picrylhydrazyl (DPPH) scavenged amounts, and thiobarbituric acid (TBA) values, were used to predict the extent of aging in bottled lager beer, using both multiple linear regression and principal component analysis methods. Carbonyl compounds, higher alcohols, and TBA value were significantly and positively correlated with sensory evaluation of staling flavor. While lag time and DPPH scavenging amount were negatively correlated with taste test score. Multiple regression analysis was used to fit the sensory test data using the above chemical compound aging related parameters and evaluation indices as predictors. A variable selection method based on high loadings of varimax rotated principal components was used to obtain subsets of the predominant predictor variables to be included in the regression model of beer aging, so as to eliminate the multicollinearity of the original nine variables. It was found that staling extent was influenced significantly by higher alcohols, TBA value, and DPPH scavenging amount, and the multicollinearity of the regression model was found to be weak by examining the variance inflation factors of the new predictor variables. A mathematic model of the organoleptic test score for beer aging using these three predictors was obtained by multiple linear regression, showing that the major contributors to the sensory taste of beer aging were higher alcohols, TBA index, and DPPH scavenging amount, with the adjusted R(2) of the model being 0.62.     

Aroma extraction dilution analysis of Sauternes wines. Key role of polyfunctional thiols

The aim of the present work was to investigate Sauternes wine aromas. In all wine extracts, polyfunctional thiols were revealed to have a huge impact. A very strong bacon-petroleum odor emerged at RI = 845 from a CP-Sil5-CB column. Two thiols proved to participate in this perception: 3-methyl-3-sulfanylbutanal and 2-methylfuran-3-thiol. A strong synergetic effect was evidenced between the two compounds. The former, never mentioned before in wines, and not found in the musts of this study, is most probably synthesized during fermentation. 3-Methylbut-2-ene-1-thiol, 3-sulfanylpropyl acetate, 3-sulfanylhexan-1-ol, and 3-sulfanylheptanal also contribute to the global aromas of Sauternes wines. Among other key odorants, the presence of a varietal aroma (alpha-terpineol), sotolon, fermentation alcohols (3-methylbutan-1-ol and 2-phenylethanol) and esters (ethyl butyrate, ethyl hexanoate, and ethyl isovalerate), carbonyls (trans-non-2-enal and beta-damascenone), and wood flavors (guaiacol, vanillin, eugenol, beta-methyl-gamma-octalactone, and Furaneol) is worth stressing.     

Odor-active headspace components in fermented red rice in the presence of a monascus species

Headspace components from rice and agar with (experimental) and without (control) inoculation with a Monascus spp. were investigated. Kinetics studies were carried out. Using rice as a substrate, 10 and 19 compounds were found for the control and the experimental groups, respectively, at day 14. Experimental group compounds were composed mainly of alcohols, ketones, and esters, whereas control group compounds were composed of aldehydes and ketones. With agar as a substrate, only five and three components were found in the control and experimental groups, respectively. Five alcohols, four esters, two ketones, and one furan with odor activity values (OAV) >1 dominated the overall flavor of the product. With liquid inoculation, the first six components with high OAVs were in the following order: 3-methyl-1-butanol (17) > ethanol (14) > ethyl acetate (10) > 2-methyl-1-propanol (15) > ethyl butanoate (11) > 3-methylbutyl acetate (13). Kinetic studies showed that most compounds reached their maximum concentrations at 10-12 days. Many compounds identified in the model red rice were reported in commercial red sufus, and several appeared to contribute solely by red rice.     

Chemical interactions between odor-active thiols and melanoidins involved in the aroma staling of coffee beverages.

Comparative aroma dilution analyses of the headspaces of aqueous solutions containing either the total volatiles isolated from a fresh coffee brew, or these volatiles remixed with the melanoidins isolated from coffee brew, revealed a drastic decrease in the concentrations of the odorous thiols 2-furfurylthiol, 3-methyl-2-butenthiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methanethiol when melanoidins were present. Among these thiols, 2-furfurylthiol was affected the most: e.g., its concentration decreased by a factor of 16 upon addition of melanoidins. This was accompanied by a decrease in the overall roasty-sulfury aroma. Quantitations performed by means of stable isotope dilution assays confirmed the rapid loss of all thiols with increasing time while keeping the coffee brew warm in a thermos flask. Using [2H2]-2-furfurylthiol as an example, [2H]-NMR and LC/MS spectroscopy gave strong evidence that thiols are covalently bound to the coffee melanoidins via Maillard-derived pyrazinium compounds formed as oxidation products of 1,4-bis-(5-amino-5-carboxy-1-pentyl)pyrazinium radical cations (CROSSPY). Using synthetic 1,4-diethyl diquaternary pyrazinium ions and 2-furfurylthiol, it was shown that 2-(2-furyl)methylthio-1,4-dihydro-pyrazines, bis[2-(2-furyl)methylthio]-1,4-dihydro-pyrazines, and 2-(2-furyl)methylthio-hydroxy-1,4-dihydro-pyrazines were formed as the primary reaction products. Similar results were obtained for models in which either 1,4-diethyl diquaternary pyrazinium ions were substituted by Nalpha-acetyl-L-lysine/glycolaldehyde, or the 2-furfurylthiol by 2-methyl-3-furanthiol and 3-mercapto-3-methylbutyl formate. On the basis of these results it can be concluded that the CROSSPY-derived pyrazinium intermediates are involved in the rapid covalent binding of odorous thiols to melanoidins, and, consequently, are responsible for the decrease in the sulfury-roasty odor quality observed shortly after preparation of the coffee brew.     

Characterization of odor-active compounds in guava wine

The volatile compounds of guava wine were isolated by continuous solvent extraction and analyzed by GC-FID and GC-MS. A total of 124 volatile constituents were detected, and 102 of them were positively identified. The composition of guava wine included 52 esters, 24 alcohols, 11 ketones, 7 acids, 6 aldehydes, 6 terpenes, 4 phenols and derivatives, 4 lactones, 4 sulfur-compounds, and 5 miscellaneous compounds. The aroma-active areas in the gas chromatogram were screened by application of the aroma extract dilution analysis and by odor activity values. Twelve odorants were considered as odor-active volatiles: (E)-β-damascenone, ethyl octanoate, ethyl 3-phenylpropanoate, ethyl hexanoate, 3-methylbutyl acetate, 2-methyltetrahydrothiophen-3-one, 2,5-dimethyl-4-methoxy-3(2H)-furanone, ethyl (E)-cinnamate, ethyl butanoate, (E)-cinnamyl acetate, 3-phenylpropyl acetate, and ethyl 2-methylpropanoate.     

采用气相色谱-离子迁移谱分析黄大茶加工过程挥发性成分

茶叶加工对茶叶香气的形成至关重要。为了研究黄大茶加工过程中香气成分的组成及变化规律,采用气相色谱-离子迁移谱(Gas Chromatography-Ion Mobility Spectrometry,GC-IMS)技术对黄大茶加工过程的挥发性成分进行分析。定性分析、鉴定茶叶挥发性成分,构建黄大茶加工过程挥发性成分的差异谱图,并以鉴定的挥发性成分对黄大茶加工过程进行主成分分析。共鉴定出挥发性成分40种,主要有醇类、酮类、醛类、酯类和杂环类化合物。杂环类和醛类化合物是黄大茶挥发性成分的主体部分,且杀青之后,杂环类化合物的含量随着加工过程的进行逐渐增加,醛类化合物的相对含量在初烘之后呈现显著性增加,而醇类及酮类挥发性成分的相对含量在初烘之后显著性降低(P0.05)。具花香的氧化芳樟醇只在初闷之前的样品中得到鉴定,在鲜叶中的含量最高,达21.98%,而1-辛烯-3-酮及苯乙酮只在初烘之后的样品中得到鉴定。通过GC-IMS的指纹图谱可知,苯甲醛、2,5-二甲基呋喃、糠醛及二甲基二硫等挥发性成分构成了经"拉老火"工序的黄大茶的特征峰区域。在一定程度上,主成分分析能够将黄大茶加工过程样品进行区分,表明气相色谱-离子迁移谱分析可为黄大茶加工过程的判别区分提供可能。相较于传统的茶叶挥发性成分检测分析技术,气相色谱-离子迁移谱具有快速、高效、绿色环保的特点。研究结果提供一种新的茶叶挥发性成分的检测分析方法,同时为茶叶加工过程监测及品质控制等提供了一定参考依据和理论基础。     

海水净化过程中球等鞭金藻对硬壳蛤风味品质的影响

为了探究微藻在贝类净化中的作用,以及净化处理对贝类风味成分的影响,本研究以球等鞭金藻作为净化贝类的食物来源,通过多元统计及判别分析,对比添加球等鞭金藻净化前后贝肉挥发性成分的变化.结果表明,净化后贝类中绝大多数特征性风味成分含量增加,如醛、醇、酯、酮类化合物;其中含量增加最明显的风味成分是具有黄油、肉香的酮类;而部分具...     

Interactions between methyl ketones and beta-lactoglobulin: sensory analysis, headspace analysis, and mathematical modeling

Interaction of flavor compounds with proteins is known to have an influence on the release of flavor from food. Hydrophobic interactions were found between beta-lactoglobulin and methyl ketones; the affinity constant increases by increasing the hydrophobic chain. Addition of beta-lactoglobulin (0.5 and 1%) to aroma solutions (12.5, 50, and 100 microL L(-)(1)) of three methyl ketones induces a significant decrease in odor intensity. The chosen methyl ketones were 2-heptanone (K(b) = 330), 2-octanone (K(b) = 950), and 2-nonanone (K(b) = 2440). The release of these flavor compounds (50 microL L(-)(1)) was studied by static headspace in water solution (50 mM NaCl, pH 3) with different concentrations of beta-lactoglobulin (0, 0.5, 1, 2, 3, and 4%). Increasing the concentration of protein increases the retention of volatiles, and this effect is greatest for 2-nonanone, the compound with the highest affinity constant, and lowest for 2-heptanone. A mathematical model previously developed to describe flavor release from aqueous solutions containing flavor-binding polymers (Harrison, M.; Hills, B. P. J. Agric. Food Chem. 1997, 45, 1883-1890) was used to interpret the data. The model assumes that the polymer-flavor interaction is reversible and the rate-limiting step for release is the transfer of volatiles across the macroscopic gas-liquid interface. This model was used to predict the equilibrium partitioning properties and the rate of release of the three methyl ketones. Increasing the affinity constant leads to decreased release rates and a lower final headspace aroma concentration.