New constituents related to 3-methyl-2,4-nonanedione identified in green tea

The volatile constituents of two exquisite green tea varieties, Kiyosawa tea from Japan and Long Jing tea from China, were investigated in order to identify new compounds responsible for the characteristic flavor of a green tea brew. The extracts were prepared by solid-phase extraction using Oasis-HLB-cartridges. Besides the common compounds of green tea chemistry, the already described compounds 3-methyl-2,4-nonanedione (1) and 3-hydroxy-3-methyl-2,4-nonanedione (2), products of degradation of furan fatty acids, as well as three new compounds related to compound 1 were identified. These were 1-methyl-2-oxopropyl hexanoate (3), 1-methyl-2-oxoheptyl acetate (4) and 2-butyl-4,5-dimethyl-3(2H)-furanone (5). Their syntheses and spectroscopic data are reported. Compound 2 increases the sweet, creamy aroma and the characteristic mouthfeel of a green tea flavor, compounds 3 and 4 contribute to its floral, juicy notes and compound 5 exhibits an interesting sweet, buttery flavor.     

Instrumental and sensory characterization of heat-induced odorants in aseptically packaged soy milk

Predominant heat-induced odorants generated in soy milk by ultrahigh-temperature (UHT) processing were evaluated by sensory and instrumental techniques. Soy milks processed by UHT (143 degrees C/14 s, 143 degrees C/59 s, 154 degrees C/29 s) were compared to a control soy milk (90 degrees C/10 min) after 0, 1, and 7 days of storage (4.4 +/- 1 degrees C). Dynamic headspace dilution analysis (DHDA) and solvent-assisted flavor evaporation (SAFE) in conjunction with GC-olfactometry (GCO)/aroma extract dilution techniques and GC-MS were used to identify and quantify major aroma-active compounds. Sensory results revealed that intensities of overall aroma and sulfur and sweet aromatic flavors were affected by the processing conditions. Odorants mainly responsible for the changes in sulfur perception were methional, methanethiol, and dimethyl sulfide. Increases in 2-acetyl-1-pyrroline, 2-acetyl-thiazole, and 2-acetyl-2-thiazoline intensities were associated with roasted aromas. A marginal increase in intensity of sweet aromatic flavor could be explained by increases in 2,3-butanedione, 3-hydroxy-2-butanone, beta-damascenone, and 2- and 3-methylbutanal. Predominant lipid-derived odorants, including (E,E)-2,4-nonadienal, (E,E)-2,4-decadienal, (E,Z)-2,4-decadienal, (E)-2-nonenal, (E)-2-octenal, 1-octen-3-one, 1-octen-3-ol, and (E,Z)-2,6-nonadienal, were affected by processing conditions. Intensities of overall aroma and sulfur notes in soy milk decreased during storage, whereas other sensory attributes did not change. Color changes, evaluated by using a Chroma-meter, indicated all UHT heating conditions used in this study generated a more yellow and saturated color in soy milk in comparison to the control soy milk.     

Aroma of fresh oysters Crassostrea gigas: composition and aroma notes

In contrast to many foods, very little is known about the aroma of fresh oysters. This study deals with the relationship between extracted volatiles of oysters and their olfactory properties. Nearly 50 volatiles were identified: most of them were principally related to fatty acid oxidation (86%) and particularly to n-3 polyunstaturated fatty acid oxidation (66%). Only one volatile arose from amino acid degradation. Panelists detected 42 odors by sniffing. Among them, only 12 odors were definitely attributed to identified volatile. These odors were green/sulfur/crustacean, mushroom/citrus, and marine/cucumber notes and were attributed to dimethyl sulfide, 1-penten-3-one, hexanal, (2,4)-E,E-heptadienal, 1-octen-3-one, 1-octen-3-ol, 6-methyl-5-hepten-3-one, octanal, (E,Z)-2,6-nonadienal, (E)-2-octenal, and decanal, respectively.     

适宜氮肥施用量显著提升夏季绿茶品质

  【目的】  我国30%的茶园氮肥施用过量。氮肥过量施用不仅造成能源浪费和茶园土壤质量恶化 (如酸化、板结等)，还使茶叶特别是绿茶增产提质边际效应逐渐下降。夏季绿茶品质 (尤其是香气) 往往低于春茶，但其产量却远大于春茶，因此，研究施氮对夏季绿茶的品质影响，为夏季绿茶提质增效提供理论依据。  【方法】  茶园氮肥长期定位试验位于浙江杭州，始于2005年。氮肥施用水平分别为0、119、285、474、569和712 kg/hm2。采集连续施用12年氮肥的茶树夏季新梢一芽二叶制成绿茶样。采用GB/T 23776—2018茶叶感官审评方法、茚三酮/福林酚-比色法、CN分析仪、氨基酸自动分析仪、顶空固相微萃取法结合气相色谱–质谱联用技术，分别对绿茶感官品质、氨基酸和茶多酚总量、氮含量、氨基酸组分以及香气组分进行检测分析。  【结果】  不同氮肥施用水平对绿茶香气影响较大。在施N 0～474 kg/hm2范围内，绿茶氨基酸总量随着施氮量增加而升高，在施N 474 kg/hm2时达到最高。施氮量提高到569和712 kg/hm2后，绿茶氨基酸总量降低，茶多酚总量升高，对应的酚氨比升高，而绿茶样品氮含量反而低于N 474 kg/hm2处理。在鉴定到的16种氨基酸组分中，大部分氨基酸含量在施氮量285和474 kg/hm2时达到最高，包括决定成品茶鲜爽味的茶氨酸、谷氨酸和天冬氨酸含量，而当施氮量超过474 kg/hm2时，这些氨基酸的含量开始下降。醇类、酮类、烯类、醛类、酯类以及其他香气化合物受氮素供应水平影响存在差异，主导绿茶呈香的醇类物质相对含量在施N 0～285 kg/hm2范围内，随着施氮量的升高而增加，其中以占醇类物质总量比重最高的β-芳樟醇和橙花叔醇变化最为明显。酮类香气化合物在不同氮素供应水平下变化趋势与醇类一致，但受氮素供应水平影响小于醇类。烯类香气物质对氮素供应水平的响应与醇类和酮类则完全相反，总量随着施氮量增加逐渐降低，而醛酯类等其他香气化合物在不同施氮水平下无规律性变化。  【结论】  茶园施氮量在285～474 kg/hm2时，有利于提高茶叶品质，决定成品茶滋味的茶氨酸、谷氨酸等氨基酸组分和主导绿茶呈香的β-芳樟醇和橙花叔醇含量最高。     

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。     

Effect of cold storage and packaging material on the major aroma components of sweet cream butter

The major aroma compounds of commercial sweet cream AA butter quarters were analyzed by GC-olfactometry and GC-MS combined with dynamic headspace analysis (DHA) and solvent-assisted flavor evaporation (SAFE). In addition, the effect of long-term storage (0, 6, and 12 months) and type of wrapping material (wax parchment paper vs foil) on the aroma components and sensory properties of these butters kept under refrigerated (4 degrees C) and frozen (-20 degrees C) storage was evaluated. The most intense compounds in the aroma of pasteurized AA butter were butanoic acid, delta-octalactone, delta-decalactone, 1-octen-3-one, 2-acetyl-1-pyrroline, dimethyl trisulfide, and diacetyl. The intensities of lipid oxidation volatiles and methyl ketones increased as a function of storage time. Refrigerated storage caused greater flavor deterioration compared with frozen storage. The intensity and relative abundance of styrene increased as a function of time of storage at refrigeration temperature. Butter kept frozen for 12 months exhibited lower styrene levels and a flavor profile more similar to that of fresh butter compared to butter refrigerated for 12 months. Foil wrapping material performed better than wax parchment paper in preventing styrene migration into butter and in minimizing the formation of lipid oxidation and hydroxyl acid products that contribute to the loss of fresh butter flavor.     

Volatile composition of sunflower oil-in-water emulsions during initial lipid oxidation: influence of pH.

The formation of odor active compounds resulting from initial lipid oxidation in sunflower oil-in-water emulsions was examined during storage at 60 degrees C. The emulsions differed in initial pH, that is, pH 3 and 6. The volatile compounds were isolated under mouth conditions and were analyzed by gas chromatography/sniffing port analysis. The lipid oxidation rate was followed by the formation of conjugated hydroperoxide dienes and headspace hexanal. The initial pH affected the lipid oxidation rate in the emulsions: the formation of conjugated diene hydroperoxides and the hexanal concentration in the static headspace were increased at pH 6. Pentanal, hexanal, 3-pentanol, and 1-octen-3-one showed odor activity in the emulsions after 6 days of storage, for both pH 3 and 6. Larger amounts of odor active compounds were released from the pH 6 emulsion with extended storage. It was shown that this increased release at pH 6 was not due to increased volatility because an increase in pH diminished the static headspace concentrations of added compounds in emulsions.     

Light-induced off-flavor development in cloudy apple juice

Cloudy apple juice has been found to develop off-flavors during storage in daylight. The development of off-flavors and volatile compounds was monitored in reconstituted juice prepared from 'Golden Delicious' and 'Fuji' apple concentrates stored in glass bottles under fluorescent light (3000 lx, 8 degrees C). A strong metallic off-flavor was formed by photooxidation. A major contributor to the off-flavor was identified as 1-octen-3-one by gas chromatography-olfactometry. In addition, six volatile compounds, pentanal, 2-methyl-1-penten-3-one, hexanal, (E)-2-heptenal, 6-methyl-5-hepten-2-one, and (E)-2-octenal, increased significantly after light exposure and could contribute to the off-flavor. Except for pentanal and hexanal, these volatiles were found only after light exposure. Higher levels of volatiles were observed in juice from 'Golden Delicious' apples than in juice from 'Fuji' apples, and this difference was consistent with higher levels of suspended solids. When the suspended solids were removed by centrifugation, the development of volatiles on exposure to light was reduced significantly.     

Effect of preparation conditions on release of selected volatiles in tea headspace

The release of volatile compounds from infused tea was monitored using on-line atmospheric pressure chemical ionization (APCI) mass spectrometry. Assignment of the APCI ions to particular compounds was achieved using gas chromatography of tea headspace with dual electron ionization and APCI-MS detectors. Six ions in the APCI spectrum could be assigned to individual compounds, five ions were associated with isobaric compounds (e.g., 2- and 3-methylbutanal and pentanal) or stereoisomers (e.g., heptenals or heptadienals), and a further four ions monitored were identified compounds but with some unknown impurities. Reproducibility of infusion preparation and the analytical system was good with percentage variation values generally below 5%. The analysis was used to study the effect of infusion and holding temperatures on the volatile profile of tea headspace samples, and this was found to be compound-dependent. Both the extraction of volatiles from leaf tea and the release of volatiles into the headspace play a role in creating the aroma profile that the consumer experiences.     

Variation of major volatile constituents in various green teas from Southeast Asia

A total of 15 green tea samples were prepared from fresh tea leaves obtained from three different countries: two from Laos, seven from Myanmar, and six from Vietnam. The volatile aroma constituents of the 15 samples were analyzed by gas chromatography/mass spectroscopy. Eleven aroma constituents were chosen from over 100 chemicals found in the samples to compare differences among various teas. They were hexanal, 1-penten-3-ol, heptanal, 1-pentenal, (Z)-2-penten-1-ol, (Z)-3-penten-1-ol, linalool oxide (trans-furanoid), linalool oxide (cis-furanoid), linalool, linalyl propanoate, and geraniol. Generally, concentrations of linalool and hexanal seem to play an important role in the quality of green teas. Green teas from Laos and Myanmar contained heterocyclic compounds, such as pyridines and pyrazines, formed by high-temperature processing. The presence of these heterocyclic compounds suggested that the temperature used for tea processing plays an important role in the formation of aroma chemicals in green teas.     

Influence of manufacturing conditions and crop season on the formation of 4-mercapto-4-methyl-2-pentanone in Japanese green tea (sen-cha)

4-Mercapto-4-methyl-2-pentanone is one of the most strongly contributing odorants in the volatile fraction of a Japanese green tea (sen-cha) infusion, and on the basis of the results of an aroma extract dilution analysis, the contribution of this compound to the flavor of the sen-cha infusion varied according to the degree of heating of the tea leaves during the roasting process. The concentration of this odorant in the sen-cha infusion, as with other roasty odorants, increased with the increasing roasting temperature. However, the slope of the increase curve differed with the odor compound, and even if roasting was done at a low temperature, at which the other roasty odorants hardly increased, 4-mercapto-4-methyl-2-pentanone still increased and reached a maximum at 112 degrees C. On the other hand, the amount of 4-mercapto-4-methyl-2-pentanone in sen-cha was a maximum in the first crop, then decreasing in the order of the second and third crops. These results suggested that the amount of 4-mercapto-4-methyl-2-pentanone was closely involved with the quality of sen-cha and that the concentration was dependent on the roasting conditions for the green tea leaves, which might be accompanied by an enzymatic reaction.     

Preservation of kombucha tea-effect of temperature on tea components and free radical scavenging properties

Kombucha tea is sugared black tea fermented with a consortium of acetic acid bacteria and yeasts (tea fungus) for 14 days. The tea tastes slightly sweet and acidic. The formation of tea fungal biofilms during storage is a big problem when kombucha tea is being stored and commercialized. Various thermal treatments have been tried for long-term storage of kombucha tea. The present study revealed the influence of heat on the biochemical constituents and the free radical scavenging properties of kombucha tea. Heat treatment at 60, 65, and 68 degrees C for 1 min controlled biofilm formation in kombucha tea without changing its clarity, taste, and flavor. However, tea polyphenols and black tea quality parameters showed varying stability during the storage period. A decrease in free radical scavenging properties was also found during the storage period. Because the biological activities of kombucha tea depended on the biochemical constituents, it was concluded that heat treatment was not a suitable method for kombucha tea preservation.     

Comparison of the most odor-active compounds in fresh and dried hop cones (Humulus lupulus L. variety spalter select) based on GC-olfactometry and odor dilution techniques

Application of aroma extract dilution analysis on the volatiles obtained from dried cones of Spalter Select hops grown in the German hop-growing area of Hallertau revealed 23 odorants in the flavor dilution (FD) factor range of 16-4096, 20 of which could be identified. On the basis of high FD factors, trans-4, 5-epoxy-(E)-2-decenal, linalool, and myrcene were identified as the most potent odorants, followed by ethyl 2-methylpropanoate, methyl 2-methylbutanoate, (Z)-1,5-octadien-3-one, nonanal, (E,Z)-1,3, 5-undecatriene, 1,3(E),5(Z),9-undecatetraene, propyl 2-methylbutanoate, 4-ethenyl-2-methoxyphenol, and 1-octen-3-one. Ten of the high-impact hop aroma compounds had previously not been identified as hop constituents and, in particular, 1,3(E),5(Z), 9-undecatetraene has not yet been reported as a food odorant. In an extract obtained from fresh hops, in addition to the odorants found in dry hops, (Z)-3-hexenal was characterized as a further key odorant rendering an additional green aroma note to the fresh material.     

Flavor characteristics of lapsang souchong and smoked lapsang souchong, a special Chinese black tea with pine smoking process

The major volatile constituents of lapsang souchong, smoked lapsang souchong, and smoked souchong, a group of special black teas in China, were analyzed with GC and GC-MS analyses. Forty-nine constituents were identified. Longifolene and alpha-terpineol were the most abundant compounds in the aroma. Due to its special production process, the compounds longifolene, longicyclene, guaiacol, 4-methylguaiacol, 4-ethylguaiacol, etc., were identified only in this kind of black tea. The aroma constituents of tea origin decreased during the smoking process, whereas the pine terpenoids and the thermal pyrolysis products of the pine wood increased markedly. The pine material for smoking was also analyzed for the volatile constituents showing apparent selectivity of the tea leaves to absorb. There were apparent differences among the tea samples in the contents of aroma constituents. The characteristics of the aroma of the teas are discussed with their processes and the features of sensory qualities.     

Identification of impact odorants contributing to fresh mushroom off-flavor in wines: incidence of their reactivity with nitrogen compounds on the decrease of the olfactory defect

Analysis of wines from different grape varieties marked by sometimes intense aromatic nuances of fresh mushroom was performed by gas chromatography coupled with olfactometry. This analysis has led to the identification of several odoriferous zones, which were recalling a fresh mushroom odor. Two trace compounds responsible for these odoriferous zones, 1-nonen-3-one and 1-octen-3-one, have been identified and their content has been determined by using either a multidimensional gas chromatography technique coupled to olfactometry and mass spectrometry detection (in the case of 1-nonen-3-one) or the preparation of the derivative with O-2,3,4,5,6-pentafluorobenzylhydroxylamine hydrochloride in the presence of the deuterated form, as the internal standard (in the case of 1-octen-3-one), then gas chromatography coupled to mass spectrometry detection. The assays allowed the quantification of these compounds at concentration levels sometimes well above their detection and recognition olfactory threshold. We show that adding nitrogen compounds to the altered wines, such as an amino acid (glycine) or a tripeptide (glutathione), led to lower concentrations of 1-octen-3-one in wines and diminished smell of fresh mushrooms. The study of the reaction in a model medium, whose composition is close to wine, by liquid chromatography coupled to mass spectrometry demonstrated the formation of adducts between 1-octen-3-one and glycine, and 1-octen-3-one and glutathione characterized by NMR.     

Characterization of epoxydecenal isomers as potent odorants in black tea (Dimbula) infusion

In a black tea (Dimbula) infusion, the potent "sweet and/or juicy" odorants were identified as the cis- and trans-4,5-epoxy-(E)-2-decenals by comparison of their gas chromatography retention indices, mass spectra, and odor quality to those of the actual synthetic compounds. Of the two odorants, cis-4,5-epoxy-(E)-2-decenal has been identified for the first time in the black tea. On the basis of the aroma extract dilution analysis on the flavor distillate obtained using the solvent-assisted flavor evaporation technique from the black tea infusion, these isomers showed higher flavor dilution (FD) factors. The FD factors and concentrations of these odorants in the black tea infusion were observed to be much higher than those from Japanese green tea. In addition, the model studies showed that these odorants were generated from linoleic acid and its hydroperoxides by heating, but the generated amounts of these odorants from linoleic acid were much less than those of its hydroperoxides. It can be assumed from these results that the withering and fermentation, which are characteristic processes during the manufacturing of the black tea, which includes the enzymatic reaction such as lipoxygenase, is one of the most important factors for the formation of the epoxydecenal isomers.     

Changes in the concentrations of acrylamide, selected odorants, and catechins caused by roasting of green tea

This research aims to optimize roasted green tea (Houjicha) processing by using roasting treatments to achieve acrylamide mitigation without compromising the quality. 2-Ethyl-3,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine were identified as potent odorants by aroma extract dilution analysis. In preliminary sensory experiments, the desirable Houjicha flavor was produced in products roasted at 160 degrees C for 30 min and at 180 degrees C for 15 min. Under these conditions, potent odorants were formed at levels adequate for contributing to the Houjicha flavor. Acrylamide amounts in tea infusions were 2.0 and 4.0 microg/L by roasting at 160 degrees C for 30 min and at 180 degrees C for 15 min, respectively. Compared to roasting at 180 degrees C, the degradation of tea catechins was suppressed by roasting at 160 degrees C. Hence, roasting at 160 degrees C for is recommended for Houjicha processing for acrylamide mitigation, formation of potent odorants, and suppression of degradation of tea catechins.     

Effect of selenium on preservation quality of green tea during autumn tea-processing season

Selenium-enriched green tea leaves were prepared by foliar applications of selenium-amended fertilizer during autumn season. The influence of selenium (Se) on preservation quality of tea during 4-month storage was determined. The results showed that the Se and vitamin C contents of green tea were significantly increased by selenium spraying during the autumn tea-producing season. The vitamin C content of Se-enriched green tea was higher and its decline was significantly slower during storage compared to normal green tea. However, there was no significant difference between the contents of chlorophyll and polyphenol of Se-enriched and regular tea. During the first 60 days, the color of green tea extract in Se-enriched green tea and normal tea showed no significant difference. However, the color of green tea extract in Se-enriched green tea was more stable compared with normal tea during the storage period. The sweetness and aroma of extracts of Se-enriched green tea were also significantly higher than that of normal tea and the bitterness of extracts of Se-enriched green tea was significantly lower compared with normal tea. These results showed that selenium application can slow the reduction of tea's major component and thus improve preservation qualities of green tea.     

Identification and comparison of phenolic compounds in the preparation of oolong tea manufactured by semifermentation and drying processes

Oolong tea manufactured via a semifermentation process possesses a taste and color somewhere between green and black teas. Alteration of constituents, particularly phenolic compounds, in the infusion of oolong tea resulting from its manufacture, was analyzed by high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The identified constituents contained 2 alkaloids, 11 flavan-3-ols, 8 organic acids and esters, 11 proanthocyanidin dimers, 3 theaflavins, and 22 flavonoid glycosides, including 6 novel acylated flavonol glycosides. The tentative structures of these 6 novel compounds were depicted according to their mass fragmentation patterns in MS(n) (n = 1-4). In comparison with caffeine as an internal standard, relative contents of the constituents in the infusions of fresh tea shoot and different oolong tea preparations were examined. Approximately, 30% catechins and 20% proanthocyanidins were oxidized during the manufacture of oolong tea from fresh tea shoots, and 20% of total flavonoids were decomposed in a follow-up drying process. Gallocatechin-3-O-gallate and theaflavins putatively produced in the semifermentation process of oolong tea were not detected in fresh tea shoots, and the majority of theaflavins were presumably transformed into thearubigins after drying.     

Characterization of the key aroma compounds in the beverage prepared from Darjeeling black tea: quantitative differences between tea leaves and infusion

By application of the aroma extract dilution analysis on the volatile fraction isolated from a black tea infusion (Darjeeling Gold Selection), vanillin (vanilla-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (caramel), 2-phenylethanol (flowery), and (E,E,Z)-2,4,6-nonatrienal (oat-flake-like) were identified with the highest flavor dilution (FD) factors among the 24 odor-active compounds detected in the FD factor range of 4-128. Quantitative measurements performed by means of stable isotope dilution assays and a calculation of odor activity values (OAVs; ratio of concentration to odor threshold in water) revealed, in particular, the previously unknown tea constituent (E,E,Z)-2,4,6-nonatrienal as a key odorant in the infusion and confirmed the important role of linalool and geraniol for the tea aroma. An aroma recombinate performed by the 18 odorants for which OAVs > 1 were determined in their "natural" concentrations matched the overall aroma of the tea beverage. In the black tea leaves, a total of 42 odorants were identified, most of which were identical with those in the beverage prepared thereof. However, quantitative measurements indicated that, in particular, geraniol, but also eight further odorants were significantly increased in the infusion as compared to their concentration in the leaves.