五九香梨贮藏期间挥发性化合物和理化性状的变化(英)

利用高效液相色谱法测定贮藏期间五九香梨的糖和有机酸的组成及变化,采用固相微萃取方式（SPME）进行萃取,并结合气相色谱和质谱（GC/MS）分析检测梨果实中的挥发性香气成分。得出以下主要结论：果糖是五九香梨的主要糖类,其次是葡萄糖和蔗糖。随着贮藏期的延长,果糖先有增加的趋势,在贮藏的第三个月内,果糖含量处于最高,而蔗糖和葡萄糖减少趋势不明显。五九香梨果实中的主要有机酸是苹果酸和柠檬酸,整个贮藏期间,柠檬酸和酒石酸含量处于上升趋势,苹果酸和奎宁酸含量在第一、二月贮藏期间增加,而后开始下降;莽草酸含量在贮藏期第一到第三阶段上升,而后略下降;琥珀酸含量在第一到第二阶段变化不明显,接着有上升的趋势,在第三阶段含量达到最高,第四和第五阶段略低于第三阶段;乙酸含量变化不明显。梨果实的硬度略有下降,贮藏的前3个月,可溶性固形物含量有上升的趋势,随后开始缓慢下降。五九香梨的主要香气成分化合物有乙酸己酯 (49.35%),乙酸丁酯 (19.56%),己酸乙酯 (5.16%),丁酸乙酯 (4.92%),乙酸乙酯 (1.08%),(E,Z)-2,4-癸二烯酸乙酯 (0.84%)等。在整个贮藏期间,部分香气成分随着贮藏期的延长而略有增加,尤其是酯类化合物。结果显示：果实硬度、可溶性固形物、糖、有机酸和香气的组成与变化对五九香梨果实的品质都有一定的影响。     

Formation of volatile organic products in soils under anaerobiosis—II: Metabolism of amino acids

Volatile organic compounds generated microbiologically under anaerobic conditions from various soils amended with glucose and amino acids were identified by combined gas chromatographymass spectrometry. Volatile compounds were usually found up to 4 weeks and sometimes longer. Acetaldehyde, acetone, methyl ethyl ketone, methyl propyl ketone, diacetyl, ethanol, n- and iso-propanol, n-, 2- and iso-butanol, acetic acid, butyric acid, ethyl acetate, ethyl butyrate, butyl acetate, butyl butyrate, methane thiol, dimethysulfide, dimethyldisulfide and methyl thioacetate were detected at various time intervals. Volatile organic sulfur compounds were evolved from soils amended with glucose and methionine but not with glucose and cysteine. Volatile nitrogen containing organic compounds were not detected with any of the amended soils.     

Effect of Germination on Flavor Volatiles of Cooked Brown Rice

The effect of germination on flavor volatiles of cooked brown rice among three different rice cultivars was investigated using the headspace solid‐phase microextraction method combined with gas chromatography‐mass spectrometry. The results showed that some flavor compounds varied significantly throughout the germination process and others did not show distinct changes. The amount of total volatiles, most lipid‐oxidation products, and phenolic compounds decreased in the initial stage of germination but increased significantly at a later stage. The amounts of ethanol and ethyl acetate increased significantly in the initial stage of germination and maintained almost the same levels during further germination. The amount of dimethyl sulfide increased significantly during germination; it showed the most significant change among all volatile compounds.     

Monoterpene composition of essential oil from peppermint (Mentha x piperita L.) with regard to leaf position using solid-phase microextraction and gas chromatography/mass spectrometry analysis.

Monoterpene compounds of leaf pairs and flowers of Mentha x piperita have been studied by direct headspace sampling using solid-phase microextraction coupled with gas chromatography/mass spectrometry (SPME-GC/MS). The content of peppermint-characteristic compounds such as menthol, menthyl acetate, and neomenthol increased in a basipetal direction (older plant parts), whereas menthone and isomenthone showed higher levels in the acropetal direction (younger plant parts). Higher levels of menthofuran were found in peppermint flowers in contrast to the leaves. SPME sampling resulted in relatively higher amounts of high-volatile monoterpenes and lower detection of less volatile compounds such as menthol and menthone, compared to solvent-based samples from essential oil distillation.     

The chemistry of humic and fulvic acids extracted from argentine soils—II. Permanganate oxidation of methylated humic and fulvic acids

Five humic and three fulvic acids, extracted from Argentine soils, were methylated and oxidized with KMnO* solution. The oxidation products were extracted into ethyl acetate, remethylated, separated by preparative gas chromatography and identified by comparing their mass and micro-IR spectra with those of authentic specimens.The major oxidation products from the humic acids were benzenetetra, -penta-, and -tricarboxylic and hydroxybenepentacarboxylic acid. The major compounds isolated from the fulvic acid oxidation products were aside from benzenecarboxylic and phenolic acids, substantial amounts of ethyl-benzylsulfonate and N-methyl-benzylsulfonamide, one complex aromatic ester and two anhydrides. The origin of the S-containing compounds is uncertain; they could be impurities. Weight ratios of benzenecarboxylic to phenolic acids averaged 5·8 for humic acids but only 0·9 for fulvic acids, suggesting an enrichment in phenolic structures in the fulvic acids. Possible structural arrangements for humic and fulvic acids are discussed.     

Volatile components of Loureira, Dona Branca, and Treixadura wines.

White wines experimentally produced from the white grape varieties Loureira, Dona Branca, and Treixadura have been analyzed over four consecutive harvests. The contents of monoterpenes, volatile phenols, alcohols, sulfur components, acetates, fatty acids, and ethyl esters were determined by gas chromatography (FID) and gas chromatography-mass spectrometry. The mean values from four vintages confirmed that these wines have characteristic profiles. Loureira wines are characterized by a high content of free terpenes, 1-hexanol, ethyl acetate, and fatty acids. Dona Branca wines present the highest concentrations of methanol and sulfur constituents, and the lowest concentrations of higher alcohols, acetates, diethyl succinate, and ethyl esters. The levels of monoterpenes in Treixadura wines are very low, but they have the highest concentrations of volatile phenols, principally due to the vanillin, diethyl succinate, ethyl lactate, and ethyl esters. These results were confirmed by principal component and linear discriminant analysis, which show a clear differentiation among these wines as a function of the varietal origin.     

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.     

Flavor Volatiles of Rice During Cooking Analyzed by Modified Headspace SPME/GC‐MS

The flavor volatiles in three Japanese rice cultivars, Nihonbare, Koshihikari, and Akitakomachi, during cooking were directly extracted by using a modified headspace solid‐phase microextraction (SPME) method and analyzed by gas chromatography‐mass spectrometry (GC‐MS). A total of 46 components were identified, including aldehydes, ketones, alcohols, and heterocyclic compounds, as well as fatty acids and esters, phenolic compounds, hydrocarbons, etc. The amount of key odorant compounds increased with cooking, while the amount of low‐boiling volatiles decreased. The similarities and differences of the three rice cultivars were determined through a comparison of their volatile components. Nihonbare was characterized by a higher amount of indole but an absence of the chemical class of fatty acid esters. In contrast, both Koshihikari and Akitakomachi had a higher amount of 4‐vinylphenol and an abundance of those esters. Koshihikari and Akitakomachi were quite similar in regard to those flavor volatiles. Furthermore, the observations in the research may suggest that the volatile components at cooking stage (I) were the representatives of the flavor volatiles of uncooked rice, while the volatile constituents at cooking stage (IV) were the representatives of the flavor volatiles of cooked rice.     

Purification of citrus peel juice and molasses

Citrus peel juice and molasses are extremely bitter and unpalatable byproducts of orange and grapefruit juice production. Major components of interest are soluble sugars, glucose, fructose, and sucrose, which account for 60-70% of the dry solids. Analyses indicate that the remaining components are suspended tissue fragments, proteins, organic acids, mineral ions, phenolic compounds, and polyols. A purification sequence that removed a majority of bitter limonoids and phenolic compounds by adsorption on nonionic, macroporous resins was tested. Residual phenolic compounds were removed by adsorption on activated carbon or anion-exchange resin, which also removed anions of organic and inorganic acids. Taste panel results suggested that debittered products could be acceptable for food uses.     

Chemical composition and antioxidant properties of extracts of fresh fruiting bodies of Pleurotus sajor-caju (Fr.) Singer

The chemical composition and in vitro antioxidant activity of aqueous butanol and ethyl acetate extracts of Pleurotus sajor-caju were investigated in this study. Twenty-two compounds comprising methyl esters, hydrocarbon fatty acids, ethyl esters, and sterols were identified in ethyl acetate extracts, while cinnamic acid, nicotinamide, benzeneacetamide, and 4-hydroxybenzaldyhde were identified in butanol extracts by gas chromatography-mass spectrometry and NMR analysis. The antioxidant activity was determined by a β-carotene bleaching method, ferric reducing antioxidant power, trolox equivalent antioxidant capacity, and lipid peroxidation assays, while the total phenolic content in P. sajor-caju was assessed by Folin-Ciocalteau's method. The aqueous and butanol extracts exhibited the highest antioxidant activity, corresponding to the total phenolic content. The subfractions from the ethyl acetate extract (EP1, EP2, EP3, and EP4), however, showed moderate antioxidant activity. The regular consumption of P. sajor-caju as a part of our diet may render nutritional and nutraceuticals benefits for good health.     

Tequila volatile characterization and ethyl ester determination by solid phase microextraction gas chromatography/mass spectrometry analysis

Solid phase microextraction (SPME) and gas chromatography were used for tequila volatile characterization and ethyl ester quantitation. Several factors determined the differences in tequila volatile profiles obtained by the SPME technique, namely, sampling mode, fiber coating, and fiber exposure time. Each of these factors determined the most suitable conditions for the analysis of volatile profiles in tequila. Volatile extraction consisted of placing 40 mL of tequila in a sealed vial kept at 40 degrees C. A poly(dimethylsiloxane) fiber was immersed in the liquid for 60 min and desorbed for 5 min into the gas chromatograph. The identified volatiles by mass spectrometry were mainly alcohols, esters, and ketones. The calibration curves for ethyl hexanoate, octanoate, and decanoate followed linear relationships with highly significant (p < 0.001) determination coefficients (R2 = 0.99). The coefficients of variation of less than 10% for ethyl ester concentrations indicated that the technique was reproducible. The limits of quantitation for ethyl esters were 0.05 parts per million, which were below the concentration range (0.27-15.03 ppm) found for different tequila samples. Quantitative differences in ethyl esters were found for the four most commonly known tequila types: silver, gold, aged, and extra-aged.     

Analysis of volatile compounds released during the grinding of roasted coffee beans using solid-phase microextraction

A dynamic solid-phase microextraction (SPME) method to sample fresh headspace volatile compounds released during the grinding of roasted coffee beans was described and the analytical results using gas chromatography/mass spectrometry (GC/MS) and GC/olfactometry (GC/O) were compared to those of the conventional static SPME sampling methods using ground coffee. Volatile compounds released during the grinding of roasted coffee beans (150 g) were obtained by exposing the SPME fiber (poly(dimethylsiloxane)/divinylbenzene, PDMS/ DVB) for 8 min to nitrogen gas (600 mL/min) discharged from a glass vessel in which the electronic coffee grinder was enclosed. Identification and characterization of volatile compounds thus obtained were achieved by GC/MS and GC/O. Peak areas of 47 typical coffee volatile compounds, separated on total ion chromatogram (TIC), obtained by the dynamic SPME method, showed coefficients of variation less than 5% (n = 3) and the gas chromatographic profile of volatile compounds thus obtained was similar to that of the solvent extract of ground coffee, except for highly volatile compounds such as 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 4-ethenyl-2-methoxyphenol. Also, SPME dilution analysis of volatile compounds released during the grinding of roasted coffee beans showed linear plots of peak area versus exposed fiber length (R (2) > 0.89). Compared with those of the headspace volatile compounds of ground coffee using GC/MS and GC/O, the volatile compounds generated during the grinding of roasted coffee beans were rich in nutty- and smoke-roast aromas.     

Characterization of aroma compounds in apple cider using solvent-assisted flavor evaporation and headspace solid-phase microextraction

The aroma-active compounds in two apple ciders were identified using gas chromatography-olfactometry (GC-O) and GC-mass spectrometry (MS) techniques. The volatile compounds were extracted using solvent-assisted flavor evaporation (SAFE) and headspace solid-phase microextraction (HS-SPME). On the basis of odor intensity, the most important aroma compounds in the two apple cider samples were 2-phenylethanol, butanoic acid, octanoic acid, 2-methylbutanoic acid, 2-phenylethyl acetate, ethyl 2-methylbutanoate, ethyl butanoate, ethyl hexanoate, 4-ethylguaiacol, eugenol, and 4-vinylphenol. Sulfur-containing compounds, terpene derivatives, and lactones were also detected in ciders. Although most of the aroma compounds were common in both ciders, the aroma intensities were different. Comparison of extraction techniques showed that the SAFE technique had a higher recovery for acids and hydroxy-containing compounds, whereas the HS-SPME technique had a higher recovery for esters and highly volatile compounds.     

施有机肥及套袋对鸭梨果实风味品质的影响

为探讨施有机肥和套袋对鸭梨果实风味品质的影响,采用气相色谱-质谱联用技术（GC-MS）及高效液相色谱技术（HPLC）,研究了生长期施有机肥和套袋对鸭梨果实挥发性成分、 糖类和有机酸组分等风味物质的组成和含量的影响。结果表明, 供试鸭梨共检测到挥发性物质3类30种,其中酯类26种、 烯类3种、 醇类1种。施有机肥和套袋改变了鸭梨果实的特征香气成分的种类和含量。施用有机肥使套袋和不套袋鸭梨香气物质种类分别增加8种和6种,香气物质总量分别增加182.89%和127.16%。套袋使施有机肥和复合肥鸭梨的香气物质种类分别减少了8种和10种,香气物质总量分别减少66.32%和72.98%。不同处理鸭梨共检测到4种糖、 7种有机酸组分,其中糖组分主要为果糖,其次为蔗糖、 山梨醇、 葡萄糖; 有机酸组分主要为苹果酸,其次为乙酸、 柠檬酸、 莽草酸、 奎宁酸、 酒石酸、 琥珀酸。施用有机肥使鸭梨糖总量和酸总量升高,套袋使鸭梨糖总量和有机酸总量降低。施有机肥使鸭梨果实香气物质种类和含量增加,糖类和有机酸含量升高,而套袋使鸭梨果实香气物质种类和含量减少,糖类和有机酸含量降低。     

Phenolic compounds and chromatographic profiles of pear skins (Pyrus spp.)

A standardized profiling method based on liquid chromatography with diode array and electrospray ionization/mass spectrometric detection (LC-DAD-ESI/MS) was used to analyze the phenolic compounds in the skins of 16 pears (Pyrus spp.). Thirty-four flavonoids and 19 hydroxycinnamates were identified. The main phenolic compounds (based on peak area) in all of the pear skins were arbutin and chlorogenic acid. The remaining phenolics varied widely in area and allowed the pears to be divided into four groups. Group 1, composed of four Asian pears (Asian, Asian brown, Korean, and Korean Shinko), contained only trace quantities of the remaining phenolics. Yali pear (group 2) contained significant amounts of dicaffeoylquinic acids. Fragrant pear (group 3) contained significant quantities of quercetin glycosides and lesser quantities of isorhamnetin glycosides and the glycosides of luteolin, apigenin, and chrysoeriol. The remaining 10 pears (group 4) (Bartlett, Beurre, Bosc, Comice, D'Anjou, Forelle, Peckham, Red, Red D'Anjou, and Seckel) contained significant quantities of isorhamnetin glycosides and their malonates and lesser quantities of quercetin glycosides. Red D'Anjou, D'Anjou, and Seckel pears also contained cyanidin 3-O-glucoside. Thirty-two phenolic compounds are reported in pear skins for the first time.     

Depolymerization and degradation of humic acids with sodium perborate

Two humic acids of different origin (peat and soil) were degraded with a 5% sodium perborate solution (140°C). This degradation process consists mainly of a stoichiometric production of hydrogen peroxide while the perborate is reacting with carboxyl groups of the oxidized polymers. A single perborate treatment degraded more than 40% of the humic acids to soluble products, but a 5-step oxidation was necessary for total degradation, the sample being transformed into soluble oligomers with properties similar to those of fulvic acids. The oligomeric fractions with lowest molecular weights, including individual molecules (soluble in ethyl acetate), were purified by adsorption chromatography and studied by GC-MS after methylation. The higher molecular weight fractions of oligomers were recovered over polyvinylpyrrolidone, eluted by alkali, and purified by ion-exchange chromatography (47% peat HA; 25% soil HA).Degradation products included alkanes, fatty acids and dicarboxylic acids. Aromatic compounds (mainly phenolic, benzenecarboxylic and cinnamic acids), amounted to 24–50% of the total volatile degradation products. There were striking differences between peat and soil humic acids, the former yielding typical lignin degradation products. Independently checked, the perborate degradation products were not the same as those obtained by mild treatment with hydrogen peroxide under alkaline conditions.     

Changes in the volatile compounds and in the chemical and physical properties of snake fruit (Salacca edulis Reinw) Cv. Pondoh during maturation

During the maturation of snake fruit (Salacca edulis Reinw) Pondoh, the contents of sucrose, glucose, fructose, and volatile compounds changed drastically. The glucose, fructose, and volatile compounds contents showed their maximum levels at the end of maturation; however, the sucrose content decreased. During maturation, the flesh firmness tended to increase; however, at the end of maturation (6 months), the flesh became soft. The major volatile aroma in solvent-assisted flavor evaporation (SAFE) and solvent extracts were identified to be methyl esters of butanoic acids, 2-methylbutanoic acids, hexanoic acids, pentanoic acids, and the corresponding carboxylic acids. Furaneol (4-hydroxy-2,5-dimethyl-3(2H)-furanone) was also identified as a minor aroma constituent in the SAFE residue. The methyl esters were found to increase dramatically during stages 4-6 (5-6 months after the pollination) to exceed the amounts of carboxylic acids, whereas the acid amount increased gradually until stage 5 (5.5 months after the pollination) to reach the maximum at stage 6 (6 months after the pollination).     

Antioxidant capacity of 26 spice extracts and characterization of their phenolic constituents

Total equivalent antioxidant capacity (TEAC) and phenolic content of 26 common spice extracts from 12 botanical families were investigated. Qualitative and quantitative analyses of major phenolics in the spice extracts were systematically conducted by reversed-phase high-performance liquid chromatography (RP-HPLC). Many spices contained high levels of phenolics and demonstrated high antioxidant capacity. Wide variation in TEAC values (0.55-168.7 mmol/100 g) and total phenolic content (0.04-14.38 g of gallic acid equivalent/100 g) was observed. A highly positive linear relationship (R2= 0.95) obtained between TEAC values and total phenolic content showed that phenolic compounds in the tested spices contributed significantly to their antioxidant capacity. Major types of phenolic constituents identified in the spice extracts were phenolic acids, phenolic diterpenes, flavonoids, and volatile oils (e.g., aromatic compounds). Rosmarinic acid was the dominant phenolic compound in the six spices of the family Labiatae. Phenolic volatile oils were the principal active ingredients in most spices. The spices and related families with the highest antioxidant capacity were screened, e.g., clove in the Myrtaceae, cinnamon in the Lauraceae, oregano in the Labiatae, etc., representing potential sources of potent natural antioxidants for commercial exploitation. This study provides direct comparative data on antioxidant capacity and total and individual phenolics contents of the 26 spice extracts.     

Antioxidant activity of phenolic compounds isolated from Mesona procumbens Hemsl

The antioxidant activity of phenolic compounds isolated from Mesona procumbens Hemsl. (Hsian-tsao) was investigated. Hsian-tsao was extracted with various solvents, and the results showed that the fraction treated with acidic ethyl acetate (pH 2) possessed large amounts of phenolic compounds and a strong antioxidant activity on peroxidation of linoleic acid. The antioxidant activity (inhibition of peroxidation, IP%) of the acidic ethyl acetate of Hsian-tsao extract at 50 microg/mL (98.9%) was stronger than those of 50 microg/mL alpha-tocopherol (78%) and BHA at 10 microg/mL (90%). When fractionated with Amberlite XAD-7 gel chromatography, the acidic ethyl acetate fraction of Hsian-tsao extract was separated into four subfractions (A-D). Subfraction B, with high yield and strong antioxidant activity, was further isolated and purified and then identified as containing protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, and syringic acid by means of UV, EI-MS, and (1)H and (13)C NMR. The antioxidant capability of isolated compounds was also determined using the thiocyanate system and the erythrocyte ghost system. The results indicate that the phenolic acids could be important antioxidant components in Hsian-tsao, among which caffeic acid with the highest antioxidant activity and the greatest content is most important.     

Interactions between artificial saliva and 20 aroma compounds in water and oil model systems

The interactions between saliva components and 20 aroma compounds in water and oil model systems were systematically evaluated as a function of saliva composition and saliva/model system ratio. Air/liquid partition coefficients of dimethyl sulfide, 1-propanol, diacetyl, 2-butanone, ethyl acetate, 1-butanol, 2-pentanol, propyl acetate, 3-methyl-1-butanol, ethyl butyrate, hexanal, butyl acetate, 1-hexanol, 2-heptanone, heptanal, alpha-pinene, 2-octanone, octanal, 2-nonanol, and 2-decanone were determined by static headspace gas chromatography. Chain length of compounds within the homologous series determined the extent of interactions with the model system or saliva. Salts in the artificial saliva hardly interacted with aroma compounds. On the other hand, saliva proteins lowered retention of highly volatile compounds and increased retention of less volatile, hydrophobic compounds. Significant differences in volatility of compounds when artificial saliva or water was added indicated that saliva could not be sufficiently replaced by water. The model system/saliva ratio influenced air/liquid partitioning of the aroma compounds significantly for both model systems. Although saliva composition affected volatility of the aroma compounds, the saliva/model system ratio was of much greater influence.