Major Volatiles Research Articles

Development of supercritical CO2 extraction of bioactive phytochemicals from black poplar (Populus nigra L.) buds followed by GC–MS and UHPLC-DAD-QqTOF-MS

The supercritical CO2 (SC-CO2) extraction process of black poplar (Populus nigra L.) buds was optimized (pressure, temperature) based on the yields of major phytochemicals (volatiles and non-volatiles). The optimal settings were 30 MPa/60 °C. Major volatiles determined by GC–MS in the optimized SC-CO2 extract (mg of benzyl salicylate equivalent (BSE) per 100 g of buds) were: pinostrobin chalcone (1574.2), β-eudesmol (640.8), α-eudesmol (581.9), 2-methyl-2-butenyl-p-coumarate (289.9), pentyl-p-coumarate (457.0), γ-eudesmol (294.4), and benzyl salicylate (289.2). Partial qualitative similarity was observed between SC-CO2 extracts and corresponding hydrodistilled essential oil dominated by sesquiterpenes, but with lower yields. Major compounds (mg per 100 g of buds) identified by UHPLC-DAD-QqTOF-MS in the optimized SC-CO2 extract were: pinostrobin (751.7), pinocembrin (485.6), 3-O-pinobanksin acetate and methyl-butenyl-p-coumarate (290.2; 144.9 of pinobanksin and p-coumaric acid equivalents, respectively). SC-CO2 extraction was found useful for green, efficient and simultaneous extraction of both volatile/non-volatile, bioactive phytochemicals of poplar buds – precursors of poplar-type propolis.

Contrasting insect attraction and herbivore-induced plant volatile production in maize.

The maize inbred line W22 has lower herbivore-induced volatile production than B73 but both fall armyworm larvae and the wasps that parasitize them prefer W22 over B73. Maize inbred line W22 is an important resource for genetic studies due to the availability of the UniformMu mutant population and a complete genome sequence. In this study, we assessed the suitability of W22 as a model for tritrophic interactions between maize, Spodoptera frugiperda (fall armyworm) and the parasitoid wasp Cotesia marginiventris. W22 was found to be a good model for studying the interaction as S. frugiperda prefers W22 over B73 and a higher parasitism rate by C. marginiventris was observed on W22 compared to the inbred line B73. W22 also produced lower amounts of many herbivore-induced volatile terpenes and indole emission upon treatment with S. frugiperda oral secretions. We propose that some of the major herbivore-induced terpene volatiles are perhaps impeding S. frugiperda and C. marginiventris preference and that as yet unidentified compounds are produced at low abundance may be positively impacting these interactions.

Antennal olfactory sensory neurones responsive to host and nonhost plant volatiles in gorse pod moth Cydia succedana

AbstractWe investigate the response profiles of the antennal olfactory sensory neurones (OSNs) in male and female gorse pod moth Cydia succedana to host and nonhost volatiles, using the single sensillum recording technique. Eight different classes of olfactory sensilla are identified in female C. succedana and five different classes of olfactory sensilla in males. Nineteen different classes of OSNs are identified from the sensilla in females, and nine different classes of OSNs in the male sensilla. All classes of sensilla, except class F7 and class M1 sensilla, co‐compartmentalize two or three OSNs in each sensillum, and the OSNs present in the same sensillum are specialized for different volatiles. Most plant‐volatile OSNs exhibit phasic‐tonic type of temporal responses, whereas the pheromone OSNs in male C. succedana show rather phasic responses. The majority of OSNs identified in C. succedana display highly specialized responses to a narrow range of volatiles, whereas only a small proportion of OSNs show broad response spectra. Two most abundant classes of OSNs exhibit highly specialized responses to β‐myrcene and (E)‐β‐ocimene, two major volatiles released by gorse (Ulex europaeus), the main host of C. succedana. By contrast, several other classes of OSNs exhibit highly specialized responses to geraniol, (Z)‐3‐hexen‐1‐ol, (±)‐α‐terpineol, citral and benzyl acetate, which are produced by various nonhost plants. Taking the results of the present study together, we suggest that C. succedana use the combinational input from a set of highly specialized OSNs for host plant volatiles and another set of highly specialized OSNs for nonhost volatiles to discriminate between hosts and nonhosts.

Developmental variation in floral volatiles composition of a fragrant orchid Zygopetalum maculatum (Kunth) Garay

Emitted scent volatile profile of an orchid species Zygopetalum maculatum was studied using dynamic headspace sampling technique with four different adsorbent matrices, namely Porapak Type Q polymer (mesh size: 80/100), Tenax (mesh size: 60/80), activated charcoal and graphite. In addition, developmental variations in scent emissions and endogenous volatile levels were also investigated. Gas chromatography-mass spectrometry analysis revealed the presence of 21 volatile compounds in the headspace, which was predominantly enriched with benzenoid compounds. Among these benzenoids, o-diethylbenzene and p-diethylbenzene were the major compounds followed by benzyl acetate and methyl salicylate. Among the phenylpropanoid compounds, 2-phenylethyl acetate was the major volatile. However, as compared to benzenoids, the quantity was much lesser, indicating the inclination of phenylalanine flux towards benzenoid pathway. The outcome of this study has the implications in enhancing fragrance and vase life of orchids of the Sikkim Himalaya region and thus may further help to meet the growing market demand.

Validation of a gas chromatography-flame ionization method for quality control and spoilage detection in wine and cider

A GC-FID method for major volatile analysis in cider and wine was validated under the requirements of the ISO/IEC 17025 regulation using a split mode injection. This method presented a good linearity (R2>0.999, Cm>99%), a wide range of calibration, the maximum random errors for repeatability and intermediate precision were 5% and 8%, respectively, and the maximum limit of quantification and limit of detection were 14.1 mg l–1 and 4.6 mg l–1, respectively. Trueness, expressed as recovery (%), was successfully validated by means of two different methods, standard addition (92–110%) and comparison against reference materials (93–115%). Expanded uncertainty estimated at 95% confidence level ranged between 11% for methanol and 7% for allyl alcohol. The validated method was successfully applied for the analysis of major volatiles in ciders and wines, and to detect yeast and lactic acid bacteria spoilage.

Acrolein as a Major Volatile in the Early Stages of Fish Oil TAG Oxidation.

Fish oil rich in docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) is known to have an unpleasant smell, even at low oxidation levels. Therefore, it is highly important to know the major volatiles formed during the early stages of fish oil oxidation. Comparative study with solid-phase microextraction (SPME) and static headspace (SHS) methods showed that 2-propenal (acrolein) was formed as the major volatile from the beginning of fish oil triacylglycerol (TAG) oxidation. The effectiveness of SPME extraction on each volatile was different from each fiber. Among the three different SPME fibers used in the present study, carboxen/polydimethylsiloxane (CAR/PDMS) was determined to be a better fiber for measuring the volatiles, including acrolein. The present study also showed that the non-selective SHS method is useful for determining the characteristic volatile formation in the early stages of fish oil TAG oxidation.

Volatile Profile Comparison of Raw and Dried Rizhome of Atractylodes japonica

Atractylodes japonica is a source of herbal medicinal material “Sab-Joo” for herbal medicine “Baekchul” in Korea. Volatile aroma compounds may play some valuable therapeutic activities. Volatiles in raw and dried Sab-Joo(the rhizome of A. japonica) were analyzed by GC-MS after a dynamic headspace method. The mashed samples were stabilized at 40°C for 30min and volatile compounds were captured by 100 □ polydimethylsiloxane coated SPME fiber just before DB-5MS column separation followed by mass spectrometric analysis (with electron impact mode). Among 58 detected peaks, the 15 major components were observed for their fate after drying of Sab-Joo. β-Elemene, β-maaliene, 2, 3, 4, 5-tetramethyltricyclo[3.2.1.02, 7] oct-3-ene, curcumene, 1-(3, 3-dimethyl-but-1-ynyl)-1, 2-dimethyl-3-methylene-cyclopropane, guaia-10, 11 diene, and furanodiene were diminished after drying. α-Selinene and valencene were almost disappeared in dried Sab-Joo. Among the eight volatiles relatively increased after drying, five components, such as β-patchoulene, valencene, α-selinene, 9, 10-dehydro-Isolongifolene, and (−)-aristolene were more than doubled up(percent change over 100%). β-Patchoulene, valencene increased about four times after drying. The major volatiles over 5%(NPA%) in the dried sample were all sesquiterpenes having molecular formula (MW=204). The relative quantitative volatile profiles were quite different before and after drying Sab-C15H24 Joo. Therefore the fate of the pharmaceutically/toxicallyimportant volatile components by the simple drying process should be carefully studied to maximize the efficacy and minimize the risk of the final product.

Profiling of volatile fragrant components in a mini-core collection of mango germplasms from seven countries.

Aroma is important in assessing the quality of fresh fruit and their processed products, and could provide good indicators for the development of local cultivars in the mango industry. In this study, the volatile diversity of 25 mango cultivars from China, America, Thailand, India, Cuba, Indonesia, and the Philippines was investigated. The volatile compositions, their relative contents, and the intervarietal differences were detected with headspace solid phase microextraction tandem gas chromatography-mass spectrometer methods. The similarities were also evaluated with a cluster analysis and correlation analysis of the volatiles. The differences in mango volatiles in different districts are also discussed. Our results show significant differences in the volatile compositions and their relative contents among the individual cultivars and regions. In total, 127 volatiles were found in all the cultivars, belonging to various chemical classes. The highest and lowest qualitative abundances of volatiles were detected in ‘Zihua’ and ‘Mallika’ cultivars, respectively. Based on the cumulative occurrence of members of the classes of volatiles, the cultivars were grouped into monoterpenes (16 cultivars), proportion and balanced (eight cultivars), and nonterpene groups (one cultivars). Terpene hydrocarbons were the major volatiles in these cultivars, with terpinolene, 3-carene, caryophyllene and α-Pinene the dominant components depending on the cultivars. Monoterpenes, some of the primary volatile components, were the most abundant aroma compounds, whereas aldehydes were the least abundant in the mango pulp. β-Myrcene, a major terpene, accounted for 58.93% of the total flavor volatile compounds in ‘Xiaofei’ (Philippens). γ-Octanoic lactone was the only ester in the total flavor volatile compounds, with its highest concentration in ‘Guiya’ (China). Hexamethyl cyclotrisiloxane was the most abundant volatile compound in ‘Magovar’ (India), accounting for 46.66% of the total flavor volatiles. A typical aldehydic aroma 2,6-di-tert-butyl-4-sec-butylphenol, was detected in ‘Gleck’. A highly significant positive correlation was detected between Alc and K, Alk and Nt, O and L. Cultivars originating from America, Thailand, Cuba, India, Indonesia and the Philippines were more similar to each other than to those from China. This study provides a high-value dataset for use in development of health care products, diversified mango breeding, and local extension of mango cultivars.

Characterization of free and bound volatile compounds in six Ribes nigrum L. blackcurrant cultivars

This study investigated the profiles of free and bound volatile compounds of six currant cultivars grown in China. Results showed that 166 free and 111 bound volatiles were found in these cultivars with esters and terpenoids as the major volatiles. Additionally, 10 hydroxy esters were detected in these cultivars for the first time. Floral, fruity, and sweet flavors appeared to be the feature aroma in these cultivars, which resulted from the contribution of 17 volatiles. Principal component analysis indicated the cultivar “Fertodi”, “Risagar” and “Liangye” had the similar profiles of free and bound volatile compounds, whereas the cultivar “Brodtrop” and “Yadrionaya” exhibited the similarity on their free and bound volatiles. The cultivar “Sofya” showed a different volatile composition. Cluster analysis revealed the cultivar “Fertodi”, “Risagar”, and “Liangye” had the similar profiles of free and bound volatile compounds, whereas the similar free and bound volatile compositions were observed in the cultivar “Sofya” and “Yadrionaya”. This study could provide useful information on quality control of commercial currant products.

Comparative study of the essential oils of four Pinus species: Chemical composition, antimicrobial and insect larvicidal activity

Comparative analysis of the chemical composition and biological activity of the essential oils from the needles of four Pinus species (P. mugo subsp. mugo, P. nigra subsp. nigra, P. sylvestris and P. peuce) from the central Balkans was performed. Although different chemical profiles of the dominant terpenes for each species were determined, essential oils were, generally, dominated by monoterpenes with α-pinene as one of the first two major volatiles. Tested oils showed inhibitory action against respiratory pathogenic bacterial strains, isolated from human swabs, in the range of 1.25–20.00mg/mL (MICs) and bactericidal effect (MBCs) at concentrations from 2.50 to 40.00mg/mL. Considering cell wall composition, there were no significant differences in sensitivity between Gram-positive and Gram-negative strains. In addition, the place of isolation did not provide evidences for higher susceptibility/resistance of the strains obtained from the particular infection site. On the other hand, toxicity of essential oils towards developing Drosophila melanogaster larvae was low, except P. mugo subsp. mugo oil, which did not show any signs of toxicity at concentrations up to 3%. Highest mortality of larvae and adults of D. melanogaster was noted for P. sylvestris essential oil with an estimated LC50 at the end of experiment (14days) of 2.78% with a 95% confidence interval of 2.15–3.42%. Short-term 96h LC50 values due to low mortality at larval stage could not be calculated for any oil and are expected to be much higher than 3%. According to the obtained antimicrobial activity and toxicity towards D. melanogaster, the oils can be arranged in the following order: P. sylvestris>P. peuce>P. nigra subsp. nigra>P. mugo subsp. mugo.

Identification and Characterization of (3Z):(2E)-Hexenal Isomerases from Cucumber.

E-2-hexenal is a volatile compound that is commonly emitted by wounded or stressed plants. It belongs to the group of so-called green leaf volatiles (GLVs), which play an important role in transferring information to plants and insects. While most biosynthetic enzymes upstream of E-2-hexenal have been studied extensively, much less is known about the enzyme responsible for the conversion from Z-3- to E-2-hexenal. In this study we have identified two (3Z):(2E)-hexenal isomerases (HIs) from cucumber fruits by classical biochemical fractionation techniques and we were able to confirm their activity by heterologous expression. Recombinant protein of the HIs did not only convert the leaf aldehyde Z-3-hexenal to E-2-hexenal, but also (Z,Z)-3,6-nonadienal to (E,Z)-2,6-nonadienal, these last two representing major flavor volatiles of cucumber fruits. Transient expression of the cucumber HIs in Nicotiana benthamiana leaves drastically changed the GLV bouquet of damaged plants from a Z-3- to an E-2-enriched GLV profile. Furthermore, transcriptional analysis revealed that the two HIs showed distinct expression patterns. While HI-1 was specifically expressed in the flesh of cucumber fruits HI-2 was expressed in leaves as well. Interestingly, wounding of cucumber leaves caused only a slight increase in HI-2 transcript levels. These results demonstrate that cucumber HIs are responsible for the rearrangement of Z-3-aldehydes in both leaves and fruits. Future research will reveal the physiological importance of an increased conversion to E-2-aldehydes for plants and insects.

Volatile-Mediated Attraction of Greenhouse Whitefly Trialeurodes vaporariorum to Tomato and Eggplant.

The behavior of the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), is known to be affected by plant volatile cues, but its attraction or repellent to specific volatile cues has not been deeply studied yet. Therefore, the aim of our study was to identify the most attractive plant among cultivars of tomato (Solanum lycopersicum) and eggplant (Solanum melongena) to evaluate the volatiles of plants to identify the chemical compound(s) that attract T. vaporariorum. We speculated that whitefly–host plant interaction primarily depends on plant volatile emissions and that once the plant is damaged, it might attract more whiteflies. Three intact (uninfested) tomato, four intact eggplant cultivars and whitefly infested plants of the most whitefly attractive tomato and eggplant cultivars were examined by behavioral assay experiments for attractiveness to T. vaporariorum and headspace volatile were determined by solid-phase microextraction (SPME) and gas chromatography-mass spectrometry. Whiteflies had the highest preference for the intact eggplant Kuai Yuan Qie (KYQ) among the eggplant and the tomato plant cultivars in bioassay experiments. Although both male and female whiteflies were significantly more attracted to infested KYQ plants than to intact plants, whitefly females did not select conspecific-infested YG plants. The volatile emissions among different plant cultivars in individual species and infested versus intact plants were significantly different. Among these volatiles, identified major green leaf volatiles [(Z)-3-hexen-1-ol] and terpenoids [α-pinene, (E)-β-caryophyllene, α-humulene, azulene] showed a constitutive relationship with the most whitefly preference plants. Our findings provide new insights into the chemical compounds that attract or repel whiteflies.

Evaluation of natural occurring bioactive compounds and antioxidant activity in Nuragus white wines

The aim of the present study is to highlight volatile and targeted non-volatile bioactive compounds in Nuragus wines, as a part of Italian DOC (Controlled Origin Designation) white wines. So far there has not been any systematic study of the chemical compositions and antioxidant activity of this monovarietal wine. Phenolic compounds, volatiles and organic acids were analysed and antioxidant capacity was assessed by spectrophotometric assays. Chromaticity coordinates and technological parameters (alcohol, reducing sugars, pH, total and volatile acidity) were also evaluated. Gallic acid (128±87mg/L), trans-caftaric acid (81±27mg/L) and tyrosol (25±8mg/L) were the most abundant phenolic compounds. The major headspace volatiles were isoamyl alcohol (35.8–76.6%) and 2-phenylethanol (5.9–24.9%). In the wine extracts, the most abundant were 2-phenylethanol (12.3–40.0%), 4-hydroxy-2-phenylethanol (12.5–33.3%), diethyl succinate (5.8–30.3%), (Z)-octadec-9-en-1-ol (5.9–18.3%) and tryptophol (2.8–15.6%). Nuragus wines exhibited an excellent antioxidant capacity. The data obtained may help Nuragus wine producers to promote this monovarietal wine as a valid complement associated with the Mediterranean diet.

Semiochemicals released from five bacteria identified from animal wounds infested by primary screwworms and their effects on fly behavioral activity.

BackgroundThe Primary screwworm, Cochliomyia hominivorax (Coquerel), is a serious pest feeding on living flesh of any warm-blooded animal, including humans. It was eradicated from the United States in the early 1980s using the sterile male technique. However, it was recently detected in populations of wild deer and pets in the Florida Keys of the US. For monitoring purposes, screwworm flies are normally trapped using attractant bait with liver. However, there has been little effort to develop an efficient monitoring system for detection of screwworm flies using a specific synthetic attractant blend. Several studies have shown that odors from animal wound fluids attract screwworm adults, particularly gravid females. Bacteria associated with animal wounds have been identified that act as a major source for this attraction. To understand what volatiles attract screwworms we inoculated bovine blood with previously identified bacteria. We identified volatile chemicals released from the inoculated blood and other selected media over time and assessed the effect of those chemicals on behavioral activity of adult screwworm flies.Methodology/Principal findingsA total of 7 volatile compounds were collected from bacteria incubated in either broth or blood using solid-phase microextraction, and their chemical structures were identified by their characteristic mass spectrum fragments and confirmed by retention times in comparison to those of synthetic standards via gas chromatograph combined mass spectrometry analyses. Five major volatiles including dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol and indole were detected from a mixture of 5 bacteria incubated in blood. The ratios of volatiles released differed among different incubation media, time and individual bacteria. A synthetic mixture containing the five compounds was demonstrated to be attractive to adult screwworm flies both in laboratory assays and field trapping trials.Conclusions/SignificanceThe results obtained from this study may assist in developing an efficient trapping system using the identified attractant blend to detect the infestation of primary screwworms. This is also the first study to explore the complex systems in volatile release profiles from 5 bacteria isolated from screwworm-infested animal wounds that are incubated with different media and incubation time, as well as individual and multi-species bacterial communities.

Evidence for depletion of heavy silicon isotopes at comet 67P/Churyumov-Gerasimenko

Context. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) was designed to measure the composition of the gas in the coma of comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. In addition to the volatiles, ROSINA measured refractories sputtered off the comet by the interaction of solar wind protons with the surface of the comet. Aims. The origin of different solar system materials is still heavily debated. Isotopic ratios can be used to distinguish between different reservoirs and investigate processes occurring during the formation of the solar system. Methods. ROSINA consisted of two mass spectrometers and a pressure sensor. In the ROSINA Double Focusing Mass Spectrometer (DFMS), the neutral gas of cometary origin was ionized and then deflected in an electric and a magnetic field that separated the ions based on their mass-to-charge ratio. The DFMS had a high mass resolution, dynamic range, and sensitivity that allowed detection of rare species and the known major volatiles. Results. We measured the relative abundance of all three stable silicon isotopes with the ROSINA instrument on board the Rosetta spacecraft. Furthermore, we measured $^{13}$C/$^{12}$C in C$_2$H$_4$, C$_2$H$_5$, and CO. The DFMS in situ measurements indicate that the average silicon isotopic composition shows depletion in the heavy isotopes $^{29}$Si and $^{30}$Si with respect to $^{28}$Si and solar abundances, while $^{13}$C to $^{12}$C is analytically indistinguishable from bulk planetary and meteorite compositions. Although the origin of the deficiency of the heavy silicon isotopes cannot be explained unambiguously, we discuss mechanisms that could have contributed to the measured depletion of the isotopes $^{29}$Si and $^{30}$Si.

On the attempts to measure water (and other volatiles) directly at the surface of a comet.

The Ptolemy instrument on the Philae lander (of the Rosetta space mission) was able to make measurements of the major volatiles, water, carbon monoxide and carbon dioxide, directly at the surface of comet 67P/Churyumov-Gerasimenko. We give some background to the mission and highlight those instruments that have already given insights into the notion of water in comets, and which will continue to do so as more results are either acquired or more fully interpreted. On the basis of our results, we show how comets may in fact be heterogeneous over their surface, and how surface measurements can be used in a quest to comprehend the daily cycles of processes that affect the evolution of comets.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.

Biotransformation of Volatiles in Fermented Osmanthus (Osmanthus fragrans) Flowers by Yeast

Sweet osmanthus (Osmanthus fragrans) is a species of flowering plants in Asia prized for food, flavor and fragrance industries. This work studied biotransformation of volatiles in osmanthus flowers through monoculture fermentation of infusions of sweet osmanthus flowers using yeasts, Saccharomyces cerevisiae and Williopsis saturnus. The major volatiles in two osmanthus cultivars Jingui and Yingui before and after fermentation were terpenoids and ketones. Esters, alcohols and acetic acid were only present after fermentation, and aldehydes were largely depleted after fermentation. The volatile profile of sweet osmanthus flowers fermented with S. cerevisiae was described as sweet and floral, while that of sweet osmanthus flowers fermented with W. saturnus was fruity, sweet and floral. Addition of nutrients (glucose and diammonium phosphate) increased alcohol and ester production, decreased percentage reduction of ketones and terpenes. Biotransformation of terpenes varied with each compound and fermentation treatment. Overall, yeast fermentation proved to be effective in enhancing sweet osmanthus flower fragrance for production of unique essential oils from this invaluable flower.

Phytochemicals from the Bark ofRhamnus Caroliniana

Rhamnus caroliniana (Rhamnaceae), or Carolina buckthorn, is a plant commonly found in the southeastern United States that was used in Cherokee traditional medicine. To date, there have been no reports on the phytochemical constituents of R. caroliniana. The bark of R. caroliniana was collected and extracted with chloroform. The crude chloroform extract was subjected to preparative column chromatography on silica gel leading to the isolation of two anthraquinones (chrysophanol and physcion), the bianthrone ararobinol, the dihydroxynaphthalene torachrysone, and the fatty alcohol 1-docosanol. The bark essential oil of R. caroliniana was obtained by hydrodistillation and analyzed by gas chromatography - mass spectrometry. The major bark volatiles were the anthrone chrysarobin-(24.2%), the piperidine alkaloid piperine (15.4%), and the dibenzoxepin pacharin (7.5%).

Identification of key volatiles responsible for aroma changes of egg white antioxidant peptides during storage by HS-SPME-GC-MS and sensory evaluation

The present study detects the volatiles of egg white antioxidant peptides (EWAPs) with molecular weight range from 1 to 3 kDa and identifies the key volatiles responsible for the aroma changes under different storage conditions using HS-SPME-GC-MS and sensory evaluation. In comparison, the original samples and samples stored at 4 °C and 50% relative humidity (RH), 4 °C and 75% RH, 25 °C and 50% RH, 25 °C and 75% RH, presented 24, 27, 27, 28 and 30 major volatiles, respectively. The cluster analysis and principal component analysis (PCA) both showed that storage environment had a significant effect on the aroma changes. The sensory evaluation demonstrated that EWAPs stored at the same temperature had similar aroma profiles and the samples stored at a higher RH 75% had much stronger aroma intensity, because high temperature and RH may be more suitable to promote some chemical reactions. In Addition, the sensory evaluation of EWAPs samples and the verification experiment about contributions of volatiles, temperature and RH to the changed aroma were conducted, the results further revealed that 3-ethyl-2,5-dimethyl-pyrazine and benzothiazole may be the key volatiles responsible for aroma changes. The results attained in this study may help to explore the methods to prevent or retard the deterioration, and it is also expected to contribute to further research on the stabilization and productization of EWAPs as nutritional and functional food.

Sensory specificity and speciation: a potential neuronal pathway for host fruit odour discrimination in Rhagoletis pomonella.

Behavioural changes in habitat or mate choice can trigger population divergence, leading to speciation. However, little is known about the neurological bases for such changes. Rhagoletis pomonella (Diptera: Tephritidae) is a model for ecological speciation via host plant shifts. Within the past 180 years, Rhagoletis flies infesting hawthorn (Crataegus spp.) shifted to attack domesticated apple (Malus pumila). The two populations differ in their olfactory preferences for apple versus hawthorn fruit. Here, we looked for patterns of sensory organization that may have contributed to this shift by characterizing the morphology, specificity and distribution of olfactory sensory neurons (OSNs) on the antennae of Rhagoletis responding to host fruit and non-host volatiles. Of 28 OSN classes identified, two colocalized OSN pairs were found that specifically responded to the major behavioural attractant and antagonist volatiles for each fly population. A reversal in the response of these OSNs to fruit volatiles, either through a switch in receptor expression between these paired neurons or changes in neuronal projections in the brain, could therefore account for the behavioural difference between apple and hawthorn flies. The finding supports the hypothesis that relatively minor changes in olfactory sensory pathways may contribute to rapid host shifting and divergence in Rhagoletis.