Differences In Volatile Profiles Research Articles

Electronic nose as an innovative tool for the diagnosis of grapevine crown gall

For the first time, a portable electronic nose was used to discriminate between healthy and galled grapevines, experimentally inoculated with two tumourigenic strains of Agrobacterium vitis. The volatile profile of target cutting samples was analysed by headspace solid phase microextraction coupled with gas chromatography–mass spectrometry. Spectra from tumoured samples revealed the presence of styrene which is compatible with decarboxylation of cinnamic acid involved in secondary metabolism of plants. Principal Component Analysis confirmed the difference in volatile profiles of infected vines and their healthy controls. Linear Discriminant Analysis allowed the correct discrimination between healthy and galled grapevines (83.3%, cross-validation). Although a larger number of samples should be analysed to create a more robust model, our results give novel interesting clues to go further with research on the diagnostic potential of this innovative system associated with multi-dimensional chemometric techniques.

Songbird chemosignals: volatile compounds in preen gland secretions vary among individuals, sexes, and populations

Chemical signaling has been documented in many animals, but its potential importance in avian species, particularly songbirds, has received far less attention. We tested whether volatile compounds in the preen oil of a songbird (Junco hyemalis) contain reliable information about individual identity, sex, or population of origin by repeated sampling from captive male and female juncos originating from 2 recently diverged junco populations in southern California. One of the populations recently colonized an urban environment; the other resides in a species-typical montane environment. The birds were field-caught as juveniles, housed under identical conditions, and fed the same diet for 10 months prior to sampling. We used capillary gas chromatography-mass spectrometry to quantify the relative abundance of 19 volatile compounds previously shown to vary seasonally in this species. We found individual repeatability as well as significant sex and population differences in volatile profiles. The persistence of population differences in a common environment suggests that preen oil chemistry likely has a genetic basis and may thus evolve rapidly in response to environmental change. These finding suggest that songbird preen oil odors have the potential to function as chemosignals associated with mate recognition or reproductive isolation.

Characterisation of odour active volatile compounds of New Zealand sea urchin ( Evechinus chloroticus) roe using gas chromatography–olfactometry–finger span cross modality (GC–O–FSCM) method

Sea urchin roe is a high value product; however, previous attempts to market the roe from the New Zealand sea urchin ( Evechinus chloroticus) have been unsuccessful due to its inconsistent sensory quality. The current study investigated the odour active volatile profiles of roe from male and female sea urchins, harvested from two locations in New Zealand, using solvent assisted flavour evaporation (SAFE) extracts and a gas chromatography–olfactometry–finger span cross modality (GC–O–FSCM) method. Panellists detected 81 odour active compounds, 18 of which were identified using GC–mass spectrometry (MS). Generalised procrustes analysis (GPA) of the data revealed that there were differences in the volatile profile that were location and gender specific. These differences may have contributed to the inconsistent sensory properties of sea urchin roe. The differences in volatile profiles between sea urchin populations and genders must be appreciated before developing effective strategies to produce consistent sea urchin roe quality.

Chemical Characteristics and Volatile Profile of Genetically Modified Peanut Cultivars

Genetic engineering has been used to modify peanut cultivars for improving agronomic performance and pest resistance. Food products developed through genetic engineering have to be assessed for their safety before approval for human consumption. Preservation of desirable chemical, flavor and aroma attributes of the peanut cultivars during the genetic modifications is critical for acceptance of genetically modified peanuts (GMP) by the food industry. Hence, the main objective of this study is to examine chemical characteristics and volatile profile of GMP. The genetically modified peanut cultivars, 188, 540 and 654 were obtained from the USDA-ARS in Stillwater, Oklahoma. The peanut variety Okrun was examined as a control. The volatile analysis was performed using a gas chromatograph/mass spectrometer (GC/MS) equipped with an olfactory detector. The peanut samples were also analyzed for their moisture, ash, protein, sugar and oil compositions. Experimental results showed that the variations in nutritional composition of peanut lines examined in this study were within the values reported for existing cultivars. There were minor differences in volatile profile among the samples. The implication of this study is significant, since it shows that peanut cultivars with greater pest and fungal resistance were successfully developed without major changes in their chemical characteristics.

The role of the plant in attracting parasitoids: response to progressive mechanical wounding

AbstractBased on the model system of Brussels sprouts [Brassica oleracea var. gemmifera (Brassicaceae)], the herbivore cabbage white caterpillar, Pieris brassicae (L.) (Lepidoptera: Pieridae), and the parasitoid wasp, Cotesia glomerata (L.) (Hymenoptera: Braconidae), the influence of plant damage type, and damage duration were assessed on plant volatile emission and subsequent recruitment of natural antagonists of the herbivore. Plants were damaged by three methods for a period of either 3 or 8 h: herbivore damage (HD), progressive mechanical damage, and final mechanical damage inflicted in a single event. Wind‐tunnel bioassays evaluated whether the mode of damage affected female parasitoid oriented flight. After both periods of damage, all treatments were highly significantly preferred by naïve C. glomerata to undamaged control plants. After 3 h, herbivore‐damaged plants were significantly preferred to plants with final damage (FD). Most remarkably, following 8‐h damage, the parasitoid preferred both herbivore‐damaged and progressively damaged plants to plants with FD and did not significantly discriminate between herbivore and progressively damaged plants, thus indicating a similarity in plant response to herbivore and progressive mechanical damage. In addition to wind‐tunnel bioassays, emitted plant volatiles were collected and analysed by thermal desorption gas chromatography/mass spectrometry, following 3 and 8 h of damage in order to correlate volatiles released from different damage types with the attraction of the parasitoid. Differences in volatile profiles from all damage types were similar following both 3 and 8 h of damage, with only (Z)‐3‐hexenyl acetate found to be emitted in significantly higher quantities by final mechanical damage compared with HD after 3 h. In conclusion, the plant's response to progressive mechanical damage was more similar to HD than final mechanical damage deployed at a single point in time, irrespective of damage duration, and C. glomerata did not significantly discriminate between progressive damage and HD.

Influence of a defined-strain starter and Lactobacillus plantarum as adjunct culture on volatile compounds and sensory characteristics of Manchego cheese

Three batches of Manchego cheese were manufactured using one of the following starter culture systems: (1) a defined strain starter culture comprising Lactococcus lactis subsp. lactis and Leuconostoc mesenteroides subsp. dextranicum; (2) the above-defined strain starter culture and an adjunct culture (Lactobacillus plantarum), all these strains being isolated from high-quality Manchego cheeses and (3) a commercial starter consisting of two strains of Lactococcus lactis. Differences in volatile profile and the sensory characteristics of these cheeses were studied. After 4 months of ripening, the two batches of cheese made with the defined strain starter cultures obtained the highest scores for sensory attributes and for the overall impression. Additionally, Purge & Trap and SDE analysis showed a more complex volatile profile in these cheeses than in those made with the commercial starter. Extending the maturation time to 8 months for cheeses made with the defined starter cultures led to significant higher levels of free fatty acids and ethyl esters in those cheeses made without adjunct culture. However, panelists did not find significant differences among the sensory characteristics of the two cheeses.

Evaluation of tomato maturity by electronic nose

Over the past years, electronic nose (E-nose) technology opened has enhanced the possibility of exploiting information on behavior aroma to assess fruit ripening stage. The objective in this study was to evaluate the capacity of electronic nose to monitor the change in volatile production of ripeness states for tomato, using a specific electronic nose device with 10 different metal oxide sensors (portable E-nose, PEN 2). Principal component analysis (PCA) and linear discriminant analysis (LDA) were used to investigate whether the electronic nose was able to distinguishing among different ripeness states (unripe, half-ripe, full-ripe and over-ripe). The loadings analysis was used to identify the sensors responsible for discrimination in the current pattern file. The results prove that the electronic nose PEN 2 could differentiate among the ripeness states of tomato. The electronic nose was able to detect a clearer difference in volatile profile of tomato when using LDA analysis than when using PCA analysis. Using LDA analysis, it was possible to differentiate and to classify the different tomato maturity states, and this method was able to classify 100% of the total samples in each respective group. Some sensors in E-nose have the highest influence in the current pattern file for electronic nose PEN 2. A subset of a few sensors in E-nose can be chosen to explain all the variance. This result could be used in further studies to optimize the number of sensors.

Production of volatile compounds by Rhizopus oligosporus during soybean and barley tempeh fermentation

Rhizopus oligosporus Saito can ferment soybeans or cereal grains to tempeh, a sliceable cake with improved nutritional properties. Volatiles produced by different R. oligosporus strains grown on malt extract agar (MEA), barley and soybean were investigated. The effect of co-cultivation with Lactobacillus plantarum on the production of volatiles was also studied. Volatile compounds were collected in situ by headspace diffusion and identified by GC–MS. The ten R. oligosporus strains that had different colony morphologies on MEA produced very similar volatile profiles, except for slight variations among the minor volatile compounds (e.g. sesquiterpenes). Likewise, practically no differences in volatile profiles were observed between three of the strains grown on soybeans. In contrast, the R. oligosporus volatile profile on soybean was different from that on barley from the same strain. Co-cultivation with L. plantarum did not influence volatile production by R. oligosporus. The dominant compounds produced on all three substrates were ethanol, acetone, ethyl acetate, 2-butanone, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Acetaldehyde and 2-methyl-propanal were also produced on MEA and barley, while 2-pentanone, methyl acetate, 2-butanol and 3-methyl-3-buten-1-ol were observed on soybeans. Ethanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most abundant volatile compounds produced on MEA and barley, while 2-butanone was the dominant volatile metabolite on soybean. The mushroom odour compounds, 3-octanone and 1-octen-3-ol, were only detected from soybean and soybean tempeh.

Generic system for the detection of statutory potato pathogens

Methods for detecting and discriminating volatile organic compounds emitted by statutory pathogens in potato tubers are reported. Analyses were performed utilising headspace solid phase microextraction gas chromatography–mass spectrometry (HS-SPME-GC–MS). Principal component analysis of the data highlights the difference in volatile profiles of infected tubers and their controls. An instrument was developed comprising an automated SPME sampler and 8-metal oxide sensor array and was demonstrated to be capable of identification of infected material.

FRUIT FLAVOR FORMATION IN WILD AND CULTIVATED STRAWBERRY

In recent years we have used various genomics tools to investigate ripening in strawberry, in particular the process of fruit flavor biogenesis. The combination of biochemical analysis, generation of a strawberry Expressed Sequence Tags (EST) collection and gene expression analysis using cDNA microarrays resulted in the identification of several genes playing a key role in the formation of volatile flavors during strawberry fruit ripening. Genes associated with the biosynthesis of lipid-derived flavors, such as esters, and those involved in the formation of mono- and sesquiterpenes have been isolated. In this report we summarize the main results obtained by functional characterization of the genes identified. Moreover, differences in volatile profiles between the wild, diploid strawberry and the cultivated, octaploid strawberry allowed us to obtain insight into the molecular processes which resulted in the formation of a certain flavor component and the loss of another.

Electronic nose technique potential monitoring mandarin maturity

Over the past years, electronic nose technology opened the possibility to exploit information on behavior aroma to assess fruit ripening stage. The objective in this study was to evaluate the capacity of electronic nose to monitoring the change in volatile production of mandarin during different picking-date, using a specific electronic nose device (PEN 2). Principal component analysis (PCA) and linear discriminant analysis (LDA) were used in order to investigate whether the electronic nose was able to distinguish among different picking-date (ripeness states). The loadings analysis was used to identify the sensors responsible for discrimination in the current pattern file. The results obtained prove that the electronic nose PEN 2 can discriminate successfully different picking-date on mandarin using LDA analysis. But, electronic nose was not able to detect a clear difference in volatile profile on mandarin using PCA analysis. During external validation using LDA was obtained to classified 92% of the total samples properly. Some sensors have the highest influence in the current pattern file for electronic nose PEN 2. A subset of few sensors can be chosen to explain all the variance. This result could be used in further studies to optimize the number of sensors.