Headspace volatile markers for sensitivity of cocoa (Theobroma cacao L.) somatic embryos to cryopreservation

The mechanisms that reduce the viability of plant somatic embryos following cryopreservation are not known. The objective of the present study was to evaluate the sensitivity of cocoa (Theobroma cacao L.) somatic embryos at different stages of an encapsulation-dehydration protocol using stress-related volatile hydrocarbons as markers of injury and recovery. The plant stress hormone ethylene and volatile hydrocarbons derived from hydroxyl radicals (methane) and lipid peroxidation (ethane) were determined using gas chromatography headspace analysis. Ethylene and methane were the only volatiles detected, with both being produced after each step of the cryogenic protocol. Ethylene production was significantly reduced following exposure to liquid nitrogen, but then increased in parallel with embryo recovery. In contrast, the production of methane was cyclic during recovery, with the first cycle occurring earlier for embryos recovered from liquid nitrogen and desiccation than those recovered from earlier steps in the protocol. These results suggest that loss of somatic embryo viability during cryopreservation may be related to the oxidative status of the tissue, and its capacity to produce ethylene. This study has demonstrated that headspace volatile analysis provides a robust non-destructive analytical approach for assessing the survival and recovery of plant somatic embryos following cryopreservation.

Plant chemistry and aphid parasitoids (Hymenoptera : Braconidae): Imprinting and memory

Emerging parasitoids of aphids encounter secondary plant chemistry from cues left by the mother parasitoid at oviposition and from the plant-feeding of the host aphid. In practice, however, it is secondary plant cheinistry oil the Surface of the aphid mummy which influences parasitoid olfactory behaviour. Offspring of Aphidius colemani reared oil Myzus persicae on artificial diet did no distinguish between the odours of bean and cabbage, but showed a clear preference for cabbage odour if sinigrin had been painted oil the back of the mummy. Similarly Aphidius rhopalosiphi reared on Metopolophium dirhodum on wheat preferred the odour of wheat plants grown near tomato plants to odour of wheat alone if the wheat plants oil which they had been reared had been exposed to the volatiles of nearby tomato plants. Aphidius rhopalosiphi reared on M dirhodum, and removed from the mummy before emergence, showed a preference for the odour of a different wheat cultivar if they had contacted a mummy from that cultivar, and similar results were obtained with A. colemani naturally emerged from M. persicae mummies. Aphidius colemani emerged from mummies oil one crucifer were allowed to contact in sequence (for 45 min each) mummies from two different crucifers. The mumber of attacks made in 10 min oil M. persicae was always significantly higher when aphids were feeding oil the same plant as the origin of the last MUMMY offered, or oil the second plant if aphids feeding on the third plant were not included. Chilling emerged A. colemani for 24 h at 5 degrees C appeared to erase the imprint of secondary plant chemistry, and they no longer showed host plant odour preferences in the olfactometer. When the parasitoids were chilled after three Successive mummy experiences, memory of the last experience appeared at least temporarily erased and preference was then shown for the chemistry of the second experience.

Histone H4 gene expression and morphological changes on shoot apices of strawberry (Fragaria x ananassa Duch.) during floral induction

To investigate flower induction in June-bearing strawberry plants, morphological changes in shoot apices and Historic H4 expression in the central zone during flower initiation were observed. Strawberry plants were placed under flower inducible, short-day conditions (23 degrees C/17 degrees C, 10 h day length) for differing number of days (8, 16, 20, 24 or 32 days) and then these plants were transferred to non-inducible, long-day conditions (25 degrees C/20 degrees C, 14 h day length). The shoot apices of plants placed under short-day conditions for 8 days were flat, similar to shoot apices of plants in the vegetative phase of development, and Histone H4 was not expressed in the central zone during the experimental period. On the other hand, the shoot apices of plants placed under short-day conditions for 16 days remained flat, similar to shoot apices of plants placed under short-day conditions for 8 days, but Histone H4 was expressed in the central zone at the end of the short-day treatment. Morphological changes in the shoot apices of these plants were observed 8 days after the change in day-length. These plants developed differentiated flower organs after they were grown for another 30 days under long-day conditions. These results indicate that changes in the expression pattern of the Histone H4 gene occur before morphological changes during flower induction and that the expression of the gene in the central zone can be used as one of the indicators of the flowering process in strawberries. (c) 2006 Elsevier B.V. All rights reserved.

Characterisation of the thermodormancy response in the everbearing strawberry 'Everest'

Temperature regimes that induce and ameliorate cropping troughs ("thermodormancy") were evaluated over two seasons for the everbearing strawberry 'Everest'. When plants were exposed to 26 degrees C for 5, 10, 20 or 30 d in July, heat-induced troughs in cropping were observed in August. An important discovery was that cool (13 degrees C) night temperatures ameliorated the severity of thermodormancy. In this study, thermodormancy appeared to be due principally to flower abortion post-anthesis, as large numbers of flowers emerged in mid-July, during the high temperature treatments, but went on to produce low fruit numbers in mid-August. Flower initiation itself (monitored by crown dissection) was not reduced by high temperatures. The observation that night-time temperature is critical for thermodormancy has significance for commercial production, in which protected cropping tends to increase average temperatures throughout the season, and venting tends to focus on day-time temperatures.

Far-red light filtering by plastic film, greenhouse-cladding materials: effects on growth and flowering in Petunia and Impatiens

Photoselective plastic films with low transmission to far-red (FR) light (700-800 nm) are now available so that plants grown in greenhouses clad with such plastics exhibit reduced stem extension and, consequently, plant height. Here we compare the action of three FR-absorbing polythene films on extension growth of Petunia (Petunia X hybrida) cv. 'Express Blue' and Impatiens walleriana cv. 'Accent Deep Pink' with plants grown under a control polythene film (standard UVI/EVA film). Half of the plants under the control film were treated with a chemical plant growth regulator (PGR; diaminozide, B-Nine) and half were sprayed with water alone. Possible negative effects of such film plastics on flowering, and on fresh and dry weight accumulation, were also quantified. Plants were harvested destructively when all plants in each treatment had reached the first open flower stage. In Petunia, plant height was reduced by all three FR-filtering films and by PGR-treatment. The FR-filtering films giving the highest R:FR ratios also reduced plant height in Impatiens. Leaf number, leaf area and total dry Weight in both species. were greatest in the controls and smallest under films with the lowest PAR transmission. The film giving the highest R:FR ratio and PAR transmission also produced the most compact Petunia plants;, while the film. with. the lowest PAR transmission produced the least compact plants in both species. There was no significant effect of treatments on time to first flower in Impatiens. However, Petunia plants under low PAR transmission films took longer to flower. Plastic-films which filter out FR light to increase the R:FR ratio, combined With high PAR transmission, can therefore be used as an alternative to conventional PGRs.

Statistical deconvolution of enthalpic energetic contributions to MHC-peptide binding affinity

Background: MHC Class I molecules present antigenic peptides to cytotoxic T cells, which forms an integral part of the adaptive immune response. Peptides are bound within a groove formed by the MHC heavy chain. Previous approaches to MHC Class I-peptide binding prediction have largely concentrated on the peptide anchor residues located at the P2 and C-terminus positions. Results: A large dataset comprising MHC-peptide structural complexes was created by remodelling pre-determined x-ray crystallographic structures. Static energetic analysis, following energy minimisation, was performed on the dataset in order to characterise interactions between bound peptides and the MHC Class I molecule, partitioning the interactions within the groove into van der Waals, electrostatic and total non-bonded energy contributions. Conclusion: The QSAR techniques of Genetic Function Approximation (GFA) and Genetic Partial Least Squares (G/PLS) algorithms were used to identify key interactions between the two molecules by comparing the calculated energy values with experimentally-determined BL50 data. Although the peptide termini binding interactions help ensure the stability of the MHC Class I-peptide complex, the central region of the peptide is also important in defining the specificity of the interaction. As thermodynamic studies indicate that peptide association and dissociation may be driven entropically, it may be necessary to incorporate entropic contributions into future calculations.

Recent work on entropically-driven ring-opening polymerizations: some potential applications

The entropically-driven ring-opening polymerization of macrocyclic monomers (> ca. 14 ring atoms per repeat unit) and/or macrocyclic oligomers is a relatively new method of polymer synthesis that exploits the well-known phenomenon of ring-chain equilibria. It attracts interest because of its novel features. For example, these ring-opening polymerizations emit no volatiles and little or no heat. This review considers the principles of entropically-driven ring-opening polymerizations, gives selected examples and discusses potential applications. The latter include micromolding, high throughput syntheses and the synthesis of supramolecular polymers. Copyright (c) 2005 John Wiley T Sons, Ltd.

A study of the aroma of fried bacon and fried pork loin

Aroma compounds in the headspace volatiles of fried bacon and fried pork loin were identified. The concentrations of volatiles in bacon were much lower than those in pork loin, except for nitrogen compounds. It is likely that these differences were caused by the presence of nitrite in bacon. Characteristic aromas for fried bacon, described variously as bacon-, fried meat-, roast meat- and cooked meat-like, were found through olfactory testing. These aromas were not present in the pork loin samples. Compounds such as pyrazines, pyridines and furans are thought to be responsible for these meaty aromas. (C) 2004 Society of Chemical Industry.

Volatile compounds produced by the probiotic strain Lactobacillus plantarum NCIMB 8826 in cereal-based substrates

The production of volatile compounds by the probiotic strain, Lactobacillus plantarum NCIMB 8826, in cereal-based media (oat, wheat. barley and malt) was investigated. Sixty compounds, including fatty acids and their esters, amides, alcohols, aldehydes, aromatic hydrocarbons, furans, ketones, peroxides and pyrans, were identified. L. plantarum significantly changed the aroma profile of the four cereal broths. and each substrate showed a specific volatiles profile. Oat and barley media were the substrates more influenced by the fermentation process. The most abundant volatiles detected in oat, wheat, barley and malt were oleic acid, linoleic acid. acetic acid, and 5-hydroxymethylfurfural, respectively. Analysis of these products confirmed the heterofermentative pathway of L plantarum. Maillard compounds were not detected during sterilisation and fermentation. This study is the first to report the volatile composition of probiotic drinks produce with non-supplemented cereal-based media and the results obtained could contribute to the development of new non-dairy probiotic formulations. (C) 2009 Elsevier Ltd. All rights reserved.

Interaction of sulphur-containing aroma compounds with proteins in both model systems and real food systems

Irreversible binding of key flavour disulphides to ovalbumin has been shown previously to occur in model systems. The extent of binding is determined by the availability of the sulphydryl groups to participate in disulphide exchange, influenced either by pH, or the state of the protein (native or heat-denatured). In this study, two further proteins, one with sulphydryl groups available in the native state (beta-lactoglobulin) and one with no sulphydryl groups in the native state (lysozyme) were used to confirm this hypothesis. When the investigation was extended to real food systems, a similar effect was shown when a commercial meat flavouring containing disulphides was added to heat-denatured ovalbumin. Furthermore, comparison of the volatiles generated from onions, cooked either alone, or in the presence of meat, showed a significant reduction of key onion-derived disulphides when cooked in the presence of meat, and an even greater reduction of trisulphides. These findings may have implications for consumer acceptance of food products; where these compounds are used as flavourings or where they occur naturally.

Influence of sulfur amino acids on the volatile and nonvolatile components of cooked salmon (Salmo salar)

Volatile and nonvolatile compounds, which could contribute to flavor, were analyzed in salmon. One hundred twenty-three volatile compounds were identified in the headspace of two different samples of cooked salmon, including lipid-derived volatiles, Maillard-derived volatiles, sulfur volatiles, Strecker aldehydes, nitrogen heterocyclic compounds, terpenes, and trimethylamine. Significant differences between samples were found for 104 of the volatiles. Although the levels of free cysteine and methionine were low in the salmon, sulfur volatiles were formed in the cooked fish, demonstrating that there were sufficient sulfur amino acids present for their formation. Notable differences in sulfur compounds between the samples suggested that small changes in sulfur amino acids could be responsible. When this hypothesis was tested, salmon heated with cysteine had increased levels of many thiophenes, thiazoles, alicyclic sulfides, and nitrogen heterocycles. With the addition of methionine, levels of dimethyl sulfides, two alicyclic sulfides, pyrazines, some unsaturated aldehydes, and alcohols and 2-furanmethanethiol increased. The largest difference found among the nonvolatile (low molecular weight water-soluble) compounds was in inosine monophosphate.

Volatile flavour profile of goat meat extracted by three widely used techniques

Three procedures for the isolation of volatiles from grilled goat meat were compared: dynamic headspace entrainment on Tenax TA, simultaneous steam distillation-extraction, and solid-phase microextraction. Headspace entrainment on Tenax TA extracted the highest number of Maillard-derived volatile compounds. Two hundred and three volatile components were identified: 159 are reported for the first time in goat meat. Most of the volatiles detected (155) were lipid oxidation products, such as hydrocarbons, aldehydes, alcohols, ketones, carboxylic acids and esters. Forty-eight Maillard-derived compounds were identified. comprising pyrazines, pyrroles, thiophenes, furanthiol derivatives, alkyl and alicyclic sulphides, pyridines, and thiazoles. Some reported character impact compounds of cooked meat, e.g., 12-methyltridecanal, (EE)-2,4-decadienal, methional, and dimethyl trisulphide were identified in the volatile profile of goat meat, together with a series of C-2 to C-5 alkylformylcyclopentenes, which have been reported in cooked chicken, pork, beef and lamb, as being important for the characteristic flavour impression of different animal species. (C) 2009 Published by Elsevier Ltd.

Effect of citric acid and glycine addition on acrylamide and flavor in a potato model system

Acrylamide levels in cooked/processed food can be reduced by treatment with citric acid or glycine. In a potato model system cooked at 180 degrees C for 10-60 min, these treatments affected the volatile profiles. Strecker aldehydes and alkylpyrazines, key flavor compounds of cooked potato, were monitored. Citric acid limited the generation of volatiles, particularly the alkylpyrazines. Glycine increased the total volatile yield by promoting the formation of certain alkylpyrazines, namely, 2,3-dimethylpyrazine, trimethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, tetramethylpyrazine, and 2,5-diethyl-3- methylpyrazine. However, the formation of other pyrazines and Strecker aldehydes was suppressed. It was proposed that the opposing effects of these treatments on total volatile yield may be used to best advantage by employing a combined treatment at lower concentrations, especially as both treatments were found to have an additive effect in reducing acrylamide. This would minimize the impact on flavor but still achieve the desired reduction in acrylamide levels.

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 Ix, 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)-2octenal, 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.

Volatile oxidation compounds in a conjugated linoleic acid-rich oil

In this Study, volatile oxidation compounds formed in a commercial conjugated linoleic acid (CLA)-rich oil were quantified and results compared to those found in safflower oil (rich in linoleic acid, LA). Intact oil samples and pure triacylglycerols obtained following elimination of tocopherols and minor compounds were oxidised at 60 degrees C, and volatile oxidation compounds were analysed by solid phase microextraction-gas chromatography with flame ionisation detector and mass spectrometer. Results showed that while, as expected, hexanal was the major volatile oxidation compound found in oil and triacylglycerols rich in LA, both hexanal and heptanal equally were the most abundant compounds in oil and triacylglycerols rich in CLA. Besides, samples rich in CLA also showed significantly high quantities of trans-2-octenal and trans-2-nonenal and the latter, along with heptanal, were absent in samples rich in LA. Results for CLA samples were not easy to interpret since major volatiles found are not expected from theoretically stable hydroperoxides formed in CLA and could in part derive from dioxetanes coming from 1,2-cycloadclitions of CIA with oxygen. Overall, results obtained support evidence that oxidation mechanisms of CLA may differ than those of LA. Also, it was concluded that heptanal determination could serve as a useful marker of oxidation progress in CLA-rich oils. (C) 2008 Elsevier Ltd. All rights reserved.