124 research outputs found
Residuen op groenten en fruit ter discussie
No full textDe nVWA en het RIVM doen al jaren onderzoek naar residuen van giftige stoffen op groenten en fruit. Uit onderzoek blijkt dat met name peuters en baby’s meer groenten en fruit binnenkrijgen dan eerder werd gedacht. Met meer groenten en fruit zouden ze ook meer residuen binnenkrijgen. Ernst Woltering van Wageningen Universiteit plaatst het één en ander in perspectief
Tomato aroma volatiles measured by PTR-MS following artificial chewing
No full textThe aim of this study was to develop an analytical system to study the tomato aroma profile as closed as possible to the real human perception. An artificial chewing device coupled to a PTR-MS was developed to study the release kinetics of volatiles during eating and the possibility to consider volatile concentration similar to in vivo condition presenting in the human mouth during chewing.
Based on multivariate statistical analysis, data obtained by the PTR-MS system showed a better correlation to the outcome of the quantitative descriptive analysis (QDA) than SPME-GC-MS
Caspase inhibitors affect the kinetics and dimensions of tracheary elements in xylogenic Zinnia (<it>Zinnia elegans</it>) cell cultures
No full textAbstract Background The xylem vascular system is composed of fused dead, hollow cells called tracheary elements (TEs) that originate through trans-differentiation of root and shoot cambium cells. TEs undergo autolysis as they differentiate and mature. The final stage of the formation of TEs in plants is the death of the involved cells, a process showing some similarities to programmed cell death (PCD) in animal systems. Plant proteases with functional similarity to proteases involved in mammalian apoptotic cell death (caspases) are suggested as an integral part of the core mechanism of most PCD responses in plants, but participation of plant caspase-like proteases in TE PCD has not yet been documented. Results Confocal microscopic images revealed the consecutive stages of TE formation in Zinnia cells during trans-differentiation. Application of the caspase inhibitors Z-Asp-CH2-DCB, Ac-YVAD-CMK and Ac-DEVD-CHO affected the kinetics of formation and the dimensions of the TEs resulting in a significant delay of TE formation, production of larger TEs and in elimination of the 'two-wave' pattern of TE production. DNA breakdown and appearance of TUNEL-positive nuclei was observed in xylogenic cultures and this was suppressed in the presence of caspase inhibitors. Conclusions To the best of our knowledge this is the first report showing that caspase inhibitors can modulate the process of trans-differentiation in Zinnia xylogenic cell cultures. As caspase inhibitors are closely associated with cell death inhibition in a variety of plant systems, this suggests that the altered TE formation results from suppression of PCD. The findings presented here are a first step towards the use of appropriate PCD signalling modulators or related molecular genetic strategies to improve the hydraulic properties of xylem vessels in favour of the quality and shelf life of plants or plant parts.</p
Non-destructive detection of flawed hazelnut kernels and lipid oxidation assessment using NIR spectroscopy
No full textMicrobial contamination, seed browning, bad taste and lipid oxidation are primary causes of quality deterioration in stored hazelnuts, affecting their marketability. The feasibility of NIR spectroscopy to detect flawed kernels and estimate lipid oxidation in in-shell and shelled hazelnuts was investigated. ‘Mortarella’ hazelnuts were measured twice by NIR spectroscopy, first in-shell, and then as kernels. Afterwards, the kernels were evaluated visually, externally and internally, and by sensory evaluation with a subsequent measurement of fat oxidation. A satisfactory PLS model was created for the detection of flawed kernels. For lipid oxidation estimation the best performance of PLS models was obtained by first removing the flawed kernels from the calibration set. The PLS model for the K232 extinction coefficient, that is indicative of lipid primary oxidation, was able to predict K232 for both in-shell (R2 = 0.79) and shelled (R2 = 0.85) hazelnuts. Our results suggest, for shelled hazelnuts, a two-step NIR procedure: a first PLS model to detect and separate flawed kernels and then a second PLS model to grade healthy kernels by lipid oxidation levels
Ethylene production of Botrytis cinerea in vitro and during in planta infection of tomato fruits
No full textContains fulltext :
34799.pdf (Publisher’s version ) (Open Access)Symposium on the Plant Hormone Ethylene, 18 juni 200
Rapid tomato volatile profiling by using proton-transfer reaction mass spectrometry (ptr-ms)
No full textContains fulltext :
94030.pdf (Publisher’s version ) (Open Access
Low temperature-induced lycopene degradaton in red ripe tomato evaluated by remittance spectroscopy
No full textTomatoes are mostly harvested at the orange and red-ripe stages. A survey among consumers indicated that tomatoes are most often stored in the refrigerator well below 10 °C, a temperature considered harmful for chilling sensitive products such as tomato. Also during distribution, tomatoes may be exposed to chilling temperatures. The effects of storage at chilling temperatures on quality aspects of tomatoes were investigated. The colour and lycopene content of red ripe tomatoes of two cultivars (cocktail and round type) was evaluated during 20 days of storage at 4, 8, 12 and 16 °C. Colour was repeatedly measured over time by tristimulus colour measurements, RGB image analysis and colour intensity was scored by eye using a consumer panel. Lycopene content was repeatedly assessed by following the NAI index over time. This index, obtained from remittance VIS spectroscopy, was found to relate closely to the lycopene level as measured by HPLC measurements of pericarp tissue. Temperatures below 12 °C resulted in lycopene loss in ripe-red tomatoes and substantial colour loss well assessed by visual evaluation. Colour measurement using tristimulus colour measurements and RGB image analysis did not correlate well with lycopene content. Prior hot water treatment did not prevent lycopene loss. Results show that storage of red ripe tomatoes at chilling temperatures reduces the nutritional and presumed health promoting value and affects fruit visual quality
E-selectin as anti-inflammatory drug target : expression, purification and charactrization for structural studies : assay development for antaginists evaluation
No full textE-, P- and L-selectin belong to the C-type lectin family of cell adhesion molecules that
initiate inflammatory response. Infammation per se is a physiologocal defense
mechanism, but excessive leukcyte extravasation leads to numerous pathoIogical and
disease states, as well as metastatic cancer spread. Leukocyte tethering and rolling
toward inflammatory site start with the interaction of selectins and the carbohydrate
epitope of their glycoprotein ligands, sialyl Lewisx. Therefore inhibitors of selectin-ligand
interaction are of high pharmaceutical interest as potent anti-inflammatory agents.
Tetrasaccharide sialyl Lewisx serves as a lead strucure in chemical and computational
search for selectin antagonists. Structural NMR and X-ray studies indicated binding
mode of sialyl Lewisx with E-, and P-selectin, but improved structural studies with the
second and third generation antagonists is missing.
We expressed recombinant human E-, P- and L-selectin/IgG as secreted proteins in
mammalian expression system and purified them to homogniety. Acitivity of the proteins
was confirmed with blocking monoclonal antibodies and ligand binding confirmed by
NMR.
Bioassays were developed in cell-free and cell-based formats with E-selectin/IgG to
evaluate inhibitory potencies of in-house synthesized selectin antagonists. Due to
variation and instabilities on day-to-day and batch-to-batch basis, assays were used only
for preliminary antagonists screen.
To enhance further structural studies, we developed a new system for the expression of
truncated form of human E-selectin (lectin and EGF-like domains). Initialy we tried to
express these two domains in E.coli, but refolding of expressed inclusion bodies was
inefficient. Therefore lectin and EGF-like domains of human E-selectin were expressed
as secreted form in baculovirus-infeced insect cells with a flag-epitope on its C-terminus.
Expressed protein (LecEGFFlag) was monomeric in solution, correctly folded and active,
as confirmed in the reaction with monoclonal blocking antibodies, and NMR studies.
Protein was expressed in two distinct glycosylation forms, with apparent molecular
weigts of 19.96 kDa and 21.15 kDa.
In addition, we developed for the first time a cell-free assay with truncated form of Eselectin
(aforementioned LecEGFFlag) for the evaluation of of E-selectin inhibitors. In a
proof-of-concept manner, three different E-selectin antagonists were tested and obtained
IC50 values were in close agreement with published results. Reproducibility and stability
of the assay on day-to-day and batch-to batch basis make it suitable not only for the
preliminary screening, but also to quantify inhibitory potencies of E-selectin antagonists.
Developed system is suitable for expression and similar characterization of P- and Lselectin
as well
Factors affecting the postharvest performance of fresh-cut lettuce
No full text The quality of fresh-cut fruits and vegetables is often offset by a rapid deterioration, due to severe physical stress, such as peeling, cutting, slicing, shredding, and trimming. Due to this wounding, the already short shelf-life of these harvested products is even more reduced in the market place. In addition, consumers have become more critical on the use of synthetic and chemical additives to preserve quality attributes of fresh-cut produce. Developing new, effective, non-invasive and non-chemical techniques for improving and maintaining quality in fresh-cut produce are the timely questions of the industry. The work reported in this thesis adds to the increasing knowledge and understanding on how pre- and postharvest factors affect the storability of fresh-cut leafy vegetables. This work focused in particular on factors that up to date have not been systematically investigated such as (i) environment and genetic dependent antioxidant levels, (ii) plant age at harvest, (iii) light during post-processing storage and (iv) duration and conditions of storage prior to processing. The factors under investigation are discussed in the light of their effects on the shelf-life of fresh-cut tissue as related to a number of physiological processes associated with tissue browning and senescence. We found that plant age at harvest and storage of the harvested crop prior to processing are important determinants of fresh-cut performance: the younger the plant and the shorter the storage period prior to processing, the longer the shelf life of the fresh-cut product. In addition, the application of low levels of light during storage and display of the fresh-cut product greatly prolonged the shelf-life. The physiological and biochemical background of these phenomena was investigated.</p
Signal transduction pathway(s) in guard cells after prolonged exposure to low vapour pressure deficit
No full textKeywords: Abscisic acid, Arabidopsis thaliana, calcium, CYP707As, desiccation, environmental factors, guard cells’ signalling pathway, hydrogen peroxide, natural variation, nitric oxide, photosystem II efficiency, RD29A, relative water content, secondary messengers, stomata, vapour pressure deficit, Vicia faba In short-term, guard cells close stomata in response to an increase in vapour pressure deficit (VPD) and they open the stomata after exposure to low VPDs. However, in long-term responses to low VPD, adaptation processes occur which make stomata less sensitive to stimuli which usually induce stomatal closure (stomatal malfunctioning). Cellular mechanism(s) leading to occurrence of stomatal malfunctioning is (are) still unknown. The aim of this project was to elucidate the processes that are involved in the malfunctioning of stomata after long-term exposure to low VPD. To elucidate whether the problem of stomatal malfunctioning is due to alterations in stomatal morphology and leaf anatomy or in the ABA signalling pathway, fava bean plants were grown at low or moderate VPDs and some plants that developed their leaves at moderate VPD were then transferred for four days to low VPD. Leaf anatomical and stomatal morphological alterations due to low VPD were not the main reason of stomatal malfunctioning in response to ABA and desiccation. Within one day exposure to low VPD, the level of foliar ABA decreased to the same level as in low VPD-grown plants, while the level of ABA-glucose ester was not affected. Spraying ABA during a 4-day exposure to low VPD maintained closing ability of the stomata after 4-day low VPD-exposure. Therefore, alteration in the signalling pathways due to low foliar ABA level was recognized as the main reason for stomatal malfunctioning after long-term low VPD-exposure. Coincidence in changes of Ca2+, ABA receptors, and positive and negative regulators of ABA signalling are proposed as early steps for stomatal malfunctioning induced by low VPD-exposure. Transcriptional activators, transcriptional repressors as well as E3 ligases are proposed for long-term adaptation of cellular processes which consequently cause decreased stomatal response to closing stimuli afterwards. In order to find the molecular mechanism(s) of stomatal malfunctioning, possible variation in stomatal response to closing stimuli was studied among Arabidopsis thaliana accessions after a 4-day low VPD-exposure. Accessions could be grouped to very sensitive, moderately sensitive and less sensitive to closing stimuli using principle component analysis. A positive correlation was found between foliar ABA level (before desiccation) and stomatal closure response to ABA (but not to desiccation) after exposure to different VPDs. Stomatal response to desiccation was positively correlated with the foliar ABA level after desiccation. In order to elucidate the molecular network underlying stomatal malfunctioning in response to ABA due to long-term low VPD-exposure, two groups of Arabidopsis accessions were used as accessions that maintained responsiveness to ABA after low VPD-exposure and accessions with low VPD induced non-ABA-responsive stomata. The foliar ABA content in all accessions correlated with the stomatal response to ABA: only when the ABA level was above a threshold value, stomata responded to ABA. After low VPD-exposure, mainly due to catabolism of ABA, the foliar ABA content decreased. This decrease in ABA level resulted in down regulation of RD29A, which caused decreased stomatal responsiveness to ABA. </p
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