Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Radical-Scavenging Compounds from Olive Tree (Olea europaea L.) wood
    Pérez-Bonilla, M. ; Salido, S. ; Beek, T.A. van; Altarejos, J. - \ 2014
    Journal of Agricultural and Food Chemistry 62 (2014)1. - ISSN 0021-8561 - p. 144 - 151.
    solid-phase extraction - antioxidant activity - phenolic-compounds - complex-mixtures - pruning biomass - potential uses - food-industry - plants - hplc - identification
    The purpose of this study was to complete knowledge on the chemical composition and radical-scavenging activity of olive tree wood. Two new monoterpene glycosides, (-)-oleuropeic acid 6'-O-a-d-glucopyranosyl ester (6a) and (-)-perillic acid 1'-O-ß-d-primeverosyl ester (8), together with the known compounds (-)-oleuropeic acid (1), (-)-olivil (2), the aldehydic form of oleuropein aglycone (3), (+)-1-hydroxypinoresinol 1-O-ß-d-glucopyranoside (4), (-)-oleuropeic acid 1'-O-ß-d-glucopyranosyl ester (5), (-)-oleuropeic acid 6'-O-ß-d-glucopyranosyl ester (6b), and (-)-olivil 4-O-ß-d-glucopyranoside (7) were isolated from an ethyl acetate extract. The radical scavengers found (2–4 and 7) were detected and isolated with the help of the online HPLC-DAD-DPPH/ABTS technique. Compounds 2–4 and 7 displayed a higher antioxidative effect against the free radical DPPH than the reference BHT and lower than hydroxytyrosol, whereas compounds 1, 5, 6a, 6b, and 8 showed no activity.
    Eggspectation: organic egg authentication method challenged with produce from ten different countries
    Ruth, S.M. van; Koot, A.H. ; Brouwer, S.E. ; Boivin, N. ; Carcea, M. ; Zerva, C.N. ; Haugen, J.E. ; Hohl, A. ; Koroglu, D. ; Mafra, I. ; Rom, S. - \ 2013
    Quality Assurance and Safety of Crops & Foods 5 (2013)1. - ISSN 1757-8361 - p. 7 - 14.
    laying hens - carotenoids - quantification - identification - zeaxanthin - lutein - hplc - yolk
    Many consumers are willing to pay a higher price for organic eggs. Since these eggs retail at a higher price than conventional eggs and their identity is difficult to verify, they are susceptible to fraud. For the authentication of Dutch eggs RIKILT developed an analytical test method based on carotenoid profiling. In the present study, the method was challenged with eggs from 10 countries. Eggs from 94 farms (65 organic, 29 conventional) were subjected to the carotenoid High Performance Liquid Chromatography Diode Array Detection profiling combined with k-nearest neighbour classification chemometrics to predict the farming management system category: organic or conventional. The eggs from 39 of the 40 EU organic farms and the eggs of 27 of the 29 EU conventional farms, as well as eggs from 17 of the 25 organic farms from outside the EU were classified correctly. The latter lower rate was mainly due to eggs from Turkey; 78% of which were misclassified. The methodology was successful in farming management prediction of the EU eggs, as well as for eggs from Canada, Israel and Norway. The identity of the eggs from Turkey was consistently incorrectly predicted and needs further research.
    UHPLC/PDA–ESI/MS Analysis of the Main Berry and Leaf Flavonol Glycosides from Different Carpathian Hippophaë rhamnoides L. Varieties
    Pop, R.M. ; Socaciu, C. ; Pintea, A. ; Buzoianu, A.D. ; Sanders, M.G. ; Gruppen, H. ; Vincken, J.P. - \ 2013
    Phytochemical Analysis 24 (2013)5. - ISSN 0958-0344 - p. 484 - 492.
    isotope dilution assay - sea buckthorn berries - mass-spectrometry - ms analysis - hplc - glycosylation - cultivars - stability - storage - juice
    Introduction - Sea buckthorn (Hippophaë rhamnoides L.) is known to be rich in many bioactive compounds (such as vitamins, phenolics, carotenoids) important for human health and nutrition. Among the phenolics, berries and leaves contain a wide range of flavonols that are good quality and authenticity biomarkers. Objective - To compare the composition of the main flavonols of Romanian sea buckthorn berry and leaf varieties and to identify the specific biomarkers that contribute to sample differentiation among varieties. Material and methods - Six varieties of cultivated sea buckthorn (ssp. Carpatica) berries and leaves were analysed by UHPLC/PDA–ESI/MS. Results - Berries and leaves contained mainly isorhamnetin (I) glycosides in different ratios. Whereas I-3-neohesperidoside, I-3-glucoside, I-3-rhamnosylglucoside, I-3-sophoroside-7-rhamnoside and free isorhamnetin were predominant for berries (out of 17 compounds identified), I-3-rhamnosylglucoside, I-3-neohesperidoside, I-3-glucoside, quercetin-3-pentoside, kaempferol-3-rutinoside, and quercetin-3-glucoside were predominant in leaves (out of 19 compounds identified). Berries contained, on average, 917¿mg/100¿g DW flavonol glycosides. Leaves had higher content of flavonol glycosides than berries, on average 1118¿mg/100¿g DW. The variation of the quantitative dataset analysed using principal component analysis accounted for 91% of the total variance in the case of berries and 73% in case of leaves, demonstrating a good discrimination among samples. Conclusion - Based on quantitative analysis, by principal component analysis, the flavonol derivatives can be considered as biomarkers to discriminate among varieties and to recognise specifically the berry versus leaf composition
    Pitfalls in the desulphation of glucosinolates in a high-throughput assay
    Hennig, K. ; Verkerk, R. ; Bonnema, A.B. ; Dekker, M. - \ 2012
    Food Chemistry 134 (2012)4. - ISSN 0308-8146 - p. 2355 - 2361.
    brassica-oleracea - broccoli - vegetables - breakdown - napus - hplc - food - ms
    Glucosinolates are phytochemicals with health promoting properties. Determination as desulpho-glucosinolates is widely used and adesulphation in microtiter plates has been applied to reach highthroughput. The use of various sulphatase concentrations and volumes throughout literature necessitates the identification of an appropriate desulphation procedure in microtiter plates. High sulphatase concentrations (¿15 mg/ml) decreased the concentration of the internal standard glucotropaeolin, whereas the other glucosinolates were less affected. Due to the calculation based on the recovery of glucotropaeolin, this leads to an overestimation of GL concentrations after desulphation with high sulphatase concentrations. A glucosidase side-activity, present in the crude sulphatase powder, is likely causing this phenomenon. At lower sulphatase concentrations (1 mg/ml) glucoiberin and glucoraphanin were insufficiently desulphated. Combining these effects results in a small range of applicable sulphatase concentrations. A purified sulphatase preparation resulted in good recoveries for a diversity of samples and is hence recommended for highthroughputdesulphation in microtiter plates.
    Animal feedingstuffs - determination of hydrocyanic acid by HPLC: results of the collaborative study : mandate 382 to CEN/TC 327
    Beek, W.M.J. ; Jong, J. de - \ 2011
    Wageningen : RIKILT (Report / RIKILT 2011.001) - 38
    waterstofcyanide - hplc - voer - analytische scheikunde - hydrogen cyanide - hplc - feeds - analytical chemistry
    Determination of pectin content of eucalyptus wood
    Coetzee, B. ; Schols, H.A. ; Wolfaardt, F. - \ 2011
    Holzforschung 65 (2011)3. - ISSN 0018-3830 - p. 327 - 331.
    quince chaenomeles-japonica - cell - polysaccharides - degradation - substances - responses - fruits - plants - hplc - wall
    Very little is known about the occurrence of pectin in wood and it is speculated that between 10 mg g-1 and 40 mg g-1 of wood consists of pectin. The present study aimed to quantify pectin in eucalyptus wood and to determine the influence of tree species, yield potential of the site, tree age class and wood tissue type on its occurrence. Wood was hydrolysed using the Saeman procedure and the neutral and acidic monosaccharides quantified with high-performance liquid chromatography (HPLC). The d-galacturonic acid was the predominant pectic monosaccharide followed by d-galactose, l-arabinose and l-rhamnose. Through the addition of all pectic monosaccharides, it was determined that eucalyptus wood contained between 15.2 mg g-1 and 25.8 mg g-1 pectin. Wood tissue type had a major influence on the total pectin content of the samples. The cambium contained the highest concentration of pectin, reflecting more active growth. These results contribute to the understanding of wood biochemistry and can be useful in the industries producing biofuels or paper.
    The concentration of trans-lycopene in postharvest watermelon: An evaluation of analytical data obtained by direct methods
    Dimitrovski, D. ; Bicanic, D.D. ; Luterotti, S. ; Twisk, C. van; Buijnsters, J.G. ; Doka, O. - \ 2010
    Postharvest Biology and Technology 58 (2010)1. - ISSN 0925-5214 - p. 21 - 28.
    tomato products - liquid-chromatography - prostate-cancer - beta-carotene - hplc - paste - vegetables - cultivars - accurate - humans
    The performance of the newly proposed laser-based optothermal window (OW) method and colorimetry for quantification of trans -lycopene in 10 watermelon homogenates has been evaluated. Reverse phase HPLC served as an established reference method. Both, OW and colorimetry are direct methods as they, contrary to the HPLC, obviate the need for extraction, which leaves homogenization of the sample as the only preparatory step prior to the analysis itself. The evaluation of analytical performance of each method leads to the conclusion that the OW method and colorimetry are both suitable for quick screening of the trans -lycopene concentration of red-fleshed watermelon homogenates. Linear correlation is highest ( R = 0.917) for the laser-based OW method. This detection concept offers an additional but very unique advantage. By virtue of the operational principle of the OW method, it is possible to avoid the effect of saturation, a phenomenon known to cause difficulties when interpreting data collected by other analytical methods
    Estimating rapidly and precisely the concentration of beta carotene in mango homogenates by measuring the amplitude of optothermal signals, values of chromaticity indices and the intensities of Raman peaks
    Bicanic, D.D. ; Dimitrovski, D. ; Luterotti, S. ; Tiwisk, C. van; Buijnsters, J.G. ; Doka, O. - \ 2010
    Food Chemistry 121 (2010)3. - ISSN 0308-8146 - p. 832 - 838.
    liquid-chromatography - lycopene - window - quantification - spectroscopy - vegetables - separation - fruits - hplc
    Rapid, quantitative information about the micronutrients (including beta carotene) in mango fruit is often desired. High performance liquid chromatography (HPLC) and spectrophotometry (SP), the two widely used methods in practice to quantify carotenoids, both require a time consuming and expensive extraction of a pigment prior to the analysis itself. This paper compares the performances of the three candidate methods for the assessment of beta carotene in twenty one different mango homogenates to that of the HPLC as an established standard technique. The extraction is imperative in neither of the methods: the laser based optothermal window (OW), the resonance Raman spectroscopy and the tristimulus colorimetry. For the quantitative analysis however the availability of the calibration curve is a necessity. All candidate methods and in particular OW technique (compact instrument, low cost and the ease of operation) hold promise for a rapid screening/quantitative assessment of beta carotene in mango fruit
    Evaluation of size exclusion chromatography (SEC) for the characterization of extracellular polymeric substances (EPS) in anaerobic granular sludges
    Simon, S. ; Pairo, B. ; Villain, M. ; Abzac, P. D'; Hullebusch, E. ; Lens, P.N.L. ; Guibaud, G. - \ 2009
    Bioresource Technology 100 (2009)24. - ISSN 0960-8524 - p. 6258 - 6268.
    activated-sludge - extraction methods - part i - exopolymers - biofilms - polysaccharides - complexation - separation - protocols - hplc
    The extracellular polymeric substances (EPS) extracted from three granular and one flocculant anaerobic sludges were characterised by size exclusion chromatography (SEC) using two serially linked chromatographic columns in order to obtain more detailed chromatograms. A Superdex peptide 10/300 GL (0.1-7 kDa) and Superdex 20010/300GL (10-600 kDa) from Amersham Biosciences were used in series with a mobile phase at pH 7 with an ionic strength of 0.223 M (phosphate buffer 50 mM and NaCl 150 mM). A part of the EPS molecules displays hydrophobic and/or ionic interactions with the column packing. Interactions could be modified by changing the mobile phase ionic strength or polarity (addition of acetonitrile). The detection wavelength (210 or 280 nm) affects strongly the EPS chromatogram. For a sludge originating from the same type of biofilms (i.e., anaerobic granules), the differences in EPS fingerprints are mainly due to differences in the absorbance of the chromatographic peaks, linked to EPS molecules content and composition. The EPS fingerprint changes significantly when the EPS originate from another type of anaerobic sludges. In addition, EPS fingerprints were affected by the extraction method used (centrifugation only; heat and centrifugation or cationic exchange resin and centrifugation). This phenomenon was observed mainly for the largest and smallest molecules and molecules which display interactions with column packing.
    C22 Isomerization in a-Tomatine-to-Esculeoside A Conversion during Tomato Ripening Is Driven by C27 Hydroxylation of Triterpenoidal Sekeleton
    Yamanaka, T. ; Vincken, J.P. ; Zuilhof, H. ; Legger, A. ; Takada, N. ; Gruppen, H. - \ 2009
    Journal of Agricultural and Food Chemistry 57 (2009)9. - ISSN 0021-8561 - p. 3786 - 3791.
    steroidal alkaloid glycosides - pulsed amperometric detection - lycopersicon-esculentum - fruits - plant - dehydrotomatine - glycoalkaloids - performance - maturation - hplc
    Compositional analysis by liquid chromatography/mass spectrometry of triterpenoid glycosides in different tomato cultivars, ripening stages, and parts of fruits showed that alpha-tomatine was generally most abundant in the flesh of the mature green stage, whereas esculeoside A was predominant in that of the red ripe stage. The sum of these glycoalkaloids was more or less constant, suggesting that alpha-tomatine is converted to esculeoside A during ripening. Besides various substitutions, the C22alphaN -> C22ßN isomerization is an important step in this transformation. By quantum chemical calculations it was shown that hydroxylation at C27 of the triterpenoidal skeleton is the driving force behind the isomerization. For the protonated form of the glycoalkaloid (predominant at the pH of tomato tissue), the C22ßN configuration becomes more favorable than that of C22alphaN, through the extra energy provided by the hydrogen bond between the protonated nitrogen and the lone pair of the oxygen of the C27-OH
    Microfluidic devices for sample clean-up and screening of biological samples
    Tetala, K.K.R. - \ 2009
    Wageningen University. Promotor(en): Ernst Sudhölter, co-promotor(en): Teris van Beek. - [S.l. : S.n. - ISBN 9789085852896 - 123
    monstervoorbehandeling - hplc - analytische methoden - microanalyse - sample pretreatment - hplc - analytical methods - microanalysis
    Analytical chemistry plays an important role in the separation and identification of analytes from raw samples (e.g. plant extracts, blood), but the whole analytical process is tedious, difficult to automate and time consuming. To overcome these drawbacks, the concept of μTAS (miniaturized total analysis systems) was proposed by researchers in the early 90’s. The research described in this thesis, aimed towards the development of a microfluidic device that can be used for sample clean-up and screening of biological samples. Both solid phase extraction and liquid-liquid phase extraction have been investigated.

    The aim in chapter 2 to chapter 5 is to develop a microfluidic device that can selectively adsorb products from a process stream (plant extracts and serum samples) through molecular interactions. To realize this, first a protocol for carbohydrate immobilization on glass surfaces was developed and later the developed protocol was employed to prepare carbohydrate modified capillary columns to study specific carbohydrate-lectin interactions. However, due to low column capacity, the carbohydrate capillary columns are not efficient to bind lectins. To improve the column capacity, monoliths, a new generation of stationary phases, were chosen for carbohydrate immobilization. Two protocols were developed (a three-step protocol and a single step protocol). The advantage of the single step protocol is the lower amount of time needed to prepare an affinity monolithic column. The carbohydrate monolithic columns efficiently captured lectins (α-mannose column captured Concanavalin A and Lens culinaris, β-galactose column captured Arachis hypogaea), and antibodies (GM1 and GM2 columns specifically captured IgM antibodies) from serum samples of patients suffering from Guillain-Barré syndrome (GBS). These columns can also be used to study the dissociation constants (Kd) of carbohydrate-lectin interactions. The carbohydrate monolith prepared in a microchip gave identical results as the carbohydrate monolith in a capillary. The initial attempt to prepare a carbohydrate monolithic array microfluidic chip was successful. However, the fluid flow in the two channels varied due to the difference in permeability of the two affinity columns. Further fine tuning of the permeability of the two columns is necessary to use this array microfluidic chip for screening of analytes.

    The aim in chapter 6 is develop a three-phase microfluidic chip (liquid-liquid extraction) for efficient sample clean-up and screening of acidic or basic molecules in aqueous solution. The extraction of strychnine was studied using a two-phase microchip, followed by “simultaneous extraction and back extraction” of strychnine using a three-phase microchip. Maximum extraction of strychnine was achieved at longer residence times i.e. lower flow rates. A good correlation between experimental results and model data was found for both two-phase and three-phase microchips. Sample clean-up of a Strychnos seed extract was successful with the three-phase microchip. The developed model can be used to predict the extraction outcome by changing various parameters e.g. chip design, partition coefficient, and viscosity. On-line screening of strychnine was demonstrated by interfacing the two-phase microchip with nanospray ESI-MS. The initial interfacing of a three-phase microchip with nanospray ESI-MS led to the disturbance of the phase separation in the chip due to pressure differences in the three channels. Fine tuning of the interface connections between microchip and MS could enhance the chance of using this three-phase microchip for on-line screening of plant extracts.

    Comparison of atmospheric pressure chemical ionization and electrospray ionization mass spectrometry for the detection of lignans from sesame seeds
    Struijs, K. ; Vincken, J.P. ; Gruppen, H. - \ 2008
    Rapid Communications in Mass Spectrometry 22 (2008)22. - ISSN 0951-4198 - p. 3615 - 3623.
    isoflavones - oil - quantification - identification - macromolecule - glucosides - precursors - indicum - hplc
    In sesame seeds, high concentrations of lignans are present. When these lignans are fermented in the human colon, a range of structurally different lignans is formed. A good liquid chromatography/mass spectrometry (LC/MS) protocol for the analysis of lignans in complex mixtures is lacking. In order to develop such a protocol, electrospray ionization (ESI)-MS and atmospheric pressure chemical ionization (APCI)-MS, both in the positive and negative ionization mode, were compared. An extract from defatted sesame meal was analyzed by APCI-MS and ESI-MS, before and after deglucosylation. APCI-MS was found to be a more generic method than ESI-MS because lignans, especially sesamolin, sesamin and pinoresinol, were better detected by APCI-MS than by ESI-MS. Positive and negative ionization modes had to be combined in order to detect all lignans in a bacterial culture grown on aglyconic, acid-treated lignans from sesame oil and defatted sesame meal. Lignans with methylenedioxy-bridged furanofuran structures mostly lack phenolic hydroxyl groups and were, therefore, optimally detected in positive ionization mode. Dibenzylbutadiene lignans, which were formed during fermentation, carry hydroxyl groups and were better detected in negative ionization mode.
    Quality control of Chinese herbal tonic wine by high performance liquid chromatography fingerprint
    Wei, X.J. ; Zhang, H. ; Wang, W.F. ; Li, B. ; Yang Zhu, Yang - \ 2007
    Agro Food Industry Hi-Tech 18 (2007)5. - ISSN 1722-6996 - p. 39 - 40.
    hplc - medicines - food
    Herbal tonic wines are alcoholic drinks in which medicinal herbs are soaked and extracted. These drinks are considered having various health functions. However, the quality of herbal products is largely influenced by the origin and harvest season of the herbs. Due to its high commercial value, counterfeit often happens. We used high performance liquid chromatography to establish a fingerprint chromatogram of a Chinese herbal tonic wine for its quality control. Samples of 10 different production batches were analyzed to calculate the relative retention time a and the relative peak area A(r) Eight peaks with common characteristics were identified and used to evaluate the existence of main representative components. The results show that the method was convenient and applicable for the quality control of Chinese herbal tonic wine, in particular to monitor quality consistency and to detect counterfeit products.
    New methods for the screening of antioxidants in three Sideritis species
    Koleva, I. - \ 2007
    Wageningen University. Promotor(en): Aede de Groot, co-promotor(en): Teris van Beek; Jozef Linssen. - [S.l.] : S.n. - ISBN 9789085046851 - 197
    antioxidanten - sideritis - chemische samenstelling - hplc - gaschromatografie - analytische scheikunde - antioxidants - sideritis - chemical composition - hplc - gas chromatography - analytical chemistry
    This thesis describes the rapid and robust evaluation of antioxidant activity of complex mixtures such as plant extracts. The study was directed to establish the best screening and isolation procedures for components with antioxidative properties to ensure the development of an “algorithm” for studying natural antioxidants. Three different screening methods (the b-carotene bleaching test (BCBT), the headspace GC method (HS-GC) and the off-line radical scavenging assay with the DPPH radical (DPPH method) and various extraction schemes were used. Three plants from the genus Sideritis grown in Bulgaria (S. scardica, S. syriaca and S. montana) served as test species. The strengths and limitations of each method were illustrated by testing a number of extracts of different polarity. A novel HPLC-DPPH method to rapidly and sensitively pinpoint individual antioxidants in complex mixtures with as little as possible fractionation procedures was developed. The use of the alternative ABTS·+ radical cation made the method in most cases even more sensitive. The instrumental set-up and physico-chemical parameters of both methods were studied. The methods were successful for qualitative and semi-quantitative measurements of pure antioxidants and extracts. A review is under preparation on the use of on-line methods. As a result, a range of flavonoid-, phenylpropanoid- and iridoid glycosides were isolated. The radical scavenging activity of the isolated compounds by off- and on-line DPPH methods was studied. Three novel compounds were isolated: flavonoid glycosides luteolin-4'-methylether-7-O-[6'''-O-acetyl-β-D-allopyranosyl-(1-2)-β-D-glucopyranoside and hypolaetin-4'-methylether-7-O-[β-D-allopyranosyl-(1-2)-6''-O-acetyl-β-D-glucopyranoside, and iridoid glycoside 3''-O-p-coumaroyl-6''-O-acetyl melittoside from Sideritis species. Preliminary studies by the HS-GC method were applied to investigate how Sideritis extracts and pure components would behave in real systems: bulk oils and oil-in-water emulsions. Conjugated dienes and hexanal formation were monitored using rosmarinic acid and BHT as standards. They showed good inhibitory effects with regard to dienes and hexanal formation in both test systems.
    The derivatisation of avermectins and milbemycins in milk: new insights and improvements of the procedure
    Berendsen, B.J.A. ; Mulder, P.P.J. ; Rhijn, J.A. van - \ 2007
    Analytica Chimica Acta 585 (2007)1. - ISSN 0003-2670 - p. 126 - 133.
    fluorescence detection - liquid-chromatography - moxidectin residues - mass-spectrometry - liver - eprinomectin - ivermectin - doramectin - abamectin - hplc
    Derivatisation of the avermectines ivermectin (IVM), doramectin (DOR), abamectin (ABA) and eprinomectin (EPR), and the milbemycin moxidectin (MOX) to fluorescent derivatives is commonly used for quantitative analysis at relevant levels using high performance liquid chromatography (HPLC) with fluorescence detection. Problems associated with the differences in reactivity towards derivatisation (EPM) and limited stability of the derived products (IVM, DOR, ABA) may seriously hamper the applicability of the method and the reliability of the obtained results. A study was performed to obtain more insight in this derivatisation process from an organic chemistry point of view. This study demonstrated the occurrence of two main fluorescent derivatives: the trifluoroacetyl esters (flu-TFA) and the derivatives with a free hydroxy group at the glycosidic ring (flu-OH). Optimisation of the derivatisation conditions resulted in a fast and reproducible formation of the fluorescent derivatives for all analytes including EPM. The improved procedure involves the addition of 1-methylimidazole (MI), trifluoroacetic anhydride (TFAA), triethylamine (TEA) and trifluoroacetic acid (TFA) with a subsequent incubation for 30 min at 70 °C. With this procedure for IVM, DOR and ABA flu-TFA derivatives are obtained instead of flu-OH derivatives as generally described in literature. The derivatisation is reproducible in different milk samples and the derivatives proved to be stable for at least 80 h at room temperature. Using the optimised procedure a limit of detection (LoD) of 0.1 ¿g kg¿1 in milk was readily obtained.
    Quantification of lycopene in tomato products: comparing the performances of a newly proposed direct photothermal method and high-performance liquid chromatography
    Bicanic, D.D. ; Fogliano, V. ; Luterotti, S. ; Swarts, J.J. ; Piani, G. ; Graziani, G. - \ 2005
    Journal of the Science of Food and Agriculture 85 (2005)7. - ISSN 0022-5142 - p. 1149 - 1153.
    carotenoid content - cancer - paste - vegetables - accurate - systems - fruits - hplc
    A new photothermal method suitable for direct, accurate and highly reproducible quantitative measurements of lycopene in tomato products has been introduced. The intrinsic precision of the method is typically better than 0.2%; the repeatability of determination is comparable to that of high-performance liquid chromatography, with 0.86% least overall error.
    Direct quantification of lycopene in products derived from thermally processed tomatoes: optothermal window as selective, sensitive and accurate method without the need for preparatory steps
    Bicanic, D.D. ; Swarts, J.W. ; Luterotti, S. ; Pietrapierza, G. ; Doka, O. ; Rooij, H. de - \ 2004
    Analytical Chemistry 76 (2004)17. - ISSN 0003-2700 - p. 5203 - 5207.
    beta-carotene - cancer - paste - food - chromatography - vegetables - plasma - fruits - hplc
    The concept of the optothermal window (OW) is proposed as a reliable analytical tool to rapidly determine the concentration of lycopene in a large variety of commercial tomato products in an extremely simple way (the determination is achieved without the need for pretreatment of the sample). The OW is a relative technique as the information is deduced from the calibration curve that relates the OW data (i.e., the product of the absorption coefficient ß and the thermal diffusion length µ) with the lycopene concentration obtained from spectrophotometric measurements. The accuracy of the method has been ascertained with a high correlation coefficient (R = 0.98) between the OW data and results acquired from the same samples by means of the conventional extraction spectrophotometric method. The intrinsic precision of the OW method is quite high (better than 1%), whereas the repeatability of the determination (RSD = 0.4-9.5%, n = 3-10) is comparable to that of spectrophotometry.
    Isolation and Identification of Kairomone(s) in the Daphnia-Scenedesmus System
    Holthoon, F.L. van - \ 2004
    Wageningen University. Promotor(en): Aede de Groot, co-promotor(en): Teris van Beek; E. van Donk. - Wageningen : S.n. - ISBN 9789085040668 - 154
    daphnia - predator prooi verhoudingen - waarschuwingsferomonen - isolatietechnieken - chemische structuur - fractionering - hplc - kernmagnetische resonantiespectroscopie - daphnia - predator prey relationships - alarm pheromones - isolation techniques - chemical structure - fractionation - hplc - nuclear magnetic resonance spectroscopy
    Infochemicals play an important role in interactions between living organisms in aquatic environments. Although the presence of these chemical cues is confirmed in more and more systems, the chemical structures of the compounds involved remain predominantly elusive and the identification of these compounds is essential to advance the research on chemical communication. An overview of chemical cues involving Daphnia (either as producer or receiver) is given and the progress towards their isolation and structure elucidation is described (Chapter 1). Most of the research so far has concentrated on the elucidation of kairomones produced by predators of Daphnia (especially Chaoborus and several species of fish). Less study has been devoted to the isolation of the infochemical exuded by Daphnia that causes colony formation in its prey Scenedesmus. One of the main aims of this study was the isolation and identification of this chemical cue. Colony formation in Scenedesmus only occurs when unicellular populations are exposed to either Daphnia or water that had contained Daphnia. It was concluded that the responsible cue had a chemical rather than a mechanical nature, since filtered Daphnia water also showed the colony formation activity. This colony formation was the basis for the development of a bioassay (Chapter 2). A bioassay is a test that is used to measure biological activity (in this case colony formation) of chemical mixtures or biological parameters. Colonies are indicated by high values and single cells are indicated by low values. Unfortunately over time a gradual decline of the difference between negative and positive controls was observed and efforts were undertaken to determine the cause for this decline. Several conditions were investigated (such as time, temperature, algae strain, culture medium, location, incubator, Erlenmeyer size, bacterial growth and microevolution). Additionally some general properties of the kairomone (such as thermal decomposition, biodegradation and concentration) were tested. A correlation between any of the above mentioned factors and the gradual decline of the difference between negative and positive controls was not found. Given that the bioassay was performed under such highly variable and not strictly controlled circumstances, this particular bioassay seems to be rather robust. However this does not defer from the fact that the quality of the bioassay did decline over time. Until the variable is identified that is responsible for the observed decline in difference between positive and negative controls, more care should be taken to standardise as many variables as possible. Despite its drawbacks, a bioassay still remains the best option to guide isolations of bioactive compounds through controlled experiments as long as observed differences are statistically significant. To find the most suitable and practical method for the analysis of Daphnia test water several sample pre-treatment methods were compared (Chapter 3), such as liquid-liquid extraction, solid-phase extraction, stir-bar sorptive extraction, solid-phase disk extraction. A test mixture with ten known natural compounds differing in polarity (log K o/w between -4.34 and 3.70) was used. The best method for small amounts of sample was either 'stirred' SPE or 'cartridge' SPE, but for large amounts of sample (sometimes up to 20 L) 'syringe' SPE was more suited. Consequently an SPE analysis protocol was developed that could elute the active compound in one fraction (Chapter 4). The experiments were performed with different concentrations of organic solvents and different sorbents (endcapped C 18 , MF C 18 , non-endcapped C 18 , C 8 , C 2, CN, ENV + and Oasis ® HLB). Endcapped C 18 was eventually chosen for further experiments (other sorbents did not perform better) and extracted with differing concentrations of methanol in water (50%, 85%) and pure methanol (100%). The chemical cue was most often recovered from the 85% aqueous methanol fraction, which indicates the cue is moderately non-polar.Biological activity was lost when active Daphnia water was partitioned at pH 12.0 against ethyl acetate. The aqueous and organic layer were both inactive, either by inactivation of the kairomone by the basic conditions in the aqueous layer or possibly more than one compound is present with synergistic effects. At lower pH (2.0 and 7.0) biological activity was recovered from the organic layer. This could be an indication that the active compound contains an anionic group. Experiments performed with ion exchange materials (SAX, SCX and Amberlite IRA-400) focused initially on the anion exchanger (SAX). However colony formation activity was recovered from the unretained fraction in contrast to what had been reported previously. This unexpected result prompted extraction with a cation exchanger (SCX). To exclude problems related to pH sensitive silica based sorbents, experiments were repeated on a resin based sorbent (Amberlite IRA-400),however a similar result was obtained as with the SAX sorbent. No satisfying explanation was found for the presence of biological activity in the unretained fractions and absence from the retained fractions, but different counterions on the ion exchangers could play a role. The enriched extracts obtained by SPE (C 18 ) were fractionated by high performance liquid chromatography. One fraction showed a significantly higher biological activity relative to the control ('Fraction C'). Further fractionation yielded three active fractions (C2, C3,C6). This could be an indication that more than one compound is responsible for the activity. Several natural products were biologically inactive when screened in the bioassay. They were, ecdysterone and juvenile hormone III (important hormones in other Crustaceae ), urea (proposed as kairomone in Daphnia - Scenedesmus system ), and geranic acid (reference compound). Although an assumption was made to ignore possible synergistic or additive effects in these experiments, the possibility of synergism or additivity should not be ignored, given that most likely more than one active fraction is present. At this point, due to the lack of reproducible and significant results from bioassay-guided separations, another way to identify possible candidates for the role of kairomone had to be used. Daphnia and control water were first extracted using SPE and then analysed with chromatographic techniques. Chromatograms of biologically active extracts were then compared with chromatograms of non-active control extracts to determine and recognise unique peaks (i.e. peaks only present in active Daphnia test water extracts). In an attempt to maximise the available data on the unknown colony inducing compound(s) several techniques were applied simultaneously, such as gas and liquid chromatography (Chapter 5). Several small unique peaks were recognised in the silylated extracts of Daphnia test water with GC-MS analysis. Some of these were tentatively identified as dodecanol, azelaic acid, sebacic acid and veratroylformic acid, but they did not induce colonisation. HPLC detection was performed not only with ultraviolet spectroscopy but also with evaporative light scattering and by electrospray ionisation-mass spectrometry to avoid overlooking compounds without a UV chromophore. LC analysis on four columns with different packings ensured that peaks were well separated on at least one column. Chromatograms with the best resolution were obtained on a C 18 column with an ACN-H 2 Ogradient and UV detection. High noise levels reduced the usefulness of ELS detection. Several peaks unique to 90% aqueous MeOH extracts of Daphnia test water were detected, but unfortunately not identified. Some of the recognised unique peaks ( B, G,K ) eluted in previously identified active regions ('Fraction C'). Especially peak B ([M-H] ¯ = 752.8 ?,lmax227 nm) was present in high amounts and well separated from neighbouring peaks. Therefore this peak was further analysed by liquid chromatography-nuclear magnetic resonance. Peaks from several extracts were trapped onto one SPE cartridge. This way a sufficient amount of analyte could be transferred into the NMR probe to allow recording of a 1-dimensional 1 H-spectrum. Unfortunately the spectrum did not lead to elucidation of the structure of peak B . One aliquot of this collected fraction was therefore analysed by high-resolution mass spectrometry and liquid-chromatography-quadrupole time-of-flight mass-spectrometry to obtain an accurate mass, while another aliquot was checked for biological activity in a bioassay. Unfortunately analysis with HRMS was unsuccessful and analysis with LC-QTOF has not yet yielded results. The peak with a possible pseudo molecular mass of 752.8 ([M-H] ¯) could not be detected. The other aliquot that was tested for biological activity in the bioassay showed significant differences between the negative control, positive control and peak B . This peak could therefore play a role in the induction of colonies in Scenedesmus , although it is still unclear whether it acts alone. Should peak B prove to be (partly) responsible for colony formation in Scenedesmus then the most important objective of this study has been partly reached, namely the isolation of kairomone(s) in the Daphnia - Scenedesmus system. This information will enable and facilitate research into the other objectives.
    Analytical procedure for the in-vial derivatization-extraction of phenolic acids and flavonoids in methanolic and aqueous plant extracts followed by gas chromatography with mass selective detection.
    Fiamegos, Y.C. ; Nanos, C.G. ; Vervoort, J.J.M. ; Stalikas, C.D. - \ 2004
    Journal of Chromatography. A, Including electrophoresis and other separation methods 1041 (2004)1-2. - ISSN 0021-9673 - p. 11 - 18.
    performance liquid-chromatography - solid-phase extraction - antioxidant activity - caffeic acid - diode-array - identification - spectrometry - hplc - l. - validation
    An in-vial simple method for the combined derivatization and extraction of phenolic acids and flavonoids from plant extracts and their direct determination with GC-MS, is described. The method is taking advantage of the beneficial potentials of phase transfer catalysis (PTC). Catalysts in soluble and polymer-bound form were tested with the latter being the format of choice due to its high reaction yield and facile separation from the rest of the reaction system. Optimization of experimental conditions was established. Chromatographic separation of eight phenolic acids and four flavonoids methylated via the PTC derivatization step was achieved in 45 min. The detection limits for the described GC-MS(SIM) method of analysis ranged between 2 and 40ng/ml whereas limits of quantitation fall in the range 5-118 ng/ml, with flavonoids accounting for the lowest sensitivity due to their multiple reaction behavior. Four methanolic extracts from Tilia europea, Urtica dioica, Mentha spicata and Hypericumperforatum grown wild in north-westem Greece and four aquatic infusions from commercially available Mentha spicata, Origanum dictamnus, Rosemarinus officinalis and Sideritis cretica were analyzed. Good trueness of the method was demonstrated as no matrix effects were found for the analytes concerned. (C) 2004 Elsevier B.V. All rights reserved.
    CANFAS : 2nd collaborative study for the determination of olaquindox in feedingstuffs by HPLC
    Driessen, J.J.M. ; Tomassen, M.J.H. ; Jong, J. de - \ 2002
    Wageningen : State Institute for Quality Control of Agricultural Products (RIKILT) (Report / RIKILT 2002.005) - 18
    hplc - olaquindox - voer - onderzoeksprojecten - europese unie - hplc - olaquindox - feeds - research projects - european union
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