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.

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Recent developments in the rapid analysis of plants and tracking their bioactive constituents
Beek, T.A. van; Tetala, K.K.R. ; Koleva, I. ; Dapkevicius, A. ; Exarchou, V. ; Jeurissen, S.M.F. ; Claassen, F.W. ; Klift, E.J.C. van der - \ 2009
Phytochemistry Reviews 8 (2009)2. - ISSN 1568-7767 - p. 387 - 399.
desorption electrospray-ionization - performance liquid-chromatography - 2-dimensional gas-chromatography - mass-spectrometric detection - radical scavenging compounds - nuclear-magnetic-resonance - thin-layer-chromatography - natural-products - biochemical detec
Natural products chemistry has witnessed many new developments in the last 5 years like extractions with subcritical water and ionic liquids, LC/HRMS and LC/SPE/cryo-NMR, UHPLC, TLC/MS, MS-based preparative HPLC, comprehensive chromatography (GC × GC, LC × LC), high-throughput screening, introduction of monolithic columns, miniaturisation, and automated structure identification. Nevertheless identifying bioactive constituents in complex plant extracts remains a tedious process. The classical approach of bioassay guided fractionation is time-consuming while off-line screening of extracts does not provide information on individual compounds and sometimes suffers from false positives or negatives. One way out of this is by coupling chromatography with chemical or biochemical assays, so called high resolution screening. An example is the development of HPLC on-line assays for antioxidants. By the post-column addition of a relatively stable coloured radical like DPPH¿ or ABTS¿+, radical scavengers are detected as negative peaks because in a reaction coil they reduce the model radical to its reduced, non-coloured form. When combined with LC/DAD/MS and LC/SPE/NMR, reliable identification of active constituents becomes possible without the necessity of ever isolating them in a classical sense. Also for finding leads for new drugs, combining HPLC with biochemical assays is interesting but technically more difficult. Most enzymes do not work at the organic modifier concentrations commonly encountered in RP-HPLC and the reaction time is often longer requiring dilution and lengthy coils respectively. Therefore, new techniques have to be implemented to gain the required sensitivity for on-line enzyme assays. For stable analytes, high temperature LC offers a solution to the organic modifier problem. When enzymes are highly expensive, like those used in the screening for Cytochrome P450 inhibitors, miniaturisation to chip format may offer a way out. Microreactors (chips) are not only useful for miniaturising larger assays but also offer completely new prospects in phytochemical analysis. One such application is in the sample clean-up of acids and bases like alkaloids. In a lay-out of three parallel channels of 100 ¿m width with the middle one containing organic phase and the two outer ones water of high pH (feed phase) and low pH (trapping phase) such a chip replaces two classical LLE steps but is much faster and requires less solvents and less manpower input.
Preservation of blue-jack mackerel (Trachurus picturatus Bowdich) silage by chemical and fermentative acidification
Enes Dapkevicius, M.L.N. ; Nout, M.J.R. ; Rombouts, F.M. ; Houben, J.H. - \ 2007
Journal of Food Processing and Preservation 31 (2007)4. - ISSN 0145-8892 - p. 454 - 468.
lactic-acid bacteria - rainbow-trout - fish silage - products - glucose - viscera - offal
We compared acidified and lactic acid fermented silage approaches for the preservation of blue-jack mackerel. Silages acidified with formic and propionic acids had stable pH (3.8) and low (19 mg/g N) levels of volatile nitrogen compounds (total volatile basic nitrogen, TVBN), but relatively high (82 g/100 g) final non-protein-nitrogen (NPN) values. The silage was fermented with Lactobacillus plantarum LU853, a homofermentative lactic acid bacterium with a high growth (0.51/h) and acidification rate at 37C (optimum temperature), able to grow in the presence of 40 g/L NaCl and to ferment sucrose and lactose. The silages at 37C reached safe pH <4.5 values within 48¿72 h, either (F2a) or not (F0), in combination with 20 g/kg salt addition; F2a acidified more rapidly, which may be an advantage for its microbiological stability. Proteolysis resulting in 53¿59 g NPN/100 g N was lower in fermented than in acidified silages; however, in fermented silages, the levels of TVBN were much higher (50¿80 mg TVBN/g N) than generally considered acceptable.
Isolation and Structure Elucidation of Radical Scavengers from Thymus vulgaris Leaves
Dapkevicius, A. ; Beek, T.A. van; Lelyveld, G.P. ; Veldhuizen, A. van; Groot, Æ. de; Linssen, J.P.H. ; Venskutonis, R. - \ 2002
Journal of Natural Products 65 (2002)6. - ISSN 0163-3864 - p. 892 - 896.
lithospermum-ruderale - antioxidant activity - polyphenolic acids - carvacrol - extracts - mixtures - herbs
2,2-Diphenyl-1-picrylhydrazyl radical (DPPH*) scavenging activity-guided fractionation of a leaf extract of Thymus vulgaris led to the isolation of the radical scavengers rosmarinic acid 1, eriodictyol, taxifolin, luteolin 7-glucuronide, p-cymene 2,3-diol, p-cymene 2,3-diol 6-6'-dimer, carvacrol, thymol, and a new compound, 2. The fractionation was considerably facilitated by using an on-line HPLC detector for radical scavenging activity. In this detector activity is monitored as the disappearance of the color of a postcolumn added stable radical after reacting with radical scavengers in a reaction coil. Compound 2, which consists of rosmarinic and caffeic acid moieties linked via a C-3'-C-8" ether bridge, was mainly elucidated by various NMR techniques and CD. Phenylpropanoid trimer 2 was a weaker and stronger radical scavenger than rosmarinic acid 1 in off-line TEAC and DPPH. assays, respectively.
Biological ensilage of fish : optimization of stability, safety and functionality
Enes Dapkevicius, M.L.N. - \ 2002
Wageningen University. Promotor(en): F.M. Rombouts; M.J.R. Nout; J.H. Houben. - S.l. : [s.n.] - ISBN 9789058085702 - 170
voedselmicrobiologie - kuilvoerbereiding - micromestistius poutassou - trachurus - scomber scombrus - biogene aminen - lipiden - eiwitafbraak - food microbiology - silage making - micromestistius poutassou - trachurus - scomber scombrus - biogenic amines - lipids - protein degradation
This thesis deals with stability, safety, and functionality aspects of biological fish silage (BFS) obtained by lactic acid fermentation. BFS may provide an economically viable, environment friendly way of upgrading fish waste.

BFS has been found advantageous when compared to the so-called acid process, since it yielded lower levels of peroxides in the silage oil and led to lower non-protein nitrogen values. Fermentation by lactic acid bacteria (LAB) was shown to efficiently inhibit pathogens such as L. monocytogenes and E. coli O157:H7 as well as some spoilage microorganisms. Histamine degradation by some of the most promising available LAB strains was also tested, as an innovative means of ensuring low levels of this amine in the fermented product. Several potential starter strains were found to degrade histamine as single strain cultures and could find application in fish silage and other fish products in which histamine accumulation might pose a certain risk.

Temperatures of 35 - 37°C were regarded as most suitable from the point of view of starter growth and acidification. Strains with a short acidification lag time, such as Lb. plantarum 009, or with very fast growth and good antibacterial properties, such as Lb. curvatus 15.35, are most suitable.

Sodium chloride inhibited growth of biogenic amine producing bacteria and additionally decreased non-protein nitrogen and total volatile basic nitrogen values in BFS. Potassium sorbate was shown to inhibit growth and/or acidification by potential starter lactic acid bacteria.

Isolation, identification and evaluation of natural antioxidants from aromatic herbs cultivated in Lithuania
Dapkevicius, A. - \ 2002
Wageningen University. Promotor(en): Æ. de Groot; T.A. van Beek; J.P.H. Linssen. - S.l. : S.n. - ISBN 9789058085788 - 154
antioxidanten - keukenkruiden - thymus vulgaris - lipidenperoxidatie - spectroscopie - hplc - antioxidants - culinary herbs - thymus vulgaris - lipid peroxidation - spectroscopy - hplc
Oxidative spoilage of lipid-rich foods decreases their shelf-life and leads to undesirable chemical and physical changes. Nowadays natural antioxidants are generally preferred. The major part of industrially used antioxidants consists of radical scavengers, which inhibit the oxidative chain reaction by inactivating free radicals formed during peroxidation of lipids. Aromatic and medicinal herbs are rich sources of natural radical scavenging compounds. The research described in this thesis focuses on the evaluation of several aromatic plants grown in Lithuania as a possible source of food antioxidants. Various aspects of lipid oxidation, of antioxidative mechanisms and of natural sources of radical scavenging antioxidants are outlined in Chapter 1.

Employment of model systems for antioxidant studies is often preferred over lipid stability tests due to their speed and the simplified comparison and interpretation of the obtained results. Preliminary screening of extracts from aromatic plants was carried out using theβ-carotene-linoleic acid model system (β-CLAMS). The method is based on a competition between the plant antioxidant and an oxidisable indicator (β-carotene) for free radicals, which are generated during temperature-accelerated oxidation of linoleic acid. The agar-diffusion and spectrophotometricβ-CLAMS tests singled out thyme ( Thymus vulgaris L.) and sage ( Salvia officinalis L.) as the most promising sources of natural antioxidant compounds (Chapter 2). The screening results also revealed that supercritical fluid extraction (SFE) as well as solvent extraction with acetone and methanol-water were the two most efficient techniques for isolation of antioxidant constituents from sage and thyme (Chapter 2). In further antioxidant activity tests, the spectrophotometricβ-CLAMS technique was adapted to microtiter plates, which gave a better reproducibility and a shorter analysis time. The modified and improved spectrophotometricβ-CLAMS confirmed the preliminary screening results. Sage and thyme acetone extracts again demonstrated the highest radical scavenging activity with relative antioxidant activities similar to those of 2,6-di- tert -butyl-4-methylphenol (BHT) (Chapter 3).

The activity of primary antioxidants can be evaluated directly by monitoring the reduction of free radicals. Such experiments can be carried out off-line, i.e. by the introduction of previously isolated antioxidant compound(s) into an equilibrated free radical containing model system, or on-line, by adding a solution of a free radical to the eluate of an HPLC column. The on-line techniques allow for a rapid and selective detection of radical scavenging substances in the presence of many inactive constituents with a minimum of preparatory manipulations. Two on-line model systems based on the reduction of radical intermediates of the luminol chemiluminescence (CL) reaction and on the reduction of the stable 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH·) were used for the detection of antioxidant compounds in thyme and sage isolates. Ten compounds in the thyme acetone oleoresin and six in sage gave an inhibition signal on the CL detector (Chapter 4).

An adequate HPLC separation and a sensitive detection of radical scavenging are two key-elements that determine the success of on-line experiments. Improved separation efficiency especially for polar analytes was observed after an acetonitrile/water gradient program was introduced and after lowering of the pH of the HPLC solvents (Chapter 5). A stable, pulse-free flow, appropriate instrumental set-up and optimised compositions of the CL and the DPPH·reagents improved the sensitivity of the on-line detection. The minimum detectable amounts registered in this study varied from 0.06 ng for rosmarinic acid to 2400 ng for carvacrol (HPLC-CL detection) and from 0.2 ng for eugenol to 19 ng for BHT (HPLC-DPPH·detection) (Chapter 5). It was found that the HPLC-CL system was on average more sensitive, however the HPLC-DPPH·method was more robust.

The on-line HPLC-DPPH·method as well as TLC plates sprayed with DPPH·solution were used for the activity-guided isolation of radical scavenging compounds from a leaf extract of thyme. Nine active compounds were isolated from the methanolic and the acidic aqueous alcoholic extract by means of solvent partitioning, normal phase chromatography, size exclusion chromatography and reversed phase MPLC or HPLC (Chapter 6). Rosmarinic acid, eriodictyol, taxifolin, luteolin 7-glucuronide, p -cymene 2,3-diol and p -cymene 2,3-diol 6-6´-dimer were identified by a combination of UV, CD, mass spectrometry and 1H and 13C NMR. Two weakly active, volatile compounds, thymol and carvacrol, were identified by GC-MS and their structures confirmed by GC and TLC analysis with reference compounds. The structure of a highly active new phenylpropanoid trimer 3'-O-(8''-Z-caffeoyl)-rosmarinic acid was elucidated from its UV and CD spectra, FD mass spectrum, and 1H-, 13C-, COSY and direct and long range 1H-13C NMR spectra (Chapter 6). In off-line Trolox Equivalent Antioxidant Capacity (TEAC) and DPPH·assays, this compound was a weaker and stronger radical scavenger than rosmarinic acid, respectively.

The presence in T. vulgaris of radical scavenging compounds of different polarity and with distinctive reactivity to different radicals offers the possibility to use extracts from this plant as natural antioxidants for various lipid-containing food systems.

Evaluation and comparison of two improved techniques for the on-line detection of antioxidants in liquid chromatography eluates
Dapkevicius, A. ; Beek, T.A. van; Niederländer, H.A.G. - \ 2001
Journal of Chromatography. A, Including electrophoresis and other separation methods 912 (2001). - ISSN 0021-9673 - p. 73 - 82.
Biogenic amine formation and degradation by potential fish starter microorganisms
Enes Dapkevicius, M.L.N. ; Nout, M.J.R. ; Rombouts, F.M. ; Houben, J.H. ; Wymenga, W. - \ 2000
International Journal of Food Microbiology 57 (2000). - ISSN 0168-1605 - p. 107 - 114.
Screening, Isolation and Identification of Antioxidants From Lithuanian and Bulgarian Herbs
Dapkevicius, A. ; Koleva, I. ; Pukalskas, A. ; Niederländer, H.A.G. ; Beek, T.A. van - \ 2000
In: Flavour and Fragrance Chemistry : International Symposium of the Phytochemical Society of Europe, Campobasso, Italy, January 13 - 16, 2000 / Lanzotti, V., Taglialatela-Scafati, O., Dordrecht : Kluwer Academic Publishers - ISBN 9780792362111 - p. 187 - 199.
On-Line Detection of Antioxidative Activity in High-Performance Liquid Chromatography Eluates by Chemiluminescence
Dapkevicius, A. ; Beek, T.A. van; Niederländer, H.A.G. ; Groot, C.P.G.M. de - \ 1999
Analytical Chemistry 71 (1999)3. - ISSN 0003-2700 - p. 736 - 740.
Antioxidant activity of extracts obtained by different isolation procedures from some aromatic herbs grown in Lithuania.
Dapkevicius, A. ; Venskutonis, R. ; Beek, T.A. van; Linssen, J.P.H. - \ 1998
Journal of the Science of Food and Agriculture 77 (1998). - ISSN 0022-5142 - p. 140 - 146.
Rapid spectroscopic screening for antioxidant activity in sage, thyme and oregano isolates with the beta-carotene-linoleic acid model system.
Dapkevicius, A. ; Beek, T.A. van; Linssen, J.P.H. ; Venskutonis, R. - \ 1998
In: Symposium Natural Product Analysis: Chromatography, Spectroscopy, Biological Testing. P. Schreier, M. Herderich, H.U. Humpf, W. Schwab (eds.) Friedr. Vieweg and Son Verlagsgesellschaft mbH, Braunschweig/Wiesbaden, Germany - p. 235 - 237.
Lipid and protein changes during the ensilage of blue whiting (Micromesistius poutassou Risso) by acid and biological methods.
Lurdes Enes Dapkevicius, M. de; Batista, I. ; Nout, M.J.R. ; Rombouts, F.M. ; Houben, J.H. - \ 1998
Food Chemistry 63 (1998). - ISSN 0308-8146 - p. 97 - 102.
Rapid spectroscopic screening for antioxidant activity in Sage, Thyme and Oregano isolates with the beta-carotene-linoleic acid model system.
Dapkevicius, A. ; Beek, T. van; Linssen, J.P.H. ; Venskutonis, R. - \ 1997
In: Conference Natural Products Analysis: Chromatography, Spectroscopy and Biological Testing, Würzburg, Germany (1997).9
Biogenic amine formation and degradation as criteria for the selection of safe fish starter microorganisms.
L. Dapkevicius Nunes Enes, M. de; Nout, M.J.R. ; Rombouts, F.M. ; Houben, J.H. - \ 1996
In: Abstract 16th Int. Symp. IUMS-ICFMH Food Micro '96, Budapest, Hungary - p. 81 - 81.
Essential oils of fennel (Foeniculum vulgare Mill.) from Lithuania.
Venskutonis, P.R. ; Dapkevicius, A. ; Beek, T.A. van - \ 1996
Journal of Essential Oil Research 8 (1996). - ISSN 1041-2905 - p. 211 - 213.
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