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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    Oligomerization and hydroxylation of green tea catechins by oxidative enzymes
    Verloop, J.W. - \ 2016
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Jean-Paul Vincken. - Wageningen : Wageningen University - ISBN 9789462577770 - 146
    green tea - oxidation - theaflavine - peroxidase - oxygenases - flavanols - phenolic compounds - catechol oxidase - mass spectrometry - maldi-tof - process control - groene thee - oxidatie - theaflavine - peroxidase - oxygenasen - flavanolen - fenolverbindingen - catechol oxidase - massaspectrometrie - maldi-tof - procesbewaking

    Black teas are known for their characteristic brown colour, bitter taste and astringent mouth feel. These sensory characteristics are mainly influenced by the phenolic oxidation products present in black tea. The oxidation of phenolics from green tea leaves during black tea manufacturing is an uncontrolled process. With the objective to make tea oxidation a more controlled process, the aim of this thesis was to understand the enzymatic oxidation reactions occurring during tea oxidation, and to enable more rapid analysis of complex mixtures of phenolics. By incubating green tea catechins with an exogenous tyrosinase, a black tea-like phenolic profile was obtained, enriched in theaflavins, which are important for quality of tea. Further oxidation of theaflavins yielded theatridimensins, in which an epicatechin is coupled to the benzotropolone ring of theaflavin. By using MS/MS on selected ions these theatridimensins were shown to occur in black tea. This MS method could also be used to distinguish isomeric procyanidins and dehydrocatechins based on MS2 fragments, as well as the different interflavanic configurations occurring in dehydrodicatechins. The dehydrocatechins were shown to occur in black tea as well. Besides these oligomerization reactions mediated by tyrosinase, oxidation of tea phenolics also comprised hydroxylation. The enzymatic activity from tea leaves responsible for this hydroxylation reaction, was found to be peroxidase. All findings were condensed into a new version of the ‘oxidative cascade hypothesis’, describing the oxidation reactions towards formation of a black tea.

    Biorefinery of leafy biomass using green tea residue as a model material
    Zhang, C. - \ 2016
    Wageningen University. Promotor(en): Johan Sanders, co-promotor(en): Marieke Bruins. - Wageningen : Wageningen University - ISBN 9789462576902 - 156
    biorefinery - biomass conversion - leaves - biomass - green tea - tea - alkaline pulping - pectins - lignocellulose - environmental impact - processes - plant protein - food - biobased economy - bioraffinage - biomassaconversie - bladeren - biomassa - groene thee - thee - alkalische pulpbereiding - pectinen - lignocellulose - milieueffect - processen - plantaardig eiwit - voedsel - biobased economy


    With the rapidly growing world population and improving living standards, food demand is increased with a simultaneous desire for less human impact on the environment, such that “Twice the food production at half the ecological footprint” could be the EU goal for 2050. In fact, a boost in food demand is mainly required in developing countries, where the farmlands are limited and/or they are of poor quality. Rather than improving crop-production yield, developing biorefinery technology with unused biomass, such as leaves, in developing countries may be the key to fulfil the food demand.

    Four major components, protein, pectin, lignin, and (hemi-) cellulose, account for more than 70% of the materials in leaves in almost all species. Among these components, protein and pectin can be used in food and animal feed, and they are key components for supplementing food production. However, the production and application of leaf products is limited for four reasons: unstable raw materials, complex components, rigid plant cell walls, and underdeveloped leaf logistics and economics. The limitations cause low pectin and protein yields, and low cost-efficiency in current extraction technologies, including mechanical milling, chemical extraction (acid and alkaline), solvent extraction, and ammonia protein extraction. Development of an integrated process for multiple products might be a good option for leaf biorefinery, but the compatibilities of these processes were unknown.

    The aim of this study was to develop new processes and applications that optimally utilize all components, particularly protein, of leafy biomass in the feed and/or food industry using green tea residues as a starting material. The method should also be applicable to other leafy biomass. The research started from the development of alkaline protein extraction technology as presented in Chapter 2. We found that in alkaline protein extraction, temperature, NaOH amount, and extraction time are the parameters determining protein yield, while pH and volume of extraction liquid are critical parameters for production cost. After optimization, more than 90% of leaf protein could be extracted at a cost of 102€/ton protein by single step alkaline extraction. The extracted protein nutritional value was comparable to soybean meal and this technique can be adapted to various leafy biomass. Main drawback of this technique is the overuse of alkali, generation of salts, and the destruction of key amino acids, such as lysine, during the extraction. We tried to overcome its drawbacks by developing integrated process with a recycle for chemicals.

    Chapter 3, 4, 5, and 6 refer to the integrated biorefinery. For a better design, we investigated how the alkali aided protein extraction (Chapter 3), and proved that alkaline protein extraction was not facilitated by increased solubility or hydrolysis of protein, but positively correlated to leaf tissue disruption. HG pectin, RGII pectin, polyphenols, and organic acids can be extracted before protein. Protein extraction can then be followed by the extraction of cellulose and hemi-cellulose. RGI pectin and lignin yield were both linearly correlated to protein yield, which indicated that they are likely to be the key limitation to leaf protein extraction. Based on the above findings, an integrated biorefinery that combined protein extraction with a pre-treatment was proposed. In Chapter 4, ethanol, viscozyme, and H2O2 were selected for pre-treatments targeting on the removal of polyphenols and pigments, carbohydrates, and lignin accordingly. Ethanol and viscozyme could extract their targeting components efficiently while H2O2 could bleach GTR with no lignin extracted. The best pre-treatment was the combination of viscozyme and 50% ethanol extraction, which not only reduced the use of alkali by 50%, but also improved protein content and its nutritional value. As pectin can be applied for food or chemicals, enzyme and PBS buffer were investigated for pectin extraction (Chapter 5). Both enzyme and PBS buffer extraction could not only extract high yield HG pectin (predominated by galacturonic acid) with no protein extraction, but also reduced alkali usage in subsequent protein extraction. Pectin obtained using PBS buffer could be present in its native form, which can be precipitated by 40% ethanol. Buffer is suggested to extract pectins when pectins are to be used in food. Otherwise, hydrolyzed pectin that mainly contains galacturonic acid, can be converted to other useful chemicals. For this the enzymatic methods, such as using Viscozyme® L, are recommended.

    Alkali usage was further optimized. It was found that by using potassium hydroxide, the protein extraction efficiency was similar to that using sodium hydroxide. The waste water, mainly containing potassium salts, can then be used as fertilizer. This technique is highly depending on the location of factories, which should be built close to the field. Alternatively, calcium hydroxide can be used. As calcium salts can be precipitated by CO2 and calcium hydroxide can be regenerated through burning of the precipitate, this scheme is sustainable and adaptable to most situations. However, as calcium also precipitated pectin, ployphenols, and even proteins, the protein yield is relatively low. Although a pre-treatment can improve extraction efficiency of calcium hydroxide, economic results suggested that a pre-treatment is not necessary unless the products obtained by pre-treatment have an attractive market value.

    In Chapter 7, we extend our knowledge on leaf biorefinery with some additional experiments and literature. Simplified models of leaf tissues and cell walls were proposed and used to explain the mechanism of alkaline protein extraction. The models were also used to explain other mechanisms for protein extraction; mechanical milling, steam explosion, acid, and enzyme aided extraction. The possible improvements of leaf biorefinery economics were illustrated either by reducing production cost, by e.g. using counter current extraction or ultrafiltration, or by upgrading product value by applying protein and pectin in food. The processes recommended in this thesis show an excellent prospective, in which they are applicable to other leaf biomass and suitable for small-scale production.

    Coffee and tea consumption, genotype-based CYP1A2 and NAT2 activity and colorectal cancer risk—Results from the EPIC cohort study
    Dik, V.K. ; Bueno-de-Mesquita, H.B. ; Oijen, M.G.C.T. van; Siersema, P.D. ; Uiterwaal, C.S.P.M. ; Gils, C.H. van; Duijnhoven, F.J.B. van - \ 2014
    International Journal of Cancer 135 (2014)2. - ISSN 0020-7136 - p. 401 - 412.
    colonic aberrant crypts - green tea - components kahweol - black tea - caffeine - cafestol - polyphenols - health - cells - rat
    Coffee and tea contain numerous antimutagenic and antioxidant components and high levels of caffeine that may protect against colorectal cancer (CRC). We investigated the association between coffee and tea consumption and CRC risk and studied potential effect modification by CYP1A2 and NAT2 genotypes, enzymes involved in the metabolization of caffeine. Data from 477,071 participants (70.2% female) of the European Investigation into Cancer and Nutrition (EPIC) cohort study were analyzed. At baseline (1992–2000) habitual (total, caffeinated and decaffeinated) coffee and tea consumption was assessed with dietary questionnaires. Cox proportional hazards models were used to estimate adjusted hazard ratio's (HR) and 95% confidence intervals (95% CI). Potential effect modification by genotype-based CYP1A2 and NAT2 activity was studied in a nested case–control set of 1,252 cases and 2,175 controls. After a median follow-up of 11.6 years, 4,234 participants developed CRC (mean age 64.7¿±¿8.3 years). Total coffee consumption (high vs. non/low) was not associated with CRC risk (HR 1.06, 95% CI 0.95–1.18) or subsite cancers, and no significant associations were found for caffeinated (HR 1.10, 95% CI 0.97–1.26) and decaffeinated coffee (HR 0.96, 95% CI 0.84–1.11) and tea (HR 0.97, 95% CI 0.86–1.09). High coffee and tea consuming subjects with slow CYP1A2 or NAT2 activity had a similar CRC risk compared to non/low coffee and tea consuming subjects with a fast CYP1A2 or NAT2 activity, which suggests that caffeine metabolism does not affect the link between coffee and tea consumption and CRC risk. This study shows that coffee and tea consumption is not likely to be associated with overall CRC.
    Rapid and sustained systemic circulation of conjugated gut microbiol catabolites after single-dose black tea extract consumption
    Duynhoven, J.P.M. van; Hooft, J.J.J. van der; Dorsten, F.A. van; Peters, S. ; Foltz, M. ; Gomez-Roldan, V. ; Vervoort, J.J.M. ; Vos, R.C.H. de - \ 2014
    Journal of Proteome Research 13 (2014)5. - ISSN 1535-3893 - p. 2668 - 2678.
    randomized controlled-trial - red wine/grape juice - green tea - mass-spectrometry - in-vitro - dietary polyphenols - blood-pressure - catechins - metabolites - humans
    Gut microbial catabolites of black tea polyphenols (BTPs) have been proposed to exert beneficial cardiovascular bioactivity. This hypothesis is difficult to verify because the conjugation patterns and pharmacokinetics of these catabolites are largely unknown. The objective of our study was to identify, quantify, and assess the pharmacokinetics of conjugated BTP metabolites in plasma of healthy humans by means of an a priori untargeted LC–MS-based metabolomics approach. In a randomized, open, placebo-controlled, crossover study, 12 healthy men consumed a single bolus of black tea extract (BTE) or a placebo. The relative and, in several cases, absolute concentrations of a wide range of metabolites were determined using U(H)PLC-LTQ-Orbitrap-FTMS. Following BTE consumption, a kinetic response in plasma was observed for 59 BTP metabolites, 11 of these in a quantitative manner. Conjugated and unconjugated catechins appeared in plasma without delay, at 2–4 h, followed by a range of microbial catabolites. Interindividual variation in response was greater for gut microbial catabolites than for directly absorbed BTPs. The rapid and sustained circulation of conjugated catabolites suggests that these compounds may be particularly relevant to proposed health benefits of BTE. Their presence and effects may depend on individual variation in catabolic capacity of the gut microbiota.
    Population-based nutrikinetic modelling of phytochemical exposure
    Velzen, E.J.J. van; Westerhuis, J.A. ; Grün, C.H. ; Duynhoven, J.P.M. van; Jacobs, D.M. ; Eilers, P.H.C. ; Mulder, T.P. ; Foltz, M. ; Garczarek, U. ; Kemperman, R. ; Vaughan, E.E. ; Smilde, A.K. - \ 2014
    Metabolomics 10 (2014)6. - ISSN 1573-3882 - p. 1059 - 1073.
    red wine/grape juice - black tea - dietary polyphenols - phenolic metabolites - nutrition research - food sources - human plasma - green tea - gut model - pharmacokinetics
    The beneficial health effects of fruits and vegetables have been attributed to their polyphenol content. These compounds undergo many bioconversions in the body. Modeling polyphenol exposure of humans upon intake is a prerequisite for understanding the modulating effect of the food matrix and the colonic microbiome. This modeling is not a trivial task and requires a careful integration of measuring techniques, modeling methods and experimental design. Moreover, both at the population level as well as the individual level polyphenol exposure has to be quantified and assessed. We developed a strategy to quantify polyphenol exposure based on the concept of nutrikinetics in combination with population-based modeling. The key idea of the strategy is to derive nutrikinetic model parameters that summarize all information of the polyphenol exposure at both individual and population level. This is illustrated by a placebo-controlled crossover study in which an extract of wine/grapes and black tea solids was administered to twenty subjects. We show that urinary and plasma nutrikinetic time-response curves can be used for phenotyping the gut microbial bioconversion capacity of individuals. Each individual harbours an intrinsic microbiota composition converting similar polyphenols from both test products in the same manner and stable over time. We demonstrate that this is a novel approach for associating the production of two gut-mediated ¿-valerolactones to specific gut phylotypes. The large inter-individual variation in nutrikinetics and ¿-valerolactones production indicated that gut microbial metabolism is an essential factor in polyphenol exposure and related potential health benefits
    Interactions of blacktea polyphenols with human gut microbiota: implications for gut and cardiovascular health
    Duynhoven, J.P.M. van; Vaughan, E.E. ; Dorsten, F. van; Gomez-Roldan, V. ; Vos, R. de; Vervoort, J.J.M. ; Hooft, J.J.J. van der; Roger, L. ; Draijer, R. ; Jacobs, D.M. - \ 2013
    American Journal of Clinical Nutrition 98 (2013)6. - ISSN 0002-9165 - p. 1631S - 1641S.
    red wine/grape juice - density-lipoprotein oxidation - coronary-artery-disease - vein endothelial-cells - human fecal microbiota - in-vitro - phenolic-acids - green tea - ellagitannin metabolites - dietary polyphenols
    Epidemiologic studies have convincingly associated consumption of black tea with reduced cardiovascular risk. Research on the bioactive molecules has traditionally been focused on polyphenols, such as catechins. Black tea polyphenols (BTPs), however, mainly consist of high-molecular-weight species that predominantly persist in the colon. There, they can undergo a wide range of bioconversions by the resident colonic microbiota but can in turn also modulate gut microbial diversity. The impact of BTPs on colon microbial composition can now be assessed by microbiomics technologies. Novel metabolomics platforms coupled to de novo identification are currently available to cover the large diversity of BTP bioconversions by the gut microbiota. Nutrikinetic modeling has been proven to be critical for defining nutritional phenotypes related to gut microbial bioconversion capacity. The bioactivity of circulating metabolites has been studied only to a certain extent. Bioassays dedicated to specific aspects of gut and cardiovascular health have been used, although often at physiologically irrelevant concentrations and with limited coverage of relevant metabolite classes and their conjugated forms. Evidence for cardiovascular benefits of BTPs points toward antiinflammatory and blood pressure–lowering properties and improvement in platelet and endothelial function for specific microbial bioconversion products. Clearly, more work is needed to fill in existing knowledge gaps and to assess the in vitro and in vivo bioactivity of known and newly identified BTP metabolites. It is also of interest to assess how phenotypic variation in gut microbial BTP bioconversion capacity relates to gut and cardiovascular health predisposition.
    Predicting foliar biochemistry of tea (Camellia sinensis) using reflectance spectra measured at powder, leaf and canopy levels
    Bian, B.M. ; Skidmore, A.K. ; Schlerf, M. ; Wang, T. ; Liu, X. ; Zeng, R. ; Fei, T. - \ 2013
    ISPRS Journal of Photogrammetry and Remote Sensing 78 (2013). - ISSN 0924-2716 - p. 148 - 156.
    near-infrared spectroscopy - green tea - chlorophyll content - squares regression - amino-acids - hyperspectral measurements - imaging spectrometry - vegetation indexes - continuum removal - forest canopy
    Some biochemical compounds are closely related with the quality of tea (Camellia sinensis (L.)). In this study, the concentration of these compounds including total tea polyphenols, free amino acids and soluble sugars were estimated using reflectance spectroscopy at three different levels: powder, leaf and canopy, with partial least squares regression. The focus of this study is to systematically compare the accuracy of tea quality estimations based on spectroscopy at three different levels. At the powder level, the average r2 between predictions and observations was 0.89 for polyphenols, 0.81 for amino acids and 0.78 for sugars, with relative root mean square errors (RMSE/mean) of 5.47%, 5.50% and 2.75%, respectively; at the leaf level, the average r2 decreased to 0.46-0.81 and the relative RMSE increased to 4.46-7.09%. Compared to the results yielded at the leaf level, the results from canopy spectra were slightly more accurate, yielding average r2 values of 0.83, 0.77 and 0.56 and relative RMSE of 6.79%, 5.73% and 4.03% for polyphenols, amino acids and sugars, respectively. We further identified wavelength channels that influenced the prediction model. For powder and leaves, some bands identified can be linked to the absorption features of chemicals of interest (1648nm for phenolic, 1510nm for amino acids, 2080nm and 2270nm for sugars), while more indirectly related wavelengths were found to be important at the canopy level for predictions of chemical compounds. Overall, the prediction accuracies achieved at canopy level in this study are encouraging for future study on tea quality estimated at the landscape scale using airborne and space-borne sensors.
    Efficacy of Food Proteins as Carriers for Flavonoids
    Bohin, M.C. ; Vincken, J.P. ; Hijden, H.T.W.M. ; Gruppen, H. - \ 2012
    Journal of Agricultural and Food Chemistry 60 (2012)16. - ISSN 0021-8561 - p. 4136 - 4143.
    isothermal titration calorimetry - tea catechins - bitter taste - green tea - binding - casein - flavan-3-ols - astringency - iron
    Enrichment of flavonoids in food is often limited by their off-tastes, which might be counteracted by the use of food proteins as carriers of flavonoids. Various milk proteins, egg proteins, and gelatin hydrolysates were compared for their binding characteristics to two flavan-3-ols. Among the proteins tested for their affinities toward epigallocatechin gallate (EGCG), ß-casein and gelatin hydrolysates, in particular fish gelatin, were found to be the most promising carriers with an affinity on the order of 104 M-1. A flexible open structure of proteins, as present in random coil proteins, was found to be important. The saturation of binding observed at high flavonoid/protein ratios was used to estimate the maximal binding capacity of each protein. To reach a daily intake of EGCG that has been associated with positive health effects, only 519 mg of gelatin B and 787 mg of ß-casein were required to complex EGCG on the basis of their maximal binding capacity. When the absence of turbidity is taken into account, ß-casein prevails as carrier. Three selected proteins were further investigated for their binding potential of representative flavonoids differing in their C-ring structure. An increase in hydrophobicity of flavonoids was related to a higher affinity for proteins, and the presence of a gallic acid ester on the C-ring showed an overall higher affinity.
    Tea consumption and incidence of type 2 diabetes in Europe: the EPIC-InterAct case-cohort study
    Feskens, E.J.M. ; Groenendijk-van Woudenbergh, G.J. ; Kuijsten, A. - \ 2012
    PLoS ONE 7 (2012)5. - ISSN 1932-6203 - 8 p.
    black tea - green tea - oolong tea - coffee - risk - obesity - plasma - cancer - milk - metaanalysis
    Background In previous meta-analyses, tea consumption has been associated with lower incidence of type 2 diabetes. It is unclear, however, if tea is associated inversely over the entire range of intake. Therefore, we investigated the association between tea consumption and incidence of type 2 diabetes in a European population. Methodology/Principal Findings The EPIC-InterAct case-cohort study was conducted in 26 centers in 8 European countries and consists of a total of 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,835 individuals from a total cohort of 340,234 participants with 3.99 million person-years of follow-up. Country-specific Hazard Ratios (HR) for incidence of type 2 diabetes were obtained after adjustment for lifestyle and dietary factors using a Cox regression adapted for a case-cohort design. Subsequently, country-specific HR were combined using a random effects meta-analysis. Tea consumption was studied as categorical variable (0, >0-
    Structural elucidation and quantification of phenolic conjugates present in human urine after tea intake
    Hooft, J.J.J. van der; Vos, R.C.H. de; Mihaleva, V. ; Bino, R.J. ; Ridder, L.O. ; Roo, N. de; Jacobs, D.M. ; Duynhoven, J.P.M. van; Vervoort, J.J.M. - \ 2012
    Analytical Chemistry 84 (2012)16. - ISSN 0003-2700 - p. 7263 - 7271.
    tandem mass-spectrometry - green tea - black tea - metabolite identification - ellagic acid - metabolomics - polyphenols - nmr - ingestion - phytochemicals
    In dietary polyphenol exposure studies, annotation and identification of urinary metabolites present at low (micromolar) concentrations are major obstacles. In order to determine the biological activity of specific components, it is necessary to have the correct structures and the quantification of the polyphenol-derived conjugates present in the human body. We present a procedure for identification and quantification of metabolites and conjugates excreted in human urine after single bolus intake of black or green tea. A combination of a solid phase extraction (SPE) preparation step and two high pressure liquid chromatography (HPLC)-based analytical platforms was used; namely, accurate mass fragmentation (HPLC-FTMSn) and mass-guided SPE-trapping of selected compounds for nuclear magnetic resonance spectroscopy (NMR) measurements (HPLC-TOFMS-SPE-NMR). HPLC-FTMSn analysis led to the annotation of 138 urinary metabolites, including 48 valerolactone and valeric acid conjugates. By combining the results from MSn fragmentation with the one dimensional (1D)-1H-NMR spectra of HPLC-TOFMS-SPE trapped compounds, we elucidated the structures of 36 phenolic conjugates, including the glucuronides of 3’,4’-di, and 3’,4’,5’-trihydroxyphenyl-¿-valerolactone, three urolithin glucuronides, and indole-3-acetic acid glucuronide. We also obtained 26 hours of quantitative excretion profiles for specific valerolactone conjugates. The combination of the HPLC-FTMSn and HPLC-TOFMS-SPE-NMR platforms results in the efficient identification and quantification of low abundant phenolic conjugates down to nanomoles of trapped amounts of metabolite corresponding to micromolar metabolite concentrations in urine
    Enhanced NMR-based profiling of polyphenols in commercially available grape juices using solid-phase extraction
    Savage, A.K. ; Duynhoven, J.P.M. van; Tucker, G. ; Daykin, C. - \ 2011
    Magnetic Resonance in Chemistry 49 (2011)1. - ISSN 0749-1581 - p. S27 - S36.
    nuclear-magnetic-resonance - fruit juices - h-1-nmr spectroscopy - liquid-extraction - by-products - green tea - wine - quality - identification - chromatography
    Grapes and related products, such as juices, and in particular, their polyphenols, have previously been associated with many health benefits, such as protection against cardiovascular disease. Within grapes, a large range of structurally diverse polyphenols can be present, and their characterisation stands as a challenge. 1H NMR spectroscopy in principle would provide a rapid, nondestructive and straightforward method for profiling of polyphenols. However, polyphenol profiling and identification in grape juices is hindered because of signals of prevailing carbohydrates causing spectral overlap and compromising dynamic range. This study describes the development of an extraction method prior to analysis using 1H NMR spectroscopy, which can, potentially, significantly increase the number of detectable polyphenols and aid their identification, by reduction of signal overlap and selective removal of heavily dominating compounds such as sugars.
    Reflectance spectroscopy of biochemical components as indicators of tea, Camellia Sinensis, quality
    Bian, B.M. ; Skidmore, A.K. ; Schlerf, M. ; Fei, T. ; Liu, Y.F. ; Wang, T. - \ 2010
    Photogrammetric Engineering and Remote Sensing 76 (2010)12. - ISSN 0099-1112 - p. 1385 - 1392.
    kruger-national-park - green tea - hyperspectral measurements - spectral characteristics - pattern-recognition - field spectrometry - total polyphenols - vegetation - chemistry - imagery
    The potential of reflectance spectroscopy to estimate the concentration of biochemical compounds related to tea (Camellia sinensis (L.)) quality (total tea polyphenols and free amino acids) is demonstrated. Partial least squares regression (PLSR) was performed to establish the relationship between reflectance and biochemicals for leaf powders as well as fresh leaves. Highest accuracy was found for tea powders with a cross-validated r2 of 0.97 for tea polyphenols and 0.99 for free amino acids, and the root mean square error of cross validations (RMSECVS) are 8.36 mg g-1 and 1.01 mg g-1 for the two chemicals. The accuracy achieved at leaf level was slightly lower, with results yielding cross-validated r2 of 0.91 and 0.93 with RMSECVS of 13.74 mg g-1 and 2.32 mg g-1 for tea polyphenols and free amino acids, respectively. Important wavelengths for prediction of the two biochemicals from powder and leaf spectra were identified using the PLSR bcoefficients as indicators. Wavelengths of 1,131 nm, 1,654 nm, 1,666 nm, 1,738 nm and 1,752 nm were identified as bands related to absorption by total tea polyphenols, while 1,492 nm represented the absorption feature of free amino acids. The results obtained using fresh leaves indicate that hyperspectral remote sensing may be useful for routine monitoring of tea chemistry at landscape scale.
    Some Phenolic Compounds Increase the Nitric Oxide Level in Endothelial Cells in Vitro
    Appeldoorn, M.M. ; Venema, D.P. ; Peters, T.H.F. ; Koenen, M.E. ; Arts, I.C.W. ; Vincken, J.P. ; Gruppen, H. ; Keijer, J. ; Hollman, P.C.H. - \ 2009
    Journal of Agricultural and Food Chemistry 57 (2009)17. - ISSN 0021-8561 - p. 7693 - 7699.
    rat thoracic aorta - dependent relaxation - red wine - blood-pressure - peanut skins - grape seeds - green tea - flavonoids - synthase - cocoa
    The vasorelaxing properties of chocolate and wine might relate to the presence of phenolic compounds. One of the potential mechanisms involved is stimulation of endothelial nitric oxide (NO) production, as NO is a major regulator of vasodilatation. This study aimed to develop an in vitro assay using the hybrid human endothelial cell line EA.hy926 to rapidly screen phenolic compounds for their NO-stimulating potential. The assay was optimized, and a selection of 33 phenolics, namely, procyanidins, monomeric flavan-3-ols, flavonols, a flavone, a flavanone, a chalcone, a stilbene, and phenolic acids, was tested for their ability to enhance endothelial NO level. Resveratrol, a well-known enhancer of NO level, was included as a positive control. Of the 33 phenolics tested, only resveratrol (285% increase in NO level), quercetin (110% increase), epicatechingallate (ECg) (85% increase), and epigallocatechingallate (EGCg) (60% increase) were significant (P = 0.05) enhancers. Procyanidins showed a nonsignificant tendency to elevate NO level. Concentration-dependent correlations between enhanced NO level and endothelial nitric oxide synthase (eNOS) expression were demonstrated for the three polyphenols tested (resveratrol, ECg, and EGCg). Thus, an easy screening tool for change in cellular NO level was developed. Use of this assay showed that only a limited number of phenolic compounds might enhance NO level with an increased amount of eNOS enzyme as a possible contributing mechanism.
    Role of Catechin Quinones in the Induction of EpRE-Mediated Gene Expression
    Muzolf-Panek, M. ; Gliszczynska-Swiglo, A. ; Haan, L.H.J. de; Aarts, J.M.M.J.G. ; Szymusiak, H. ; Vervoort, J.J.M. ; Tyrakowska, B. ; Rietjens, I.M.C.M. - \ 2008
    Chemical Research in Toxicology 21 (2008)12. - ISSN 0893-228X - p. 2352 - 2360.
    tea polyphenol (-)-epigallocatechin-3-gallate - activated protein-kinases - green tea - anticancer properties - medicinal benefits - phenolic-acids - in-vitro - keap1 - nrf2 - quercetin
    In the present study, the ability of green tea catechins to induce electrophile-responsive element (EpRE)-mediated gene expression and the role of their quinones in the mechanism of this induction were investigated. To this end, Hepa1c1c7 mouse hepatoma cells were used, stably transfected with a luciferase reporter gene under the expression regulation of an EpRE from the human NAD(P)H:quinone oxidoreductase 1 (NQO1) gene. The results obtained show that several, but not all, catechins tested are able to induce EpRE-mediated gene transcription, with epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG), both containing a pyrogallol and a galloyl moiety, being the most powerful inducers. Moreover, it was demonstrated that the EpRE-mediated response to catechins was increased in cells with reduced cellular glutathione (GSH) levels and decreased in cells with increased levels of GSH, corroborating a role for catechin quinones. The intrinsic capacity of catechins to form quinone type metabolites upon their oxidation was demonstrated using incubations of epigallocatechin (EGC) and EGCG with tyrosinase and the GSH-trapping method. Glutathione conjugates formed in these incubations were identified as 2¿-glutathionyl-EGC, 2¿,6¿-diglutathionyl-EGC, 2¿-glutathionyl-EGCG, and 2¿,6¿-diglutathionyl-EGCG, supporting the formation of quinone type metabolites involving especially the pyrogallol moiety of these catechins. Formation of the EGCG-quinone-glutathionyl adducts was also observed in the EpRE-LUX cellular system. This further supports the importance of the pyrogallol moiety for the quinone chemistry of the catechins. Finally, the presence of the pyrogallol moiety in the catechins also results in a relatively lower half-wave oxidation potential (E1/2) and calculated heat of formation (DHF) for conversion of the catechins to their corresponding quinones, pointing at an increased ability to become oxidized. Altogether, our studies reveal that catechins, especially those containing a pyrogallol moiety, induce EpRE-mediated detoxifying gene expression and that this induction is likely to be the result of their quinone chemistry.
    Chronic quercetin exposure affects fatty acid catabolism in rat lung
    Boer, V.C.J. de; Schothorst, E.M. van; Dihal, A.A. ; Woude, H. van der; Arts, I.C.W. ; Rietjens, I.M.C.M. ; Hollman, P.C.H. ; Keijer, J. - \ 2006
    Cellular and Molecular Life Sciences 63 (2006)23. - ISSN 1420-682X - p. 2847 - 2858.
    dependent anion channel - diet-induced obesity - colon-cancer cells - gene-expression - dna microarray - green tea - in-vitro - polyphenols - inhibition - mice
    Dietary quercetin intake is suggested to be health promoting, but this assumption is mainly based on mechanistic studies performed in vitro. Previously, we identified rat lung as a quercetin target tissue. To assess relevant in vivo health effects of quercetin, we analyzed mechanisms of effect in rat lungs of a chronic (41 weeks) 1% quercetin diet using whole genome microarrays. We show here that fatty acid catabolism pathways, like beta-oxidation and ketogenesis, are up-regulated by Dietary quercetin intake is suggested to be health promoting, but this assumption is mainly based on mechanistic studies performed in vitro. Previously, we identified rat lung as a quercetin target tissue. To assess relevant in vivo health effects of quercetin, we analyzed mechanisms of effect in rat lungs of a chronic (41 weeks) 1% quercetin diet using whole genome microarrays. We show here that fatty acid catabolism pathways, like beta-oxidation and ketogenesis, are up-regulated by the long-term quercetin intervention. Up-regulation of genes (Hmgcs2, Ech1, Acox1, Pcca, Lpl and Acaa2) was verified and confirmed by quantitative real time PCR. In addition, free fatty acid levels were decreased in rats fed the quercetin diet, confirming that quercetin affects fatty acid catabolism. This in vivo study demonstrates for the first time that fatty acid catabolism is a relevant process that is affected in rats by chronic dietary quercetin
    Absorption, bioavailability and metabolism of flavonoids
    Hollman, P.C.H. - \ 2004
    Pharmaceutical biology 42 (2004)suppl.. - ISSN 1388-0209 - p. 74 - 83.
    lactase-phlorhizin hydrolase - human plasma - red wine - quercetin glycosides - cocoa procyanidins - urinary-excretion - mass-spectrometry - black tea - green tea - humans
    To unravel mechanisms of action of dietary flavonoids in their potential role in disease prevention, it is crucial to know the factors that determine their release from foods, their extent of absorption, and their fate in the organism. Research on absorption, metabolism, and bioavailability of flavonoids will answer these questions. The subclass, flavonols, with quercetin as the major dietary flavonol, was the first to be studied, and information on other subclasses of flavonoids is emerging. Most flavonoids, except for the subclass of catechins, are present in plants bound to sugars as ß-glycosides. This structural feature determines whether the flavonoid can be absorbed from the small intestine or has to go to the colon before absorption can occur. Generally, but exceptions have been described, glucosides are the only glycosides that can be absorbed from the small intestine. Absorption from the small intestine is more efficient than from the colon and will lead to higher plasma values. After absorption from the small intestine, flavonoids are conjugated with glucuronic acid or sulfate or O-methylation may occur. The conjugation reactions, which occur in the small intestine upon absorption, are very efficient. As a result, no free flavonoid aglycones can be found in plasma or urine, except for catechins. Plasma concentrations due to a normal diet will be less than 1 µM. Flavonoids that cannot be absorbed from the small intestine, and absorbed flavonoids secreted with bile, will be degraded in the colon by microorganisms, which will break down the flavonoid ring structure. The resulting phenolic acids have partly been characterised. These phenolic acids can be absorbed and have been measured in plasma and urine. Future research will need to address tissue distribution, cellular uptake, and cellular metabolism
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