TY - JOUR A1 - Walzel, Erwin A1 - Ozierenski, Bärbel A1 - Stark, Claudia A1 - Kroll, Jürgen T1 - Der Einfluß von niederverestertem Pektin und Pektinabbauprodukten auf die Inkorporation von Blei bei konventionalisierten und keimfreien Ratten Y1 - 1996 ER - TY - JOUR A1 - Walzel, Erwin A1 - Kroll, Jürgen T1 - Kritische Spurenelemente in der Ernährung Y1 - 1995 ER - TY - JOUR A1 - Stark, Claudia A1 - Walzel, Erwin A1 - Ozierenski, Bärbel A1 - Kroll, Jürgen T1 - Die Wirkung von Pektin bei aktueller Bleiexposition Y1 - 1995 ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Wollenberger, Ursula A1 - Kroll, Jürgen T1 - Enzyme acitivity of alpha-chymotrypsin after derivatization with phenolic compounds Y1 - 2003 ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Rober, M. A1 - Kroll, Jürgen T1 - Reactions with phenolic substances can induce changes in some physico-chemical properties and activities of bromelain - the consequences for supplementary food products N2 - Bromelain was allowed to react with phenolic compounds. The activity and selected physico-chemical properties of the resulting derivatives were characterized. In vitro experiments showed that the proteolytic activity of bromelain was inhibited. Bromelain also serves as a food protein, because food stuffs based on pineapple contain relatively high concentrations of bromelain. In vitro digestion of bromelain derivatives with the main proteolytic enzymes of the gastrointestinal tract was also adversely affected. A covalent attachment of the phenolic compounds was identified at the tryptophan, free amino (lysines and N-terminal) and thiol groups of bromelain. A decrease in solubility of the derivatives was observed. The isoelectric point was shifted to lower pH values and high molecular weight fractions were identified. All effects observed depended on the reactivity of the phenolic substances. Two supplementary food products containing both bromelain and quercetin were also tested in terms of their proteolytic activity and digestibility Y1 - 2005 SN - 0950-5423 ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Pietruschinski, Nadine A1 - Kroll, Jürgen T1 - In vitro inhibition of alpha -chymotryptic activity by phenolic compounds N2 - alpha-Chymotrypsin was modified by covalent attachment of selected phenolic and related compounds (caffeic acid, chlorogenic acid, ferulic acid, gallic acid, quinic acid, m-/o-/p-dihydroxybenzene and p-benzoquinone) at pH 9. The derivatives formed were characterised in terms of their activity and selected physicochemical properties. In vitro experiments showed that the proteolytic digestion of food proteins with alpha-chymotrypsin derivatives was adversely affected. This decrease depended on the reactivity of the phenolic and related substances tested as well as on the kind of substrate applied. The derivatisation was accompanied by a reduction in the amount of free lysine and tryptophan residues. Moreover, the solubility of the derivatives decreased over a broad pH range, with a parallel increase in the hydrophobicity. The isoelectric point was shifted to a lower pH value, and formation of high-molecular-weight fractions was documented by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Y1 - 2001 UR - http://www3.interscience.wiley.com/cgi-bin/abstract/86510624 ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen T1 - Antioxidant activity of protein-bound quercetin N2 - Bovine serum albumin (BSA) was derivatized by covalent attachment of different amounts of quercetin (ratios of BSA : quercetin were 20:1, 10:1, 7:1, 5:1, 2:1 (w/w)). The antioxidant activity of the protein-phenol derivatives was investigated using a modified TEAC assay. The results show that the covalent attachment of quercetin to BSA decreases the total antioxidant activity in comparison to an equivalent amount of free quercetin depending on the degree of derivatization. The derivative with the highest amount of covalently bound quercetin (2:1 derivative) showed an antioxidant activity of only 79% compared to an equivalent amount of free quercetin. After the enzymatic proteolysis of the BSA quercetin derivatives with trypsin, the total antioxidant activity of the degradation products increases in comparison to the respective undigested derivatives, but does not reach the activity of an equivalent amount of free quercetin. Even after 240 minutes of tryptic degradation there is still a lack in antioxidant activity (for the 7:1 derivative nearly 33%) as compared to free quercetin. Y1 - 2004 UR - http://pubs.acs.org/cgi-bin/article.cgi/jafcau/2004/52/i15/html/jf0496797.html ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen T1 - Inhibitory effects of plant phenols on the activity of selected enzymes N2 - Selected enzymes (alpha-amylase, trypsin, and lysozyme) were allowed to react with some simple phenolic and related compounds (caffeic acid, chlorogenic acid, ferulic acid, gallic acid, m-, o-, and p-dihydroxybenzenes, quinic acid, and p-benzoquinone). The derivatized enzymes obtained were characterized in terms of their activity. In vitro experiments showed that the enzymatic activity of the derivatives was adversely affected. This enzyme inhibition depended on the reactivity of the phenolic and related substances tested as well as on the kind of substrate applied. The decrease in the activity was accompanied by a reduction in the amount of free amino and thiol groups, as well as tryptophan residues, which resulted from the covalent attachment of the phenolic and related compounds to these reactive nucleophilic sites in the enzymes. The enzyme inhibition correlates well with the blocking of the mentioned amino acid side chains. Y1 - 2002 UR - http://pubs.acs.org/journals/jafcau/abstract.cgi/jafcau/2002/50/i12/abs/jf011714b.html ER - TY - JOUR A1 - Rohn, Sascha A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen T1 - Influence of plant phenols on selected enzymes N2 - Secondary plant metabolites are important native food components, which are becoming more and more interesting due to their physiological effects on humans. Some representatives of these compounds are very reactive and can interact with other main food components like proteins resp. enzymes. This work deals with the reactions of selected enzymes (trypsin, alpha-chymotrypsin and alpha-amylase) with simple phenolic and related substances (caffeic acid, chlorogenic acid, ferulic acid, gallic acid, meta-, ortho- and para-dihydroxybenzene, 1,4-benzoquinone, quinic acid). The derivatives formed were characterized in terms of their activity and selected physicochemical properties. In vitro experiments showed that the proteolytic digestion of food proteins with trypsin and alpha-chymotrypsin derivatives was adversely affected. This decrease depends on the reactivity of the phenolic and related substances tested as well as on the kind of substrate applied. Reactions of phenolic compounds with other enzymes (alpha-amylase and lysozyme) showed similar results with regard to physicochemical properties and their activities. Y1 - 2002 ER - TY - JOUR A1 - Rohn, Sascha A1 - Petzke, Klaus-Jürgen A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen T1 - Reactions of chlorogenic acid and quercetin with a soy protein isolate - Influence on the in vivo food protein quality in rats JF - Molecular nutrition & food research : bioactivity, chemistry, immunology, microbiology, safety, technology N2 - Plant phenolic compounds are known to interact with proteins producing changes in the food (e.g., biological value (BV), color, taste). Therefore, the in vivo relevance, especially, of covalent phenolprotein reactions on protein quality was studied in a rat bioassay. The rats were fed protein derivatives at a 10% protein level. Soy proteins were derivatized with chlorogenic acid and quercetin (derivatization levels: 0.056 and 0.28 mmol phenolic compound/gram protein). Analysis of nitrogen in diets, urine, and fecal samples as well as the distribution of amino acids were determined. Depending on the degree of derivatization, the rats fed with soy protein derivatives showed an increased excretion of fecal and urinary nitrogen. As a result, true nitrogen digestibility, BV, and net protein utilization were adversely affected. Protein digestibility corrected amino acid score was decreased for lysine, tryptophan, and sulfur containing amino acids. KW - amino acid score KW - plant phenolic compounds KW - protein derivatization KW - protein digestibility KW - soy protein Y1 - 2006 U6 - https://doi.org/10.1002/mnfr.200600043 SN - 1613-4125 VL - 50 SP - 696 EP - 704 PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Rohn, Sascha A1 - Kruse, Hans-Peter A1 - Kroll, Jürgen T1 - Structural changes induced in bovine serum albumin by covalent attachment of chlorogenic acid N2 - Bovine serum albumin (BSA) was modifed by covalent attachment of chlorogenic acid using different concentrations at pH 9. The derivatization was accompanied by a reduction of lysine, cysteine and tryptophan residues. The isoelectric points were shifted to lower pH values and formation of high molecular weight fractions was noted. The structural changes were studied using circular dichroism, differential scanning calorimetry (DSC), intrinsic fluorescence, and binding of anilinonaphthalenesulfonic acid. The results showed that the content of alpha-helix decreased with a parallel increase in unordered structures with higher degrees of derivatization. DSC revealed a decrease in both denaturation temperature and enthalpy. Surface hydrophobicity declined, indicating that hydrophilic regions were exposed on the molecular surface. Proteolytic digestion showed that, at a lower degree of derivatization,the tryptic degradation was most adversely effected, whereas the peptic digestion declined with increasing modification. A trypsin inhibitory effect of the breakdown products released from derivatized BSA was also observed. Y1 - 2002 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Rohn, Sascha A1 - Kroll, Jürgen A1 - Schweigert, Florian J. T1 - Surface enhanced laser desorptions ionization-time of flight-mass spectrometry analysis in complex food and biological systems Y1 - 2005 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Rohn, Sascha A1 - Kroll, Jürgen T1 - Characterisation of 11S protein fractions and phenolic compounds from green coffee beans under special consideration of their interactions - A review N2 - The intention of this study was to increase the knowledge on the composition and structure of coffee bean proteins and the changes induced in them especially with regard to their interactions with the phenolic compounds also present. For this purpose green coffee beans were extracted by means of standard methanol extraction to quantify the chlorogenic acid content. Different solubilisation buffers were applied to extract the protein fractions with or without prior fat removal. The protein samples thus obtained were analysed by different methods (RP-HPLC, SDS-PAGE and SELDI-TOF- MS). Preliminary model studies were performed to characterize the interactions between the isolated green coffee protein fractions and chlorogenic acid (the major phenolic compound in coffee beans) with the intention of fulfilling the ultimate goal of characterizing such reactions in roasted coffee. The results show that the content of chlorogenic bound covalently to the protein increases. A reaction with the nucleophilic protein side chains (tryptophan, cystein and lysine) was recorded. Cross-inked protein polymers were also detected, whereby the a-chain was found to be more reactive. These reactions effect the solubility of the coffee bean proteins, the latter in turn becoming more acidic in nature. The secondary structure was affected only slightly as determined by circular dichroism. The in-vitro tryptic digestibility was also influenced, where again the cc-chain seems to be more susceptible. The observed polymerisation due to derivatisation by chorogenic acid declines the digestion. Similar digestion behaviour was also observed during tryptic hydrolysis of roasted coffee compared to that of green coffee, roasting allowing more stronger denaturation caused by the accompanying Maillard reaction. The derivatised green coffee bean proteins were found to have moderate antioxidative capacity Y1 - 2005 SN - 0012-0413 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Rohn, Sascha A1 - Kroll, Jürgen T1 - Influence of a sugar moiety (rhamnosylglycoside) at 3-O position on the reactivity of quercetin with whey proteins Y1 - 2003 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Rohn, Sascha A1 - Kroll, Jürgen T1 - Reactions of selected secondary plant metabolites (glucosinolates and phenols) with food proteins and enzymes - Influence on physicochemical properties, enzyme activity and proteolytic dagradation Y1 - 2000 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Ranters, Holger A1 - Rohn, Sascha A1 - Kroll, Jürgen T1 - Assessment of the reactivity of selected isoflavones against proteins in comparison to quercetin N2 - Selected isoflavones (genistein, daidzein, formononetin, prunetin, biochanin A and two synthetic isoflavones) were allowed to interact with soy and whey proteins. The reaction products were analyzed in terms of covalent binding at the nucleophilic side chains of proteins. Changes in molecular properties of the proteins derivatives were documented by SDS-PAGE, IEF and SELDI-TOF-MS. The structural changes induced were studied using circular dichroism (CD). The in vitro digestibility was assessed with trypsin. The results show that the occurrence of the catechol moiety, i.e. the two adjacent (ortho) aromatic hydroxyl groups on ring B of the flavonoid structural skeleton appears to be perquisite condition for covalent binding to proteins. The catechol moiety on ring A was less reactive. Its absence lead to a slight or no significant reaction, although non-covalent interactions may still be possible even when lacking this structural element. A comparison of the data is also made with quercetin representing the flavonols. Y1 - 2004 UR - http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15291506 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Meidtner, Karina A1 - Kroll, Jürgen T1 - Binding of selected phenolic compounds to proteins N2 - In the context of this study, the noncovalent binding of selected phenolic compounds (chlorogenic, ferulic, and gallic acids, quercetin, rutin, and isocluercetin) to different proteins (human serum albumin, bovine serum albumin, soy glycinin, and lysozyme) was studied with direct (Hummel- Dreyer/size exclusion chromatography) and/or indirect methods (fluorescence absorbance properties of the binding components). In the latter case, the measurement of the phenol binding was achieved by exploiting the intrinsic fluorescence emission properties of cluercetin as a probe. From the data obtained, the binding constants and the number of binding sites were calculated. The binding parameters were influenced by different factors, where, e.g., increasing temperature and ionic strength as well as decreasing pH cause a diminished binding. The structures of the proteins as determined by circular dichroism indicate changes in the tertiary structure with the secondary structure remaining intact Y1 - 2005 SN - 0021-8561 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen A1 - Schröder, Insa Sigrid T1 - In vitro enzymatic digestion of benzyl- and phenylisothiocyanate derivatized food proteins Y1 - 1998 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen A1 - Schröder, Insa Sigrid T1 - Reactions of isothiocyanates with food proteins : influence on enzyme activity and degradation Y1 - 1998 ER - TY - JOUR A1 - Rawel, Harshadrai Manilal A1 - Kroll, Jürgen A1 - Rohn, Sascha T1 - Reactions of phenol substances with lysozyme - physicochemical characterisation and proteolytic digestion of the derivatives Y1 - 2000 ER -