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- Institut für Ernährungswissenschaft (49) (remove)
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.
The noncovalent binding of selected phenolic compounds (chlorogenic-, ferutic-, gallic acid, quercetin, rutin, and isoquercetin) to proteins (HSA, BSA, soy glycinin, and lysozyme) was studied by an indirect method applying the quenching of intrinsic tryptophan fluorescence. From the data obtained, the binding constants were calculated by nonlinear regression (one site binding; y = Bx/k + x). It has been reported that tannins inhibit human salivary amylase and that these complexes may reduce the development of cariogenic plaques. Further, amylase contains two tryptophan residues in its active site. Therefore, in a second part of the study involving 31 human subjects, evidence was sought for noncovalent interactions between the phenols of green tea and saliva proteins as measured by the fluorescence intensity. Amylase activity was determined before and after the addition of green tea to saliva of 31 subjects. Forty percent of the subjects showed an increase in amylase activity contrary to studies reporting only a decrease in activity. The interactions of tannin with amylase result in a decrease of its activity. It still remains to be elucidated why amylase does not react uniformly under conditions of applying green tea to saliva. Further, in terms of using phenols as caries inhibitors this finding should be of importance.
The addition of lysozyme amounting to 1000 mg/l wine does neither effect its total phenol content (Folin-Ciocalteu-Method), nor wine colour (measured by extinction at 512 nm) nor its antioxidative capacity (TEAC-Assay). No covalent binding of wine phenols to the enzyme was observed during lysozyme addition, although non-covalent interactions are possible. Lysozyme activity is not influenced by the presence of malvidin-3-glucoside and resveratrol in model experiments, whereas pH and ethanol content produce a corresponding alteration in lysozyme activity. With regard to red wine, a significant effect was noted in the presence of wine components.
Die Sojabohne : Inhalsstoffe und deren Lebensmittelchemische und ernährungsphysiologische Bedeutung
(2006)
The soy bean contains besides comparatively large amounts of nutritionally and physiologically valuable proteins and lipids, also a series of other minor components termed as secondary plant metabolites. In this respect most of the research focus has been directed to the group of isoflavones. Epidemiological studies as well as model and animal experiments document that the consumption of soy products/-components is accompanied by many postive physiological effects, which are discussed shortly in this paper
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
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
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
During processing and storage, phenolic compounds (PCs) may react with food protein bound amino acids (AAs). Such reactions have been reported to change physicochemical and to decrease in vitro digestion properties of proteins. A rat growth and nitrogen (N) balance study was conducted to prove whether derivatization with chlorogenic acid (CA) affects the nutritional quality of beta-lactoglobulin (beta-LG). Test diets (10% protein level) contained nonderivatized beta-LG (LG, treated under omission of CA), low derivatization level beta-LG (LGL), high derivatization level beta-LG (LGH), or casein supplemented with L-methionine (0.3% of diet; C+met) as an internal standard. An additional group received untreated beta-LG supplemented with pure CA (1.03% of diet; LG+CA). The AA composition of test proteins, plasma AAs, and liver glutathione (GSH) concentrations were determined. Protein digestibility-corrected amino acid score (PDCAAS) was calculated using human or rat AA requirement patterns and rat fecal digestibility values. N excretion was significantly higher in feces and lower in urine of rats fed with LGH as compared to LG and LGL. Consequently, true N digestibility (TND) was significantly lower with LGH as compared to LG and LGL. The lower content of methionine, cysteine, lysine, and tryptophan in LGH corresponded to a reduced TND. Net protein utilization (NPU) was not different between treated beta-LG fed diet groups but was lower than in LG+CA and C+met fed groups. Only at a relatively high level of derivatization with CA, the otherwise good nutritional quality of beta-LG is affected so that TND is reduced, while NPU still remains unaffected. Derivatization of beta-LG with CA does not seem to lead to an additional deficiency in a specific indispensable AA in growing rats fed with 10% protein
The structure of interaction products resulting from the reaction of unmodified glucose with benzyl isothiocyanate is reported. Prior to their identification, the main products of this reaction were isolated using solid- phase extraction (SPE) as well as preparative HPLC. They were then identified by NMR and MS as 3-benzyl-4-hydroxy-5-(D- arabino-1,2,3,4-tetrahydroxybutyl)- 1,3-oxazolidine-2-thione, 3-benzyl-4-hydroxy-4-hydroxymethyl-5-(D-erythro-1,2,3- trihydroxypropyl)- 1,3-oxazolidine-2-thione, N-benzyl-(D-gluco-4,5-dihydroxy-6-hydroxymethyl-tetrahydropyrano)[2,3-b] oxazolidine-2-thione and 3-benzyl-4-(N-benzyl amino)-5-(D-arabino-1,2,3,4-tetrahydroxybutyl)-1,3-thiazolidine-2-thione . The identity of the last compound was secured by X-ray crystal structure data. (C) 2004 Elsevier Ltd. All rights reserved