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Die Bedeutung von Cassava (Manihot esculenta Crantz) als Hauptnahrungsmittel in tropischen Ländern
(2003)
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.
Soy glycinin (SG) and soy trypsin inhibitor (STI) were derivatized by chlorogenic- and caffeic acid (cinnamic acids, C6 - C3 - structure), and by gallic acid representing hydroxybenzoic acids (C6 - C1 - structure). Further, the flavonoids, flavone, apigenin, kaempferol, quercetin and myricetin (C6 - C3 - C6 - structure) were also caused to react with soy proteins to estimate the influence of the number and the position of hydroxy substituents. The derivatization caused a reduction of lysine, cysteine and tryptophan residues in the soy proteins. The isoelectric points of the derivatives were shifted to lower pH values and formation of high molecular fractions was documented. The derivatives were characterized in terms of their solubility at different pH-values to document the influence on the functional properties. The structural changes induced were studied using circular dichroism (CD), differential scanning calorimetry (DSC) , intrinsic fluorescence, and binding of anilinonaphthalenesulfonic acid. The influence of derivatization on the in-vitro digestibility with trypsin, chymotrypsin, pepsin and pancreatin was also assessed. The effect on the trypsin inhibitor activity of all the resulting STI derivatives was studied, the latter being reduced.
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
The application of mass spectrometry for the characterization of food proteins represents one of the most important tools in food chemistry and nutritional science. In the last few years there has been a tremendous development in the classical questions with regard to determination of molecular mass, identification amino acid sequence and structure of proteins. With these technical improvements, it is becoming more and more interesting to characterize the changes involved in proteins embedded in the food matrix as a result of their technological processing, especially in terms of the influence on their functional, nutritional and phsiological properties. Many such posttransational protein modifications occuring due to reactions with other food constituents (e.g. secondary plant metabolites) provide a series of possible fields for application of a sample preparation with a soft ionisation technique using mass spectrometry. The matrix assisted laser desorptions/ionisation ? time of flight ? mass spectrometry (MALDI-TOF-MS) and the surface enhanced laser desorptions/ionisation ? time of flight ? mass spectrometry (SELDI-TOF-MS) have become since than two of the most important methods of choice for solving of such questions and these both techniques have been described here with correponding examples.
Soya glycinin was derivatized with different phenolic substances (caffeic-, chlorogenic-, gallic acid and quercetin). The protein derivatives formed have been characterized in terms of their properties where they showed changes in the content of free epsilon-amino groups, tryptophan and thiol groups. The derivatives have also been characterized in terms of their solubility at different pH-values to document the influence on the functional properties. Another objective of this paper was to demonstrate the influence on the digestibility of the proteins with one of the main enzymes of the gastro-intestinal tract (pancreatin) on the basis of in vitro experiments after derivatization with phenolic substances. The enzymatic digestion of the derivatized proteins was promoted.
Selected food proteins (myoglobin and soy glycinin) were caused to react with flavonoids (apigenin and quercetin) to estimate the influence of the number and the position of hydroxy substituents. The protein derivatives formed have been charcterized in terms of their properties where they showed changes in the content of free amino groups, tryptophan, and thiol groups. The myoglobin derivatives have also been characterized in terms of their solubility at different pH-values to document the influence on the functional properties. The influence of myoglobin derivatives on the in vitro digestibility with trypsin was also demonstrated, with the digestion of the derivatized myoglobin being favored.