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1.
The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (> 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λmax) of up to 8.8 nm. The highest quenching constant (Kq) and the number of binding sites (n) were 0.92 (±0.01) × 1013 m ?1 s?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.  相似文献   

2.
Tea polyphenol (TP) inhibits digestive enzymes and reduces food digestibility. To explore the interaction between TP with digestive enzymes, bindings of ‐epigallocatechin‐3‐gallate (EGCG) to trypsin and α‐chymotrypsin were studied in detail using fluorescence, resonance light‐scattering, circular dichroism, fourier transform infrared spectroscopy methods and protein‐ligand docking. The binding parameters were calculated according to Stern–Volmer equation, and the thermodynamic parameters were determined by the van't Hoff equation. The results indicated that EGCG was capable of binding trypsin and α‐chymotrypsin with high affinity, resulting in a change of native conformation of these enzymes. EGCG had a greater influence on the structure of α‐chymotrypsin than trypsin. This study can be used to explain the binding interaction mechanism between TP and digestive enzymes.  相似文献   

3.
Epigallocatechin‐3‐gallate (EGCG) is the major and most potent representative in green tea, which has been proved to modulate myocardial contractility. Whether EGCG has some negative effects on cardiac function is not known. In the present study, we investigated the effects of EGCG at different doses on cardiac contraction and explored whether β2‐adrenoceptor (β2AR) was involved in EGCG‐induced cardiac effects. Isolated rat hearts were mounted on the Langendorff system and perfused with different concentrations of EGCG in low or normal calcium Krebs–Henseleit (KH) buffer. The contraction of hearts was measured. Ventricular myocytes were cultured with EGCG and isoprenaline (ISO, 10?7 M) for 12 h. ICI118,551 (55 nM) was used to inhibit β2AR. Cardiomyocyte shortening, viability, and responsiveness to ISO (10?9 M) were measured. EGCG dose dependently enhanced contractility of perfused heart in low calcium KH buffer. In the normal calcium KH buffer, EGCG at low dose (20 μM) increased heart contraction, while at high dose (50 μM), it increased the incidences of arrhythmia and diastolic dysfunction. In isolated ventricular myocytes, EGCG at the concentration of 0.001 to 1.0 μΜ did not affect their contraction. However, the responsiveness to ISO and the survival of myocytes were increased by EGCG (0.01 μM). The increased responsiveness was partially abolished by ICI118,551. The data obtained in this study demonstrated that EGCG at low dose conferred cardioprotection, yet at high dose increased the incidences of arrhythmia and diastolic dysfunction. β2AR was involved in EGCG‐induced cardiac effects.  相似文献   

4.
Low‐field nuclear magnetic resonance (NMR) spin–spin relaxation (T2) measurements were used to study the denaturation and aggregation of β‐lactoglobulin (β‐LG) solutions of varying concentrations (1–80 g L?1) as they were heated at temperatures ranging from ambient up to 90 °C. For concentrations of 1–10 g L?1, the T2 of β‐LG solutions did not change, even after heating to 90 °C. A decrease in T2 was only observed when solutions having higher concentrations (20–80 g L?1) were heated. Circular dichroism (CD) spectroscopy and fluorescence tests using the dye 1‐anilino‐8‐naphthalene sulfonate (ANS) on 0.2 and 1 g L?1 solutions, respectively, indicated there were changes in the protein's secondary and tertiary conformations when the β‐LG solutions reached 70 °C and above. In addition, dynamic light scattering (DLS) showed that protein aggregation occurred only at concentrations above 10 g L?1 and for heating at 70 °C and above. The hydrodynamic radius increased as T2 decreased. When excess 2‐mercaptoethanol was added, the changes in both T2 and the hydrodynamic radius followed the same trend for all β‐LG protein concentrations between 1 and 40 g L?1. These observations led to the conclusion that the changes in T2 were due to protein aggregation, not protein unfolding. Copyright © 2007 Society of Chemical Industry  相似文献   

5.
Rice bran albumin protein (RAP) is sensitive to thermal changes and tends to degrade when exposed to high‐temperature processing. In this work, RAP–epigallocatechin‐3‐gallate (EGCG) complex (RAPE) was prepared and the thermal stability was evaluated. Fluorescence results showed that EGCG could interact with RAP with a binding number n of 0.0885:1 (EGCG:RAP, w/w) and a binding constant K of 1.02 (± 0.002) ×104/M, suggesting both hydrogen bonding and van der Waals forces played an important role. FTIR analysis demonstrated that EGCG could induce secondary structural changes in RAP above a ratio of 1.6:1 (EGCG:RAP, w/w). Interestingly, the secondary structure changes of RAPE at different temperatures (25, 50, 60, 70, and 80 °C) were inhibited compared with that for RAP, suggesting RAPE was more resistant and stable to the heat treatment. In addition, a dense porous structure of RAPE was achieved due to the EGCG binding after thermal treatment. Furthermore, the Tpeak temperature of RAPE increased significantly from 64.58 to 74.16 °C and the enthalpy also increased from 85.53 to 138.52 J/g with a mass ratio increasing from 0 to 3.2 (EGCG:RAP, w/w), demonstrating the thermal stability of RAPE. In addition, the valine, methionine, and lysine content in RAPE were significantly higher than RAP following 80 °C treatment for 20 min (P < 0.05), exhibiting enhanced amino acid profiles, which might be due to EGCG–RAP interactions and microenvironment changes around relevant amino acids. These findings demonstrate that EGCG has the potential to improve the thermal stability of sensitive proteins and is beneficial for usage in the food industry.  相似文献   

6.
BACKGROUND: Recent studies indicate that the bioavailability of anthocyanins is extremely low. One of the possible reasons could be their binding to proteins. Therefore, the binding affinity of cyanidin‐3‐glucoside (Cy3glc) to HSA and α‐amylase was investigated by the quenching of protein tryptophan fluorescence. From data obtained, the binding constants and the free Gibbs energy were calculated. The changes in conformation of the proteins tested were studied with circular dichroism and the influence of binding on α‐amylase activity determined. RESULTS: Cy3glc quenched the tryptophan fluorescence and upon ligand binding a change in protein structure was observed related to the corresponding decrease in the α‐amylase activity. The association constants of 25 to 77 × 103 L mol?1 were calculated for different proteins, indicating weak interactions of non‐covalent nature. Competitive binding with HSA in the presence of 8‐anilino‐1‐naphthalene sulfonic acid suggest involvement of hydrophobic interactions, in the case of HSA the possible site being subdomain IIA. CONCLUSION: The strongest affinity of Cy3glc for HSA being at pH 7 underlines its potential in transport and distribution of the phenolic compounds in organisms. An influence on salivary amylase activity is possible when drinking berry juices with high anthocyanins content. Copyright © 2008 Society of Chemical Industry  相似文献   

7.
Epigallocatechin‐3‐O‐(3‐O‐methyl) gallate (EGCG3″Me) has been reported to inhibit type I allergy better than epigallocatechin gallate (EGCG), a major catechin in tea leaves (Camellia sinensis L). We examined the effects of extraction and sterilization on the catechin content and histamine release from mast cells, as a representative reaction of early phase allergy, in the manufacture of ‘Benifuuki’ green tea beverage. Among various varieties of tea, the cultivar ‘Benifuuki’ contains approximately 2% of EGCG3″Me. Ester‐type catechins and their epimers increased with the increased extraction temperature of the tea. A tea infusion, extracted at 90 °C, strongly inhibited histamine release from mast cells. Furthermore, sterilization affected the catechin content in the manufactured green tea beverage. Sterilization at high temperature promoted the isomerization of catechins and the sterilized green tea beverage had a strong inhibitory effect. When EGCG3″Me, EGCG, epicatechin‐3‐O‐gallate (ECG) and their epimers, GCG3″Me (gallocatechin‐3‐O‐(3‐O‐methyl) gallate), GCG (gallocatechin‐3‐O‐gallate) and CG (catechin‐3‐O‐gallate) were compared, the anti‐allergic effect of GCG3″Me was strongest, and the order of activity was GCG3″Me > EGCG3″Me > GCG > EGCG. We consequently suggest that it was necessary to extract components from tea at the highest temperature possible, and to pasteurize under retort conditions (118.1 °C, 20 min), to manufacture functional green tea beverage with an anti‐allergic action. Copyright © 2005 Society of Chemical Industry  相似文献   

8.
The heat stability of β-lactoglobulin (β-lg) is usually described with reference to a concentration-dependent pseudo-rate constant k. Kinetic and thermodynamic parameters for the irreversible denaturation of β-lg, in a whey protein mixture dissolved in Tris-HCl buffer, were examined over a wide temperature range 75–120°C and for degrees of denaturation [(Co-Ct)/Co] up to about 90%. The first-order kinetic model best described β-lg denaturation over the temperature range 75–85°C, whereas the second-order model applies in the range 90–120°C. A comparison between β-lg thermostability in buffer and literature data pertaining to more complex heating media (whey and milk), over the range 75–120°C, was carried out on the basis of changes in activation free energy (ΔG#), which itself takes into account changes in both activation enthalpy (ΔH#) and activation entropy (ΔS#). It was found that the thermal stability of β-lg in different media, and irrespective of the kinetic model assumed in the present study, can be ranked: buffer ≪ whey>milk for the temperature range 75–85°C. On the contrary, at the higher temperature range, 90–120°C, the ranking is buffer<whey<milk, when using the second-order model to describe the present data. For such comparisons to be valid the initial concentration of β-lg in various studies, as well as the reaction order applied, should be taken into consideration. © 1997 SCI.  相似文献   

9.
BACKGROUND: A new fermented tea produced by tea‐rolling processing of loquat (Eriobotrya japonica) leaf with green tea leaf (denoted as LG tea) showed a potent antihyperglycaemic effect in maltose‐loaded rats. The aim of this study, therefore, was to identify α‐glucosidase inhibitors in the antihyperglycaemic tea product. RESULTS: LG tea had a threefold higher maltase‐inhibitory activity (IC50 0.065 mg dried extract mL?1) than either the constituent loquat leaf or green tea alone. In addition, LG tea favourably inhibited maltase action rather than sucrase action. As a result of bio‐guided high‐performance liquid chromatography separations of LG tea, theasinensin A, theasinensin B, strictinin and 1,6‐digalloylglucose were newly identified as maltase inhibitors with IC50 values of 142, 225, 398 and 337 µmol L?1 respectively, along with previously identified catechins and theaflavins. CONCLUSION: Judging from the magnitude of the α‐glucosidase‐inhibitory contribution of each isolated compound to the overall inhibition of LG tea, catechins were the main candidates responsible for α‐glucosidase or maltase inhibition in LG tea, followed by theaflavins, theasinensins, strictinin and 1,6‐digalloylglucose. Copyright © 2010 Society of Chemical Industry  相似文献   

10.
Mango (Mangifera indica L cv Alphonso) was found to contain three isoforms (I, II and III) of β‐galactosidase which, upon purification on Sephadex G‐200, had relative abundances of 44, 38 and 18%, respectively. The total specific activity increased from 20 to 727 µmol l?1 upon purification, representing a ~36‐fold increase with a recovery of 0.28 U U?1. The optimal pH for activity and stability were in the ranges 3.6–4.3 and 4–6.2, respectively. The optimal temperature for β‐galactosidase activity was between 42 and 47 °C with Tm in the range 45–51 °C. The Km for pNP‐β‐galactopyranoside was 0.98, 1.11 and 0.95 mM , and Vmax was 0.56, 0.53 and 0.35 µmol pNP min?1, respectively for isoforms I, II and III. Hg2+ caused strong inhibition, whereas galacturonic acid, galactose, xylose, fucose and mannose slightly inhibited the activity of β‐galactosidase isoforms. The apparent molecular weights by GPC were 78, 58 and 91 kDa for isoforms I, II and III, respectively. The ability of these isoforms to degrade the endogenous substrate (arabinogalactan) possibly suggests a role in pectin dissolution during tissue softening/fruit ripening. Copyright © 2004 Society of Chemical Industry  相似文献   

11.
In this study, α‐amylase was immobilized on glutaraldehyde activated silanized calcium carbonate nanoparticles by a using covalent binding method. The surface modified nano calcium carbonate (CaCO3) were characterized using FTIR and SEM. Immobilization yield was found as 199.43 mg/g of calcium carbonate nanoparticles. The maximum activity was observed at pH 6.5. The immobilized enzyme had a higher activity at elevated temperature (50–90°C) than the free one. Reuse studies demonstrated that the immobilized enzyme could reuse 25 times while retaining 18.2% of its activity. Free enzyme lost its activity completely within 15 days. Vmax values for the free and immobilized enzymes were calculated as 10 and 0.35 mg/mL/min, respectively.  相似文献   

12.
An α‐l ‐rhamnosidase secreted by Penicillium citrinum MTCC‐8897 has been purified to homogeneity from the culture filtrate of the fungal strain using ammonium sulphate precipitation and cation‐exchange chromatography on carboxymethyl cellulose. The sodium dodecyl sulphate/polyacrylamide gel electrophoresis analysis of the purified enzyme gave a single protein band corresponding to the molecular mass 51.0 kDa. The native polyacrylamide gel electrophoresis also gave a single protein band confirming the enzyme purity. The Km and Vmax values of the enzyme for p‐nitrophenyl α‐l ‐rhamnopyranoside were 0.36 mm and 22.54 μmole min?1 mg?1, respectively, and kcat value was 17.1 s?1 giving kcat/Km value of 4.75 × 104 m ?1 s?1. The pH and temperature optima of the enzyme were 7.0 and 60 °C, respectively. The purified enzyme liberated l ‐rhamnose from naringin, rutin, hesperidin and wine, indicating that it has biotechnological application potential for the preparation of l ‐rhamnose and other pharmaceutically important compounds from natural glycosides containing terminal α‐l ‐rhamnose and also in the enhancement of wine aroma.  相似文献   

13.
Arabinoxylans (AXs) from wheat malts potentially affect beer quality and production. β‐ d ‐Xylosidase is a key enzyme that degrades the main chains of AXs to produce xylose. This study performed a partial characterization of β‐ d ‐xylosidase from wheat malts. The optimal temperature was 70 °C and the enzyme exhibited excellent thermostability, that is, residual activities were 92.6% at 60 °C for 1 h. The enzyme was stable over a pH range of 3.0–6.0 and showed optimum activity at pH 3.5 and 4.5. Kinetic parameters Km and Vmax of wheat malt β‐ d ‐xylosidase against p‐nitrophenyl‐xyloside were 1.74 mmol L−1 and 0.76 m m min−1, respectively. The enzyme activity was severely inhibited by Cu2+, moderately inhibited by Mn2+, Mg2+, Al3+, Ca2+, Ba2+ and Na+ and mildly inhibited by Fe3+ and Fe2+. The partial enzymatic characterization achieved in this study can be used as a theoretical basis for purifying β‐ d ‐xylosidase from wheat malts. Copyright © 2015 The Institute of Brewing & Distilling  相似文献   

14.
γ‐Aminobutyric acid (GABA) is a major functional ingredient in Chinese rice wine. A new HPLC method for determining GABA using pre‐column derivatization with dansyl chloride was developed. The HPLC operating conditions were as follows: a Hypersil ODS2 C18 column; mobile phase, methanol and water (1:1); gradient elution; absorption at 254 nm; flow rate, 1 mL/min; pH 9; and column temperature, 30 °C. Under optimal HPLC conditions, the linear equation was y = 3.5 × 10?7x ? 0.014. The precision (relative standard deviation, RSD) was 0.54%, the stability (RSD) was 0.21%, the recovery ratio was 97.4% and reproducibility (RSD) was 1.57%. This new method appears to be sensitive, accurate, convenient, steady and relatively fast. The results suggest that the new method is also more reliable. Copyright © 2015 The Institute of Brewing & Distilling  相似文献   

15.
In this work, crude polysaccharide extracts were extracted from pumpkin (Cucurbita moschata) fruit by hot water. After removal of proteins and purification, polysaccharides of pumpkin fruit (PP1‐1) were subjected to structural identification. Gas chromatography analysis indicated that PP1‐1 comprised of galactose (86.4%), and glucose (13.6%). The molecular weight of PP1‐1 was measured to be 0.87 × 104 Da by gel permeation chromatography. The inhibitory kinetic evaluation showed that it was non‐competitive inhibition of PP1‐1 on the α‐glucosidase‐catalysed hydrolysis of PNPG. The Michaelis–Menten constant (Km) was 0.106 m , and the inhibitory constants (Ki), 0.435 mg.  相似文献   

16.
Among several bacteria examined in this study, a hyper acidophil and thermostable Micrococcus sp.NS 211 designated as M.Amy NS 211 was selected for production of amylase using starch agar plates with following incubation at 85°C. Identification by 16SrRNA on selected bacterium disclosed the highest similarity for protean regions of this gene, 27 F and 1492R as Micrococcus sp.NS 211. Although activity of M.Amy NS 211 was established at temperatures between 70 and 110°C and pH ranges 1.2–8.0, the optimum temperature and pH was achieved at 85°C and 3.5 in sodium citrate buffer system respectively. Two‐step chromatography was performed using (CM Bio‐Gel A) and (Bio‐Gel A‐150) columns to purify 84 kDa hyper acidophil and thermostable α‐amylase. SDS‐PAGE analysis showed molecular mass and amylolytic activity as single band. Enhancement of enzyme activity was obtained in presence of 5 mM MnCl2 (298%), CaCl2 (347%), FeCl2 (211%), MgCl2 (253%), ZnCl2 (146%), NiCl (142%), NaCl (141%), Na‐sulfate (153%) while inhibition was observed with (5 mM) EDTA, PMSF (3 mM), urea (8 M), and SDS (1%) at 143, 134, 43, and 119%, respectively. M.Amy NS 211 can be applied in laundry detergents, textile, and modern relevant industrial processes at extreme temperatures and under acidic conditions.  相似文献   

17.
Green tea (–)‐epigallocatechin‐3‐gallate (EGCG) is known as to regulate obesity and fat cell activity. However, little information is known about the effects of EGCG on oxidative reactive oxygen species (ROS) of fat cells. Using 3T3‐L1 preadipocytes and adipocytes, we found that EGCG increased ROS production in dose‐ and time‐dependent manners. The concentration of EGCG that increased ROS levels by 180–500% was approximately 50 μM for a range of 8–16 h of treatment. In contrast, EGCG dose‐ and time‐dependently decreased the amount of intracellular glutathione (GSH) levels. EGCG was more effective than (–)‐epicatechin, (–)‐epicatechin‐3‐gallate, and (–)‐epigallocatechin in changing ROS and GSH levels. This suggests a catechin‐specific effect. To further examine the relation of GSH to ROS as altered by EGCG, we observed that exposure of preadipocytes and adipocytes to N‐acetyl‐L ‐cysteine (a GSH precursor) blocked the EGCG‐induced increases in ROS levels and decreases in GSH levels. These observations suggest a GSH‐dependent effect of EGCG on ROS production. While EGCG was demonstrated to alter levels of ROS and GSH, its signaling was altered by an EGCG receptor (the so‐called 67 kDa laminin receptor(67LR)) antiserum, but not by normal rabbit serum. These data suggest that EGCG mediates GSH and ROS levels via the 67LR pathway.  相似文献   

18.
Sorghum malt α‐amylase can compete with bacterial α‐amylase in industrial applications, if sufficiently stable and produced in a large enough quantity. Conditions for maximal α‐amylase production in sorghum malt and the physico‐chemical properties of the α‐amylase so produced are reported in this study. Sorghum grains were steeped in buffers with varying pH (4.0–8.0) for 24 h, at room temperature, and germinated for another 48 h to obtain the green malt. The buffer that induced the highest quantity of α‐amylase was chosen as the optimal pH and served as the medium for further steeping experiments conducted at different temperatures (10, 20, 30, 40, 50 and 60°C). The α‐amylase activity in the extract was determined in order to obtain the optimum temperature for α‐amylase induction at this particular pH. For the purpose of comparison, the α‐amylase produced at the optimum pH and temperature was purified to apparent homogeneity by a combination of ion‐exchange and size‐exclusion chromatography, and further characterized. Eight‐fold higher α‐amylase activity was induced in pH 6.5 buffer at 20°C compared with water, the traditional steeping medium. The Km and Vmax were estimated to be 1.092 ± 0.05 mg mL?1 and 3516 ± 1.981 units min?1, respectively. The activation energy of the purified amylase for starch hydrolysis was 6.2 kcal K?1 mol?1. Chlorides of calcium and manganese served as good activators, whereas CuSO4 inhibited the enzyme with a 42% loss in activity at 312 mm salt concentration. Copyright © 2012 The Institute of Brewing & Distilling  相似文献   

19.
An α‐l ‐rhamnosidase producing fungal strain has been isolated from decaying lemon fruit. The fungal strain has been identified as Aspergillus flavus. The α‐l ‐rhamnosidase has been purified from the culture filtrate of the fungal strain using ultra filtration and cation exchange chromatography on carboxy methyl (CM) cellulose. The molecular mass of the purified enzyme determined by SDS–PAGE analysis was 41 kDa. The Km values of the enzyme using p‐nitrophenyl‐α‐l ‐rhamnopyranoside and naringin as the substrates were 1.89 and 1.6 mm respectively. The pH and temperature optima of the enzyme were 11.0 and 50 °C respectively. The effects of various chemical species present in grape fruit juice and wine on the activity of the enzyme have been determined.  相似文献   

20.
Cyclodextrins (CDs) are cyclic oligosaccharides derived from the enzymatic degradation of starch. Emulsifying functionality of β‐cyclodextrin (β‐CD) upon its complexation with selected solvents (octanol, decane, and toluene) was studied. In several tests, the three‐phase systems containing the emulsion fraction in the middle position were obtained. The examination of variations in the phase behavior of the test systems showed that the decane/β‐CD/water system had the highest emulsion phase volume when β‐CD at concentration of 10% w/v was used. A reduction in interfacial tension (IFT) of the oil–water interface in each test system was observed with the following order: toluene, decane, and octanol. The precipitated fraction obtained upon centrifugation of the emulsion phase, was structurally characterized as the inclusion complex (IC) formed between β‐CD and each of the three test solvents. The wettability of the IC particles was determined through contact angle measurement and formation of the oil‐in‐water (O/W) Pickering emulsions was confirmed (θow<90°). With use of size distribution data, the ICs particles as the microparticles (1–10 µm) were found to be the main species involved in the formation and stabilization of the emulsions.  相似文献   

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