1,720,961 research outputs found
Cocoa brew inhibits in vitro α-glucosidase activity: The role of polyphenols and high molecular weight compounds
No full textCocoa brew showed a dose-dependent inhibitory activity against α-glucosidase (IC50 7.87 mg/mL). The cocoa brew was fractionated by ultrafiltration in a low molecular weight fraction (LMW 30 kDa) and intermediate molecular weight (IMW 10-30 kDa) fractions. All fractions tested caused some inhibition with IMW that was the most active (IC50 2.37 mg/mL). LMW fraction was separated with Sephadex LH-20 in an unbound (containing monomeric and dimeric catechins) and a bound fraction. All the inhibitory activity was recovered in the unbound fraction. All the phenolic compounds identified with HPLC showed α-glucosidase inhibitory activity. IMW and HMW fractions were fractionated by ethanol precipitation. The fractions from IMW precipitated with 75 and 25% ethanol were found to contain power inhibitors of α-glucosidase activity (IC50 0.87 and 1.01 mg/mL, respectively). In the HMW sample, the fractions precipitated with 50 and 75% ethanol were found to be active against α-glucosidase activity. Most of the inhibitory activity against α-glucosidase of cocoa brew was due to the LMW fraction (56%) whereas IMW and HMW contributed for about 47% of the inhibitory activity. This study suggests that different components of cocoa may influence α-glucosidase activity
The gastro-intestinal tract as the major site of biological action of dietary melanoidins
No full textEmerging evidence from laboratory researches has highlighted the bioactivity of food melanoidins and melanoproteins. Whilst such studies have been carried out with different in vitro systems, information about melanoidins absorption and bio-availability are scarce. However, they are generally considered as poorly absorbable and bio-available compounds. Therefore, we present a review in which the gastro-intestinal tract is hypothesized to be the main site of action of food melanoidins and melanoproteins biological activity. We described recent data supporting this hypothesis both in vitro model systems and in vivo. Importantly, we focused this review only on the effect of melanoidins and melanoproteins extracted from food. Most of the studies had been carried out using water-soluble carbohydrate-based melanoidins isolated from different food sources (beer, barley coffee, coffee). In bakery products, melanoidins are protein-based structure (melanoproteins) which are largely insoluble in water. Dietary melanoidins and melanoproteins have been demonstrated to exert in vitro antioxidant and metal chelating ability in the gastro-intestinal tract reducing the formation of lipid hydroperoxides and advanced lipid oxidation end products during the digestion of meat. The reduction in the formation of these pro-atherogenic compounds has been shown to be followed by a decrease in their absorption in human volunteers. Food melanoidins have also shown in vitro anti-caries and prebiotic activities. We conclude by underlining the possible role of food melanoidins in the prevention of gastro-intestinal tract cancers. We hope this review will stimulate further research on food melanoidins and their biological activities in the gastro-intestinal tract
Mechanism of inhibition of protein glycation by polyphenols
No full textWe have observed that protocatechuic (PC) and 3,4-dihydroxyphenylacetic (DHPA) acids, found in human plasma after the consumption of foods rich in anthocyanins and flavanols, inhibit the formation of advanced glycation endproducts (AGEs).
We have investigated the mechanisms of inhibition incubating for 7 days bovine serum albumin (BSA) (50 mg/mL) and glucose (0.8 mol/L) in the presence and absence of these polyphenols at various concentrations. Fluorescence emission at 405 nm was used to evaluate AGEs formation. Carboxymethyl-lysine (CML), Amadori products and quinoproteins were determined by ELISA, NBT assay and electrophoresis, respectively. Both PC and DHPA were able to decrease the formation of Amadori products, fluorescent AGEs and CML. These decreases were concentration dependent. Quinoproteins formation increases with the increase of polyphenol concentration. BSA was also incubated with 0.5 and 1.0 mmol/L of phenols in the absence of glucose. After 7 days of incubation the unbound polyphenols were removed by ultrafiltration. The phenols-treated BSA was incubated with glucose for 7 days. No significant differences are observed in the inhibition of AGEs formation between phenol pre-incubated and non pre-incubated BSA.
These results and the formation of quinone modified BSA suggest that polyphenols are pre-Amadori inhibitors of AGEs formation. Phenols bind BSA and decrease glucose binding. They are oxidized (pH 7.5, 37°C) in the reactive quinones intermediates and react with BSA amino groups forming quinone modified BSA and decreasing the AGEs formation
Pomegranate ellagitannins inhibit α-glucosidase activity in vitro and reduce starch digestibility under simulated gastro-intestinal conditions
No full textPomegranate extract was tested for its ability to inhibit α-amylase and α-glucosidase activity. Pomegranate extract strongly inhibited rat intestinal α-glucosidase in vitro whereas it was a weak inhibitor of porcine α-amylase. The inhibitory activity was recovered in an ellagitannins-enriched fraction and punicalagin, punicalin and ellagic acid were identified as α-glucosidase inhibitors (IC50 of 140.2, 191.4 and 380.9 μmol/L, respectively). Kinetic analysis suggested that the pomegranate extract and ellagitannins inhibited α-glucosidase activity in a mixed mode. The inhibitory activity was demonstrated using an in vitro digestion system, mimicking the physiological gastro-intestinal condition, and potatoes as food rich in starch. Pre-incubation between ellagitannins and α-glucosidase increased the inhibitory activity, suggesting that they acted by binding to α-glucosidase. During digestion punicalin and punicalagin concentration decreased. Despite this loss, the pomegranate extract retained high inhibitory activity. This study suggests that pomegranate ellagitannins may inhibit α-glucosidase activity in vitro possibly affecting in vivo starch digestion
Cocoa extract inhibits in vitro α-glucosidase activity: the role of polyphenols and melanoidins
No full textStudies on the health benefits of cocoa have recently focused on the anti-diabetic potential of cocoa extract. The intake of cocoa has been related to a reduction in the post-prandial levels of blood glucose in diabetic rats. A possible explanation for these observations is that cocoa extract possesses the ability to inhibit enzymes involved in the digestion of carbohydrate, attenuating the post-prandial increase in glycemia. Using an in vitro model, the activity of rat intestinal α-glucosidase has been determined in the absence and presence of cocoa extract and fractions. The addition of cocoa extract inhibited α-glucosidase activity with an IC50 of 7.9 mg/mL. The cocoa extract was further fractionated by ultrafiltration in a polyphenolic–rich fraction (10 KDa). Both the fractions were able to inhibit α-glucosidase with an IC50 of 2.3 and 3.9 mg/mL, respectively. To identify the bioactive compounds, the polyphenolic–rich fraction was further fractionated with Sephadex LH-20 columns to separate tannins from low molecular weight flavanols. Furthermore, the melanoidins-rich fraction was separated in two fractions using ultrafiltration at 30 KDa. All the obtained fractions were characterized for their ability to inhibit α-glucosidase and for their content in polyphenolic compounds
Composition and properties of peptides that survive standardised in vitro gastro-pancreatic digestion of bovine milk
No full textThere are conflicting results on the release and conservation of bioactive protein sequences during in vitro digestion. Only the peptides that are released and survive may exert their action. Peptides <3 kDa were determined by mass spectrometry after standardised in vitro gastro-pancreatic digestion of bovine milk. At a degree of digestion of 30.7%, 384 peptides were obtained from 2 to 25 residues in length. Five other peptides were recovered after reduction of disulphide bonds. Due to the presence of proline residues at the last or second last position at the C-terminus, a high number of peptides with ACE-inhibitory activity were obtained. Peptides with opioid, antimicrobial, immunomodulatory and antithrombotic activities were recovered, with many precursors and degradative products. Peptides with opioid and antimicrobial activities may be the result of evolutionary processes. The peptides obtained were similar to those released in the human jejunum
Characterization of dietary melanoidins and evaluation of the cytotoxic activity against colon cancer cells
No full textEmerging evidence from in vitro and in vivo studies suggested that the gastro-intestinal tract may be the key site for the biological action of food melanoidins. Recently, Vitaglione et al. reviewed the possible mechanisms by which coffee melanoidins may influence the risk of colorectal cancer development. In this work, we tested high molecular weight melanoidins (HMWM) extracted from different food sources for their cytotoxic activity against colon cancer cell lines. Water soluble HMWM were extracted by ultrafiltration (cut-off 10 kDa) from instant coffee, cocoa brew, dark beer and instant barley coffee. HMWM have been chemically characterized for their content in total polyphenols, protein, and polysaccharides, antioxidant activity as well as their spectroscopic properties. These extracts were assessed using two colon cancer cell lines: Caco-2 and SW480. Cytotoxic activity was assayed by MTT and data are presented as the dose that inhibited 50% control growth (IC50). All of the assessed HMWM were cytotoxic against Caco-2 cell line. Coffee HMWM were the most effective (IC50 of 1042 and 857 μg/mL after 24 and 48h of treatment, respectively) followed by dark beer, barley coffee and cocoa HMWM. Meanwhile, they are less effective against SW480 with coffee HMWM that were the most effective (IC50 of 2038 μg/mL after 48h) followed by cocoa, dark beer and barley coffee. Considering that the colon accumulates its content over at least 24h in a maximum volume of 2 litres, and that the daily intake of coffee melanoidins range between 0.5 and 2.0 g , it is possible to calculate a hypothetical concentration of coffee melanoidins in the colon between 0.25 and 1 mg/mL, which are values comparable to the IC50 for the cytotoxic activity against colon cancer cells
Pomegranate ellagitannins inhibit in vitro carbohydrate digestion
No full textPomegranate is an ancient fruit studied for its anti-diabetic properties. The aim of the present work was to identify the α-glucosidase inhibitors in a pomegranate juice polyphenol-rich extract (PPRE). The PPRE, obtained using C18 solid-phase extraction, contained 5.87 ± 0.26 mmol of ellagic acid equivalent (EAE)/L and showed an inhibitor activity on rat intestinal α-glucosidase with an IC50 value of 922.2 ± 7.1 μmol of EAE/L.
The PPRE was fractioned in three different fractions using C18 columns and glucosidase inhibitory activity was recovered in an ellagitannins-enriched fraction. After HPLC separations punicalagin, punicalin and ellagic acid were identified as α-glucosidase inhibitors with IC50 values of 140.2 ± 1.1, 191.4 ± 1.3 and 380.9 ± 3.5 μmol/L, respectively.
Kinetic analysis showed that the inhibition is of mixed type with a Ki of 903.0 ± 74.7 μmol/L.
Pomegranate ellagitannins interact directly with the α-glucosidase and the non-specific binding of ellagitannins may alters the protein structure reducing the velocity of the catalysis and altering the accessibility to the active site of the substrate.
The inhibitory effect on carbohydrate hydrolysis of PPRE was tested against a real food system (potatoes) using an in vitro digestion protocol. The presence of PPRE produced a decrease in the amount of released glucose. During digestion punicalin and punicalagin concentration decreased as a consequence of their binding to salivary or potatoes proteins and of their hydrolysis. Despite this loss, the PPRE retained high inhibitory activity.
In conclusion, our data are consistent with the hypothesis that pomegranate juice can be considered a very useful food supplement to ameliorate postprandial hyperglycemia linked to type 2 diabetes and hyperglycemia-induced vascular complications
Identification of ACE-inhibitory peptides from Phaseolus vulgaris after in vitro gastrointestinal digestion
No full textThe objective of this study was to identify the angiotensin I-converting enzyme (ACE)-inhibitory peptides released from thermally treated Phaseolus vulgaris (pinto) whole beans after in vitro gastrointestinal digestion. The degree of hydrolysis increased during digestion reaching a value of 50% at the end of the pancreatic digestion. The<3 kDa fraction of the postpancreatic sample showed high ACE-inhibitory activity (IC50=105.6±2.1 mug of peptides/mL). Peptides responsible for the ACE-inhibitory activity were isolated by reverse-phase high-performance liquid chromatography (HPLC). Three fractions, showing the highest inhibitory activity, were selected for tandem mass spectrometry (MS/MS) experiments. Eleven of the identified sequences have previously been described as ACE-inhibitors. Most of the identified bioactive peptides have a hydrophobic amino acid, (iso)leucine or phenylalanine, or proline at the C-terminal position, which is crucial for their ACE-inhibitory activity. The sequence of some peptides allowed us to anticipate the presence of ACE-inhibitory activity
- …
