ANTI-AMYLASE, ANTI-GLUCOSIDASE AND ANTI-ANGIOTENSIN I-CONVERTING ENZYME POTENTIAL OF SELECTED FOODS

α‐Amylase and α‐glucosidase have been targeted as potential avenues for modulation of postprandial hyperglycemia through mild inhibition of the enzymatic breakdown of complex carbohydrates to decrease meal‐derived glucose absorption. Water‐soluble extracts with optimized phenolic content of selected American and Asian foods were investigated for inhibitory activity against α‐amylase and α‐glucosidase, as well as angiotensin I‐converting enzyme (ACE), which has been linked to hyperglycemia‐associated hypertension. Porcine pancreatic α‐amylase (PPA) was allowed to react with each phenolic‐optimized food extract, and the derivatized enzyme–phytochemical mixtures obtained were characterized for residual amylase activity. The α‐glucosidase and ACE activities were determined in the presence of each phenolic‐optimized food extract. The amylase activity was inhibited more than the glucosidase activity in the presence of these phytochemical extracts, and more so by Asian foods than by American foods. The Asian spice ginger was found to possess strong ACE inhibitory activity in addition to significant anti‐amylase activity. The α‐amylase enzyme inhibition was positively associated with extract antioxidant activity and negatively with extract protein content. The significance of food‐grade, plant‐based amylase inhibitors for modulation of carbohydrate breakdown and control of glycemic index of foods in the context of preventing hyperglycemia and diabetes mellitus complications in the long term and ACE inhibitors for modulation of associated hypertension is hypothesized and discussed.     

Extraction,optimisation and characterisation of phenolics from Thymus vulgaris L.: phenolic content and profiles in relation to antioxidant,antidiabetic and antihypertensive properties

The objectives of this study were to examine varying extraction conditions of Thymus vulgaris L. as related to phenolic content and profiles of the extracts and their antioxidant, antihypertensive and antidiabetic properties. Phenolics were extracted under various conditions pertaining to free and bound phenolics, solvent type and combination of extraction time and temperature, and these extracts were evaluated in terms of their antioxidant activities and inhibitory activities of angiotensin‐converting enzyme (ACE), α‐glucosidase and α‐amylase. The acetone–water solvent mixture (1:1; v/v) produced the extract with the greatest phenolic content, antioxidant activity and inhibitory activities of ACE and α‐glucosidase. The optimal extraction temperature for maximum phenolic content and antioxidant activity associated with methanol extraction was 60 °C, whereas a lower temperature at 40 °C was required to maximise inhibitory activities for ACE, α‐glucosidase and α‐amylase. An inverse relationship was seen between antioxidant and glucosidase inhibitory activities vs. the ACE and α‐amylase inhibitory activities, which suggests the need for extractions to be directed to specific bioactivities of thyme extracts. Generally, the results indicate major differences in phenolic profiles among the tested extraction conditions with thymol as the predominant phenolic seen in most extractions, while gallic acid, rosmarinic acid or diosmin also predominated in other extracts. Extracts with the same predominant phenolic compound and similar phenolic content showed major disparities in their ACE, glucosidase and α‐amylase inhibitory activities, indicating that the major phenolic profiles of thyme extracts may not be necessarily related to the degree of inhibition of ACE, glucosidase and α‐amylase enzymes.     

Molecular Weight Affected Antioxidant,Hypoglycemic and Hypotensive Activities of Cold Water Extract from Pleurotus citrinopileatus

Cold water extract of P. citrinopileatus (CWEPC) was fractioned into 4 fractions, PC‐I (<1 kDa), PC‐II (1‐3.5 kDa), PC‐III (3.5‐10 kDa), and PC‐IV (>10 kDa), by ultrafiltration. The antioxidant activities, the inhibition of pancreatic α‐amylase, intestinal α‐glucosidase, and hypertension‐linked angiotensin converting enzyme (ACE), as well as the contents of polysaccharides, protein, and phenolic compounds of 4 fractions were determined. The results showed that lower MW fractions exerted a higher antioxidant activity, which was correlated to phenolic contents. The high molecular fraction (PC‐IV) exhibited significantly higher inhibitory activity on α‐amylase, α‐glucosidase, and ACE compared to CWEPC and the other 3 lower MW fractions (<10 kDa), which was more related to protein contents. The inhibition capability of CWEPC and PC‐IV on α‐amylase activity was 1/13.4 to 1/2.7 relative to that of acarbose, respectively. Kinetic data revealed that PC‐IV fraction followed a noncompetitive inhibition pattern on α‐glucosidase activity. The study demonstrated that various MW fractions and types of components contribute to different biological functions of P. citrinopileatus and it is protein constituents but not peptides responsible for the hypoglycemic potential of CWEPC.     

EVALUATION OF PEPPER (CAPSICUM ANNUUM) FOR MANAGEMENT OF DIABETES AND HYPERTENSION

Natural α‐amylase and α‐glucosidase inhibitors from food‐grade plants offer an attractive strategy to control postprandial hyperglycemia for type 2 diabetes management. Concurrently associated macrovascular complication of hypertension can be managed by similar extracts by inhibition of angiotensin I‐converting enzyme (ACE ). In this study, nine types of pepper were investigated for inhibitory activity against said enzymes. Several pepper extracts had high α‐glucosidase inhibitory activity, which was not correlated to total phenolic content and free radical scavenging‐linked antioxidant activity. Select extracts such as Green pepper and Long hot pepper had less or no inhibitory effect on the α‐amylase activity, which indicates the potential for reduced side effects. Among various water extracts, Yellow, Cubanelle and Red pepper had the highest ACE inhibitory activity. Therefore, combinations of pepper could be screened for dietary management of type 2 diabetes, associated hypertension and microvascular complications linked to oxidative dysfunction, and provide the basis for clinical studies.     

INHIBITORY POTENTIAL OF WINE AND TEA AGAINST α-AMYLASE AND α-GLUCOSIDASE FOR MANAGEMENT OF HYPERGLYCEMIA LINKED TO TYPE 2 DIABETES

ABSTRACT

Natural α‐amylase and α‐glucosidase inhibitors from food‐grade plants offer an attractive strategy to manage postprandial hyperglycemia for type 2 diabetes management via control of starch breakdown and intestinal glucose absorption. In this study, four random sources of red and white wines as well as four types of teas were investigated for α‐amylase and α‐glucosidase inhibitory potential. Water extracts of black tea had the highest α‐glucosidase inhibitory activity, followed by white tea and oolong tea. All the randomly selected red wines had significant α‐glucosidase inhibitory activity compared to white wine. The α‐glucosidase inhibitory activity of the tea and wines correlated to the phenolic content, antioxidant activity and phenolic profile of the extracts. Further, these extracts had less or no α‐amylase inhibitory activity, indicating potential to overcome the side effects of undigested starch. This research has relevance for managing hyperglycemia and related oxidation‐linked dysfunction and concurrently reducing problems of undigested starch.

PRACTICAL APPLICATIONS

In this study anti‐diabetic‐relevant potential of wines and teas were confirmed in four types of red and white wines as well as four types of commonly available teas using in vitro enzyme assays for alpha‐glucosidase and alpha‐amylase inhibitory activities. In vitro inhibitory activities of these enzymes provide a strong biochemical rationale for further in vivo studies and dietary management strategy for type 2 diabetes through the control of glucose absorption. Further this phenolic antioxidant‐enriched dietary strategy using specific beverage combinations can generate a whole food profile that has the potential to reduce hyperglycemia‐induced pathogenesis and also associated complications linked to cellular oxidation stress.     

AMYLASE AND HELICOBACTER PYLORI INHIBITION BY PHENOLIC EXTRACTS OF PINEAPPLE WASTES BIOPROCESSED BY RHIZOPUS OLIGOSPORUS

This study focused on the potential functional activity of phenolic‐enriched pineapple wastes bioprocessed by Rhizopus oligosporus. Using the phenolic‐enriched bioprocessed extracts, amylase inhibition relevant to Type 2 diabetes and Helicobacter pylori inhibition linked to stomach ulcer were investigated. Two treatments were studied: 9 g of pineapple residue plus 1 g of soy flour (P9) and 5 g of pineapple residue plus 5 g of soy flour (P5). Extracts obtained after 2 and 10 days of growth were selected to represent early and late stages of bioprocessing based on phenolic content. Potent α‐amylase inhibition was found in P9 treatment at 2 days of fungal growth and was maintained after subsequent boiling, freeze‐drying and/or autoclave treatment. Amylase inhibitory activity did not correlate with the DPPH radical scavenging antioxidant activity of the extracts and therefore it is likely linked to the structure of the phenolic compounds. H. pylori inhibitory activity was found in P5 treatment after 10 days of R. oligosporus growth and may be linked to phenolic compounds present at this stage.     

Screening grape seeds recovered from winemaking by‐products as sources of reducing agents and mammalian α‐glucosidase and α‐amylase inhibitors

Grape seeds collected from vinification of various grape varieties were extracted by supercritical CO₂ for oil recovery. The defatted residues thus obtained were considered as a re‐utilisable co‐product and assessed for phenolic content, reducing capacity and inhibitory activities against mammalian α‐amylase and α‐glucosidase enzymes. Supercritical CO₂ treatment led to higher recovery of anthocyanins. Reducing capacity of phenolic extracts reached up to ~2200 mmolFe(II) kg^?1, much higher than that of various natural phenolic sources. The anthocyanin‐rich extracts showed the highest inhibitory effectiveness towards α‐glucosidase (I₅₀ value equal to ~40 μg gallic acid equivalents (GAE)/mL ~ half than acarbose). Inhibitory effectiveness towards α‐amylase activity was similar among grape varieties, with I₅₀ values comparable to that of acarbose and correlated with proanthocyanidin contents. These results could pave the way for an efficient processing of grapes, including cascade processes, namely: winemaking, oil extraction from recovered grape seeds and phenolic extraction from defatted grape seeds as potential cost‐effective nutraceuticals.     

Identification and functional characterisation of bioactive peptides in rice bran albumin hydrolysates

The potential heath‐benefitting bioactivities of rice bran albumin hydrolysates were investigated. The antioxidant and α‐glucosidase‐ and angiotensin‐converting enzyme (ACE)‐inhibitory activities of the crude hydrolysates and their fractions were determined. The fractions with the highest bioactivities were analysed by liquid chromatography–tandem mass spectrometry/mass spectrometry to identify the active peptide sequences. Hydrolysates produced by commercial proteases Alcalase and Protamax exhibited the highest α‐glucosidase‐ and ACE‐inhibitory activities, resulting in 43.1 ± 2.1% and 54.4 ± 5.1% inhibition of the enzymes, respectively. Inhibitory activities against both enzymes were highest in the MW<3‐kDa fractions that were eluted under alkaline conditions. A number of peptide sequences were identified in the fractions, which contained several sequences with reported α‐glucosidase‐ or ACE‐inhibitory activities. This is the first time that such activities are reported for rice bran albumin hydrolysate, and it demonstrated that the hydrolysates may be developed into nutraceuticals useful in managing diabetics and hypertension.     

α-Glucosidase- and α-amylase-inhibitory activities of phlorotannins from Eisenia bicyclis

BACKGROUND: In an effort to develop alternative therapeutic agents, strong inhibitory activity against α‐glucosidase and α‐amylase was detected in Eisenia bicyclis methanolic extract. RESULTS: In this study, two phlorotannins were isolated from E. bicyclis and characterised by chromatography and nuclear magnetic resonance. The active substances were identified as fucofuroeckol A (FF) and dioxinodehydroeckol (DD). To the authors' knowledge, this is the first report of the identification of these substances in E. bicyclis. However, to date, no antidiabetic activity of FF and DD has been reported. Both phlorotannins demonstrated significant inhibitory activity against α‐glucosidase and α‐amylase. FF showed potent antidiabetic activity, with IC₅₀ values of 131.34 nmol L^?1 against α‐glucosidase and 42.91 µmol L^?1 against α‐amylase. The corresponding IC₅₀ values of DD were 93.33 nmol L^?1 and 472.7 µmol L^?1. Furthermore, kinetic analysis revealed that FF and DD exhibited non‐competitive inhibitory activity against α‐glucosidase. CONCLUSION: These results suggest that FF and DD may be candidates for the development of an antidiabetic pharmaceutical agent or food additive. Copyright © 2012 Society of Chemical Industry     

Interaction of aqueous extracts of two varieties of Yam tubers (Dioscorea spp) on some key enzymes linked to type 2 Diabetes in vitro

This study sought to assess the effect of processing of yam flour [from white yam (Dioscorea rotundata) and water yam (Dioscorea alata)] to paste, on the antioxidant properties and inhibition of key enzymes linked to type‐2 diabetes (α‐amylase and α‐glucosidase). The phenolic content (phenol and flavonoid), antioxidant properties, α‐amylase and α‐glucosidase inhibitory properties of the aqueous extracts of the yam products were determined. Processing into paste caused significant (P < 0.05) percentage decrease in their total phenol and flavonoid content of the yam varieties. However, significant increase (P < 0.05) in the antioxidant properties of the yam varieties was observed after processing. Furthermore, the yam extracts inhibited α‐amylase and α‐glucosidase activities in vitro in a dose‐dependent parttern (1–4 mg mL^?1), however, the pasting process caused significant (P < 0.05) decrease in the α‐amylase inhibitory and α‐glucosidase inhibitory activities. Therefore, processing the yam varieties into paste (browned) could potentially increase their antioxidant capacity as well as decreasing their α‐amylase and α‐glucosidase inhibitory properties.     

Production of soy yogurt enriched with glyceollins

Soy milk was prepared from regular soybean (M1), soybean germinated for 3 days at 25°C (M2), and soybean germinated under fungal infection (M3). Rhizopus microsporus var. oligosporus ATCC 22959 was used as the elicitor for glyceollin production. Each soy milk was fermented with Streptococcus infantarius 12 and Weissella sp. 4 (1:5, v/v) for 12 h at 37°C. Significant induction of glyceollins was confirmed only in M3 soy milk and glyceollins maintained stably during 12 h fermentation period. The concentration of glyceollins in M3 yogurt was 2,400.4±83 and 2,525.2±158 μg/g dry matter (d.m.) at 0 and 12 h, respectively. The amount of daidzein was significantly higher in M3 yogurt (635.1±21) than that of M1 (417±11) and M2 (545±17 μg/g d.m.) yogurt in 12 h (p<0.05). M2 yogurt had the highest amount of genistein (695.3±17) followed by M3 (634.5±26) and M1 (612.5±14 μg/g d.m.) yogurt. M3 soy yogurt also showed the highest content of total phenolic compounds (5.37 mg/g) and antioxidant activity. The results indicated that functional soy yogurt can be prepared from soybean enriched with glyceollins.     

Inhibitory potential of phenylpropanoid glycosides from Ligustrum purpurascens Kudingcha against α‐glucosidase and α‐amylase in vitro

The leaves of Ligustrum purpurascens are used in a Chinese traditional tea called small‐leaved kudingcha, which is rich in phenylpropanoid glycosides (PPGs) and has many beneficial properties. Two critical exoacting glycoside hydrolase enzymes (glucosidases) involved in carbohydrate digestion are α‐glucosidase and α‐amylase. We investigated the properties of PPGs from L. purpurascens for inhibiting α‐amylase and α‐glucosidase activity in vitro and found IC₅₀ values of 1.02 and 0.73 mg mL^?1, respectively. The patterns of inhibiting both α‐amylase and α‐glucosidase were mixed‐inhibition type. Multispectroscopy and molecular docking studies indicated that the interaction between PPGs and α‐amylase and α‐glucosidase altered the conformation of enzymes, with binding at the site close to the active site of enzymes resulting in changed enzyme activity. Our studies may help in the further health use of small‐leaved kudingcha.     

Phytochemicals content,antioxidant and hypoglycaemic activities of commercial nutmeg mace (Myristica fragrans L.) and pimento (Pimenta dioica (L.) Merr.)

Commercially dried powder of nutmeg mace (Myristica fragrans) and pimento (Pimenta dioica) spices was investigated for their high performance liquid chromatography phenolic profile and their antioxidant and hypoglycaemic properties by α‐amylase and α‐glucosidase inhibition tests. Generally, mace showed the most promising activity. An interesting protection of lipid peroxidation with an IC₅₀ value of 7.7 μg mL^?1 was found. A significant result was also obtained in ferric reducing ability power assay if compared to the positive control butylated hydroxytoluene (IC₅₀ value of 68.7 μg mL^?1 vs. 63.2 μg mL^?1, respectively). Mace also exhibited the highest carbohydrate‐hydrolysing enzyme inhibitory activity with IC₅₀ values of 62.1 and 75.7 μg mL^?1 against α‐amylase and α‐glucosidase, respectively. Overall, these results support the use of these spices not only as flavouring agent but also as food preservative and functional ingredients.     

α‐Glucosidase and α‐amylase inhibitory activities of phloroglucinal derivatives from edible marine brown alga,Ecklonia cava

BACKGROUND: Diabetes mellitus (DM) is a chronic metabolic disorder characterized by defects in insulin secretion and action, which can lead to damaged blood vessels and nerves. With respect to effective therapeutic approaches to treatment of DM, much effort has being made to investigate potential inhibitors against α‐glucosidase and α‐amylase from natural products. The edible marine brown alga Ecklonia cava has been reported to possess various interesting bioactivities, which are studied here. RESULTS: In this study, five phloroglucinal derivatives were isolated from Ecklonia cava: fucodiphloroethol G ( 1 ), dieckol ( 2 ), 6,6′‐bieckol ( 3 ), 7‐phloroeckol ( 4 ) and phlorofucofuroeckol A ( 5 ); compounds 1, 3 and 4 were obtained from this genus for the first time and with higher yield. The structural elucidation of these derivatives was completely assigned by comprehensive analysis of nuclear magnetic spectral data. The anti‐diabetic activities of these derivatives were also assessed using an enzymatic inhibitory assay against rat intestinal α‐glucosidase and porcine pancreatic α‐amylase. Most of these phlorotannins showed significant inhibitory activities in a dose‐dependent manner, responding to both enzymes, especially compound 2 , with the lowest IC₅₀ values at 10.8 µmol L^?1 (α‐glucosidase) and 124.9 µmol L^?1 (α‐amylase), respectively. Further study of compound 2 revealed a non‐competitive inhibitory activity against α‐glucosidase using Lineweaver‐Burk plots. CONCLUSION: These results suggested that Ecklonia cava can be used for nutritious, nutraceutical and functional foods in diabetes as well as for related symptoms. Copyright © 2009 Society of Chemical Industry     

The Advantages of Using Natural Substrate‐Based Methods in Assessing the Roles and Synergistic and Competitive Interactions of Barley Malt Starch‐Degrading Enzymes

Existing methods of assay of malt starch‐degrading enzymes were critically appraised. New methods based on natural substrates, namely starch and its natural intermediate‐derivative, were developed for all the enzymes, except limit dextrinase for which pullulan was used. Thermostability, optimal temperatures and pHs were established. α‐Amylase and limit dextrinase were the most thermostable and β‐amylase, α‐glucosidase and maltase were the least stable while diastase occupied an intermediate position. The optimal temperatures were congruent with thermostability, β‐ amylase having the lowest (50°C) and α‐amylase the highest (65°C) with the remaining enzymes, including diastase, falling in between. In contrast, α‐amylase has the lowest optimal pH (pH 4.5) and β amylase the highest (pH 5.5) while the others have pHs in between the two values. The roles of the enzymes were evaluated taking into account the level of activity, thermostability, optimum pH, the nature of the product(s), and the relevance to brewing. β‐Amylase production of maltose was synergistically enhanced, mostly by α‐amylase but also limit dextrinase. α‐Glucosidase and maltase are unimportant for brewing, because of their low activity and the negative impact on β‐amylase activity and the negative effect of glucose on maltose uptake by yeast. The starch‐degrading enzymes (diastase) in a gram of malt were able to degrade more than 8 g boiled starch into reducing sugars in 10 min at 65°C. The latter, suggests that it will be possible to gelatinise most of the malt starch at a higher temperature and ensure its hydrolysis to fermentable sugars by mixing with smaller portions of malt and mashing at lower temperatures e.g. 50–60°C.     

Development of the Rhodiola rosea Fuqu and Rhodiola rosea soy sauce,and the determination of their functional properties

A mixed starter, composed of high‐quality Rhodiola rosea Fuqu, was developed. Compared with normal Fuqu, Rhodiola rosea Fuqu demonstrated higher spore numbers, spore germination rates, protease activity, liquefying amylase activity and total acid and amino acid nitrogen. Specifically, the spore number was 1.36 times that of regular Fuqu. Protease activity, liquefying amylase activity, total acid and amino acid nitrogen were 0.475 g/100 mL, 104.16 U/g dry Qu, 35.67 mmol/L and 26.08 g/100 mL, respectively. These values were 21.48, 7.41, 6.07 and 67.82% higher than the regular Fuqu. The Rhodiola rosea soy sauce indices were also better than those for the control. The DPPH scavenging abilities of R. rosea soy sauce, control soy sauce, market soy sauce 1 and market soy sauce 2 were 74.25, 44.01, 34.73 and 11.38%, respectively. The total phenolic content in these four samples was 387.38, 309.23, 212.85 and 202.60 mg GAE/g, respectively. As observed with the DPPH and total phenolic assay, the R. rosea soy sauce showed the highest antioxidant capacity. A simple, rapid, and sensitive determination method of salidroside in R. rosea Fuqu and R. rosea soy sauce using HPLC‐ESI‐MS/MS was developed and validated with multiple reaction monitoring in the negative mode.     

SOLID-STATE BIOCONVERSION OF PHENOLIC ANTIOXIDANTS FROM DEFATTED SOYBEAN POWDERS BY RHIZOPUS OLIGOSPORUS: ROLE OF CARBOHYDRATE-CLEAVING ENZYMES

Consumption of soybeans has been linked to a reduction in risk of numerous chronic diseases. The health benefits of soybean consumption have been linked to nutritionally functional phenolic compounds known as isoflavones. As the majority of plant phenolics exist naturally as glucoside‐bound moieties, we investigated the efficacy of increasing phenolic content in defatted soybean powder by fermentation with a glucosidase‐excreting fungus, Rhizopus oligosporus, and further investigated the involvement of carbohydrate‐cleaving enzymes (α‐amylase, α‐/β‐glucosidase) in phenolic antioxidant mobilization. Phenolic content increased 41% in water extracts and 255% in ethanol extracts after 10 days of fermentation, and associated with β‐glucosidase activity. The results suggest that solid‐state fermentation with R. oligosporus is an excellent strategy for increasing phenolic content in defatted soybean powder and that β‐glucosidase is the main carbohydrate‐cleaving enzyme that is required for efficient phenolic mobilization from powdered soybean. The results have potential importance for the commercial development of enzymatic strategies for utilizing the maximal phenolic potential of soybean substrates for use as nutritionally functional food ingredients.     

Total Phenol Content,Antioxidant Activities and α‐Glucosidase Inhibition of Sesame Cake Extracts

Sesame cake, the byproduct obtained after the removal of oil is presently used as cattle field. Present study evaluates the α‐glucosidase, α‐amylase inhibition and antioxidant properties of black sesame cake extracts. For that purpose, defatted seeds were sequentially extracted with ethyl acetate, methanol, methanol‐water 70:30 (v/v) and water. Among the extracts tested, methanol extract demonstrated better antioxidant activities (2,2‐diphenyl‐1‐picrylhydrazyl, hydroxyl and superoxide radical) and total phenol content. But the total flavonoid content and the total reducing power was high for methanol‐water. Most active methanol extract was further screened for α‐glucosidase and α‐amylase inhibition. The extract showed strong α‐glucosidase inhibitory potential and mild α‐amylase inhibition. The study indicated that the extraction yield and the antioxidant activities were strongly dependent on the solvent, antioxidant assays and extract concentration. These results demonstrated that sesame meal can be exploited as source of protein and bioactive for the development of functional food.     

Inhibitory activities of kaempferol,galangin, carnosic acid and polydatin against glycation and α‐amylase and α‐glucosidase enzymes

The activities of four natural phenolics, kaempferol, galangin, carnosic acid and polydatin in scavenging free radicals, inhibiting advanced glycation end‐product (AGE) formation, α‐amylase and α‐glucosidase and trapping methylglyoxal (MGO), were evaluated in this study. Carnosic acid and galangin had the highest activity in scavenging free radicals. Kaempferol and galangin had the greatest activity in preventing bovine serum albumin (BSA) against glycation and reducing glycated proteins. Polydatin had the greatest performance in trapping MGO to reduce glycation reaction. However, there was no significant difference for kaempferol, galangin and carnosic acid in inhibiting AGE formation by BSA‐MGO reaction. Kaempferol, galangin and carnosic acid were the competitive inhibitors for α‐amylase, while kaempferol and carnosic acid were noncompetitive inhibitors for α‐glucosidase. However, polydatin showed as a mixed noncompetitive inhibitor for both α‐amylase and α‐glucosidase. The results indicated that the four natural phenolics have potential in inhibiting AGE production and the digestive enzymatic activity with different mechanisms.     

QIGLF, a novel angiotensin I-converting enzyme-inhibitory peptide from egg white protein

BACKGROUND: Novel angiotensin I‐converting enzyme (ACE)‐inhibitory peptides from egg white protein can be rapidly screened by liquid chromatography/tandem mass spectrometry (LC/MS/MS). In this study, several peptides with higher ACE‐inhibitory activity were prepared from egg white protein by enzymatic hydrolysis with Alcalase, purified with Sephadex G25, identified by LC/MS/MS and their structure determined by circular dichroism (CD) spectroscopy. RESULTS: Peptide sequences DHPFLF, HAEIN and QIGLF that showed ACE‐inhibitory activity were investigated further for their stability in gastrointestinal solution and for changes in their secondary structure in solution mixtures. QIGLF exhibited the highest activity (IC₅₀ = 75 µmol L^?1) and was resistant to digestion by proteases of the gastrointestinal tract. The CD spectrum of QIGLF showed the presence of the α‐helix conformation. CONCLUSION: Three peptides were identified by LC/MS/MS and synthesised by Fmoc solid phase synthesis. Of the three, only the peptide sequence QIGLF was a potential ACE inhibitor, with an IC₅₀ value of 75 µmol L^?1. Moreover, QIGLF showed low gastrointestinal enzyme susceptibility and contained a relatively high amount of α‐helix. Copyright © 2011 Society of Chemical Industry