Dog rose and pomegranate extracts as agents to control enzymatic browning

To demonstrate that two natural products obtained with minimal processing can be used as antibrowning agents, extracts of dog rose hips and pomegranate arils were assayed for inhibition of tyrosinase and polyphenol oxidase activity. The efficiency of antibrowning activity was evaluated in terms of absorbance and polyacrylamide gel zymograms. In addition to the in vitro studies, melanosis in foods such as artichokes, mushrooms and pear juice was evaluated. The results revealed that dog rose hip extract was more effective than pomegranate aril extract. Moreover, high performance liquid chromatography analysis showed that extracts from both sources had many potential inhibitors of polyphenol oxidase and tyrosinase activity.     

In vitro inhibitory effects of cranberry bean (Phaseolus vulgaris L.) extracts on aldose reductase, α‐glucosidase and α‐amylase

The in vitro inhibitory activities of different seed extracts prepared from cranberry bean mutant SA‐05 and its wild‐type variety Hwachia against aldose reductase, α‐glucosidase and α‐amylase were examined. The results indicated that the polyphenolics‐rich extracts obtained using 800 g kg^?1 methanol and 500 g kg^?1 ethanol demonstrated inhibitory activities against aldose reductase (IC₅₀ of 0.36–0.46 mg mL^?1) and α‐glucosidase (IC₅₀ of 1.32–1.94 mg mL^?1). The 500 g kg^?1 ethanol extracts also showed α‐amylase inhibitory activities (IC₅₀ of 70.11–80.22 μg mL^?1). Subsequent extracts, prepared further with NaCl and H₂O from precipitates of 800 g kg^?1 methanol or 500 g kg^?1 ethanol extracts, exhibited potent α‐amylase inhibitory activities (IC₅₀ of 17.68–38.68 μg mL^?1). A combination of 500 g kg^?1 ethanol extraction plus a subsequent H₂O extraction produced highest polyphenolics and α‐amylase inhibitors. The SA‐05 α‐amylase inhibitor extracts showed greater inhibitory activities than that of Hwachia. Thus, cranberry bean mutant SA‐05 is an advantageous choice for producing anti‐hyperglycaemic compounds.     

α‐Glucosidase Inhibitory Activities of Fatty Acids Purified from the Internal Organ of Sea Cucumber Stichopus japonicas

α‐Glucosidase inhibitory activities of the various solvent fractions (n‐hexane, CHCl₃, EtOAc, BuOH, and water) of sea cucumber internal organ were investigated. 1,3‐Dipalmitolein (1) and cis‐9‐octadecenoic acid (2) with potent α‐glucosidase inhibitory activity were purified from the n‐hexane fraction of sea cucumber internal organ. IC₅₀ values of compounds 1 and 2 were 4.45 and 14.87 μM against Saccharomyces cerevisiae α‐glucosidase. These compounds mildly inhibited rat‐intestinal α‐glucosidase. In addition, both compounds showed a mixed competitive inhibition against S. cerevisiae α‐glucosidase and were very stable at pH 2 up to 60 min. The K_I values of compounds 1 and 2 were 0.48 and 1.24 μM, respectively. Therefore, the internal organ of sea cucumber might be a potential new source of α‐glucosidase inhibitors suitably used for prevention of obesity and diabetes mellitus.     

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.     

Potent Antidiabetic Activity and Metabolite Profiling of Melicope Lunu‐ankenda Leaves

Diabetes mellitus is normally characterized by chronic hyperglycemia associated with disturbances in the fat, carbohydrate, and protein metabolism. There is an increasing trend of using natural products instead of synthetic agents as alternative therapy for disorders due to their fewer side effects. In this study, antidiabetic and antioxidant activities of different Melicope lunu‐ankenda (ML) ethanolic extracts were evaluated using inhibition of α‐glucosidase and 2,2‐diphenyl‐l‐picrylhydrazyl (DPPH) radicals scavenging activity, respectively; whereas, proton nuclear magnetic resonance (¹H NMR) and ultra‐high performance liquid chromatography‐tandem mass spectrometric (UHPLC‐MS/MS) techniques were used for metabolite profiling of ML leaf extracts at different concentrations of ethanol and water. Sixty percent of ethanolic ML extract showed highest inhibitory effect against α‐glucosidase enzyme (IC₅₀ of 37 μg/mL) and DPPH scavenging activity (IC₅₀ of 48 μg/mL). Antidiabetic effect of ML extracts was also evaluated in vivo and it was found that the high doses (400 mg/Kg BW) of ML extract exhibited high suppression in fasting blood glucose level by 62.75%. The metabolites responsible for variation among ML samples with variable ethanolic levels have been evaluated successfully using ¹H‐NMR–based metabolomics. The principal component analysis (PCA) and partial least squares(PLS) analysis scores depicted clear and distinct separations into 4 clusters representing the 4 ethanolic concentrations by PC1 and PC2, with an eigenvalue of 69.9%. Various ¹H‐NMR chemical shifts related to the metabolites responsible for sample difference were also ascribed. The main bioactive compounds identified attributing toward the separation included: isorhamnetin, skimmianine, scopoletin, and melicarpinone. Hence, ML may be used as promising medicinal plant for the development of new functional foods, new generation antidiabetic drugs, as a single entity phytomedicine or in combinational therapy.     

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.     

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     

Metabolite profiling,antioxidant activity,and glycosidase inhibition property of the mesocarp tissue extracts of sugar date palm [Phoenix sylvestris (L.) Roxb.] fruits

Phoenix sylvestris is an underutilized seasonal fruit in West Bengal, India. Methanol extract and extracts after alkaline hydrolysis of the mesocarp tissue of full-mature edible fruits of P. sylvestris were analyzed by GC-MS following a metabolomics approach. The fractions were tested for their antioxidant and inhibitory properties against the two key enzymes involved in diabetes, α-amylase, and α-glucosidase. Total 71 metabolites belonging to organic acids, amino acids, sugars, sugar alcohols, fatty acids, and phenols were identified in the methanol extract and in fractions after saponification. All the extracts and fractions showed high antioxidant, α-glucosidase, and α-amylase inhibitory activities. Sugars like raffinose (IC₅₀ = 0.36 μM), sucrose (IC₅₀ = 0.51 μM), trehalose (IC₅₀ = 0.85 μM), and phenols like taxifolin (IC₅₀ = 0.31 μM), benzoic acid (IC₅₀ = 2.74 μM) inhibited only the enzyme α-amylase. Phenolic components which inhibited both the enzymes were caffeic acid (IC₅₀ = 1.42 μM for α-amylase and IC₅₀ = 1.8 μM for α-glucosidase), 3, 4-dihydroxy benzoic acid (IC₅₀ = 0.23 μM for α-amylase and IC₅₀ = 2.58 μM for α-glucosidase), and quinic acid (IC₅₀ = 4.91 μM for α-amylase and IC₅₀ = 4.95 μM for α-glucosidase). Ferulic acid (IC₅₀ = 0.52 μM) and 4-hydroxycinnamic acid (IC₅₀ = 0.23 μM) inhibited only α-glucosidase. This study suggested that the metabolites present in the fruit mesocarp tissue showed the potential antioxidant activity and properties to inhibit the enzymes α-amylase and α-glucosidase. Further in vivo study is to be carried out to prove the efficacy of the fruits.

Abbreviations: FM: crude methanol extract; SI: ethyl acetate extract after alkaline hydrolysis step I; SII: ethyl acetate extract after alkaline hydrolysis step II     

Identification of α‐glucosidase inhibitors from a new fermented tea obtained by tea‐rolling processing of loquat (Eriobotrya japonica) and green tea leaves

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     

Anti‐acetylcholinesterase,antidiabetic, anti‐inflammatory,antityrosinase and antixanthine oxidase activities of Moroccan propolis

Biological properties of Moroccan propolis have been scarcely studied. In the present work, the total phenols and flavonoids from 21 samples of propolis collected in different places of Morocco or 3 supplied in the market were determined, as well as the in vitro capacity for inhibiting the activities of acetylcholinesterase, α‐glucosidase, α‐amylase, lipoxygenase, tyrosinase, xanthine oxidase and hyaluronidase. The results showed that samples 1 (region Fez‐Boulemane, Sefrou city) (IC₅₀ = 0.065, 0.006, 0.020, 0.050, 0.014 mg mL^?1) and 23 (marketed) (IC₅₀ = 0.018, 0.002, 0.046, 0.037, 0.008 mg mL^?1) had the best in vitro capacity for inhibiting the α‐amylase, α‐glucosidase, lipoxygenase, tyrosinase and xanthine oxidase activities, respectively. A negative correlation between IC₅₀ values and concentration of phenols, flavones and flavanones was found. These activities corresponded to the generally higher amounts of phenols and flavonoids. In the same region, propolis samples have dissimilar phenol content and enzyme inhibitory activities.     

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.     

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.     

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.     

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.     

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     

Instrumental measurement of pomegranate texture during four maturity stages

Texture of pomegranate fruit and arils are the main quality attributes in the food process industries. In this study, the texture properties of pomegranate fruit and arils (cv. “Ashraf”) at four different stage of maturity (88, 109, 124, and 143 days after full bloom) were evaluated using the puncture test (rupture force and rupture energy) and compression test (bioyield force, rupture energy, and young modulus). The tests showed that all studied textural parameters were sensitive textural parameters for distinguishing the maturity stages. Rupture force and rupture energy of pomegranate fruit were determined at top, middle, and bottom positions of the fruit. The results showed that compression load values of aril increased with advances in maturity stage of fruit, while puncture load values of fruit decreased. The textural properties of pomegranate fruit and arils exhibited a strong dependence (p < .05) on the degree of maturity at harvesting time. Also results showed that rupture force of three different studied positions of fruit was severely different. The highest and lowest values were observed at top and middle position, respectively.     

Angiotensin I-converting enzyme inhibitor from Grifola frondosa

To investigate the hypotensive compounds from edible mushroom, extracts from 10 fruit bodies of mushrooms were screened for the inhibitory activity against angiotensin I converting enzyme (ACE). The most potent ACE inhibitory activity (58.7%) was detected in a cold water extract of Grifola frondosa, with an IC₅₀ of 0.95 mg. The ACE inhibitory activities of the cold and hot water extracts increased as the extraction time increased, but decreased slightly 15 h and 90 min, respectively, after extraction. After the purification of ACE inhibitory peptides with acetone fractionation and column chromatography, we obtained an active fraction with an IC₅₀ of 0.13 mg and a yield of 0.7%. The purified inhibitor showed competitive inhibition on ACE and this peptide maintained inhibitory activity even after digestion by intestinal proteases.     

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.     

Screening of Some Essential Oil Constituents as Potential Inhibitors of the ATP Synthase of Escherichia coli

Many novel bacterial targets and natural inhibitors of enzymes are currently being considered to overcome antibiotic resistance of Escherichia coli. Hence, in this study, 20 essential oil constituents were screened for their potential inhibitory effect on E. coli ATP synthase. This enzyme is involved in the hydrolysis of ATP into ADP and inorganic phosphate (Pi). First, E. coli membrane ATP synthase was isolated via cell lysis. A spectrophotometric method was optimized to quantify the released phosphate from ATP hydrolysis in order to follow the enzymatic activity. The method was validated by determining the kinetic parameters of this reaction (K_m = 144.66 μM and V_max = 270.27 μM/min), and through the inhibition assays of ATP synthase using three reference inhibitors, thymoquinone (half maximal inhibitory concentration [IC₅₀] = 50.93 μM), resveratrol (maximum inhibition of 40%), and quercetin (IC₅₀ = 29.01 μM). Among the studied essential oil components, α‐terpinene was the most potent inhibitor (IC₅₀ = 19.74 μM) followed by β‐pinene, isoeugenol, eugenol, and estragole.     

Tannin fraction from Ampelopsis grossedentata leaves tea (Tengcha) as an antioxidant and α‐glucosidase inhibitory nutraceutical

Leaf of Ampelopsis grossedentata is a new resource of functional foods with healthful properties. Antioxidant and α‐glucosidase inhibitory activities of water extract (made in the style of drinking), tannin fraction (TF) and dihydromyricetin (DMY) from A. grossedentata leaves were evaluated. The main component of TF was identified as gallotannins. DPPH and ABTS radical scavenging activities and reducing power of TF were superior to those of water extract, however, inferior to those of DMY. In no PBS wash protocol of cellular antioxidant activity assay, DMY and TF exhibited similarly, while in PBS wash protocol, the value of TF was higher than that of DMY. In addition, TF possessed the highest α‐glucosidase inhibitory activities (IC₅₀ = 1.94 μg mL^?1), followed by water extract (IC₅₀ = 23.10 μg mL^?1) and DMY (IC₅₀ = 72.21 μg mL^?1). The strong α‐glucosidase inhibitory activity of TF may attribute to the binding capacity to enzymes, as confirmed by fluorescence analysis.