Antioxidant activity and contents of essential oil and phenolic compounds in flowers and seeds of Alpinia zerumbet (Pers.) B.L. Burtt. & R.M. Sm

Alpinia zerumbet leaves and rhizomes have been extensively studied for their chemical compositions and biological activities. However, less attention has been given to its flowers and seeds. In our study, essential oil, total phenolics and antioxidant capacities assayed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and β-carotene bleaching methods were evaluated in flowers and seeds of A. zerumbet. In addition, their phenolic composition was determined by GC–MS and HPLC. 1,8-Cineol, camphor, methyl cinnamate and borneol were the major constituents in flower oils, whereas the main components in seeds oil were α-cadinol, T-muurolol, α-terpineol, δ-cadinene and terpinene-4-ol. The results showed that the hexane extract of flowers contained a significantly higher quantity of dihydro-5,6-dehydrokawain (DDK) than that of seeds. Total phenolic contents of flower and seed extracts were measured as 56.7 and 13.7 mg gallic acid equivalent per gram extract, respectively. The ethyl acetate extract of flowers and seeds possessed a high antiradical activity and prevented the bleaching of β-carotene. The HPLC analysis indicated that p-hydroxybenzoic acid, ferulic acid and syringic acid were the predominant phenolics in the ethyl acetate extract of flowers, whilst p-hydroxybenzoic acid, syringic acid and vanillin were the major phenolics in seeds.     

Essential oils,kava pyrones and phenolic compounds from leaves and rhizomes of Alpinia zerumbet (Pers.) B.L. Burtt. & R.M. Sm. and their antioxidant activity

During essential oil production from Alpinia zerumbet, large volumes of water and solid wastes are produced and subsequently discarded. An extraction protocol to obtain essential oil, dihydro-5,6-dehydrokawain (DDK) and enriched antioxidant phenolic extracts from fresh leaves or rhizomes of A. zerumbet and their wastes was developed. The main components determined in leaf oil were 1,8-cineol, camphor and methyl cinnamate, whereas rhizome oil mainly contained DDK and methyl cinnamate. The highest DDK content was found in the hexane extract of fresh rhizomes. Ethyl acetate extracts from leaves showed higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities than those from rhizomes. Ethyl acetate extract from wastewater of leaves possessed the strongest inhibition to β-carotene oxidation. Ferulic and p-hydroxybenzoic acids were the major phenolics present in these extracts. The results indicate that disposed wastes produced during essential oil production from A. zerumbet leaves or rhizomes may be utilized in foodstuffs as a cheap source of natural antioxidants.     

Correlation of methylglyoxal with acrylamide formation in fructose/asparagine Maillard reaction model system

α-Dicarbonyl compounds were highly reactive intermediates formed in Maillard reaction (MR), and o-phenylenediamine (OPD) was widely used as a trapping agent for α-dicarbonyl compounds. Both aqueous fructose/asparagine (Fru/Asn) and fructose/asparagine/o-phenylenediamine (Fru/Asn/OPD) model systems were heated at 150 °C for up to 30 min. Methylglyoxal (MG) was the main α-dicarbonyl compounds formed in MR, which was chosen as a representative of α-dicarbonyl compound to investigate the influence on acrylamide (AA) formation. The concentrations of AA, MG and Asn were detected during MR by HPLC method. The results indicated that the formation of AA increased with the heating time, and nearly 75% of AA was formed through the participation of α-dicarbonyl compounds. The amounts of formation and consumption of MG increased with heating time, and from 12 min of reaction, the consumed amounts of MG accounted for 62.1–90.3% on the basis of total amounts of MG formed in MR, suggesting that most of the MG took part in further reactions. Meanwhile, Asn concentration decreased with heating time in both models. The formation of AA and consumption of Asn were highly correlated with MG. Indeed, as MG concentration in MG/Asn model system decreased during heating at 150 °C, the concentration of AA significantly increased. The coefficient of correlation between consumed amounts of MG and the formed amounts of AA was 0.931, demonstrating that MG plays a role in AA formation.     

α-Glucosidase inhibitors from the bulb of Eleutherine americana

One effective way to treat diabetes is by suppressing carbohydrate digestion due to the utilisation of α-glucosidase inhibitors (AGIs). The determination of prospective herbs, done in vitro by using enzyme assay, resulted in the finding of Eleutherine americana, which showed a potent inhibitory activity. A 50% aqueous methanol-soluble extract of bulbs of E. americana was chromatographed successively and the active fractions were further purified with preparative high performance liquid chromatography (HPLC) to isolate active compounds against α-glucosidase. Structure determination by mass and NMR analysis revealed that these isolated compounds were eleutherol (1), eleutherinoside A (2), and eleuthoside B (3) based on comparisons with the reference data. Considering the amount and the inhibitory activity of each naphthalene in the whole extracts, the bulb of E. americana inhibitory activity against α-glucosidase might be a result of compound 2 (IC₅₀ = 0.5 mM, yield = 5 mg/50 g plant sample, with a characteristic structure which has never been found in other AGIs. AGIs play an important role for the treatment of diabetes, therefore these results may suggest novel alternatives for diabetes treatment management.     

Novel α-glucosidase inhibitors from Macaranga tanarius leaves

One of the hyperglycaemic remedies is glucose absorption reduction by suppressing carbohydrate digestion due to utilisation of α-glucosidase inhibitors (AGIs). Determination of prospecting herbs done in vitro by using enzyme assay resulted in the finding of Macaranga tanarius, which showed a potent inhibitory activity. An EtOAc-soluble extract of M. tanarius leaves was chromatographed by a Diaion HP-20 column and the active fractions were further purified with high performance liquid chromatography (HPLC) to isolate active principles against α-glucosidase. Five ellagitannins were successfully isolated and identified. Structure determination revealed that these isolated compounds were mallotinic acid (IC₅₀ > 5.00 mM), corilagin (IC₅₀ = 2.63 mM), chebulagic acid (IC₅₀ = 1.00 mM), and two novel compounds named macatannins A (IC₅₀ = 0.80 mM) and B (IC₅₀ = 0.55 mM). AGIs play an important role for the treatment of diabetes, therefore this research results may suggest novel alternatives for diabetes treatment management.     

α-Glucosidase inhibitors from Chinese Yam (Dioscoreaopposita Thunb.)

The inhibitory activities of crude extracts and purified constituents from the fresh tuberous rhizomes of Chinese Yam (Dioscorea opposita Thunb.), which is commonly called Huai Shan Yao in Chinese, were evaluated against yeast α-glucosidase in order to search for the active principals for treatment of diabetes. Bioassay-guiding isolation gave four compounds: trans-N-p-coumaroyltyramine (1) (IC₅₀ = 0.40 μM), 1,7-bis(4-hydroxyphenyl)heptane-3,5-diol (2) (IC₅₀ = 0.38 mM), 6-hydroxy-2,4,7-trimethoxyphenanthrene (3) (IC₅₀ = 0.77 mM) as α-glucosidase inhibitors, and cis-N-p-coumaroyltyramine (4), an isomer of compound 1, which showed no inhibitory activity against α-glucosidase. Furthermore, the separation and purification of compound 3 from Chinese Yam (Huai Shan Yao) was conducted by high-speed counter-current chromatography (HSCCC) using hexane–ethyl acetate–methanol–water (1:1:1:1, v/v/v/v). Compound 1, 2 and 4 were isolated from or detected in the Dioscoreaceae family for the first time.     

α-Glucosidase inhibitors from Devil tree (Alstonia scholaris)

α-Glucosidase inhibitors are used in the treatment of non-insulin-dependent diabetes mellitus. We attempt to isolate α-glucosidase inhibitors from 24 traditional Thai medicinal plant samples. Potent α-glucosidase inhibitory activity was found in aqueous methanol extract of dried Devil tree (Alstonia scholaris) leaves. Active principles against α-glucosidase, prepared from rat small intestine acetone powder, were isolated and identified. The structures of these isolated compounds were found to be quercetin 3-O-β-d-xylopyranosyl (1? → 2″)-β-d-galactopyranoside and (−)-lyoniresinol 3-O-β-d-glucopyranoside on the basis of chemical and spectral evidence. The latter exhibited an inhibitory activity against both sucrase and maltase with IC₅₀ values of 1.95 and 1.43 mM, respectively, whereas the former inhibited only maltase with IC₅₀ values of 1.96 mM. This preliminary observation will provide the basis for further examination of the suitability of Alstonia scholaris as a medicinal supplement that contributes toward the treatment and prevention of diabetes.     

Flavonoids isolated from Syzygium aqueum leaf extract as potential antihyperglycaemic agents

Syzygium aqueum is a medicinal plant which is grown in tropical regions. In this study, the ethanolic extracts of S. aqueum leaf were investigated for its antihyperglycaemic activity. Our investigation revealed its effectiveness in inhibiting the carbohydrate hydrolysing enzymes, α-glucosidase (EC₅₀ = 11 μg/ml) and α-amylase (EC₅₀ = 8 μg/ml), at significant level than the commercial drug acarbose (EC₅₀ = 28 μg/ml, α-glucosidase; EC₅₀ = 12 μg/ml, α-amylase). In addition, the ethanolic leaf extracts were able to inhibit the key enzyme in the polyol pathway, aldose reductase (EC₅₀ = 0.03 μg/ml) and prevent the AGEs formation by 89%. Six flavonoid compounds, 4-hydroxybenzaldehyde (1), myricetin-3-O-rhamnoside (2), europetin-3-O-rhamnoside (3), phloretin (4), myrigalone-G (5) and myrigalone-B (6), were isolated from the ethanolic leaf extracts. Compounds (2) and (3) showed high inhibitory activities, with EC₅₀ values of 1.1 μM and 1.9 μM against α-glucosidase and EC₅₀ values of 1.9 μM and 2.3 μM against α-amylase, respectively. These findings provide a strong rationale to establish S. aqueum’s capability as an antihyperglycaemic agent.     

Rhus verniciflua Stokes flavonoid extracts have anti-oxidant,anti-microbial and α-glucosidase inhibitory effect

We isolated four compounds, fustin, gallic acid, 3′,4′,7-trihydroxyflavone, and fisetin from Rhus verniciflua. These compounds showed electron donation ability (87–94%) that was stronger than butylated hydroxyanisole (52%). Gallic acid (OD₇₀₀ = 1.98) showed the highest reducing power, and the other isolated compounds (OD₇₀₀ = 0.66–1.31) showed stronger activity than α-tocopherol (OD₇₀₀ = 0.21). The ethyl-acetate fraction had the highest phenolic content (723 mg GAE/g), followed by the 80% ethanolic extract (597 mg GAE/g). For Gram-negative bacteria, fisetin had the most potent anti-bacterial activity (MIC = 8 μg/ml) against Escherichia coli. 3′,4′,7-Trihydroxyflavone (106%), the 80% ethanolic extract (101%), and ethyl-acetate (98%) had the most powerful α-glucosidase inhibitory effect at 50 μg/ml. R. verniciflua extracts have potential as functional food additives.     

Inhibitory effects of guava (Psidium guajava L.) leaf extracts and its active compounds on the glycation process of protein

Hyperglycaemia causes increased protein glycation and the formation of early glycation products and advanced glycation end products (AGEs) which are major factors responsible for the complications of diabetes. This study investigated the ability of guava leaf and compounds to inhibit glycation process in an albumin/glucose model system and compared the potency of these extracts with Polyphenon 60 which is a commercial polyphenol product extracted from green tea and with the standard antiglycation agent, aminoguanidine. The results showed that the inhibitory effects of guava leaf extracts on the formation of α-dicarbonyl compounds were over 95% at 50 μg/ml. Phenolic compounds present, namely gallic acid, catechin and quercetin exhibited over 80% inhibitory effects, but ferulic acid showed no activity. The guava leaf extracts also showed strong inhibitory effects on the production of Amadori products and AGEs from albumin in the presence of glucose. The phenolic compounds also showed strong inhibitory effects on the glycation of albumin, especially quercetin exhibited over 95% inhibitory effects at 100 μg/ml. According to the results obtained, guava leaf extracts are potent antiglycation agents, which can be of great value in the preventive glycation-associated complications in diabetes.     

α-Glucosidase and α-amylase inhibitory activities of Nepalese medicinal herb Pakhanbhed (Bergenia ciliata, Haw.)

Herbal medicine has been used for many years by different cultures around the world for the treatment of diabetes. The Nepalese herb Pakhanbhed, is one of the traditional remedies used for diabetes since prehistoric times. In this study, we examined the anti-diabetic activity using an in vitro model and isolated the active compounds from Pakhanbhed. Extraction and fractionation of the extract lead to the isolation of two active compounds, (−)-3-O-galloylepicatechin and (−)-3-O-galloylcatechin and these are reported from this plant species for the first time. These isolated compounds demonstrated significant dose dependent enzyme inhibitory activities against rat intestinal α-glucosidase and porcine pancreatic α-amylase. IC₅₀ value for sucrose, maltase and α-amylase were 560, 334 and 739 μM, respectively for [(−)-3-O-galloylepicatechin] and 297, 150 and 401 μM, respectively for [(−)-3-O-galloylcatechin]. Our study, for the first time, revealed the anti-diabetic potential of Pakhanbhed and this study could be helpful to develop medicinal preparations or nutraceutical and functional foods for diabetes and related symptoms.     

Antioxidation and antiglycation of 95% ethanolic extracts prepared from the leaves of black nightshade (Solanum nigrum)

Hyperglycemia results in the formation of advanced glycation end-products (AGE), resulting in an inflammatory response that induces insulin resistance. Evidence indicates that antioxidants can suppress the formation of reactive oxygen species, decrease levels of AGEs by inhibiting glycation. Black nightshade (Solanum nigrum) can be used as a medicinal food for improving blood glucose; however, the identities of the active compounds and how they counteract diabetes remain unknown. This study demonstrate that 95% ethanolic extracts of black nightshade exerted significant antioxidative activity compared with 50% ethanolic extracts and aqueous extracts. Moreover, 95% ethanolic extracts of black nightshade produced antiglycative activity, which contributed to the inhibition of fructosamine and generation of α-dicarbonyl compounds. The concentrations of solasonine and solamargine in the 95% ethanolic extracts were 0.484 and 0.183 mg/mg, respectively. These results suggest that black nightshade might serve as a novel source of functional ingredients that exert antiglycation and anti-diabetes activities.     

槲皮素与葛根素对食品体系中非酶糖基化的抑制作用

通过对果糖胺、二羰基化合物、5-羟甲基糠醛（5-hydroxymethylfurfural,5-HMF）和荧光性末端产物的检测,考察槲皮素和葛根素对食品体系非酶糖基化反应的抑制作用。结果表明：槲皮素能促进非酶糖基化早期产物果糖胺和5-HMF的生成,对反应中期的二羰基化合物和非酶糖基化末端产物（advanced glycation end products,AGEs）具有较强的抑制作用;葛根素能促进果糖胺的生成,抑制二羰基化合物的生成,对5-HMF和AGEs无影响。这可能与槲皮素与葛根素的结构差异有关。     

Optimization of SC–CO2 extraction of zerumbone from Zingiber zerumbet (L) Smith

Response surface methodology (RSM) was applied to optimize the variables affecting the Supercritical carbon dioxide (SC–CO₂) extraction of non-polar compounds from Zingiber zerumbet using the Box-Behnken design (BBD). Dependent variables were the percentage of the chemical components in the ginger vis a vis α-caryophyllene (y₁), camphene (y₂), and zerumbone (2,6,10-cycloundecatrien-1-one, 2,6,9,9-tetramethyl-) (y₃). Pressure was the most significant parameter affecting the amount of each compound extracted. When temperature was kept constant and pressure was increased, all of the dependent variables increased concomitantly. Since pressure and temperature are two of the major influential factors in the extraction using SC–CO₂, any combination of these two parameters could be selected to ascertain the optimum combination for a particular compound in the extract. Extraction at 30 °C and 55 MPa with total amount of 30 g of CO₂ used was found to maximize all the responses.     

Control of the Maillard reaction by ferulic acid

This study investigated how ferulic acid (FA) affects the formation of certain Maillard reaction products (MRPs), i.e., early MRPs, fluorescent and non-fluorescent advanced glycation end products (AGEs), and melanoidins in model systems. Glycation mixtures were prepared containing soy glycinin or bovine serum albumin (final concentration 10 mg/ml) and fructose (222 mM) in 0.2% KOH in the presence or absence of FA (12.95 mM) and incubated at 60 °C for 60 min. The extent of the MR was estimated by analysis of free amino groups, the incorporation of sugar into the protein backbone as well as the formation of N^?-(carboxymethyl)lysine (CML), fluorescent AGEs (λ_exc = 337 nm, λ_em = 350–550 nm) and melanoidins (absorbance at 420 nm). Formation of CML and fluorescent AGEs was reduced by nearly 90% by the addition of FA while early MRPs and melanoidins were inhibited to a lesser extent (∼10% and 28%, respectively) compared to AGE formation. A controlled formation of early MRPs was achieved by use of FA, and it is a new finding. To the best of our knowledge, for the first time the use of FA as a reliable means of obtaining novel glycoprotein preparations containing low amounts of AGEs, with the potential to be used as functional food ingredients, is proposed.     

Isolation and characterisation of an α-glucosidase inhibitory substance from fructose–tyrosine Maillard reaction products

An α-glucosidase inhibitory substance was isolated and characterised from fructose–tyrosine Maillard reaction products (MRPs) and the inhibition mode of the active substance determined. The ethyl acetate fraction of fructose–tyrosine MRPs showed strong α-glucosidase inhibitory activity; this fraction was isolated and purified using silica gel column chromatography and semi-preparative RP-HPLC. The structure of the purified compound was determined using spectroscopic methods. The isolated compound was identified as 2,4-bis (p-hydroxyphenyl)-2-butenal (C₁₆H₁₄O₃, HPB242). This is the first report of baker’s yeast α-glucosidase inhibitory activity of HPB242 isolated from fructose–tyrosine MRPs. The IC₅₀ value of HPB242 on α-glucosidase inhibition was 4.00 ± 0.09 μg/ml. Kinetic data revealed that HPB242 inhibits the p-NPG hydrolysing activity of baker’s yeast α-glucosidase noncompetitively with a K_i value of 0.870 mM.     

Regulation of lipid disorders by ethanol extracts from Zingiber zerumbet in high-fat diet-induced rats

The aim of this study was to investigate the antihyperlipidaemic effects of the ethanol extract of Zingiber zerumbet (L) Smith (EEZZ). After being fed a high-fat diet (HFD) for 2 weeks, rats were dosed orally with EEZZ (100, 200 or 300 mg/kg) or fenofibrate (100 mg/kg) once daily for 8 weeks. EEZZ (300 mg/kg/day) produced effects similar to fenofibrate in reducing body weight gain, visceral fat-pad weights and plasma lipid levels. EEZZ caused reductions in hepatic triglyceride and cholesterol content, and lowered hepatic lipid droplet accumulation and the size of epididymal adipocytes. HFD-induced reductions in the hepatic proteins of peroxisome proliferator-activated receptor (PPAR) α, acyl-CoA oxidase (ACO) and cytochrome P450 isoform 4A1 (CYP4A1) were reversed by EEZZ. These results suggest that EEZZ reduced the accumulation of visceral fat and improved hyperlipidaemia in HFD-fed rats by increasing fatty acid oxidation, an effect which is likely to be mediated via up-regulation of hepatic PPARα.     

The essential oil of Glossogyne tenuifolia

Glossogyne tenuifolia (Labill) Cass. (Compositae) is a traditional anti-pyretic and hepatoprotective herb in The Pescadores Islands. The essential oil of the dried herb, from four seasons, was isolated using a simultaneous steam-distillation and solvent-extraction (SDE) apparatus. The essential oil contents were in the range of 0.48–0.77 mg g⁻¹, with an average of 0.66 mg g⁻¹, and declined with the seasons. Generally, the essential oils from four seasons exhibited similar volatile profiles. A total of 62 different compounds were isolated by the SDE method and, among them, 30 compounds were identified, including 13 terpenes, 16 oxygen-containing compounds (eight alcohols, five aldehydes, one ester and two ketones) and one other compound. Terpenes were predominantly present in the essential oil and accounted for 61.3–76.0% of the essential oil with an average of 69.1%. The second most abundant class was alcohols, accounting for 12.4–15.9% of the essential oil, with an average of 14.1%. Consistently for four seasons, the most abundant eight compounds were in the descending order: p-cymene > β-pinene > β-phellandrene > limonene > cryptone > α-pinene > 4-terpineol + γ-muurolene. However, these eight compounds accounted for 71.5% of the average of the essential oil and, in combination, might give rise to the overall citrus-like aroma of the G. tenuifolia.     

Comparative chemical composition,antioxidant and hypoglycaemic activities of Juniperus oxycedrus ssp. oxycedrus L. berry and wood oils from Lebanon

Juniper (Juniperus oxycedrus) is used in European cuisine for its distinguishing flavour. J. oxycedrus ssp. oxycedrus berry and wood essential oils were tentatively identified by GC and GC/MS. Fifty compounds were identified in the berry oil and 23 compounds were identified in the wood oil. The J. oxycedrus ssp. oxycedrus berry oil was characterised by high contents of α-pinene (27.4%) and β-myrcene (18.9%). Other important compounds were α-phellandrene (7.1%), limonene (6.7%), epi-bicyclosesquiphellandrene (2.3%) and δ-cadinene (2.2%) while, in the wood oil, δ-cadinene (14.5%) is a major main component, together with cis-thujopsene (9.2%) and α-muurolene (4.9%). In vitro evaluation of antioxidant activity by the DPPH method showed a significant activity for both oils with IC₅₀ values of 1.45 μl/ml for wood and 7.42 μl/ml for berries. Hypoglycaemic activity was investigated through the inhibition of α-amylase. The results revealed that oil obtained by hydrodistillation from J. oxycedrus ssp. oxycedrus wood exhibits an interesting activity with IC₅₀ of 3.49 μl/ml.     

Comparative evaluation of rosmarinic acid,methyl rosmarinate and pedalitin isolated from Rabdosia serra (MAXIM.) HARA as inhibitors of tyrosinase and α-glucosidase

Rabdosia serra has been used in traditional Chinese medicine for centuries. In order to illustrate the pharmaceutical activity of R. serra as hypoglycaemic and skin-whitening agents, rosmarinic acid (confirmed as the major compound in R. serra), methyl rosmarinate and pedalitin isolated from R. serra were evaluated for their inhibitory effects and mechanisms on tyrosinase and α-glucosidase. The inhibitory effects on both tyrosinase and α-glucosidase were in decreasing order, pedalitin > methyl rosmarinate > rosmarinic acid. The IC₅₀ values for the tyrosinase and α-glucosidase activity inhibited by pedalitin were 0.28 and 0.29 mM, respectively. Both rosmarinic acid and methyl rosmarinate were considered as noncompetitive inhibitors of tyrosinase, while pedalitin was suggested to be a mixed-type inhibitor of tyrosinase. In the assay of α-glucosidase inhibition, rosmarinic acid was found to be a competitive inhibitor, whereas both methyl rosmarinate and pedalitin were considered as mixed-type inhibitors.