Factors influencing antioxidant activities and total phenolic content of guava leaf extract

The aim of this study is to investigate the influence of certain factors on the yield, antioxidant activity (AA) and total phenolic content (TPC) of guava leaf extract. The effects of pretreatment of leaf sample prior to extract, extraction method, and the leaf age were investigated. Folin-Ciocalteau was used to determine the TPC. Trolox equivalent antioxidant capacity (TEAC) and equilibrium concentration (EC) were used for evaluation of AA. Results indicated that ultrasonication is the most suitable method for guava leaf extraction as it yielded the extract with the significantly highest TPC and AA. Blanching followed by ice water cooling (BCD) was suggested for the pretreatment process of guava leaves. The study of leaf maturity demonstrated that the highest activity was from the young leaves. Hot water was the best solvent to extract the active principles. The extract of BCD pretreated young leaves, extracted by hot water exhibited the highest TPC and AA with the TEAC and EC values of 24.30 ± 0.50 and 20.41 ± 0.67 mM/mg, respectively. These values are 1.88 and 8.72 times higher than the synthetic antioxidant butylated hydroxy toluene (BHT) and 1.75 and 1.21 times higher than vitamin E, respectively. It was concluded that pretreatment and drying process, method of extraction and leaf maturity played important roles on the bioactive compounds and their antioxidant power of guava leaf extract.     

Evaluation of antioxidant ability of ethanolic extract from dill (Anethum graveolens L.) flower

Antioxidant activities of ethanolic extract from dill flower and its various fractions were evaluated with 2,2-diphenyl-1-picrylhydrazyl radical scavenging, Trolox equivalent antioxidant capacity, reducing power, chelating power, and β-carotene bleaching assays. The flower extract was successively separated into n-hexane, ethyl acetate and ethanol soluble fractions by liquid–liquid partition. Dill leaf and seed extracts were used for comparison. In all assays, the flower extract showed higher antioxidant activity than the leaf and seed extracts. With regard to various fractions of the flower extract, the sequence for antioxidant activity was ethyl acetate fraction > ethanol fraction > original flower extract > n-hexane fraction. Phenols including flavonoids and proanthocyanidins should be responsible for antioxidant abilities of the flower extract. Chlorogenic acid, myricetin, and 3,3’,4′,5,7-pentahydoxyflavan (4 → 8)-3,3′,4′,5,7-pentahydoxyflavan were the major phenolic acid, flavonoid, and proanthocyanidin, respectively, in the dill flower extract.     

Total phenolics, flavonoids and antioxidant activity of tropical fruit pineapple

Pineapple has several beneficial properties including antioxidant activity. The fruit of pineapple was extracted with ethyl acetate, methanol and water. The phenolic content of the extracts was determined by Folin-Ciocalteu method and antioxidant activity was assayed through some in vitro models such as antioxidant capacity by phosphomolybdenum, ??-carotene-linoleate, and radical scavenging activity using ??,??-diphenyl-??-picrylhydrazyl (DPPH) method. The phenolic contents of the extracts as caffeic acid equivalents were found to be highest in methanol (51.1%) followed by ethyl acetate (13.8%) and water extract (2.6%). Antioxidant capacity of the extracts as equivalent to ascorbic acid (??mol/g of the extract) was in the order of methanol extract > ethyl acetate extract > water extract. In comparison with butylated hydroxyanisole (BHA), at 100 ppm of concentration, the antioxidant and free radical scavenging activities of the extracts assayed through ??-carotene-linoleate and DPPH method were also found to be highest with methanol extract followed by ethyl acetate and water extracts. The results indicated that the extent of antioxidant activity of the extract is in accordance with the amount of phenolics present in that extract and the pineapple fruit being rich in phenolics may provide a good source of antioxidant.     

Total phenolic content and antioxidant capacity of extracts obtained from six important fruit residues

The extracts from kinnow peel, kinnow seeds, litchi pericarp, litchi seeds, grape seeds, and banana peel were screened for total phenolic content (TPC), trolox equivalent antioxidant capacity (TEAC), 1,1 diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity, as well as reducing power. Kinnow peel extract exhibited the highest reducing power, TEAC, and DPPH free radical scavenging activity, whereas, the phenolic content of 37.4 mg GAE/g-dw was highest for grape seed extract. Banana peel extract with a low TPC showed the lowest reducing power, TEAC as well as DPPH free radical scavenging activity among the fruit residue extracts examined in the present study. Correlation analysis between the reducing power and DPPH radical scavenging ability; reducing power and ABTS radical scavenging activity; and ABTS and DPPH radical scavenging abilities showed a high degree of correlation (r² = 0.85-0.91). However, r² of 0.36, 0.66, and 0.49 between TPC and DPPH radical scavenging activity; TPC and reducing power; and TPC and ABTS radical scavenging ability, respectively, indicated that some non-phenolic compounds also contributed to the total antioxidant activity in fruit residue extracts examined in this study. To the best of our knowledge, this is the first paper presenting comprehensive data on TPC, reducing power, and antioxidant activity for the six fruit residues. This study demonstrated that kinnow peel, litchi pericarp, litchi seeds, and grape seeds, can serve as potential sources of antioxidants for use in food and pharmaceutical industry.     

Radical scavenging and reducing properties of extracts of cashew shoots (Anacardium occidentale)

The total phenolic content and antioxidant activities of methanol, hexane and ethyl acetate extracts of the shoots of Anacardium occidentale were measured. Total phenolic content was assessed by the Folin–Ciocalteau assay whereas antioxidant activities were assessed by measuring the ability of the extracts to scavenge the ABTS^·+ and DPPH^· radicals, superoxide anion radicals and nitric oxide radicals as well as their ability to reduce ferric ions. Results indicated that the methanol extract of A. occidentale was the most potent reducing agent and radical-scavengers compared to the other two extracts. The ethyl acetate extract exhibited some antioxidant activities whereas the hexane extract is the least reactive. The order of the antioxidant potency of the plant extract is methanol > ethyl acetate > hexane. The methanol extract contained more than 7 fold of total phenolic content compared to the hexane and ethyl acetate extracts indicating the likely possibility that the observed antioxidant activities were partly contributed by the phenolics. The results suggest that the shoots of A. occidentale are a source of natural antioxidants.     

Phenolic content and antioxidant activity of cantaloupe (cucumis melo) methanolic extracts

The objectives of this study were to determine phenolic content and antioxidant activity of methanolic extracts from different parts of cantaloupe (leaf, stem, skin, seed and flesh). The flesh extract afforded the highest yield (89.6 ± 0.3%) whilst the lowest yield was obtained from the seed (13.7 ± 0.5%) (p < 0.05). The leaf extract showed the highest total phenolic content (26.4 ± 0.3 mg GAE/g extract) and total flavonoid content (69.7 ± 3.37 μg RE/g extract) accompanied with best antioxidant activity through all antioxidant assays (p < 0.05). In addition, the stem extract also exhibited good antioxidant activity. Thus, these results suggest that methanolic extracts of cantaloupe leaf and stem may serve as a potential source of natural antioxidant for food and nutraceutical application.     

Profiling of in vitro neurobiological effects and phenolic acids of selected endemic Salvia species

The ethyl acetate and methanol extracts from 16 Salvia L. species were screened for their inhibitory activity against acetylcholinesterase, butyrylcholinesterase, lipoxygenase, and tyrosinase; the enzymes linked to neurodegeneration. Their antioxidant activity was also tested using DPPH radical scavenging, metal-chelation, and ferric-reducing antioxidant power (FRAP) assays. Total flavonoid content of the extracts was determined by AlCl₃ reagent, while HPLC technique was applied for analysis of various phenolic acids in the extracts. The extracts exerted weak cholinesterase and tyrosinase inhibition, and remarkable inhibition against lipoxygenase (13.07 ± 2.73-74.21 ± 5.61%) at 100 μg ml⁻¹. The methanol extracts showed higher antioxidant activity in DPPH radical scavenging and FRAP assays. The extracts were analyzed for their gallic, protocateuchic, p-hydroxy-benzoic, vanillic, caffeic, chlorogenic, syringic, o- and p-coumaric, ferulic, rosmarinic, and tr-cinnamic acid contents and the methanol extract of Salvia ekimiana (153.50 mg 100 g⁻¹) was revealed to be the richest in terms of rosmarinic acid.     

Studies on the dual antioxidant and antibacterial properties of parsley (Petroselinum crispum) and cilantro (Coriandrum sativum) extracts

Antioxidant and antibacterial activities of freeze-dried and irradiated parsley (Petroselinum crispum) and cilantro (Coriandrum sativum) leaves and stems were determined on methanol and water extracts. The total phenolic content was quantified with the Folin–Ciocalteau reagent. Several mechanisms of potential antioxidant activity of all extracts, including determining relative free radical-scavenging and ferrous ion-chelating activities, as well as reducing power, were examined. Assessment of the total antioxidant activity of all extracts was done using an iron-induced linoleic acid oxidation model system. Antimicrobial activity towards Bacillus subtilis and Escherichia coli by different extracts was assessed by determining cell damage. Total phenolic content varied between parsley and cilantro, leaf and stem, as well as methanol and water extracts. Methanol-derived leaf extracts exhibited significantly (p < 0.05) greater radical-scavenging activity towards both lipid- and water-soluble radicals, which was attributed to the total phenolic content. Ferrous ion-chelating activity was significantly (p < 0.05) greater in the stem methanol extracts, and corresponded to antioxidant activity. Prooxidant activity was a feature of all aqueous extracts and corresponded to the reducing activity of both leaf and stem parts of parsley and cilantro. Bacterial cell damage, resulting in significant (p < 0.05) greater growth inhibition of B. subtilis and E. coli, corresponded to ferrous sequestering activity of methanol-derived stem extracts.     

Effects of various solvents on the extraction of antioxidant phenolics from the leaves, seeds, veins and skins of Tamarindus indica L.

The effects of solvents, of varying polarities, on the extraction of antioxidant phenolics from the leaves, seeds, veins and skins of Tamarindus indica (T. indica) were studied. The efficiencies of the solvents for extraction of the antioxidant phenolics were in the order: methanol > ethyl acetate > hexane. Phenolic content ranged from 3.17 to 309 mg of gallic acid equivalents/g. Methanol leaf extract (MEL) had the highest phenolic content and was the most potent scavenger of DPPH and superoxide radicals. Methanol vein extract had the highest ferric reducing activity whereas methanol seed extract was the most potent ABTS radical-scavenger. A positive correlation existed between phenolic content and antioxidant activities of the plant parts. HPLC analyses of MEL revealed the presence of catechin, epicatechin, quercetin and isorhamnetin. Overall, methanol was the most effective solvent for extraction of antioxidant phenolics from T. indica. T. indica, particularly the leaf, can be a useful source of natural antioxidants.     

Antioxidant capacity of pummelo and navel oranges: Extraction efficiency of solvents in sequence

Extraction efficiency of five different solvents on the antioxidant capacities of pummelo and navel oranges was measured by five widely used antioxidant methods. Freeze-dried edible parts of pummelo and navel oranges were extracted with five different solvents such as hexane, ethyl acetate, acetone, methanol and methanol:water (8:2). The total phenolic content of the extracts was determined by Folin-Ciocalteu method and expressed as catechin equivalents. The highest phenolic content was obtained from ethyl acetate and the minimum phenolic content was found in methanol extract. The dried extracts were screened for their radical scavenging activity using three different methods such as α,α-diphenyl-β-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical assay and ORAC methods. Ethyl acetate extract from navel orange and pummelo was found to be most active radical scavenging activity, whereas hexane extract from pummelo and methanol extract from navel orange was found to be lowest activity. Moreover, all the extracts from pummelo and navel orange were studied for their antioxidant capacity by the formation of phosphomolybdenum complex and reducing power by potassium ferricyanide reduction method at various concentrations. The order of antioxidant capacity of pummelo and navel orange was found to be ethyl acetate>acetone>MeOH:water>methanol> hexane and ethyl acetate>MeOH:water>acetone>methanol>hexane, respectively. Acetone and methanol extracts from pummelo and navel oranges showed highest reducing power than other extracts at 1000 μg/ml. Significant differences in antioxidant capacity were found between the values obtained by the same method in different solvents and as well as each extract antioxidant capacity obtained by the different method. Results of the present study may be due to the extent of antioxidant capacity of each extract is in accordance with the amount of carotenoids, phenolics and vitamin C present in the extracts.     

Antioxidant and tyrosinase inhibitory activities of different parts of guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.)

The antioxidant and the tyrosinase inhibitory activities of 4 different solvents (acetone, ethanol, methanol, and water) for preparation of extracts from guava (branch, fruit, leaf, and seed) were evaluated by measuring total phenolic contents (TPC), DPPH radical scavenging activity, ABTS radical scavenging activity, reducing power (RP), and tyrosinase inhibitory activity. The extracts of branch and leaf showed relatively higher antioxidant properties than those of fruit and seed. The highest TPC (141.28 mg/g gallic acid equivalents), DPPH radical scavenging activity (IC₅₀=34.01 μg/mL), ABTS radical scavenging activity (IC₅₀=3.23 μg/mL), and RP (IC₅₀= 75.63 μg/mL) were found in acetone extract of leaf, while water extract of seed had the lowest antioxidant activity. The tyrosinase inhibitory activity of ethanol extract from guava leaf was 69.56%, which was the highest activity among the extracts. These results indicate that useful bioactive substances exist in the guava branch as well as leaf extracts.     

Antioxidant capacity of the extracts from pulp of Osmanthus fragrans and its components

In this study, a significant inhibitory effect (EC₅₀ = 50.29 μg/ml) on the ABTS free radicals was detected in the crude ethanol extracts (CEE) of Osmanthus fragrans' pulp. Then, CEE was separated into methanol soluble fraction (MSF) and a methanol insoluble fraction (MISF), and their scavenging activities on the ABTS free radicals ascended in the order: MSF > CEE > MISF, respectively. Accordingly, the total phenolic (TP) contents of MSF, CEE and MISF were 40.53 ± 0.27, 35.37 ± 0.18 and 29.62 ± 0.23 mg/g (dry weight), respectively. Furthermore, salidroside (tyrosol 8-O-β-glucopyranoside), which showed powerful antioxidant activities in all test system was isolated from MSF. The antioxidant activity of salidroside (81.54 μg/ml) on DPPH free radicals was found to be nearly twice of that of MSF (144.78 μg/ml), and its total antioxidant activity is superior to that of the synthetic antioxidant butylated hydroxytoluene (BHT). In conclusion, our results suggested that O. fragrans' pulp, which was often considered as agricultural wastes, could be a promising source of natural antioxidants, and that MSF and salidroside may be good candidates for further development as natural antioxidants.     

Determination of antioxidant compounds and antioxidant activity in commercial oilseeds for food use

Different commercial edible oilseed samples were analyzed in order to evaluate the compounds involved in antioxidant activity. Fatty acids, triacylglycerols, tocopherols, chlorophylls, β-carotene, squalene, phenolic compounds and CIE L^∗a^∗b^∗ coordinates were assayed. Strong chemical variability depending on the oilseed variety was observed. Antioxidant activity was evaluated for the oils, both for their methanol-soluble phase and the fraction insoluble in methanol. DPPH radical scavenging activity expressed in TEAC ranged between 0.45 and 2.30 mmol/l in peanut and maize oils, respectively. Free radical scavenging activity was mainly influenced by tocopherols content (r = +0.70) in oils and polyunsaturated fatty acids (r = +0.61) in the fraction nonsoluble in methanol. Variability of the correlation between the antioxidant activity and the composition of the oilseeds could be attributed to the differences in the squalene, chlorophylls, carotenoids, and phenols contents of the oils and their mutual interactions.     

The antioxidant, angiotensin converting enzyme inhibition activity, and phenolic compounds of bamboo shoot extracts

This study was undertaken to evaluate the functional properties of two of the most popular species of edible bamboo shoots in Korea (Phyllostachys pubescens and Phyllostachys nigra). Powdered bamboo shoots were extracted with methanol and an aqueous suspension of the obtained methanol extract was partitioned successively with chloroform, ethyl acetate, and butanol, leaving a residual water extract. All obtained extracts were evaluated for their antioxidant capacity and antimicrobial activity, angiotensin converting enzyme (ACE) inhibition activity, and ascorbic acid and phenolic compound content. Methanol and water fractions showed a particularly high ascorbic acid contents. The ethyl acetate fraction contained a high concentration of phenolic compounds. Among all extracts, the ethyl acetate and butanol fractions showed particularly high antioxidant activity. Methanol extract had a significantly higher ACE inhibitory activity than other extracts. None of the extracts inhibited the tested bacteria.     

Antioxidant properties and quantitative UPLC-MS analysis of phenolic compounds from extracts of fenugreek (Trigonella foenum-graecum) seeds and bitter melon (Momordica charantia) fruit

Freeze-dried fenugreek (Trigonella foenum-graecum) seeds and bitter melon (Momordica charantia) fruit were extracted sequentially using non-polar to polar solvents, with further separation carried out on polar extracts by molecular weight cut off dialysis. The fenugreek ethyl acetate crude extract (FGE3) demonstrated the highest antioxidant activity, in terms of Trolox Equivalents (TE), for both the DPPH (35.338 ± 0.908 mg TE/g) and FRAP (77.352 ± 0.627 mg TE/g) assays. This extract also contained the highest phenolic content, in terms of Gallic Acid Equivalents (GAE) (106.316 ± 0.377 mg GAE/g). Despite having considerably lower antioxidant activity than fenugreek, the highest antioxidant activities for bitter fruit were observed in the hexane (BME1) and methanol hydrophilic < 3.5 kDa dialysed (BME4 < 3.5 kDa) extracts, while the highest phenolic content was found in the methanol hydrophilic > 3.5 kDa (BME4 > 3.5 kDa) dialysed extract. UPLC-MS was used to quantify 18 phenolic compounds from fenugreek and 13 from bitter melon in active crude extracts. The flavonoids apigenin-7-O-glycoside (1955.55 ng/mg) and luteolin-7-O-glycoside (725.50 ng/mg) were the most abundant compounds in FGE3, while bitter melon extracts contained only small amounts of mainly phenolic acids. A further 5 fenugreek and 1 bitter melon compounds were identified in trace amounts from the same extracts, respectively.     

Dose-effect study on the antioxidant properties of leaves and outer bracts of extracts obtained from Violetto di Toscana artichoke

Artichoke (Cynara scolymus L.) is an edible vegetable largely used in the Mediterranean diet and in folk medicine. The present paper discusses the analysis of the polyphenol content of leaves and outer bracts of Violetto di Toscana artichoke using different extraction procedures with the aim of establishing a correlation between polyphenol subclasses and antioxidant activity measured on human LDL oxidized by copper ions. HPLC/DAD and HPLC/MS analyses revealed that both the matrixes contain identical polyphenol subclasses, with mainly quantitative differences. The antioxidant effect of four artichoke extracts decreases in the following order when the sum of total phenolic compounds was considered: ethanolic extract from leaves (IC₅₀ = 2.92 ± 0.46 μM); ethanolic extract from outer bracts (IC₅₀ = 4.04 ± 0.21 μM); ethyl acetate extract from leaves (IC₅₀ = 4.91 ± 0.11 μM); ethyl acetate extract from outer bracts (IC₅₀ = 10.18 ± 1.6 μM). IC₅₀ were also calculated considering the concentrations of single polyphenol subclasses. In both cases, the potency of antioxidant properties was not related to the amount of total polyphenols or the single subclasses.     

Phenylalanine ammonia lyase (PAL) enzyme activity and antioxidant properties of some cyanobacteria isolates

In the present study, six cyanobacteria isolates were evaluated for the PAL enzyme activity, and their methanol extracts were assessed for the total phenolic amount and other antioxidant parameters. Synechocystis sp. BASO444 and Synechocystis sp. BASO673 isolates with high levels of total phenols (66.0 ± 1.2 μg/mg, 78.1 ± 1.8 μg/mg, respectively) also showed high levels of PAL activities (20.5 ± 3.1 U/mg protein, 17.2 ± 2.3 U/mg protein, respectively) and strong antioxidant activities. To understand the effect of l-phenylalanine (l-phe) on the PAL activity, total phenolic amount, and phenolic constituents, isolates were evaluated with 100 mg/l l-phe. While PAL activities exhibited no significant change with l-phe addition, total phenolic amount of the isolates significantly increased. HPLC analysis revealed gallic acid, trans-cinnamic acid, p-coumaric acid, and ferulic acid as the main compounds. Results suggested that the two isolate mights be an important source for the l-phe inducible phenolic compounds.     

Estimation of neuroprotective effects of Laurocerasus officinalis Roem. (cherry laurel) by in vitro methods

Dichloromethane, ethyl acetate, acetone, methanol, and water extracts prepared from the fruits and leaves of Laurocerasus officinalis Roem. (LO) (Rosaceae) were screened for their cholinesterase inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), the key enzymes in pathogenesis of Alzheimer's disease (AD), using ELISA microplate reader at 50, 100, and 200 ??g mL⁻¹. As AD is associated with oxidative stress, the antioxidant activity of the extracts was also tested by radical-forming methods against 2,2-diphenyl-1-picrylhydrazyl (DPPH), N,N-dimethyl-p-phenylendiamine (DMPD), and superoxide radicals as well as iron-related methods; iron-chelating capacity and ferric-reducing antioxidant power (FRAP) assays. Total phenol and flavonoid quantification was achieved using Folin-Ciocalteau and AlCl₃ reagents, respectively. The highest AChE (44.01 ± 1.75%) and BChE (19.91 ± 0.37%) inhibition was caused by the LO-leaf-methanol extract 200 ??g mL⁻¹, while it showed the best radical-scavenging activity against DPPH at 2000 ??g mL⁻¹. Only, the dichloromethane and water extracts of the fruits and the leaf water extract had an iron-chelating capacity, while the leaf methanol extract displayed the highest FRAP. The leaf methanol extract (113.45 ± 0.71 mg g⁻¹ extract) was found to be the richest in total phenols, while the leaf acetone extract (139.90 ± 4.64 mg g⁻¹ extract) had the most abundant amount of total flavonoids.     

Antioxidant, antiacetylcholinesterase and antimicrobial activities of Cymbopogon schoenanthus L. Spreng (lemon grass) from Tunisia

Aqueous extract, proanthocyanidin rich extract, and organic extracts of Cymbopogon schoenanthus L. Spreng (lemon grass) shoots from three different locations in South Tunisia were screened for their antioxidant, acetylcholinesterase and antimicrobial activities. In addition to the evaluation of these activities, the contents of flavonoids and total phenolic compounds were determined.Antioxidant activity measured by DPPH assay showed that the proanthocyanidin extract exhibited higher antioxidant activity than the aqueous extract. Extract concentration providing 50% inhibition (IC₅₀) ranged from 16.4 ± 6.8 μg/mL to 26.4 ± 6.8 μg/mL. The antioxidant activity was also determined using the β-carotene/linoleic acid bleaching test. The best results (IC₅₀ = 0.11 ± 0.10 mg/mL) were obtained with the proanthocyanidin extract of the plants collected from the desert region (Dhibat).The greatest acetylcholinesterase inhibitory activity (IC₅₀ = 0.23 ± 0.04 mg/mL) was exhibited by the ethyl acetate and methanol extracts of the plants collected from the mountainous region. It seems that extracts obtained with more polar solvents gave better results.The proanthocyanidin extracts showed a good antimicrobial activity against Streptococcus sobrinus at low concentration (MIC = 4 mg/mL). Therefore, these extracts could be used to prevent carious lesions by inhibiting S. sobrinus growth.