Antioxidant Potential of Phytoconstituents with Special Emphasis on Curcumin

Abstract

Various fruits, vegetables, cereal grains, edible macrofungi, microalgae, and medicinal plants are containing phytoconstituents which are considered to be antioxidants. Polyphenols and carotenoids are the two main kinds of antioxidant phytochemicals and they contribute the most to the antioxidant properties of plant and its derivatives are widely employed as antioxidants. Turmeric is a rhizomatous herbaceous perennial plant (Curcuma longa) of the ginger family. The medicinal properties of turmeric, the source of curcumin, have been known for thousands of years; however, the ability to determine the exact mechanism(s) of action and to determine the bioactive components have only recently been investigated. Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), also called diferuloylmethane, is the main natural polyphenol found in the rhizome of Curcuma longa (turmeric) and in others Curcuma spp. Curcumin, a polyphenol, has been shown to target multiple signaling molecules while also demonstrating activity at the cellular level, which has helped to support its multiple health benefits such as antioxidant, anti-inflammatory, antimutagenic, antimicrobial and anticancer properties. Curcumin has received worldwide attention for its multiple health benefits, which appear to act primarily through its anti-oxidant and anti-inflammatory mechanisms.

1. Introduction

Free radicals are produced during routine cellular metabolic processes. These free radicals are considered as important part of the pathological complications including diabetes mellitus, cardiovascular disorders, neurodegenerative disorders, cancer, cataracts, asthamatic conditions, rheumatoid arthritis, inflammatory conditions, intestinal complications, ischemic and postischemic conditions.

Antioxidants are those substances which at very low concentrations are capable of significantly reducing or preventing the oxidation of the substrates which can be oxidized are called as antioxidants. There is a highly complex system including enzymatic and non-enzymatic systems which is effective in synergistic way with each other, so as to protect the body cells and different organs from the damage caused b free radicals. There are different types such as endogenous antioxidants and exogenous antioxidants such as the diet or various dietary supplements. There are different examples of dietary substances which actually do not scavenge the free radicals but they stimulate the endogenous activity ultimately categorized as antioxidants. An antioxidant which are considered as ideal, should easily absorbed and eliminate the free radicals and can able to cause chelation of redox metal ions at the levels which are considered as physiologically suitable. This should be active at the aqueous and/or in the membrane domains and can result in effective expression of gene at a positive direction. These endogenous antioxidants suppose to be highly potential in maintain the optimum cellular functioning and ultimately systemic healthy conditions and the well being also. But many a times, these endogenous antioxidants are considered as insufficient to support the oxidative or nitrosative stress, so along with it dietary antioxidants are important for maintain the highest cellular functioning. The highly potential enzymatic antioxidants consist of glutathione peroxidase, catalase, superoxide dismutase. Various examples in nonenzymatic antioxidants are vitamin C, vitamin E, thiol antioxidants including lipoic acid, glutathione etc., carotenoids, melatonins, flavanoids and other resembling compounds. One of the mechanisms called as antioxidant network, which involves the regeneration of the original properties of one antioxidant after interaction with other antioxidants. In various diseased conditions, it is reported that there is established link between the raised levels in ROS or RNS and deterioration of actions related to enzymatic or non enzymatic antioxidants [1, 2, 3].

2. Enzymatic and non enzymatic antioxidants

2.1 Enzymatic antioxidants

2.1.1 Glutathione peroxidase

The oxidation of the glutathione directed as hydroperoxide which can be considered as hydrogen peroxide or others for example lipid hydroperoxide.

$$\mathrm{ROOH}+2\mathrm{G}\mathrm{S}\mathrm{H}\to \mathrm{GSSG}+{\mathrm{H}}_2\mathrm{O}+ROH$$E1

Selenium dependent that is GPx, EC 1.11.1.19 and independent on selenium for example glutathione S transferase, GST, EC 2.5.1.18 are considered as the two different forms. In the humans, reported are four types of se-dependent glutathione peroxidases which are mentioned as addition of two electrons to carry out reduction of peroxides through formation of selenole (SeOH) and these antioxidant properties of the selenoenzymes carries elimination of peroxides as important substrate for the reaction termed as Fenton reaction. Along with the tripeptide glutathione that is GSH, selenium dependent glutathione peroxides will be acting, and it exists in comparatively higher concentrations present in the cells and also catalyses the formation of hydrogen peroxide or the organic peroxide into water or alcohol, while causing oxidation of GSH simultaneously. It is able to compete with that of catalase and hydrogen peroxide as a substrate so, considered as an important source of giving protection against oxidative or the nitrosative stress which at very low levels [4].

2.1.2 Catalase

The first antioxidant enzyme was considered as the Catalase that is EC 1.11.1.6 and it was reported to carry out the conversion of hydrogen peroxide into the water and oxygen as indicated:

$${\mathrm{H}}_2{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$$E2

Amongst all the enzymes, catalase was reported to have the highest rate of turnover, one molecule of the catalase is having capacity to converting around 6 millions of hydrogen peroxides to water and oxygen, each of minute. Some from this catalase is found in all the tissues, majorly activity of catalase is found in liver and erythrocytes [5].

2.1.3 Superoxide dismutase

One from the enzymatic antioxidants that is superoxide dismutase called as EC 1.15.1.1, can reported to be an intracellular enzymatic antioxidant and is responsible to convert superoxide dismutase anions in dioxygen and ions of hydrogen peroxide as:

$${{\mathrm{O}}_2}^{-}+{{\mathrm{O}}_2}^{-}+2\mathrm{H}+\to {\mathrm{H}}_2{\mathrm{O}}_2+{\mathrm{O}}_2$$E3

This superoxide dismutase, is existing in the form of various isoforms, which majorly different in the natures of the active metal centre, composition of the amino acids, cofactors and other related features. Three different froms related to SOD are available in the human beings for example cytosolic, Zinc- SOD, mitochondrial Mn-SOD, and extracellular SOD. By undergoing successive oxidative and reductive pathways related to transition metal ions at their sites of activity, neutralization of superoxide ions by superoxide dismutase is carried out [6].

2.2 Nonenzymatic antioxidants

2.2.1 Vitamin E

Vitamin E majorly available as fat soluble and it can be found in eight different varieties [7]. A chromanol ring along with the phytyl tail and difference in numbers and position related to methyl groups in these rings are observed in the tocopherols including α, β, γ, and δ. These substances are reported to be lipid soluble with a prominent antioxidant potential. According to the literature, these are found to be more active than that of polyunsaturated fatty acids which are having peroxyl radicals and thus show their action by breaking the lipid peroxidation [8].

The important role of this vitamin is to give protection from the lipid peroxidation and also literature is available to support this, there is synergestic effect of ɑ tocopherol and ascorbic acid, involved in cyclic type reactions. Due to the donation of the hydrogen from ɑ tocopherol to the lipid radical or lipid peroxide radical and it gets converted to ɑ tocopherol radical. Further, this ɑ tocopherol radical can get reduced in the form of ɑ tocopherol due to the ascorbic acid [9].

2.2.2 Vitamin C-ascorbic acid

This considered as one of the antioxidants reported to work in an aqueous medium of the body. In the presence of metal ions it is oxidized into dehydroascorbic acid in an extracellular environment of the body, which is further carried into the cells with help of glucose transporters. It works alone with the antioxidant enzymes and also Vitamin E and carotenoids are termed as its primary partners. From the ɑ tocopherol radicals it forms ɑ tocopherol in the membranes and lipoproteins, vitamin C plays an important role along with vitamin E, ultimately it increases the levels in glutathione in cells, thus protecting the protein thiol groups against oxidative damage. It is present in the reduced form in the cells, due to reaction with glutathione, thus catalyzing protein disulfide isomerase and glutaredoxins. Ascorbic acid is reported as the best potential reducing agent that effectively causes neutralization of ROS for example hydrogen peroxide [10].

2.2.3 Thiol antioxidants

This is a very important intracellular thiol antioxidant which is present in intracellular region is tripeptideglutathione which is also known as GSH. Acoording to the literature, it is considered as a redox buffer of the cell. It is found to be present in the cytosol, mitochondria and nuclei and present in the soluble form of antioxidants in these compartments. The levels of glutathione are important for inducing the postmititic phenotype, which are confirmed based upon the studies on the human fibroblasts, and hence it is reported that the implementation of the depletion of glutathione has very important role during the control in aging at cellular level from human skin.

As this glutathione acts as cofactor for various enzymes which cause detoxifying actions, its participation in the amino acid transport through the plasma membrane, scavenging of hyrdroxyl radical and direct scavenging of the singlet oxygen, regeneration of the active forms of vitamin C and E, has a very potential role for protective action against oxidative or nitrosative stress [11].

Decrease in the glutathione levels are the signals of the oxidative stress which is increased in the ischemic brain disorders, cancer, cardiovascular disorders and decreased concentrations of glutathione are also indicative of both that is type 1 and type 2 diabetes mellitus [12, 13, 14, 15, 16].

2.2.4 Thioredoxin

Another potential example of the thiol antioxidants is thioredoxin which is also known as TRX system, which are the types of proteins available both in the mammalian and prokaryotic cells and capable of oxidoreductase activity. It is consisting of disulphide and two cysteins which are redox active with conserved active sites as Cys- Gly-Pro-Cys. This antioxidants consists of two –SH groups which are adjacent forms which are present in the reduction form, then are converted into disulphide units in the oxidized form as TRX after it undergoes redox reactions including multiple proteins in it. The levels of thioredoxin is comparatively lesser than that of GSH, but these may be having functions which are overlapping and in similar compartments related to the stimulation and regulation of various transcription factors. Many of the normal and neoplastic cells, secrets this thioredoxin in the oxidative or nitrosative stress and also in the inflammatory conditions [17, 18].

2.2.5 α-Lipoic acid—1, 2-dithione-3-pentanoic acid

Metal chelating and antiglycation potentials are associated with this third thiol antioxidant which is present as natural substance called as α-Lipoic acid called as ALA. Different than other antioxidants which are either lipid soluble or soluble in aqueous medium, lipoic acid can be considered as active in the aqueous as well as lipid phases. In most of the tissues, lipoic acid is transferred to dihydrolipoic acid that is DHLA through the action of NADH or NADPH, and then it can be readily digested and absorbed too. There are various actions which are related to lipoic acid such as direct termination of the free radicals, chelation of transition metal ions for example copper and iron, glutathione levels observe to be increased, vitamin C levels and prevention of the toxicities which are associated with their loss [19].

Lipoic acid is also capable of crossing the blood brain barrier and thus it can be covered by all central and peripheral regions of nervous system. For the free radicals associated with the oxidative stress, lipid peroxides that is LPO is considered as the biomarker. A sequence of the reactions is initiated after the action of free radicals on the polyunsaturated fatty acids called as PUFA in the biological systems, which ultimately results in the production of the conjugated dienes and lipid peroxidases [20].

2.2.6 N-acetylcysteine

To decrease the conditions related oxidative or nitrosative stress, one of the thiol antioxidant is N-acetylcysteine. It prevents from liver damage related to paracetamol caused in the human beings, causes attenuation in liver damage and also reported to prevent the GSH depletion in the mice [21].

N-acetylcysteine also possesses properties such as metachelation, and is implemented in several clinical conditions. Due to the thio groups present in this N-acetylcysteine, it decreases the free radicals and supplies chelation sites to that for metals. Hence, in the metal poisoning conditions and various diseased conditions, N-acetylcysteine is found to have a potential role as is effective in renovating inbalanced prooxidant and antioxidant conditions.

2.2.7 Melatonin

The melatonin shows its free radical scavenging potential due to donation of electron so as it can release variety of ROS or RNS, containing majorly toxic hydroxyl radicals. Along with that melatonin also increases an enzymes which are considered as antioxidative such as superoxide dismutase, glutathione peroxidase, glutathione reductase, catalase etc [22].

This efficiency related to electron transport chain is reported to be increased and as a result decreased electron leakage and production of the free radicals. Due these highly potential actions of melatonin, it is considered as a very important entity used in treating variety of neurological diseases which are having oxidative damage as a part of the etiology concerned [23].

2.2.8 Carotenoids

One of the potential antioxidants, which are reported to be lipid soluble and containing isoprenoid carbok skeleton is the carotenoids. These are reported to be present in the membranes along with the lipoproteins and a very useful example is ɑ- carotene. The efficiency of these antioxidants is considered to be as equivalent as that of ɑ tocopherol as they effectively scavenge singlet oxygen and also result in trapping of the peroxyl radicals at low levels of oxygen pressures (Table 1). Those caratenoids show brings are distinguished with the pro-vitamin A activity. As in β- carotene, it indicates presence of two brings on the both the ends related to carbon chain, it possesses highest activity. Vitamin A is also reported to show highly potential antioxidant activity which is independent on that of the oxygen concentration [24].

ROS	Neutralizing antioxidants
Hydroxyl radical	Vitamin C, glutathione, Flavonoids, lipoic acid
Superoxide radical	Vitamin C, glutathione, Flavonoids, SOD
Hydrogen peroxide	Vitamin C, glutathione, beta Carotene, vitamin E, CoQ10, Flavonoids, lipoic acid
Lipid peroxides	β-carotene, vitamin E, ubiquinone, flavonoids & Glutathione peroxidase

Table 1.

Various reactive oxygen species and their neutralizing antioxidants.

2.2.9 Flavonoids

One of the highly potential antioxidants which are considered as a part of regular diet and considered as a wide class of plant metabolites having a low molecular weight are Flavanoids. These are considered as the groups of derivatives of benzo-γ- pyrone which are made up of phenolic and the pyrane ring with attached hydroxyl groups are added during normal metabolism. The most important activity of flavanoids is considered as their protective action against that of oxidative or nitrosative stress. The catalytic breakdown of the hydrogen peroxide radicals that is Fentonn chemistry, is resulted due to the scavenging of peroxyl radicals, minimizing lipid peroxidation, chelation of redox active metals. In other certain conditions, flavanoids are reported to indicate the poroxidant activity which is considered to be in direct proportion to the presence of total hydroxyl groups and as per literature also indicated cell signaling modulation [25].

The process called as Oxidation, involves the formation of various intermediates which are reactive and can cause aerobic cell metabolism. Thus it is reported that the cells are having a chance of damage which is protected by this antioxidant systems in the cells. Different pathological conditions such as cancerous conditions, cardiovascular disorders, cataract, diabetes mellitus, gastrointestinal disorders, liver disorders, macular degenerations periodontal disorders, other inflammatory conditions are observed due to loss of balance in the ROS production and defence to antioxidants thus causing oxidative stress as a result of deregulation of the cellular functioning [26].

3. Turmeric containing curcumin as potential phytoconstituent

Curcuma longa, as turmeric is one of the perennial herbs and classified under the family Zingiberaceae. This is cultivated majorly in India and China. Yellow powder of the rhizome from the plant is considered for many of the medicinal purpose. Dried form of Curcuma longa that is turmeric used as an ingredient in many of the food preparations. It is known by many other names such as Indian saffron Curcum in the, Arab region, Jianghuang (yellow ginger in Chinese), Haridra (Sanskrit, Ayurvedic), Kyoo or Ukon (Japanese) [27].

Powder of Turmeric is applicable as flavoring and coloring agent in various food preparations. For maintaining oral hygiene, it has been in use from many years [28]. In India and China, turmeric is considered as the choice of treatment for jaundice and other liver problems. This is one of the potential herbs having different pharmacological potentials including anti-protozoal, anti-venom activities, antioxidant, anti-microbial, anti-angiogenic, anti-malarial, anti-inflammatory, anti-proliferative, anti-tumor and anti-aging properties [29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]. It has also been used to treat parasitic infections, ulcers, skin disorders, immunity related disorders and curing the symptoms of colds and flus [41]. Curcumin (CUR) and two related compounds demethoxy curcumin (DMC) and bisdemethoxycurcumin (BDMC) are considered as important curcuminoids responsible for the pharmacological action of turmeric. The active constituents of present are considered as a mixture of bisdesmethoxycurcumin, curcumin (diferuloylmethane), monodexmethoxycurcumin. Around 90% of curcuminoids are present in turmeric. Apart from this it also consists of proteins, sugars, and resins 0.3–5.4% of curcumin is found to be present in the raw turmeric [42].

Turmeric is containing a mixture of three curcuminoids: curcumin (diferuloylmethane), demethoxycurcumin and bisdemethoxycurcumin, along with that volatile oil containing atlantone, zingiberone and tumerone, proteins resins and sugars. Lipophilic polyphenol that is Curcumin is nearly insoluble in water but is found to be stable in the acidic pH of the stomach [43].

Curcumin is containing phenolic groups due to which it can eliminate free radicals derived from oxygen.

The free radicals such as hydroxyl radical, singlet oxygen, superoxide radical, nitrogen dioxide and NO which can be eliminated by curcumin [44].

Curcumin and its derivatives has the most potential biological effects disease prevention and health promotion including inflammatory, antioxidant and anticancer potential [45].

3.1 Anti-inflammatory properties

Curcumin activity for inflammation after giving oral administration was comparable to that of cortisone or phenylbutazone. Curcuma longa after this treatment has potentially reduced inflammatory swelling. This effect can be resulted due to its potential of inhibiting biosynthesis of inflammatory prostaglandins from arachidonic acid and neutrophil function during inflammatory states [46, 47].

3.2 Hepatoprotective activity

Turmeric is having hepatoprotective activity similar to that of silymarin. From studies, it can be concluded that turmeric has hepatoprotective potential in various including carbon tetrachloride (CCl4), acetaminophen (paracetamol) and galactosamine. This hepatoprotective effect is mainly a observed due to the antioxidant activity of turmeric along with its ability to decrease the formation of proinflammatory cytokines. Administration of curcumin is resulted in decrease of liver injury [48, 49, 50].

3.3 Anticarcinogenic properties

All three stages of this carcinogenesis-initiation, promotion, and progression are inhibited by curcumin.

During initiation and promotion, curcumin modulates transcription factors controlling phase I and II detoxification of carcinogens; down-regulates proinflammatory cytokines, free radical-activated transcription factors, and arachidonic acid metabolism vicyclooxygenase and lipoxygenase pathways and scavenges free radicals [51, 52].

3.4 Antidiabetic activity

ar-turmerone, ar-turmerone, curcumin, demethoxycurcumin and bisdemethoxycurcumin present in hexane and ehanol extract had reported to stimulate adipocyte differentiation in a dose dependent manner. The results also concluded that turmeric ethanolic extract found to contain curcuminoids and sesquiterpenoids is more strongly hypoglycemic as compared to either sesquiterpenoids or curcuminoids [53].

3.5 Antimicrobial activity

Antibacterial, antifungal, cytotoxic, insecticidal and phytotoxic activity of an ethanolic extract of turmeric was evaluated. The extract showed antifungal activity against Trichophyton longifusus and Microsporum canis and weak antibacterial activity against Staphylococcus aureus. Toxic activity was observed against Lemna minor [54].

3.6 Antidepressant properties

In cases of chronic mild stress that is CMS model, curcumin was studied for antidepressant activity.

Ethanolic extract had indicated increase in sucrose intake as compared to normal control levels, reduction in serum IL-6 and TNF-α and CRF levels in medulla oblongata and serum to limits lower than normal.

Cortisol levels were found to be reduced than the normal levels. Through the inhibition of monoamine oxidize, it had shown its antidepressant activity. It caused reversal of decreased serotonin, dopamine and noradrenalin concentrations and increase in the turnover of serotonin [55, 56].

3.7 Cardiovascular diseases

The protective effect was observed due to lowering of triglyceride and cholesterol levels and decrease in LDL and also due to inhibition of aggregation of platelet [57].

Effect of turmeric extract on cholesterol levels may be due to decreased cholesterol uptake in the intestines and increased conversion of cholesterol to bile acids in the liver. Inhibition of platelet aggregation by C. longa constituents is thought to be via potentiation of prostacyclin synthesis and inhibition of thromboxane synthesis [58].

Oral intake of 500 mg/d of curcumin was given for 7 days and further it resulted in comparable decrease in the serum peroxide levels by 33% and increase in HDL cholesterol by 29% and decrease in level of total serum cholesterol by 12% [59].

3.8 Dyspepsia and gastric ulcer

During a phase II clinical trial for peptic ulcer which was diagnosed with endoscopically in 45 subjects, given with 600 mg curcumin five times daily for 12 weeks, it was observed that ulcers were absent in 48% patients after 8 weeks, and in 76% patients after 12 weeks. In remaining patients also within 1-2 weeks abdominal pain and other symptoms had decreased significantly [60].

3.9 Irritable bowel syndrome

The most common symptoms of irritable bowel syndrome (IBS) are considered as altered bowel habits, abdominal pain, bloating etc.

After pilot study for eight week of IBS patients, it was found that 53% and 60% reduction in IBS prevalence. In post-study analysis, abdominal pain and discomfort scores were reduced by 22 and 25% [61].

3.10 Inflammatory bowel disease

Ulcerative colitis (UC) and Crohn’s disease (CD) are considered as two types of IBD, inflammatory bowel disease. In a pilot study performed in 2005, hematological, erythrocyte sedimentation rate (ESR) and biochemical blood analysis, C-reactive protein (CRP) (the latter two inflammatory indicators), sigmoidoscopy, and biopsy were all performed. The authors from this study concluded that curcumin plus standard therapy was more effective in maintaining remission than placebo plus standard UC treatment [62, 63].

3.11 Neurological disorders

Investigations on animal models for Alzheimer’s disease (AD) was indicated a direct effect curcumin in reducing the amyloid pathology of AD.

Results have also shown that curcumin exhibited multiple effects in brain. Curcumin is considered as a future drug of therapy for the treatment of various neurological disorders including tardive dyskinesia, diabetic neuropathy and depression [64].

3.12 Antioxidant potential

The two primary mechanisms as antioxidant and anti-inflammatory which explain the benefits of curcumin have proven for various pharmacological actions. Systemic marker of oxidative stress have been found to be improved due to presence of curcumin. Also, from previous literature, it had proven to increase serum activities of important antioxidants such as superoxide dismutase (SOD).

A recent data and analysis of randomized control studies related to the potential effect of supplementation with purified curcuminoids on various oxidative stress parameters had indicated a significant effect on plasma activities of SOD and catalase, as well as serum concentrations of glutathione peroxidase (GSH) and lipid peroxides. The activity of Curcumin on free radicals has been performed based upon many mechanisms. Many forms of free radicals are scavenged by Curcumin, including reactive oxygen and nitrogen species (ROS and RNS, respectively), and can also it was found to alter the activity of GSH, catalase, and SOD enzymes during the neutralization of free radicals and resulted in inhibition of ROS-generating enzymes such as lipoxygenase/cyclooxygenase and xanthine hydrogenase/oxidase. In addition to this, curcumin is considered as a lipophilic compound that makes it an effective scavenger of peroxyl radicals, hence can be effective as a chain-breaking antioxidant [65, 66, 67, 68, 69, 70, 71].

Antioxidant activity of the turmeric is evaluated by performing DPPH radical scavenging activity and FRAP values. Many of the literature suggest that, various extracts of turmeric are having antioxidant activities calculated referring to the DPPH radical-scavenging potential.

In this method, 1 mL of the extract was added to around 1.2 mL of 0.003% DPPH in methanol using at varying concentrations (2.5–80.0 μg/mL). The percentage of DPPH inhibition was then calculated using the equation: % of DPPH inhibition = [(ADPPH − AS ADPPH)] × 100, in this ADPPH is the absorbance measured for DPPH in the absence of a sample and AS is the absorbance value of DPPH in the presence of either a sample or the standard. DPPH scavenging activity can be given as concentration of a sample required to reduce absorbance of DPPH by 50% (IC50). This value then graphically determined once after plotting the absorbance that is percentage inhibition of DPPH radicals against the log concentration of DPPH, further determining the slope of the nonlinear regression.

Ferric Reducing Antioxidant Power (FRAP) assay was carried out for confirmation of antioxidant potential of the turmeric. Complex of ferric tripyridyltriazine is reduced into ferrous form which then resulted in an intense blue color observed at low pH range. This colour intensity further confirmed by measuring its absorbance value at 593 nm. 200 𝜇L of the extract solution prepared in varying concentrations from 62.5–1000.0 μg/mL was then added to 1.5 mL of the previously prepared FRAP reagent, then reaction mixture was incubated at 37⁰ C for 4 min. FRAP reagent was prepared by adding 10 volumes of 300 mM acetate buffer having pH 3.6 with 1 volume of 10 mM TPTZ solution in 1 volume of 20 mM ferric chloride (FeCl₃.6H₂O) and 40 mM hydrochloric acid. The FRAP reagent was then prewarmed to 37°C and was used when freshly prepared. Plotting of the standard curve was then done A using an aqueous solution of ferrous sulfate (FeSO₄.7H₂O) (100–1000 μmol), with FRAP values expressed as micromoles of ferrous equivalent (μM Fe [II] per 100 g of sample).

The obtained results from antioxidant studies indicated that the free radical scavenging activity may be due to to the high contents of phenolics and flavonoids having a higher reducing capacity. FRAP assay treats the antioxidants in the sample as reductants in a redox reaction and measures the reducing potential of the test sample. These antioxidants exert their activities by donating electron or hydrogen atoms to the ferric complex which converts to ferrous complex (Fe³⁺ to Fe²⁺ -TPTZ complex), thus breaking the radical chain reaction.

Many major diseases such as liver problem, myocardial infarction, diabetes, cancer are believed to be associated with lipid peroxidation and thus causing major cell damage. Curcuminoids and other polyphenols in turmeric can ameliorate and prevent lipid peroxidation, can stabilize the cell membrane, hence proving its significant role in prevention of atherosclerosis. Inhibitory action of turmeric polyphenols such as curcuminoids on lipid accumulation, oxidation, nitric oxide as well as the formation of inflammatory molecules, nuclear factor-kappa B- (NF-kB-) dependent gene expression, and its activation can thus influence therapeutic potential of turmeric in the treatment of pancreatic, hepatic, cancer and intestinal diseases. The ethanolic extract of turmeric can produce promisable symptomatic relief on external cancerous lesions in human. Along with this, curcumin has resulted to be effective in preventing and treatment of many of the neurodegenerative disorders as a free radical scavenger including Alzheimer’s disease. Also after giving short-term supplementation it has proved to reduce hematuria, proteinuria, including systolic blood pressure in patients with relapsed or refractory lupus nephritis. By referring all the literature, Curcumin can be considered as a safe adjuvant therapy. The previous studies had indicated that the high antioxidant properties of turmeric was found to inhibit cellular lipid peroxidation and can also ameliorate other oxidative damage caused by free radicals [72, 73, 74, 75, 76].

Thus Turmeric is proven to be an important source of high contents of flavonoids, polyphenols, tannins and ascorbic acid. Curcumin as important phytoconstituent of turmeric varieties is and effective and important antioxidant compound and which can be effective in management of various diseased conditions.

Conflicts of interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.