Evaluation of Antioxidant Activity of Medicinal Plant Extracts Produced for Commercial Purpose

The antioxidant potential of some herbal plant extracts (commercial products) was measured using various in vitro assays. Among the extracts from Curcuma longa, Caffea arabica, Tribulus terrestris, Bacopa monnieri and Trigonella foenumgraecum, the Curcuma longa and coffee bean extract (Caffea arabica) showed greater antioxidant activity measured as scavenging of DPPH, superoxide radicals, reducing power and inhibition of microsomal lipid peroxidation.


Introduction
The many number of medicinal plants are used in the cellular and metabolic disease treatment such as diabetes, obesity and cancer etc. There are some speculations that the generation of free radicals inside the body in some physiological conditions is resulted in the cellular changes and development of cancer etc. and this could be neutralized by the antioxidants from different medicinal plants. Several studies have shown that plant derived antioxidant neutraceuticals scavenge free radicals and modulate oxidative stress-related degenerative effects 1,2 . Free radicals have been implicated in many diseases such as cancer, atherosclerosis, diabetes, neurodegenerative disorders and aging 3,4 . Previous research reports suggest that higher intake of antioxidant rich food is associated with decreased risk of degenerative diseases particularly cardiovascular diseases and cancer 5 .
The free radical neutralizing property of several plants was reported by previous studies. The extracts from number of medicinal plants which are known to have some biologically active principles are used in ayurvedic preparations and these extracts are prepared in bulk for commercial purpose. In this present study we have measured antioxidant activity of various extracts like Curcuma longa, Coffee bean extract (Caffea arabica), Tribulus terrestris, Bacopa monnieri and fenugreek (Trigonella foenum graecum) employing various in vitro assay methods, such as scavenging activity of DPPH, superoxide radical, inhibition of microsomal lipid peroxidation and reducing power.

Preparation of herbal extracts
The above said herbs were selected and procured from the approved supplier. They were washed with water and then powdered. The powder was taken and extraction was carried out in large scale capacity reactor using 75% methanol and concentrated. The concentrated extract was spray dried and the dried powder was taken to check the antioxidant activity.

DPPH radical scavenging assay
DPPH radical scavenging activity was done using the reported method 6 ; the reaction mixture containing 1 mL of DPPH solution (0.1 mmol /L, in 95% ethanol v/v) with different concentrations of the extract was shaken and incubated for 20 min at room temperature and the absorbance was read at 517 nm against a blank. The radical scavenging activity was measured as a decrease in the absorbance of DPPH and calculated using the following equation:

Superoxide radical scavenging assay
The superoxide radical scavenging activity of the extracts was measured according to the literature method 7

Inhibition of microsomal lipid peroxidation
Liver excised from adult male Wister rats, was homogenized (20 g /100 mL tris buffer) in 0.02 mol/L, tris buffer (pH 7.4). Microsomes were isolated by the calcium aggregation method 8 . 100 µL of liver microsomal suspension (0.5 mg protein) was incubated with 1 mmol /L each of FeSO 4 and ascorbic acid with or without extract in a total volume of 1 mL in 0.1 mol/L phosphate buffer (pH 7.4). After incubation at 37 o C for 60 min, TBA (0.67g/100 mL water) was added to the reaction mixture and boiled for 15 min. The TBA reactive substances (TBARS) was calculated from the absorbance at 535 nm 9 where BHA was used as the positive control.

Measurement of reducing power
The extracts were taken in different concentrations in phosphate buffer (0.2 mol /L, pH 6.6) and incubated with potassium ferricyanide (1 g /100 mL water) at 50 o C for 20 min. the reaction was terminated by adding TCA solution (10 g /100 mL water), centrifuged at 3000 rpm for 10 min and the supernatant was mixed with ferric chloride (0.1 g/100 mL water), the absorbance measured 10 at 700 nm. The increased absorbance of the reaction mixture indicated increased reducing power.

Results and Discussion
Extracts were subjected for the evaluation of antioxidant activity by using various in vitro model systems. DPPH radical scavenging activity was observed in all the extracts, the curcuma extract showed dominant activity followed by coffee bean extract (Figure 1) among the extracts. The IC 50 values were calculated and are depicted in (Table 1). Proton radical scavenging action is an important attribute of antioxidants, which is measured by DPPH radical scavenging assay. Hydrogen donating ability of the antioxidants molecules contributes to its free radical scavenging nature. Figure 1. DPPH radical scavenging assay data represents, mean ±SEM, for n=3 Superoxide radical scavenging activity was shown by both curcuma and coffee bean extracts and was concentration dependent with an IC 50 value of 0.4±0.14 and 0.52±0.18 mg /mL respectively (Table 2 and Figure 2). Curcuma extract was markedly a more potent scavenger of superoxide anion than the CBE followed by the others.
As shown in Figure 3 Curcuma extract showed dominant activity followed by CBE, whereas, less activity was observed in case of methi extract. All the extract showed antioxidant activity in concentration dependent manner.
It had been broadly defined as the oxidative deterioration of polyunsaturated lipids. Initiation of a peroxidation sequence in a membrane or polyunsaturated fatty acid is due to abstraction of a hydrogen atom from the double bond in the fatty acid. The free radical tends to stabilized by a molecular rearrangement to produce a conjugated diene. This reacts with oxygen molecule to give a peroxy radical. Peroxy radical can abstract a hydrogen atom from another molecule to give lipid hydro peroxide.

Conclusion
In order to characterize antioxidant activity of a plant extract, it is desirable to subject it for the tests that evaluate the range of activities such as scavenging of the reactive oxygen species, inhibition of membrane LPO and metal ion chelation. Antioxidant-rich plant extracts serves as sources of nutraceuticals that alleviate the oxidative stress and therefore prevent or slow down the degenerative diseases. An effort has been made to explore the antioxidant properties of commercial available herbal extracts. This indicates the potential of the extracts as a source of natural antioxidants or nutraceuticals with potential application to reduce oxidative stress with consequent health benefits.