Elsevier

Food Chemistry

Volume 131, Issue 2, 15 March 2012, Pages 441-448
Food Chemistry

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

https://doi.org/10.1016/j.foodchem.2011.09.001Get rights and content

Abstract

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.

Highlights

► We extract antioxidant phenolics from the leaf, seed, vein and skin of Tamarindus indica. ► Methanol is the best solvent for extraction of phenolics in T. indica. ► Water, ethyl acetate and hexane are less suitable for phenolic extraction. ► Methanol leaf extracts have the highest phenolic content and antioxidant activities. ► Epicatechin, catechin, quercetin and isorhamnetin are present in T. indica leaf.

Introduction

Oxidative damage by free radicals is implicated in the aetiology of many diseases, cancer and heart diseases being the more common ones (Azad et al., 2008, Heitzer et al., 2001, Madamanchi et al., 2005).

Antioxidants are useful for providing protection against oxidative damage. Antioxidants, such as glutathione, ubiquinone, uric acid and the antioxidant enzymes glutathione peroxidase, superoxide dismutase and catalase, can be generated in the body; however, the amounts maybe inadequate, particularly under conditions of oxidative stress or inflammation where production of free radicals is increased. Hence, adequate amounts of antioxidants are important to prevent build up of free radicals and oxidative damage in the body.

Plants are rich alternative sources of natural antioxidants which can complement the antioxidants produced by the human body. Various studies have shown plants to be a rich source of antioxidants. Compounds with antioxidant properties found in plants include the vitamins A, E and C and phenolic compounds, including flavonoids, tannins and lignins (Boots et al., 2008, Valko et al., 2006). Flavonoids are one of the main phenolics studied, due to their documented potent antioxidant activities (Rice-Evans, Miller, & Paganga, 1996), some are more potent than the well known antioxidant vitamins. In addition, correlation studies have demonstrated a link between antioxidant activities in plants and their phenolic content, underlining the significant contribution which phenolics can make to antioxidant activities (Cai et al., 2004, Kaur and Kapoor, 2002, Razab and Abdul Aziz, 2010). In view of the potential of plants to provide a natural source of antioxidants, studies are on-going in search of plants with extracts of high phenolic content and antioxidant activities.

Tamarindus indica (T. indica), commonly known as tamarind, is ubiquitously found in tropical countries although it originated from Africa. It is a tree from the family Fabaceae. The pulp of this plant is used in cooking due to its sour taste and particularly to impart flavour to savoury dishes. T. indica is also used medicinally for gastric and digestion . problems. An animal study, using hamsters, demonstrated the hypolipidaemic effect of the seeds of T. Indica (Martinello et al., 2006). The fruits and seeds of this plant showed anti-bacterial, anti-inflammatory and anti-diabetogenic effects (Maiti et al., 2004, Paula et al., 2009). Most research on T. indica has concentrated on the fruits and seeds of this plant, mainly extracted using polar solvents (Luengthanaphol et al., 2004, Razali et al., 2010, Siddhuraju, 2007, Soong and Barlow, 2004, Sudjaroen et al., 2005). However, not much information is available on the antioxidant potential of the other parts of T. indica or the effect of various types of solvents on extraction of antioxidants from this plant. Hence, the aim of this study was to analyse the effectiveness of methanol, ethyl acetate and hexane for the extraction of antioxidant phenolics from the leaves, seeds, skins and veins of T. indica. Such study can provide complete information on the in vitro antioxidant potential of the other parts of this plant that are less well researched but nonetheless important.

Section snippets

Chemicals

All reagents used in the experiments were of analytical grade and obtained mostly from Fluka and Sigma. Solvents used for extraction of plant samples were purchased from Fisher Scientific. The phenolic standards were obtained from Sigma. Water used was of Millipore quality.

Plant material

Leaves, veins, skins and seeds of T. indica were collected from Kedah, northern part of Malaysia. The material was identified by a taxonomist of Rimba Ilmu Herbarium, University of Malaya, Malaysia. A voucher specimen was

Extraction yield and phenolic content

Table 1 shows the extraction yield of the various plant parts which range from 20 to 320 mg/g dried weight. The extraction yields, in descending order, were: methanol > ethyl acetate > hexane. This shows that methanol was the best solvent for extraction of compounds from the various parts of the T. Indica plant.

Phenolic compounds are secondary plant metabolites with beneficial biological effects, e.g. as anti-bacterial, anti-inflammatory and anti-allergic agents (Koshihara et al., 1983, Schramm and

Conclusion

Analyses of the phenolic content and antioxidant activities of the various parts of T. indica, extracted with solvents of varying polarities, are useful in providing information on the potential of this plant as a source of phenolic antioxidants. At the same time, they also provide data on the characteristics of the antioxidants present in the various parts of the plants. Overall, methanol was the most effective solvent for extraction of antioxidant phenolics from various parts of T. indica.

Acknowledgements

This research project was funded by research grants (RG127/09HTM, FS353/2008C and H-20001-00-E000009) from University of Malaya, Kuala Lumpur, Malaysia.

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