Evaluation of nutraceutical properties of selected small millets

Abstract

Objective:

The aim of this study was to evaluate the nutraceutical properties and nutritional value of grains of four selected small millets viz. finger millet, foxtail millet, prosomillet and khodomillet.

Materials and Methods:

The qualitative analysis of phytochemicals viz. phenolics, flavonoids, alkaloids and saponins present in the four small millets was done. The water-soluble proteins, crude fiber content and the reducing power of the grains of these four millets were analyzed.

Results and Conclusions:

The khodomillet showed maximum phenolic content (10.3%) and foxtail millet showed minimum phenolics (2.5%). As far as reducing capacity was concerned, finger millet was highest (5.7%). The prosomillet showed least reducing property (2.6%). The finger millet (391.3 mg/g each) showed maximum reducing sugar content. The prosomillet showed minimum reducing sugar (195 mg/g). The foxtail millet showed maximum protein content (305.76 mg/g) and prosomillet showed minimum protein content (144.23 mg/g). The khodomillet showed maximum crude fiber content (14.3%).The finger millet showed maximum reducing sugar content (391.3 mg/g) whereas, the khodomillet showed minimum reducing sugar (130.43 mg/g).

The small millets are small-grained cereals and are the staple food of the millions inhabitating the arid and semiarid tropics of the world. They are distributed in most of the Asian and African countries and parts of Europe. The grains of small millets, being nutritionally superior to rice and wheat, provide cheap proteins, minerals and vitamins to poorest of the poor where the need for such ingredients is the maximum.[1]

The concepts of food are changing from a previous emphasis on survival, hunger satisfaction, absence of adverse effects on health, and health maintenance to a current emphasis on the use of nutraceutical foods which promise to promote better health and well-being, thus helping to reduce the risk of chronic illnesses such as cardiovascular diseases, some cancers and obesity. An important factor of the nutraceutical food which is required to reduce the risk of chronic illness is “antioxidants”. Antioxidants are micronutrients that have gained interest in recent years due to their ability to neutralize the actions of free radicals.[2] Free radicals are potentially harmful products generated during a number of natural processes in the body and associated with ageing of cells and tissues. Failure to remove active oxygen compounds, over a long term, can lead to cardiovascular disease, cancer, diabetes, arthritis and various neurodegenerative disorders.[3] Hence the recent research on development of healthy foods focuses on antioxidant properties. Many synthetic antioxidants like Butylated hydroxy anisole and Butylated hydroxy toluene are used in food industry. However, both consumers′ preference and toxicological investigations have diverted the interest in research towards natural antioxidants. At first the attention was given to natural compounds such as vitamin C, carotenoids, etc. In recent years the powerful antioxidant properties of phenolics aroused more interest.[4] The small millets are cheap sources nutrients for poor and the working class people and hence their health depends on the quality of food consumed.[1] By considering these points, a study was conducted on evaluating the nutraceutical properties of four selected small millets.

Materials and Methods

The nutraceutical properties of four small millets viz. finger millet (Eleusine coracana), foxtail millet (Setaria italica), prosomillet (Panicum miliaceum) and khodomillet (Paspalum scrobiculatum) were analyzed in the present study.

Extraction

Each sample (50 g of seeds) was homogenized in 100 mL of methanol using a Waring blender at high speed for 1 min at 4°C. The extract was stirred for 10 min at 4°C and filtered through four layer of cheesecloth and the residue was re-extracted under the same condition with 100 mL of methanol. The combined filtrate was concentrated under vacuum at 65°C to dryness and the dry residue was dissolved in 10 mL of methanol. These methanolic extracts were used for the determination of total phenolics, reducing capacity (RP).[5] For the estimation of water soluble proteins and reducing sugars, water extracts of the sample was used.

Phytochemical analysis

All the methanolic extracts were tested for the presence of phenols, flavonoids, alkaloids and saponins by following standard methods.[6,7]

Total phenolics

Total phenolics of each extract were quantified colorimetrically using Folin-Ciocalteu reagent and chlorogenic acid as standard.[8] Five milliliters of Folin-Ciocalteu (diluted ten-fold in distilled water), 2 mL of sodium bicarbonate (200 g.L^-1) and 2 mL of distilled water were added to 1 mL of extract. After 15 min incubation at room temperature, the absorbance was read at 730 nm using an UVmini-1240 recording spectrophotometer (Shimadzu, Kyoto, Japan).

Reducing capacity assessment

The RP of each extract was assessed as described by Oyaizu.[9] Two milliliters of extracts were added to potassium ferricyanide (2.5 mL, 10 g.L^-1) and the mixture incubated at 50°C for 20 min. Trichloroacetic acid (2.5 mL, 100 g.L^-1) was added to the mixture, which was then centrifuged at 650×g for 10 min. The supernatant (2.5 mL) was mixed with distilled water (2.5 mL) and ferric chloride (0.5 mL, 1 g.L^-1). The absorbance was read at 700 nm. Higher absorbance indicated greater RP.

Water-soluble protein content

The water-soluble protein content of each sample was determined as per Lowry's method.[10]

Reducing sugar content

The reducing sugar content present in the samples was analyzed using dinitrosalicylic acid method.[11]

Crude fiber

The crude fiber content present in each sample was analyzed using gravimetric method.[10]

Results and Discussion

The qualitative analysis for different bioactive phytochemical compounds reveals that, all the small millets tested were found to contain phenol, tannins, alkaloids, flavonoids and saponins [Table 1]. Alkaloids affect a lot of metabolic activities in the body and most of them possess dramatic physiological activities hence they are widely used in medicine. Flavonoids have been reported to possess certain biological properties such as antibacterial, antitoxic and anti-inflammatory activities and often function as strong antioxidants, free radical scavengers and metal chelators. In addition, the possible anti tumor action of certain flavonoids has also generated interest .Saponins have been reported to possess anti-carcinogenic properties, immune modulation activities and regulation of cell proliferation as well as health benefits such as inhibition of the growth of cancer cells and cholesterol lowering activity.[12] In the light of these observations the presence of phenols, tannins, alkaloids, flavonoids and saponins in the millets samples indicates that they have medicinal properties.

Table 1.

Qualitative test results for the presence of some important chemicals in selected small millet seeds

The khodomillet showed maximum phenolic content (10.3%) followed by finger millet (7.2%). The foxtail millet showed minimum phenolics (2.5%).As for as RP is concerned finger millet was having the highest (5.7%) followed by foxtail millet (4.8%). The prosomillet [Table 2] showed least reducing property (2.6 %). Davies[12] reported that the oxidative damage is very important effect of cellular-free radicals which can leads to damage of cellular constituents. Their repair depends on presence of antioxidants. The antioxidant can donate either an electron or hydrogen to cellular molecules oxidized by free radicals .They can thus prevent damage of cellular constituents, including DNA, proteins and lipids membranes from free radicals.[13] In the light of above observation an important point RP found in all the millets can help in reducing the oxidative damage caused by free radicals.

Table 2.

Total phenolics and reducing capacity found in selected small millet seeds

Among four millets tested, the finger millet showed maximum reducing sugar content (391.3 mg/g) and the khodomillet showed minimum reducing sugar (130.43 mg/g).Overall, the reducing sugar content of these small millets ranges between 130.43 and 391.30 mg/g [Table 3]. The water-soluble protein content was maximum in foxtail millet (305.76 mg/g) and minimum in prosomillet (144.23 mg/g).

Table 3.

Reducing sugar and soluble proteins in selected small millet seeds

Table 4 represents the crude fiber content of the four small millets tested. From this table it is very clear that all the selected millet grains tested found to contain crude fiber content ranging from 13.3 to 14.3%. The khodomillet showed maximum crude fiber content (14.3%). This information supports that the selected small millets are healthy sources of carbohydrates for persons with insulin sensitivity or diabetes. The high-crude fiber in the millets may enhance their digestibility and also aid the peristaltic movement of the intestinal tract.[12]

Table 4.

Crude fiber in selected small millet seeds

Conclusions

Millets occupy an important place in the world food and economy .They can adapt themselves to marginal soils and varied environmental conditions. Millets are staple diet for nearly 1/3^rd of the world's population. By considering these points an evaluation of nutraceutical property of selected small millet was conducted. All the four millets tested contain large quantities of phenolics and other compounds which prevent deterioration of human health.