Analysis of Nutritional Diversity and Antioxidant Activity of Finger Millet Landraces

Finger millet [Eleusine coracana (L.) Gaertn.] is one of the most important millet grown in India and Africa. In India. Eleusine coracana. Most of the farmers, specifically from hilly regions are using conventional seeds for cultivation (landraces) other than varieties releases by Agricultural Universities. As these landraces are region specific, exhibit variation in their morphological and nutritional attributes. In most of the parts, these landraces perform better over to varieties in terms of nutritional components. Despite of this, these landraces have not been explored for its nutritional and antioxidant potential. 
       
Finger millet has gained importance because of a higher amount of calcium (344 mg/100 gm), iron 3.9 mg% (Gopalan et al., 2009), phenolic compounds and antioxidant activity (Geetha et al.,1990) and of its functional components, such as slowly digestible starch (Wadikar et al., 2007), protein (5-8%), carbohydrates (65-75%), dietary fiber (15-20%) and minerals (2.5-3.5%) (Chethan and Malleshi, 2007). As of now, it is the richest and cheapest source of calcium and iron for all people, specifically; people reside in the hilly regions.
       
The high levels of polyphenols in millets are identified to play an important role in lowering the rate of fat absorption and slow release of sugars (low glycemic index) thereby reducing the risk of heart disease, diabetes and high blood pressure (Kumar et al., 2018). It is now established that phytates, polyphenols and tannins can contribute to the antioxidant activity of the millet foods, which is an important factor in health, aging and metabolic diseases (Bravo 1998). The finger millet grain are rich in polyphenols compared to many other continental cereals (Viswanath et al., 2009).
       
On this backdrop, exploration of landraces are indispensable for the conservation of nutritionally rich landraces and as a source of nutritional traits for crop improvement programme.

Germplasm collection
 
Sixty-four finger millet landraces were collected from Nashik, Ahmednagar, Dhule and Kolhapur districts of Maharashtra, India. The accession numbers were given to the collected landraces from T1 to T64. To identify potential landraces, morphological studies has been carried out (Auti et al., 2017, Kazi and Auti, 2017). Based on the morphological characters, the 33 landraces (T1-T33) have been selected for nutritional and antioxidant studies. The Dapoli-1 variety developed by Dr. Balasaheb Sawant Kokan Krishi Vidyapeeth, Dapoli, Maharastra (India) was considered as control.
 
Biochemical analysis
 
Biochemical studies were carried out by following standard procedures. Nitrogen in the samples was estimated by the standard micro-Kjeldahl procedure and multiplied by the factor 6.25 to obtain crude protein (Sahrawat et al., 2002). The total carbohydrates were estimated by Anthron reagent (Dreywood, 1946) and reducing sugars by the dinitrosalicylic acid method (Nelson, 1944). Ghosh et al., (1963) method, estimated vitamin C. The total phenols were analyzed by the Folin-Phenol reagent method as used by Farkas and Kiraly (1962) and flavonoids by aluminium chloride reagent method (Chang et al., 2002). Tannin was estimated by Folin-Denis method (Pearson 1976). The radical scavenging activity was determined by the DPPH assay (Blois 1958).
 
Statistical analysis
 
The triplicate data of nutritional contents were statistically analysed by IBM-SPSS 9 (Software version- v20). Data, expressed as Mean±SD was statistically analysed using one-way ANOVA was used to compare means and significance was accepted at p>0.05.

Results of the analyses revealed that there were significant differences in the nutritional composition, phytochemicals and antioxidant activity among finger millet landraces (T1-T33) and as compared to control. Obtained results are represented in Table 1 and 2.
 

 

 
Nutritional composition
 
Protein
 
From the above results, it can be observed that the T1 (18.20%) contains the highest levels of protein across all the other landraces and as compared to control (7.10%).
       
The high content of protein ranging from 10.32% to 14.5% was exhibited by T10, T14, T15, T25, T32 and T33, demonstrating the finger millet as a significant source of proteins. Overall, the other landraces demonstrate significant yields of protein ranging from 3.55% to 9.90%.
 
Carbohydrates
 
In the case of carbohydrates, the control T (79.67 mg/100 gm) contains the highest levels of carbohydrates as compared to all the other landraces; however, significant levels of carbohydrates are demonstrated by T4, T5, T21 and T23 within the range of 70.33% to 78.33%. Moderate amount of carbohydrate from 40% to 67.3% was noted in other landraces.
 
Reducing sugar
 
Further, significant variations in the reducing sugar content were observed in the landraces. The landraces T2, T3, T12, T14, T16, T17, T18, T25, T28, T29, T30 and T32 (375 mg/100 gm to 666 mg/100 gm) showed high levels of reducing sugars as compared to control. In the rest of the landraces, the amount of reducing sugar was in the range of 144 mg/100 gm to 324 mg/100 gm.
 
Vitamin C
 
For the vitamin C content, all the samples exhibit relatively higher content of vitamin C except T7, T21, T23 and T33 when compared with control T (0.12 mg/100 gm). Also, the significantly highest content of vitamin C was shown by T2 (0.2 mg/100 gm) and T15 (0.18 mg/100 gm). Significant variations were not observed among landraces.
 
Phytochemical composition
 
Phytochemical contents along with the antioxidant activity of landraces are given in Table 2.
 
Total phenol content
 
In case of phenolic content, significant variations were noted among the landraces. In control 434.33 mg/100 gm phenolic content was noted while in finger millet landraces amount ranges from 355.33 mg/100 gm to 1617 mg/100 gm. T2 landrace being white showed less amount (355.33 mg/100 gm) while red to brown colour landraces possess high phenolic content.
 
Total flavonoid content
 
Flavonoid content showed a higher level in case of finger millet landraces as compared to control. The amount of flavonoids ranges from 24.33 mg/100 gm to 84.5 mg/100 gm, while least in control i.e. 6.50 mg/100 gm.
 
Tannin
 
In the case of tannins, the control shows lower levels as compared to the selected landraces, the landraces T16 and T17 show remarkably higher levels of tannins (4945.33 mg/100 gm and 7444.67 mg/100 gm) respectively. The least amount of tannin 1347 mg/100 gm was noted in the T2 (white) landrace.
 
Antioxidant activity
 
For the antioxidant potential, the majority of landraces showed significantly high antioxidant activity with T1, T2, T4, T10, T13, T14, T16, T17, T19, T20, T21, T22, T23, T24, T26, T29, T30 and T31 showing the maximum antioxidant capacity over 70%. The highest activity was noted in T1 (84.95%), T19 (81.41%) and T29 (80.53%) landraces.
       
Results obtained in the present study are supported by many researchers viz., Barbeau and Hilu (1993); Sripriya et al., (1997); Chetan and Malleshi (2007); Shobana et al., (2010); Marathe and Bhaskar (2011); Singh and Raghuvanshi, (2011) David et al., (2016); Katake et al., (2016); Udeh et al., (2018) and Kumar et al., (2018).
       
According to FAO, (2016) millets exhibit the presence of major nutrients containing carbohydrates (60-70%), crude fibre (2-7%), proteins (7-11%), fat (1.5-5%), vitamins and minerals. Sripriya et al., (1997) detailed that carbohydrate content in finger millet is approximately 81.5%, crude fiber 4.3%, protein 9.8% and mineral 2.7% that is practically comparable to different varieties of millet. Malleshi, (2003) revealed that finger millet is a decent source of dietary sugars.
       
Arora et al., (2003) revealed that the presence of anti-nutrients in millet, like phytate, polyphenols, oxalates, affected mineral bioavailability. Dharmaraj and Malleshi (2011) reported 6-8% protein, 1-1.7% fat, 65-75% starch, 18-20% dietary fiber and 2-2.5% minerals in finger millet.
       
Marathe and Bhaskar, (2011) reported insoluble protein content between 3.01% to 4.00%  and carbohydrate content from 41% to 50% in 11 finger millet landraces from Thane district, Maharashtra. Further, Shimelis et al., (2009) analyzed nine finger millet genotypes from Africa and reported protein in range from 6.26 g/100 g to 10.5 g/100 g. In the present study significantly higher amount of protein (3.55% to 18.20%), carbohydrates (40% to 78.33%) and reducing sugar (144 mg/100 gm to 666 mg/100 gm) was noted.
       
Varietal variations in phenolic contents were reported by Chetan and Malleshi (2007) and noted a higher level of phenolic compounds in brown variety as compared to the white variety. Both free and bound forms of phenolic acids are reported in finger millet (Rao and Murlikrishna 2002).
       
Siwela et al., (2007) reported red-colored varieties of finger millet showed more tannin may be due to pigmented testa. Considerable differences (0.19 3.37%) in the total polyphenol contents among 85 Indian finger millet varieties have been reported by Shankara, (1991).
       
Among millets finger millets have been reported to contain high amounts of tannins ranging from 0.04 to 3.74% of catechin equivalents (Antony and Chandra, 1999). Rao and Prabhavati (1982) have reported 360 mg/100 g tannins in brown finger millet. Finger millet is the sole millet reported to have condensed tannins.
       
Flavonoids and tannins present in millet seed coat are multifunctional and they act as reducing agents (free radical terminators), metal chelators and singlet oxygen quenchers (Rao and Murlikrishna, 2002). Finger millet is a potent source of antioxidants and this has high radical-scavenging activity higher than that of wheat, rice and other millets. The brown or red variety of finger millet had higher activity (94%) using the DPPH method than the white variety (4%), as reported by Dykes and Rooney (2006) and Sripriya et al., (1997). In contrast in the present study even white landrace (T2) showed higher antioxidant activity (73.45%) using the DPPH method. This might be due to the presence of compounds other than phenolic responsible for antioxidant activity. Identification and evaluation of these components has been a subject of research.
       
With variation in the phenolic content, the antioxidant properties are also altered, as there exists a significant correlation between the two parameters. Kumari et al., (2017) reported the highest phenolic content (15.1-55.3 μmol of ferulic acid /gm) and antioxidant activities (45% to 82%) among different millet such as finger, proso and foxtail millet.
       
Variation in the amount of biochemical is influenced by several factors like genotype, various agro-climatic factors. In our survey, we noted that cultivation practices vary from region wise and this might be one the cause for variation in nutritional components and phytochemicals.

Results of the present studies focus on nutritional diversity and variation in antioxidant activity existed among the landraces. Work provides nutritious landraces such as T1 contain higher amount of protein, T1, T19 and T29 exhibit high antioxidant activity. These landraces can be serve as a natural source of nutritional compounds. Further, these landraces serve as a good source of anti-oxidants and important phytochemicals. Grains of nutritional landraces or use of value addition technique may help to minimise micronutrient deficiencies specifically in the remote regions. Despite nutritional landraces can be serve as a source of nutritional traits in crop improvement programme.

The authors thanks to Principal, H.P.T. Arts and R.Y.K. Science College, for providing all the required facilities.  One of the authors (T.K.) thanks University Grants Commission, New Delhi, India for Financial assistance under Maulana Azad National Fellowship (MANF-2015-2017-MAH-54464).