Effect of soaking conditions on chemical composition, antioxidant activity, total phenols, flavonoids and anti-nutritional contents of finger millet

Abstract

Finger millet (Eleusine coracana) is a staple cereal grain in certain parts of the world with low income populations. It is a minor cereal grain grown extensively in some areas of Africa and consumed for its several health benefits. Finger millet is nutritionally dense as well as a gluten-free food crop that is stable on storage, but less utilized in tropical and semi-arid regions of the world due to the presence of anti-nutrients. This study investigated the effect of soaking as a pretreatment method on the chemical composition, anti-nutrients, phenolic content, flavonoids and antioxidant properties of finger millet. Finger millet seeds were soaked in water at different temperatures (30, 40 and 50 °C) and time intervals (0, 6, 12, 18 and 24 h). Samples were taken at 6 h intervals, washed, dried in the oven at 50 °C to a constant weight, milled into flour and sieved to obtain fine flour (100 µm). The flour samples were analyzed for proximate composition, anti-nutrients, phenolic content, flavonoids and antioxidant activity. All data obtained were subjected to analysis of variance. The moisture, protein, fat, ash, crude fibre, and carbohydrate ranged between 7.08-9.41, 4.16-9.47, 2.91-5.32, 0.82-2.48, 1.32-2.95, and 73.57-78.47%, respectively. Residual anti-nutrients in the flour ranged from 1.20-2.23, 0.38-0.75 mg/100g, 2.30-6.73%, and 0.39-1.48 mg/100 g for tannin, phytate, trypsin and oxalate, respectively. Phosphorus, sodium, calcium, potassium, and iron ranged from 24.3-98.8, 0.123-0.90, 142.24 -192.16, 105-396, and 2.20-6.59 mg/100 g, respectively. Total phenolics ranged from 16.00 to 40.29 mg/100g. The flavonoid and antioxidant activity of the soaked finger millet flour increased with increased soaking time and temperature. This study has established that soaking can be used as a pretreatment method in reducing the anti-nutrient content, improving nutrients, enhancing the mineral content of the grains, and hence, maximize the potentials of finger millet for the production of value-added products. Key words: Finger millet, proximate, polyphenols, minerals, anti-nutrients, pretreatment, antioxidant activity, flavonoids