Optimization of Process Parameters for Decortication of Finger Millet Through Response Surface Methodology.

Decorticated finger millet is prepared by hardening
the endosperm by hydrothermal processing and polishing the
processed grains. The yield of the decorticated grains is of
paramount importance in the millet industry. Milling yield
depends on the grain moisture content and incipient moisture
conditioning during milling. It was found that steaming
conditions such as steaming time and steam pressure
significantly influenced the milling yield. Hence, studies were
undertaken to determine the influence of moisture and
steaming conditions on the yield of decorticated millet.
Steaming conditions were optimized through response surface
methodology. The responses studied were hardness, milling
yield, porosity and water uptake of hydrothermally processed
millet. The studies indicated that hydrothermally processed
millet with 16±1%moisture content, tempered with 5%added
water at I stage and 4% water in the II stage milling,
resulted in a yield of 64.6%. The relationship of milling
yield, hardness and porosity of the millet was quadratic
with the severity of steaming conditions, while water
uptake of the steamed millet exhibited a linear relationship.
Based on the regression analysis, optimum
conditions estimated for steaming time and pressure
were 17.5 min and 313.8 kPa, respectively. At this
condition, the milling yield, water uptake, porosity and
hardness values were also predicted and the values were
68.33 g/100 g, 63.43 g/100 g, 52.23% and 204.01 N,
respectively. The studies indicate that steaming the
millet at elevated pressure and temperature increases
the milling yield and steaming beyond the threshold
level has a detrimental effect on the yield of head
grains.