Effect of steeping additives on tef starch extraction and its quality

Abstract

Tef is an indigenous African cereal and considered as lost crop of Africa. There is no research on the effect of steeping additives on the quality of isolated tef starch. A white tef grain was milled and steeped in distilled water, sodium hydroxide, lactic acid, metabisulfite, and a combination of lactic acid and metabisulfite. A combination of metabisulfite and lactic acid improves the starch yield, but steeping with sodium hydroxide produces the highest starch purity (lowest protein content). Both the Rapid Visco Analyzer and a Rheometer showed similar pasting properties of starches independent of the treatment. The different steeping additives showed differences in pasting properties. Sodium hydroxide showed the highest peak, breakdown and set back viscosity compared to the other steeping additives. Extracted tef starches using sodium hydroxide as steeping additives also showed higher gelatinization temperatures. According to principle component analysis (PCA), the different properties of tef starch extracted with sodium hydroxide steeping is apparently due to its lower protein content. SEM and CLSM indicated that sodium hydroxide is a very effective solvent to solubilize the protein matrix surrounding the compound starch granule to produce more single starch granule during extraction. The low protein content probably result in faster water absorption and higher peak viscosity and lower pasting temperature. Different steeping additives can affect the functionality of tef starches and this need to be considered when comparing properties of starches extracted with different additives.