Synthesis, physicochemical characterization, and functional properties of an esterified starch from an underutilized source in Nigeria

Acha (Digitaria exilis Stapf), also known as Findi, Hungry rice, Petit mil and White fonio, is a small seeded cereal, indigenous to West Africa, which is generally classified as millet. It grows in various parts of Nigeria, Sierra Leone, Ghana, Guinea Bissau and Benin Republic. That species is the most important of a diverse group of wild and domesticated Digitaria species that are harvested in the savannas of West Africa. It is one of the primary cereals of southern Sudan and Ethiopia in Africa. It has potential to improve human nutrition, boost food security, foster rural development and support sustainable use of lands. In this study, acha starch wassubjected to modification by acetylation. The acetylated acha starch with degree of modification 0.78 had reduced foaming capacity and amylose contents. The starches have similar organoleptic properties ranging from white, gritty, non sticky to bland tastes. Physicochemical indices investigated such as true density, bulk and tapped densities, water absorption capacity, moisture content, total and acid insoluble ash,and pH were reduced by the acetylation of acha starch. The modification resulted in a significant (P < 0.05) increase in the solubility as well as water and oil absorption capacities of the starch. Scanning electron microscopy revealed starch granules that were predominantly polygonal in shape. Acetylation did not alter the granule morphology. X-ray pattern of the native starch was A type, with similar pattern in the acetylated derivative. Fourier transform infrared spectroscopy (FTIR) results revealeda new band at 1728 cm-1. Thermogravimetry revealed 3 phase  decomposition of both the native and modified starches. The acetylation as revealed by Differential scanning calorimetry studies improved the gelation capacity of the native starch and revealed two endothermic peaks and one exothermic peak each for both starches. There was considerable reduction in the peak temperature of gelatinization (Tp) of native starchand a significant (P < 0.05) decrease in the enthalpy of gelatinization (DH) was noticed after acetylation.