The Effects of Modifications on the Functional Characteristics of Native and Chemically Modified Starches Isolated from Two Digitaria Varieties

Abstract

Starch, the most abundant carbohydrate in nature has various industrial and domestic applications and is extracted from main sources like grains and tubers. Native starch has limited applications due to low shear resistance, thermal decomposition and retrogradation that necessitate modifications. Obtaining starch from common sources leads to competitive demand which necessitated sourcing starch among underutilised crops such as Digitaria exilis (De) and Digitaria iburua (Di). Therefore, the aim of this study was to extract starches from De and Di, modify the starches and determine their physicochemical and functional properties.

The yields of starch in De and Di were 88.0% and 76.1%, respectively. Moisture, ash, fat and protein contents of De and Di native and modified starches ranged from 8.4-13.5%; 0.6-1.2%; 0.1-0.4% and 0.3-1.1%, respectively. Increase in temperature improved the swelling power and solubility by 6.0-7.0% and 2.0-3.1%, respectively, with highest swelling in oxidised De (13.0g/g) and Di (13.1g/g), and highest solubility in acetylated De (10.1g/g) and Di (10.1g/g). Native and modified starches formed gel at concentration ≥ 12.0% for all the samples. The WAC decreased in all the modified starches (0.4-0.8g/g) when compared to the native (1.0g/g), and the highest WAC was observed in oxidised De (0.8g/g) and Di (0.8g/g). Amylose content present in native and modified starches ranged from 20.7-26.1%. The native starches had the lowest pasting temperature at 77.0 ^oC, while the acetylated starches had the highest at 91.3 ^oC, indicating reorientation of starch granules chains. The final viscosity decreased with chemical modifications with a range of 1957-3458, 1334-1398 and 604-608 RVU for acetylation, oxidation and acid-thinning, against 4215-4720 RVU for native De and Di, respectively.

Chemical modifications improved the swelling power, solubility, gelation capacity and water absorption capacity of Digitaria exilis and Digitaria iburua starches, affording them potential for industrial applications.