Characterization Of Starch Accumulation In Storage Root Of Marama (Tylosema Esculentum)

ABSTRACT

Starch is of substantial industrial significance for food and non-food uses. Plant roots and tubers such as potato and cassava are rich in starch and they are among the sources of starch for food consumption and industrial use. With climatic changes it is important to find crops that can be used as food and will still be able to survive the arid conditions. Marama is a plant that grows in the arid Namibian conditions, that bears a storage root that it is underutilized and has a potential to serve as an alternative source of starch. The main aim of this study was to determine the most suitable time for harvesting by evaluating the quality of marama root and its starch at the different harvest times. Effects of harvesting time on the proximate analysis of the marama roots as well as the thermal properties, size and physicochemical properties of the starch were investigated. Total starch of the marama roots (dry basis) increased with harvesting time, it ranged from 25.9 to 60.1% while the amylose content on starch basis decreased with harvesting time, ranging from 21.4-50.7%. Starch content was determined by enzymatic hydrolysation of starch to glucose and quantified colorimetrically by the Glucose oxidase-peroxidase reaction. Whereas amylose content was determined by the precipitation of amylopectin with lecin Concanavalin-A protein, amylose was then enzymatically hydrolysed to glucose and quantified using Glucose oxidase-peroxidase. Marama root starch granules were spherical, oval and lenticular in shape, the size of the granules increased with harvesting time and the mean granule (diameter) size ranged from 8.6 – 15.1µm. The youngest (2 month old) marama root had the highest crude protein content (33.6%). Crude protein content decreased from 33.6% down to 2.7% at the 12 months harvest time.