Physicochemical and functional characteristics of starch extracted from Marama bean tuber (Tylosema esculentum Burchell A. Schreiber)

Abstract

Marama bean (Tylosema esculentum Burchell A. Schreiber) is a highly nutritious plant and is currently regarded as a prospective crop for the future in arid zone agri-ecologies of the world. Starch is a major storage component in higher plants and it is used in both food and non-food industries. The marama bean plant is a creeper with stems that lie prostrate on the ground in several directions up to six metres long in length which spread from a tuberous root below the ground. The tuber has a reddish brown bark and it can weigh about 1 kg and up to more than 10 kg. The plant produce attractive bright yellow flowers along the stems, each with erect petals and stamens, and are followed by marama fruits or bean. Mature marama bean cotyledons are white to cream in colour, encapsulated in hard, woody seed coats, reddish to brownish black in colour. Until recently, the basic knowledge of the physicochemical and functional properties of marama tuber starch is has not been yet reported. The present study reports for the first time the physicochemical and functional properties of marama tuber starch and makes a possible provision for a new starch source. Native marama starch content was 87.38 mg starch/gram fresh weight and the total amylose content was 35%. Phosphate at the C-6 position determined as Glucose-6-Phosphate was 0.788 nmol G6P/mg. The starch granules were round to elliptical with smooth surfaces and their sizes ranged from 8 -20 μm. The pasting properties of pasting temperature, host paste, peak, final viscosity, breakdown and set back showed higher values for marama starch in contrast to commercial potato starch. This study has clearly contributed to starch biology by making known for the first time the physicochemical and functional properties of marama tuber starch. It is hoped that by further exploring the potential of marama starch as a raw material, it can be applied in various applications in both industry and food processing that will produce high valued products.