PHYSICOCHEMICAL CHARACTERIZATION OF STARCH ISOLATED FROM ETHIOPIAN POTATO (PLECTRANTHUS EDULIS)

Abstract

Starch from the tubers of Ethiopian potato (Plectranthus edulis) (Fam. Lamiaceae) has been isolated and examined for its chemical composition, amylose content and physicochemical properties. The starch yield was about 80.4% on dry weight basis. The proximate composition of the starch on dry weight basis was found to be 0.14% ash, 0.21% lipid, 0.43% protein, and 99.2% starch. The amylose content was 30.6%. Its true density and moisture content values were 1.47 g/mL and 11.2%, respectively. Scanning electron microscopy (SEM) of the starch granules showed characteristic morphology that was by and large oblong (elliptical) with some oval-shaped granules. The starch has normal granule size distribution with a mean particle size of 36.2 µm. The DSC thermograms of the starch obtained from starch-water mixtures (1:1), exhibited gelatinization onset temp. (To) of 69.2 ^oC, peak temp. (Tp) of 74.3 ^oC and endset temp. (Te) of 83.3 ^oC. X-ray diffraction pattern of the starch was typical B-type with a distinctive maximum peak at 17.5^o 2θ.The starch possesses higher swelling power and moisture sorption pattern but lower solubility values than those of potato starch at all temperatures studied. Considering the high yield and some similar physicochemical properties to those of potato starch, P. edulis (Ethiopian potato) can be explored as an alternative source of starch for various applications.