Extraction and Characterisation of Starch Obtained from Livingstone Potato (Plectranthus esculentus)

Abstract

Plectranthus belongs to the family Lamiaceae. It is a perennial crop which is sparsely branched and grows up to 2m in height. In the year 2000, the world starch market was estimated to be 48.5 million tons, including native and modified starches. Starch from the tubers of Livingstone potato (Plectranthus esculentus) (Fam. Lamiaceae) has been isolated and examined for its chemical composition, amylose content and physicochemical properties. The study aims to extract and characterise starch obtained from the living stone potato. Potato tubers were obtained from Gembu Mambilla Plateau, Taraba, Nigeria. Four grams (4 g) of the starch sample was heated in an oven at 105 0C. Two grams (2 g) of the powder sample were weighed into a round-bottom flask, then one tablet of catalyst (copper) and 25 mL concentrated sulfuric acid (H2SO4) were added in the fume cupboard and heated till the solution assumed a green colour. The starch yield was about 86.4% on a dry weight basis. The proximate composition of the starch on a dry weight basis was found to be 0.12% ash, 2.50% lipid, 3.25% protein, and 86.13% 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 a normal granule size distribution with a mean particle size of 36.2 μm. The DSC (Differential Scanning Calorimetry) thermograms of the starch obtained from starch-water mixtures (1:1), exhibited gelatinisation 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 2θ. At every temperature examined, the starch had a lower solubility value than potato starch but a higher swelling power and moisture sorption pattern. P. esculentus (Livingstone potato) can be investigated as a substitute source of starch for a variety of uses due to its high yield and some physicochemical characteristics that are comparable to those of potato starch. At every temperature examined, the starch had a lower solubility value than potato starch but a higher swelling power and moisture sorption pattern.