TECHNO-FUNCTIONAL CHARACTERIZATION OF TUBERS, FLOURS AND STARCHES FROM THREE CULTIVARS OF LIVINGSTONE POTATOES (Plectranthus esculentus N.E. Br)

Abstract

Livingstone potato is a neglected and underutilized root crop that is indigenous to Africa, and there is a need to identify its potential for use in both food and non-food applications. The physical properties of tubers, proximate composition of flours, and physicochemical (starch yield, amylose content, water-binding ability, bulk density, starch size) and pasting properties of starches from three cultivars (Riyon, Laongat, and Bebort) of Livingstone potatoes were examined using standard laboratory procedures. All the cultivars had the same shape but showed different physical characteristics, in terms of colour, length and circumference. Laongat had the highest dry matter (1.70%,) and protein content (6.66%), while highest crude fat (0.03%) and carbohydrate content (78.29%) was recorded for Bebort cultivar. Significant (p<0.05) variation in starch yield and amylose content was recorded, with values of 8.49% - 11.40% and 26.09% - 31.21%, respectively. Laongat cultivar gave the highest values for both parameters. Values ranging from 1.74-1.95%, 10.47-12.95%, 0.72-0.87 g/mL were observed for swelling index, water absorption capacity, bulk density of the starches, respectively, while all the starches fall in the category of large granule size (130 - 200 nm). Laongat cultivar gave the highest peak viscosity (580.80 RVU) but lowest pasting temperature (74.03 °C) while Bebort cultivar had the highest values for trough (265.60 RVU), breakdown (99.96 RVU), and final (392.50 RVU) viscosities and the lowest peak time (4.80 min.). The pasting temperature ranged between 74.03 and 81.15 °C. Laongat cultivar had higher dry matter content, protein content, amylose content and starch yield than others. However, Bebort cultivar could find application in foods that require reduced cooking loss, slow retrogradation, higher digestibility, tolerance for high temperature heating and ability to cook faster due to its higher trough values, lower setback viscosity, higher breakdown viscosity and lowest peak time than other cultivars.