Functional and pasting properties of starches isolated from unripe and ripe cultivars (two) of aerial yam bulbils

The impact of the harvesting period (sixth, seventh and eighth month) on functional and pasting properties of starches from Tob2857 and Tob3059 cultivars of aerial yam was investigated. Matured yam bulbils were classified into two; matured ripe bulbils (MRB) and matured unripe bulbils (MUB) based on their peel colors at harvest. Starch content, amylose, resistant starch (RS), pasting and morphological characteristics of starches were evaluated using standard methods. RS (5.11-12.37%), amylose (14.88-20.15%) and solubility (1.16-3.98%) were higher in MUB than MRB starches and varied with the harvesting period. Pasting profiles revealed that peak, hot, break down, cold paste and set back viscosities, respectively ranged thus; (261.50-528.92 RVU), (269.00-458.38 RVU), (16.95-70.54 RVU), (304.14-576.79 RVU) and (71.42-118.41 RVU). Pasting time and temperature ranged from 4.68-5.92 min and 84.18-88.26 °C, respectively. The swelling power (0.53-9.85%) varied significantly between the cultivars and ripeness of the bulbils. The starch granules showed similar shapes (ovo-triangular-oblong) and granule size (16.80-32.34 µm) varied significantly with the harvesting period. The starch of good functionality was obtained from the MRB of both cultivars in the 8th month. The variation in functionality of aerial yam starch cultivars at different harvesting periods in this study could be exploited for the postharvest valorization of aerial yam starches.