ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 90 Number 2
Physico - chemical properties of five cultivars of sweet potato (Ipomea batatas Lam (L)) root tubers grown in Sri Lanka. (87)
The flours and starches obtained from mature tubers of five different cultivars of sweet potato (Ipomea batatas .Lam) cultivars commonly grown in Sri Lanka (SWP1 – Wariyapola red, SWP3 – Wariyapola white, SWP4 – Pallepola variety, SWP5 - Malaysian variety and SWP7 – CARI 273) showed significant differences in the chemical composition and slight variation in functionality. Starch levels in studied cultivars on dry weight basis were significantly different at P<0.05 and SWP7 contained the highest (64.1±0.1%) while SWP1 contained the lowest (33.7±1.7%). The protein levels ranged from 1.2 ± 0.1 to 3.0 ± 0.1% and the total fat levels in tubers varied ranging from 1.1 ± 0.1 to 1.7 ± 0.1%. The crude fibre contents in tubers were found to range from 2.1 ± 0.2 to 13.6 ± 0.3% and SWP7 contained a significantly higher level of fibre (P<0.05) than the other cultivars. The ash levels ranged from 1.9 ±0.2 to 2.8 ±0.1. The sweet potato contained higher levels of calcium and iron and high level of magnesium was observed in SWP5. Lowest swelling was observed in the SWP7 cultivar and there was no significant difference in swelling of the starches obtained from the other cultivars. Scanning electron microscopic studies showed different shapes such as oval, pentagonal and hexagonal in the native starches of studied cultivars. Based on the thermal properties, SWP7 starch showed a high energy requirement and thus gelatinized at a higher temperature. High peak viscosity, high breakdown and high final viscosity were observed in the SWP4 cultivar and lower values for those parameters were observed in SWP7. The high level of enthalpy and the low level of peak viscosity in SWP7 were associated with its low level of swelling. The DSC curves of the melting properties of retrograded amylopectin were similar in all tested cultivars because melting temperature reflects the quality and the perfection of the crystallites. Results revealed a high nutritional significance and possible application of sweet potato flour and starch as jelling and/ or thickening agents in food industry.
Keywords: Chemical composition, Ipomea batatas, swelling power, mineral elements, thermal properties