Abstract
The general and rheological properties of yam starch (Ichoimo, Tsukuneimo and Nagaimo) and Mukago starch were investigated.
The amylose content of each starch was approximately 20%, with the values for Nagaimo and Mukago being slightly higner. The X-ray diffractogram of the Ichoimo and Tsukuneimo-starches indicated the C type, which is very similar to the B type, while Nagaimo and Mukago were of the C type. The granular size of the starches was from 15.5 to 19.5 μm.
The starting temperature for gelatinization by photopastegraphy was 63.0°C for Ichoimo, 63.2°C for Tsukune imo, 64.0°C for Nagaimo and 63.5°C for Mukago. The dissolution percentage of starch granules by pancreatin was generally low, being 13.5% in Ichoimo, 12.5% in Tsukuneimo, 10.0% in Nagaimo and 7.5% in Mukago.
The dynamic viscoelasticity of each starch during the gelatinization process was measured for a 10% starch suspension, both the storage modulus (G′) and loss modulus (G″) increasing in proportion to the increase in temperature. The increase of temperature for both G′ and G″was 10°C higher than the starting temperature of gelatinization by photopastegraphy. The gelatinization process started rapidly in Ichoimo and slowly in Mukago. The tan δ (tan δ=G″/G′) value in each starch deer eased with increasing temperature, being lowest (0.11) for Ichoimo and highest for Mukago.
The static viscoelasticity was measured for a 10% starch gel and showed a creep curve, most of which indicated progressive change that could reduced to a dynamic model of 4 elements. The elasticity and viscosity percentages in each starch gel tended to decrease in proportion to an increase of temperature, the elasticity percentage of the Mukago starch gel being approximately twice that of the Yam (Ichoimo, Tsukuneimo and Nagaimo) starch gel. The percentage recovery against the whole strain after eliminating the loading weight was 50% in the Yam starch gel and 88% in the Mukago starch gel at a temperature of 10°C.
