Thermal properties of new varieties of yam starches

Abstract

Starches isolated from yam varieties of Dioscorea alata and Dioscorea cayenensis‐rotundata species were prepared at different time–temperature conditions and characterised by DSC, amperometric iodine titration, light microscopy and rheology and compared to native and chemical modified tapioca starches. The observation by light microscopy showed different morphologies of the granules when heated above 100°C and the tendency for disintegration decreased in the order native tapioca starch > yam starch > modified tapioca starch. Differences between yam and tapioca starches were also revealed by DSC. Yam starch enthalpy is higher than tapioca starch, but the peak temperature is low. However, the significant differences between yam and the other tested starches were found in terms of their rheological behaviour. The viscosity of yam starch was very stable at high temperatures on the viscograph. With this property, yam starch can be used as thickening and gelling agent in food.

Isolation, Composition, Structure, Properties, Modifications, and Uses of Yam Starch

“…Flow curves of yam starches in comparison with potato and tapioca (cassava) starches are presented in Figure , showing the higher viscosity of yam starches at the beginning of shearing. This was attributed to better preservation of granular structure upon heating and the subsequent destruction of the granule remnant by stronger shearing during the rheological analysis, as evidenced by microscopic analysis (Brunnschweiler and others ; N'da Kouamé and others ). There was a lack of correlation analysis between rheological properties and structural factors such as granular and molecular structure of starch.…”

“…Comparative analysis in the same study placed yam starch uniquely among starches from other botanical origins (Moorthy and others ). Differences in rheological properties were noted among starches from yams and other tubers and roots including cassava, elephant yam, tannia, Queensland arrowroot, taro, yam bean, and arrowroot (Freitas and others ; Brunnschweiler and others ; Moorthy and others ; N'da Kouamé and others ). Dynamic oscillatory analysis, including temperature (15 to 85 °C) and frequency (0.01 to 10 Hz) sweeps, showed that yam starch ( D. alata ) had a higher gelatinization temperature, higher G ′ and G ′′, and stronger gel compared to cassava starch (Freitas and others ).…”

“…Some rheological tests other than pasting, such as flow and dynamic oscillatory analysis, have been conducted on yam starches to gain alternative information on starch gelatinization and retrogradation (Freitas and others ; Brunnschweiler and others ; Moorthy and others ; Yeh and others ; N'da Kouamé and others ). The instrumentation and experimental conditions varied greatly among various studies, making direct comparison of data hardly possible.…”

“…This could be at least partially attributed to the higher amylose content of the former. Flow analysis (subjecting starch gel to a range of shear stress while recording the viscosity change), coupled with pasting data, showed that, compared to cassava and potato starch gels, gels from D. alata and D. cayenensis‐rotundata had both rather high viscosity at low stress and strong shear‐thinning behavior (Brunnschweiler and others ; N'da Kouamé and others ). Flow curves of yam starches in comparison with potato and tapioca (cassava) starches are presented in Figure , showing the higher viscosity of yam starches at the beginning of shearing.…”

“…Compared to potato starch, firming of starch gel ( D. alata and D. cayenensis‐rotundata ), as measured by uniaxial compression (Figure ), was rather prominent during the first days after gelatinization, suggesting the role of amylose in the initial gelling of starch (Brunnschweiler and others ). Combining rheological and gelling analysis suggested that starches of D. alata and D. cayenensis‐rotundata can be suitable as thickening and gelling agents for food (Brunnschweiler and others ; N'da Kouamé and others ). The retrogradation kinetics of heated flour dough of D. rotundata was followed by textural analysis (compression) (Brennan and Sodah‐Ayernor ).…”