Isolation, physicochemical characterization and application of yam (Dioscorea spp.) starch as thickening and gelling agent

Yam starch of the species Dioscorea alata and D. cayenensis-rotundata was isolated, characterized by differential scanning calorimetry (DSC), X-ray diffraction iodine titration, hot-stage microscopy and rheology, and compared to potato (Solarium tuberosum) and tapioca (Manihot esculenta) starch. The amylose content of yam starch was around 24% and tended to decrease during postharvest storage. Wide-angle X-ray diffraction showed a mixed A- and B-type crystalline packing. Differences between yam starches from different species and varieties were revealed by DSC. However, the largest differences between the different yam starches were found in terms of their rheological behavior. Yam starch shows an intermediate viscosity increase upon initial heating, but a stable viscosity during further thermal treatment in the Viscograph. Hot-stage microscopy showed a good preservation of the granular yam structure during heating, which is thought to be responsible for a rather high viscosity at low stress paired with a strong shear-thinning effect. The mechanical properties of yam starch gels suggest that the preservation of the granular integrity upon swelling limits amylose leaching, but that the aging behavior is primarily determined by the short-term changes of the amylose fraction. Yam starch has potential as thickening and gelling agent in food.