Abstract
Cell structure and the contents and status of starch and water in tuberous root tissues were investigated in various sweetpotato cultivars in relation to the texture of steamed tuberous roots. In cultivars having a mealy or moderately mealy texture such as "Konahomare" and "Beniazuma", the cells after steam cooking kept their original shape even when they were filled with gelatinized starch. On the other hand, in the cultivars having a soggy or moderately soggy texture such as "Benihayato" and "Benimasari", the cells contained a smaller amount of starch and larger amount of moisture (water), and melted together with the adjacent cells after steaming. Magnetic resonance imaging (MRI) analysis revealed that the root tissue of mealy type-cultivars contained a smaller amount of free water than that in the soggy type-cultivars, showing heterogeneous distribution of the free water within the root tissue. The pasting properties of starch isolated from the cells, however, did not show any significant difference between the two types of cultivars. These results indicated that the texture of steamed tissue of tuberous root in sweetpotato is closely associated with the contents of starch and water in the root tissues. However, the pasting properties of intracellular starch that could be affected by the physical and chemical properties of cell wall were also suggested to be important for the texture.
