Fresh sweet potato roots from a selected cultivar (VIII-18) were either boiled or steamed, with or without a precooking step. Significant struc-tural and physicochemical changes occurred as a consequence. Whatever the cooking procedure, native starch granules were gelatinised and starch macromolecules were totally reorganised, forming networks inside the cells. The structure of the starch network and the pore sizes were dependent upon the method of cooking and highly variable from one cell to another. Cell walls were less damaged when roots were submitted to a precooking stage before cooking. However, cell walls were drastically damaged by steaming, even when roots were precooked, giving rise to a soggy texture. Physical and biochemical analysis showed a dual behaviour: an increase in cell wall strength could be related to an increase in insoluble cell wall polysaccharides due to cooking, whereas a part of cell wall being solubilised in cooking water.
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Valetudie et al. (1999) studied this question.