Influence of cooking procedures on structure and biochemical changes in sweet potato

Fresh sweet potato roots from a selected cultivar (VIII-18) were either boiled or steamed, with or without a precooking step. Significant structural and physicochemical changes occurred as a consequence. Whatever the cooking procedure, native starch granules were gelatinized and starch macromolecules were totally reorganized, 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 solubilized in cooking water.