Characterization of changes in potato tissue during cooking in relation to texture development

Texture of cooked potatoes is an important quality aspect. The diversity in texture types was sensory evaluated. Most of the differences between texture types could be explained by differences between mealy and non-mealy characteristics. Furthermore, cultivars with similar mealy/non-mealy characteristics could be discriminated on basis of firmness of cooked potato tissue.Cryo-scanning electron microscopy showed differences in intercellular contact and appearance of cell walls between fracture planes of cooked tissue from mealy and non- mealy cooking potato cultivars. Therefore, further research was focused on structure and composition of cell walls from the mealy cooking cv. Irene and the nonmealy cooking cv. Nicola.The degradation of middle lamellae during cooking was determined by recording the release of pectic material in cooking media. It was found that a given percentage release of pectic material results in more cell sloughing for cv. Irene than for cv. Nicola.Firstly, the effect of differences in ionic conditions in cell walls and middle lamellae on the degradation of pectic material was studied by recording the transfer of calcium, potassium and citrate during cooking of potato tissue. The transfer rates of potassium and citrate for cv. Irene are lower than expected in comparison with cv. Nicola. Calcium showed a deviant behaviour, since 80% of the calium initially present remains in tissue during cooking.Furthermore, composition and structure of the pectic polysaccharides in the cell walls and middle lamellae of both cultivars were studied. Although, isolated cell wall material has a comparable molar composition for both cultivars, different types of pectic polysaccharides are solubilized during cooking.The structure of pectic polysaccharides; was further elucidated using chemical fractionation and enzymic degradation. It is proposed that the pectin matrix in the primary cell wall of cv. Irene had a thicker and/or less porous structure than the matrix in the cell wall of cv. Nicola. Additionally, the primary cell wall of cv. Irene has a more dense and/or thicker cellulose-xyloglucan network than the primary cell wall of cv. Nicola.