Cell wall material (CWM) was isolated from noncooked, 5 min cooked, and 15 min cooked potato tissue and accompanying cooking media from the cultivars Irene and Nicola. A mass balance of the material in the different fractions obtained during isolation was made. Chemical compositions of the CWM and cell size distributions of the potato tissues were analyzed. The mealy cooking cv. Irene had more CWM per unit cell surface area than the nonmealy cooking cv. Nicola. These results confirmed observations of the potato cell walls made by transmission electron microscopy. The molar composition of the CWM was comparable for both cultivars. During cooking, for both cultivars relatively more unbranched than branched pectic polysaccharides were solubilized. However, the type of pectin solubilized after 15 min of cooking was different for the two cultivars. This pectin was relatively more branched, more methylated, and more acetylated for cv. Irene than for cv. Nicola. Keywords: Potato; Solanum tuberosum L.; cooking; texture; cell wall; middle lamella; transmission electron microscopy (TEM)

The texture of steam-cooked potatoes from ten cultivars was sensory evaluated after two, four and nine months storage for three consecutive years. The sensory data were analyzed using Principal Component Analysis (PCA) and regression analysis. PCA revealed that the first two principal components explained 95% or more of the variance between the data. The first principal component was dominated by the descriptors meal.v (M)/crumbly (A/M) on the positive side and the descriptors waxy (A/M) on the negative side. The descriptor firm (M) had a high positive loading on the second principle component. Regression analysis showed that cultivar effects dominated storage effects. Based on these data. a proposal is made to divide the ten cultivars in four groups which differ for the descriptors mealy (M)/erumbly (A/M), waxy (A/M) andfirm (M).During storage, potato texture became more waxy (A/M) and sticky (A/M) with respect to both appearance and mouthfeel. Other changes in texture as a result of storage were strongly cultivar dependent.

Cell wall material (CWM) isolated from non-cooked potato tissue of the cultivars Irene (mealy cooking) and Nicola (non-mealy cooking) was successively extracted with buffer, CDTA, Na 2 CO 3 at 4 and 20 °C and 0.5 M KOH. The sugar composition of fractions and the remaining residues was determined. Information about the structure of the pectic polysaccharides was obtained by studying the degradation of the fractions and residues with purified polygalacturonase (PG) and rhamnogalacturonase (RGase). The results indicated that the pectic polysaccharides extracted by buffer, CDTA, and cold Na 2 CO 3 contain more and/or longer side chains for cv. Irene than for cv. Nicola. From the CWM of cv. Nicola more branched and a higher amount of branched pectic polysaccharides were extracted with Na 2 CO 3 at 20 °C and 0.5 M KOH, respectively, while the remaining CWM of cv. Irene contained 24% more residue.

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