Nutritional composition of UK retail potatoes, both raw and cooked

Over two seasons, four maincrop potato cultivars together with early varieties, were purchased from a range of retail outlets in three principal consumer areas (London, Birmingham and Glasgow). Samples were analysed for moisture, total nitrogen, non‐protein nitrogen, fat, carbohydrates (sugars, starch and dietary fibre), vitamins and minerals. Analyses were carried out on both the raw and cooked (boiled, baked, roast and chipped) tubers every 12 weeks. Values for raw and cooked materials were compared with previously published figures, and cultivar, centre and seasonal effects were identified by analysis of variance. Nutrients found to be lower than the Food Composition Table data were riboflavin and niacin (50%), potassium (40%), iron, copper and zinc (20–30%); thiamin and total folate were 2–3 times higher, total ascorbate, initially similar, declined more rapidly after harvest. These differences were reflected in the values obtained for the cooked potato where the major difference was a reduction in the fat content of chips by about 40%. Cooking losses were similar to those in the Food Composition Tables. The main varietal effects were confined to the vitamins. Centre effects showed that potatoes from Glasgow had less ascorbate and dry matter but slightly more free sugars. The only significant seasonal effect was for total ascorbate where the second season was higher than the first.