Free sugar composition of sweetpotato cultivars after storage

The concentrations of fructose, glucose, sucrose, and maltose in sweetpotato (Ipomoea batatas (L.) Lam.) roots, following an 8-month storage period, were assessed by high performance liquid chromatography (HPLC). Imported cultivars and breeding lines were compared in both the raw and cooked state against New Zealand standards. Strong linear relationships were demonstrated between concentrations of the sugars (fructose, glucose, and sucrose) in cooked roots, and the corresponding sugars in raw roots (R-2 of 93.5, 93.8, and 88.8% respectively). The relative proportion of fructose to glucose 0.44 : 0.56 was very stable across all cultivars, and independent of the total concentration of the three sugars-fructose, glucose, and sucrose. The negative relationship between sucrose and the levels of fructose + glucose was significant (P < 0.001) excluding cultivars 'Jewel' and 'Toka Toka Gold'. All of the clones produced considerable amounts of maltose during cooking, which was significantly (P < 0.001) related to % dry weight. Using canonical variates to group the clones, 'Owairaka Red', the New Zealand standard cultivar, was shown to cluster with the Japanese cultivar, 'Beniazuma', and the Taiwanese breeding line, '93N12/1', on the basis of high dry matter and low fructose + glucose levels. The minor New Zealand cultivar, 'Toka Toka Gold', clustered near the North American cultivar, 'Jewel', on the basis of low maltose, high sucrose, and medium dry weight. 'Toka Toka Gold' had a higher fructose + glucose than its sucrose concentration would predict, as well as a lower maltose level than estimated from its dry matter content.