Influence of growth conditions on the value of crisphead lettuce. 4. Quality changes during storage.

Crisphead lettuce (Lactuca sativa L. var capitata cvs. Marius and Saladin) were grown with a nitrogen supply from 50 to 200 kg N/hectare. Heads were stored for one or two weeks at 1 degree C in cold storage or ice bank cooling. Samples were taken for measurement of dry matter, sugars, vitamin C and nitrate. The content of dry matter, sugars (glucose, fructose) and vitamin C decreased with increasing level of nitrogen, and the content of nitrate increased. Except for nitrate the contents of the other quality attributes decreased at all nitrogen supply levels during storage. No differences were found between the storage systems, and beside fructose no significant differences were found between the two cultivars. The content of dry matter, vitamin C, and nitrate decreased from the outer to the inner head fraction, while the content of sugars increased. Trimming decreased the content of dry matter, vitamin C and nitrate and increased the content of sugars. To obtain heads from storage with a relatively high content of dry matter, sugars and vitamin C, and a relatively low content of nitrate the nitrogen supply must be as low as possible. Except for nitrate where no distinct results were found in this experiment it must also be recommended to store the heads as short time as possible. Possibly the cv. Saladin has some advantage quality attributes after storage compared with the cv. Marius.