CONTENT OF MINERALS, VITAMINS, AND SUGARS IN ICEBERG LETTUCE (LACTUCA-SATIVA VAR CAPITATA L) GROWN IN THE GREENHOUSE DEPENDENT ON CULTIVAR AND DEVELOPMENT STAGE

The content of nitrate, vitamin C, beta-carotene, lutein, reducing sug ars, and minerals was determined in five iceberg lettuce cultivars, gr own in the greenhouse from 23. August to 23. October 1995. Amounts wer e measured at three development stages: ''A'' - heads begin to form, ' 'B'' - head development nearly complete, ''C'' - head development comp lete. With the exception of nitrate and reducing sugars in the cultiva r 'Beatrice', the content of measured components did not differ among cultivars. In development stage ''C''; mean head weight was 840 +/- 89 g, with heads containing an average of 925 +/- 166 mg nitrate/kg fres h matter, 1.9 +/- 0.5 mg vitamin C, 0.34 +/- 0.07 mg beta-carotene, 0. 41 +/- 0.07 mg lutein, and 1.23 +/- 0.17 g reducing sugars/100 g fresh matter. The content of measured components decreased as development p rogressed from stage ''A'' to stage ''C'', with the exception of reduc ing sugars, which in creased. This is due to their differing outer, me dium, and inner leaf shares and to the changing ratio of these leaves during heading. Mineral contents also decreased in the inner head, wit h the exception of P, Zn and Cu.