INFLUENCE OF GROWTH-CONDITIONS ON THE VALUE OF CRISPHEAD LETTUCE .3. PROTEIN-QUALITY AND ENERGY DENSITY AS DETERMINED IN BALANCE EXPERIMENTS WITH RATS

Crisphead lettuce was cultivated under different growth conditions. Si xteen batches differed in time of planting (early and late), total nit rogen supply (200 kg N/ha, 150 kg N/ha, 100 kg N/ha, 50 kg N/ha) and t ime of harvest (early and late). Based on chemical analysis and balanc e studies on rats the nutritive value of each 16 batches was determine d. The protein content increased progressively from 16.00 to 19.88% wi th fertilization level. This increase in protein caused a significant drop in essential amino acids (g/16 g N) demonstrating a lower biologi cal value of this protein. Early planting or early harvest resulted in a higher protein content than in lettuce of late planting or late har vest. Total dietary fibre content was approximately 25% of DM - and th is value was not much influenced by the different growth conditions. S oluble dietary fibre was approximately 20-25% of total dietary fibre. Due to the high fibre content, energy digestibility was relatively low . The contents of Cd and Pb were below what is considered as 'acceptab le' levels.