PROTEIN-QUALITY AND ENERGY DENSITY OF LEEK (ALLIUM-PORRUM L) AS INFLUENCED BY WATER AND NITROGEN SUPPLY AND PLANT-AGE AT HARVEST

Leeks were cultivated under conditions differing in level of nitrogen (N) supply (100 kg N ha(-1), 160 kg N ha(-1), 220 kg N ha(-1), 280 kg N ha(-1)), lever of water supply (normal, low) and time of harvest (Se ptember, October, November). Based on chemical analysis and balance st udies on rats the nutritive value of the 26 batches of leek was determ ined. The protein content of the leeks increased progressively from 90 g kg(-1) DM to 163 g kg(-1) DM with N-supply. This increase in protei n was associated with a reduction of all essential amino acids (g per 16 g N) and, subsequently, a reduction of the biological value. Protei n and energy digestibilities increased with level of N-supply. Leeks h arvested in September had a higher protein content, but had at the sam e time the lowest biological value as compared to leeks harvested in O ctober or November. This was due to a lower content of essential amino acids (g per 16 g N) in leeks harvested in September as compared to l eeks of later harvest. Only small differences between the two levels o f water supply were observed in the chemical composition of the leeks. The content of non-starch polysaccharides (NSP) was rather high in al l samples of leek (approximately 240-280 g kg(-1) DM) and appeared to be unaffected by the growth conditions applied in the investigation. S oluble-NSP constituted approximately half of the total NSP.