Tronchuda cabbage (Brassica oleracea L. var. costata DC) leaf free amino acid profile

Free amino acid profile of eighteen samples of tronchuda cabbage (Brassica oleracea L. var. costata DC) leaves was determined by a reversed-phase HPLC/UV-Vis methodology, after pre-column derivatization with dabsyl chloride. Samples were harvested in three collection months and internal and external leaves were separated.

Tronchuda cabbage leaf total free amino acid content varied from 50 to 221g/kg of lyophilized aqueous extract. Generally, arginine was the major compound (36%), followed by proline (17%), threonine (9%), glutamine (7%), cysteine (5%) and glutamic acid (5%).

In external leaves, proline and arginine were the major free amino acids, representing about 56% of the total content. Threonine, glutamine, glutamic acid and lysine were present in medium proportions (5–6%). However, internal leaves presented a different quantitative profile. Arginine was the main free amino acid (46.9%), followed by threonine (11.9%), glutamine (8.2%) and cysteine (6.5%). Proline was present in a very lower amount (1.7%) than in external leaves. Significant differences (p≤0.05) were observed in the valine, proline, arginine, leucine, cysteine, lysine, histidine and tyrosine contents.

Significant differences (p≤0.05) were also found in the free amino acid profiles of tronchuda cabbage leaves among samples harvested in the three different months, in terms of glutamic acid, serine, valine, leucine, cysteine and ornithine contents and aspartic acid, arginine and total contents in external and internal leaves, respectively.

In conclusion, tronchuda cabbage leaves (internal and external) have high nutritional value and constitute a great natural source of free amino acids.

Acknowledgements: Fundação Calouste Gulbenkian, Branca M. Silva. Fundação para a Ciência e a Tecnologia (PTDC/AGR-AAM/64150/2006), David M. Pereira.