A field experiment was carried out to investigate the effect of fertilization level on the phenolic composition of tronchuda cabbage (Brassica oleracea L. var. costata DC) external and internal leaves.
Eight different plots were constituted: a control without fertilization, one with organic matter, and six
experiments with conventional fertilizers (nitrogen, boron, and sulfur, two levels each). The phenolic
compounds were analyzed by reversed-phase HPLC-DAD. External and internal leaves revealed
distinct qualitative composition. In the internal leaves were found 15 phenolics (5 kaempferol and 10
cinnamic acid derivatives), whereas the external leaves presented 3-p-coumaroylquinic acid and 13
kaempferol derivatives. Principal component analysis (PCA) was applied to assess the relationships
between phenolic compounds, agronomical practices, and harvesting time. Samples obtained with
conventional practices were quite effectively separated from organic samples, for both types of leaves.
In general, samples developed without any fertilization presented the highest phenolics amounts:
external and internal leaves contained 1.4- and 4.6-fold more phenolic compounds than the ones
that received conventional fertilizer, respectively, and the internal leaves presented 2.4 times more
phenolics than the ones grown with organic amendment. Additionally, samples from organic production
exhibited higher total phenolics content than those from conventional practices, collected at the same
time. Samples harvested first were revealed to be distinct from the ones collected later. The results
show that it is possible to grow tronchuda cabbage without excess fertilizers, with highest amounts
of phenolics and reduced environment contamination.
