Phenolics and organic acids with potential bioactivity in Pieris brassicae L. reared on Brassica rapa var. rapa L

Pieris brassicae, an insect whose larvae constitute a frequent pest of some Brassica species, was studied in order to use it as source of health interesting compounds. The phenolic profiles of P. brassicae at different development stages, its excrements and its host plant Brassica rapa var. rapa L. were determined by HPLC-DAD-MS/MS-ESI. Twenty five acylated and non-acylated flavonoid glycosides and ferulic and sinapic acids were identified in host plant, from which only twelve compounds were found in the excrements. The excrements showed the presence of sulphate flavonoids and other flavonoid glycosides not detected in the leaves of the host plant. In the larvae kept without food for twelve hours, only three compounds common to the plant material and two others also present in the excrements were characterized. The organic acids profile of the distinct matrices was determined by HPLC/UV and revealed to be composed by citric, malic, shikimic and fumaric acids. The antioxidant potential of P. brassicae material and of B. rapa var. rapa leaves were evaluated and a concentration dependent scavenging activity was observed against DPPH and against both reactive oxygen (superoxide radical) and nitrogen species (nitric oxide), for all matrices. Aqueous extracts of the different stages of P. brassicae and B. rapa var. rapa leaves were further tested for antimicrobial potential and no activity was found against representative bacterial (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) and fungal (Candida albicans, Aspergillus fumigatus and Microsporum gypseum) species.

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