From Robinia pseudoacacia L. nectar to Acacia monofloral honey. Biochemical changes and variation of biological properties

BACKGROUND: Robinia pseudoacacia L. nectar and its derivative monofloral honey were systematically compared in this study,to understand how much the starting solution reflected the final product, after re-elaboration by Apis mellifera ligustica Spinola. RESULTS: Subjected to dehydration in the hive, nectar changed in its water and sugar content when transformed into honey,as physicochemical and gas chromatographic–mass spectrometric analyses revealed. Spectrophotometric measurements andcharacterization by high-performance liquid chromatography–diode array detection of 18 plant molecules demonstratedhoney to be richer than nectar in secondary metabolites. For the first time, the hypothesis of the existence of a nectar redox cyclein R. pseudoacacia was reported, as previously described for Nicotiana sp., based on 1D-protein profiles, western blot analysisand detection of H2O2and ascorbate. The bioactivity of both matrices was also investigated. Antiradical in vitro tests showedthat Acacia honey was more antioxidant than nec tar, which was even able to induce oxidative stress directly in a eukaryoticcell system. Antimicrobial assays demonstrated that nectar was bacteriostatic, due to H2O2activity, whereas honey was evenbactericidal. CONCLUSION: All these data support the ecological role of nectar and honey in nature: protection of the gynoecium frompathogens and preservation from degradative processes, respectively.