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 and characterization by high‐performance liquid chromatography–diode array detection of 18 plant molecules demonstrated honey to be richer than nectar in secondary metabolites. For the first time, the hypothesis of the existence of a nectar redox cycle in R. pseudoacacia was reported, as previously described for Nicotiana sp., based on 1D‐protein profiles, western blot analysis and detection of H2O2 and ascorbate. The bioactivity of both matrices was also investigated. Antiradical in vitro tests showed that Acacia honey was more antioxidant than nectar, which was even able to induce oxidative stress directly in a eukaryotic cell system. Antimicrobial assays demonstrated that nectar was bacteriostatic, due to H2O2 activity, whereas honey was even bactericidal. CONCLUSION All these data support the ecological role of nectar and honey in nature: protection of the gynoecium from pathogens and preservation from degradative processes, respectively.