Profile of bioactive secondary metabolites and antioxidant capacity of leaf exudates from eighteen Aloe species

Over the past years, interest in the phytochemical profile of Aloe species (family: Xanthorrhoeaceae) has been on the rise, compelled by its popularity as an ingredient in cosmetic formulations, food supplements and drug design. It is surprising that only few Aloe spp. have been grown and commercialized; this might be due to the very limited knowledge of their potent bioactive compounds. The phytochemical profile of eighteen Aloe species was investigated using colorimetric assays, triple quadrupole and time-of-flight mass spectrometry, focusing on bioactive secondary metabolites in leaf exudates. The phytochemical profile of leaf exudates from different species was widely diverse and included free and glycosylated chromones (mainly aloeresins, with a content of aloeresin A up to 843.4 g 100 g(-1)) followed by the anthraquinones aloin (0.66-4.96 g 100 g(-1)) and hydroxyaloins. Among the examined species A. marlothii, and A. melanacantha were found to be richest in total polyphenols (14.3 and 6.4 g gallic acid equivalents 100 g(-1)), flavonoids (up to 7.1 g rutin equivalents 100 g(-1)), flavonols (up to 5.0 g rutin equivalents 100 g(-1)), and presented the highest antioxidant activity (up to 810.3 mu mol g(-1) trolox for DPPH, and 453.4 mu mol g(-1) trolox for ORAC), aloin, and aloeresin A contents. A second cluster, including A. arborescens and A. nyeriensis, was characterized by high contents of total phenolics and aloenin. These findings highlight for the first time the complex profile of phytochemicals in aloe leaf exudates and open new horizons to the industrial use of these Aloe species, which could represent a smart approach to increase the growers' income.