Seasonal variation in the antioxidant phytocompounds production from the Morus nigra leaves

Morus nigra L. has demonstrated a wide range of biological properties potentially related to its antioxidant capacity. However, there are a few investigations on climate seasonal variation impacting on the phytocompounds yield. The monitoring of seasonal influences is a promising research area to optimize the specific production of metabolites. This study evaluated the seasonal phytochemical profile and antioxidant activity of the M. nigra leaves (MN), thereby correlating with climatic data during the period of two years. Furthermore, the cytotoxicity and the antioxidant effect of MN extract and its major compound, syringic acid (SA), against H2O2 were determined. The MN recorded diverse seasonal tendencies in their phytocompounds production, since the higher concentration of total phenolics was observed in the Summer/2016, flavonoids and carotenoids in the Spring/2014 and 2015, respectively, whilst the ascorbic acid was more abundant in the Autumn/2014. However, the Pearson’s correlation revealed weak to moderate influence of the climate parameters on the phytoconstituents measured. Indeed, both DPPH-scavenging and β-carotene/linoleic acid co-oxidation assays demonstrated a high antioxidant activity of MN correlated to the polyphenolic index. The MN and SA did not present cytotoxicity, since L929 cells treated with different concentrations maintain the cell viability. Moreover, the doses of the MN (3–30 μg/mL) and SA (60–250 μg/mL) were able to reduce the mortality induced by H2O2 demonstrated in both, MTT and LDH assays. The leaves of MN could be an antioxidant source of potential use in food and supplements for either human or animal production due to its attractive biomass yield, palatability and nutritional value.