Postharvest delivery of Bacillus G36 metabolites formulated in AgNP modifies Salvia rosmarinus Spenn. bioactive profiles

Abstract This study explores the biological synthesis of silver nanoparticles (AgNPs) using elicitors (ML) from the beneficial bacterium Bacillus G36 and evaluates their potential to enhance bioactive compound production in postharvest rosemary (Salvia rosmarinus Spenn.). To determine optimal synthesis conditions, different ratios of ML to AgNO3 1mM were mixed, for 24 h, evaluating a range of temperatures (28–37) and pH (5, 7, 9), with and without rosemary extracts, which were characterized by TEM, FTIR, XRD and Zpotential. Two NP were selected based on size and organic crown for biological assay on rosemary. The best conditions were a 1:1 (vv) mixture of ML and silver nitrate, pH 9, 37 °C, producing nanoparticles with an average size of 7.5 nm (S3). These small AgNPs have shown great biological activity. In contrast, adding rosemary extract (RE) to nucleation media, in order to increase reductive media potential, yielded larger particles (≈ 63.9 nm) and reduced their effectiveness. Biological assays showed that S3 AgNPs significantly increased total phenol and flavonol contents in rosemary when applied in postharvest, while ML alone did not, highlighting the better effect of elicitors when formulated in NP. Remarkably, only S3 AgNPs enhanced rosmarinic acid levels by 50%. Both S3 AgNPs and live Bacillus G36 cells also boosted diterpene (carnosic acid equivalents) concentrations. Despite effects on bioactives, only S3 and ML treatments increased the total antioxidant capacity of the extracts. Overall, the study demonstrates that biosynthesized S3 AgNPs from Bacillus G36 metabolites offer a sustainable and efficient approach to producing small, bioactive nanoparticles capable of improving and maintaining valuable phytochemicals in rosemary postharvest.