Effects of different silver nanoparticle concentrations on quantitative germination parameters and bioactive properties of white mustard seeds (Sinapis alba L.)

Germination induces biochemical transformations that enhance the bioactive properties of seeds, while the application of nanoparticles emerges as a strategy to optimize this process. The aim of this study was to evaluate the effect of silver nanoparticle application on quantitative parameters and bioactive properties of white mustard seeds (Sinapis alba L.) during germination. Silver nanoparticles (AgNPs) were synthesized from silver nitrate. The UV-Vis absorption spectrum was measured in the 200-700 nm range to validate the plasmonic band, and the AgNP suspension concentration (mg/mL) was determined gravimetrically. White mustard seeds were treated with silver nanoparticles at concentrations of 1 and 5 μg/mL during the imbibition (12 hours) and germination stages. The process was conducted in the dark at 25 °C for 96 hours in a germination chamber. Untreated germinated seeds served as the control. The germination rate (GR) and index (GI) were determined as percentages. Antioxidant properties were measured using ABTS, DPPH, and FRAP assays, and total phenolic content was quantified as mg of gallic acid equivalents per gram of sample (mg GAE/g). Phenolic compounds were identified by HPLC-DAD in the sample with the highest antioxidant activity, the control consisted of seeds subjected only to imbibition. AgNP application increased the GR compared to the control (72%), reaching 98% and 96% at
concentrations of 1 and 5 μg/mL, respectively. The results revealed that the application of AgNPs during germination did not produce statistically significant differences (p > 0.05) between the two applied concentrations. Samples germinated and treated with 1 μg/mL of nanoparticles showed increases of 13% and 105% in the DPPH (41.47 μmol TE/g) and FRAP (53.96 μmol TE/g) assays, respectively, compared to the control. Samples treated with 5 μg/mL demonstrated a 31% increase in antioxidant activity in the FRAP assay (34.49 μmol TE/g) compared to the control. The lower AgNP concentration did not result in significant differences in antioxidant activity by the ABTS assay, while the higher concentration showed no significant differences by the ABTS and DPPH assays (p > 0.05). Only the application of 1 μg/mL AgNPs resulted in an increase in total phenolic content, representing a 57% rise. The results indicate a trend toward more favorable effects at lower AgNP concentrations, suggesting a possible dose-dependent response. Four compounds were identified by HPLC in the control sample (protocatechuic, ρ-coumaric, and sinapic acids and rutin), while nine were identified in the sample germinated and treated with 1 μg/mL AgNPs, five of which were additional to those found in the control (chlorogenic, caffeic, and ferulic acids, myricetin, and quercetin). Applying a controlled concentration of AgNPs during mustard seed germination represents a promising strategy to modulate plant metabolism and enhance the biosynthesis of bioactive compounds without compromising the physiological performance of the sprouts.