The effect of silver nanoparticles (Ag NPs) obtained in the presence of royal jelly (RJ) on the growth of yeast Candida guilliermondii NP-4, on the total and H⁺-ATPase activity, as well as lipid peroxidation process and antioxidant enzymes (superoxide dismutase (SOD), catalase) activity was studied. It has been shown that RJ-mediated Ag NPs have a fungicide and fungistatic effects at the concentrations of 5.4 µg mL⁻¹ and 27 µg mL⁻¹, respectively. Under the influence of RJ-mediated Ag NPs, a decrease in total and H⁺-ATPase activity in yeast homogenates by ~ 90% and ~ 80% was observed, respectively. In yeast mitochondria total and H⁺-ATPase activity depression was detected by ~ 80% and ~ 90%, respectively. The amount of malondialdehyde in the Ag NPs exposed yeast homogenate increased ~ 60%, the catalase activity increased ~ 70%, and the SOD activity—~ 30%. The obtained data indicate that the use of RJ-mediated Ag NPs have a diverse range of influence on yeast cells. This approach may be important in the field of biomedical research aimed at evaluating the development of oxidative stress in cells. It may also contribute to a more comprehensive understanding of antimicrobial properties of RJ-mediated Ag NPs and help control the proliferation of pathogenic fungi.

Fruit peels as a lignocellulosic biomass are rich in sugars and nutrients, thus making them favorable medium for yeast growth and various materials production. This study showed the potential of fuit peels hydrolysate (FPH) as a substrate for single-cell protein (SCP) and bioethanol production, depending on substrate concentration, pH, oxygen availability. The highest specific growth rate (0.50 ± 0.01 h^- 1) was observed at pH 6.5 in non-diluted hydrolysates, which corresponds to ~ 250.0 g L^- 1 carbohydrates and 0.2 g L^- 1 total nitrogen concentration. The maximal protein production yield (~ 50% by dry weight) was recorded during 24 h cultivation of S. cerevisiae ATCC 13,007 under oxygen-limited conditions at pH 6.5, while the maximal ethanol production (109.00 ± 4.00 g L^- 1) was observed at 6 h for S. cerevisiae ATCC 9804 and ATCC 13,007 starins under aerobic conditions. The maximal fermentation efficiency (~ 99%) was observed at 24 h cultivation of S. cerevisiae ATCC 13,007 in 2-fold diluted hydrolysate under oxygen-limited conditions at pH 6.5, while the same strain exhibited the highest carbon conversion efficiency (CCE) (~ 56%) during aerobic cultivation in 2-fold diluted hydrolysate at pH 3.0. Thus, FPH can serve as a favorable substrate for SCP and bioethanol production using S. cerevisiae strains ATCC 13,007 and ATCC 9804. Nitrogen supplementation and combination with fruit and vegetable processing industries could further enhance SCP production and process efficiency which aligns with circular economic strategy.