**5. Conclusions**

The active research in the field of membrane biophysics deepens the understanding of the structural and functional membrane features in regard to vital processes in cells. In the present study a step forward is performed toward revealing the impact of small carbohydrates on the bilayer electrical properties, structure and organization. Modulation of membrane dielectric properties (capacitance and relative permittivity) is reported at moderate concentrations (above 200 mmol/L) of sucrose in the bulk phase. The above parameters are insensitive to the presence of fructose or glucose in the aqueous solution. A cooperative effect of sodium chloride and sucrose on membrane properties is suggested. As obtained by FFT EIS, all three of the small carbohydrate molecules studied here contribute to increased bilayer electric resistance. A qualitatively different behavior of the hydrocarbon fluidity in the two types of phosphatidylcholine bilayers, POPC and SOPC, upon the addition of sucrose in the aqueous surroundings is found. The hypothesis about sucrose ordering effect in membrane in the proximity of the glycerol backbone is supported here. The reduction in rotational diffusion and degree of hydration for the corresponding fluorophore is larger in the presence of the disaccharide studied. Sucrose is found to induce larger changes in lipid ordering at the glycerol level rather than in the hydrophobic core. A slight increase in the dipole potential is reported for POPC and SOPC bilayers upon the addition of sodium chloride, glucose, fructose and sucrose. The presented results are expected to be useful for the appropriate choice of carbohydrates, when the efficiency of the application targets the preservation of membrane electric properties. Gaining knowledge of the modulation of membrane molecular organization and its electric characteristics (capacitance, dielectric permittivity and resistance) by small carbohydrates would foster the elaboration of sugar-based lipid biomimetic systems for electric field-assisted applications in food industry, biotechnology and medicine.

**Author Contributions:** Conceptualization, V.V.; methodology, V.V., G.S. and G.P.; software, G.P.; validation, V.V., G.S. and G.P.; investigation, V.Y., O.P., A.S.-I. and K.A.; writing—original draft preparation, V.V.; writing—review and editing, G.S. and G.P.; visualization, V.V.; supervision, V.V.; project administration, V.V.; funding acquisition, V.V. and G.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research and the APC were funded by Bulgarian National Science Fund, grant numbers DN18/15-2017 and DO1-154/28/08/2018, Scientific Infrastructure on Cell Technologies in Biomedicine (SICTB)—Bulgarian Ministry of Education and Science.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
