Preparation of Propolis Hydroalcoholic Extract Nanoemulsion by Freeze Drying Technique and Evaluation of Its Physicochemical Properties as a Food Preservative

Propolis as a by-product of bee activity has been known for its unique antioxidant properties and antimicrobial activity against broad range of microorganisms. In the present study, hydroalcoholic extract of propolis was prepared (the ratio of ethanol to the water was 80:20). After removing the solvent from the extract using a vacuum rotary evaporator, the dried powder of propolis was produced using a freeze dryer at -70 ºC after 40 h. Also, the nanoemulsion of propolis was synthesized using the powder. GC-MS analyses of samples showed numerous phenolic and flavonoid compounds in the produced powder. Total phenolic and flavonoid contents, and antioxidant activity of the produced nanoemulsion were 86.93, 34.21 (mg/ g gallic acid), and 97.68 %, respectively. The particle size, polydipersity index and zeta potential in the nanoemulsion were 86 nm, 0.299 and -23.34 mV, respectively. The results of this study showed that the hydroalcoholic extract and powder of propolis prepared by the freeze drying method had high phenolic and flavonoid content and antioxidant properties. However, these properties in the powder were higher than that was detected for the hydroalcoholic extract. According to the findings of this study, using a freeze dryer, it is possible to produce the powder of propolis hydroalcoholic extract with spherical and nano-sized particles, which can easily be applicable as a preservative in the food industry.