Effects of various water-based biocompatible solvents on the extraction of propolis from Artvin, Türkiye: Physicochemical properties, biological activity, and phenolic profile

Propolis is a multicomponent material collected by honeybees (Apis mellifera L.) from different plants to insulate and repair their hives, protect against microorganisms and foreign bodies, and maintain a sterile environment. This natural product, which attracts attention due to its wide range of biological effects, is often examined in scientific studies using ethanolic extracts, as its bioactive components are mostly soluble in ethanol. The limited bioactive component yield of water extracts, which are more biocompatible and safer compared to ethanol extracts, can be increased by using co-solvents including propylene glycol and glycerol. In this research, we focused on the antioxidant potentials and antimicrobial properties exhibited by different solvent profiles of aqueous (WPe), propylene glycol: aqueous (WPGPe), and glycerol: aqueous (WGPe) extracts of propolis. For this purpose, the physicochemical profile of the extracts, including soluble solids content (SSC), pH, titration acidity (TA), color, total phenolic and total flavonoid contents (TPC and TFC), antimicrobial activity, antioxidant activity, and phenolic component profiles, were subsequently determined using RP-HPLC-UV. L*, a*, and b* values of the extracts ranged between 41.17 and 50.66, 0.00 and 2.17, and 17.90 and 22.09, respectively. The SSC, pH, and TA values were highest for WPGPe and lowest for WPe. Caffeic acid, p-coumaric acid, and ferulic acid were the prominent phenolic acids in all extracts. In terms of total phenolic and total flavonoid content, as well as DPPH, ABTS, and FRAP antioxidant activity analyses, the WPGPe was found to be the most superior extract at a statistically significant level (p < 0.01). Principal component analysis and hierarchical cluster analysis revealed that WPGPe was richer in terms of individual phenolic compounds and other measured biological activity analyses, and therefore formed a statistically distinct group from the other extracts. The antimicrobial capacity of the extracts was evaluated against two Gram (-) bacteria, two Gram (+) bacteria, one yeast and one mould. This study offers practical guidance for the food and nutraceutical sectors on identifying suitable solvents and processing conditions for developing efficacious propolis-based formulations.