Searching for Alternative Solvents for Extracting Green Propolis Type

Propolis has been used by humankind due to its many medicinal properties. Hydro-ethanolic liquid extracts are the most common forms of commercial propolis. However, due to the intolerance of people to ethanol, its inadequacy for ex-alcoholic people or for ingestion by children, other extraction media are of interest. Natural deep eutectic solvents (NADES) have been demonstrated as efficient low toxicity solvents to extract complex matrices. This work aimed to find alternatives to efficiently extract green propolis. Only low toxicity chemicals were employed to prepare sixteen NADES, including L-Lysine, an essential amino acid that could act as an alternative hydrogen bond acceptor for new NADES preparation. Neat or aqueous NADES components and honey which was hypothesise here as a potential NADES were also tested as extracting media. Results were compared head to head to those obtained with soovents commercially employed to extract propolis: EtOH:Water 7:3 (v/v), EtOH, propylene glycol (PG) and water. The monitored parameters were HPLC chromatographic profiles, total peak area and artepillin C content (biomarker for green propolis type). The best results for extractions were achieved at 50 °C for choline chloride (CC):propylene glycol (PG) 1:1 (mol/mol), followed by EtOH:Water 7:3 (v/v), CC:PG 1:2 (mol/mol), EtOH, CC:DL-Lactic acid (LA) 1:2 (mol/mol) and LA:Water 85:15 (v/v). Lysine:Water 1:10 (wt/wt) also appeared as a potential substituent for aqueous green propolis solutions available. At room temperature, extraction efficiencies decreased by ≤17% as observed for CC:PG 1:2 (mol/mol), EtOH:Water 7:3 (v/v), EtOH, concentrated PG and LA solutions. Decreases of ≤76% were observed for NADES more viscous NADES containing LA or glycerol. These findings evidenced that different CC:PG and CC:LA based NADES as well as aqueous concentrated solutions (LA and Lys) can be successfully used for extracting green propolis. Also, they strongly suggest that honey definition as a supersaturated solution should be revisited.

Financial support: This work was supported by a FAPESP SPRINT 4th Edition 2015 grant and the Australian Research Council’s Discovery funding scheme (grant no. 16/50009-2 and DP130101471, respectively). V.S.B., A.J.C., C.S.F., and K.F. are supported by the São Paulo Research Foundation (grant no. 013/07600-3, no. 13/15086-8 and no. 2017/06216-6). A.S. acknowledges the Australian Commonwealth government for an RTP scholarship.