Improving the Extraction Potential of Polygodial from Horopito using Pulsed Electric Field and Deep Eutectic Solvent

Abstract

New Zealand is a country with a variety of unique flora and fauna due to its geographically isolated position. One of them is horopito (Pseudowintera colorata), an ancient native plant that contains a bioactive compound known as polygodial in the essential oils of its leaves, which plays the most important role in horopito’s well-known antifungal properties. This study investigated the potential of two emerging technologies/methods to improve the extraction of polygodial from horopito leaves, namely pulsed electric field (PEF) and deep eutectic solvent (DES) that both have immense scope for the extraction of bioactive compounds from plant material. PEF was studied both as a pre-treatment prior to solvent extraction and as a direct extraction method of polygodial from horopito leaves with different processing parameters (pulsation time, electric field strength). Results revealed that PEF pre-treatment has the potential to improve the extraction yield of polygodial from horopito leaves. The maximum improvement was obtained at electric field intensity and frequency of 5 kV/cm and 800 Hz for 348 μs, where the extraction yield of polygodial from PEF pre-treated leaves was found to be 15.9% higher than non PEF-treated leaves. Meanwhile, a few selected DESs were investigated as alternative to commonly used conventional solvents, in terms of their extractability and stability of polygodial, as well as reusability of the solvent. Two new types of DESs, namely tetrabutylammonium chloride:polyethylene glycol-300 (TBAC:PEG-300) and tetrabutylammonium chloride:1-dodecanol (TBAC:1-dodecanol), were introduced to successfully extract polygodial with comparable extraction yield to that of ethanol. Among these two DESs, TBAC:1-dodecanol showed higher polygodial extractability and was studied further for optimization using response surface methodology. Under optimized conditions, the extraction yield obtained with TBAC:1-dodecanol DES (12.35 ± 0.05 mg/g dried leaves) was better than that of ethanol (10.58 ± 0.18 mg/g dried leaves). It was found that both technologies have the potential to improve polygodial extraction, from technological and environmental perspectives.