Abstract
The extraction of proanthocyanidins (PACs), despite being an important and limiting aspect of their industrial application, is still largely unexplored. Herein, the possibility of combining eutectic solvents (ESs) with microwave assisted extraction (MAE) in the extraction of PACs from grape pomace (GP) is explored, aiming to improve not only the extraction yield but also the mean degree of polymerization (mDP). The combination of choline chloride with lactic acid was shown to be the most effective combination for PACs extraction yield (135 mgPAC/gGP) and, despite the occurrence of some depolymerization, also enabled us to achieve the highest mDP (7.13). Additionally, the combination with MAE enabled the process to be completed in 3.56 min, resulting in a considerably reduced extraction time.
Highlights
Proanthocyanidins (PACs), or condensed tannins, are polymeric phenolic compounds that consist of flavan-3-ol monomers and its derivatives, and can be found throughout the plant kingdom [1]
In order to determine this, solutions of 20 mgPAC/gES of PAC reference material obtained from white grape pomace (GP) were prepared in eutectic solvents (ESs) composed of 37.5% (m/m) of hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), and 25% (m/m) of water
Depolymerization products were quantified by high performance liquid chromatography (HPLC) in a Accela 80 Hz (Thermo Fisher Scientific, San Jose, CA, USA) (Figure S1 in Supplementary Materials) and peak attribution was made by electrospray ionisation mass spectrometry (ESI-MS) in a LCQ Fleet ion trap mass spectrometer (ThermoFinnigan, San Jose, CA, USA) (Table S1 in Supplementary Materials) operated as described elsewhere [32]. mean degree of polymerization (mDP) was calculated by dividing the sum of terminal and extension units by the sum of terminal units and the %Gal was calculated by dividing the sum of galloylated units by the sum of all units
Summary
Proanthocyanidins (PACs), or condensed tannins, are polymeric phenolic compounds that consist of flavan-3-ol monomers and its derivatives, and can be found throughout the plant kingdom [1]. MAE has been described as a good candidate in the extraction of PACs from agroforestry by-products in combination with conventional solvents such as ethanol:water mixtures in the extraction of PACs from maritime pine bark [15] Neoteric solvents such as ionic liquids have been suggested in the extraction of PACs from cortex cinnamomic with a 1.25 M aqueous solution of 3-methylimidazolium bromide that resulted in an yield improvement of 125% when compared to the conventional MAE combined with water [16]. After selecting the combination of choline chloride with lactic acid or glycerol as the best candidates in MAE of PACs, the impact that the content of each ES component has on relevant parameters of the final extract such as YPAC, mDP, and %Gal was assessed. The impact that MAE conditions, namely temperature (T), biomass percentage (%BM), and extraction time (t) have on the mentioned parameters of the final extract was assessed
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