Abstract
Rutin is a known antioxidant compound that displays a broad range of biological activities and health-related benefits but presents a low water solubility that can be overcome by its polymerization. In this work, biocompatible aqueous biphasic systems composed of the ionic liquid cholinium dihydrogen phosphate ([CH][DHph]) and the polymer poly(ethylene glycol) 600 (PEG 600) were investigated as an efficient integrated reaction–separation platform for the laccase-catalyzed oligomerization of rutin. Two different approaches were studied to reuse laccase in several oligorutin production cycles, the main difference between them being the use of monophasic or biphasic regimes during the oligomerization reaction. The use of a biphasic regime in the second approach (heterogeneous reaction medium) allowed the successful reuse of the biocatalyst in three consecutive reaction–separation cycles while achieving noteworthy rutin oligomerization yields (95% in the first cycle, 91% in the second cycle, and 89% in the last cycle). These remarkable results were caused by the combination of the increased solubility of rutin in the PEG-rich phase together with the enhanced catalytic performance of laccase in the [Ch][DHph]-rich phase, alongside with the optimization of the pH of the reaction medium straightly linked to enzyme stability. Finally, a life-cycle assessment was performed to compare this integrated reaction–separation platform to three alternative processes, reinforcing its sustainability.
Highlights
Rutin (2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-oxo-4H-chromen-3-yl 6-O-(6-deoxy-α-L-mannopyranosyl)-β-D-glucopyranoside) is a flavonoid compound present in fruits, vegetables, and plant-derived beverages.[1]
In order to identify an effective aqueous biphasic systems (ABS) for the oligomerization of rutin, i.e., where the enzyme and the product should preferentially concentrate in opposite phases, preliminary studies to determine the partition of laccase and oligorutin were carried out with ABS formed by combinations of poly(ethylene glycol) (PEG) with a molecular weight of 600 g·mol−1 (PEG 600) and different cholinium-based ionic liquids (ILs), namely cholinium acetate ([Ch][Ac]), cholinium glycolate ([Ch][Gly]), and cholinium dihydrogen phosphate ([Ch][DHph])
In a first approach we studied the synthesis of oligorutin in a homogeneous medium to take advantage of the thermoreversible behavior of the selected ABS, previously described by Pereira et al.[20] and here confirmed for a lower temperature interval (Figure S3)
Summary
Rutin (2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-oxo-4H-chromen-3-yl 6-O-(6-deoxy-α-L-mannopyranosyl)-β-D-glucopyranoside) is a flavonoid compound present in fruits, vegetables, and plant-derived beverages.[1]. These oxidative enzymes catalyze the formation of phenoxyl radicals that, following a further oxidative coupling, lead to the production of higher molecular weight polyphenols,[7] improving the solubility, stability, and, in some cases, the bioactive properties of phenolic compounds like rutin.[8]
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