Abstract
3-Isobutyl-2-methoxypyrazine (IBMP), the most prevalent grape-derived methoxypyrazine, can contribute green bell pepper, vegetative and herbaceous aromas and flavours to wines. At elevated concentrations, this potent odorant may mask desirable fruity and floral aromas in wine and may be considered as a fault. A new remediation method for wines with elevated IBMP levels has been trialled using magnetic polymers, prepared in the same way as ordinary polymers but with the incorporation of iron oxide nanoparticles as magnetic substrates. Characterisation by Fourier transform-infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed no difference between thermally synthesised and microwave synthesised polymers. Magnetic polymers were found to have removed over 40% of the IBMP present in spiked model wine and white wine within ten minutes. The addition of magnetic nanoparticles and microwave-induced polymerisation did not affect the adsorption properties of the polymer in model wine and the polymer could be regenerated at least five times. Both Langmuir and Freundlich isotherms were found to fit the data for both types of polymer. However, attempts to produce imprinted polymers were not achieved, as they were found not to be differentiated from non-imprinted counterparts via adsorption tests.
Highlights
Alkylmethoxypyrazines (MPs) are aroma volatiles noted for their potency and ability to impart sensory characters of green bell pepper, grass, and vegetables to wine [1]
In an attempt to produce molecularly imprinted polymers, 2-methoxypyrazine was employed as a template to overcome the ‘template bleeding’
Magnetic polymers were synthesised, characterised, and found to remove up to 40% or more of the IBMP in model wine solutions and two white wines
Summary
Alkylmethoxypyrazines (MPs) are aroma volatiles noted for their potency and ability to impart sensory characters of green bell pepper, grass, and vegetables to wine [1]. Three grapederived MPs have been uncovered in recent decades—3-isobutyl-2-methoxypyrazine (IBMP), 3-isopropyl-2-methoxypyrazine (IPMP) and 3-sec-butyl-2-methoxypyrazine (SBMP) [1]—that are mainly located in grape stems, followed by skins and seeds [2]. Another source of MPs in wines originates from the contamination of grapes by Coccinellidae beetles, leading to a wine fault known as ‘ladybug taint’ (LBT) [3,4]. Sauvignon Blanc, and Carmenere [6]; high levels (≥20 ng/L) can be overpowering and cause undesirable ‘green’ and ‘unripe’ characters [7] due to the extremely low sensory thresholds of MPs. The detection and recognition thresholds of IBMP determined in red wine are 10 ng/L and 15 ng/L, respectively [8]. The level of IBMP may be utilised as an indicator of the overall green character potential of grapes and wines
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