Bioconversion of Napier grass to 2-phenylethanol: unveiling the synergy of pretreatment with deep eutectic solvents and yeasts

2-Phenylethanol (2-PE), a valuable flavor compound with high market demand, can be produced from readily available lignocellulosic biomass. This study explored the potential of Napier grass, a fast-growing energy crop, as a substrate for 2-PE production. Napier grass was pretreated using three different deep eutectic solvents (DES) formulated with choline chloride (ChCl) combined with lactic acid (LA), glycerol (Gly), or urea (Urea). DES pretreatment partially removed hemicellulose and increased cellulose content (up to 40%) in the biomass. Subsequent enzymatic hydrolysis revealed the highest glucose yield, from ChCl/LA pretreated biomass, almost 25% more than the native biomass. Fermentation optimization for temperature and nitrogen content identified strain-specific optimal conditions for 2-PE and ethanol production using two non-conventional yeasts, Kluyveromyces marxianus and Pichia kudriavzevii. Notably, ChCl/Gly pretreated biomass with P. kudriavzevii produced the highest 2-PE yield (510.51 ppm) alongside significant ethanol production (30.63 g/L). This study paves the way for a more sustainable approach to producing 2-PE, a valuable flavor compound, using readily available biomass and non-conventional yeasts.