Sustainable eutectic mixture-based ultrasound assisted multifaceted valorisation of pineapple waste for bromelain and bioethanol production

Abstract

A large number of pineapple residues like peels, leaves and stems generated during processing remains underutilized. The current investigation provides one-pot task-specific valorisation of these residues by sequential extraction of bromelain and saccharification of cellulose residue for bioethanol production. Employing natural deep eutectic solvents (NADES) prepared by mixing ammonium salts with imidazole and glycerol has guaranteed sustainable extraction of bromelain. Ultrasound-assisted liquid phase microextraction (UA-LPME) was performed and NADES with moderate density (TBC:I:G/sodium sulphate) was observed to have a higher bromelain yield and purity. Response Surface Methodology-based optimization of UA-LPME was carried out and solid: liquid ratio (25 ml/g), ultrasound time (17.5 min) and ultrasound temperature (45 °C) were observed to be influential variables resulting in an optimal bromelain yield of (87%). Sequential fractionation of the enzyme concentrate with gel filtration chromatography and anion exchange chromatography has resulted in a corresponding purity fold of 89.27. The cellulose-rich residue remaining after bromelain extraction was enzymatically saccharified (Cellic CTec2) for bioethanol production (12.7 g/L). This novel approach guarantees sustainable valorisation of pineapple waste using NADES as a sustainable extraction medium.