Sustainable extraction and in situ separation of bromelain from pineapple peel using deep eutectic solvent/salt system: molecular mechanism, hydrolytic activity and stability.

To make full utilization of pineapple peel, which is usually discarded as pineapple processing waste, deep eutectic solvents (DESs) were screened to disrupt cell wall for the extraction of bromelain, and then in situ DES/salt aqueous two-phase system was constructed for the efficient purification of bromelain. The degree of cell wall disruption was tuned effectively by adjusting the interactions between DESs and cell wall components. ChCl:Gly reconstructed the hydrogen bonding network between lignin and itself to selectively remove lignin in compound middle lamella and cell corners, and retain hemicellulose and cellulose, which gave high extraction yield (6.4 mg/g), high activity (88.7 U/mg) and high purity under the optimum conditions. The unique hydrogen bonding environment constructed by ChCl:Gly maintained the conformation and enhanced the stability of bromelain. The crude extracts containing ChCl:Gly was further subjected to aqueous two-phase system to obtain the purified bromelain, where extraction efficiency of 96% with activity recovery of 111% and 2.58-fold purification was achieved. More importantly, ChCl:Gly exhibited the capacity for multiple recycling and reuse cycles with stable extraction efficiency, activity recovery and purification fold. The proposed platform integrates extraction, purification and enrichment in one step, achieving green and sustainable extraction of high-yield and high-purity bromelain from pineapple peel.