Natural Deep Eutectic Solvents Extraction and Purification of Rice Bran Esterase and Its Characteristics

Objective: Rice bran esterase was extracted from rice bran using natural deep eutectic solvents (NADES) as media and the extraction processing of parameters was systematically optimized. The higher purity of rice bran esterase was obtained after purified with DEAE column and its enzyme properties were also investigated. Methods: Ten kinds of NADES including organic acids-based, polyols-based, amine-based and amino acids-based NADES were prepared. The extraction procedures including water bath agitation and ultrasonication were carried out. The effects of single factor such as the solid-to-liquid ratio, water content, extraction temperature and time on enzyme activity was studied. And then response surface methodology was used for optimization of the extraction processing. The crude enzyme solution was purified using DEAE column, as well as its enzyme characteristics were investigated. Results: The rice bran esterase activity of 2.96 U was obtained under the extraction conditions of proline-glycerol (molar ratio 1:2, contained 5% of water), 74.0 ℃, 3 h and a rice bran to NADES ratio of 9:30. The higher purity of rice bran esterase was obtained after purification with DEAE column. The purification efficiency and the recovery of rice bran esterase were 1.74 times, 69.40%, respectively. The molecular weight of rice bran esterase was approximately 35 kDa. The optimal substrate was a p-nitrophenyl acetate, and the optimal temperature and pH were 40.0 ℃, 8.0, respectively. The better stability of rice bran esterase could be maintained under 30.0~40.0 ℃ and pH7.0~9.0, as well as the similar performance in choline chloride-glycerol and proline-glycerol. Conclusion: Natural deep eutectic solvents used as a medium for extraction procedure is a simple and green extraction route, which would provide the understanding of extraction strategies for preparation of function compounds.