Gauze-reinforced electrospun regenerated cellulose ultrafine fibers for immobilizing bromelain

This work aims to reuse bromelain, a cysteine protease isolated from stems of pineapples, and to improve its thermal stability by immobilization onto gauze-reinforced regenerated cellulose (RC) fibers. To obtain RC fibers (358 ± 53 nm), cellulose acetate (CA, M.W. ∼3 × 10⁴ g/mol) fibers (307 ± 59 nm) were electrospun from 17% w/w CA mixed with 5% w/w Tween 80 in acetic acid: water of 3:1 by weight at an applied voltage of 17.5 kV and a fiber collection distance of 10 cm. The fiber surface was treated with 0.5 M potassium hydroxide in ethanol, functionalized by coupling with 12% w/v glutaraldehyde using aluminium sulfate as a catalyst, and immobilized with bromelain. Effects of temperature and pH on an enzyme activity of bromelain-immobilized fibers (bromelain-RC) were investigated by a casein assay with a spectrophotometer at 275 nm. Results show that bromelain-RC functioned at 70, 80 and 90 °C at pH 8 better than bromelain did. However, there was no difference in the activities of bromelain and bromelain-RC with the pH change. Bromelain-RC could be reused at least 9 times with >60% of the original activity and had a heat resistance higher than bromelain had. The tensile strength of bromelain-RC (14.2 ± 2.5 MPa) was higher than that of the RC fibers (6.9 ± 1.4 MPa). Therefore, bromelain-RC are potentially used as a heterogeneous catalyst under the conditions that bromelain cannot endure.