Abstract:

The activity of acid protease immobilized in different composite gel carriers made from sodium alginate (SA)
combined separately with three natural polymers was measured to select the best immobilization carrier and conditions
using single factor experiments and orthogonal array design. The results showed that the best carrier was composed
of SA and xanthan gum and the best immobilization conditions were determined as follows: CaCl2 concentration,
5.0 g/100 mL, SA to xanthan gum ratio, 6:1, and immobilization time, 2.5 h. Experiments conducted under these conditions
gave an activity recovery of 74.12%. The enzymatic properties of immobilized protease indicated there was no variation
in optimum pH and optimum temperature when compared with the free enzyme. Compared with the free enzyme, thermal
stability of immobilized acid protease was enhanced, and the kinetic parameter Km was improved. The half-life of the
immobilized protease was 17.28 d.

Key words: acid protease, immobilized enzyme, carrier, recovery, enzymatic property