**4.2 Optimization of** *Penicillium aurantiogriseum* **protease immobilization on magnetic nanoparticles for antioxidant peptides' obtainment**

In this work, magnetic nanoparticles coated with polyaniline were used to immobilize protease from *Penicillium aurantiogriseum* and applied to the production of antioxidant peptides derived from bovine casein [5]. The casein was hydrolyzed using the magnetic bio-derivative, uncovering its peptides that were sequenced and had antioxidant properties tested through 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging and hydrogen peroxide scavenging assays. After being reused for five times, the magnetic bioderivative was able to maintain more than 74% of the initial activity. Hydrolyzed casein presented similar peptide when used; the free and immobilized enzyme and prevalent peptides could be sequenced. When comparing the reactive oxygen species (ROS) scavenging activity, the hydrolysates presented 2.5 times more than nonhydrolyzed casein, which allows the use of an immobilized protease to obtain natural ingredients derived from casein attractive, indicating potential use in the production of functional foods.
