**Response Surface Methodology for the Optimization of Keratinase Production in Culture Medium Containing Feathers by** *Bacillus* **sp. UPM-AAG1**

#### **Aa'ishah Abdul Gafar, Mohd Ezuan Khayat, Siti Aqlima Ahmad, Nur Adeela Yasid and Mohd Yunus Shukor \***

Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Serdang 43400, Malaysia; aishababa93@gmail.com (A.A.G.); m\_ezuan@upm.edu.my (M.E.K.); aqlima@upm.edu.my (S.A.A.); adeela@upm.edu.my (N.A.Y.)

**\*** Correspondence: mohdyunus@upm.edu.my; Tel.: +603-97696722

Received: 17 June 2020; Accepted: 7 July 2020; Published: 29 July 2020

**Abstract:** Keratinase is a type of proteolytic enzyme with broad application in industry. The main objective of this work is the optimization of keratinase production from *Bacillus* sp. strain UPM-AAG1 using Plackett-Burman (PB) and central composite design (CCD) for parameters, such as pH, temperature, feather concentration, and inoculum size. The optimum points for temperature, pH, and inoculum and feather concentrations were 31.66 ◦C, 6.87, 5.01 (w/v), and 4.53 (w/v), respectively, with an optimum keratinase activity of 60.55 U/mL. The keratinase activity was further numerically optimized for commercial application. The best numerical solution recommended a pH of 5.84, temperature of 25 ◦C, inoculums' size of 5.0 (v/v), feather concentration of 4.97 (w/v). Optimization resulted an activity of 56.218 U/mL with the desirability value of 0.968. Amino acid analysis profile revealed the presence of essential and non-essential amino acids. These properties make *Bacillus* sp. UPM-AAG1 a potential bacterium to be used locally for the production of keratinase from feather waste.

**Keywords:** RSM; numerical optimization; keratinase; feather; *Bacillus* sp.; amino acids
