This study focused on the isolation of actinobacteria capable of producing extracellular keratinase from keratin-rich residues, which led to the selection of an actinobacterial strain referenced as Streptomyces strain DZ 06 (ES41). The Plackett–Burman screening plan was used for the statistical optimization of the enzymatic production medium, leading to the identification of five key parameters that achieved a maximum activity of 180.1 U/mL. Further refinement using response surface methodology (RSM) with a Box–Behnken design enhanced enzyme production to approximately 458 U/mL. Model validation, based on the statistical predictions, demonstrated that optimal keratinase activity of 489.24 U/mL could be attained with 6.13 g/L of chicken feather meal, a pH of 6.25, incubation at 40.65 °C for 4.11 days, and an inoculum size of 3.98 × 10⁷ spores/mL. The optimized culture conditions yielded a 21.67-fold increase in keratinase compared with the initial non-optimized standard conditions. The results show that this bacterium is an excellent candidate for industrial applications when optimal conditions are used to minimize the overall costs of the enzyme production process.

Ultrasound is a non-thermal technology increasingly applied in food processing to modulate enzyme activity. This study investigated the effects of ultrasonic irradiation on the activity of a commercial thermostable α-amylase. Enzyme activity was determined by quantifying reducing sugars released from starch using the 3,5-dinitrosalicylic acid method, and protein concentration was measured by the Bradford assay. A one-factor-at-a-time approach was used to evaluate the effects of ultrasonic amplitude, treatment time, enzyme concentration, incubation temperature, and calcium ion concentration. Subsequently, a Box–Behnken design was applied to analyze the combined influence of amplitude, treatment duration, temperature, and calcium concentration on residual activity. The enzyme exhibited an initial activity of 46.27 ± 3.63 U/mL under standard assay conditions. Moderate ultrasonic amplitudes enhanced activity, whereas prolonged exposure and elevated temperatures promoted inactivation. Statistical analysis showed that the incubation temperature and calcium concentration significantly influenced residual activity, and the quadratic model provided a good fit (R² = 0.94). Optimal inactivation conditions were identified at 60% amplitude, 9 min treatment, 85 °C, and 9 ppm calcium, resulting in 66.3% enzyme inactivation. These findings support the use of ultrasound-assisted processing as a controllable strategy to regulate thermostable α-amylase activity in industrial enzyme applications.