Response Surface Methodology (RSM) Optimization on Extraction and Antioxidant Activity Evaluation of Peptide From Enzymatic Hydrolysates of Housefly ( <i>Musca domestica</i> ) Larvae

Response surface methodology (RSM) was applied to determine the optimal enzymatic hydrolysis conditions for obtaining antioxidant peptides from <i>Musca domestica</i> (MDPs). The results indicated that neutral protease was the most effective enzyme for producing MDPs. Under the optimized conditions (time: 3.2 h, temperature: 43.0°C, enzyme dosage: 5300.0 U/g, pH: 6.4), the DPPH radical scavenging rate of MDPs reached 70.9% ± 0.2%. The model demonstrated high reliability, as evidenced by the close agreement between experimental and predicted values, with <i>R</i> ² _adjusted and <i>R</i> ² _predicted both exceeding 0.9036. Subsequently, the particle size, zeta potentials, and structural features of MDPs were characterized using ultraviolet-visible (UV) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The analyses revealed statistically significant differences in the physicochemical properties among MDPs, MDPs_{> 10 kDa}, and MDPs_{< 10 kDa}. Furthermore, both MDPs_{> 10 kDa} and MDPs_{< 10 kDa} were rich in amino acids associated with antioxidant activity. Compared to MDPs_{> 10 kDa}, the MDPs_{< 10 kDa} exhibited superior antioxidant activities, including DPPH radical scavenging, hydroxyl radical scavenging, and reducing power. This study highlights the potential of <i>M. domestica</i>-derived peptides as natural antioxidants, supporting their future application in supplements, functional foods, and pharmaceuticals, and promoting the sustainable utilization of this resource.