Optimizing protein yield in black soldier fly larvae through liquid milk waste utilization: A response surface methodology approach

Black soldier fly (Hermetia illucens) larvae have emerged as an effective bioconversion agent capable of transforming organic waste into high-protein biomass that is suitable for animal feed applications. This study aimed to analyze the effectiveness of liquid milk waste feeding on the protein content of black soldier by optimizing feed amount and harvest age using response surface methodology (RSM). A laboratory-scale experiment was conducted using a central composite design (CCD) with 13 experimental runs. Four-day-old black soldier (30 g per treatment) were fed varying amounts of liquid milk waste (2.3–3.7 liters) and harvested at different ages (4–10 d). Environmental conditions were monitored daily, maintaining temperatures of 28.8–29.7 °C and humidity of 71–75%. Protein content was determined through laboratory analysis, and the data were analyzed using ANOVA and RSM optimization. The highest protein content achieved was 12.93% at a feed amount of 3.5 L with harvest on day 5, while the lowest was 10.18% at a feed amount of 3 liters feed with harvest on day 10. The quadratic model demonstrated an excellent fit (R² = 0.9666), with both feed amount (p = 0.0001) and harvest age (p < 0.0001) significantly affecting protein content. RSM optimization suggested optimal conditions of 3.4 liters feed with day-5 harvest, predicting 13.034% protein content. Validation experiments confirmed this prediction with a protein content of 12.96 %. In conclusion, liquid milk waste effectively supports black soldier protein production, demonstrating its potential for sustainable waste valorization and alternative protein source development.