Optimization of Extraction Parameters and Functional Evaluation of Samia ricini Pupae Protein for Starch-Based Bioplastic Films

The escalating global demand for sustainable protein sources and eco-friendly packaging necessitates the valorization of underutilized agricultural by-products. This study systematically optimized the processing of Samia ricini (Eri) silkworm pupae, a high-quality sericulture by-product, to maximize protein isolation and evaluate its application in biocomposite edible films. A three-stage optimization process was implemented: 1) steaming pretreatment, 2) ethanol defatting, and 3) alkaline protein extraction. The optimal parameters identified were 6-8 minutes of steaming (for lowest moisture and the highest initial protein content), a 16-hour ethanol defatting duration (achieving 64.19% protein content post-defatting), and a brief 30-minute alkaline extraction (yielding a high-purity protein isolate of 94.94%). The resulting optimal protein isolate was then combined with different starch sources (corn, tapioca, and blend) to produce edible films. Protein incorporation significantly enhanced the film's functional properties, notably reducing the water vapor permeability (WVP) across all formulations (p ≤ 0.05). The protein–corn–tapioca starch blend demonstrated superior barrier performance with the lowest WVP value of 2.49 ± 0.10 g/h⋅m2. Conversely, while the incorporation of protein and different starches did not result in statistically distinct tensile strength values (p > 0.05), films made with corn starch exhibited the best qualitative handling properties (uniformity and peelability). These findings demonstrate the potential of Samia ricini pupae protein as a bio-derived functional ingredient for developing high-performance, sustainable bioplastic films and supporting the circular utilization of sericulture waste resources.