Valorization of pea haulm phenolics for structurally reinforced and antioxidant-active soy protein films

This study investigated soy protein isolate (SPI) films incorporated with pea haulm biomass phenolic extracts (PHBPE) obtained through ultrasound-assisted extraction following freeze-drying (FD) or oven-drying (120 °C) in three concentration levels (1, 5, and 10 wt%, w/w relative to SPI dry weight). In addition, a SPI film prepared without the addition of PHBPE was used as the control sample for all comparisons. Freeze-dried extracts retained the highest phytochemical activity (total phenolic content: 27.50 ± 3.37 mg GAE/g DM; total flavonoid content: 15.20 ± 0.57 mg CTE/g DM; antioxidant activity: 123.30 ± 2.41 μM TE/g DM), while oven-dried extracts at 120 °C showed comparable results to FD extracts. Mechanical testing demonstrated that SPI films with 5% PHBPE achieved optimal tensile strength, TS (FD_5%: 5.45 MPa) and puncture strength, PS (120 °C_5%: 3.98 MPa), outperforming the control (TS: 2.07 MPa; PS: 2.18 MPa). PHBPE incorporation also reduced solubility (to ∼23–24% at 10% PHBPE vs. 49% in control) and enhanced opacity (FD_10%: 7.68 mm −1 ). Thermal analysis revealed higher char residues (up to 19.99% at 120 °C_10%) compared to 10.13% in control. Soil burial confirmed complete degradation within 10 days. Unlike conventional studies that primarily focused on adding plant extracts to edible films, this work uniquely integrates upstream biomass processing (drying and ultrasound-assisted extraction) with downstream film functionality, demonstrating how extract preparation governs protein–phenolic interactions and final film performance. Moreover, the valorization of pea haulm biomass as a sustainable source of functional phenolics introduces a circular-bioeconomy approach for designing performance-tuned, biodegradable active packaging materials.