Optimization and characterization of ultrasonic-assisted protein isolation from groundnut (Arachis hypogaea L.) oilseed cake

Defatted groundnut (Arachis hypogaea L. ) oilseed cake represents a rich, underutilized agro-industrial byproduct. Conventional alkaline extraction is constrained by long processing times, environmental burdens, and compromised functional quality. This study optimized ultrasound-assisted extraction (UAE) parameters to maximize protein recovery and evaluated the mechanistic impact of acoustic cavitation on the structural and techno-functional attributes of groundnut protein isolate (GPI). Response Surface Methodology (RSM) based on an I-optimal design was employed to optimize processing parameters across key extraction variables. Physicochemical, hydration, interfacial, thermal and enzymatic properties of the optimized isolate were systematically evaluated. Optimal UAE conditions were established at an ultrasonication time of 12.79 min, acoustic amplitude of 15%, solid-to-liquid ratio of 1:20 w/v, and probe frequency of 23 kHz (20–25 °C). Under these conditions, an experimental protein yield of 85.86% and an isolate protein content of 85.59 ± 0.24 g /100 g (dry basis) were achieved, demonstrating strong agreement with model predictions (85.86 g /100 g). Consequently, the optimized GPI exhibited exceptional nitrogen solubility (>88% in alkaline media), high water holding capacity (2.12±0.08 g/g), superior oil holding capacity (2.85±0.11 g /g), and improved in vitro protein digestibility. Ultrasound-assisted extraction is an efficient, sustainable green technique for upcycling groundnut oilseed cake into high-purity, functional protein isolates suitable for novel food formulations.