The valorization of underutilized legume varieties supports biodiversity and enhances food system sustainability, while offering plant-based protein ingredients with distinctive structural and colloidal functionality suitable for tailored food applications. This study investigated the effects of ultrasound-assisted extraction on the physico-chemical and functional properties of protein isolates from two neglected black chickpea (Cicer arietinum L.) cultivars originating from Sicily, southern Italy. These varieties, which were abandoned over time due to their dark color and lengthy preparation time, are today reconsidered for their tolerance to drought and high temperatures, underscoring their importance in the context of climate change.

To valorize these legumes as sustainable protein sources, conventional alkaline extraction (ST-treated) was compared with ultrasound-assisted extraction (US-treated), both performed at pH 9 and a 1:10 (w/v) solid-to-liquid ratio. Ultrasound was applied at 20 kHz and 80% amplitude for 5, 10, or 15 minutes, and the colloidal behavior of the resulting isolates was further examined through the preparation of model oil-in-water emulsions using high-pressure homogenization.

Ultrasound improved protein extraction performance, acting as an effective green processing strategy. The US treatments increased protein extraction yield (20–27%) and recovery (17–23%), producing isolates with high purity (85–91%) and solubility (74–94%). FTIR analysis revealed structural rearrangements, with decreased intermolecular β-sheets and increased α-helix content, while compositional analysis indicated a relative enrichment in hydrophobic amino acids, features consistent with enhanced interfacial activity. Mineral content analysis confirmed the high food safety of the isolates, with heavy metal concentrations below the limit of quantification.

Functionally, the structural modifications induced by ultrasound translated into improved interfacial performance. Model oil-in-water emulsions were prepared by homogenizing 1% (w/v) protein solutions with 5% (v/v) oil. All emulsions stabilized by the isolates maintained excellent electrostatic stability (ζ-potential ≈ –30 mV) over 10 days. Moreover, US-treated proteins generated significantly finer emulsions, with an average droplet size of approximately 0.60 µm compared with 0.81 µm in the ST-treated, reflecting their superior stabilizing capacity and enhanced exposure of hydrophobic residues. Overall, the isolates demonstrated promising emulsifying performance and stability for food applications. Emulsifying properties and stability will be explored by image analysis (CLSM and cryo-TEM) and discussed during the presentation.

These results highlight the suitability and potential of black chickpea protein isolates as hydrocolloids in the development of plant-based food products.