Assessment of Pre-Treatment Effects on Adzuki Bean (Vigna angularis) Samples for the Production of Protein Concentrates

 Adzuki bean (Vigna angularis), is rich in dietary fiber, proteins, carbohydrates, vitamins, and minerals, while presenting only a small lipid fraction. Due to these nutritional attributes and its relatively balanced composition, adzuki bean has drawn attention as a potential raw material for the development of protein-based food ingredients. In light of the increasing demand for sustainable and functional protein sources, it is important to evaluate both nutritional quality and techno-functional performance. Accordingly, the present study investigated the effects of ultrasound treatment and enzymatic application on the obtention of adzuki bean protein concentrates, with particular emphasis on their techno-functional properties. The parameters evaluated included total and free sulfhydryl content and functional properties such as gel formation capacity, water and oil absorption, solubility, emulsifying activity, foam formation, and stability. The protein preparations showed contents ranging from 46.98% to 59.27%, as determined by the Bradford method. Water absorption varied from 1.82±0.15mg/mg for the protein obtained by precipitation at the isoelectric point (PI) to 2.42±0.11mg/mg for protein recovered through enzymatic treatment with Cellulase FoodPro®. Oil absorption, in turn, reached the highest value (2.84±0.2mg/mg) for protein obtained by ultrasound combined with α-amylase Termamyl^®. Emulsifying activity revealed distinct responses. The protein obtained by precipitation at PI exhibited the maximum emulsifying capacity (99.99%), while ultrasound and enzymatic treatments resulted in slightly lower but still high values. The minimum emulsifying capacity (96.16%) was observed in proteins treated with ultrasound and the combined enzymes α-amylase Termamyl^® and Cellulase FoodPro^®. Foam formation, however, showed the opposite trend, increasing significantly in samples treated with ultrasound and enzymes (64.10%), compared with the protein obtained by isoelectric precipitation. Regarding gelation, protein obtained through ultrasound and α-amylase Termamyl^® treatment displayed the lowest concentration required for gel formation (0.7g/5mL), indicating enhanced network-building ability. The solubility and sulfhydryl analyses confirmed that the treatments induced structural modifications. The Solubility of the protein obtained by combined ultrasound-enzyme treatment enzyme (α-amylase Termamyl^® and Cellulase FoodPro^®) decreased at pH 3–5 and 8 compared to the PI protein, but increased remarkably at pH 9, reaching higher solubility 71%. Total sulfhydryl contents were also elevated in proteins subjected to ultrasound with α-amylase Termamyl®, supporting the evidence of conformational rearrangements. Overall, these findings demonstrate that ultrasound and enzymatic treatments act synergistically to enhance key techno-functional properties of adzuki bean proteins. Such improvements broaden their potential applications in food systems, reinforcing the value of adzuki bean as an emerging source of plant proteins.