Structural, Functional and Antioxidant Properties of Soy Protein Concentrates Enriched with Black Mulberry Pomace.

RESEARCH BACKGROUND: The incorporation of fruit processing residues into protein-rich ingredients is attracting attention as a sustainable strategy to enhance the nutritional and functional value of plant-based formulations. However, the effect of adding black mulberry pomace on protein matrix structure, functionality and digestibility remains insufficiently explored. This study investigates the potential of black mulberry pomace as a co-ingredient to modify and improve the characteristics of soy protein concentrate derived from moderately toasted soy flour.

EXPERIMENTAL APPROACH: Soy protein concentrates were obtained by washing soy flour with ethanol after blending it with increasing mass fractions of black mulberry pomace. The chemical composition, in vitro digestibility, hydration and emulsifying properties, and antioxidant potential of the prepared samples were examined using standard radical scavenging and metal-chelating assays. Structural characteristics were analysed using infrared spectroscopy and electron microscopy. Relationships among compositional, functional, and antioxidant parameters were explored using multivariate statistical analyses.

RESULTS AND CONCLUSIONS: The addition of small amounts of black mulberry pomace improved hydration and emulsifying properties, as well as antioxidant potential through the incorporation of phenolic compounds. These enhancements were attributed to interactions between phenolic compounds and protein structures, confirmed by spectroscopic and microscopic evidence. However, higher pomace mass fractions negatively affected protein digestibility, likely due to matrix densification and aggregation. Correlation and multivariate analyses confirmed close associations between antioxidant activity, protein solubility, and techno-functional performance. These findings suggest that low to moderate pomace mass fractions are sufficient to induce positive changes without compromising digestibility.

NOVELTY AND SCIENTIFIC CONTRIBUTION: This work provides new insights into the dual role of black mulberry pomace as a functional and antioxidant-enhancing agent in plant protein systems. It demonstrates a sustainable approach to developing value-added protein ingredients by integrating underutilised agri-food residues. The comprehensive chemical, functional, and structural analyses presented in this study contribute to a better understanding of how co-ingredient interactions can shape the bio-functional performance of soy-based matrices.