Effect of Formulation and Fermentation on Protein Structure, Nutritional Characteristics and Techno-Functional Properties of Hemp–Oat Press Cake Matrices

The valorization of plant-based press cakes as sustainable food ingredients requires understanding how formulation and processing affect their properties. This study investigated mixed formulations of hemp press cakes and oat press cakes subjected to pasteurization and lactic acid fermentation using a single independently prepared batch per formulation × treatment condition. A multi-analytical approach was applied, including protein solubility, SDS-PAGE, particle size analysis, evaluation of amino acids and biogenic amines, protein oxidation, phytic acid content, and techno-functional properties (water- and oil-holding capacities). The relative importance of formulation and processing was parameter-dependent. Formulation was the main source of variation in total amino acid composition, phytic acid levels, biogenic amine accumulation, and protein solubility under multi-bond disruption conditions. Processing was associated with protein aggregation, confirmed by SDS-PAGE and particle size increases, whereas fermentation was associated with partial solubility restoration, possibly through pH-mediated changes and structural rearrangements. Nutritional parameters showed formulation–processing interactions, affecting amino acid release, biogenic amine formation, protein oxidation and phytic acid levels, with the latter two remaining relatively high across all conditions. Water-holding capacity varied mainly with formulation, while oil-holding capacity varied with both factors and showed strong interaction patterns. Among the formulations studied, the 75:25 hemp-to-oat ratio represented the most balanced option, offering nutritional and functional improvements over pure hemp press cakes without substantially compromising protein content. Overall, these findings suggest that hemp–oat press cake matrices behave as interaction-sensitive materials and that combined formulation and fermentation strategies may be used to tailor functional and nutritional properties for food applications.