Impact of chemical and enzymatic modification on structural, techno-functional, and rheological properties of Sacha inchi (Plukenetia volubilis L.) press cake flour

Abstract

Sacha inchi ( Plukenetia volubilis L.) press cake is a protein-rich agro-industrial by-product whose functional utilization is constrained by antinutritional factors and suboptimal techno-functional properties. To improve its performance as a protein ingredient, the effect of chemical modification under acidic, neutral, and alkaline conditions (pH 4, 7, and 9) and enzymatic (Protease, Neutrase, and Alcalase) treatments on the composition, protein structure, antinutritional factors, and rheological behavior of the defatted material was evaluated. Protein content ranged from 62 to 75%; protein digestibility increased significantly in enzymatically treated samples (67–69%) relative to the untreated control (18%), confirming that controlled proteolysis enhances enzymatic accessibility during digestion. Extractable phenolic content was highest at pH 7, yet antioxidant activity did not follow a proportional relationship with total phenolic concentration, indicating the contribution of additional matrix components to radical scavenging capacity. Extractable tannin content was lowest under alkaline conditions, whereas extractable phytic acid was highest at pH 9, reflecting treatment-dependent changes in extractability rather than actual removal. Fourier transform infrared analysis revealed a redistribution of secondary structural elements, with an increase in less ordered conformations under alkaline treatment; as this technique is primarily sensitive to secondary structure, modifications at the primary structure level could not be assessed. At pH 4, heat-induced gel formation was inhibited; at pH 7, weak viscoelastic networks formed and lost rigidity over 24 h; and at pH 9, progressive structural reinforcement was observed, with an approximately 200% increase in the storage modulus. Protease treatment produced a comparable consolidation effect, whereas Alcalase generated high initial stiffness followed by time-dependent structural weakening. The results indicate that the functional performance of Sacha inchi press cake is closely related to the balance between controlled denaturation, conformational reorganization, and degree of proteolysis.