Optimized Solid-State and Submerged Fermentation of Pea Protein-Enriched Flour To Compare The Effects on Protein Quality and Functional Properties

The goal of this research project was to benchmark the optimal solid-state (SSF) and submerged (SmF) fermentation parameters for five generally regarded as safe (GRAS) microorganisms on pea protein-enriched flour (PPEF) to achieve limited protein hydrolysis (10% DH) and evaluate the effects of microbial SSF and SmF on the protein quality and functional properties of PPEF. PPEF was inoculated with Aspergillus oryzae NRRL 5590, Rhizopus oryzae NRRL 395, Rhizopus oligosporus NRRL 2710, Lactobacillus plantarum NRRL B4496, and Bacillus subtilis ATCC 6051 and evaluated at two temperatures (30C and room temperature) over a 120-h fermentation time course. A degree of hydrolysis of 10% DH was chosen as the limit for protein hydrolysis to improve the protein quality and functional properties of PPEF. Under SSF at 10% DH, protein content for all samples significantly increased and lipid content decreased significantly, while ash content did not change. Surface properties of all SSF samples showed an increase in zeta potential while surface hydrophobicity decreased. Under SSF, the functional properties of PPEF were affected significantly but did not improve with the exception of water hydration capacity (WHC) and oil-holding capacity (OHC): Solubility decreased in all fermented samples at both pH 4 and pH 7; Emulsifying activity (EA) decreased for all fermented samples at pH 4, but at pH 7 PPEF fermented with A. oryzae and R. oligosporus increased; Emulsion stability (ES) increased for all fermented samples at pH 7, but at pH 4 only PPEF fermented with A, oryzae and R. oligosporus increased; Foaming capacity (FC) and foam stability (FS) decreased for all fermented samples at both pH 4 and pH 7 whereas WHC and OHC increased for all fermented PPEF samples. Under SmF at 10% DH, protein, ash, and lipid contents all increased significantly. Under SmF, the surface charge (zeta potential) of PPEF increased for all samples while the surface hydrophobicity of PPEF decreased for all samples, as seen for SSF. The functional properties of PPEF subjected to SmF was significantly affected but also did not improve any parameters other than WHC and OHC: Solubility decreased for all SmF fermented PPEF samples at both pH 4 and pH 7, along with the following functional effects: EA decreased at both pH 4 or pH 7, ES increased at pH 4 but decreased at pH 7, FC decreased at both pH 4 and pH 7, and FS increased at pH 4 but decreased at pH 7. Protein digestibility of PPEF increased following fermentation with either platform (i.e., SSF, SmF), but due to limiting amino acids, their protein digestibility-corrected amino acid score (PDCAAS) values were below 1.0. Solid-state and submerged fermentations of PPEF with microorganisms have significant potential to improve the functional properties and protein digestibility of PPEF, but at 10% DH, only WHC and OHC were improved. Different degrees of hydrolysis of PPEF should be explored to further examine the possibilities of improvement in functionalities as novel food ingredients