Impact of Solid-State Fermentation with <i>Aspergillus niger</i> on the Chemical Composition of Yellow Pea (<i>Pisum sativum</i> L.) Flour and Its Application for Obtaining Protein Products

Given the growing interest in sustainable alternatives to animal derived proteins, strategies such as fermentation have emerged as promising tools to enhance the production and modification of the characteristics and functional properties of plant-based protein ingredients. This study evaluated the impact of solid-state fermentation with Aspergillus niger on the processing of yellow peas (Pisum sativum L.) and the properties of the derived protein products. Fermentation was conducted for 6, 24, 96, and 168 h in sterile column bioreactors, followed by alkaline extraction and isoelectric precipitation using generally recognized as safe (GRAS) agents, including lactic acid and lactic acid bacteria (a mixture of Lactiplantibacillus plantarum and Lactococcus lactis). The most notable improvements were observed after 96 h of fermentation, which increased the protein content of yellow pea flour by 122% and reduced carbohydrates by 42%. The protein product obtained through fermentation, alkaline extraction and precipitation with lactic acid, reached 72.2 ± 2.6% protein (dry basis) and displayed improved water and oil retention capacities, as well as significantly enhanced antioxidant activity, without compromising solubility or emulsifying performance. Analysis of both total and essential amino acids indicated an improvement in quality of the protein product obtained through fermentation. The use of solid-state fermentation as a pretreatment led to distinct advantages in functional properties of the protein products, with comparable values of the overall protein recovery yield, productivity, and specific water consumption, which demonstrates that the proposed bioprocessing strategy is effective in producing high-quality protein ingredients tailored for diverse food applications.