Solid-State Fermentation of Quinoa Flour: An In-Depth Analysis of Ingredient Characteristics

Plant protein ingredients are gaining attention for human nutrition, yet they differ significantly from animal proteins in functionality and nutrition. Fungal solid-state fermentation (SSF) can modulate the composition and functionality, increasing their applicability in foods. Quinoa flour (QF) served as a substrate for Aspergillus oryzae and Rhizopus oligosporus, resulting in two fermented ingredients (QFA and QFR) with different nutritional, functional, and aroma characteristics. A higher increase in protein (+35%) and nitrogen (+24%) was observed in the QFA, while fat was predominantly increased in the QFR (+78%). Fermentable oligo-, di-, monosaccharides and polyols (FODMAPs) decreased in the QFR but increased in the QFA due to polyol production. Metabolomic analysis revealed higher lactic acid concentrations in the QFA, and higher citric, malic, and fumaric acid contents in the QFR. The SSF reduced most antinutrients, while R. oligosporus produced saponins. Olfactometry showed the development of fruity ester compounds and a decrease in metallic and cardboard aromas. Both ingredients showed an enhanced water-holding capacity, with the QFA also demonstrating an increased oil-holding capacity. Complex formation increased the particle size, reduced the solubility, and decreased the foaming properties. Mycelium production darkened the ingredients, with the QFR having a higher differential colour index. This study highlights the potential of SSF to produce ingredients with improved nutritional, sensory, and functional properties.