Microbial protein production during fermentation of starch-rich legume flours using Aspergillus oryzae and Lactobacillus plantarum starter cultures

Starch-rich faba bean, yellow lentil, and yellow field pea flours were subjected to submerged fermentation using Aspergillus oryzae and Lactobacillus plantarum starter mono- or co-cultures, to increase protein contents of the flours. Fermentation mixes were supplemented with up to 35 g/L urea, ammonium sulfate and/or monoammonium phosphate as nitrogen sources. Protein contents of the flours increased 2–2.5-fold, i.e., total protein contents of up to 33 % were achieved following fermentation with A. oryzae monoculture or A. oryzae‒L. plantarum co-culture. Therefore, A. oryzae was capable of efficient legume starch utilization and protein production. Using A. oryzae‒L. plantarum co-culture led to the highest yields of at least six of microbially produced amino acids. After fermentation by L. plantarum monoculture, protein contents remained largely unchanged. However, in vitro protein digestibility of flours improved to a greater extent after fermentation with L. plantarum monoculture than with either A. oryzae monoculture or the co-culture. Hence, during fermentation with L. plantarum monoculture, microbially mediated hydrolysis of legume protein (generating smaller and easier digestible peptides), rather than microbial starch utilization, was the predominant process.