Enzyme-driven bioprocessing for enhanced bio-ammonia production from soybean meal protein isolate

To achieve sustainable ammonia production, a bioprocessing approach that uses enzymes and hyperammonia-producing bacteria (HAB) was developed to convert soybean meal protein isolate (SMPI) to bio-ammonia—an ammonia and ammonium solution. The potential of multiple industrial proteolytic enzymes (alcalase (A), flavourzyme (B), neutrase (C), and protamex (D)) to produce SMPI-hydrolysates that aid bio-ammonia production was evaluated in separate and simultaneous hydrolysis and fermentation systems. When used singly, the bio-ammonia yield trend was B > A > D > C hydrolysates, which was in line with their degree of hydrolysis (DH). In combination, when two or more enzymes were mixed in the same reaction, AD combination yielded hydrolysates converted to the highest ammonia titer of 1304 mg/L. The enhancement of bio-ammonia production in AD hydrolysates was the combined effect of an increase in the DH and the release of soluble hydrolysates during fermentation. In a multi-enzyme process, enzyme compatibility was more important towards bio-ammonia production. Hydrolyzing SM protein isolates for 6 or 24 h followed by 120 h HAB fermentation produced up to 1.2 g/L bio-ammonia in the separate hydrolysis and fermentation system. However, a peak ammonia titer of ~1.4 g/L was obtained in the simultaneous hydrolysis and fermentation (SHF). Consequently, the use of the enzyme mixture AD in an SHF system improved bio-ammonia production. The result from this work will be valuable for industrial bioprocessing of soybean meal protein to bio-ammonia synthesis.