Effects of soybean meal hydrolysate as the nitrogen source on seed culture morphology and fumaric acid production by Rhizopus oryzae

• Soybean meal hydrolysate (SMH) was used as nitrogen source to control the morphology of R. oryzae.
• Uniformly dispersed mycelial clumps with a diameter of ∼0.1 mm were formed.
• This morphology was superior to the larger pellets generated with urea or yeast extract.
• Fumaric acid production reached 50.2 g/L with a yield of 0.72 g/g glucose in fermentation.
• This is the first study demonstrating the advantages of SMH in fumaric acid fermentation.

Fumaric acid production by fungal fermentation from renewable resources has received much attention, but suffers from low productivity and yield largely because of poor cell morphology limiting mass transfer. In this study, a simple seed culture medium was developed with soybean meal hydrolysate (SMH) as the nitrogen source for controlling the morphology of Rhizopus oryzae ATCC 20344. With the optimal seed culture conditions (pH 3.0, SMH concentration: 30% (v/v), and inoculation spore concentration: 8 × 107/L), uniformly dispersed mycelial clumps with a diameter of ∼0.1 mm were formed, which gave high fumaric acid production from glucose in shake flasks, reaching a fumaric acid titer of 50.2 g/L and yield of 0.72 g/g glucose. Compared to the fermentation with cell pellets, the fermentation with mycelial clumps generated with SMH as nitrogen source increased fumaric acid production because of improved mass transfer. This process can lower the cost for bio-based fumaric acid and provide a novel way of using soybean meal besides its current use as animal feed supplement.