Optimization of fermentation conditions for propionic acid production by immobilized cells of Propionibacterium acidipropionici with sodium alginate-polyvinyl alcohol

Abstract

Propionic acid (PA), a widely utilized food preservative and mold inhibitor, offers significant advantages when produced via microbial fermentation compared to chemical synthesis, including sustainable raw material utilization, simplified operational conditions, and reduced environmental impact. However, traditional free-cell fermentation faces limitations in productivity and process stability. In this study, sodium alginate and polyvinyl alcohol were utilized as composite carriers, with Propionibacterium acidipropionici FS1026 serving as the target bacterium for the preparation of immobilized pellets for PA fermentation. The conditions for the preparation of these immobilized pellets and the fermentation process for PA production were optimized separately. The results indicated that: (1) the optimal immobilization conditions were as follows: polyvinyl alcohol concentration of 10.8 g/L, sodium alginate concentration of 1.5 g/L, immobilization solution consisting of a mixture of 2 % CaCl₂ and 50 g/L boric acid, a bacterial inclusion amount of 12 %, and an immobilization time of 8 h; (2) the optimal medium for PA fermentation using the immobilized cells contained: glucose at 75.41 g/L, yeast powder at 30 g/L, peptone at 16.31 g/L, K₂HPO₄ at 24 g/L, and MgSO₄ at 0.7 g/L; (3) the immobilized cells maintained stable PA production over 10 consecutive fermentation batches, achieving an average yield of 26.31 g/L, thereby confirming operational robustness; (4) optimization of the fermentation process revealed that pH adjustment using ammonia was superior to that using Ca(OH)₂, and the optimal glucose replenishment interval was every 24 h, with a replenishment of 35 g/L, resulting in a PA yield of up to 42.76 g/L—significantly higher than the yield from free cell fermentation (20.33 g/L). This study demonstrates that immobilized cell fermentation establishes a novel technical approach for PA production, exhibiting promising industrial scalability and environmental sustainability.