Improved propionic acid production from glycerol: Combining cyclic batch- and sequential batch fermentations with optimal nutrient composition

Propionic acid was produced from glycerol using Propionibacterium acidipropionici. In this study, the impact of the concentrations of carbon and nitrogen sources, and of different modes of high cell density fermentations on process kinetics and -efficiency was investigated. Three-way ANOVA analysis and batch cultivations at varying C/N ratios at pH 6.5 revealed that propionic acid production rate is significantly influenced by yeast extract concentration. Glycerol to yeast extract ratio (w w−1) of 3:1 was required for complete glycerol consumption, while maintaining the volumetric productivity. Using this optimum C/N ratio for propionic acid production in cyclic batch fermentation gave propionate yield up to 93 mol% and productivity of 0.53 g L−1 h−1. Moreover, sequential batch fermentation with cell recycling resulted in production rates exceeding 1 g L−1 h−1 at initial glycerol up to 120 g L−1, and a maximum of 1.63 g L−1 h−1 from 90 g L−1 glycerol.