Conversion of phenylalanine to phenylpyruvic acid by microbial fermentation

Phenylpyruvic acid (PPA) is an alpha keto acid, which has the potential to be used in monogastric animals' diets to prevent excessive nitrogen accumulation in their manure and adverse effects on the environment. PPA is also used as a flavor enhancer in the food industry and for kidney patients' diets to decrease urea accumulation in the body. However, high production costs are limiting the use for these applications. Therefore, this project was undertaken to enhance PPA production by submerged fermentation. Firstly, microorganism selection was performed and Proteus vulgaris was determined to be the best strain for PPA production among four evaluated strains. Thereafter, growth parameters  such as temperature, pH, and aeration as well as concentrations of significant medium ingredients  such as glucose, yeast extract, and phenylalanine were optimized in 2-L bioreactors by using Box-Behnken Responce Surface designs. As a result, the optimum temperature, pH, and aeration levels were determined to be 34.5^oC, 5.12, and 0.5 vvm, respectively. Also, optimum concentrations for glucose, yeast extract, and phenylalanine were determined as 119 g/L, 3.68 g/L, and 14.84 g/L, respectively in the fermentation medium. Under these optimum conditions, 1349 mg/L PPA was produced by Proteus vulgaris in submerged fermentation, whish is 3-fold improvement compared to shake flask fermentation (358 mg/L PPA).