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, the high production cost of PPA is 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. Growth parameters (temperature, pH, and aeration) and concentrations of medium ingredients (glucose, yeast extract, and phenylalanine) were optimized in 2-L bioreactors by using a Box-Behnken design. The optimum temperature, pH, and aeration levels were determined to be 34.5°C, 5.12, and 0.5 vvm, respectively. Concentrations for optimizing the fermentation medium for glucose, yeast extract, and phenylalanine were 119, 3.68, and 14.84 g/L, respectively. Under these optimum conditions, 1349 mg/L PPA was produced by Proteus vulgaris in submerged fermentation. This study demonstrated about a 3-fold improvement compared to shake flask fermentation (358 mg/L PPA).