Studies on L-phenylalanine production by fermentation

The aim of this project was: (1) to study the effects of different carbohydrates, various nitrogen supplements, corn steep liquor, sodium chloride and potassium phosphate on L-phenylalanine production by Brevibacterium lactofermentum and Corynebacterium glutamicum; (2) to determine the effects of various co-factors on L-phenylalanine production by Brevibacterium lactofermentum and Corynebacterium glutamicum; (3) to examine the relationship between cell growth, L-phenylalanine production and substrate concentration during batch fermentation through kinetic study and modelling; and (4) to investigate and model byproduct formation during L-phenylalanine production.;The results of the nutrient studies showed that Brevibacterium lactofermentum and Corynebacterium glutamicum had different nutrient needs. The inhibition of high glucose concentrations on L-phenylalanine production was observed in both Brevibacterium lactofermentum and Corynebacterium glutamicum depending on nitrogen and corn steep liquor supplements.;The influence of various co-factors on the production of L-phenylalanine was different in Brevibacterium lactofermentum and Corynebacterium glutamicum and affected by the medium composition.;Kinetic studies revealed that L-phenylalanine production by Brevibacterium lactofermentum was partly growth-associated and partly nongrowth-associated. At the end of the fermentation processes, nongrowth-associated/growth-associated L-phenylalanine production ratio was about 1.07-4.33 at 20-100 g/l initial glucose and 1-12 g/l initial corn steep liquor concentrations. Corn steep liquor increased L-phenylalanine production by increasing the growth-associated production. A maximum productivity ((dP/dt);L-Tyrosine was produced as a byproduct during L-phenylalanine production by Brevibacterium lactofermentum. Depending on initial glucose and corn steep liquor concentrations, 0.09-0.51 g of L-tyrosine was produced at the end of fermentation processes in relation to a unit g L-phenylalanine formation. L-Tyrosine formation was also partly growth-associated and partly nongrowth-associated. Depending upon the initial glucose and corn steep liquor concentrations, 23-70% of total L-tyrosine formation at the end of fermentation processes was due to nongrowth-associated production. L-Tyrosine formation was also modelled by the Luedeking-Piret equation. At different initial glucose and corn steep liquor concentrations, good agreement was found between the model and the experimental data.