Uysal, Utku
Succinic acid is a highly versatile building block that is used in a wide range of industrial applications. The biological production of succinic acid has emerged in the last years as an efficient alternative to the chemical production based on fossil fuels. However, in order to fully replace the competing petro-based chemical process from which it has been produced so far, some challenges remain to be surpassed. In particular, one main obstacle would be to reduce its production costs, mostly associated to the use of refined sugars. The present work is focused on the development of a sustainable and cost-effective microbial production process based on cheap and renewable resources, such as dairy wastes. Hence, cheese whey, which is a by-product of cheese making process that mostly unutilized and disposed as a waste in industry, were identified as promising feedstock and used as inexpensive carbon sources for the bioproduction of succinic acid. Actinobacillus succinogenes, one of the best natural succinic acid producing strains, has employed in the fermentative production of succinic acid from cheese whey. Aiming at obtaining high succinic acid yield and production rate, Actinobacillus succinogenes cells were immobilized in alginate beads. The production of succinic acid from cheese whey, was studied both with immobilized and free cells of Actinobacillus succinogenes. In order to compare the efficiency of the process, pure glucose and lactose were also used as substrates in fermentations. Process optimization was conducted by the trial of different neutralizing agents, indirect CO2 sources and varied initial sugar concentrations in fermentations. To improve the system efficiency even further, durability of alginate beads was assessed and improved by using an alginate-whey mixture in immobilization procedure. In the study, fermentations were performed under three operation modes namely; batch, repeated-batch and continuous. Batch fermentations with free cells were conducted using cheese whey, lactose and glucose, highest succinic acid production was achieved with cheese whey (24.9 g L-1) with 35 g L-1 starting lactose concentration. From immobilized batch fermentations, 74.9% yield and 1.09 g L-1 h-1 of productivity was achieved with cheese whey. Repeated-batch fermentations conducted with whey using the same beads in 5 repeated cycles (144 h) and 0.89 g L-1 h-1 of productivity was achieved. For continuous fermentations with whey and immobilized cells, maximum 0.84 g g-1 succinic acid yield was achieved in a 13 days of operation. Based on the results obtained from this research, it was suggested that immobilizing A. succinogenes with alginate-whey mixture is an effective technique and cheese whey is a valuable resource for the production of succinic acid.


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