Amino acids find several industrial applications and are especially widely-used in animal husbandry as well as in pharmaceutical and food industry. In this work an attempt was made to determine the best experimental conditions for the recovery of amino acids as protein degradation products by sub-critical water hydrolysis. Bovine Serum Albumin (BSA) was used as sample protein. Experiments were performed continuously in pipe reactors of different sizes in order to achieve different residence times varying between 4 and 900 s. Amino acid compositions were analyzed by HPLC. The results were compared with conventional acid hydrolysis in HCl for 24 h. At a residence time of 30 s the highest amount of amino acids was obtained at 583 K and 250 bar. Due to the formation of simple amino acids as alanine and glycine from complex amino acids, in particular the amount of these components increased with increasing temperature up to 583 K (29% and 18% of the values obtained by HCl hydrolysis, respectively) and decreased thereafter due to further degradation of the products. No significant influence of operating pressure (150-270 bar) could be observed at the tested temperature (523 K) and residence time (30 s). The amino acid formation increased with increasing residence time between 8 and 300 s at the tested temperature (523 K) and decreased thereafter. The addition of carbon dioxide led to carbon acid formation and to an increase in amino acid yield due to the acceleration of acid hydrolyzed catalysis steps. This protein treatment may provide a practical and economical solution for the disposal of protein-rich sources like hairs and feathers, which are considered as waste so far.
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