From Batch to Continuous Flow Bioprocessing: Use of an Immobilized γ-Glutamyl Transferase from B. subtilis for the Synthesis of Biologically Active Peptide Derivatives

γ-Glutamyl-peptides are frequently endowed with biological activities. In this work, " kokumi peptides" such as γ-glutamyl-methionine ( 1 ) and γ-glutamyl-( S )-allyl-cysteine ( 2 ), as well as the neuroprotective γ-glutamyl-taurine ( 3 ) and the antioxidant ophthalmic acid ( 4 ), were synthesized through an enzymatic transpeptidation reaction catalyzed by the γ-glutamyl transferase from Bacillus subtilis ( Bs GGT) using glutamine as the γ-glutamyl donor. Bs GGT was covalently immobilized on glyoxyl-agarose resulting in high protein immobilization yield and activity recovery (>95%). Compounds 1 - 4 were obtained in moderate yields (19-40%, 5-10 g/L) with a variable purity depending on the presence of the main byproduct (γ-glutamyl-glutamine, 0-16%). To achieve process intensification and better control of side reactions, the synthesis of 2 was moved from batch to continuous flow. The specific productivity was 1.5 times higher than that in batch synthesis (13.7 μmol/min*g), but it was not accompanied by a paralleled improvement of the impurity profile.