Impact of milieu conditions on the α-lactalbumin glycosylation in the dry state

Abstract

Maillard reaction is influenced by protein and sugar properties, water activity (aw) as well as the glycosylation time and temperature. The aim of this work was to investigate the influence of environmental parameters on the glycosylation reaction kinetics and to develop a technology platform for protein glycosylation as a possible substrate pre-treatment. The glycosylation reaction of bovine α-lactalbumin (α-La) was performed with lactose and maltodextrin in the dry-state at 40, 50 or 60°C performed at aw of 0.33, 0.44 or 0.58 for reaction times of 8, 24 or 48h. The degree of glycosylation (DG) was determined as the loss of lysine using the ortho-phthalaldehyde (OPA) method. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) with Coomassie and glycoprotein staining was also performed. The reaction with lactose reached higher DG values in all cases as compared to reactions with maltodextrin (maximum DG of 85% and 31%, respectively, at aw=0.58 after 48h). Lactosylation kinetics showed that the second order rate constants increased with increasing temperature and were highest at aw=0.58 in all cases. The activation energies were determined as 97.1±37.7, 193.9±9.1 and 136.6±15.6kJ/mol for aw=0.33, 0.44 and 0.58, respectively and showed an increasing trend with increasing temperature. Glycosylation of α-La offers a new process for improvement of functional properties as well as being a substrate pre-treatment process to control enzymatic digestion in order to generate tailor-made peptides as food additives with important health benefits like probiotics due to glycoprotein resistance to further enzyme hydrolysis.