Enzymatically oxidized lactose and derivatives thereof as potential protein cross-linkers

The enzyme galactose oxidase [EC 1.1.3.9] was applied to convert lactose, lactylamine and lactobionic acid into their corresponding 6′-aldehyde compounds. The potential protein cross-linking ability of these oxidized lactose and derivatives thereof was investigated using n-butylamine as the model compound. First, oxidized lactose gave double Maillard reaction products that were stable under mild alkaline conditions. Second, reductive amination of lactose followed by enzymatic oxidation gave cross-links that were stable under both neutral and alkaline conditions. Third, stable cross-links were obtained through enzymatic oxidation and amidation of lactobionic acid.