Susceptibility of an industrial α-lactalbumin concentrate to cross-linking by microbial transglutaminase

The susceptibility of an industrial α-lactalbumin concentrate to cross-linking with a microbial transglutaminase from Streptoverticillium mobaraense was investigated. At a protein concentration of 0.5% w v⁻¹, the maximum cross-linking was observed at 50°C, pH 5 and at 5 h of incubation time. Results from sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis showed that most of the monomeric form of α-lactalbumin was converted to polymers too large to move into the gel matrix. Addition of ethylenediamine tetraacetic acid or SDS prior to the incubation of protein–enzyme mixture, further enhanced the transglutaminase reaction with the industrial α-lactalbumin. Results from reverse phase chromatography indicated that cross-linking caused a broadening of the α-lactalbumin peak with little change in the average hydrophobicity of the protein. In contrast to the reported results on pure α-lactalbumin, the industrial α-lactalbumin concentrate showed considerable cross-linking with transglutaminase even without the reduction of the disulphide bonds. This difference was attributed to the partially unfolded secondary structures in the industrial α-lactalbumin concentrate.