Structure modification of stirred fermented milk gel due to laccase-catalysed protein crosslinking in a post-processing step

Laccases are a promising candidate for crosslinking milk proteins in stirred fermented milks. It was applied in a post-processing step due to its acidic pH optimum reported in literature for rebodying of the gel and an improvement in structure. A laccase preparation from Trametes versicolor had a lower oxidation activity in ultrafiltration permeate than in model buffer systems, and a pH optimum of 4.5. It was applied to stirred skim milk gels but no significant change in the storage modulus or apparent viscosity of yoghurt occurred. Confocal laser scanning micrographs showed a more porous structure of the milk gel. Some fresh cheese samples had improved rheological properties. A competing crosslinking activity and peptidolytic activity was assumed and smaller peptides were detected in acidified milk by fluorescence. Mass spectrometry of the laccase preparation returned mainly laccase sequences. Although this does not exclude proteases, it indicates that the radical mechanism of laccases may lead to protein degradation. Enzymatic modification of milk proteins can alter the structure of fermented milk gels and even create new structures. Rheological properties can be improved via crosslinking, thus reducing costs due to the addition of protein powders or stabilisers. An innovative approach to combining biotechnology and food science and engineering is investigated. The study is interesting for both enzyme manufacturers and dairy companies as it aims to at least partially fill the knowledge gap between enzymology and their real-world application in dairy products. However, enzymatic treatment is an additional step and also incurs costs which should be taken into account. •Enzymatic protein crosslinking is expected to improve the structure of milk gels.•Acidified skim milk gels were treated with a laccase preparation.•No significant improvement in storage modulus or apparent viscosity was observed.•Competing peptidolysis resulted in structure degradation and protein fragments.