Natural diversity of aminotransferases and dehydrogenase activity in a large collection of Lactococcus lactis strains

The natural diversity of Lactococcus lactis was studied with respect to the flavour-generating enzymes leucine (Leu-AT) and aromatic (AraT) aminotransferase, and hydroxyisocaproic acid dehydrogenase (HicDH). The screening of 175 L. lactis strains required the development of enzyme assays to enable the use of high throughput screening facilities. Natural diversity was expressed as the difference between 10% of the strains with the highest and lowest enzyme activity. The natural diversity found for Leu-AT, AraT and HicDH activity was 13-, 49- and 30-fold, respectively. Leu-AT activity showed a weak correlation with the AraT and HicDH activity, whereas there was no correlation between AraT and HicDH activity. In the group of strains with the highest Leu-AT activity, 5- and 6-fold differences of AraT and HicDH activities were found, respectively. These results demonstrated that it is possible to select strains with specific combinations of important ripening enzymes that could enhance cheese flavour formation.