Strain and starter-culture engineering for steering product functionality
Milk fermentation is a key process in adding functional properties, such as flavour, texture and shelf life, to dairy products. Cheese starter-cultures consist of simple or complex mixtures of Lactococcus lactis strains, sometimes together with other species of the genera Leuconostoc and/or Lactobacillus. These bacteria actively cooperate in microbial consortia.
We have learned, during the last decade, that not all cells within a pure bacterial culture exhibit the same behaviour. It is reasonable to assume that such culture heterogeneity also applies to industrial fermentations. We used Lactococcus lactis as a model organism for dairy fermentation and, by using fluorescent proteins, we demonstrated culture heterogeneity under industrially-relevant conditions. In a complementary approach, using RNAseq, we identified more than 200 small RNA molecules and improved the annotation of the model L. lactis, strain MG1363.
Another level of heterogeneity in cheese starter-cultures is their strain diversity. Complex, undefined starter cultures are very robust in production processes and their final product-properties are mostly superior to those derived from less-complex starter cultures. We studied population dynamics and used genome-scale metabolic models and experimental evolution of mixed-cheese starter cultures to understand the underlying microbial interactions necessary for their functionality. Results showed that bacteriophages are vital to sustaining biodiversity in mixed dairy-starter cultures.
Another topic within this project was the physical interaction of microbial cells with matrix components, in cheese and fermented milk. The detailed characterisation and alteration of lactococcal surface properties, in an isogenic bacterial background, facilitated our study of the influence of surface properties on starter-culture functionalities.
This work will support the dairy industry in the development of healthier and tastier fermented products.