Characterisation of lactococci isolated from natural niches and their role in flavour formation of cheese

This thesis focuses on the biodiversity of lactococci isolated from various natural niches and their exploitation in enhancing the flavour diversity in cheese. Large numbers of wild strains were tested for their flavour forming abilities, characteristics, behaviour in defined strain starter (DSS) cultures and for their potential application in cheese. Several strains were able to produce unusual flavours distinct from those produced by industrial strains and were found prototrophic for most amino acids reflecting their high biosynthetic capacity. Many wild strains were growing well together in DSS and with industrial strains, different interactions were observed in population dynamics between strains. Moreover, an enhanced flavour production by co-cultivation of some strains was observed and resulted from the completion of whole flavour-formation pathways between the interacting micro-organisms. The results described in this thesis offer new opportunities for the development of tailor-made starter cultures, based on the knowledge of both population dynamics of the strains and their flavour-forming abilities.Key words : lactic acid bacteria, Lactococcus lactis, artisanal starters, wild (natural) strains, cheese making, flavour, Gouda cheese, Proosdij cheese, population dynamics, bacteriocins.