Growth rate influences flavour formation in Lactococcus cremoris independently of metabolic protein levels

Dairy starter cultures are often optimized for rapid acidification, but the relationship between growth rate and secondary metabolite (e.g. flavour) formation is unclear. We here investigated this relationship by modulating the growth rate of L. cremoris NCDO712 using partial translation inhibition (allowing growth at slower rates) or by varying temperatures in defined media and milk. Subsequently the proteome was conserved by full translational inhibition and cells were incubated in defined medium or in a cheese model system for up to 14 days to assess volatile compound formation. Proteome analysis of the cells revealed three protein clusters: ribosome-related (A), metabolism-related (B), and core (constant). Partial translation inhibition of the pre-cultures in defined media increased ribosome-related proteins and decreased amino acid metabolism proteins, including those involved in 3-methylbutanal formation. However, temperature-driven growth rate changes and partial translation inhibition in milk showed minimal changes in ribosome-related and metabolic protein fractions. Crucially, slower pre-culture growth significantly reduced key flavour compound production (up to 30-fold). These findings demonstrate that rapid growth does not necessarily sacrifice metabolic protein levels in L. cremoris NCDO712, and that pre-culture growth rates can influence secondary metabolite production, independent of enzyme levels.