Cheddar - Streptococcus versus Lactococcus

[Northern_Brewer]

https://www.nature.com/articles/s41467-023-41059-2
Here, we studied the roles of microbial interactions in flavour formation in a year-long Cheddar cheese making process, using a commercial starter culture containing Streptococcus thermophilus and Lactococcus strains. By using an experimental strategy whereby certain strains were left out from the starter culture, we show that S. thermophilus has a crucial role in boosting Lactococcus growth and shaping flavour compound profile. Controlled milk fermentations with systematic exclusion of single Lactococcus strains, combined with genomics, genome-scale metabolic modelling, and metatranscriptomics, indicated that S. thermophilus proteolytic activity relieves nitrogen limitation for Lactococcus and boosts de novo nucleotide biosynthesis. While S. thermophilus had large contribution to the flavour profile, Lactococcus cremoris also played a role by limiting diacetyl and acetoin formation, which otherwise results in an off-flavour when in excess. This off-flavour control could be attributed to the metabolic re-routing of citrate by L. cremoris from diacetyl and acetoin towards α-ketoglutarate. Further, closely related Lactococcus lactis strains exhibited different interaction patterns with S. thermophilus, highlighting the significance of strain specificity in cheese making.

 

[McMullan]

Very interesting. I've been saying for years how brewing scientists have failed miserably to apply omics to real scientific research like this. Instead they p*ss around with academic 'stamp collecting' of mainly untestable hypotheses called 'phylogenies' and other backwater pursuits associated with time wasting.

 

[bernardsmith]

Sounds as if these folk are using freeze dried lab cultured strains of bacteria and not the bacteria found in raw milk. Or using clabbered milk as their culture source or indeed, backslopping with whey from a previous batch. Single use cultures may provide the labs that produce these products with lots of moolah, but the cheese making processes are fundamentally unsustainable and demolish traditional processes and practices. Moreover, any phages that attack your or their cultures create huge problems that I believe simply don't happen when using indigenous colonies of cultures in the milk .