All the thousands of types of cheeses created by people have something in common: they are home to their own special communities of microbes
Cheese: Truly, the holiday season is the cheese season. These few weeks around Christmas and New Year’s is the time of the year when I miss cheese the most. (I’m vegan and have been so for many years.) Why do cheeses taste so incredible?
An international team of scientists based throughout Europe investigated this very important question for a time period of a year and now they’re sharing their findings with us. As many cheese connoisseurs know, the color, appearance, texture, smell and taste of cheeses are shaped by their special microbial zoos; the distinctive nutty, fruity, creamy and buttery flavors of different types of cheeses are the result of a variety of complex biochemical reactions carried out by its microbial community. And each type of cheese is home to its own special mix of microbes.
Although the compositional dynamics of cheese microbiomes are relatively well-known, the mechanistic roles and interactions of these microbes with each other in creating the flavor of cheeses is not at all well understood. For example, which microbes create which flavors?
“Cheese fermentation and flavour formation are the result of complex biochemical reactions driven by the activity of multiple microorganisms,” the study’s authors write in their paper (ref).
To better identify which microbes create which cheese flavors, the research team made their own Cheddar cheese. Cheddar cheese is a relatively hard cheese, off-white (or orange) in color, and it can be sharp-tasting.
Originating in the English village of Cheddar in Somerset, England, Cheddar is the most popular cheese in the UK, accounting for 51% of the country’s £1.9 billion annual cheese market and is the second-most popular cheese in the United States behind mozzarella. Further, Cheddar is the world’s most popular cheese and is the most studied cheese by scientists.
To address the secrets of the flavor of Cheddar cheese, the study’s lead author, microbial ecologist Chrats Melkonian, a postdoc at Utrecht University and Wageningen University, collaborated with the study’s senior author, microbiologist Ahmad Zeidan, R&D Director of Systems Biology and the Bioinformatics & Modeling Department at Chr. Hansen A/S, a global food science company. Dr Melkonian investigates the governing principles behind microbial community assembly, and Dr Zeidan’s main research interest is bridging the gap between computational biology and industrial biotechnology.
“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,” the team write in their paper.
Together, Dr Melkonian, Dr Zeidan and collaborators prepared batches of cheddar cheese, using warm milk and starter cultures containing coagulants and either the presence or absence of Streptococcus thermophilus, Lactobacillus lactis and L. cremoris strains, before packing the fresh cheeses into blocks and allowing them to age for one year. In addition to the presence or absence of particular microbes, these cheeses were prepared using a variety of methods, including one prepared under industrial conditions whilst another was prepared by hand.
“The cheeses were vacuum-packed and stored at 9°C until sampling,” the team wrote (ref).
“Following the acidification phase, we sampled the resulting cheddar cheeses in 5 time points over the one year period.”
The research team discovered that both bacteria species under investigation had important roles, but Streptococcus thermophilus was especially important.
“S. thermophilus has a crucial role in boosting Lactococcus growth and shaping flavour compound profile,” the authors noted in their study.
“While S. thermophilus had a 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.”
When L. cremoris was removed from the starter culture, four flavor compounds could be detected. These included 2,3-pentanedione (which gives the flavor of nuts, cream, and butter), along with heptanal and hexanal (fruity and fatty flavors). But when L. cremoris was present, another set of flavor compounds could be detected in higher amounts, particularly 2-methyl-3-thiolanone (a meaty flavor) as well as the esters, ethyl acetate and ethyl hexanoate (fruity flavors), according to the study authors.
Although I’m certain the scientists actually tasted their cheeses, the reported flavor profile was precisely identified by genome sequencing, and by analyzing small samples of the cheese to identify the compounds present.
Deciphering the particular contribution that each bacterial strain makes to the final flavor of a cheese is complex because of the multitude of biochemical reactions that each microbe strain carries out. Further, cheese flavor depends on the interactions between the many microbes present, which represents an important consideration for future applications — and will perhaps even help scientists design cheese microbiomes to improve existing cheeses as well as to develop new ones.
The authors point out that more experiments and research are needed, but they anticipate that in the future “artificial intelligence can be used to predict which organisms and in what quantities can produce desirable flavors.”
“Our results show how strain-specific metabolic interactions between microbes shape the biochemical profile of cheese, and provide targets towards the rational design and assembly of microbial communities with the aim of fine-tuning cheese flavour,” the team concluded.
Overall, the authors suggest their findings highlight the important role of competitive and cooperative microbial interactions in shaping the flavor of Cheddar and other cheeses.
Chrats Melkonian, Francisco Zorrilla, Inge Kjærbølling, Sonja Blasche, Daniel Machado, Mette Junge, Kim Ib Sørensen, Lene Tranberg Andersen, Kiran R. Patil & Ahmad A. Zeidan (2023). Microbial interactions shape cheese flavour formation, Nature Communications 14:8348 | doi:10.1038/s41467-023-41059-2