(CNN) – The inhabitants of Bronze Age desert tombs unearthed in what is now northwestern China they were buried with cheese spread over their heads and necks, perhaps as a snack for the afterlife.
A decade after the discovery of dairy products in surprisingly intact remains mummified by the arid conditions of the Taklamakan Desert, scientists have extracted and sequenced DNA from the 3,600-year-old cheese, the oldest in the archaeological record.
The analysis revealed how people at the Xiaohe burial complex made cheese, showing how humans harnessed microbes to improve their food and how microbes can be used to trace cultural influences through the centuries.
The findings, published Wednesday in the magazine cellopen a “new frontier in ancient DNA studies,” with this “type of research unthinkable even a decade ago,” said Christina Warinner, John L. Loeb Associate Professor of Social Sciences and Anthropology at Harvard University. Warinner was not involved in the investigation.
“Today’s fermented foods are overwhelmingly produced using only a handful of commercial strains of bacteria and yeast, mostly lab-grown,” he said.
“Little is known about the diverse range of inherited microbes that people used in the past to produce today’s most iconic foods, ranging from bread to cheese and from beer to wine.”
A team led by Chinese paleogeneticist Qiaomei Fu identified goat and cattle DNA in samples of the cheese. The researchers were also able to sequence the DNA of the microbes contained in the cheese, confirming that it was kefir, a type of cheese that is still widely produced and consumed today. Fu is director of the ancient DNA laboratory at the Beijing Institute of Vertebrate Paleontology and Paleoanthropology.
In the 1990s, hundreds of mummified individuals were found in what is known as the Xiaohe cemetery in the Tarim Basin, an inhospitable desert area in China’s Xinjiang region. Naturally preserved by dry desert air, their facial features and hair color are clearly discernible despite being up to 4,000 years old.
Buried in felt and woven clothing in unusual boat tombs, the so-called mummies of the Tarim Basin and their variety of cultural influences have long baffled archaeologists. Despite belonging to a genetically isolated group, individuals adopted new ideas and technologies, according to an October 2021 study.
The new research suggested that the Xiaohe people did not mix different types of animal milk when making kefir, a common practice in traditional cheese-making in the Middle East and Greece, although it is not clear why.
“The Xiaohe would have made the cheese in the same way that traditional producers make kefir cheese today, using previously made kefir grains (similar to kombucha mother or bread starter) that were passed down through the family. , friends and other social contacts,” said Taylor Hermes, an associate professor in the anthropology department at the University of Arkansas, who was not involved in the research.
“This is what makes the study so important: We can see how these microbial products were transmitted and spread throughout Asia,” Hermes said.
Fu’s team found that the three cheese samples from the tombs contained bacterial and fungal species, including Lactobacillus kefiranofaciens and Pichia kudriavzeviirespectively, both very common in current kefir grains. The grains are a mixture of probiotic bacteria and yeasts that ferment milk to obtain kefir cheese.
Fu and his colleagues also sequenced the bacterial genes of ancient kefir cheese, revealing information about how probiotic bacteria evolved over the past 3,600 years.
Currently, there are two main groups of bacteria Lactobacillus: one that originated in Russia and another in Tibet, an autonomous region of China, according to the study. The Russian type is widely used around the world, including in the United States, Japan, and European countries, to make yogurt and cheese.
When Fu and his colleagues compared the Lactobacillus kefiranofaciens of ancient kefir cheese with the modern species, they found that it was closely related to a less common group of Lactobacillus which originated in Tibet.
The origin of the bacteria challenges the long-held belief that kefir originated only in the Caucasus Mountain region, Fu said.
“This is an unprecedented study that allows us to observe how a bacteria evolved over the last 3,000 years. Furthermore, by examining dairy products, we have gained a clearer picture of ancient human life and its interactions with the world,” Fu said in a statement. “This is just the beginning.”
It was remarkable that not only had the cheese survived, but that it was possible to sequence the food’s DNA, Hermes said. “The analysis of ancient DNA, especially from microbes, is plagued by technical problems, mostly arising from contamination by modern bacteria,” he added.
When did cheese making really start?
It’s not surprising that the Xiaohe fermented cheese, Warinner said. The process made the milk easier to digest, while the microbes generated lactic acid, causing the milk to curdle and become the base for cheese.
“In the absence of refrigeration, it is essentially impossible to store milk for more than a few hours with spontaneous fermentation, so there was probably never a time when milk and dairy products were used without fermentation,” he said.
“However, over time people became increasingly better at controlling fermentation and selecting specific microbes that produced the most desirable effects in the production of dairy products,” he added.
While the dairy product found with the mummies is the oldest intact cheese in the archaeological record, other evidence, such as animal proteins in human dental calculus and milk residue on pottery, suggests that cheesemaking originated much earlier. , probably more than 9,000 years ago in Anatolia or the Levant, Warinner noted.
The genomic analysis the team performed was truly groundbreaking, said William Taylor, associate professor of anthropology at the University of Colorado at Boulder and curator of archeology at the school’s Museum of Natural History.
“It’s amazing to see the complexity of the products that people made, which is not normally preserved in the archaeological record,” said Taylor, who was not involved in the research.
“These incredible finds show us that cheese and other dairy products were really the basis of an entire lifestyle that would remain important for millennia and is still an important part of life today.”
