The oldest samples of cheese found to date were in an unexpected place: the necks and heads of several mummies from China’s Tarim Basin, dating back about 3,600 years. The discovery is published Wednesday in a paper in the journal cellin which a team of researchers from the Chinese Academy of Sciences describes how they managed to extract and analyze the DNA of this substance which turned out to be kefir cheese, a curious mixture similar to cottage cheese whose composition serves to shed light on the evolution of probiotic bacteria.
“This is the oldest sample of cheese discovered in the world,” says Qiaomei Fu, lead author of the work, who insists to elDiario.es that it is a cheese made from kefir and not kefir. “Foods like cheese are extremely difficult to preserve for thousands of years, which makes this a unique and valuable opportunity. “The in-depth study of ancient cheeses can help us better understand the diet and culture of our ancestors.”
Cow and goat milk
Archaeologists who examined the mummies about two decades ago suspected that the mysterious white substances smeared on the heads and necks of several mummies found in the Xiaohe Bronze Age cemetery might be some type of fermented milk product, but they couldn’t identify what exactly it was.
A 2015 paper had already pointed to the possibility that it was cheese, but advances in ancient DNA analysis techniques have now allowed the authors to identify genetic material from cows and goats in the samples and confirm that the white substances were in fact kefir cheese. The analysis allows them to learn that the ancient Xiaohe people used different types of animal milk in separate batches, a practice different from the mixing of milk types common in cheesemaking in the Middle East and Greece. And they also found that the samples contained bacterial and fungal species, including Lactobacillus kefiranofaciens And Pichia Kudriavzeviiwhich is found in today’s kefir grains.
The discovery is an apparent double mystery, because it is not known how this white cheese could have reached the mummies, in a region of the planet where populations are lactose intolerant and have not developed the ability to digest dairy products, contrary to what is known in parts of Europe and Africa.
The secrets of dairy fermentation
Kefir grains are symbiotic cultures that contain several species of probiotic bacteria and yeast that ferment milk into kefir cheese, much like sourdough. By sequencing the bacterial genes in ancient kefir cheese, the team was able to trace the evolution of probiotic bacteria over the past 3,600 years, comparing ancient genes Lactobacillus kefiranofaciens old kefir cheese with current species.
Currently, there are two main groups of bacteria Lactobacilli: one from Russia and one from Tibet. The Russian variety is the most widely used in the world, especially in the United States, Japan and European countries, to make yogurt and cheese. The team found that the Lactobacillus kefiranofaciens In the samples, it was most closely related to the Tibetan group, contradicting the long-held belief that kefir originated only from the mountainous North Caucasus region in present-day Russia.
This is a unique study that allows us to observe how a bacterium has evolved over the last 3,000 years.
Fu Qiaomei
— Paleogeneticist and main author of the work
“Our observation suggests that kefir culture has been maintained in the Xinjiang region of northwest China since the Bronze Age,” Fu says. The study also reveals how Lactobacillus kefiranofaciens have exchanged genetic material with related strains, improving their genetic stability and milk fermentation capabilities over time. Compared to the old LactobacilliModern bacteria are less likely to trigger an immune response in the human gut. This suggests that genetic swaps also helped Lactobacilli to better adapt to human hosts over thousands of years of interaction.
“This is a unique study that allows us to observe how a bacterium has evolved over the last 3,000 years,” he concludes. “By examining dairy products, we have gained a clearer picture of ancient human life and its interactions with the world. “This is just the beginning, and with this technology we hope to explore other previously unknown artifacts.”
Regarding the presence of this dairy product in the mummies, Fu believes that it was a very important food for their daily lives, just like wheat, which also appears in the burials. And regarding the adaptation to lactose, let’s remember that the strain we have here corresponds to that of Tibet, a region of Asia where adaptation to the consumption of dairy products actually occurred. “The reconstructed ancient strains are at the base, which suggests an additional route of diffusion of kefir production technology from Xinjiang to the interior of East Asia through technocultural exchanges,” he explains to elDiario.es.
A form of cottage cheese
For geneticist Carles Lalueza-Fox, a specialist in ancient DNA and director of the Museum of Natural Sciences in Barcelona who was not involved in the study, this is a new and original application of ancient DNA techniques. “The authors were able to recover from 3,600-year-old kefir not only the DNA of the goats that produced the milk, but also the genome of the bacteria.” Lactobacilli used in fermentation,” he explains. Since ancient times, people have been looking for ways to preserve food, whether by smoking, salting or fermenting it, recalls Lalueza-Fox. “Kefir, fermented milk, was used in Asian cultures where the mutation that allows lactose to be digested in adulthood is almost absent,” he concludes. This work is proof, according to him, that “these bacteria, domestic animals and us, have co-evolved thanks to food.”
These bacteria, pets and us co-evolved through diet
Carles Lalueza-Fox
— Specialist in ancient DNA and director of the Museum of Natural Sciences in Barcelona
For Miriam Cubas, a researcher at the Department of Prehistory at the University of Alcalá de Henares (UAH), what they call “cheese” in the article would be a kind of “drained kefir”, which we could understand in our culture as a kind of cottage cheese. “The evidence of the consumption of dairy products, especially those from livestock, has been well known in Europe for 8,000 years,” he emphasizes. Although this evidence is indirect and comes mainly from lipids preserved in Neolithic ceramic vessels, in this case it is based on the analysis of visible remains of “cheese” recovered from two burials. “This article opens a promising line of research aimed at identifying the bacteria responsible for the fermentation of dairy products based on the genetic sequencing of the bacteria themselves, the agents and the causes of the fermentation process,” concludes the specialist.
