Scientists have used bacteria to turn the leftover sugars and acids from Greek yogurt into molecules that could be used in bio-fuels or safe feedstock additives. Waste whey from Greek yogurt production is made up mostly of the familiar milk sugar lactose, the fruit sugar building block fructose, and the fermentation product lactic acid.
Researchers at Cornell University in the US and the University of Tubingen in Germany used bacteria to turn this mixture into an extract containing two more useful compounds: caproic acid (n-hexanoic acid) and caprylic acid (n-octanoic acid). Both of these compounds are ‘green antimicrobials’ that can be fed to livestock in lieu of antibiotics.
With energy needs in mind, further processing could stitch the six-, seven-, and eight-carbon backbones of the obtained molecules into the chains of up to 14 needed to qualify as ‘drop-in’ biofuels for jet fuel. Both options have economic and social allure, researchers said.
“The agricultural market might seem smaller, but it has a very large carbon footprint, and turning acid whey into a feedstock that animals can eat is an important example of the closed cycles that we need in a sustainable society,” said Lars Angenent, senior author of the study published in the journal Joule.
“The fuel market, of course, operates at a lower price, but its demand is virtually unlimited,” said Angenent. Traditionally, suppressing oxygen while feeding biodegradable waste to microbes results in the production of methane-rich gas through anaerobic digestion.
Instead, the researchers strung together two ‘open-culture’ reactors – the first tuned for heat-loving microbes fond of temperatures of 50 degrees Celsius, the second set at a more welcoming 30 degrees Celsius mark.
After seeding each reactor with a previously studied microbiome, and opening the setup to the acid whey and its own rich assortment of bacteria (such as common gut microbiota from the Lactobacillus family), caproic acid, caprylic acid, and other minor products could be continually extracted over a period of several months.