Researchers Select Microbes to Improve Chocolate


It may seem hard to imagine improving on the world’s best chocolates, but that is the goal of a team of microbiologists from the Free University of Brussels, Belgium. Raw cocoa beans have an astringent, unpleasant taste, and must be cured—which involves fermenting the beans—prior to drying and roasting. The Belgian researchers aim to improve the fermentation process, as well as the taste and health benefits of the resulting chocolate, by optimizing a microbial starter culture. The research is published in the December 2010 issue of the journal Applied and Environmental Microbiology.


Creating chocolate from the beans within the raw cocoa pods, which have roughly the size and shape of rugby balls, is a multistep process. The farmers open the pods manually, depositing beans and pulp in heaps of roughly 150 kg onto banana leaves or into boxes, to ferment in the sun, for up to six days, says corresponding author Luc De Vuyst, of the Free University of Brussels. First, yeast ferment sugars to ethanol. Next, lactic acid bacteria convert citric acid and any remaining sugars to lactic acid, and acetic acid bacteria convert ethanol to acetic acid. Acetic acid then penetrates the cocoa beans, releasing enzymes and substrates within to interact with each other, forming the precursors of the chocolate flavor. Only then are the beans dried, and then transported to chocolate companies, where they are roasted, converting the precursors to flavors


In their quest for a superior starter culture, the researchers are conducting fermentation experiments to investigate growth and metabolite production using strains of lactic and acetic acid bacteria which they isolated from fermentation heaps from different locations. (They showed that the species composition of the fermentation heaps is identical regardless of location of origin, although bacterial strains vary from place to place.) Since the times which fermentation experiments can be carried out onsite are limited to two short growing seasons, and travel from Belgium to Africa or South America is dear, the researchers have developed a cocoa bean pulp simulation medium so that they could conduct their experiments in their laboratory.


“We were able to determine the role of specific bacteria during the fermentation process,” says De Vuyst. “In this way, we can select certain strains of the most relevant bacterial communities to use as starter cultures in later experiments in the jungle. For example, one species of acetic acid bacteria was notable for its ability to oxidize ethanol and lactic acid, its general tolerance of acidity, and its moderate heat tolerance, he says. We hope not only to improve the fermentation process, but also to improve the flavor, and health benefits of chocolate.”


“Note that the best chocolates of the world are already produced in Belgium,” brags De Vuyst. “But we want to produce even better and more diverse chocolates.”


(T. Lefeber, M. Janssens, N. Camu, and L. De Vuyst. Kinetic Analysis of Strains of Lactic Acid Bacteria and Acetic Acid Bacteria in Cocoa Pulp Simulation Media toward Development of a Starter Culture for Cocoa Bean Fermentation . Appl. Environ. Microbiol. 76: 7708-7716.)