It can be consumed as a dessert or used as an ingredient in food and cosmetics.
The work is published in the journal ACS Sustainable Chemistry & Engineering, and an illustration of the study is on the cover.
The scientists used honey from local stingless bees as an edible solvent to extract bioactive substances - including theobromine and caffeine, linked to heart health - from the cocoa bean shells. Normally, these shells are simply discarded in the production of chocolate and cocoa products.
The extraction was carried out using ultrasound: a probe, similar to a metal handle, was lowered into the mixture of honey and shells. The sound waves created microbubbles that collapsed and briefly raised the temperature, breaking down the plant material and helping the compounds to transfer into the honey. This method is considered a "green" technology: it is faster and more efficient than traditional methods and requires fewer resources.
Additionally, the honey was enriched with phenolic compounds with antioxidant and anti-inflammatory properties. According to Felipe Sanchez Bragagnolo, the first author of the paper, depending on the ratio of honey to cocoa shells, the product can have a distinct chocolate flavour, although full sensory tests are still to come.
For the experiments, honey from five bee species common in Brazil was used: borá (Tetragona clavipes), jataí (Tetragonisca angustula), mandaçaia (Melipona quadrifasciata), mandaguari (Scaptotrigona postica) and moça-branca (Frieseomelitta varia). Initially, the process was optimised on mandaguari bee honey, as it has intermediate values in terms of water content and viscosity. Then the fine-tuned scheme was applied to the rest of the samples. The authors emphasise that the method can be adapted to any available local honey.
Separately, the team evaluated the sustainability of the process using the Path2Green programme developed at UNICAMP. Twelve principles of green chemistry were taken into account, from logistics and post-processing to purification and application. The use of a local edible solvent that does not require additional preparation was a key plus factor. On an integral scale of -1 to +1, the technology received a score of +0.118.
The scientists believe that the compact ultrasonic equipment could be of interest to co-operatives and small businesses already working with cocoa and honey from local bees: such "chocolate" honey could become a high value-added product, including for haute cuisine.
The team is preparing new studies to evaluate the impact of ultrasound on the microbiology of honey. As with plant material, the method destroys the cell membranes of microorganisms, which could reduce bacteria and extend shelf life. This is particularly relevant for honey from stingless bees, which typically requires refrigeration, ripening, dehydration or pasteurisation and is worse stored at room temperature than honey from European bees (Apis mellifera).
In the future, the researchers plan to use honey from local bees as a natural solvent and to recycle other plant waste using ultrasound.
Maria Grynevych