There are many of us that have a ‘sweet tooth,’ but what is sweet enough for one person might be too sweet for another. Thus, this ability to recognize the sweetness of a substance is crucial for the survival of humans to help us better control caloric intake and develop a preference for certain foods and tastes.
However, the range of subjective variability makes it difficult to fully quantify what level of sweetness fits the ‘goldilocks principle’ (just right the right amount). This means that for food and beverage manufacturers, finding an objective method to identify the true ‘sweet spot’ is crucial for their product development.
Now, a team of researchers based in Korea have developed an extremely sensitive bioelectric tongue that mimics human taste buds and can objectively measure varying levels of sweetness. Published in the journal ACS Applied Materials and Interfaces, the team reported how their device was able to evaluate the inhibition and enhancement effects on sweet taste receptors.
Venus Flytrap Domain
During the development of the bioelectric tongue, the researchers set out to replicate the primary ligand-binding domain of a human sweet taste receptor known as the venus flytrap domain or T1R2 VFT.
The bioelectric tongues that have been manufactured in the lab previously have lacked the ability to fully replicate human tongue functionality and are often complicated to make. The sweet taste receptors on a human tongue are two large complex domains (the venus flytrap domain) that bind to sugar compounds.
Borrowing its name from the venus flytrap plant due to its resemblance with the plant’s leaves, the hinged two-lobed molecular structure on the human tongue interacts with the sweet and sugar compounds a person consumes – carbohydrates, the main energy source of the human diet.
Our T1R2 VFTfunctionalized bioelectronic tongue device could be used to detect sweet substances with a concentration down to 0.1 fM in drink samples such as apple juice and chamomile herb tea. It indicates a 107 times higher sensitivity compared with previously reported sweet taste sensors.
Corresponding Authors Tai Hyun Park and Seunghun Hong, Seoul National University, Korea
As carbohydrates are a key part of the human diet, they play a key role in a wide range of physiological processes, from energy storage to helping regulate the immune system as well as cell development. However, an excess of carbohydrates in a diet can lead to the formation of chronic diseases such as hypertension, obesity and diabetes.
A Powerful Tool
Therefore, ensuring appropriate amounts of sugars in the products we consume, including in food and pharmaceuticals, is key to controlling the appropriate carbohydrate intake for maintaining human health.
While there are methods for evaluating sweet substances and sugars in products, limitations do exist as slow test speeds, and deviations in taste sensitivity occur. From human sensory evaluation to high-performance liquid chromatography, it is difficult to mimic the human taste system fully and objectively.
In the study, the researchers used bacteria to make their venus flytrap domain and then attached them to a gold electrode. By connecting multiple gold electrodes together using carbon nanotubes, they were able to fabricate their device.
When the device came into contact with naturally sweet solutions, the response to solutions was decreased down to the 0.1 femtomolar level – this is 10 million times more sensitive than previous bioelectronic sensors.
The results indicate that our sensor could discriminate sweet substances from other tastants with a high selectivity just like a human tongue.
Seunghun Hong, Seoul National University, Korea
The device was able to detect sweet substances in commercial beverages, including apple juice and chamomile tea. However, the device did demonstrate some limitations when cellobiose (a tasteless sugar) was introduced.
The sweet taste bioelectric tongue could be a powerful tool for various applications in the food and pharmaceutical industry, can be stored for long periods of time and used repeatedly.
The team stated that further work would be needed to evaluate the effectiveness of this method on other domain receptors.
References and Further Reading
Jeong, J. and Cha, Y., et al., (2022) Ultrasensitive Bioelectronic Tongue Based on the Venus Flytrap Domain of a Human Sweet Taste Receptor. [online] ACS Publications. Available at: https://pubs.acs.org/doi/abs/10.1021/acsami.1c17349