Light micrograph of glucose crystals imaged with crossed polars.

The sweetness of glucose crystals (pictured) seems to be linked to the strength of chemical bonds glucose forms with nearby molecules. Credit: Stefan Ebhard/Wellcome collection

Physical chemistry

The bonds that set a sugar’s sweetness

Hydrogen bonds between sugar and nearby molecules help to determine the level of sweetness.

Sugars are thought to owe their sweet taste to the particular pattern of bonds that atoms in sugar molecules form with receptor proteins in taste buds. But most types of sugar have a similar arrangement of atoms, so why some taste sweeter than others has proved puzzling.

To study the molecules’ 3D structures, Maria Antonietta Ricci at the Roma Tre University in Rome and her colleagues scattered neutrons off three types of sugar dissolved in water. This allowed them to measure the length of particular bonds between sugar molecules and other molecules nearby. The bonds, known as hydrogen bonds, form between positively charged hydrogen atoms and electron-rich atoms such as oxygen.

The researchers found that fructose, glucose and mannose each formed hydrogen bonds of different lengths: sweeter-tasting sugars formed tighter, stronger bonds. The strength of the molecules’ hydrogen bonds may be the primary factor in determining a sugar’s level of sweetness, the authors suggest.