The chemistry of taste – why sugar is sweet, and what makes some sugars sweeter than others

Sugar in its many naturally occurring forms is the original source of sweetness, one of the five fundamental tastes that bring flavour to food and drink. But how does our body recognise sweet tastes, and why are some sugars more intensely sweet than others? In this blog, we explain the chemistry behind taste and recent advances in our understanding of why some sugars are sweeter than others.   

Taste is a collection of sensations transmitted to our brain through sensors mostly in our mouth, nose and throat. As many of us perceive flavours through the appearance and texture of what we consume, for a truly holistic taste experience those sensors arguably include our eyes, fingertips and even ears. There’s nothing quite like that cracking sound when a spoon breaks the sugar crust of a classic crème brûlée, meaning that exquisite, sweet vanilla flavour is not far behind.

The taste sensors in the mouth, nose and throat are triggered by chemical signatures found in food and drink, which in turn send signals to our brain telling us ‘that’s sweet’, that’s sour’ or, more often, ‘that’s apple flavoured’. The taste sensors are mostly our taste buds, which are found in small bumps, called papillae, on the tongue’s surface at the back of the throat and the top of the oesophagus (gullet).

We also use sensors in our nose to augment that taste experience. Some of the sensors we use for taste are not taste buds, but they detect touch and temperature, and behave in the same way as pain sensors elsewhere on the body. These detect, for example, hot and spicy tastes that could cause damage to our body.

Adults can have between 2,000 and 8,000 taste buds, found in differently-shaped papillae. The papillae shapes, and the shape of the tongue and mouth, are all specifically designed to efficiently channel substances into the taste buds, which are made up of collections of sensory cells.

The substances we eat and drink are collections of molecules of various shapes and sizes, and with chemically-active components. When these molecules are channelled into our taste buds, they are recognised by specific sensor cells, or receptors, triggering chemical reactions in the sensor cell.

This triggers other cells to send signals to our brain via nerve cells. A taste cell may have a receptor optimised to recognise sodium chloride (NaCl), so when that molecule hits the receptor, it reacts to send the ‘salty’ message. Our brain processes this collection of messages from the various taste receptors in our mouth, throat, nose, ears and other places into flavours and taste, generating that holistic taste experience.

The brain then triggers our body to prepare for food, which may be the production of saliva and stomach acids to digest it efficiently. This is why we get phrases like ‘mouth-watering flavours’ because some flavours may trigger us to produce more saliva in anticipation of the nutrients arriving.          

There are five basic flavours that make up taste: sweet, sour, salty, bitter and savoury, also known as umami. The latter is related to specific proteins found in what most of us perceive as ‘savoury food’. Ongoing research into taste is exploring the possibility that there are more basic tastes, such as receptors that recognise fats and alkaline substances, like brine and metallic flavours.  

These basic tastes are the result of evolutionary hard-wiring and determines how we perceive taste and flavour. Each taste represents a grouping of chemical substances, usually with a specific molecular structure or active molecule, that the receptors in taste bud cells recognise as ‘sweet’, ‘salty’, ‘bitter’ and so on.

Sweet-tasting substances will usually contain carbohydrates such as sugars. Those commonly found in foods include sucrose, glucose, fructose, galactose, dextrose, lactose, maltose and agave nectar.

However, there are other naturally occurring substances that also trigger receptors which recognise sweet flavours to send a signal to our brain saying ‘sweet’. These include sugar alcohols, or polyols, found in fruit juices and alcoholic drinks, and certain amino acids trigger the sweetness receptor in taste buds.

Artificial sweeteners are molecules that have been specifically designed in a laboratory to mimic the structure or activity that a naturally sweet substance exhibits to trigger the same result in our taste buds. 

There are two specific receptors, or sensors, in the taste bud that detect sweet-tasting molecules: T1R2 and T1R3. They are often put together and referred to as the T1R2/T1R3 sweet taste receptor. Receptors are proteins – complex collections of molecules which chemically react with other specific molecules. Or put another way, the receptor is like a space in a jigsaw puzzle awaiting a specifically shaped food molecule that fits it.

The specific shape of parts of a sugar/artificial sugar molecule or polyol fits into what are called binding pockets in the receptor (the space in the puzzle). As the name suggests, the process chemically binds the sugar molecule to the receptor protein molecule. This binding reaction starts the process of sending the message to the brain saying ‘this tastes sweet’.

Different types of sugars can have varying levels of sweetness. For example, when refined white crystalline sugar, disaccharide sucrose, is dissolved in a solution and broken down via the inversion process it becomes fructose and glucose (read about the inversion process on our invert sugar syrup product page). We routinely apply the inversion process in the Ragus factory to create invert sugar syrup and partial invert sugar syrups, such as golden syrup.

Invert sugar syrups are used in a wide variety of food and beverage applications. When most of the sucrose has been inverted into fructose and glucose, the resulting syrup is known as a full invert. This syrup is typically 40% sweeter than sucrose and the intense sweetness is ideal for soft drinks and fondants (fully inverted sugar syrup has many other qualities other than sweetness that make it such an effective ingredient). A partial invert, such as golden syrup, is 20% sweeter than sucrose because less of the original sucrose is inverted into fructose and glucose.

So, why does some sugar taste sweeter? According to relatively recent research, it has to do with the interaction of water molecules with the sugar and the length of the hydrogen bonds between the sugars in solution and water molecules. The shorter the bond, the higher the sweetness.

When you drink a sugary soft drink, the fructose molecule that’s in a solution of the soft drink and saliva forms bonds with the hydrogen in that solution. It is channelled by the shape of the tongue and the taste buds into the T1R2/T1R3 receptor, and because it is in the shape of a sugar molecule, it fits neatly into the binding pocket in the receptor.

Because fructose forms those shorter bonds, the receptor tells the brain that ‘this is a really sweet drink’. Exactly why shorter bonds are interpreted by the receptor as being sweeter is not yet known, but it does help us understand why different levels of fructose, or other sugar molecules, results in varying intensity of sweetness.

Ragus supplies high-quality pure sugar syrups and crystalline sugars to industrial food and beverage producers that enhance product tastes, textures and appearance. Our pure sugars always fit neatly into the T1R2/T1R3 receptor binding pocket.

To learn more about our pure sugar products, contact our Customer Services Team. For more sugar news and Ragus updates, keep browsing SUGARTALK and follow Ragus on LinkedIn.