Sugar in soft drinks is often blamed for contributing to increased obesity. The first diet cola was introduced in 1959, but it has only been in the past couple decades that diet drinks have become increasingly popular, as consumers try to reduce their calorie intake by switching to no-cal and low-cal versions of their favourite soft drinks. 

However, the speed of this switchover has been slowed by one word: taste.

WHAT IS TASTE?

Although highly complex, taste can be seen as a triangle. The three corners are flavour, sweetness and texture. A change to any one of the corners affects the other two. When producing reduced-calorie beverages, manufacturers typically lower the sugar content.

It is common to add zero-calorie or low-calorie sweeteners to make up for the loss is sweetness. But swapping one sweetener for another alters the beverages taste in two ways. On one hand, it changes the flavour, so manufacturers add flavour modifiers to compensate for the loss of sweetness. On the other, it affects texture, prompting consumers to describe the drink as having a thin mouthfeel.

To address the problem of mouthfeel, manufacturers have for decades used rheology to measure the viscosity of the beverage and then made adjustments to the recipe, thinking that a thicker viscosity would remove the sensation of thinness. 

For example, gums are often added to diet beverages to create a level of viscosity on par with full calorie beverages. But in sensory testing, consumers complain that diet drinks still lack body or richness despite having greater viscosity. 

Rheology, it seems, does not offer a complete picture of mouthfeel.

UNDERSTANDING MOUTHFEEL

Mouthfeel refers to the tactile sensations perceived by the lining of the mouth, including the tongue, gums and teeth. Scientists working at the Cargill Global Food Research Group set about finding a new way to model mouthfeel that went beyond rheology, to more accurately mimic what goes on inside the mouth when a beverage is consumed.

Their work led them to realise that when you swallow, the tongue rubs against the teeth, gums and roof of the mouth. This creates friction, and the beverage has a lubricating effect between the tongue and the rest of the mouth, which affects mouthfeel.

But how do you measure lubricity?

ENTER TRIBOLOGY

The food research group borrowed technology from the most unexpected place: the automotive industry. Carmakers use a science called tribology to measure surfaces that interact together in relative motion, such as in automobile engines.

Tribology is a field of study in friction between two interacting surfaces relating to wearing, tearing and lubrication. The friction coefficient is the most important parameter of tribology measurements.

When two surfaces are in relative movement at a steady speed of V, the frictional force Fr in N can be expressed as Fr=μ x Fl. When a lubricant is applied, the friction coefficient is an effective indication of the lubricating status between the two surfaces.

Using tribology, Cargill scientists found that food texture perceived during the oral process has three dimensions: the degree of structure, the mechanical/rheological behaviour, the degree of lubrication, the oral experience or saliva participation, and the time, sequences of oral processing.

Using the findings, the scientists are able to predict and shape mouthfeel.

The results of their predictions have been confirmed by extensive sensory and consumer testing conducted at North Carolina State Universitys Sensory Science Center. 

The testing shows a direct connection between key mouthfeel sensations and consumer preference. It enables Cargill to create taste profiles based on consumer likings.

NO MORE HIT AND MISS

Until recently, creating new reduced calorie drinks has been a rather hit and miss process. There was no reliable way to predict how customers would react to the taste and mouthfeel of a new beverage formulation. 

Tribology technology, which takes into account all three corners of the taste triangle, enables the optimisation of the balance between the flavour, sweetness and mouthfeel of reduced calorie beverages to match the taste profiles preferred by consumers.

Lubricity is correlated to mouthfeel attributes and tribology can mimic lubricity dynamics, the way a beverage interacts with the mouth during the swallowing process. Mouthfeel measurement through tribology collects multiple data points to show the friction profile over time.

APPLICATIONS

An example of tribology application for beverage products is an evaluation done on lemon-lime soft drinks. A total of 18 commercial lemon-lime soft drinks, including 7Up, Diet 7Up, Fanta Lemon (Belgium), Fanta Zero (Belgium), Mountain Dew, Diet Mountain Dew, San Pelegrino Limonata, Sprite and Sprite Zero, were studied, with 10 of them being full calorie drinks, while the other eight were diet drinks.

The samples were evaluated on 28 attributes in quadruplicate by a panel of 11 trained professionals. The attributes include feeling factors, afterfeel, aromatics, flavour in mouth, basic taste and aftertaste. 

In addition, parameters such as viscosity, density, brix and pH values were measured.

By using Cargills Trilisse series texturisers, the lubricant gap between regular soft drink and zero calorie drinks can be reduced. The ingredient can modify the lubricant property of beverages with zero or low calorie content. 

Another example of tribology application can be found in dairy drinks. Theoretically, the higher the milk content in dairy drinks, the more lubricant property they have and the creamier, smoother and more slippery they will be in terms of mouthfeel.

Using solution from the company, the friction of 50 percent milk can be increased to values between that of 80 percent and 100 percent milk. The ingredient is able to improve mouthfeel by modifying the lubricant property. The tribology result is also consistent with that of inner sensory results.

The application of tribology technology in food and beverage enables manufacturers to deliver products with reduced sugar, calorie and milk content without any compromise on mouthfeel. The mouthfeel optimisation technology can ensure that a companys sensory promise to consumers is delivered.