Fat & lubrication: Scientists explore what happens in the mouth when chocolate is consumed

13 Jan 2023 --- Scientists have decoded the physical process when a piece of chocolate is eaten, as it changes from a solid into a smooth emulsion in the mouth. The researchers found that what makes chocolate “feel so good” is not necessarily the amount of fat, but where it’s placed in the product and how it interacts with saliva.

By analyzing each of the steps, the interdisciplinary research team at the University of Leeds, UK, hopes to develop a new generation of luxury chocolate that will have the same melt-in-your-mouth feel and texture but be healthier to consume.

The sensation of chocolate arises from how it is lubricated, either from ingredients in the chocolate itself or from saliva or a combination of the two. 

Speaking to FoodIngredientsFirst, Anwesha Sarkar, professor of colloids and surfaces in the School of Food Science and Nutrition at Leeds, discusses how lubrication levels vary from person to person. 

A confocal microscope image of molten dark chocolate. (Photo credit: Dr Siavash Soltanahmadi.)“Tongue papillae are different in size, shape and distribution. Saliva is also different and varies not only between individuals but also on many factors, time of day, exposure to food and so on. Indeed, saliva impacts the lubricity.”

The science behind the fat
Fat plays an essential function almost immediately when a piece of chocolate is in contact with the tongue. After that, solid cocoa particles are released, and they become important in terms of the tactile sensation, so fat deeper inside the chocolate plays a relatively limited role and could be reduced without impacting the feel or sensation of chocolate. 

“Lubrication science gives mechanistic insights into how food feels in the mouth. You can use that knowledge to design food with better taste, texture or health benefits,” Sarkar continues.  

If chocolate has 5% or 50% fat, it will still form droplets in the mouth, giving you the chocolate sensation that people know and love. However, it is the location of the fat in the make-up of the chocolate which matters in each stage of lubrication, and that has been rarely researched, she underscores. 

“We are showing that the fat layer needs to be on the outer layer of the chocolate, which matters the most, followed by an effective coating of the cocoa particles by fat, this helps to make chocolate feel so good.”  

The study – published today in the scientific journal ACS Applied Materials and Interfaces – did not investigate how chocolate tastes. Instead, the investigation focused on its feel and texture. 

Analytical techniques 
Tests were conducted using a luxury brand of dark chocolate on an artificial 3D tongue-like surface designed at the University of Leeds. The researchers used analytical techniques from a field of engineering called tribology to conduct the study, which included in situ imaging. 

Tribology is about how surfaces and fluids interact, the levels of friction between them and the role of lubrication: in this case, saliva or liquids from the chocolate. Those mechanisms are all happening in the mouth when chocolate is eaten.  

When chocolate is in contact with the tongue, it releases a fatty film that coats the tongue and other surfaces in the mouth. This fatty film makes the chocolate feel smooth throughout the entire time it is in the mouth.  A confocal microscope showing the structure of the molten chocolate mixed with saliva after it has experienced forces that mimic the eating. (Photo credit: Dr Siavash Soltanahmadi.)

Dr. Siavash Soltanahmadi, from the School of Food Science and Nutrition at Leeds and the lead researcher in the study, says the research could help develop next generation chocolate. 

Soltanahmadi believes this research allows manufacturers to design dark chocolate to intelligently reduce the overall fat content.  

“Dark chocolate can be produced in a gradient-layered architecture with fat covering the surface of chocolates and particles to offer the sought-after self-indulging experience without adding too much fat inside the body of the chocolate,” he explains. 

The researchers believe the physical techniques used in the study could be applied to the investigation of other foodstuffs that undergo a phase change, where a substance is transformed from a solid to a liquid, such as ice cream, margarine or cheese.  

Sarkar adds that the researchers are “not only working on sweet food applications but also various kinds of food with a multitude of textures, including plant-based foods.”

“We are working more on tactile aspects, i.e., mechanoreception, as we believe this has received relatively little attention and requires more work because most food aversion and liking comes from texture,” he concludes. 

By Elizabeth Green