Why chocolate feels so good: It’s all because of lubrication

Overview: Researchers have decoded the sensory processing mechanisms that make the sensation of eating chocolate so irresistible to most people.

Source: University of Leeds

Scientists have deciphered the physical process that takes place in the mouth when a piece of chocolate is eaten, as it turns from a solid to a smooth emulsion that many people find utterly irresistible.

By analyzing each of the steps, the University of Leeds interdisciplinary research team hopes it will lead to the development of a new generation of luxury chocolates that will have the same feel and texture, but will be healthier to consume.

During the moments when it is in the mouth, the chocolate sensation is created by the way the chocolate is spread, either by ingredients in the chocolate itself or by saliva or a combination of both.

Fat plays a key function almost immediately when a piece of chocolate comes into contact with the tongue. After that, cocoa solids are released which become important for the tactile sensation, so fat deeper in the chocolate plays a fairly limited role and can be reduced without affecting the feel or sensation of chocolate.

Anwesha Sarkar, professor of colloids and surfaces at the School of Food Science and Nutrition in Leeds, said: “Spear 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 .

“If a chocolate has 5% fat or 50% fat, it still forms droplets in the mouth and that gives you the chocolate sensation. However, it is the location of the fat in the composition of the chocolate that matters at each stage of lubrication and has rarely been explored.

“We show that the fat layer should be on the outer layer of the chocolate. This is most important, followed by effective coating of the cocoa particles by fat. These help chocolate feel so good.”

The study – published in the scientific journal ACS applied materials and interface – did not address the question of what chocolate tastes like. Instead, the research focused on the feel and texture.

Tests were carried out with 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 liquids interact, the degree of friction between them and the role of lubrication: in this case saliva or liquids from the chocolate. Those mechanisms all take place in the mouth when chocolate is eaten.

When chocolate comes in contact with the tongue, it releases a fatty film that coats the tongue and other surfaces in the mouth. It is this oily film that makes the chocolate feel smooth all the time it is in the mouth.

This shows chocolate truffles
During the moments when it is in the mouth, the chocolate sensation is created by the way the chocolate is spread, either by ingredients in the chocolate itself or by saliva or a combination of both. The image is in the public domain

Dr. Siavash Soltanahmadi, from the School of Food Science and Nutrition in Leeds and the lead researcher in the study, said: “With the understanding of the physical mechanisms that occur when people eat chocolate, we believe that a next generation of chocolate can be developed that and offers the sensation of high-fat chocolate, yet is a healthier choice.

“Our research opens up the possibility that manufacturers could intelligently design dark chocolate to reduce total fat content.

“We believe that dark chocolate can be produced in a gradient layer architecture where fat coats the surface of chocolates and particles to provide the sought-after self-indulgence experience without adding too much fat into the body of the chocolate.”

According to research by business intelligence firm MINTEL, sales of chocolate in the UK are expected to grow over the next five years. Revenue is expected to grow by 13% to £6.6 billion between 2022 and 2027.

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

financing: This project received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme.

About this sensory neuroscience research news

Writer: david lewis
Source: University of Leeds
Contact: David Lewis – University of Leeds
Image: The image is in the public domain

Original research: Open access.
“Insights into the Multiscale Lubrication Mechanism of Edible Phase Change Materials” by Anwesha Sarkar et al. ACS applied materials and interfaces

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Abstract

Understanding the multi-scale lubrication mechanism of edible phase change materials

Investigating the lubrication behavior of phase change materials (PCM) can be challenging in relative motion applications, e.gsports (skating), food (pralines), energy (cold storage), clothing (textiles with PCM), etc.

In oral tribology, a phase change often occurs in a series of dynamic interactions between the ingested PCM and oral surfaces of a to lick stage to one saliva-mixed stage on contact scales spanning micro (cellular), meso (papillae), and macro scales.

Often, lubrication performance and correlations across length scales and different stages remain poorly understood due to the lack of test rigs that mimic real human tissues.

Herein, we bring new insights into lubrication mechanisms of PCM using dark chocolate as an example on a single papilla (meso) shell and a full tongue (macro) shell uniting the solid, molten and saliva-mixed states, highly unifying advanced biomimetic mouth surfaces of on sight tribomicroscopy for the first time.

Unprecedented results from this study, supported by transcendent lubrication theories, show how the tribological mechanism in licking shifted from solid fat-dominated lubrication (low-salivary regimen) to aqueous lubrication (salivary-dominant regimen), the latter resulting in an increase in the coefficient of friction by at least threefold.

At the mesoscale, the prevailing mechanisms were cocoa butter bridging between entrapped cocoa particles and fat coalescence of emulsion droplets for the molten and saliva-mixed states, respectively.

At the macroscale, a distinctive hydrodynamically viscous film formed at the interface that controls the rate-dependent lubrication behavior indicates the salient importance of multi-scale analyses.

New tribological insights on different stages and scales of phase transition from this study will inspire rational design of next generation PCM and solid particle-containing materials.

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