For chocolate fans the taste is a key part of why they love the treat – but researchers now understand why the irresistible confectionery feels so good to eat.

Scientists decoded the physical process that takes place in the mouth when a piece of chocolate is eaten, as it changes from a solid into a smooth emulsion.

They suggest that where the fat lies within the chocolate helps to make the texture so appealing.

By analysing each of the steps, researchers at the University of Leeds hope their findings will lead to the development of luxury chocolate with the same feel and texture that is healthier to eat.

Essentially, guilt-free chocolate could be on the horizon.

When chocolate is in contact with the tongue, it releases a fatty film that coats the tongue and other surfaces in the mouth.

This makes it feel smooth the entire time it is in the mouth.

According to the study, when in the mouth the chocolate sensation arises from the way the chocolate is lubricated, either from ingredients in the chocolate itself or from saliva or a combination of the two.

Almost as soon as chocolate comes into contact with the tongue, fat has a key role to play.

After that, solid cocoa particles are released and they become important in terms of the tactile sensation.

Therefore, fat deeper inside the chocolate plays a somewhat limited role and could be reduced without the feel or sensation of chocolate being affected, the researchers suggest.

Anwesha Sarkar, professor of colloids and surfaces in the School of Food Science and Nutrition at Leeds, said: ‘Lubrication science gives mechanistic insights into how food actually 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 will still form droplets in the mouth and that gives you the chocolate sensation.

‘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.

‘We are showing that the fat layer needs to be on the outer layer of the chocolate, this matters the most, followed by effective coating of the cocoa particles by fat, these help to make chocolate feel so good.’

The study published in the ACS Applied Materials and Interfaces journal did not look at how chocolate tastes, and instead focused on feel and texture.

Tests were conducted using a luxury brand of dark chocolate on an artificial 3D tongue-like surface that was designed at the University of Leeds.

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

‘Our research opens the possibility that manufacturers can intelligently design dark chocolate to reduce the overall fat content.

‘We believe 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.’

The researchers believe the physical techniques used in the study could be applied to the investigation of other foodstuffs that undergo a phase change, such as ice-cream, margarine or cheese.

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