How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 7 October 2014

How to measure the texture of multi-textured foods

Biting into a soft-centred chocolateIt’s a routine part of every cuisine across the globe to introduce variety into the human diet through textures and flavours. 

One of the challenges of commercially manufacturing multi-textured foods is to keep the freshly created textures over a long period of time. Moisture and oil migration present difficulties and can result in a decrease of desirability as the expected sensory properties are altered. 

Some well-known multi-textured food examples include: pizza crust with sauce; ice cream in a crispy cone; baked pastry with fruit/meat filling; hard chocolates with liquid centres; chocolate covered nuts; and breakfast bars containing soft fruit.

The Kramer Shear Cell fitted to the TA.XTplus
The Kramer Shear Cell fitted to 
the TA.XTplus
What’s the Big Idea?
The confectionery market is perhaps the easiest industry in which to find multi-textured products. Food coatings and coextrusion methods result in a wide variety of dual- or multi-phase products in the confectionery sector. 

Chewing gum tablets, wafers, and layered biscuits are typical examples of food products which may be comprised of a crispy/crunchy exterior shell enclosing a soft viscous filler material of a different texture. Inherent differences in the physical state and compositions of the phases offer interesting textural variation to the consumer.

New Multi-Textured Products soon to reach the market
'Confectionery with Multiple Flavours and Textures' is a patent recently acquired by Intercontinental Great Brands. Disclosed are confectionery products having multiple flavours and multiple textures. More particularly, the confectionery products are multi-layered products comprising a powder interior with a particulate sweetener or a liquid region, a chewy confectionery composition at least partially surrounding the powder region/liquid region, and an outer coating. 

Two or more of the regions contain flavours; the flavours of each can be the same or different, and each region delivers the flavour at different time points, for different durations, at different intensities – or a combination thereof – as compared to the other regions. Furthermore, each region imparts a different physical sensation or texture. When consumed, the confectionery product exhibits a flavour sensation profile such that the consumer perceives multiple and different tastes and textures during the total chew time.

Upon consumption of the confectionery product, the powder region imparts a feeling of liquidity, which is perceived at the same time as a flavour imparted by the powder region, if flavour is used. The powder region dissolves quickly when exposed to mouth moisture such that there is no sensation of particulate matter; rather, the only sensation observed by the consumer is that of a liquid. 

Not wishing to be bound by theory, it is suggested that, upon chewing the confectionery product, the moisture of the mouth and the powder combine to result in a liquid material that has the combination of low viscosity and low surface tension such that the liquid material spreads over the tongue and contacts a large number of tongue taste receptors, thus providing an intense flavour sensation. The confectionery product also provides a mouth-watering effect, which is believed to come from the powder region quickly going into solution, thereby providing an intense liquid sensation.

This type of product is an exciting concept for both manufacturers and consumers but, when developing multi-textured products, the assessment of texture for each of these layers presents a more complex issue. It's not a problem for the TA.XTplus Texture Analyser. We've been asked this question many times before and have a number of product testing solutions.

What the testing solution?

To overcome the challenge of developing multi-texture properties in foods, most commercial products in the market are formulated with high fat levels to reduce water activity and soften the texture at high solids level, high levels of sugar and salt, polyols, film barriers, humectants etc. Measuring the success of these ingredients into the product formulation requires an objective quantified method of analysis.

In the case of dual-phase pockets (as featured in the paper by Samuel et al, 2007), the main focus of such an analysis is to differentiate between the textural properties of each phase. In order to monitor their textural quality, simple and rapid measurements are needed on the whole food. Differences in the mechanical properties of the shell and filler were used to deconvolute the textural differences between these two phases. 

Using a 2mm cylinder probe (or needle probe) attached to the Texture Analyser the multi textured products are often positioned on a holed base plate to provide the ability to penetrate through the entire structure of the sample The diagram shown depicts the working of the penetration probe and the corresponding force deformation curves for such products. The probe is effectively able to differentiate between the mechanical resistances offered by different phases. The force deformation curves show an increasing force, which is proportional to the length of the probe penetrating the firm material. Then, a sudden drop is observed, consistent with the resistance offered by the softer material. 

The increase in the force during the penetration of the softer material is much less pronounced, consistent with the properties of the softer material. The final part of the curve again shows a sudden increase in the force during deformation as expected from the firm material. The parameters derived from the force deformation curve of a penetration test in commercial pockets are shown in Figure ?

A Craft Knife (or Extended Craft Knife) has also proven suitable for the assessment of multi-layer products, due to their sharp, small contact area blade which allows the cutting of samples without the compressive action that a standard thickness blade would provide.  

Penetration test graphs for dual phase product
Above left: Different stages of a penetration test in a model pocket and the corresponding
pocket deformation curves. Right: Textural parameters derived from the force information
curve of the penetration on commercial dual-phase pocket.
Examples of multi-textured products: ice lolly, pie, apple, chewing gum
Examples of multi-textured products that can be successfully tested using various probes
on the Texture Analyser: 1: 2mm Cylinder probe; 2: Small Cylinder Probe; 3: Needle probe;
4: Craft Knife

Confectionery test graphs - chewing gum, chocolate caramel
Above left: Graph produced from cutting of chewing gum dragee using a craft knife.
Right: Graph highlighting different phases in a chocolate-filled caramel tested using
a 2mm cylinder probe.

Food Texture Design and Optimization book
Useful Literature that we recommend
‘Multi-textured foods’
is a chapter written by Arun Kilara and Tapashi Sengupta in the recently published book 'Food Texture Design and Optimization'
. The chapter considers moisture migration, its kinetics and effects on physical state of foods, methods of measuring moisture transfer and strategies to delay such undesirable changes. It also discusses an exhaustive survey of the effects of water, water activity and its role in texture modification of multi-textured foods and glass transition.

TA.XTplus texture analyser with bloom jar The
TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

To discuss your specific test requirements click here...

Watch our video about texture analysis Replicating Consumer Preferences
 Texture Analysis applications

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