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

Tuesday 24 March 2020

Making up for Texture in Egg Free Food

The rise in demand for a plant based diet brings with it a wide range of challenges. However, there is one ingredient in particular that can cause big problems in its absence: the humble egg. 

Eggs play an important part in a lot of cooking because they have so many interesting functions. They can add shine to the top of pies, emulsify sauces, aerate chocolate mousse and add moisture and fat to cake.

When a whole egg is used in a recipe, they combine the individual properties of the yolk and white. They emulsify, bind ingredients and solidify when heated to provide mechanical support. When sugar is added, eggs are excellent at trapping air, adding lightness to a recipe. Whole eggs are used in waffles, brownies, muffins, cookies and sponge cake to name a few. The components of an egg may be used separately, too. When an egg white is whipped, it forms a stable foam. This is useful in macarons, marshmallows and meringues. A yolk, when used alone, exploits its high fat content and emulsification properties. Yolks are used alone in ice cream, custard, creme brulee and pastry cream.

Vegans have long been replacing eggs in their cooking with weird and wonderful ingredients. Now most supermarkets have a ‘plant based’ aisle, manufacturers have caught up with the home cooks and are selling products made with replacement ingredients, or else adjusted recipes. Egg free does not necessarily mean a product is vegan – dairy products may be included for those following an egg free diet. As with any new food product, it is crucial that its texture is tested thoroughly before it is released onto the market, or else it will be passed over in favour of a brand who have carried out the necessary research and set the golden standard.

The first product that springs to mind as ‘impossible without eggs’ is meringue. However, egg free meringue is made a possibility by the fact that chickpea water, otherwise known as ‘aquafaba’, forms into soft peaks when whipped, just like egg whites. The most important attribute of a meringue is its crispness. As meringues often come in irregular shapes, their crispness is most easily measured using a penetration test. A 2mm cylinder probe allows multiple test sites on the same sample, and is best applied to areas with a flat surface. A crisp meringue will show a definite force peak with a sharp drop off; a flaccid meringue will show a more gradual peak.
Volscan Profiler C
Volscan Profiler C

Eggs help to give brioche its fluffy texture, rich flavour and yellow colour. They can be replaced, however, with the addition of buttermilk and yellow food colouring, but this can compromise the fluffiness of the loaf, impacting both its softness and volume. Brioche volume can be measured using a simple measurement in the Volscan Profiler within 30 seconds. This is a benchtop laser-based scanner that measures the volume, density and dimensional profiles of solid products. 

Bread V Squeeze Rig
Brioche softness is often tested by the consumer in-store by squeezing it between the thumb and fingers, creating a ‘V’ shape with the hand. The Bread V Squeeze Rig imitates this process and allows the bakery’s R&D department to perform repeatable, scientific analysis of the freshness and appeal of bread products. Its V-shaped ‘fingers’ are pressed into a packaged or unpackaged loaf, and the force required to compress the bread is measured. Post-test calculations are then used as an indication of freshness – the lower the force and higher the value of springiness, the fresher the loaf. This non-destructive test offers simplicity and speed as the loaf requires no sample preparation and can be analysed within its packaging.

Compression test
Compression test 
In a similar vein, sponge cake relies on eggs for its richness and structure, although some recipes call for golden syrup or even vinegar replacements. As its name suggests, springiness is of high importance in a sponge cake – when squeezed, it should push back and return back to its original size. This property can be measured using a relaxation test, during which the Texture Analyser compresses a sample by a specific amount over a given time period. The analysis capabilities of Exponent software allow the springiness to be calculated from the force-time graph.

Three Point Bend Rig
Three Point Bend Rig
Although a crisp English biscuit rarely contains any eggs, its chewy American counterpart relies on them. This chewiness is difficult to replicate, but careful research and recipe control can give success. This usually calls for a recipe adjustment (in the form of increased water and fat contents) rather than an additional ingredient. A three-point bend test is a quick and simple way to assess chewiness. Unlike the desired sudden force drop in a meringue penetration test, a three-point bend of a chewy cookie should show a shallow profile, just as a customer would feel a gradual increase in force as they tear it in half between their hands.

TTC Spreadability Rig
Moving into the realm of semi-solids, both eggless pastry cream and eggless mayonnaise can be bought in specialist shops. Pastry cream replaces eggs with custard powder or potato starch; mayonnaise can use thickened soya milk. In both cases, their consistency should be soft and smooth. As mayonnaise is generally used as a sauce base or spread thinly on sandwiches, it has a lower viscosity than pastry cream (which must hold its shape), so their tests will not necessarily be the same. Pastry cream is well-suited to the TTC Spreadability Rig, which holds a small volume of sample in a female cone and displaces it completely with a male cone. This has the added advantage of measuring the sample’s adhesiveness during the unloading period. 

Mayonnaise is often tested using the Back Extrusion Rig. This rig is comprised of a sample container that is centrally located beneath a disc plunger. The disc plunger performs a compression test, which extrudes the product up and around the edge of the disc. This test measures the consistency of viscous products. Using the back extrusion principle (i.e. using a disc on the probe adapter) the consistency can also be determined directly in containers straight from the production line. This rules out pre-stressing of the material caused by transfilling; this cannot usually be avoided when using other methods.

The ‘egg free’ concept is such an important area of research that Campden BRI, who provide the food industry with scientific, technical and advisory services, have a new ‘club’ dedicated to egg replacements, with the aim of finding the most suitable replacement for each product category based on an increased understanding of the mechanisms of plant-based egg replacements. 

To learn about Texture Analysis techniques for your egg free range, contact Stable Micro Systems today.

We can design and manufacture probes or fixtures for the TA.XTplusC texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

TA.XTplus texture analyser with bloom jarThe
 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!

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