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

Monday, 19 June 2017

Texture tricks – using Hydrocolloids to create Textural Sensations

Texture is magical. The way a food “feels” affects the way we perceive its appearance, aroma and taste. 

And while manipulation of mouthfeel can seem mysterious, many tricks can help developers create and maintain the perfect texture – be it real or illusion. The following excerpts are from an original article written by R. J. Foster, and is a gem for those interested in the incorporation of hydrocolloids and their effect on texture. 

The texture effect  
Consumers rely on texture as an indicator for many different qualities of the foods they eat. Some textures might imply a lack of freshness: carrots that are soft or limp, bread that is hard, or a stick of chewing gum that crumbles...

In other instances, texture becomes the pivotal characteristic on which consumers base their preferences. They may love the flavour of banana bread, but not be able to eat a plain old banana, because of the soft texture.

Many people love ketchup on a burger, whereas a slice of raw tomato draws only a “no thank you.” Crackers should be hard and crunchy, but not bread. A survey of pickle consumers revealed that 90% of respondents define a good pickle as “crisp, firm and hard.”

Texture can be defined by a number of characteristics, including viscosity, smoothness, softness, hardness, rigidity and elasticity. In addition to, and perhaps even beyond, a product’s texture, is the mouthfeel, measured in terms of dryness, lubricity, smoothness, sandiness or fluffiness. Any one of these terms might represent a person’s impression of texture, but it is really a combination of pieces that interact to complete the texture puzzle. The multifaceted nature of texture is what makes quantifying and reproducing it so difficult. 

Just gellin’
Gels form when molecules of a given gelling agent interact to form three-dimensional networks. The texture of a gel is difficult to define, as the perceived mouthfeel rests not in a single moment, but every moment of consumption – the way the product breaks during the first bite, how it shatters or smears across the tongue and palate during mastication, and how long it takes to reduce the product from its original size, shape and consistency to that which is swallowed. And the characteristics that affect the perception at each of these stages of consumption are numerous.

 “Means of gelation” refers to the driving force behind gelation. Chemical gelation is driven by acidity or ionic factors. Examples of acid-driven gelation include sodium alginate and high-methoxyl pectin in the presence of sugar. Ionic gelation can be observed with sodium alginate (Ca2+), as well as kappa and iota carrageenans (K+and Ca2+, respectively).

Gels formed by heating or cooling are the result of thermo-gelation. Agar and gelatin gels form after cooling a hot solution, while heating will cause gelation of hydroxypropylmethylcellulose and methylcellulose.

Gels may be reversible or irreversible. Gelatin and carrageenan set into gels when cooled from a hot state, but will revert to a liquid state if heated again. Conversely, hydroxypropylmethylcellulose and methylcellulose will gel when heated, but return to a fluid state when cooled to room temperature.
Depending on their rheology, hydrocolloids can provide
cling, create desirable consistency and improve the
mouthfeel in reduced-fat salad dressings.

Adding it all up
Scientists have proposed various systems for evaluating food products’ texture and mouthfeel based on the factors they consider to have the greatest effect on how the product is perceived. Alina S. Szczesniak, a scientist with General Foods, White Plains, NY, developed a set of standards for classifying a food’s rheological properties based on three categories of textural character: 

Mechanical parameters – such as hardness, viscosity, elasticity, cohesiveness and adhesiveness – were further split to evaluate brittleness, gumminess and chewiness;

Geometrical characteristics included those related to particle shape and size, and those dealing with particle orientation and shape; 

The third category, “other,” encompassed attributes like oiliness, greasiness and moisture content. 

Although devised in the 1960s, this programme remains one of the most useful in the industry.

Bloom Test on the TA.XTplus Texture Analyser
Quantifying textural attributes has become more sophisticated through the years. The science of rheology (the study of the deformation and flow of materials) quantification uses a number of techniques, such as advanced sensors with an array of probes – plates, pistons, cones, needles, knives, balls and even simulated teeth – pushing against, into and through samples. 

Fluids can be evaluated by measuring resistance to rotation of metal cylinders, discs and tees, and other methods like the speed of a falling ball or measuring flow in relation to time. 

Sophisticated computer programs can analyse data from many of these tests to provide indications of textural attributes such as gel strength, film strength, break point, hardness, softness, smoothness, lumpiness, slipperiness, stickiness and spread ability. By correlating mechanical data with organoleptic data, developers and processors can often use instrument systems to quickly, accurately and economically evaluate products throughout the developmental or production process. 
Jelly with spoon

Tricks of the trade
Differences in gelling and melting temperatures are common tools exploited by food scientists, notes Joe Klemaszewski, Senior Scientist in Dairy Applications at Cargill Texturizing Solutions, Wayzata, MN. 

“The gelling temperature of egg-white proteins helps baked products hold their structure after baking,” he says. “Replacement of the egg protein with a protein that sets at a different temperature results in a loss of volume. Temperature- viscosity profiles can be varied to affect finished product and processing attributes. Gelatin is easy to process because of its low viscosity above its gelling temperature. Upon cooling and setting, it forms a thermoreversible gel. In contrast, hydroxypropylmethylcellulose thickens on heating and loses viscosity on cooling. Starches build viscosity on heating and build additional viscosity when cooled. These properties can be used when making pie fillings to maintain particulate identity during heat processing or to maximise heat transfer.” 

Thermoreversibility can also be an important consideration when looking at end use. Gelatin’s low melting temperature (77º to 82ºF, or 25º to 28°C), depending on the soluble solids of the product, provides very desirable mouthfeel and flavour release in gelled desserts. On a buffet, however, where consumers may place the gel onto a warm plate, or close to warm food items, the gel can begin to melt. Carrageenans can create a similar texture as gelatin, but with a higher melt temperature. For example, a carrageenan and locust bean gum blend can have melt temperatures above 97°F. The gel will be more stable on the warm plate, while still melting in the mouth of the consumer.

Comparing gelling agents, developers must not overlook possible effects on flavour. The low melting point of gelatin will release flavouring compounds more readily, resulting in a higher perceived flavour intensity. Higher melt temperatures for carrageenan gels can give the perception of lower flavour intensity. This same relationship holds true for aromatic impact of the gel.

As consumer demand for healthier products grows, so does the need to replace the mouthfeel of the fat removed from the traditionally formulated products, observes Joshua Brooks, Vice-President of Sales at Gum Technology Corporation, Tucson, AZ. “Whether it is for a reduced-fat mayonnaise-type dressing, or a reduced-fat chocolate-chip cookie,” he says, “if the mouthfeel of fat, such as smoothness or creaminess, are reduced, then you need to replace them with an ingredient which will mimic these properties.”

Brooks suggests a specialised blend of gums – cellulose gel, konjac and xanthan gum – to create a gel structure that mimics fat. Hydrocolloids in the blend also provide a water-binding effect that can extend the shelf life of certain fresh and frozen products. “In baked goods, for example, the stabiliser reduces staling. In frozen applications, the blend helps control ice crystallisation,” he says, noting that usage levels ranging from 0.25% to 1.00% of total formulation will not mask flavour.

Developers can also take advantage of the individual components of stabiliser blends for use in specific applications. “Many gums require heating in order to crosslink at their molecular level, which results in their gelation upon cooling,” says Brooks. “The cellulose gel component of the aforementioned blend allows for this stabiliser to gel without heating.” Gelation induced under cold conditions will, however, be slightly weaker than one formed by heating and then cooling.

Additional ingredients can enhance stabiliser blends to make them more suitable for a specific application. “A stabiliser comprised of cellulose gel, konjac and xanthan gum could incorporate sodium alginate to react with calcium present in dairy applications and further promote gelation in dairy formulations,” adds Brooks. “Such applications include reduced-fat milk puddings, reduced-fat cheese dips, reduced-fat cheese sauces, low-fat yogurt dressing and reduced-fat smoothies. Usage level would be as low as 0.10% to 0.50%.” 

Presto change-o  
While a texturising agent’s functionality may seem clear, circumstances may arise that allow an altogether different character to emerge. Xanthan gum, for example, is a consistently reliable thickening agent across pH of 1 to 12, with minimal effect from temperature. Xanthan solutions are pseudoplastic, however, meaning that a very thick solution at rest will exhibit very little apparent viscosity when pumped. Thick or thin, though, it’s always a thickener – alone.

Now, add another thickener, locust bean gum, and presto! You get a very elastic gel. 

Locust bean gum can also be added to kappa carrageenan to increase elasticity. Normally very rigid and prone to syneresis, locust bean gum increases solution viscosity and gel elasticity while reducing the amount of syneresis observed. The effect simulates a gel made with iota carrageenan; it is more elastic than kappa with lower syneresis. Locust bean gum is, however, less expensive than carrageenans, providing developers an economical alternative for creating the desired texture.

Another unique synergy can be observed by combining xanthan gum and konjac. “Formulators are now using these gums in combination, because they form an extremely elastic gel texture,” says Maureen Akins, lead Food Scientist at TIC Gums, Inc., Belcamp, MD. “We’re seeing these gums used to add texture to applications like pie fillings and chewy candy. When added to beverages, this combination provides exceptional suspension characteristics at extremely low usage levels of 0.05% or less.”

Another textural double agent is sodium alginate. “When alginate is used without calcium,” notes Akins, “it builds viscosity. When calcium is added to the system, it forms a gel. This texture trick is the subject of a lot of interest in the culinary world recently, as chefs use alginate to form caviar-like gel beads.” 

The food industry has employed this technology for many years to create the omnipresent pimento strips stuffed into olives, and more recently for restructured foods, such as fruit bits, onion rings, and uniform meat and fish shapes.

There is a wide variety of gummy creatures these days, each based on the traditionally formulated bears where high-bloom gelatin creates a very firm, elastic texture.

Formulating with pectin or agar, though, will yield a tender, short texture. Gumdrops made with thin-boiling starch will be chewy and sticky. By working with combinations of these texturising agents, developers can create any number of unique signature textures within the category of fruit gummies.

As any good magician will note, the most-important bit of any trick is the setup. “When adding a stabiliser, it is always best to start with a low usage level and adjust incrementally,” says Akins. “To get the most cost-effective use of the lowest-possible stabiliser level, it’s important to follow hydration guidelines such as available water, sufficient dispersion, order of incorporation, and appropriate hydration temperature.”

Once you have a grasp of the basics, it’s time to perform textural magic.

To read the full article: Textural Magic

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

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.

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

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