Maintaining viscosity and texture by direct injection

Caution when dispersing proteins

Proteins form agglomerates with a strong adhesive force when mixed with liquids. These must be broken down again by dispersing. In the process, shearing irreversibly damages the protein, which is already hydrated at this point. In many cases, local overheating can even occur. The product will not have as high a quality as it could have. However, it does not have to be this way, as special machines from ystral allow agglomerates to be avoided and the texture to be maintained.

The market for protein products is growing steadily. Competitive athletes, as well as private individuals, are increasingly turning to these products when doing sport. The production of yoghurt or desserts requires additional milk proteins. Proteins are important building blocks for tissue and organs. They are present in increased concentrations in food for persons in a weakened state or patients subject to enteral feeding. They are even processed in cosmetics or the feed for farm animals and domestic pets.

Manufacturing issues

However, processing the powdered proteins is not that simple. They stick, foam and clump together. Moreover, the viscosity increases very strongly at the moment at which the powder is introduced. If, for example, caseinate is added a little too quickly, the result is the consistency of a Swiss cheese fondue. You can draw metre-long threads from it.

Proteins are highly cohesive. This can be seen most impressively in the processing of gluten — also known as wheat gluten. As soon as you turn off the mixer in the gluten suspension, the entire protein flocculates together and you could take it out in one tough piece. Most proteins are also highly adhesive. Milk protein was used for centuries as casein glue to glue wood or other components. Consequently, it also sticks very well to machine parts. When cleaning splashes off painted surfaces, the paint may come off, rather than the caseinate, which has set. And cleaning machines is every bit as challenging.

If you disperse protein solutions because you have to break down the lumps and agglomerates formed during mixing, the viscosity and texture of the already hydrated protein component will be destroyed. In addition, the air contained in the powder is dispersed into stable microfoam — extremely undesirable.

However, dispersing is not always undesirable; on the contrary. Proteins have a complex structure with primary, secondary, tertiary and quaternary structures. When making firm yoghurt, it is essential not to destroy the natural protein texture. When making stirred yoghurt, you want to work it in a controlled way. In the case of stirred yoghurt, only the superordinate structures are dispersed in a very targeted way (smoothing) in order to prevent whey from separating in the bowl at a later stage. In the case of drinking yoghurt, much more dispersion is required to irreversibly prevent gel build-up and to set the desired drinking viscosity. This controlled structure manipulation is done very effectively with ystral In-Line Smoothers.

ystral In-Line Smoother for the targeted dispersion of protein solutions or yoghurt

Whereas protein structures were previously often selectively broken down by enzymes (proteases) or acids during the production of spray emulsions or protein concentrates, the use of these machines can significantly reduce their required concentration, a considerable application advantage.

However, the dispersion of lumps and agglomerates is always critical. If agglomerates are formed during when the powder is introduced, they inevitably get into the gap between rotating and stationary machine parts, stick and overheat locally. The consequences range from a yellowish discolouration and black specks to a slightly burnt taste of the end products. How can all this be prevented?

Here is the solution: agglomerates must not be allowed to form! Furthermore, no powder should be able to stick between rotating and static parts! Air must already be separated from the liquid when the protein powders are introduced. The introduction of the powder must be controlled in such a way that no localised instances of excess concentration can occur. Finally, the system must be easy to clean without disassembly.

Ystral Conti-TDS for the aspiration and dispersion of proteins

All these requirements are met by a special version of the ystral Conti-TDS. This machine was developed for highly adhesive and agglomerating powders and can easily process all protein types and, of course, protein isolates, concentrates or protein combinations with other powders. It is used in protein production and also in protein processing. The dissolving processes can be cold or hot. The areas of application range from the production of enteral nutrition to spray emulsions for baby food or muscle-building preparations, stirred yoghurt, drinking yoghurt and cosmetics. With these machines, blood protein is introduced in the production of dog or cat food, for example. Soy, faba bean or pea proteins are processed in the production of cutting-edge plant-based trend products. Proteins are used as nutrient solutions in the production of organic crop protection products.

Effective vacuum application

What is the main issue and how can it be solved? The main issue is always powder agglomerates, which form immediately when the protein is added to the liquid and whose subsequent dispersion damages the already hydrated gel.

Protein powders consist of individual particles. Even if these particles come into contact with each other, there is air between the particles — even a relatively large amount of air. At least 75% of the powder volume is air. This fact can be exploited to solve the problem because air expands in a vacuum.

The Conti-TDS creates a high vacuum precisely in its wetting zone. With this vacuum, it sucks the powder into the liquid. Regardless of whether the powder is sucked in from a bag, a hopper, a container or a silo, the vacuum increases along the suction path into the wetting zone. The air between the particles expands more and more as the vacuum increases. As a result, the distances between the particles in the powder stream, which is flowing at an increasingly higher speed, become larger and larger. The particles are already separated before wetting.

In the wetting zone, the powder particles come into contact with the liquid at speeds of almost 100 km/h and under extreme turbulence. They are individually wetted in their entirety and are broken down colloidally. Agglomerates do not form. Further dispersion is usually not necessary — unless this is desired in order to break down the structure in a controlled manner.

Separation of the powder particles on their way into the wetting zone under vacuum

In contrast to other Conti-TDS designs, there is no dispersion at the moment of wetting. The powder does not come into contact with any rotor or stator. It is sucked directly into the liquid that is flowing at a high speed (direct injection).

The powder flow is controlled in relation to the liquid flow and its existing protein content, in order to exclude local over-concentrations caused by a suction process that is too rapid. In the case of protein concentrates or protein combinations, this is done by means of control valves. For isolates and pure proteins, nozzles are used for this purpose.

Air is separated

The air previously contained in the powder and released after the powder wetting coalesces into large air bubbles under the centrifugal effect of the rotor and is transported together with the liquid to the process vessel, where it escapes via the surface of the liquid. In this way, it is not dispersed into a fine foam again.

One very impressive example is the recombining of egg yolk or whole egg powder in the production of mayonnaise or even sweet fillings. Immediately after the egg yolk powder has been added, you can see the large air bubbles escaping. Although the volume of the powder is far greater than the volume of the liquid into which it is introduced, the filling level in the process vessel rises only to a minimal degree. You can see large air bubbles with a diameter of about 10 centimetres escaping. After the introduction of the powder has been completed, the machine is left to run for a few minutes to deaerate. This enables you to achieve a deaeration to less than one per cent residual air in the product without using a vacuum container.

Design and ATEX

The process is characterised by a particularly gentle and particularly fast complete wetting and a maximum utilisation of the powdered ingredients. The machines are, of course, designed according to all the principles of hygienic design, equipped with FDA-approved elastomers and also 3A certified.

They are CIP- and SIP-compatible, can be easily dismantled and are available in four different sizes, from 4 to 90 kW.

Proteins are basically organic and, therefore, dust-ex powders. Therefore, the machines have an ATEX classification. The areas in which the protein powders are processed are often not designated as Ex-zones at all. In this case, the machines are also available in an ATEX category outside non-ex/inside dust-ex for processing dust-ex powders when installed in a non-ex area.

Conti-TDS machines are characterised by the fact that proteins are broken down better compared to other methods and the quality of the end products is increased.

They offer considerable rationalisation potential by reducing production times and lowering production costs.

Image credit: ©stock.adobe.com/au/pilipphoto