11-12/2020 | SPECIALIST ARTICLE
Avoid agglomerates when dispersing
Proteins often form highly adhesive agglomerates when mixed with liquids. These have to be broken down again by dispersing. The quality of the end products often suffers as a result. With a special version of the Conti-TDS dispersing machine from ystral, agglomerates can be avoided and the viscosity and texture of the proteins can be maintained.
The market for protein products is growing steadily. Sports nutrition, yogurts, desserts and specialty foods are often enriched with additional milk proteins. Foods for weakened or enteral-fed people also contain proteins in increased concentrations.
However, processing powdered proteins is not easy. Protein powders stick, foam and clump together. The viscosity increases considerably when the powder is added. If, for example, caseinate is added to the liquid a little too quickly, a very viscous consistency is created locally. Proteins are also highly cohesive. This can be seen most impressively in the processing of gluten. If the mixing of the gluten suspension is stopped, the entire protein clumps together into one piece. In addition, most proteins are also highly adhesive. Milk protein, i.e. casein glue, for example, has been used for centuries to glue wood or other components together. As a result, it also sticks very well to machine parts. If protein solutions are dispersed in order to break down the lumps and agglomerates formed during mixing, the viscosity and texture of the already hydrated protein component are destroyed. In addition, the air contained in the powder is dispersed to form stable microfoam - a process that is undesirable.
Machine for highly adhesive powders Dispersing lumps and agglomerates is always critical. They get into the gap between rotating and stationary machine parts, stick and overheat locally. The consequences range from yellowish discoloration and black specks to a slightly burnt taste of the end products. Agglomerates must therefore not be allowed to form in the first place and the air must be separated from the liquid as soon as the protein powder is fed in. The powder feed must be controlled in such a way that no excessive powder concentrations occur locally.
All these requirements are met by a special version of the Conti-TDS dispersing machine from ystral. This was developed for highly adhesive and agglomerating powders and can easily process all protein types and isolates, concentrates or combinations. The dissolving processes can be carried out cold and hot. Protein powders consist of individual particles and at least 75 % of the powder volume is air. The aim of the process is to produce the lowest possible residual air content in the end product.
The Conti-TDS builds up a high vacuum precisely in its wetting zone. This sucks the powder into the liquid. The air between the particles expands as the vacuum increases and the particles are separated even before wetting.
In the wetting zone, the powder particles come into contact with the liquid at speeds of almost 100 km/h and extreme turbulence and are completely wetted individually and broken down colloidally. This prevents the formation of agglomerates. Further post-dispersion is generally not required - unless this is desired in order to break down the structure in a controlled manner.
In contrast to other Conti-TDS designs, this variant does not disperse at the moment of wetting. The powder does not come into contact with either the rotor or the stator, but is sucked directly into the liquid flowing at high speed. This method is known as direct injection. The powder flow is controlled in relation to the liquid flow and the protein content already contained in the liquid in order to avoid excessive concentrations due to rapid aspiration. In the case of protein concentrates or combinations, this is done using control valves. Nozzles are used for isolates and pure proteins.
Air is separated
The air previously contained in the powder and released after powder wetting coalesces into large air bubbles under the centrifugal effect of the rotor and is transported together with the liquid to the process container, where it escapes via the liquid surface. This prevents it from being dispersed into fine foam again.
An impressive application example for these dispersing machines is the recombination of egg yolk or whole egg powder in the production of mayonnaise or sweet fillings. Air bubbles with a diameter of around 10 cm are released during this process. After the powder has been added, the machine is left to run for a few minutes to de-aerate. In this way, a residual air content of less than 1 % can be achieved in the end product without having to use a vacuum deaerator.
3A and ATEX certified
The process is characterized on the one hand by particularly gentle and on the other hand by particularly fast complete wetting and maximum utilization of the powdery ingredients. Ystral machines are constructed in accordance with all the principles of hygienic design, equipped with FDA-approved elastomers and are also 3A-certified. They are CIP and SIP-capable, can be easily dismantled and are available in four different sizes.
Proteins are basically organic and therefore dust-ex powders. The machines therefore also have an ATEX classification. They are also available in the ATEX category "outside non-Ex/inside dust-Ex" for processing dust-Ex powders in non-hazardous areas.
https://prozesstechnik.industrie.de/ | Search term: Ystral
Magazine: DEI
Issue: 12-12/2020
Author: Dr. Hans-Joachim Jacob
About the author
Dr. Jacob is Senior Expert Process and Applications at ystral. Dr. Jacob, who studied mechanical engineering, joined the company in 1990 as a process engineer and has since been responsible for our key accounts worldwide. His professional passion is the mixing and dispersion of powders in liquids. During his long career, he has gained experience in handling thousands of powders from a wide range of industries and is happy to share his expertise in various technical articles, online seminars and lectures.
About ystral
With our vast knowledge and many years of experience in Process- and Application Engineering we offer targeted, customer-oriented solutions across industries - from lab equipment to production machines or plants. Together with you, we develop concepts and implementations for your individual applications, which mean mmediately realisable and quantifiable added value for you.
