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Adding value through extrusion

02 January 2023

Dr. Christian Kern explains how extrusion technology can add value to what would traditionally be considered a byproduct, helping to reduce waste and increase profitability.

Extrusion is a versatile process technology which allows for the continuous processing of raw material using several basic unit operations such as conveying, mixing, dispersing, kneading, degassing, shaping, and cooking. 

The thermal and mechanical energy leads to a plasticised, flowable mass in the extruder which is shaped by different dies attached to the barrel section. During extrusion, the raw materials experience several chemical and physical modifications – gelatinisation of starch or plasticisation and texturisation of proteins, for example.

Twin-screw extrusion technology has been used since the 1970’s to manufacture value-added products in food industry. The advantages of hot melt extrusion include high versatility, low investment and maintenance costs, high productivity as well as the sustainability with respect to valorisation of side-streams or energy-efficiency.

Applications to demonstrate how extrusion technology can be used to produce value-added products include cereals, with several million tons of grains being processed daily in the food industry. The most important intermediate product is flour. However, byproducts include dark flour or bran. 

The protein content of flour is of minor importance when it comes to extruded and cereal-based foods, where the main structural component is starch. So, extrusion technology is not limited just to flour-based products, it is also suitable to process the side-streams of flour production which usually lack in protein/gluten. The most common extruded cereal products are breakfast cereals, flakes, infant formulas, extruded breading, and modified flours.

Modified but ‘clean label’
Modified flours are flours with tailored properties such as water absorption capacity and solubility and their application can include binders, fillers, or shelf-life extenders for pastries.

During the extrusion process parameters are adjustable to tailor the viscosity of flour-water suspension to meet specific requirements. Controlling the thermal and mechanical energy inputs during extrusion makes it possible to tailor the solubility in cold or hot water and to create a range of water absorption capacities. 

Extrusion is well-suited for the modification of flours as no chemical additions are required, offering clean label ingredients.

Innovation potential 
Side stream valorisation has a big role to play in the food industry. A pioneering application of extrusion, for example was the valorisation of soyabean press cake as a side-stream from soya oil extraction which enabled manufacturers to develop new food products in the form of texturized vegetable protein. 

Other processes have been developed over the years to fraction protein sources into protein isolates and concentrates having specific functionalities, which led to other side-streams such as fibre or starch-rich fractions from raw materials such as pulses or grains. 

Today extrusion technology enables the addition of many side-streams to create meat alternative formulations and dietary fibre ingredients. It is also possible to adapt low and high moisture extrusion to incorporate fibre- or protein-rich side-streams from other food manufacturing process such as beer brewing or juice manufacturing to support the shift towards a more circular economy. 

In conclusion, today’s extrusion technologies offer a process technology that can help increase manufacturers value chains as well as helping to reduce waste by making good use of by-products.

Dr. Christian Kern is process engineer R&D at Bühler AG, Switzerland.


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