Starch is an essential base material widely used in the food industry, especially in the production of snack foods, cereals, and pet food products. Extrusion and rheological tests were performed on samples to discover how to attain the best gelation of the product during manufacturing.
What is Starch
Starch is a type of complex carbohydrate that serves as a major energy source in many plant-based foods. It is composed of glucose molecules linked together in a branched or linear fashion. Starch is commonly found in various food sources such as grains (wheat, rice, corn), potatoes, legumes, and root vegetables.
The process of starch formation in plants involves two types of starch molecules: amylose and amylopectin. Amylose is a linear starch molecule, while amylopectin is a branched starch molecule. The ratio of amylose to amylopectin varies in different plant sources, resulting in variations in the texture and properties of starches.
Extracting Starch
To extract starch from plant sources, several methods can be used, depending on the specific source. Generally, the process involves grinding or crushing the plant material to release the starch granules. The starch is then separated from other components, such as fiber and proteins, through processes like washing, filtration, and centrifugation. Finally, the starch is dried and milled into a fine powder, which can be used in various food and industrial applications.
Extruding and Processing Starch
Food extrusion is an established and highly versatile technique for the production of food, feed, nutritional additives and flavors. It enables a continuous and cost-effective means of production, and its precise control ensures a high and constant product quality.
The screw extruder is a device consisting of one or more Archimedes’ screws that rotate in a cylindrical barrel. Material is continuously fed into the barrel and sheared between the screw and bearing wall. The material is melted by heat input in the case of hot melt extrusion or dispersed with solvents in the case of a wet extrusion. Eventually, the fluid material is compressed and pushed through a die to form the extradite.
Twin-Screw Extrusion
Twin-screw extruders are extruders with two intermeshing screws, or even extruders with multiple screws have been developed. The twin-screw melt extrusion method offers a more efficient and controlled way of extrusion. The is a continuous working instrument, which means the amount of end-product is determined by run time and does not require adaptation via different-sized production equipment as traditional batch operation does.
Extrusion cooking takes the process to the next level by utilizing the extruders’ precise temperature control and shear energy which is applied by the rotating screws. When passing through the extruder, the food is actually cooked. Due to the changed physical condition of the food, specific denaturation of proteins can occur as well as the rupture of starches resulting in such complex products as meat analogues. Simultaneously the short and controlled residence time in the extruder restricts unwanted decomposition of vitamins, amino acids and enzymes.
Experiment
We explored the influence of different extrusion conditions on the processability of starch compounds and conducted an experiment using a parallel twin-screw extruder, built with hygienic grade steel, which is suited for processing food-based materials. The extrusion process was carefully monitored, with extruder parameters like screw set-up, processing temperature, and the liquid-to-solid ratio of the raw materials adjusted to influence the resulting product’s properties.
Four key variables were evaluated during the experiment: Screw configurations, temperature profiles, speed of extruder screws, and feeding rate. Rheological tests were performed on the samples with a highly flexible modular advanced Rheometer system. Rheology plays an essential role in both product development and quality control. By measuring rheological properties, lab technicians and scientists can do everything from predicting the shelf life to improving the texture of foods to determining the viscoelastic properties of polymeric materials.
The results of the experiment led to several key observations. You can read about them in our application note: The influence of extrusion conditions on the processability of starch compounds.
Summary
We concluded that the gelation of starch is a complex process that depends on several variables. The degree of gelatinization shows a strong dependency on the processing temperature. Under the same conditions, the higher shear energy introduced into the system by the screw setup with two mixing zones degrades the three-dimensional network during the gelatinization process. However, twin-screw extrusion provides a range of processing variables that allows the user to design a starch matrix to required product properties adeptly.
The experiment shows that combining extrusion with oscillatory rheology allows for defined, precise analysis of the end product. This provides a workflow that enhances capabilities in today’s food design, allowing manufacturers to influence texture, stability, and further processability of the final product.
You can read additional details about the experiment, including extrusion conditions, equipment used, configuration, temperature, parameters, and results in the application note: The influence of extrusion conditions on the processability of starch compounds.
Additional Resources
- Application Note: The influence of extrusion conditions on the processability of starch compounds
- Online resources for compounding and extrusion instruments and applications as well as for rheometers and viscometers.
