Azad Emin from the Karlsruhe Institute of Technology discusses moves to better understand processing conditions and changes in material structure, and how this could lead to the better design of sustainable and functional food ingredients.
What benefits can extrusion technology bring to the development of sustainable and functional foods?
“One very trendy application area is the design of plant-based meat analogues. Extrusion technology is one of the main technologies used to produce these products. In fact, the majority of meat substitutes on the market are based on extruded proteins. Here, the main benefit of extrusion is its ability to process almost any type of protein such as soy, wheat, canola, pea, algae and even insect protein. This way, we don’t have to work with only one sort of protein, and have the flexibility to choose the proteins according to their sustainability.”
What other promising application areas have you identified?
“Another very promising application is the upcycling of by-products from fruit and vegetable processing, such as apple or carrot pomace from juice production or potato pulp from starch production. These by-products are very rich in dietary fibre and bioactive compounds, and also offer various techno-functional properties, if modified accordingly. For such applications, we use extruders like bioreactors to improve the functional properties (e.g. water and oil holding capacity, gelling and thickening behaviour), according to the needs of the food products of interest. This process requires limited water and no chemical additives. This way we can produce highly sustainable clean-label food ingredients with various functionalities. These intermediate products can then be applied in various food systems from sausages to bakery products and from yoghurt to smoothies to improve their stability and texture, and also increase their dietary fibre content, which is known to have many potential health benefits.”
What are some of the current limits to this technology?
“Extrusion is one of the very few food technologies, which has been continuously evolving since its invention. Although I have been working with this technology for more than ten years, I often hear about a new application. It is fair to say that it is not the technology itself but our understanding of this technology that is limited. This ends up affecting the approach we use to develop new products by extrusion technology.
“Currently, product development is mostly based on the empirical approach, or the ‘cook and look approach’. This seems to work perfectly fine for simple applications. Nowadays though, the food industry is facing major challenges in the shift from traditional foods to more sustainable foods, while promoting health and wellbeing. For this we need a better approach than the empirical approach, because it either fails to supply efficient solutions or becomes very expensive and time consuming due to the large number of trials necessary.”
Could you highlight some of the latest research developments in extrusion technology?
“We have been working on the development of an approach to analyse and control the mechanisms during extrusion processing that play a crucial role in the structuring and functionalisation of food materials. This seems to be essential to utilising the full potential of this technology. Although it sounds very challenging, we have realised that there are already many tools and methods available, which can be easily adapted and used to achieve these goals.”
“For instance, when working with alternative proteins, the control on the process and the resulting product structure is only possible if we have sufficient information on their behaviour during extrusion, such as reaction and rheological behaviour. Although there is a vast amount of work that has been done on proteins, this has been mainly performed on dilute systems. The information cannot be transferred to extrusion, as we are working with highly concentrated proteins at temperatures above 100 °C.
“About 4 years ago, we started to work with a specific rheometer, originally developed for the rubber industry at the beginning of the 1990s. The ability to measure the material behaviour during extrusion conditions gives us a whole new dimension of analysis and knowledge, which is definitely helping us to perform more targeted processing and product design. As our research focuses on the understanding of the physical and chemical mechanisms and is not based on the recipes, the approach and tools developed can be applied to any biopolymers or biopolymer mixtures of interest.”
What are your predictions for extrusion technology over the next three to five years?
“Considering that the demand on more sustainable products will continuously increase, I expect that extrusion will position itself as one of the key technologies in this field due to its flexibility with respect to raw material selection and variety of food types produced. We have already seen fast-growing interest and an increasing number of research projects in this field. In parallel, there are also extruder producers who offer extruders with scales varying from several kg to several 1000 kg per hour. This theoretically means that you could buy an extruder for your kitchen.
“In addition to products based on alternative proteins, I expect to see significantly higher number of products based on food by-products. Some of those food by-products might even become the main product, similar to what happened to whey proteins during the last 50 years. So, with the combination of new trends and related ongoing research, I expect that extrusion will change the value of many ingredients that are currently underutilised. In case of protein-rich systems, this will probably happen very quickly, whereas it might take a little longer for by-products from fruit and vegetable processing.”