Understanding interactions between proteins and phytochemicals
With more people moving towards plant-based diets, grasses can play a valuable role as a source of sustainable protein. We spoke to Mette Lübeck and Simon Gregersen Echers from Aalborg University in Denmark about their research into the interactions between proteins and phytochemicals, and how inhibiting some of them could help improve protein quality.
Green plants, such as clovers and grasses, synthesise different kinds of phytochemicals when they are cultivated. They provide protection against various different threats, such as infectious diseases, but phytochemicals can also produce certain aromas and smells. These phytochemicals interact with proteins when the plant is harvested for its protein, yet the impact of these interactions on protein quality is not currently well understood. “Some of these phytochemicals may be beneficial, others less so, and some may be actively harmful. That is something that is not really very well studied,” outlines Mette Lübeck, Professor at the Department of Chemistry and Bioscience at Aalborg University in Denmark. As Principal Investigator of a project backed by the Independent Research Fund Denmark, Professor Lübeck is now looking at these interactions in clovers and grasses and seeking to understand their impact on protein quality. “We chose to work with clover grass blends as they’re cultivated widely in Denmark, and across the Northern hemisphere,” she says.
Phytochemicals
These plants are sustainable sources of nutritionally valuable protein, providing an alternative to meat-based products, a prominent issue today with plant-based diets growing increasingly popular. However, when grass is used to make juice, phytochemicals are released from vacuoles in the plant and come into contact with proteins. “Some biochemical reactions take place when this squeezing happens, like the browning effect that you see on an apple when it is exposed to oxygen in the air. There are also oxidations of phytochemicals, and sometimes some of these phytochemicals also bind to the proteins,” explains Professor Lübeck. The project team, led on a day-to-day basis by Tenure Track Assistant Professor Simon Gregersen Echers, is now studying these interactions, looking to both prevent the harmful interactions - or limit their impact - and also harness the positive aspects of beneficial interactions. “We want to study these interactions, and to investigate whether they have a positive or negative impact. The
two main species that we want to study in depth are red clover and ryegrass,” continues Professor Lübeck.
The initial step in the project was to perform in-depth mapping of metabolites and proteins in these plants, which could then be subjected
able to identify tens of thousands of peptides, which are then effectively put back together.
“We use computing power to build proteins from the bottom up,” continues Assistant Professor Gregersen. “We identify different proteins and get lots of information about
“We want to study these interactions between phytochemicals and proteins, and to investigate whether they have a positive or negative impact on protein quality. The two main species that we want to study in depth are red clover and ryegrass.”
to detailed analysis and investigation by researchers. A technique called bottom-up proteomics, which uses mass spectrometry, is being applied in the project to essentially identify – and quantify – all the different proteins in the plants. “In bottom-up proteomics we add some enzymes that cut up the proteins into smaller pieces, called peptides. We then measure these peptides, as they are easier to handle than large, intact proteins,” explains Assistant Professor Gregersen. A typical sample consists of thousands of different proteins, and after the addition of the enzymes, researchers may be
them, including their amino-acid sequence, their size, and other properties. We can also quantify them, and figure out which proteins are more abundant than others.”
Researchers have also identified the main phytochemicals present in red clover and ryegrass, and are now looking at how they interact with proteins. “We take one phytochemical at a time, add it, then see if there are any molecular interactions between the main proteins and a particular phytochemical. We simply find out how much of a particular phytochemical is present in the leaf,” outlines Professor Lübeck. These phytochemicals
can be divided into different types, with researchers following a bottom-up approach to design relatively simple model systems.
“We don’t know if particular isoflavonoids or carotenoids play a role in protein modifications. We have identified the five most prominent isoflavonoids in red clover, but we don’t know whether any of them play a larger role than others,” says Professor Lübeck.
This is a topic researchers plan to probe during the project, alongside identifying which phytochemicals play a more general role in modifying proteins. This could then open up the possibility of adjusting processing parameters or even modifying the plant itself, thereby preventing those interactions that have detrimental effects. “We are interested in seeing if we can prevent these negative reactions. We are looking into how certain oxidation reactions can be prevented, and at what kinds of molecules act in these reactions,” says Professor Lübeck. It has not been possible to study a wide variety of plant species within the scope of the project, so Professor Lübeck and her colleagues are focusing their attention on red clover and ryegrass, which they hope will provide a solid foundation for further research.
“We hope to gain some clear indications that this bottom-up approach to developing model systems is the right approach to studying phytochemicals and their interactions with proteins,” she continues.
RuBisCO
A lot of attention in the project is focused on a protein called RuBisCO, which plays an integral role in photosynthesis and is therefore considered the most abundant protein in plants, and indeed on earth. Because of this abundance, and its exceptional nutritional and functional properties, RuBisCO is the main initial protein of interest in the project.
“The amino-acid profile of RuBisCO is very well-suited to human dietary requirements. It closely resembles the amino-acid profile that you can find in animal proteins,” explains Assistant Professor Gregersen. The ability to extract RuBisCO in its native form would be highly valuable, providing a sustainable source of high-quality protein, a goal that the project team are working towards. “We
have developed a process to remove some unwanted proteins, while retaining the nutritionally valuable ones. RuBisCO is the main goal, but we cannot separate it entirely, so it comes with some additional proteins,” says Professor Lübeck. “We want to understand which proteins we have removed, and which are retained.”
The long-term ambition is to prevent some of the adverse modifications using processing techniques, which will enhance the nutritional quality of grasses and increase their attractiveness as a source of protein for use in foods. Professor Lübeck plans to pursue this avenue of research further in future, alongside more applied investigation, with the aim of bringing more grass-based proteins to the commercial market. “We are also working on further grass-based projects, where we extract food-grade protein and study the functionality. We are looking to make prototypes, so that in future we can bring more grass-based proteins to the market,” she outlines. “We have filed a patent on this process, and we have established a spin-off company to try and commercialise it.
So we are working on this field of clover grass in a very broad sense, from a very fundamental understanding of phytochemical protein modifications, to a more applied dimension with societal impact.”
PhyPro
Phytochemical Protein Modification –Friend or Foe?
Project Objectives
Clover grasses are emerging as an environmentally beneficial and sustainable protein source for animals and humans also containing many bioactive compounds. However, interactions between proteins and bioactive molecules may deteriorate the protein quality as a food ingredient. PhyPro aims to understand these interactions using advanced molecular analysis, create models to study them, and developing strategies to sustainably inhibit unwanted interactions.
Project Funding
The PhyPro project is funded by the Independent Research Fund Denmark | Technology and Production sciences: DKK2,834,328.00
Project Partners
• Prof. Reinhard Wimmer (same affiliation), Aalborg University
• Assoc. Prof. Julia Keppler, Wageningen University
Contact Details
Project Coordinator, Prof. Mette Lübeck, Section of Bioresources and Process Engineering, Department of Chemistry and Bioscience, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg, Denmark
T: +45 9940 2589
E: mel@bio.aau.dk
W: https://vbn.aau.dk/en/projects/ phytochemical-protein-modification-friendor-foe
Prof. Mette Lübeck
Prof. Simon Gregersen Echers
Mette Lübeck is a Professor in the Department of Chemistry and Bioscience at Aalborg University in Denmark. Her research interests include the development of sustainable biorefining concepts using agricultural biomasses to create oil-based alternatives and animal-free food/feed.
Simon Gregersen Echers is a tenure track Assistant Professor in the Department of Chemistry and Bioscience at Aalborg University. His research focuses on applying mass spectrometry-based characterisation to develop sustainable protein-based food ingredients.
