Every day we experience the results of one of the most complex chemistry reactions. Cooked food. When we heat food, a series of chemical reactions take place that change the texture, taste and appearance of the raw ingredients. To a food scientist, this is the Maillard Reaction and the focus of Daniel Hemmler’s PhD research at the Technical University of Munich.
We caught up with Daniel to find out what excites him about his Mars funded PhD and his latest publication.
Chemistry sometimes struggles to achieve the same profile as other disciplines, what attracted you to a chemistry PhD? “I have always been fascinated by natural sciences. Chemistry, which links physics to biology, is the actual basis of all vital processes. I love to explore new ways of using modern analytical chemistry techniques, such as mass spectrometry, which is why I applied for this PhD. My supervisor, Prof. Schmitt-Kopplin, runs one of the most sophisticated and powerful analytical tools available around the globe at the Helmholtz Zentrum München. So when I was offered this PhD, it was a unique opportunity I couldn’t refuse!”
“If heat, sugars and amino acids (the building blocks of protein) come together, the result is mostly something tasty. Bread turns brown during baking, meat starts to smell in the pan and coffee obtains its characteristic aromas during the process of roasting. And of course, we also cook pet food in the manufacturing process. These changes in food properties have been attributed to the Maillard reaction, which was discovered over 100 years ago.
The reaction is initiated by heat and produces hundreds or even thousands of different chemical compounds within a very short time. Not all of these reaction products are beneficial to human or animal health. By understanding the entire set of chemical reactions and compounds produced we can change the way we cook or process food, including for pets. We can then avoid the production of undesirable compounds and increase the amount of beneficial compounds. My PhD is about trying to better understand the fundamental aspects of the Maillard reaction.”
With a paper recently published from your PhD research about cooking, how does that link to analytical chemistry? "Despite decades of research on the Maillard reaction and steady progress in our understanding, we have yet to resolve the entire process and the interactions of the chemical compounds. Even if only one amino acid, the smallest unit of a protein, is brought to reaction with a single sugar hundreds of compounds are produced. And this only reflects a very small part of what happens in actual foods. Most have almost identical chemical properties which makes them very difficult to characterise in a single analysis. And to make matters worse, some compounds are produced in very high concentrations while others are only generated in trace amounts. Even state-of-the art analytical tools often struggle with such a large range of concentrations. Our research group has years of experience in characterising very complex samples. So our expertise lent itself to tackling this knowledge gap of the Maillard reaction.
In our recent paper *1, we focused on the reactions and chemical compounds produced in a simplified model system, heating only two compounds, ribose and glycine, together. Glycine is the simplest of the 20 amino acids that occur in proteins and ribose is a very reactive sugar which is found in a variety of plant and meat based foods. We were able to separate and detect the majority of chemical compounds produced using a magnetic resonance mass spectrometer offering ultra-high resolving power."
"The unknown analytes or chemical molecules of a sample are ionised in an electrical field and transferred into an ion cyclotron resonance (ICR) cell. The molecular weights of the fragments are then detected. The ICR cell is surrounded by an extremely strong magnetic field. In our case, we are using a “12 Tesla superconducting magnet” which generates a magnetic field which is approximately 250 000 times stronger than the Earth’s. This enables us to distinguish the mass of single electrons that are a billion, billion, billion times smaller than a grain of sugar (or 9 x 10-31 kg) and determine chemical make up of each of the analytes at the same time. This meant that we could unravel the exact composition of hundreds of distinct chemical compounds in our samples. Using modern data visualisation tools and statistical methods, it was possible to map a wide set of chemical interactions and to identify important processes."
With only the simplest amino acid (glycine) and a simple sugar (ribose) in a single reaction the results were impressive. “We found far more than 300 intermediates and reaction products originating from the two initial reactants. Although such a complexity was predicted by the scientific community, it had not been possible to measure all these chemical compounds in a single experiment before. These findings confirm that the Maillard reaction is one of the main contributors to the chemical diversity we find in foods. And, despite the enormous variety, the reaction often follows very simple formation processes which can be repeated or run in parallel. By sampling at different cooking times, we were also able to visualise the duration of reaction pathways.”
"The Maillard reaction plays an important role wherever amino acids and sugars are present –food, beverages, even in the cells of living organisms, which of course, includes us! Everyone generates Maillard reaction products everyday just through cooking our daily meals. Therefore, it is really important to understand as much as we can about the behaviour of the reaction and the formation of the pathways that create different reaction products. This obviously also applies to the cooking during the manufacture of pet food and why WALTHAM are funding this research. James Marshall, Chemistry Research Manager at WALTHAM, has been a key advisor/supervisor of our work.
With the help of better understanding, it could be possible to control cooking methods. Ideally we would avoid the formation of toxic compounds (e.g. acrylamide) or bad flavours and promote desirable aromas and beneficial compounds (e.g. antioxidants).
This study highlights the analytical possibilities we have available now to screen and separate food products into its individual components on a molecular level. But the final word has to go to the Maillard reaction. It is one of the most complex reaction networks that also offers a great pool of novel chemical compounds, which could have interesting features also to other chemical disciplines and industries. As well as being a very interesting playground for food chemists."