Author: chemistadmin

Microorganisms have long used hydrogen as an energy source. To do this, they rely on hydrogenases that contain metals in their catalytic center. In order to use these biocatalysts for hydrogen conversion, researchers are working to understand the catalysis process.

A team from three Max Planck Institutes (MPI), the Center for Biostructural Imaging of Neurodegeneration (BIN) at the University Medical Center Göttingen (UMG), the University of Kiel, and the FACCTs GmbH used a chemical peculiarity of hydrogen to amplify the signals of magnetic resonance spectroscopy. In this way, the scientists were able to visualize previously unknown intermediate steps in the conversion of hydrogen. The study is published in Nature Catalysis.

As a substitute for fossil fuels, energy source, or catalyst in chemical processes—hydrogen is considered a good candidate for a sustainable energy economy. On Earth, the element occurs mainly in bound form, in water, as hydrogen gas, or in fossil raw materials such as natural gas and crude oil. To obtain hydrogen in its pure form, it must be split from the chemical compound using energy.

The most common method of producing hydrogen today is the steam methane reforming of natural gas. However, this also produces climate-damaging carbon dioxide (CO₂). In the catalytic production of hydrogen from water, electrodes made of the precious metal platinum have mostly been used up to now. This makes hydrogen production by means of catalysis comparatively expensive.

Many microorganisms are a step ahead of these production processes. To split off hydrogen to generate energy, they use three different types of hydrogenases that function without precious metals and do not release CO₂: [NiFe] hydrogenases from archaea and bacteria, [FeFe] hydrogenases from bacteria, some algae, and some anaerobic archaea, as well as [Fe] hydrogenases found only in archaea.

The latter play a key role in methanogenesis, in which CO₂ is reduced to methane (CH₄). The homodimeric [Fe] hydrogenase contains one redox-inactive iron (Fe) per subunit, which is bound to a guanylylpyridinol cofactor.

While intermediates in the catalytic cycle of [NiFe] hydrogenases and [FeFe] hydrogenases have already been well studied, the catalytic intermediates of [Fe] hydrogenases were not observable—until now. A research team has now succeeded in detecting the intermediates in the [Fe]-hydrogenases catalysis cycle for the first time.

The team was led by Stefan Glöggler (Max Planck Institute for Multidisciplinary Sciences (MPI-NAT) and the Center for Biostructural Imaging of Neurodegeneration (BIN) at the University Medical Center Göttingen (UMG), Lukas Kaltschnee (MPI-NAT and BIN at UMG, currently at the TU Darmstadt), Christian Griesinger (MPI-NAT), and Seigo Shima (MPI for Terrestrial Microbiology), and included colleagues from the MPI für Kohlenforschung, Kiel University, and the FAccTs GmbH.

The researchers made use of the fact that hydrogen occurs as so-called parahydrogen and orthohydrogen, depending on its nuclear spin. The researchers showed that nuclear magnetic resonance spectroscopy results in signal amplification when the [Fe] hydrogenase reacts with parahydrogen. This so-called parahydrogen-induced polarization (PHIP) made it possible to identify the reaction intermediates and visualize how the [Fe] hydrogenase binds hydrogen during catalysis.

The scientists’ data indicate that a hydride is formed at the iron center during catalysis. The new method also made it possible to study the binding kinetics. Due to its high sensitivity, PHIP is particularly promising for application to living cells and for investigating hydrogen metabolism in vivo. The results could help to develop (bio)catalysts for hydrogen conversion with higher productivity in the future.

Over the last decade, the global market for plant-based beverages has seen remarkable growth, with oat, almond, soy and rice drinks emerging as popular alternatives to cow’s milk in coffee and oatmeal during this time.

One of the likely reasons for millions of liters of plant-based drinks ending up in the shopping baskets of consumers is that their climate footprint is often lower than that of cow’s milk. But consumers would be mistaken if they considered plant-based beverages healthier than cow’s milk. This is highlighted in a new study conducted by the University of Copenhagen in collaboration with the University of Brescia, Italy.

In the study, published in the journal Food Research International, researchers examined how chemical reactions during processing affect the nutritional quality of 10 different plant-based drinks, comparing them with cow’s milk. The overall picture is clear.

“We definitely need to consume more plant-based foods. But if you’re looking for proper nutrition and believe that plant-based drinks can replace cow’s milk, you’d be mistaken,” says Department of Food Science professor Marianne Nissen Lund, the study’s lead author.

Long shelf life at the expense of nutrition

While milk is essentially a finished product when it comes out of a cow, oats, rice, and almonds require extensive processing during their conversion to a drinkable beverage. Moreover, each of the plant-based drinks tested underwent “Ultra High Temperature” (UHT) treatment, a process that is widely used for long-life milks around the world. In Denmark, milk is typically found only in the refrigerated sections of supermarkets and is low-pasteurized, meaning that it receives a much gentler heat treatment.

“Despite increased plant-based drink sales, cow milk sales remain higher. Consequently, plant-based drinks undergo more intense heat treatments than the milk typically sold in Denmark, in order to extend their shelf life. But such treatment comes at a cost,” says Lund.

UHT treatment triggers a so-called “Maillard reaction,” a chemical reaction between protein and sugar that occurs when food is fried or roasted at high temperatures. Among other things, this reaction impacts the nutritional quality of the proteins in a given product.

“Most plant-based drinks already have significantly less protein than cow’s milk. And the protein, which is present in low content, is then additionally modified when heat treated. This leads to the loss of some essential amino acids, which are incredibly important for us. While the nutritional contents of plant-based drinks vary greatly, most of them have relatively low nutritional quality,” explains the professor.

For comparison, the UHT-treated cow’s milk used in the study contains 3.4 grams of protein per liter, whereas eight of the 10 plant-based drinks analyzed contained between 0.4 and 1.1 grams of protein. The levels of essential amino acids were lower in all plant-based drinks. Furthermore, seven out of 10 plant-based drinks contained more sugar than cow’s milk.

Heat treatment may produce carcinogens

Besides reducing nutritional value, heat treatment also generates new compounds in plant-based drinks. One such compound measured by the researchers in four of the plant-based drinks made from almonds and oats is acrylamide, a carcinogen that is also found in bread, cookies, coffee beans and fried potatoes, including French fries.

“We were surprised to find acrylamide because it isn’t typically found in liquid food. One likely source is the roasted almonds used in one of the products. The compound was measured at levels so low that it poses no danger. But, if you consume small amounts of this substance from various sources, it could add up to a level that does pose a health risk,” says Lund.

Additionally, the researchers detected α-dicarbonyl compounds and hydroxymethylfurfural (HMF) in several of the plant-based drinks. Both are reactive substances that could potentially be harmful to human health when present in high concentrations, although this is not the case here.

While professor of nutrition Lars Ove Dragsted is not particularly concerned about the findings either, he believes that the study highlights how little we know about the compounds formed during food processing:

“The chemical compounds that result from Maillard reactions are generally undesirable because they can increase inflammation in the body. Some of these compounds are also linked to a higher risk of diabetes and cardiovascular diseases. Although our gut bacteria break down some of them, there are many that we either do not know of or have yet to study,” says Dragsted of the Department of Nutrition, Exercise and Sports.

Professor Dragsted adds, “This study emphasizes why more attention should be paid to the consequences of Maillard reactions when developing plant-based foods and processed foods in general. The compounds identified in this study represent only a small fraction of those we know can arise from Maillard reactions.”

Make your own food

According to Professor Lund, the study highlights broader issues with ultra-processed foods: “Ideally, a green transition in the food sector shouldn’t be characterized by taking plant ingredients, ultra-process them, and then assuming a healthy outcome. Even though these products are neither dangerous nor explicitly unhealthy, they are often not particularly nutritious for us either.”

Her advice to consumers is to “generally opt for the least processed foods and beverages, and to try to prepare as much of your own food as possible. If you eat healthily to begin with, you can definitely include plant-based drinks in your diet—just make sure that you’re getting your nutrients from other foods.”

At the same time, Professor Lund hopes that the industry will do more to address these issues: “This is a call to manufacturers to further develop their products and reconsider the extent of processing. Perhaps they could rethink whether UHT treatment is necessary or whether shorter shelf lives for their products would be acceptable.”