Research of Food Chemistry

Our aim is to gain knowledge of the effect of processing on the biochemical and physicochemical properties of proteins in raw materials, ingredients and foods, in relation to their functional and nutritional properties.

Since proteins vary widely in their structure, their functional properties will diverge accordingly. Additionally, the functionality of proteins is influenced by the isolation procedure, (physico-)chemical or enzymatic modification, and the composition and processing route of the food in which they are applied. Besides the use of proteins as food ingredient, we also focus on their breakdown by digestive enzymes. Knowledge of structure-function relationships of proteins in foods, and the interaction between proteins and other food constituents form the basis for the development of modern processes, new ingredients or higher quality products.

In our group, we have four main focus areas:

1. Novel and current plant proteins (including microalgae): Focused on isolation methods, complications to replace animal-based proteins, protein-phenol interactions, off-taste/off-colour formation and characterisation of the obtained concentrates/isolates.
2. Enzymatic hydrolysis of proteins: To describe the protein hydrolysis, a unique method has been developed to identify and quantify peptides in several stages of the hydrolysis process. This allowed further development of concepts to characterise this process and relevant molecular properties of both protease and substrate.
3. Maillard reactions: To understand the effects of Maillard reactions on ingredient functionality and protein digestibility, we developed adequate methods to quantify the extent of modification.
4. Foam and emulsifying properties of proteins: We develop methods and concepts to describe functional properties based on the protein molecular properties.

In our group, we have the following expertises:

• Analysis of proteins and peptides by liquid-chromatography techniques as AEC, SEC, HILIC
• Advanced analytical techniques such as LC-MS to analyse intact proteins and peptides
• We combine the information obtained with these techniques with protein conformation (circular dichroism, light-scattering) and protein functionality (several methods)
• Simulation of in vitro digestion with pH-stat units

Current trends in food and agriculture, such as the protein transition, are creating a growing interest in natural plant-based ingredients. As a result, phytochemicals (phyto meaning ‘plant’ in Ancient Greek) are becoming increasingly prevalent and important in food.

The term ‘phytochemicals’ describes a bewildering number of small molecules from plants, which can be divided into many distinct classes based on their biosynthetic origin and structure. Phytochemicals include, but are not limited to, the following classes: (iso)flavonoids (e.g. flavan-3-ols and isoflavones), stilbenoids (e.g. resveratrol), (hydroxy)cinnamic acids (e.g. coumaric acid, ferulic acid), phenolamides (e.g. avenanthramides), (neo)lignanamides (e.g. hordatines), triterpenoid glycosides (e.g. saponins), and carotenoids. Phenolic compounds, which make up several of these classes, are the most widespread and broadly studied. Phenolics and other phytochemicals can be reactive and are prone to structural changes during plant growth, and during processing and storage of plant-based food products or ingredients. These structural changes modulate phytochemicals’ molecular and functional properties.

Even though phytochemicals are present in much smaller quantities in foods than carbohydrates, proteins, and lipids, they can strongly affect food properties. These effects, ranging from enhanced bio- or techno-functionality to (undesirable) colour formation, can be due to the inherent properties of phytochemicals or due to the reactivity of these compounds. Understanding the effects of phytochemicals on the properties of food products and ingredients is essential due to the aforementioned trends in plant-based food.

The aims of the FCH theme Phytochemicals are to:

• Characterize phytochemicals from various plant materials using advanced analytical techniques
• Monitor changes in phytochemical composition during plant growth, and during processing and storage of plant-derived food products or ingredients
• Modify phytochemicals with chemical, enzymatic, or microbial approaches, to improve their properties
• Study interactions of phytochemicals with proteins and micronutrients

Advanced phytochemical analysis

Analysis and structure elucidation of phytochemicals is at the core of our work on these compounds, as it is essential in studying phytochemical reactivity. Due to the high structural diversity of phytochemicals, their analysis can be quite challenging. We develop analytical approaches to obtain structural information on individual phytochemical molecules, as well as overall compositional data of phytochemicals present in plant-derived materials (including industrial waste streams or by-products). To this end, we employ a diverse array of advanced analytical techniques, including ultra-high performance liquid chromatography (UHPLC), high-resolution mass spectrometry (HRMS), ion mobility spectrometry (IMS), and nuclear magnetic resonance (NMR) spectroscopy.

Oxidation of phenolic compounds

One of the most well-known examples of the oxidation of phenolic compounds is the enzymatic browning reaction that leads to formation of brown colour upon cutting or bruising of fruits. Besides undergoing enzymatic oxidation, phenolic compounds can auto-oxidise to form brown and insoluble reaction products. Phenolic oxidation reactions are often considered to be undesirable, as they can negatively affect the attractiveness of foods or ingredients. On the other hand, controlled (enzymatic) oxidative coupling may also be used as a tool to modulate the structure and properties of phenolic compounds, which can lead to improved bio- or techno-functionality. We study these reactions to tackle challenges associated with undesired oxidation as well as exploring the potential of controlled oxidation as a valuable universal tool to modify phenolic compounds.

Interactions of phytochemicals with other food molecules

Phytochemicals are known to interact covalently and non-covalently with various other food molecules, including proteins and metals. Protein-phenolic interactions can impact sensory, techno-functional, and bio-functional properties in plant protein products. Similar to our work on phenolic oxidation, we investigate how these interactions can be prevented or how they may be exploited to enhance the functionality of both plant proteins and phenolic compounds. With regards to metal-phenolic interactions, we study the resulting formation of dark discolouration (e.g. in iron-fortified food products) and explore opportunities related to the complexation of metals by phenolic compounds.

Plant secondary metabolism is rich in compounds (i.e. phytochemicals) with promising (bio)activities or functionalities. These (bio)active phytochemicals can be utilized for the benefit of human, animal and plant health. For instance, the rich stereochemical and functional group diversity of phytochemicals offers a wide range of functionalities, including the inhibition of unwanted microorganisms and the development of novel alternatives to traditional antimicrobials.

The Plant (bio)actives group focusses on promising antimicrobial phytochemicals. To obtain these antimicrobials, we employ two main strategies: inducing production in-planta using diverse (a)biotic elicitors and valorizing from agri-food by-products.

The work of the Plant (bio)actives group lies at the intersection of (phyto)chemistry, microbiology and (in-silico) molecular modelling. More specifically, our aim is to:

• Characterize the antimicrobial properties of phytochemicals
• Predict and rationalize their (quantitative) structure-activity relationships (QSAR)
• Elucidate their mode of action (MoA) and explore synergistic combinations

At Plant (Bio)Actives, in-silico modelling is integrated with in-vitro evidence to rationalize and predict the properties and MoA of antimicrobial phytochemicals.

Antimicrobial properties and synergistic combinations

Phytochemicals have demonstrated effectiveness as antimicrobials against bacteria (cells and spores), fungi and viruses. An interesting strategy to control microorganisms is to design multi-targeted antimicrobial combinations, mimicking how plants respond to pathogens. To develop effective synergistic combinations, it is essential to first characterize the different functionalities of different families of phytochemicals (e.g. inhibition of specific proteins, bacterial membrane disruption, efflux pump inhibition, oxidative stress induction). Quantifying their activity and mapping their spectrum of activity are critical aspects of this research. By using synergistic combinations of plant antimicrobials (i) the potency of the antimicrobial cocktail is enhanced; (ii) dosages can be reduced, making this approach more feasible for applications such as food preservation; and (iii) the risk of persistent or resistant cell survival is significantly minimised.

Structure-activity relationships (SAR)

The activity of phytochemicals is strongly linked to their structure. Rather subtle structural differences can lead to a substantial change in the antimicrobial activity. Quantitative SAR analysis is a chemometric tool that enables (i) predictive assessment for an efficient discovery and isolation of antimicrobial phytochemicals (e.g. reducing the number of purification experiments); (ii) accelerated design and optimization of lead antimicrobial scaffolds; and (iii) insights into the molecular properties critical for activity. A balanced approach that combines predictive assessment and in-vitro screening is essential to guide this research effectively.

Mode of action

To apply plant-derived antimicrobials in areas such as food, feed or environment, their molecular mechanisms should be well-defined and validated. The elucidation of the molecular targets of antimicrobial phytochemicals include in-vitro assays and in-silico tools. In-vitro assays include cell-based (fluorescence) assays, MS-based targeted analysis, and -omics profiling. In-silico tools include the calculation of molecular properties, 3D pharmacophore modelling, molecular docking and MD simulations. Strong collaborations with other fundamental research groups enable a comprehensive understanding of the mode of action.

Carbohydrates determine to a large extent quality attributes of the final food product while polysaccharides (e.g. pectic substances, hemicelluloses, cellulose) as present in fresh fruits and vegetables (e.g. ripeness, texture) determines their typical characteristics as well as their processing characteristics in the manufacture of foods (juices, nectars, purees, preserves). Polysaccharides also influence the extractability of important constituents of plant raw materials like sugar, oil, proteins, etc. Dietary fibers and prebiotic oligosaccharides, including mammalian milk oligosaccharides, play an important role in human and animal health, and their behaviour in the gastrointestinal tract strongly depend on the chemical structure of these fibers.

We aim to establish relationships between the chemical fine structure of the carbohydrate and the corresponding functional property of this carbohydrate (isolated or as present in the original product).

Typical materials studied are: cereals like wheat, corn; fruits and vegetables like apple, tomato, carrots, potatoes, soybeans; food ingredient like pectin, galactomannans, xanthan, as well as human milk and fermentation digests.   

In general, various classes of oligo- and polysaccharides as present in fruits, vegetables, cereals or food products derived here from and of agrotechnological by-products are extracted and characterised by e.g.sugar (linkage) composition, substituents, molecular weight. Unknown carbohydrate structures are separated by (preparative) chromatography and characterised using mass spectrometry and NMR. Enzymatic fingerprinting methods using pure and well characterised enzymes are being used and further developed to enable ‘sequencing’ of complex carbohydrate structures using state-of-the-art LC-MS platforms. The fate of individual prebiotic and dietary fiber structure during the digestion and fermentation in in vitro models as well in human and animals are monitored using the same analytical techniques.

We study mainly conversion of grasses, of which the plant cell walls are majorly composed of cellulose, hemicellulosic arabino-glucurono-xylan and of lignin. These three polymers contribute to the plant cell wall architecture, which influences physical characteristics like toughness (and degradability), and water binding capacity. A better understanding of the chemical fine-structure of the cell wall architecture’s network will provide a better understanding of how to influence changes in biomass architecture and it’s enzymatic (biological) degradation.

The aim of this theme is to:

• Monitor changes in lignin and plant carbohydrate levels and composition during pretreatment, fungal growth, enzymatic processes, and during animal digestion
• Understand mode-of-action of (fungal) hydrolytic and oxidative carbohydrate and lignin degrading enzymes and their effect on the chemical fine structure of natural substrates.

For the lignin analysis, we have set-up a new method via pyrolysis-GC-MS, making use of a mildly extracted 13C-lignin isolate from wheat straw as internal standard. This method allows us to specifically quantify residual lignin content in situ, while simultaneously providing structural insights. Further lignin characterisation via NMR (HSQC) has been set up. Carbohydrate analysis is applied in situ or/and after extraction polysaccharides. Examples of analysis are carbohydrate content and composition, the sugar linkage composition, the type and amount of substituents on the carbohydrates present. Various chromatographic and mass spectrometric techniques are available.

The incorporation of polyunsaturated fatty acids in food formulations could be of great interest to promote health. These polyunsaturated fatty acids are involved in the regulation of inflammation and have shown benefits for cardiovascular and cerebral functions. However, these polyunsaturated fatty acids are also very sensitive to lipid oxidation, generating unpleasant off-flavours and reducing the nutritional value of these compounds.

Lipid oxidation in food is a complex process, that could lead to the formation of hundreds of different molecules. Moreover, the type of food matrix and the presence of other components (proteins, antioxidants, metals) could influence the process, making it even more complex. In order to prevent the generation of off-flavours and the loss of nutritional value of food due to lipid oxidation, it is important to better characterize these mechanisms.  

The aim of this theme is to:

• Set up analytical tools for characterization and quantification of lipid oxidation products (radicals, hydroperoxides, oxylipins, volatiles)
• Monitor lipid oxidation in various types of food or food ingredients during storage and processing
• Understand the interaction with other food components, such as metals, proteins, and antioxidants
• Develop innovative and consumer-friendly methods to control lipid oxidation in food while maintaining the quality of the product (e.g. physical stability, digestibility and bioavailability, health benefits).

In our research, we use multiple analytical tools, such as:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Electron Spin Resonance (ESR) spectroscopy
• Chromatographic and mass spectrometric methods

Flavour is one of the primary factors influencing consumers' food choices. It primarily consists of taste, driven by non-volatile and semi-volatile compounds, and aroma, driven by volatile odorants. While tastants and aroma compounds can originate from raw foods and ingredients, a great deal of them are formed through chemical and enzymatic reactions during food processing.

Many of such flavour generating reactions remain only partly understood, which makes it difficult to control and steer them. Another challenge is that flavour compounds tend to interact with other compounds in the food matrix and/or in the oral cavity, which can alter human perception of flavour. Therefore, within the flavour chemistry theme, our goal is to gain a deeper understanding of flavour-generating reactions and flavour-matrix interactions at the molecular level.

Reaction flavours are formed when foods or food ingredients are heated. An important example is the development of meat flavour during cooking processes like frying or roasting. While the basic chemistry behind meat aroma formation is generally understood, replicating these reactions to create meat-like aromas in plant-based alternatives remains a challenge. This difficulty arises from several factors, including the distinct reaction environments in plant-based matrices, the tendency of flavour compounds to bind to these plant-based ingredients, and the presence of off-flavours in the plant-based ingredients. In this focus area, we investigate the reactions responsible for meat aroma generation and explore how to best replicate them in plant-based food systems.

In addition to tastants and odorants, flavour-enhancing and flavour-modifying compounds can form during food processing and preparation. These compounds typically possess limited inherent flavour but can significantly influence taste and smell perception already at concentrations below their intrinsic taste thresholds. As a result, they offer promising applications as functional food ingredients, potentially enabling salt or calorie reduction without compromising flavour intensity. At the Laboratory of Food Chemistry, our research focuses on the formation and mode of action of these flavour-modifying compounds. Collaborating with sensory scientists, we also explore their potential as innovative food ingredients.

Cereals are the most important staple food in many parts of the world and it is the main source of nutrients, a.o., protein, fibre and minerals in the human diet (Weegels 2019). To feed future generations better, it is of paramount importance that food safety and security of cereal-based foods is enhanced and food waste is reduced.

“To explore the potential of nature to improve the quality of life” is the mission of WUR. Sustainable production and processing of food, food safety, food security and health aspects of food belong to the focus areas to achieve this mission. Since starchy staple foods nourish the world population and because of the complexity of nutritional quality, cereal breeding and processing, Cereal Biochemistry aims to enlarge the scientific fundament to develop more nutritious cereal staple foods by bioprocessing to feed the future generations better and to increase its safety and security.

1. Coeliac disease has not been solved and patients have limited access to palatable high-quality gluten-free food
2. Non gluten wheat intolerances seem to be increasing, causing a decrease in consumption of cereal-based products. Thus, consumers are missing out on an important and cheap source of nutrients (Weegels 2019).
3. The control of digestibility of cereal-based products and its effect on nutritional status (undernutrition, obesity) is still limited.

Anti-nutritional factors in cereals

Anti nutritional factors (ANF) play an important role in cereals to protect against infestation and animal consumption. From an agronomic point of view these pest barriers are beneficial as the required pest control measures (chemical pesticides, storage facilities) is relatively limited. From a health point of view ATI’s are of special attention for human health.

• Their enzyme inhibition can reduce digestibility of food directly, which can be either beneficial (weight reduction) or negative (pathological effects, undernutrition and food insecurity). They can increase the load of allergenic peptides presented to the small intestine, thus increasing the allergenic and inflammation reactions
• Complexation behavior may strongly interact with the small intestine epithelium that can cause inflammation by itself
• the not yet completely understood cause of Bakers asthma, the major labour related allergy (Stobnicka and Górny, 2015)

·increase of the load of non-digested peptides and carbohydrates especially of non-starch polysaccharides (FODMAPS) that are a major cause of Irritable Bowel Syndrome (IBS) which affects 7% to 21% of the general population (Chey et al. 2015). Understanding the role of ATI in cereals food processing and food digestion and mitigation of the negative effects is therefore of prime importance for food safety, security and sustainability. 

Safety and quality of gluten-free foods

This is principally concerned with:

• Improving the safety and safe use of cereals in relation to celiac disease, by improved analytical methods to detect toxic epitopes (van den Broeck et al. 2010)
• Enabling the development of gluten-free bread by replacing gluten with other ingredient functionalities (van Riemsdijk, 2015)

Starch digestibility in intermediate moisture foods

Starch structuring during processing and storage is key to food structure, its digestibility and palatability. The changes in crystallinity of starch during and after processing are another important factor determining the digestibility of cereal foods. These changes depend on several factors:

• Processing (time, temperature, heat transfer)
• Food composition (a.o. presence of proteins, non-starch polysaccharides and components forming molecular complexes with starch like lipids)
• Moisture content
• Storage time and temperature after preparation

The speed of digestion of starch is linked to blood glucose levels and satiety and probably other health aspects, like obesity and cardiovascular diseases. It is, therefore, important to understand the effect of processing conditions on starch crystallinity and consequently the speed of digestion.

Most starchy staple foods are produced under low or medium moisture contents, such as baking, cooking, frying, extrusion, moulding, drying/puffing. Therefore, focus will be on intermediate moisture foods.

Digital exercises / linear cases

intensive questions and tasks with built-in feedback and hints to acquire knowledge on food chemistry. This ranges from > 100 exercises for the course Food Chemistry, several linear cases in many courses such as Food Properties and Function and Food Ingredient Functionality. Many of these exercises have been used for several years now and are highly appreciated by our students.

Pre-laboratory assignments

Assignments in which students design several experiments to answer a couple of research questions related to food chemistry.

Quantitative assignments

Assignments in which students calculate on chemical reactions in food products. These assignments are used in the course Food Chemistry since 2000.

Online Problem Based Learning (group work)

By using tools such as Google Docs, Blackboard, or even ExperD we have developed several options to implement online group work based on the principles of Problem Based Learning

Labbuddy (ExperD and WebLabManual)

A design environment for students to design their (own) lab experiments (ExperD), connected to the digital lab manual. Although developed during a PhD project at our group, this program is now hosted by Kryt bv.

LabSim (a virtual experiment environment VEE)

In this extension of labbuddy students design experiments for certain research questions and then receive the data based on the design choices students made. Students process the data to answer the research questions. VEE can prepare students for lab classes, or even replace (part of) lab classes.