Food Chemistry

Phytochemicals

The noun ‘phytochemicals’ describes a bewildering number of molecules from plants, which can be classified into distinct groups, based on their biosynthetic origin: a.o. flavonoids (with subclasses of flavan-3-ols, flavones, etc.), isoflavonoids (with subclasses of isoflavones, coumestans, pterocarpans, etc.), stilbenoids, lignans, benzoxazinoids, agmatines, avenanthramides, glucosinolates (and their respective isothiocyanates), triterpenoid glycosides (saponins, certain glycoalkaloids), carotenoids, and porphyrins (e.g. chlorophylls). Phenolics are part of (but not synonymous to) phytochemicals. They are characterized by having an aromatic ring substituted with at least one hydroxyl group. These phenolics are known to be quite reactive and are known to engage in dimerization reactions or even further oligomerization.

Description of theme

Despite the fact that phytochemicals are minor constituents of foods relative to carbohydrates, proteins, and lipids, they can impact food quality to a larger extent than one might expect from their proportion. Roughly, three impact areas of phytochemicals can be distinguished in food technology:

  • Health. Although few phytochemicals have been granted an EFSA approved Health Claim in the EU, e.g. proanthocyanidins and phytosterols have been associated with heart health, the bioactivity of many other phytochemicals is anticipated. For instance, isoflavones seem to lower the incidence of specific types of cancer by acting as hormone look-alikes. Furthermore, phenolics are known to interact with proteins (covalently or non-covalently, which can affect protein digestibility by protease in the gastro-intestinal tract. Finally, many phytochemicals serve as the plant’s weaponry against microbial pathogens. Not surprisingly, they can also have antimicrobial activity against intestinal microbiota, as well as against food-borne pathogens, such as Listeria monocytogenes. Phytochemicals have also shown antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA, an increasing cause of infection in hospitals), in doses similar to currently used antibiotics.

    Nowadays, there is a growing interest in phytochemicals from a health perspective, fueled by our ever aging population, urgency of diseases associated with a Western lifestyle (e.g. cardiovascular disease, obesity), and growing thread of infectious diseases.

  • Sensory. Phytochemicals are important in determining the attractiveness of foods, esp. with respect to color and taste. For instance, anthocyanins are responsible for the color of red wine (desirable), but enzymatic browning reactions are often regarded undesirable. Taste sensations associated with phenolics are bitterness, astringency, and intense sweetness.
  • Technofunctionality. Enzymatic browning by polyphenol oxidase (PPO) and the presence of chlorophyll are notorious problem causers when processing plant-derived raw materials into food ingredients. The properties of such food ingredients might be altered by PPO, e.g. proteins that have reacted with phenolics can show different solubility or aggregation properties, besides reduced digestibility.

The aim of FCH’s research on phytochemicals is to (i) characterize phytochemicals from various plant materials; (ii) monitor changes in phytochemical composition during plant growth, processing, storage, and passage through the gastrointestinal tract; (iii) convert phytochemicals, enzymically or microbially, in order to enhance their properties, and (iv) improve the processibility of plant materials.

Research Projects