Non-nutritive ingredients Part I: Secondary plant substances
It is estimated that 60,000 to 100,000 secondary plant substances exist. In order to fight your way through the jungle of these substances, it is advantageous to have a structured basic framework. So far, however, only a small part of the secondary plant compounds has been analysed, which is why we will start by illuminating the basic systematics of secondary plant compounds with you.
In this context, it should be noted that the knowledge about phytochemicals has greatly increased within the last few years and studies now deal with the substances more and more frequently.
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- As part of a usual mixed diet, we consume about 1.5 grams of secondary plant compounds daily. Currently, these substances are considered non-essential for the body
- Secondary plant substances serve the carriers as defense, color, fragrance and aroma substances
- Secondary plant compounds include polyphenols, carotenoids, glucosinolates, monoterpenes, phytoestrogens, phytosterols, sulfides, protease inhibitors, phytic acids and saponins:
Polyphenols:
- Found primarily in green and black tea.
- Antimicrobial, antiviral, anti-inflammatory, antithrombotic, anti-allergic, blood pressure regulating, antioxidant and cognition enhancing.
Carotenoids
- Found mainly in red, yellow and orange plants
- Have anti-inflammatory, immunomodulatory and antioxidant effects. They also have a health-promoting effect on the eyes
Glucosinolates
- Found mainly in radishes, radish and mustard.
- Have antioxidant and immunomodulatory effects. An anticarcinogenic effect is discussed
Monoterpenes
- Found mainly in essential oils and citrus oils.
- Have anesthetic, expectorant, anticarcinogenic and cholesterol-lowering effects.
Phytoestrogens
- Found in soy products, flaxseed or tofu. They are similar to the body’s own estrogens.
- Have an anticarcinogenic, antioxidant and possibly cardiovascular protective effect. A positive effect on menopausal symptoms has also been observed
Phytosterols
- Found mainly in sunflower seeds and sesame seeds.
- Have cholesterol-lowering and possibly also anticarcinogenic and cardiovascular-protective effects.
Sulfides
- Mainly found in lily plants such as onions
- Have a blood pressure-lowering, cholesterol-lowering, antioxidant, antibiotic, antithrombotic, digestive, anticarcinogenic and immunomodulatory effect.
Protease inhibitors
- Particularly rich in soybeans, various cereals and nuts
- Have anticarcinogenic, antioxidant and anti-inflammatory effects
Phytic acids
- Found mainly in nuts, seeds, raisins and beans
- Impairs the absorption of, among others, calcium, zinc, iron and magnesium
- Have a positive effect on blood sugar levels and are expected to be anticarcinogenic and antioxidant.
Saponins
- Legumes are among the rich sources of saponins
- Have a positive effect on cholesterol levels and are anticarcinogenic
The (non-essential) influence of secondary plant compounds
Secondary plant compounds are not used by the body’s biochemical cycle to the same extent as we know it from ingredients in food. Unlike proteins, lipids and carbohydrates, for example, this type of substance is not utilized in the metabolism. Secondary plant substances do, however, have an influencing effect on our metabolism. At present, it is nevertheless assumed that secondary plant substances are not essential for the body. In a normal mixed diet, we consume about 1.5 grams of them daily.
Classification of secondary plant compounds on the basis of their chemical structure
When it comes to the task of the secondary plant compounds in the plants themselves, these substances serve the defense, color, fragrance and aroma function. The individual compounds are classified into substance groups that have different chemical structures. Polyphenols, carotenoids, glucosinolates, monoterpenes, phytoestrogens, phytosterols and sulfides are distinguished. Protease inhibitors, phytic acids and saponins are also included.
Polyphenols and their multitude of positive effects
The group of polyphenols includes several subgroups. Polyphenols protect the plant especially against predators and UV radiation. This class of substances is found in all plants, especially in green and black teas. Polyphenols all have a phenolic basic structure, with significant subgroups such as flavonoids, isoflavonoids and phenolic acids.
In total, polyphenols are assigned the following properties:
- Antimicrobial / antiviral property.
- Anti-inflammatory property
- Antithrombotic and antiallergic property
- Blood pressure regulating property
- Antioxidant effect (radical scavenger) and protection against UV radiation
- Influence on cognitive performance
Studies suggest that polyphenols may reduce numerous risks for cancer and cardiovascular ailments.
Carotenoids especially good for the eyes
If you want to subdivide carotenoids further, you will come across about 800 different substances. First and foremost, a distinction is made between substances with and without oxygen. In the context of carotenoids, we also speak of trepenoid dyes, which are responsible for the red, yellow or orange coloration of various plants. An excess of energy is to be transformed by these substances into warmth, besides, the dye helps with protection against light irradiation.
Typical representatives of oxygen-free carotenoids are carotenes such as alpha- and beta-carotene and lycopene, which are found in large numbers in orange, red or yellow plants. Oxygenated carotenoids, also called xantophylls, are abundant in green leafy vegetables.
Significantly, carotenoids have anti-inflammatory, immunomodulatory and antioxidant effects. Especially in the risk reduction of age-related eye diseases, carotenoids show a positive effect. They also play a role in reducing the risk of cardiovascular diseases. However, a positive effect on the development of cancer is controversial.
Glucosinolates and their positive effect on cancer
The group of glucosinolates also includes over 120 different representatives. The enzyme myrosinase can cleave glucosinolates. This is also referred to as the glucosinolate-myrosinase system of plants. Primarily, the cleavage and the resulting substances serve as a defense. Especially radish, radish and mustard contain large amounts of glucosinolates. In addition to an antixodative and immunomodulatory effect, studies suggest that glucosinolates may have a positive effect on cancer (especially colon and prostate cancer).
Monoterpenes as radical scavengers, anti-cancer substances and cholesterol-lowering agents
It is also not surprising that among the monoterpenes, a representative of the secondary plant substances, there are more than 700 different substances. These substances are mainly found in essential oils and citrus oils, and the plant itself uses them as aroma and fragrance substances. Particularly rich in monoterpenes is caraway, lemon or mint. Some monoterpenes can not only have anesthetic effects when applied locally, but can also ignite expectorant, anticarcinogenic, and cholesterol-lowering effects.
In addition, monoterpenes are thought to have free radical scavenging properties.
Phytoestrogens resemble the well-known estrogen
The group of phytoestrogens includes isoflavonoids, lignans and coumestans. In terms of chemical structure, they are very similar to the body’s own estrogens. Soy products, flaxseed, tofu and whole grain products in particular provide numerous phytoestrogens. Overall, these secondary plant compounds are believed to have anticarcinogenic and antioxidant effects. In addition, there is circumstantial evidence that phytoestrogens protect the cardiovascular system and help women against menopausal symptoms.
It should be noted that estrogens bind to specific receptors within our body. Phytoestrogens can also do this to a certain extent, but have a lower affinity to bind to these receptors. The complexes of phytoestrogens and receptors created are still not very stable. Depending on the concentration of phytoestrogens, these substances can thus act as antiestrogens or estrogen analogs.
Phytosterols primarily lower cholesterol levels
The phytosterols found mainly in sunflower seeds and sesame have a high chemical similarity to animal sterols such as cholesterol. Currently, 44 phytosterols are known. Functionally, they are believed to have cholesterol-lowering properties. Some experiments have also shown that an anticarcinogenic and cardiovascular protective effect is possible.
Sulfides and their positive effects on the body
The group of sulfides includes sulfur-containing compounds from garlic and other lily plants such as onions. For the sake of clarity, the compounds are divided into water-soluble and fat-soluble representatives. In particular, alliin, which is contained in garlic, is relatively well known and causes its typical odor.
Sulfides have many positive effects on our body:
- Blood pressure and cholesterol lowering function.
- Antioxidant, antibiotic and antithrombotic effect
- Digestive function
- Anticarcinogenic and immunomodulating effect
Protease inhibitors protect against degenerated cells
To get a better idea of protease inhibitors, it helps to look at their chemical structure. They are polypeptide chains with 100 to 200 amino acids. This group includes trypsin inhibitors, chymotrypsin inhibitors, and Bowman-Birk protease inhibitors. By their nature, these substances control proteolysis in the context of inflammatory processes. The body synthesizes selected protease inhibitors itself, but these substances are also supplied externally, particularly via soybeans, various cereals and nuts.
Protease inhibitors have not only anticarcinogenic, but also antioxidant and anti-inflammatory effects.
Advantages and disadvantages of phytic acid
As a widespread substance in products such as nuts, seeds, raisins and beans, phytic acid not only has a health-promoting effect. This is because phytic acid regrettably impedes the absorption of calcium, zinc, iron and magnesium. The reason for this is that this compound can bind the minerals listed. But besides this negative property, phytic acid also has a positive effect.
Since phytic acid is able to break down starch at a slower rate, this has a beneficial effect on blood sugar levels. In addition, it seems that the binding of excess ions by phytic acid, can prevent colon cancer.
In general, an antioxidant effect of phytic acid is discussed.
Saponins mainly affect cholesterol levels
The usual bitter-tasting saponins are used to protect plants from fungal attack. Due to the fact that these substances promote the formation of foam in liquids, they are often used in the food industry. For example, it is added to beer to achieve a better foaming result. Legumes are considered to be particularly rich in saponins.
In terms of their effect, saponins support cholesterol levels by binding cholesterol and promoting the excretion of cholesterol-contaminated bile. Furthermore, saponins are said to have anticarcinogenic properties. In high amounts, such phytochemicals can cause hemolysis by making the membrane of erythrocytes more permeable. However, such high concentrations are virtually inaccessible through the diet.
Text Sources:
(1) Hillebrand, Analysis of polyphenols in colored juices with regard to juice quality, color and antioxidant activity, 2004.
(2) Stodt, Polyphenols in black tea, 2016.
(3) Biesalski et al, Pocket Atlas of Nutrition, 8th edition, 2020.
(4) https://www.bio.uni-frankfurt.de/43969858/Forschung
(5) van Ohlen, Pieris rapae and the glucosinolate myrosinase system: cyanide toxicity and Lepidoptera, 2014.
(7) Zimmermann, Aromatherapy for nursing and healing professions, 3rd edition, 2006.
(8) Watzl and Leitzmann, Bioactive substances in food, 3rd edition, 2005.
(9) Hübner, Complementary Oncology, 2008
(10) Leitzmann et al, Nutrition in Prevention and Therapy, 3rd edition, 2009.
(11) Münstedt, Ratgeber komplementäre und alternative Krebstherapien, 3rd edition, 2012.
Image sources:
(12) https://unsplash.com/s/photos/red-yellow-orange-vegetables
