Coffee is not only a refreshing beverage but also rich in various beneficial components. This article systematically reviews the health value of coffee from the perspective of chlorogenic acid. As a key antioxidant, chlorogenic acid is widely present in green coffee beans and possesses multiple biological activities, including antibacterial, antiviral, and cardiovascular protective effects. The article details the chemical structure, plant sources, medical applications, and toxicity of chlorogenic acid, and compares the changes in chlorogenic acid content among different coffee varieties and roast levels. Finally, based on extraction experiment data, practical advice for daily coffee consumption is provided. Whether you are a coffee enthusiast or a reader concerned with healthy eating, you can gain a scientific and objective understanding of coffee.
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In the book "101 Reasons Coffee Is Innocent," renowned domestic health education expert and cardiovascular disease specialist Professor Hu Dayi and his collaborators pointed out through research that coffee is a functional food rich in antioxidants. To date, researchers have isolated over 1,500 substances from coffee, of which about 800 are beneficial to human health, while another 700 are neither beneficial nor harmful.
Chlorogenic acid, also known as coffee tannic acid, is a depside formed by the condensation of caffeic acid and quinic acid. It is also called coffee tannin, with the chemical name 3-O-caffeoylquinic acid, molecular formula C16H18O9, and molecular weight 354.30. It is a phenolic compound produced by plants through the shikimic acid pathway during aerobic respiration. Chlorogenic acid is widely distributed in higher dicotyledonous plants and ferns, mainly found in plants of the Caprifoliaceae family (Lonicera genus), Asteraceae family (Artemisia genus), and others. Plants with high content include Eucommia ulmoides, honeysuckle, sunflower, Loropetalum, coffee, and cacao trees. In addition, foods such as apples, pears, potatoes, soybeans, wheat, and green tea also contain chlorogenic acid compounds.
Chlorogenic acid has a relatively broad-spectrum antibacterial effect, but it is inactivated by proteins in the body. Similar to caffeic acid, oral or intraperitoneal injection of chlorogenic acid can increase central nervous system excitability in rats, enhance small intestinal peristalsis in rats and mice, and increase uterine tension in rats. It also has cholagogic effects, promoting bile secretion in rats. One of the main antibacterial and antiviral active pharmacological components of the traditional Chinese medicine honeysuckle is chlorogenic acid.
I. Which Plants Contain Chlorogenic Acid
The leaves of Eucommia ulmoides (Eucommiaceae), the dried flower buds or newly opened flowers of Lonicera japonica, Lonicera hypoglauca, Lonicera confusa, or Lonicera macranthoides (Caprifoliaceae), the fruit of Crataegus laevigata (Rosaceae), the flowers of Lythrum salicaria (Lythraceae), Dodonaea viscosa (Sapindaceae), the rhizomes of Polypodium vulgare (Polypodiaceae), the roots of Stachytarpheta jamaicensis (Verbenaceae), the stems and leaves of cabbage (Brassicaceae), the whole plant of Polygonum aviculare (Polygonaceae), the whole plant of Galium aparine (Rubiaceae), the whole plant of Sambucus javanica (Caprifoliaceae), the leaves of sweet potato (Convolvulaceae), the seeds of Coffea arabica, Coffea canephora, and Coffea liberica (Rubiaceae), and the leaves and roots of burdock (Asteraceae) all contain chlorogenic acid.
II. Chemical and Physical Properties of Chlorogenic Acid
Chlorogenic acid is an ester formed from caffeic acid and quinic acid. Its molecular structure contains three unstable parts: an ester bond, an unsaturated double bond, and a polyphenol. Research by Microherb indicates that during the extraction of chlorogenic acid from plants, isomerization often occurs due to hydrolysis and intramolecular ester group migration. Due to its special structure, chlorogenic acid can be extracted from plants using polar solvents such as ethanol, acetone, and methanol. However, because it is inherently unstable, it cannot be subjected to high temperatures, strong light, or prolonged heating during extraction. It is recommended to store it sealed, protected from light, and at low temperatures. The most stable condition for chlorogenic acid test solutions is storage in brown bottles in a refrigerator (2°C).
Chlorogenic acid hemihydrate forms needle-like crystals, becomes an anhydrous compound at 110°C, has a melting point of 208°C, and a solubility of 4% in 25°C water, with greater solubility in hot water. Chlorogenic acid is easily soluble in ethanol and acetone, and very slightly soluble in ethyl acetate. During coffee bean roasting, when the roaster temperature exceeds 208°C, chlorogenic acid begins to decompose into chlorogenic acid lactones, which are extremely bitter substances and one of the main sources of the heavy bitterness in dark-roasted coffee.
Based on the different binding sites and numbers of caffeoyl groups on quinic acid, theoretically there are 10 isomers of chlorogenic acid composed of mono-caffeoylquinic acid and di-caffeoylquinic acid: 1-caffeoylquinic acid, 3-caffeoylquinic acid, 4-caffeoylquinic acid, 5-caffeoylquinic acid, 1,3-dicaffeoylquinic acid, 1,4-dicaffeoylquinic acid, 1,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, and 4,5-dicaffeoylquinic acid. However, as of now, the following chlorogenic acid isomers have been found in plants: chlorogenic acid (5-caffeoylquinic acid), cryptochlorogenic acid (4-caffeoylquinic acid), neochlorogenic acid (3-caffeoylquinic acid), isochlorogenic acid A (3,5-dicaffeoylquinic acid), isochlorogenic acid B (3,4-dicaffeoylquinic acid), isochlorogenic acid C (4,5-dicaffeoylquinic acid), and cynarin (1,3-dicaffeoylquinic acid).
III. Medical Value and Applications of Chlorogenic Acid
Chlorogenic acid has a wide range of biological activities, and modern scientific research on it has delved into multiple fields including food, health care, medicine, and daily chemicals. As an important bioactive substance, chlorogenic acid has effects such as antibacterial, antiviral, increasing white blood cells, protecting the liver and promoting bile secretion, anti-tumor, lowering blood pressure, lowering blood lipids, scavenging free radicals, and stimulating the central nervous system.
1. Antibacterial and Antiviral
Eucommia chlorogenic acid has strong antibacterial and anti-inflammatory effects. Aucubin and its polymers have significant antibacterial effects, and aucubigenin inhibits both Gram-negative and Gram-positive bacteria. Aucubin can inhibit bacteria, promote diuresis, and promote wound healing; when aucubin is pre-cultured with glucosidase, it also produces significant antiviral effects, although it does not have antiviral function by itself. The Aichi Medical University Institute for Aging Medical Sciences in Japan has confirmed through research that alkaline substances extracted from Eucommia ulmoides have the function of resisting viruses that destroy the human immune system, and this substance is expected to be used for the prevention and treatment of AIDS.
2. Antioxidant Effects
Chlorogenic acid is an effective phenolic antioxidant, with antioxidant capacity stronger than caffeic acid, p-hydroxybenzoic acid, ferulic acid, syringic acid, butylated hydroxyanisole (BHA), and tocopherol. The reason chlorogenic acid can act as an antioxidant is that it contains a certain amount of R-OH groups, which can form hydrogen free radicals with antioxidant effects, thereby eliminating the activity of free radicals such as hydroxyl radicals and superoxide anions, thus protecting tissues from oxidative damage.
3. Scavenging Free Radicals, Anti-Aging, and Anti-Musculoskeletal Aging
The free radical scavenging effect of chlorogenic acid and its derivatives is stronger than that of ascorbic acid, caffeic acid, and tocopherol (vitamin E). It can effectively scavenge DPPH free radicals, hydroxyl radicals, and superoxide anion free radicals, and also inhibit the oxidation of low-density lipoprotein. Chlorogenic acid plays an important role in scavenging free radicals in the body, maintaining normal cell structure and function, and preventing and delaying tumor mutation and aging. Eucommia chlorogenic acid contains a special component that promotes the synthesis and decomposition of collagen in human skin, bones, and muscles, has functions of promoting metabolism and preventing decline, and can be used to prevent bone and muscle decline in astronauts caused by weightlessness in space. Research has also found that Eucommia chlorogenic acid has significant anti-free radical effects both in vivo and in vitro.
4. Inhibiting Mutation and Anti-Tumor
Modern pharmacological experiments have proven that Eucommia chlorogenic acid has anti-cancer and tumor-suppressing effects. Japanese scholars studied the mutagenicity-inhibiting effect of Eucommia chlorogenic acid and found that this effect is related to anti-mutagenic components such as chlorogenic acid, revealing the important significance of chlorogenic acid in tumor prevention.
Polyphenols such as chlorogenic acid and caffeic acid in vegetables and fruits can inhibit the mutagenicity of carcinogens aflatoxin B1 and benzo[a]pyrene by inhibiting activating enzymes; chlorogenic acid can also achieve cancer prevention and anti-cancer effects by reducing the utilization rate of carcinogens and their transport in the liver. Chlorogenic acid has significant inhibitory effects on colorectal cancer, liver cancer, and laryngeal cancer, and is considered an effective chemical protective agent against cancer.
5. Cardiovascular Protective Effects
As a free radical scavenger and antioxidant, chlorogenic acid has been proven by numerous experiments to have biological activity in protecting the cardiovascular system. Isochlorogenic acid B has a strong effect on promoting prostacyclin (PGI2) release and anti-platelet aggregation in rats; its inhibition rate on antibody-induced SRS-A release from guinea pig lung fragments reaches 62.3%. Isochlorogenic acid C also promotes PGI2 release. In addition, isochlorogenic acid B has a very strong inhibitory effect on the biosynthesis of thromboxane and endothelin damage induced by hydroperoxides.
6. Blood Pressure Lowering Effects
After years of clinical trials, it has been confirmed that Eucommia chlorogenic acid has a significant blood pressure-lowering effect, with stable efficacy, no toxicity, and no side effects. Research by the University of Wisconsin in the United States found that the effective components of Eucommia in lowering blood pressure are pinoresinol diglucoside, aucubin, chlorogenic acid, and Eucommia chlorogenic acid polysaccharides.
7. Other Biological Activities
Because chlorogenic acid has special inhibitory effects on hyaluronidase and glucose-6-phosphatase, it has certain therapeutic effects on wound healing, skin health and moisture, joint lubrication, inflammation prevention, and blood sugar balance regulation in the body. Chlorogenic acid also has strong inhibitory and killing effects on various diseases and viruses. Chlorogenic acid has pharmacological effects such as lowering blood pressure, antibacterial, antiviral, anti-inflammatory, increasing white blood cells, preventing diabetes, significantly increasing gastrointestinal peristalsis, and promoting gastric juice secretion, and has a significant therapeutic effect on acute pharyngitis. Studies have shown that oral chlorogenic acid can significantly stimulate bile secretion and has cholagogic and liver-protective effects; it can also effectively inhibit H2O2-induced hemolysis of rat red blood cells.
IV. Pharmacological Toxicity of Chlorogenic Acid
Chlorogenic acid has a sensitizing effect on humans. Inhaling plant dust containing this substance may cause allergic symptoms such as asthma and dermatitis. However, there is no such reaction when taken orally, because chlorogenic acid can be converted by small intestinal secretions into substances without sensitizing activity. Chlorogenic acid has very low toxicity; the LD50 for oral administration in young rats is greater than 1 g/kg, and for intraperitoneal injection is greater than 0.25 g/kg. Therefore, neither oral administration nor injection will cause allergies.
V. What Kind of Coffee Is Healthiest to Drink
From the above, it can be seen that the highest chlorogenic acid content in coffee is in green coffee beans, but it is not easily soluble in water and not easily extracted. After roasting, the structure of coffee beans becomes loose and sponge-like, making effective substances and flavor compounds in coffee, including chlorogenic acid, easier to extract under hot water and pressure.
The chlorogenic acid content in Robusta coffee varieties is about 7-10%, while in Arabica coffee it is 5-8%. After roasting, the chlorogenic acid content significantly decreases and cannot be fully extracted during ordinary coffee preparation. According to medical experiment testing, in every 100 grams of pure Arabica variety (sun-dried Yirgacheffe G1) coffee grounds roasted to a medium level (removed from the roaster within 208°C), the detectable effective chlorogenic acid is less than 3%; through fine grinding (Japanese鬼齿 grinder setting 2), soaking in hot water at about 90°C for 3 minutes (French press extraction), with a powder-to-water ratio of 1:15, the chlorogenic acid content in the coffee liquid is already less than 1%, and varies depending on parameters such as grind size, water ratio, and brewing time. Therefore, according to tests commissioned by Hangzhou Coffee Dream Academy and Shixia Specialty Coffee to relevant medical laboratories at Zhejiang Medical University and Zhejiang Chinese Medical University, to ingest a medicinal equivalent dose of chlorogenic acid, one would need to consume coffee brewed from more than 50 grams of coffee grounds per day, which is about 200 ml per cup of pour-over coffee, 4 cups, providing good nutritional health and antioxidant effects for our body.
Of course, the above content is obtained in a non-strict medical practice sense, and each individual's situation is different. Especially in normal pour-over coffee (and other coffee extraction methods as well), when chlorogenic acid in coffee grounds is extracted, caffeine and other substances that easily cause significant bodily reactions in the consumer are also extracted simultaneously. Therefore, although the health significance of chlorogenic acid is great, the stimulating effect of caffeine on the body cannot be ignored. If coffee is consumed excessively, caffeine may place a significant burden on the human autonomic nervous system, heart, kidneys, etc.
However, there is no doubt that coffee roasted too dark will suffer significant losses in both coffee nutrients and coffee flavor. When choosing coffee, consumers are advised to appropriately select medium-roasted specialty coffee from multiple sources.
The above content is compiled by CoffeeHunters, a coffee news website.
