Are sour cherries a good source of antioxidants?

What are antioxidants?  

Antioxidants play a crucial role in protecting cells from oxidative damage . The term "antioxidant" literally means "against oxidation." Antioxidants block the oxidation process by neutralizing free radicals. They can donate electrons to free radicals, thus interrupting their destructive chain reactions. Although they become radicals themselves after donating electrons, they are stable enough not to cause further damage. 

The human body has a complex antioxidant defense system that produces both endogenous antioxidants and has the ability to extract antioxidant compounds from food. These compounds are found in a wide variety of foods, including fruits, vegetables, seeds, nuts, and oils. The best known antioxidants include vitamin E, vitamin C, beta-carotene, polyphenols, as well as trace minerals such as selenium . 

In addition to natural antioxidants, there are also synthetic ones. These are often used in foods to extend shelf life and prevent browning. The most commonly used synthetic antioxidants are butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). However, in excessive amounts, synthetic antioxidants can have potentially harmful effects ​(1) ​. 

What are oxidants?  

The most common oxidants in the human body are so-called free radicals.
These are atoms, molecules or ions that are unstable and reactive to chemical reactions due to unpaired electrons. An unpaired electron in free radicals causes them to accept electrons from other substances to stabilize themselves. However, this process creates another free radical, resulting in a chain reaction. Free radicals can arise from oxygen, nitrogen and sulfur molecules. These molecules belong to a group of compounds called reactive oxygen species (ROS) ​(1) ​. 

Excessive amounts of ROS can cause oxidative stress , which can damage cells. ROS attack nucleic acids, proteins and fatty acids. Under normal conditions, the body can use enzymes to keep ROS levels low to maintain cellular balance. However, under stressful conditions or when cell function is disrupted, ROS levels increase , which can cause significant damage. If oxidative stress persists, it can cause various ailments and diseases. Factors that promote oxidative stress include poor diet and smoking (1, 2) . 

What are polyphenols?  

Polyphenols are secondary plant compounds that occur naturally in fruits, vegetables and grains. They are divided into complex groups of over 10,000 substances, depending on the number of their ring structures and hydroxyl groups. Plants form polyphenols to protect themselves from harmful factors such as free radicals, UV radiation and pests. 

Polyphenols were previously considered to be of no importance for health. However, in recent years, interest in studying phenolic compounds has increased as they have been associated with antioxidant properties ​(3) ​. 

Polyphenols are classified into four major groups: flavonoids, stilbenes, phenolic acids and lignans , which form the basis for further subdivision of polyphenols. Flavonoids are the most studied group and can be divided into several subgroups: flavan-3-ols, flavonols, isoflavones, flavanones and anthocyanins ​(4) ​. 

 

Fig. 1: Classification of polyphenols ​( 4 ) 

What antioxidants are contained in sour cherries?  

Sour cherries are particularly rich in antioxidants. Above all, sour cherries contain a large amount of anthocyanins . This polyphenol group is responsible for the red-blue coloring of many fruits and vegetables. To date, more than 700 different anthocyanin structures have been identified in plants (5) . 

Sour cherries contain the following polyphenols: anthocyanins such as cyanidin-3-glucoside, cyanidin-3-rutinoside, cyanidin-3-sophoroside, pelargonidin-3-glucoside, pelargonidin-3-rutinoside and 3-glucoside, peonidin-3-rutinoside. Phenolic acids include hydroxycinnamic acids such as neochlorogenic acid and p-coumaroylquinic acid as well as flavonols and flavan-3-ols such as catechin, epicatechin, quercetin-3-glucoside, quercetin-3-rutinoside and kaempferol-3-rutinoside. 

In addition to polyphenols, sour cherries contain numerous vitamins that are also known for their antioxidant effects. These include vitamin C, vitamin E and beta-carotene (6) . 

A special feature of sour cherries is that they contain the antioxidant melatonin like no other type of fruit. Melatonin is a hormone produced by the body that regulates the sleep-wake cycle and has also been found in plants. There, melatonin acts as a radical scavenger and is involved in what is known as photoperiodism . This term describes the dependence of plant metabolism on the duration of exposure to sunlight. Eating sour cherries can therefore increase the body's melatonin level and support its hormonal functions (7) . 

Are sour cherries a good source of antioxidants?  

Blando et al. measured the antioxidant capacity of tart cherries using the ORAC test method, which stands for "Oxygen Radical Absorbance Capacity". This test evaluates how well ROS can be neutralized. The values ​​are given as Trolox equivalents in micromoles per 100 g of fresh fruit. Sour cherries have a value of 1145 to 2592 µmol TE/100 g, which indicates a high antioxidant capacity . These values ​​are comparable to those of strawberries, for example, but significantly higher than the values ​​in apples or kiwis ​(8) ​. 

Studies have also shown that certain polyphenols, particularly anthocyanins and hydroxycinnamic acids, in tart cherries have stronger antioxidant activity than comparable compounds in other fruits. Compared to berries such as blackberries, raspberries, blueberries and strawberries, the polyphenols contained in tart cherries have significantly stronger antioxidant activity. 

It should also be mentioned that, due to their sour taste, sour cherries are usually consumed processed compared to sweet cherries. They are available in the form of powder, juice or juice concentrate, boiled in a jar or frozen. This offers the advantage that sour cherries can be consumed not only seasonally, but also all year round . Even after the fruit has been processed, most of the anthocyanins are retained. However, products in which sugar has been added contain smaller amounts of polyphenols (6) . 

The products that contain the most nutrients include sour cherry juice concentrates and capsules. Juice concentrates are the closest to the original form of the fruit and contain most of the original spectrum of secondary plant substances . This was proven in a study that compared various sour cherry products. The highest amount of antioxidants was found in sour cherry juice compared to frozen, preserved and dried sour cherries ​(9) ​. 

Which type of sour cherry has the most antioxidants?  

Today, 74 varieties of sour cherries are known , the polyphenol content of which varies depending on the variety. Of particular note is the Montmorency sour cherry, which has the highest concentration with 4.07 mg of polyphenols per gram . Other varieties with high polyphenol content are Royal Ann 2.29 mg/g, Bing 1.85 mg/g and Rainier 0.75 mg/g ​(10) ​. 

The content of total polyphenols also varies depending on the ripeness of the fruit. The riper the sour cherries are, the redder they become, and the amount of polyphenols increases accordingly. Sour cherries with the highest anthocyanin content are riper and have a deeper red color than young fruits, which have a lighter red color ​(11) ​. 

In addition, the Montmorency sour cherry not only has the highest content of polyphenols, but also the highest content of melatonin . With 13.46 ng of melatonin per gram, it contains significantly more melatonin than most other sour cherries and fruits. The sour cherry with the next highest levels of melatonin is the Balaton sour cherry with just 2.06 ng/g ​(7) ​. This makes Montmorency sour cherries a particularly valuable source of antioxidants . 

The most important things in brief

literature 

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9. Ou B, Bosak KN, Brickner PR, Iezzoni DG, Seymour EM. Processed tart cherry products--comparative phytochemical content, in vitro antioxidant capacity and in vitro anti-inflammatory activity. J Food Sci 2012; 77(5):H105-12. doi: 10.1111/j.1750-3841.2012.02681.x.
10. Chaovanalikit A, Wrolstad RE. Total Anthocyanins and Total Phenolics of Fresh and Processed Cherries and Their Antioxidant Properties. J Food Sci 2004; 69(1). doi: 10.1111/j.1365-2621.2004.tb17858.x.
11. Aslantas R, Angin I, Gokalp Boydas M, Ozkan G, Kara M. Fruit Characteristics and Detachment Parameters of Sour Cherry (Prunus cerasus L. cv. 'Kütahya') as Affected by Various Maturity Stages. Commercial fruit growing 2016; 58(2):127–34. doi: 10.1007/s10341-016-0270-1.