Polyphenols in sour cherries

What are polyphenols?  

Polyphenols are natural compounds that belong to the group of secondary plant substances. They are divided into various complex groups depending on the number of their ring structures and hydroxyl groups. Today, over 10,000 types of polyphenols are known ​(1) ​. 

Polyphenols can be divided into four main groups: flavonoids, stilbenes, phenolic acids and lignans. These groups form the basis for the further subdivision of polyphenols. The largest and most intensively researched group are the flavonoids. Their subgroups include flavan-3-ols, flavonols, isoflavones, flavanones and anthocyanins ​(2) ​. 

A few years ago, polyphenols were considered to have no health benefits. However, as research progressed, interest in phenolic compounds increased, mainly due to the discovery of their antioxidant properties ​(1) ​. 

Fig. 1: Classification of polyphenols ​( 2 ) 

What function do polyphenols fulfill in plants?  

Plants produce polyphenols to protect themselves from various harmful factors. Bacteria, viruses, insects, larger animals, and even UV rays can damage plants. Therefore, over the course of evolution, they have developed polyphenols to protect themselves from pathogens and predators and to ward off environmental stress (3) . 

The example of flavonoids shows that polyphenols have very different functions in plants: In addition to their defensive function, they are also responsible for the pigmentation of the fruit . Anthocyanins are responsible for the red-blue coloring of many fruits and vegetables , including sour cherries ​(4)​ . Flavones and flavonols protect the cells of flowers, leaves and stems, especially from harmful UV radiation ​(3)​ . Polyphenols also play an important role in the formation of the taste, smell and texture of the fruit ​(5)​ . 

Which polyphenols are contained in sour cherries?  

The polyphenols in sour cherries are mostly found in the skin of the fruit . They not only make it a healthy fruit, but also give it a special aroma ​(6) ​. 

Some of the polyphenols found in sour cherries are:

anthocyanins	hydroxycinnamic acids	flavan-3-ols	flavonols
cyanidin-3-glucoside   cyanidin-3-rutinoside   cyanidin-3-sophoroside   Pelargonidin-3-glucoside   Pelargonidin-3-rutinoside   Peonidin-3-rutinoside	neochlorogenic acid   p-coumaroylquinic acid	catechin   epicatechin	quercetin-3-glucoside  quercetin-3-rutinoside  kaempferol-3-rutinoside (2, 5)

Tab.1: Types of polyphenols

Do sour cherry products differ in terms of polyphenol content?  

Since sour cherries have a rather sour taste, they are rarely eaten fresh and are instead processed into various products. Sour cherries are often found in the form of juices, juice concentrates, jams, alcoholic beverages and sweets. This means that they can be consumed not only seasonally but also all year round ​(7) ​. 

Among the products with the highest nutritional content are sour cherry juices and concentrates . They are closest to the original form of the fruit and contain a large part of the original spectrum of phytochemicals . This was demonstrated in a study that compared various sour cherry products. The highest amount of polyphenols was found in sour cherry concentrate compared to frozen, preserved and dried sour cherries ​(8) ​. 

Scientists concluded in a 2021 study that sour cherry juices or concentrates are more effective than powdered sour cherry products. They point out that different manufacturing processes of sour cherry products can change the composition of nutrients , which in turn affects their effectiveness ​(9) ​. 

What is the polyphenol content in different dosage forms?  

The highest polyphenol content is found in fresh sour cherries, although the content varies depending on the degree of ripeness: the riper the fruit, the more polyphenols it contains ​(5)​ . The polyphenol content also depends on the type of sour cherry. The Montmorency sour cherry is considered to be the variety with the highest polyphenol content , as it has the highest concentration of 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)​ . 

In numerous studies, various sour cherry products have been examined for their polyphenol content. For example, Mayta Apaza et al. were able to show that sour cherry juices and concentrates have the highest amount of polyphenols after processing. However, the addition of sugar to the juices can reduce the amount of polyphenols ​(6) ​. 

Another study examined other processing methods. It was found that 66% of the anthocyanins were lost after 3 months when sour cherries were frozen at -23 °C . At temperatures of -70 °C, the loss after 3 months was only 10%. The amount of total polyphenols was also reduced, but significantly less ​(10) ​. 

There are differences in the drying of the fruit depending on the method, with freeze-drying being considered optimal as it results in lower losses. Extracts can also contain large amounts of polyphenols, but often certain compounds are selectively extracted, resulting in the loss of the full spectrum of valuable ingredients. Capsules offer good protection of the polyphenols when they are enclosed in biopolymers that protect them from oxygen, water and light ​(7) ​. 

What other foods are rich in polyphenols?  

In addition to sour cherries, other types of fruit and vegetables also contain polyphenols. There are usually various polyphenols in a particular fruit. However, there is often one polyphenol that predominates in the fruit. The following table lists selected types of fruit that are rich in polyphenols. The most important polyphenol contained is also listed, along with its amount in milligrams per gram. 

 

Groceries	Most important polyphenol	Amount (mg/100 g)
blackberry	hydroxybenzoic acids	9–26
raspberry	protocatechuic acid	7–9
black currant	gallic acid	5–12
blueberry	hydroxycinnamic acids	200–215
kiwi fruit	caffeic acid	65–90
blackberry	cyanidin	105–400
black currant	Pelargonidin	131–400
blueberry	Peonidin	26–500

Tab. 2: Polyphenol content in selected foods ​( 1 )  

The most important things in brief

literature 

1. Rana A, Samtiya M, Dhewa T, Mishra V, Aluko RE. Health benefits of polyphenols: A concise review. J Food Biochem 2022; 46(10):e14264. doi: 10.1111/jfbc.14264.
2. Fraga CG, Croft KD, Kennedy DO, Tomás-Barberán FA. The effects of polyphenols and other bioactives on human health. Food Function 2019; 10(2):514–28. doi: 10.1039/c8fo01997e.
3. Mazid MA, Khan TA, Mohammad F. Role of secondary metabolites in defense mechanisms of plants. Biology and medicine 2011; 3:232–49.
4. Blando F, Oomah BD. Sweet and sour cherries: Origin, distribution, nutritional composition and health benefits. Trends in Food Science & Technology 2019; 86:517–29. doi: 10.1016/j.tifs.2019.02.052.
5. Ferretti G, Bacchetti T, Belleggia A, Neri D. Cherry antioxidants: from farm to table. Molecules 2010; 15(10):6993–7005. doi: 10.3390/molecules15106993.
6. Mayta Apaza AC, Marasini D, Carbonero F. Tart Cherries and health: Current knowledge and need for a better understanding of the fate of phytochemicals in the human gastrointestinal tract. Critical Reviews in Food Science and Nutrition 2017; 59(4):626–38. doi: 10.1080/10408398.2017.1384918.
7. Yılmaz FM, Görgüç A, Karaaslan M, Vardin H, Ersus Bilek S, Uygun Ö et al. Sour Cherry By-products: Compositions, Functional Properties and Recovery Potentials - A Review. Critical Reviews in Food Science and Nutrition 2019; 59(22):3549–63. doi: 10.1080/10408398.2018.1496901.
8. 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.
9. Wangdi JT, Sabou V, O'Leary MF, Kelly VG, Bowtell JL. Use, Practices and Attitudes of Elite and Sub-Elite Athletes towards Tart Cherry Supplementation. Sports (Basel) 2021; 9(4). doi: 10.3390/sports9040049.
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.