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Polyphenol Class Examples
Aesculetin
OO
OH
OH
Scopoletin
C
H
3
O
OOOH
Resveratrol
OH
OH
OH
Myricetin
O
H
OH O
OH
O
OH
OH
OH
Quercetin
O
O
OH
OH
O
H
OH
OH
Kaempferol (and
glycosylated forms)
O
OH
OH
OOH
OH
Stilbenes
Flavonoids
Table 6.1 (Continued)
Coumarins
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Polyphenol Class Examples
Apigenin
O
O
OH
OH
OH
Luteolin
O
OOH
OH
O
H
OH
Tangeretin
OO
CH
3
O
CH
3
O
CH
3
O
CH
3
O
O
C
H
3
Nobiletin
O
CH
3
O
C
H
3
OO
CH
3
O
CH
3
O
CH
3
O
CH
3
O
Sinensetin
C
H
3
O
O
OO
CH
3
O
CH
3
O
CH
3
O
CH
3
Hesperetin
O
O
OC
H
3
OH
OH
OH
H
Flavones
Table 6.1 (Continued)
Flavonols
(Continued)
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Proanthocyanidins (tannins)
Polyphenol Class Examples
Naringenin
O
O
OH
OH
OH
H
Eriodictyol
O
O
OH
O
H
OH
OH
H
Genistein
OH
O
OH
OHO
Daidzein
O
O
OH
OH
Glycitein
C
H
3
O
O
O
OH
OH
Catechin
O
H
OH
OOH
OH
OH
H
Epicatechin
O
H
OH
OOH
OH
OH
H
Isoflavones
Table 6.1 (Continued)
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Polyphenol Class Examples
Castalin
OH
OH
OH
OH
OH
OH
OH
O
H
OH
O
O
OH
OH
O
O
O
O
OH
Vescalin
OH
OH
OH
OH
O
H
OH
OH
OH
OH
O
O
OH
OH
O
O
O
O
OH
Cyanidin
O
+
OH
OH
OH
OH
O
H
Pelargonidin
O
+
OH
OH
OH
OH
Delphinidin
OH
O
H
O
H
O
+
OH
OH
OH
Petunidin
CH
3
O
O
H
O
H
O
+
OH
OH
OH
Anthocyanins
Table 6.1 (Continued)
(Continued)
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6 Polyphenols in Food Products – Nutraceutical Applications
112
Polyphenol Class Examples
Lignans Pinoresinol
C
H
3
O
OO
OH
O
CH
3
OH
Podophyllotoxin
CH
3
O
O
CH
3
O
CH
3
O
O
O
O
OH
Steganacin
CH
3
O
O
O
O
O
O
O
C
H
3
O
CH
3
O
CH
3
6.2 Natural Sources of Polyphenols
PPHs are obtained from various plant sources [6, 7] such as fruits (oranges, apples, grapes, peaches,
grapefruit juice, cherries, blueberries, pomegranate juice, raspberries, cranberries, black elderber-
ries, blackcurrants, plums, blackberries, strawberries, apricots), vegetables (spinach, onions,
Table 6.1 (Continued)
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6.3 Polyphenols in Food 113
shallots, potatoes, black and green olives, globe artichoke heads, broccoli, asparagus, carrots),
grains (whole grain wheat, rye, oat flours), nuts, seeds and legumes (roasted soybeans, black beans,
white beans, chestnuts, hazelnuts, pecans, almonds, walnuts, flaxseed), beverages (coffee, tea, red
wine), fats (dark chocolate, virgin olive oil, sesame seed oil), and spices and seasonings (cocoa
powder, capers, saffron, dried oregano, dried rosemary, soy sauce, cloves, dried peppermint, star
anise, celery seed, dried sage, dried spearmint, dried thyme, dried basil, curry powder, dried gin-
ger, cumin, cinnamon).
Hydroxybenzoic acids can be found in tea and red fruits such as strawberries and raspberries.
Hydroxycinnamic acids are obtained from kiwis, blueberries, apples, and cereal grains such as wheat
and rice. Hydroxybenzoic and hydroxycinnamic acids have limited therapeutic applications such as
antimicrobial activity, fungitoxicity, and anti-inflammatory activity. Anti-inflammatory activity is
also observed with coumarins, stilbenes, and flavonoids. Flavonoids can be extracted from diverse
sources such as onions, curly kale, leeks, broccoli, blueberries, red wine, tea, celery, citrus fruits
(grapefruit, orange, lemon), tomatoes, mint, apricot, cherry, grape, peach, apple, and chocolate.
6.3 Polyphenols in Food
The polyphenol content in vegetables varies largely depending on their origin, harvest, and atmos-
pheric conditions [8, 9].
Table 6.2 summarizes the maximum amounts of these compounds in different types of food
according to the portion served. The amount of sinapic acid (from the class of hydroxycinnamic
acids) in coffee, anthocyanins in eggplant, blueberries, and black grapes, as well as flavones in
parsley, should be highlighted. All are derived from vegetables with strong colors, especially those
rich in anthocyanins.
Table 6.2 Polyphenols: food sources. Adapted from Ref [4]. Data refer to the maximum amount for each
food.
SOURCE (serving size) mg/kg fresh wt (or mg/L)
Hydroxybenzoic acids Blackberry (100 g) 270
Protocatechuic acid Raspberry (100 g) 100
Gallic acid Black currant (100 g) 130
p-Hydroxybenzoic acid Strawberry (200 g) 90
Hydroxycinnamic acids Blueberry (100 g) 2,200
Caffeic acid Kiwi (100 g) 1,000
Chlorogenic acid Cherry (200 g) 1,150
Coumaric acid Plum (200 g) 1,150
Ferulic acid Aubergine (200 g) 660
Sinapic acid Apple (200 g) 600
Pear (200 g) 600
Chicory (200 g) 500
Artichoke (100 g) 450
Potato (200 g) 190
(Continued)
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6 Polyphenols in Food Products – Nutraceutical Applications
114
SOURCE (serving size) mg/kg fresh wt (or mg/L)
Corn flour (75 g) 310
Flour: wheat, rice, oat (75 g) 90
Cider (200 mL) 500
Coffee (200 mL) 1,750
Anthocyanins Aubergine (200 g) 7,500
Cyanidin Blackberry (100 g) 4,000
Pelargonidin Black currant (100 g) 4,000
Peonidin Blueberry (100 g) 5,000
Delphinidin Black grape (200 g) 7,500
Malvidin Cherry (200 g) 4,500
Rhubarb (100 g) 2,000
Strawberry (200 g) 750
Red wine (100 mL) 350
Plum (200 g) 250
Flavonols Yellow onion (100 g) 1,200
Quercetin Curly kale (200 g) 600
Kaempferol Leek (200 g) 225
Myricetin Cherry tomato (200 g) 200
Broccoli (200 g) 100
Blueberry (100 g) 160
Black currant (100 g) 70
Apricot (200 g) 50
Apple (200 g) 40
Beans, green, or white (200 g) 50
Black grape (200 g) 40
Tomato (200 g) 15
Black tea infusion (200 mL) 45
Green tea infusion (200 mL) 35
Red wine (100 mL) 30
Flavones Parsley (5 g) 1,850
Apigenin Celery (200 g) 140
Luteolin Capsicum pepper (100 g) 10
Flavanones Orange juice (200 mL) 685
Hesperetin Grapefruit juice (200 mL) 650
Naringenin Lemon juice (200 mL) 300
Isoflavones Soy flour (75 g) 1,800
Daidzein Soy beans, boiled (200 g) 900
Genistein Miso (100 g) 900
Glycitein Tofu (100 g) 700
Table 6.2 (Continued)
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6.4 Nutraceutical Benefits of Polyphenols 115
SOURCE (serving size) mg/kg fresh wt (or mg/L)
Tempeh (100 g) 530
Soy milk (200 mL) 175
Monomeric flavanols Chocolate (50 g) 610
Catechin Beans (200 g) 550
Epicatechin Apricot (200 g) 250
Cherry (200 g) 220
Grape (200 g) 175
Peach (200 g) 140
Blackberry (100 g) 130
Apple (200 g) 120
Green tea (200 mL) 800
Black tea (200 mL) 500
Red wine (100 mL) 300
Cider (200 mL) 40
The content of these compounds in processed foods differs substantially from that in natural
products because of reactions that occur between functional groups and proteins, carbohydrates,
and by products from biochemical processes [10], mainly enzymatic oxidation, which act of ester-
ases, glycosidases, and decarboxylases. Enzymatic oxidation is ubiquitous in plant-derived foods,
with the reactions in coffee, black tea, and wine the most widely studied [11, 12].
Regarding the properties of P found in foods, they are generally astringent and impart a bitter
taste (except for some that are volatile, such as vanillin and eugenol, which make them excellent
flavoring agents). Their ability to interact with proteins is also responsible for their precipitation in
beverages. Anthocyanins are usually colorful, and their colors vary according to the acidity of the
food [13–15].
The interest in these compounds stems from the nutraceutical properties of the plant extracts
from which they have been isolated.
6.4 Nutraceutical Benefits of Polyphenols
6.4.1 Against Diabetes
Diabetes is a chronic disease in which the body does not produce insulin or cannot properly use
the insulin it produces. Diabetes is characterized by hyperglycemia that is caused by an imbalance
between insulin production and demand (either because of a deficiency in pancreatic secretion or
resistance mechanisms in its uptake). The International Diabetes Federation estimates that there
are currently 285 million diabetic patients worldwide [16].
Diabetes can be classified into main categories: type-1 diabetes (T1D), type-2 diabetes (T2D),
gestational diabetes (GD), and specific types because of other causes such as diseases of the exo-
crine pancreas (cystic fibrosis) or use of immunosuppressive drugs after organ transplantation
[17]. T2D is preceded by insulin resistance [18–20], one of the underlying causes of diabetes
Table 6.2 (Continued)
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6 Polyphenols in Food Products – Nutraceutical Applications
116
development. T2D is related to co-morbidities, such as cardiometabolic, as well as severe complica-
tions caused by the recent severe SARS-CoV-2 infection because of poor immune health [21, 22].
Concerning the activity of PPHs in the control of diabetes, the effect on postprandial glycemic
response is subtle, with a slight effect on the digestion and sugar absorption within the gut. Citrus
PPH metabolites also act on the modulation of hepatic glucose metabolism and insulin sensitivity
in target tissues [23]. PPH-rich foods, such as decaffeinated green tea, coffee, dark chocolate, blue-
berry jam, extra-virgin olive oil, and some vegetables, reduce plasma glucose [24].
These are just some of the many mechanisms through which PPHs can interfere with diabetes.
Table 6.3 summarizes these biochemical mechanisms. Among the most common benefits of PPHs
concerning diabetes are the reduction of glucose uptake, improvement of insulin sensitivity and/
or resistance, and increase of insulin secretion [25].
Some of the pharmacological effects of PPHs have synergistic relationships with each other. For
example, the action against diabetes, depending on the mechanism, may be related to the antioxi-
dant effect [50].
6.4.2 Against Oxidative Stress
The antioxidant effect of natural polyphenolic compounds is the most documented among known
effects. The deleterious effects of molecular oxygen on living organisms involves a reactive oxygen
species (ROS). The free radical theory proposed by Harman in 1956 establishes a correlation
between aging and dysfunction of the oxygen regulation system [1, 51].
Three mechanisms have been proposed to explain the antioxidant behavior of PPH, as illus-
trated in Figure 6.2. PPHs can inactivate free radicals via hydrogen atom transfer (HAT) (Figure
6.2a) or single electron transfer (SET) (Figure 6.2b) mechanisms, or can undergo transition metals
chelation (TMC) with pro-oxidant proteins by chelation of metal ions such as Fe
3+
, Al
3+
, or Cu
2+
(Figure 6.2c).
Direct antioxidant mechanisms (HAT/SET) of PPHs have been observed with radical species
such as superoxide radical (O
2
•
), hydrogen peroxide (H
2
O
2
), hydroxyl radical (HO
•
), singlet oxy-
gen
1
(O
2
), or peroxyl radicals (RO
2
•
) [52, 53].
The HAT mechanism depends on the substitution pattern of the phenolic ring, which affects the
bond dissociation energy of the OH group. The SET mechanism is more dependent on the ioniza-
tion potential, although this parameter influences the former mechanism as well. Chelating mech-
anisms depend on the position of the OH groups (bidentate ligands are expected to be more
efficient) and on their nucleophilicity. The high chelating efficiency of PPHs may contribute to
their antioxidant activity by preventing redox-active transition metals from catalyzing free radical
formation [54].
Concerning the TMC mechanism, the hydroxyl radical, one of the most reactive radical species
in a biological environment, can be formed from Fenton reactions with the participation of metal
ions (M
n+
) such as [55]:
HM
22
n+ .
n+
1+
O+ M HO+ HO+
→
()
¯
Fenton chemistry takes place in dopaminergic neurons of the nervous tissue, where some hydro-
gen peroxide is generated from dopamine catabolism [54]. The subsequent formation of radicals
has been associated with the occurrence of some neurodegenerative diseases alongside aging
(addressed in Section 6.4.3).
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Table 6.3 A summary of individual phenolic compounds or extracts exhibiting antidiabetic effects in preclinical and clinical studies. Adapted from Ref [20].
Phenolic
Compounds Class Compounds Role In Diabetic Complications References
Stilbenes Resveratrol Reduced blood glucose levels, insulin concentration, plasma triglycerides [26]
Increased phosphorylation of adenosine mono phosphate kinase, endothelial nitric oxide synthase
and protein kinase B, expression of glucose transporter-4 in the myocardium
[27]
Decreased fasting blood glucose, glycosylated hemoglobin, increased insulin, improved hepatic
glycogen content, increased glycogen synthase activity, and reduced glycogen phosphorylase
activity
[28]
Alleviated diabetic nephropathy by reduced renal dysfunction and oxidative stress [29]
Ameliorated cognitive decline by inhibition of hippocampal apoptosis via the B-cell lymphoma
protein 2-associated X and caspase-3 pathway, improvement of synaptic
[30]
Enhanced cerebral vasodilator function, improved cognitive performance [31]
Reduced fasting blood glucose, increased serum HDL-cholesterol levels, decreased total-/HDL-
cholesterol ratio, increased total antioxidant capacity, decreased plasma malondialdehyde (MDA)
levels, upregulation of peroxisome proliferator-activated receptor-γ and sirtuin1 in peripheral blood
mononuclear cells
[32]
Reduced foot ulcer size and plasma fibrinogen level [33]
Phenolic acids Curcumin (Hydroxycinnamic acid) Improved diabetes-induced endothelial dysfunction through superoxide reduction and protein
kinase C inhibition
[34]
Ferulic acid
(Hydroxycinnamic acid)
Decreased fasting blood glucose levels, reduced level of serum insulin and spleen size. Reduced
oxidative stress mediated inflammation and apoptosis
[35]
Gallic acid
(Hydrobenzoic acid)
Reduced fasting serum glucose and lipids, improved hepatic and pancreatic antioxidant capacity,
lowered levels of interleukin-6 and tumor necrosis factor-alpha in the liver and pancreas
[36]
Lignans +
Phenolic acids
Flaxseed extract +
ferulic acid, gallic acid equivalent,
p-coumaric acid
Reduced fasting blood glucose, plasma cholesterol,
LDL-cholesterol, triglycerides, plasma creatinine, urea and uric acid levels, partially recovers
pancreas, liver, and kidney functions
[37]
(Continued)
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