Antioxidants from fruits and berries overview

The Complete Grape Growing System

The Complete Grape Growing System

Get Instant Access

Fruits and berries are good sources of antioxidants, including carotenoids, ascorbic acid, tocopherols, flavonoids and phenolic acids. It has been known for a long time that the phenolics, as well as some of the other antioxidant components, are closely associated with the sensory attributes of fresh and processed fruits, berries and other plant foods. Especially, the contribution to colour by carotenoids (yellow to orange and red) and anthocyanins (red to purple and blue) is well known. Also the specific involvement of some of the phenolic substances in flavour development and taste sensation is amply documented.1 Phenolic compounds, including those having potent antioxidant activity, are also substrates for undesirable, oxidative browning reactions occurring during bruising of fruits, when fruits are cut or during their processing.

The possible beneficial biological functions of the traditional antioxidant vitamins, i.e. ascorbic acid, a-tocopherol and to a certain extent beta-carotene (provitamin A) have been intensively studied for at least 50 years and continue to receive high research attention. More recently, the antioxidant functions of flavonoids and other phenolic compounds have received increased attention. The biological roles of these plant phenolics that exert antioxidant activity are yet to be completely clarified, but evidence pointing to the possibility that phenolic phytochemicals also exert various protective effects in humans is accumulating. Because of the possible benefits of phenolic phytochemicals to human health, data on their quantitative occurrence and composition in various fruits and berries are gradually emerging in the literature. Therefore it is now known that flavonoids and other phenolic compounds are particularly abundant in fruits and berries. However, as it is generally recognised in relation to compilation of food compositional data, there are large variations in the levels of the constituents reported, depending on the species investigated, harvest time, fruit maturity stage, geographical origin etc. Differences in the methods employed for extraction and analyses also strongly affect the results and there are thus some inconsistencies in the available data, or very broad ranges for the levels of certain constituents in various fruits.

Some studies have evaluated the phenolic contents in fruits at more than one ripening stage. In the case of plums as well as with red grapes intended for wine making, a marked increase in the content of phenolics of potential antioxidant potency was seen in the fully ripe stage in comparison with the less ripe stage.2,3 In contrast, no clear differences were observed in other fruits, e.g. peaches and nectarines,3 so it appears that there is no general rule correlating phenolic content and antioxidant potency with the fruit ripening stage.

Antioxidant composition (anthocyanins, flavanols and proanthocyanidins, flavonols, hydroxycinnamates, carotenoids, vitamin C and vitamin E) of selected, commonly consumed fruits and berries is presented in Table 3.1. Large amounts of anthocyanins (up to 8100mgkg-1) are found in the strongly coloured fruits and berries including bilberries (wild clone of blueberries), blackcurrants, cherries, cranberries, red grapes and raspberries. The amount of flavanols is generally below 150mgkg-1 with larger amounts found in blackcurrants, cranberries, red wine grapes, peaches, plums and red raspberries. Apart from a few exceptions such as cranberries and red grapes, fruits and berries are generally also low in flavonols and high in phenolic acids such as hydroxycinnamates. Large amounts of hydroxycinnamates are present in cherries (300-1930mgkg-1), plums (121— 896mgkg-1) and peaches (81-750mgkg-1). High molecular weight phenolics, tannins, are also found in fruits and berries with large amounts of ellagitannins in red raspberries (2200 mg kg-1) and cloudberries (1800-2600 mg kg-1) and moderate amounts in strawberries (90-200mgkg-1).4 The vitamin C content of fresh fruits and berries is generally high while that of provitamin A carotenoids and vitamin E is low. Blackcurrants (1200-1500mgkg-1), cloudberries (1000mgkg-1), strawberries (550-1000 mgkg-1) and orange (510mgkg-1) are very rich in vitamin C. One exceptional berry is sea buckthorn berry with extremely large amounts of vitamin C (2000 mg kg-1) as well as high amounts of beta-carotene (15mgkg-1) and vitamin E (32mgkg-1).

Food processing of fruits and berries into juices and jams, and drying of fruits generally result in lower amounts of antioxidant compounds. For example, losses of anthocyanins in juices and purées of strawberries, strawberry and blackcurrant syrups, cranberry juice, raspberry juice and wine have been reported5-9 as well as phenolic degradation during processing of apple juice.10 On the other hand, the manufacturing process had no effect on the qualitative anthocyanin profile of commercial jams made from strawberries, blackberries, raspberries, blueberries, blackcurrants and cherries.11

In domestic berry processing practices, a quercetin loss of 15% was observed in strawberry jam, 85% loss in blackcurrant juice, 40% loss in bilberry soup and 85% loss in lingonberry juice in their making procedures.12 Flavanols are effectively extracted into apple cider, blackcurrant juice and red wine, the amounts being higher than those of the raw materials.13-17 An increase in ellagic acid in raspberry jams was reported to occur, most likely owing to release of ellagic acid from ellagitannins with the thermal treatment,18 although according to Häkkinen et al.19 ellagic acid content in strawberry jam was 80% that of unprocessed strawberries.

As for other antioxidant compounds, peeling and juicing result in substantial losses of provitamin A carotenoids, often surpassing those associated with heat treatment.20 Moreover, the stability of carotenoids differs in different foods even when the same processing conditions are used. Ascorbic acid of fruit juices such as orange, peach, grapefruit, pineapple, apple and mango juice is readily oxidised

Table 3.1 Antioxidant compounds in selected fruits and berries and their products (mg kg fresh weight)

Fruit or berry

Anthocyanins

Flavanols and proanthocyanidins

Flavonols

Hydroxycinnamates

Carotenoids (ß-carotene)

Vitamin C

Vitamin E

Apple

4—54

0-15116

17-704,74

263-3084

0.494

40117

2117

- juice

0-298118

2.5119

0.1-16210-17-120

0.2117

300117

0117

Bilberry

3450-46354

13-294

41-1954'12

170-3474

0.594

150117

19117

- soup

612

0.0194

20117

5117

Blueberry

3970-484029

63-7029

115-13929

226-31529

Blackcurrant

130-8 1 004,62

205-3744

133-157412

104-1674

194

1200117

23117

- juice

2417

3612

10.1117

380-42112,117

11117

Cherry, sweet, red

31-450022-31

20-6328-31

10-2329

100-190028-31

1.294

70121

1121

Cloudberry

7-154

2-64

34-904

90-1284

1.494

1000117

31117

Cranberry

460-17204-6-122-123

2854

139-334122-124

1914

0.294

120121

10121

- juice

18-512124

Grapes, table, red

72.5-765125

1-160118

13-25125

5-19125

0.3117

50117

7117

- wine, red

0.6-38513,15

0-500118

10-5513'15

4-1313,15

tr121

0121

0121

Grapes, table, white

0125

0125

10-13.574,125

5.5125

0.3117

50117

7117

- wine, white

015

0-10615

1-3415

tr121

0121

0121

Orange

0-570

136-163126

0-570,74

510117

4117

- juice

0.194

300-45041

2117

Peach

0-17.827

24.5-7003,27

0-11.927

5^14827

0.994

80121

10121

- canned

0127

tr127

tr127

11-29127

1.094

20117

20117

Plum

19-7631,37

140-6003

5.7-2737

500-90023,37

4.3121

54121

8.6121

- dried (prune)

037

037

4237

180037

1.494

0117

18121

Raspberry, red

200-22004,29

4—4804,29

6-394,29,128

3-3512,29

0.194

296-38012,117

11117

Sea buckthorn

15121

2000121

32121

berry

Strawberry

202-7904,29

9-1844,29

7-1744,29,128

14-694,29

0.194

420-600117,128

6117

Strawberry jam

4-2211

11.412

0.04117

80-23612,117

1.0117

© 2002 Woodhead Publishing Ltd and CRC Press, LLC

and lost during staying of the juices with losses ranging from 29 to 41% when stored at room temperature for four months.21 Kalt et al.22 found a marked difference in the stability of ascorbate in green leafy vegetables when compared with fruits. For example, in spinach more than 90% of the ascorbate was lost within three days after harvest when stored at ambient temperature while losses in ascorbate during storage of blueberries, raspberries and strawberries were minimal.22

Antioxidant activity of fruits and berries and their products reported in many studies varies widely and this is partly due to the use of different oxidation systems and methods to analyse antioxidant compounds. For antioxidant testing, either extracts or juices of fruits and berries have been used resulting in different antioxidant compositions owing to choice of extraction solvents (e.g. either water-soluble or lipid-soluble compounds extracted by one method) or use of filtration (e.g. possible losses of antioxidant compounds). The literature has much focused on the antioxidant effects of flavonoids and phenolic acids although ascorbic acid, carotenoids and tocopherols also contribute to the antioxidant activity of fruits and berries. Many of the flavonoids and phenolic acids exert comparable or better radical scavenging activity than vitamin C and E in radical scavenging activity assays.23

It is beyond the scope of the present treatise to discuss the problem that arises because the absolute and relative efficiencies of many natural antioxidants vary depending on the test method employed, and especially that the free-radical trapping methods (DPPH, ORAC, TEAC and TRAP assays) may not always mimic the complex multifunctional antioxidant mechanisms of natural anti-oxidants. It is important to note, however, that relevant antioxidant mechanisms of natural antioxidants and polyphenols such as metal chelation, inhibition of oxidative enzymes etc are overlooked in many of the currently employed rapid free-radical antioxidant test assays. In addition, the possible influences of factors such as antioxidant solubility, partitioning, ionic charge, complexing/interaction with other compounds, type of initiation, pH of the system and so on are not considered in simple radical scavenging tests (discussed in detail by Frankel and Meyer).24 Glycosides of polyphenols have often been found to be less active as antioxidants compared to the corresponding aglycones in radical scavenging tests.21 However, this may be an artefact as with more realistic substrates, for example in LDL and phospholecithin liposomes in vitro assays, the glycoside/aglycone issue appears to be more complex. Thus, when evaluated at the same micromolar addition level on copper-catalysed LDL in vitro, rutin exerted better antioxidant potency than quercetin. Likewise, chlorogenic (5'-caffeoylquinic) acid was better than caffeic acid on human LDL oxidation in vitro, when oxidation was induced with AAPH,25 while no significant differences between antioxidant potency of these two compounds could be established when the LDL oxidation was induced with copper ions.26 Some of the differences in results obtained in different in vitro antioxidant tests with anti-oxidant compounds present in fruits and berries are summarised and exemplified in Table 3.2.

Table 3.2 Radical scavenging and antioxidant activities in different test systems for ascorbic acid and selected phenolic antioxidants purified from fruits, berries and vegeta-

Compound

Inhibition (%)

Inhibition (%)

ORAC

TEAC

of LDL

of lecithin

(mM trolox

(mM trolox

oxidation at

liposome

equivalents)130-132

equivalents)133

5 mM

oxidation at

GAE29,33,64,i29

10 mM GAE64

Flavanones

Naringenin

2.67

0.72

Hesperidin

1.3723

Flavonols

Kaempferol

2.67

1.02

Quercetin

50.6

3.29

2.88

Rutin

67.6

0.56

2.423

Myricetin

68.1

4.3

3.123

Flavan-3-ols

Catechin

87.8

2.49

2.423

Epicatechin

67.6

2.36

2.523

Procyanidins

Anthocyanins

Cyanidin

79.4

pro-oxidant

2.2

2.38

Malvidin

59.3

23.9

2.0

1.80

Pelargonin

39.0

pro-oxidant

1.1

1.3023

Delphinidin

71.8

pro-oxidant

1.8

4.80

Hydroxycinnamates

p-Coumaric

24.5

1.09

1.56

Ferulic

24.3

1.33

1.75

Caffeic

96.7

2.23

0.99

Chlorogenic

90.7

Other

Ascorbic acid

45.2 (at 10 mM)

2.5 (at 10 mM)

0.52

1.05

Gallic acid

63.3

1.74

3.0123

Ellagic acid

0-36

Was this article helpful?

0 0
Berry Boosters

Berry Boosters

Acai, Maqui And Many Other Popular Berries That Will Change Your Life And Health. Berries have been demonstrated to be some of the healthiest foods on the planet. Each month or so it seems fresh research is being brought out and new berries are being exposed and analyzed for their health giving attributes.

Get My Free Ebook


Post a comment