Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2007
Volume 10
Issue 4
Topic:
Food Science and Technology
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
¦cibisz I. , Mitek M. 2007. ANTIOXIDANT PROPERTIES OF HIGHBUSH BLUEBERRY FRUIT CULTIVARS, EJPAU 10(4), #34.
Available Online: http://www.ejpau.media.pl/volume10/issue4/art-34.html

ANTIOXIDANT PROPERTIES OF HIGHBUSH BLUEBERRY FRUIT CULTIVARS

Iwona ¦cibisz, Marta Mitek
Department of Food Technology, Division of Fruit and Vegetables Technology, Faculty of Food Technology, Warsaw Agricultural University, Poland

 

ABSTRACT

Antioxidant capacity, total phenolics, total anthocyanins and chlorogenic acid contents were evaluated in fruits of 14 cultivars of highbush blueberry (Vaccinium corymbosum L.) grown in Central Poland in the years of 2002-2004. In addition, fruits were analyzed for soluble solids, pH and total acidity. The total antioxidant capacity of berries was high and ranged from 23.1 to 43.7 µmol Trolox equivalents/g of fresh fruits. The antioxidant capacity was strongly correlated with the content of total anthocyanins and total phenolics. The total anthocyanins content ranged from 97.1 to 256.5 mg·100 g-1 of fresh fruits. The highest concentration of anthocyanins was found in cv. ‘Bluegold’ and the lowest in cv. ‘Darrow’. In the year 2002, when the berries shown the lowest fruit weight, the average anthocyanins content was the highest in all years. The most common cv ‘Bluecrop’ in Poland exhibited the highest chlorogenic content (in average for three years 92 mg·100 g-1 FW). The highest concentration of soluble solids was recorded for cv. ‘Brigitta Blue’ (15.5%). Antioxidant capacity and total phenolics, anthocyanins, chlorogenic acid content of highbush blueberry were strongly affected by genotype. Highbush blueberries exhibited also significant differences in antioxidant properties as a consequence of growing season.

Key words: highbush blueberry, cultivars, growing season, antioxidant activity, phenolics.

INTRODUCTION

Epidemiological studies indicate that diets rich in antioxidants are helpful in preventing diseases caused by oxidative stress such as cardiovascular disease and cancer. Prior et al. [16] reported blueberries to be one of richest sources of antioxidants of fresh fruits and vegetables.

Highbush cultivated blueberries are native to North America. Blueberries are characterized by a large fruit with intensive dark-blue color. Blueberries are extensively cultivated in the United States and more recently also successfully grown in Central Europe [24]. In Poland, the acreage of blueberries and yields have increased significantly in the last few years. In the year of 2004 Polish growers produced 3.9 thousand tons of blueberries of which majority were marketed as fresh [27].

Antioxidant capacity of blueberries has been attributed to their high concentration of phenolic compounds, particularly anthocyanins. Blueberries are also good source of chlorogenic acid [8], quercetin [24], kaempferol [2], myricetin [7], procyanidins [17] (+)catechin, (-)epicatechin [23] resveratrol [11], vitamin C [16], that contribute to antioxidant activity. The antioxidant activity of blueberries can be due to numerous factors, including genotype [4], growing season and location [3], maturity and postharvest storage conditions [9].

Recently, fruits of highbush blueberry have become of special interest to researchers studying antioxidants because of their high antioxidant capacity. However, quantitative information on the content of blueberry anthocyanins, total phenolics, chlorogenic acid, and antioxidant properties in different genotype cultivated in Poland is not available.

Our objective was to determine the total anthocyanins, total phenolics, and antioxidant properties of selected blueberries cultivars. The purpose of this study was to compare fruit weight, soluble solids, titratable acidity, pH and phytonutritions concentration of 14 blueberry cultivars grown at the same location over three growing seasons.

MATERIALS AND METHODS

Chemicals
Chlorogenic acid and Folin Ciocalteu reagent were purchased from Sigma Chemical Co. Trolox (6-hydroxy-2,5,7,8-tetramethyl-2-carboxylic acid) and ABTS (2,2 azinobis(3-ethylbenzothiazoline-6-sulphonic acid) were obtained from Aldrich. HPLC grade methanol and acetonitrile were obtained from J.T. Baker. Myoglobin was obtained by Sigma-Aldrich Chemicals Co. Ethanol, acetic acid, acetone, methanol, formic acid were obtained from POCH S.A (Poland).

Samples
Highbush blueberry of fourteen cultivars were obtained from commercial orchard in Piskórka near Warsaw (Central Poland). Agronomic practices were done in accordance to recommendation for commercial growing. Berries were harvested in July and August in the years 2002-2004. The berries (approximately 2.5 kg of fruits from each cultivar) were picked at optimum ripe stage. The berries were not selected for size, but reflected the typical for the cultivar. The plants ranged from 6 to 8 years of age and samples were collected from three plants of each cultivar. After harvest, fruits were sorted (to remove damaged, shriveled and unripened fruits), washed in water, packed in polyethylene bags (200 g portion) and frozen. Samples were maintained at -35°C until the analysis. Before extraction the fruits were thawed at room temperature (22°C, 1.5 h).

Extractions
Total phenolics: Three grams of crushed sample were extracted with 80 ml mixture of acetone and water (7:3) for 45 min at room temperature. The extract was filtered and standardized to a volume of 100 ml.

Total anthocyanins: 5 g of crushed blueberries were twice-extracted with 80 ml a mixture of 96% ethanol and 1.5 mol·l-1 HCL (85:15) at room temperature for 45 min. Fractions were filtered through a Whatman No 1 filter paper. The ethanol extracts were combined and standardized to 100 ml.

Chlorogenic acid: Blueberries (5 g) were extracted with 80 ml of solution containing methanol/acetone/water/acetic acid (30:30:35:0.1) for 45 min at room temperature. The extract was filtered and concentrated under vacuum (T = 40°C) until acetone and methanol were removed. The extract was dissolved with 0.1% formic acid to a final volume of 25 ml. The solution (10 ml) was adsorbed into a C18Sep-Pak Cartridge (Waters) which was previously activated with methanol and then 0.1% aqueous formic acid. Sugars, acid and other water soluble compounds were eluted with 10 ml of 0.1% formic acid. Chlorogenic acid and other phenolics adsorbed into column were eluted with 75% acidified methanol (0.1% HCl). Samples were filtered trough a 0.45 µm Milipore filter (type PTFE) before HPLC analysis.

Antioxidant activity: Homogenized fruits (5 g) were extracted twice with 80 ml of a methanol/acetone/water (30:35:25) mixture and filtered with a Buchner funnel and Whatman nr 1 filter paper. Filtrates were combined and concentrated under vacuum (40°C) until methanol and acetone was removed. The extract was dissolved to a final volume of 25 ml with distilled water.

Analyses
Physical and chemical characteristics of blueberries:

The average berry weight was determined by weighing ~50 g of berries and counting the number of berries. Soluble solids concentrations were determined in an Abbe-Zeiss refractometer at 20°C. Results were determined in percent soluble solids (mass/mass) on a fresh weight basis. Total acidity was determined by potentiometric titration with NaOH 0.1 N to pH 8.2. Titratable acidity was expressed as the percentage of citric acid on a fresh weight basis. The pH was measured with a digital pH-meter at 20°C.

Total phenolics
The Folin-Ciocalteu method [15] was used to measure total amount of phenolic compounds in berries. Absorbance was measured at 700 nm and results were expressed as milligrams chlorogenic acid equivalents/100 g fruits.

Total anthocyanins
Total anthocyanins content was determined by the pH differentia spectrophotometric method of Swain and Hillis, [25]. Total anthocyanin content was calculated for cyjanidin-3-glucoside.

Chlorogenic acid
Chlorogenic acid content was determined by high-performance liquid chromatography (HPLC) using a Shimadzu apparatus equipped with a UV/VIS detector. A Luna RP – 18 (5 µm) column from Phenomenex was used. The isocratic eluent was a mixture of water, acetonitrille and formic acid (81:9:10 v/v/v) used at the flow rate of 1 ml·min-1. Chlorogenic acid was detected at 320 nm and identified according to retention time by comparing with the standard.

Antioxidant activity
Antioxidant activity was determined by measuring the ability of antioxidants to suppress the formation of ABTS•+ radical cation [13]. The radical was generated by the interaction of ABTS with ferrylmyoglobin radical species, generated by the activation of metmyoglobin with H2O2. Metmyoglobin was prepared by oxidation of myoglobin by addition of potassiumhexacyanoferrate (III) followed by purification on a Sephadex G 15 column. The extent of quenching of the ABTS radical was measured spectrophotometrically at 734 nm. Trolox, a water-soluble vitamin E analogue, was used as an antioxidant standard. Results were expressed as µmol Trolox equivalents/g.

Statistical analysis
The statistical analyses were performed with Statgraphics Plus 4.1. All data presented are means of three replications. Significant differences between the objects (cultivars and years) were calculated by analysis of the variance (ANOVA). Significant differences (p ≤ 0.05) between means were determined by Tukey’s method. Simple regression analysis was used to determine the relationship between the antioxidant activities and content of phenolics and anthocyanin of the fruits.

RESULTS AND DISCUSSION

Physical and chemical characteristics
Fruit weight, soluble solids, total titratable acidity and pH are presented in Table 1. The weight of fruit of highbush cultivars varied from 0.9 to 2.3 g/fruit. The average weight was significantly different in the three years studied. It was lower in fruits from the first growing season (1.5 g/fruit) that in the others. The seasonal differences were, however, smaller than the varietal one.

The highest concentration of soluble solids was recorded for ‘Brigitta Blue’ (15.5%) and the lowest for ‘Berkeley’ (11.7%). The samples from ‘Bluecrop’ and ‘Lateblue’ showed relatively high refractometer readings, while ‘Patriot’ and ‘Amblue’ had lower soluble solids content. There were significant differences between concentration of soluble solids of berries harvested in different years. The results from measurements of soluble solids content were similar to data from literature sources [1,6,22].

Table 1. Physical and chemical characteristics of highbush blueberry fruit cultivars harvested in the years 2002-2004

Cultivars

Fruit weight a

Soluble solids [%]

Titratable acidity [%]

pH

2002

2003

2004

Cultivar mean
(all years)

2002

2003

2004

Cultivar mean
(all years)

2002

2003

2004

Mean volume

2002

2003

2004

Cultivar mean
(all years)

Earlyblue

1.21

1.44

1.44

1.4 b

14.5

14.2

13.6

14.1 de

0.4

0.3

0.4

0.4 a

3.5

3.5

3.4

3.5 de

Duke

1.37

1.61

1.65

1.5 d

14.2

13.5

14.3

14.0 d

0.6

0.8

0.6

0.7 bc

3.3

3.3

3.2

3.3 bcde

Patriot

1.52

1.81

1.75

1.7 f

12.6

12.0

12.2

12.3 b

0.9

1.0

1.1

1.0 d

3.1

3.0

2.8

3.0 ab

Amblue

0.74

1.00

0.92

0.9 a

14.1

13.1

13.9

13.7 c

0.4

0.5

0.5

0.5 ab

3.6

3.6

3.4

3.5 e

Berkeley

1.5

1.74

1.71

1.7 f

12.4

10.5

12.2

11.7 a

0.6

0.7

0.5

0.6 b

3.3

3.3

3.2

3.3 bcde

Toro

2.17

2.39

2.41

2.3 j

14.2

14.0

14.0

14.1 de

0.5

0.5

0.6

0.5 ab

3.3

3.4

3.4

3.4 cde

Herbert

1.32

1.54

1.41

1.4 c

14.1

13.8

14.0

14.0 d

0.9

0.9

1.0

0.9 d

3.2

3.2

3.1

3.2 abcd

Bluecrop

1.61

1.79

1.6

1.7 f

14.9

14.6

14.2

14.6 hi

0.9

1.0

0.8

0.9 d

3.0

3.0

3.1

3.0 abc

Sierra

1.56

1.82

1.69

1.7 f

14.9

13.7

14.9

14.5 ghi

0.6

0.7

0.6

0.6 b

3.3

3.3

3.2

3.3 bcde

Bluegold

1.47

1.68

1.64

1.6 e

15.1

13.6

14.4

14.4 fgh

0.9

1.1

1.0

1.0 d

3.1

2.7

2.9

2.9 a

Darrow

2.11

2.40

2.24

2.3 i

14.1

14.5

14.0

14.2 def

1.0

0.9

0.9

0.9 d

3.0

3.0

3.1

3.0 abc

Nelson

1.79

2.1

2.04

2.0 g

14.3

14.0

14.6

14.3 efg

0.8

0.8

1.0

0.9 cd

3.1

3.2

3.0

3.1 abc

Brigitta Blue

2.06

2.26

2.24

2.2 h

15.9

15.0

15.7

15.5 j

0.6

0.7

0.7

0.7 bc

3.4

3.3

3.2

3.3 cde

Lateblue

1.24

1.42

1.49

1.4 bc

15.0

14.1

14.8

14.6 i

1.1

1.2

1.4

1.2 e

3.0

2.9

2.7

2.9 a

Yearly mean (all cultivars)

1.5 a

1.8 c

1.7 b

 

14.3 b

13.6 a

14.2 b

 

0.7 a

0.8 a

0.8 a

 

3.2 a

3.2 a

3.1 a

 
a – weight, grams per berry
Values within a column or row followed by different letters are significant at p≤0.05

The titratable acid content of the blueberries was expressed as citric acid equivalent units. There were significant differences due to cultivars. The titratable acid content of blueberries investigated in this study varied from 0.4 for ‘Earlyblue’ to 1.2 g·100-1 g for ‘Lateblue’. The other cultivars showed intermediate levels of acidity. Blueberries did not exhibit any significant differences in acidity as a consequence of the harvest season. In this study, values for titratable acidity in ‘Earlyblue’, ‘Bluecrop’ and ‘Berkeley’ cultivars were consistent with the one reported by Sapers et al. [18]. Our results in general seem to be similar to or little lower than some of the other reports [6,10,22].

pH level in blueberry was highly affected by the genotype. pH values for different cultivars of blueberries ranged from 2.9 to 3.5. Fruits of ‘Lateblue’ and ‘Bluegold’ cultivars consistently showed the lowest pH as compared with other cultivars. There were no significant differences between pH of blueberries harvested in different years. Our data suggest that levels of total acidity and pH mainly depended on the genotype and not on the climatic condition of the season. The pH levels observed in our work were similar to those determined by Sapers et al. [18] in berries of the same cultivars grown in the United States.

Total phenolics
The amount of total phenolics in the berry ranged from 214.1 to 455.8 mg·100g-1 (Table 2). Cultivars showed significant differences in total phenolic content. Cultivars ranking for total phenolics content was very similar to this for total anthocyanins content. ‘Bluegold’ consistently showed the highest total phenolics content (455.8 mg·100g-1) and the highest total anthocyanins measurement as compared to all cultivars. Cultivars showing large size berries (‘Nelson’, ‘Toro’ and ‘Darrow’) generally had less phenolics content (average for this group was 216 mg·100g-1) than small fruited clones such as ‘Amblue’ or ‘Earlyblue’. In general, the blueberries cultivated in 2002 had significantly higher total content of the phenolic compounds compared to those cultivated in 2003 and 2004. Our results showed that the concentration of phenolics in blueberry is mainly affected by the genotype and less by the growing season.

The concentration of total phenolics for Duke cultivar in this study (320.7 mg·100g-1) were in good agreement with blueberries grown in Maryland. Total phenolics of 313 mg·100g-1 for these fruits were reported by Zheng et al. [29]. Compared to our results, Prior et al. [16] reported lower content of the phenolics of ‘Bluecrop’ fruits. Similarly, Connor et al. [3] and Moyer et al. [14] determined that the concentration of phenols in ‘Bluecrop’ blueberry was 402 and 304 mg in 100 g of fresh products, respectively. Total phenolics of 417 mg·100g-1 of fruits in our research is higher than those reported values. Range of reported phenolics for highbush blueberries is very wide due to the variations between different environmental conditions (herbivore, disease, temperature, moisture, irradiation, soil fertility), time of harvest, and extraction procedures.

Total anthocyanins
In the present study, the total anthocyanin content in highbush blueberry measured by spectrometric method ranged from 97.1 to 256.5 mg·100g-1 (Table 2). The content of anthocyanins in blueberry was largely influenced by cultivar. ‘Bluegold’ fruits had the highest concentration. ‘Darrow’, ‘Nelson’ and ‘Toro’ contained very low amounts of anthocyanins compounds, 97.1, 101.2, and 109.9 mg·100g-1, respectively. There were significant differences in anthocyanins content between years of harvest. Blueberry had the highest levels of anthocyanins in 2002, on the average 181.3 mg·100g-1. The high levels of anthocyanins found in fruits harvested in 2002 could be explained by lower berry weight in this year. It is known, that pigment in highbush blueberries was located exclusively in the skin, in the effect of that, smaller berries contain more anthocyanins.

Table 2. Total phenolics, total anthocyanins, chlorogenic acid contents and antioxidant activity in fruits of 14 highbush cultivars harvested in the years 2002-2004

Cultivars

Total phenolics a

Total anthocyanins b

Chlorogenic acid c

Antioxidant activity d

2002

2003

2004

Cultivar mean
(all years)

2002

2003

2004

Cultivar mean
(all years)

2002

2003

2004

Cultivar mean
(all years)

2002

2003

2004

Cultivar mean
(all years)

Earlyblue

397.4

388.9

368.2

384.8 j

260.8

240.2

192.2

231.1 j

39.9

47.4

44.3

43.9e

41.3

40.8

39.2

40.4 k

Duke

330.7

321.1

310.4

320.7 f

193.5

180.4

157.4

177.1 g

38.4

40.0

37.2

38.5 c

31.2

30.9

29.0

30.4 f

Patriot

299.0

295.4

289.1

294.5 d

150.9

143.6

127.4

140.6 f

43.8

50.5

41.1

45.1 g

26.3

27.4

25.2

26.3 d

Amblue

370.8

361.1

352.5

361.5 h

225.7

207.7

204.4

212.6 h

34.7

38.4

33.5

35.5 b

36.4

35.9

35.2

35.8 h

Berkeley

257.7

248.2

242.1

249.3 c

131.8

112.9

103.6

116.1 d

32.6

34.0

30.1

32.2 a

24.7

23.4

22.1

23.4 a

Toro

220.4

209.7

218.6

216.2 ab

118.6

103.8

107.3

109.9 c

40.8

51.5

42.8

45.0 fg

24.0

23.6

21.8

23.1 a

Herbert

340.1

336.5

328.3

335.0 g

176.9

178.3

166.6

173.9 g

39.4

46.3

37.5

4.11 d

28.3

29.8

26.4

28.2 e

Bluecrop

440.2

427.5

383.3

417.0 k

164.5

139.4

94.6

132.8 e

86.3

104.9

84.9

92.0 k

32.6

32.7

28.6

31.3 g

Sierra

466.5

448.7

422.3

445.8 l

228.2

217.5

210.4

218.7 i

60.3

64.8

61.3

62.1 i

39.1

38.5

38.2

38.6 j

Bluegold

496.5

448.7

422.3

455.8 m

274.5

253.7

241.3

256.5 k

64.7

76.9

68.8

70.1 j

45.4

44.1

41.6

43.7 l

Darrow

208.4

223.5

210.5

214.1 a

98.6

102.4

90.3

97.1 a

58.7

65.4

62.0

62.0 i

24.2

24.9

23.5

24.2 b

Nelson

227.2

220.2

207.9

218.4 b

103.7

102.0

97.8

101.2 b

55.3

58.1

53.7

55.7 h

25.2

25.4

24.6

25.1 c

Brigitta Blue

320.8

307.3

310.5

312.9 e

182.2

181.3

167.4

177.0 g

42.1

47.3

43.6

44.3 ef

30.7

31.3

29.0

30.3 f

Lateblue

376.5

389.2

360.4

375.4 i

227.7

212.5

200.4

213.5 h

68.5

72.3

67.5

69.4 j

38.1

37.7

34.1

36.6 i

Yearly mean
(all cultivars)

339.4 c

330.4 b

316.2 a

 

181.3 c

169.7 b

154.4 a

 

50.4 a

57.0 b

50.6 a

 

32.0 b

31.9 b

29.9 a

 

a – data expressed as milligrams of chlorogenic acid equivalents per 100 g of fresh weight
b – data expressed as milligrams of cyjanidin-3-glucoside equivalents per 100 g of fresh weight
c – data expressed as milligrams of chlorogenic acid equivalents per 100 g fresh weight
d – data expressed as micromoles of Trolox equivalents per gram of fresh weight
Values within a column or row followed by different letters are significant at p≤0.05

We observed anthocyanin concentrations in the range of 97 mg·100g-1 for cv. Darrow berries to 256 mg·100g-1 for cv. Bluegold. The value falls within the wide range of 25 to 495 mg·100g-1 for highbush blueberries reported by Mazza and Miniati [13]. The amounts of ‘Duke’ anthocyanins in our study were lower than 216 mg·100g-1 reported by Ehlenfeldt and Prior [4]. The total anthocyanin content in the blueberry of ‘Bluecrop’ cultivars was 138.2 mg·100g-1 of fresh berries. The pigment content is in good agreement with previously reported values of 123 g·100 g-1 [3] for the ‘Bluecrop’ variety, but differ considerably from the results reported by Moyer et al. [14]. They reported a mean value of 84 mg·100g-1, which was lower than in our study. The total anthocyanin content for ‘Bluecrop’ blueberries was also higher that the amounts reported by Prior et al. [16], Sapers et al. [18], Sapers et al. [19], Taruscio et al. [26]. Several factors which influence formation of anthocyanins (e.g., geographic location, maturity, environmental factors such as light, temperature, agronomic practices, various stresses) may have contributed to the differences between our results and those obtained by the others.

Chlorogenic acid
Chlorogenic acid is a major cinnamic derivative found in large amounts in highbush blueberries. In the present study chlorogenic acid was found at the level of 38.5 to 92.0 mg·100g-1 of fresh blueberries (Table 2). Fruit of ‘Bluecrop’ was found to have the highest chlorogenic acid content among the fruits tested, whereas ‘Berkeley’ and ‘Amblue’ had the lowest. The content of chlorogenic acid also depended on the studied year. The lowest concentration was found in fruits harvested in 2003. Probably it was caused by the temperature stress due to springfrost.

In the present study the chlorogenic acid content of the blueberry cv. ‘Bluecrop’ fruit reached 92.0 mg·100g-1 fresh weight. This is much lower than the 185 mg·100g-1 reported by Schuster and Herrman [20], similar to the 97.7 mg·100g-1 reported by Gao and Mazza [5], but different considerably from the results reported by Skrede et al. [21]. They reported a mean value of 27 mg·100g-1, which was lower than in any other blueberry cultivar tested in our work. The chlorogenic acid concentration in Sierra cultivar in this study (62.1 mg·100g-1) was similar than these reported by Zheng and Wang [28] (64.5 mg·100g-1).

Antioxidant activity
The antioxidant activity of the blueberries is shown in Table 2. Antioxidant activity for the different cultivars of highbush blueberry ranged from a low 23.1 in ‘Toro’ to a high 43.7 µmol Tolox equivalents/g of fresh berries in Bluegold, reflecting 1.9-fold differences. The overall means of all cultivars harvested in three years was 31 µmol Tolox equivalents/g. Based on the antioxidant activity it is possible to select cultivars of highbush blueberry exhibiting relatively high level of phytochemicals. The cultivars having high concentration of antioxidant were ‘Bluegold’, ‘Sierra’, ’Earlyblue’ ‘Amblue’ and ‘Lateblue’.

The berries harvested in 2004 had a significantly lower antioxidant activity compared to those in 2002 and 2003. The difference was probably due to the lower concentration of anthocyanins in the berries grown in 2004 compared to those grown in 2002 and 2003. Variation in antioxidant activity between genotypes was much greater than the one between years. This indicates that genotype plays a more important role than growing season in influencing phytochemicals in blueberries.

The antioxidant activities of highbush blueberry have been previously published by other authors. Connor et al. [3], using the oxygen radical absorbing capacity method (ORAC), found markedly similar results to our observation for ‘Bluegold’, ‘Duke’ and ‘Patriot’ cultivars. On the other hand, the antioxidant activity values observed for ‘Bluegold’ and ‘Duke’ in our work were higher those that determined by Ehlenfeld and Prior [4] and Prior et al. [16]. The antioxidant activity level of ‘Bluecrop’ in our study was lower than the values reported by Moyer et al. [14] and Kalt et al. [9], but considerably higher than values reported by Prior et al. [16], Ehlenfeldt and Prior [4] and Connor et al. [3]. Differences in antioxidant activity found for the same variety by different authors might be due to the use of different extraction solvents or methods. Other factors may also be important such as the stage of ripeness, geographical location and storage time.

Results consistently indicated significant correlation between antioxidant activity and the total anthocyanins or total phenolics content. The correlation coefficient was higher between antioxidant activity and the anthocyanins (r = 0.93) compared to antioxidant activity and total phenolic content (r = 0.89). Others authors, for example Kalt et al. [9] reported that the correlation coefficient for ORAC and total anthocyanin was 0.9. A significant linear relationship between ORAC and total phenolic content was observed by Ehlenfeld and Prior, [4]. They reported lower correlation coefficient, compared to that of our study.

CONCLUSIONS

As a conclusion, our results clearly demonstrate that the fruits of highbush blueberry commonly consumed in Poland are excellent source of antioxidant. For this reason blueberry can be used in nutritional supplement formulation. The results showed linear correlation between total anthocyanin content and antioxidant activity which suggested that anthocyanins make a significant contribution to the antioxidant capacity of blueberry fruits. Studies in our laboratory suggest that antioxidant activity and chemical composition (anthocyanin, phenolic, chlorogenic acid contents) of blueberry were affected more by genotype than the growing season. This information provides further encouragement that selection of cultivars can be utilized to increase the possible health benefits of these fruits. Future research on individual bioactive compounds in blueberry needs to be done to clarify the potential health benefits of highbush blueberry fruits.

ACKNOWLEDGMENT

The authors thank Kazimierz Scibisz and Kazimierz Pliszka from Department of Pomology of Warsaw Agricultural University for selecting and providing blueberry cultivars. Research work was supported by the Ministry of Education and Science in the years 2004-2006 (grant 2 P06T 058 26).

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Accepted for print: 24.10.2007


Iwona ¦cibisz
Department of Food Technology,
Division of Fruit and Vegetables Technology,
Faculty of Food Technology,
Warsaw Agricultural University, Poland
Nowoursynowska 159C, 02-787 Warsaw, Poland
Phone: 225937545
email: iwona_scibisz@sggw.pl

Marta Mitek
Department of Food Technology,
Division of Fruit and Vegetables Technology,
Faculty of Food Technology,
Warsaw Agricultural University, Poland
Nowoursynowska 159C, 02-787 Warsaw, Poland Phone: 225937545
email: marta_mitek@sggw.pl

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