Biological Activities of Color

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of Color-fleshed Potatoes and Their Relationships. Hye Lim Jang and Kyung ... stem tubers is red, purple, blue, or orange are a recent improvement over white ... antioxidants due to their capability of scavenging free radi- cals of fatty acids and ...
Hort. Environ. Biotechnol. 53(2):175-181. 2012. DOI 10.1007/s13580-012-0048-9

ISSN (p rint) : 2211-3452 ISSN (online) : 2211-3460

Research Report

Cultivar Differences in Phenolic Contents/Biological Activities of Color-fleshed Potatoes and Their Relationships *

Hye Lim Jang and Kyung Young Yoon

Department of Food and Nutrition, Yeungnam University, Gyeongsan 712-749, Korea *Corresponding author: [email protected]

Received June 15, 2011 / Revised August 22, 2011 / Accepted August 22, 2011 GKorean Society for Horticultural Science and Springer 2012

Abstract. The current study was performed to evaluate colored potatoes (Solamum tuberosum L.) as a potential source of functional food material. We compared the total phenolic content (TPC) in potato tubers of a white-fleshed potato variety with six color-fleshed potato cultivars. We also examined their antioxidant and antiproliferative activities. The TPC of the analyzed cultivars varied between 113.3 mg100 g-1 powder (‘Superior’) and 153.3 mg100 g-1 powder (‘Blue’). The colored potato extracts showed higher radical scavenging activities than the white fleshed potato extract (‘Superior’), and all colored potato extracts, except for ‘Rose’ and ‘Haryoung’, induced significant antiproliferative activities against THP-1 cells at the tested concentrations. In particular, ‘Jaseo’ and ‘Jasim’ showed 35% and 31% cell viability, respectively, at the concentration of 100 쩋gmL-1. The greatest positive correlation was found between TPC and hydroxyl radical scavenging activity (r = 0.912, p < 0.01), and TPC also showed a strong positive correlation with nitrite scavenging ability (r = 0.808, p < 0.01). Our results indicate that color-fleshed potatoes have higher antioxidant and stronger antiproliferative activities than white-fleshed potatoes. Additional key words: antioxidant activity, antiproliferative activity, DPPH, polyphenol, Solamum tuberosum L.

Lqwurgxfwlrq Potatoes (Solanum tuberosum L.) are currently the fourth most important food crop worldwide after maize, wheat, and rice, with production of more than 323 million tons (Lachman et al., 2009). Recently, in Korea, the amount of potato consumption has increased. Due to their low cost, low fat content, and good source of carbohydrates, high quality protein, fiber, and vitamins, potatoes play an important role in human nutrition (Al-Weshahy and Rao, 2009). Generally, the skin or flesh of the stem tubers of ordinarily cultivated potato varieties is white, yellow, lemon yellow, or saffron yellow. Colored potato cultivars in which the skin or flesh of the stem tubers is red, purple, blue, or orange are a recent improvement over white fleshed potato varieties such as ‘Irish cobbler’, ‘Superior’, and ‘Atlantic’. These colored potatoes are rich in certain antioxidants such as polyphenolics and contain high amounts of nutrients compared to white fleshed potatoes (Jang et al., 2011). Colored potatoes have attracted special attention in many counties due to their colorful appeal and excellent taste (Brown, 2005; Johnson, 1995), and many are commercially available as specialty potatoes (Zhao, 2009). There has been consumer interest in

potatoes with colored flesh for use in salads and novelty crisps, especially since the color is retained after cooking or frying (Lewis et al., 1998). Furthermore, it was reported that one of the richest sources of antioxidants in the human diet is potato tubers. The main antioxidants in potatoes are polyphenols, ascorbic acid, carotenoids, tocopherols, and selenium (Lachman et al., 2006). Polyphenolic compounds, especially flavonoids, are effective antioxidants due to their capability of scavenging free radicals of fatty acids and oxygen (Good, 1994). Brown (2005) found that colored potatoes contain two-fold higher levels of phenolic acids compared to yellow-fleshed potatoes. The antioxidant capacity of red or blue colored potatoes is 2-3 times higher in comparison to potatoes with white/yellow flesh; these potatoes therefore represent the possibility of enhancing the contribution by potatoes to a portion of the antioxidants within human nutrition (Lachman and Hamouz, 2005). High levels of phenolic acids are shown to be closely related to high concentrations of anthocyanins and flavonoids in colored potato tubers (Lewis et al., 1998). It was found that pigmented potato cultivars are a rich source of anthocyanins, in particular acylated derivatives (Erichorn and Winterhalter, 2005). Although previous studies indicate that colored

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Hye Lim Jang and Kyung Young Yoon

potatoes have potential uses in the food and nutraceutical industries, most have reported on the antioxidant activity of potato peels as a by-product obtained from potato processing. Moreover, there is still a paucity of information regarding the anticancer properties of colored potatoes. Our research examined the physicochemical properties and functional abilities of colored potatoes, which are considered new cultivars. In preliminary studies, we found that colored potatoes contained higher amount of nutrients compared to a white fleshed potato variety, ‘Superior’ (Jang et al., 2011). This study analyzed the biological activity of colored potatoes in order to confirm their cytological value and development potential as functional food materials. Therefore, the aim of the present study was to investigate antioxidant activities including radical scavenging ability on 1,1-diphenyl-2picrylhydrazyl (DPPH) and hydroxyl radicals, nitrite scavenging ability, as well as the cell cytotoxicity of extracts from colored potatoes.

Pdwhuldov# dqg# Phwkrgv Fkhplfdov# dqg# Vdpsohv Folin-Ciocateu’s phenol reagent, 1,1-diphenyl-2-picryl hydrazyl (DPPH), pyrogallol, gallic acid, trichloroacetic acid (TCA), and thiobarbituric acid (TBA) were purchased from Sigma-Aldrich (St. Louis, Mo, USA). Ethanol, ethylenediaminetetraacetic acid (EDTA), sodium nitrate, acetic acid, sodium carbonate, aluminum nitrite, and hydrochloric acid were obtained from Merck (Darmstadt, Germany). All chemicals used in the experiments were of analytical grade. Samples were collected from potato cultivars produced in Chung-Buk Province, Korea (seed potatoes) in the year 2008. A white fleshed potato type (‘Superior’) and six colored potatoes (‘Red’, ‘Rose’, ‘Haryong’, ‘Blue’, ‘Jaseo’, and ‘Jasim’) were used for further analysis. The colors of the potato skin/flesh were light brown/white (‘Superior’), red/ yellow (‘Red’), red/mixed yellow and red (‘Rose’), dark purple/purple (‘Blue’), dark purple/mixed white and purple (‘Jaseo’), and purple/purple (‘Jasim’), respectively. The samples were washed, peeled, and then dehydrated, respectively, and stored at -75Gin preparation for the antioxidant activity and phenolic compound analysis. Fhoo# Olqhv# dqg# Fhoo# Fxowxuh# Human hepatoma HepG2 cells and human peripheral monocytic THP-1 cells were obtained from the American Type Culture Collection (Rockville, MD, USA). The HepG2 cells were maintained in a DMEM medium, supplemented with 10% fetal bovine serum, 50 UmL-1 of penicillin, and 50 -1 mgmL of streptomycin, at 37Gin a 5% CO2 incubator. The THP-1 cells were maintained in a RPMI1640 medium, supplemented with 10% fetal bovine serum, 50 UmL-1 of

-1

penicillin, and 50 mgmL of streptomycin, at 37Gin a 5% CO2 incubator. All cell culture reagents were obtained from GibcoBRL (Life Technologies, Cergy-Pontoise, France). Suhsdudwlrq# ri# Vdpsoh# H{wudfwv The sample extracts were obtained by water, which had shown higher antioxidant activity than 80% ethanol and 50 % methanol extractions in a preliminary experiment. Each sample (40 g) was added to 800 mL of distilled water, homogenized, and then shaken continuously on an orbital shaker for 180 min at 70. The extract was centrifuged at 16,270 × g for 30 min, and the supernatant was collected. The sample extraction was replicated three times as described above. Next, the sample extracts were condensed with a rotary evaporator (N-1000, EYELA, Tokyo, Japan) under reduced pressure at 40, and then the condensed extracts were lyophilized. The lyophilized extracts were used to prepare solutions of various concentrations, which were then analyzed for their antioxidant activities, which will be described in the following sections. Ghwhuplqdwlrq# ri# Wrwdo# Skhqrolf# Frqwhqw Total phenolic content (TPC) was determined according to the method of Al-Weshahy and Rao (2009). Each extract was dissolved in distilled water. One milliliter of each sample was mixed with 1 mL of Folin-Ciocalteu’s reagent and allowed to stand at room temperature for 3 min. Then, 1 mL of 10% Na2CO3 and 2 mL of distilled water was added to the mixture. After standing for 60 min, the absorbance was measured with a spectrophotometer (UV-2001, Hitachi, Tokyo, Japan) at 725 nm. The results were expressed as milligrams of gallic acid equivalent (GAE) per 100 g of extract powder. GSSK# Udglfdo# Vfdyhqjlqj# Dfwlylw| The free radical scavenging effects of the extracts were estimated according to the method of Chen et al. (2005) with some modifications. Two milliliters of each sample, prepared at various concentrations (250, 500, 1,000, and 2,000 µg -1 mL ), were added to 1 mL of 0.2 mM DPPH radical solution. The mixture was shaken and allowed to stand for 30 min at 37, and then the absorbance was measured at 517 nm with a spectrophotometer (UV-2001, Hitachi). The percentage of radical scavenging activity was calculated using the relationship: hŠ–•›™–“ à hšˆ”—“Œ hŠ–•›™–“

% DPPH��� scavenging activity = ć Z Î×× where Acontrol was the absorbance of the control (blank) and Asample was the absorbance of the extract.

Hort. Environ. Biotechnol. 53(2):175-181. 2012.

K|gur{|o# Udglfdo# Vfdyhqjlqj# Dfwlylw|# Hydroxyl radical scavenging activity was determined using the 2-deoxyribose oxidation assay according to Jung et al. (2008). A solution (0.2 mL) of 10 mM FeSO47H2O and 10 mM EDTA was prepared in a screw-capped test tube. Then, 0.2 mL of 10 mM 2-deoxyribose solution, individual sample, and 0.1 M sodium phosphate buffer (pH 7.4) were added to give a total volume of 1.8 mL. Finally, 200 쩋L of 10 mM H2O2 solution was added to this reaction mixture and incubated at 37Gfor 60 min. After incubation, 1 mL each of 2.8% TCA and 1.0% TBA were added to the reaction mixture. The sample was boiled at 100Gfor 10 min, cooled in ice, and then its absorbance was measured with a spectrophotometer (UV-2001, Hitachi). The hydroxyl radical scavenging ability (%) was calculated the same as for DPPH radicals as described above. Qlwulwh# Vfdyhqjlqj# Delolw|# +QVD, The nitrite scavenging ability of each sample was determined by the method of Kato et al. (1987). Each sample extract of four different concentrations (250, 500, 1,000, and -1 2,000 µgmL ) was mixed with 1 mL of 1 mM NaNO2 and adjusted to pH 1.2 using 0.1 N HCl and 0.2 N citrate buffer. The mixture was increased in volume to 5 mL, and then incubated at 37Gfor 60 min. Next, a 0.5 mL aliquot of sample was combined with 2.5 mL of 2% acetic acid and 0.2 mL of Griess reagent (1% sulfanilic acid and 1% naphthylamine in a methanol solution containing 30% acetic acid). After 15 min, the color intensity was measured by a spectrophotometer (UV-2001, Hitachi) at 520 nm. The nitrite scavenging effects were calculated the same as for DPPH radicals as described above. Dqwlsurolihudwlyh# Dfwlylwlhv# ri# Srwdwr# Fxowlyduv# rq# Kxpdq# Fdqfhu# Fhoov The effects of the potato cultivars on cancer cell proliferation were measured by colorimetric assay. HepG2 cells were seeded at a plating density of 3 × 104 cells per well and cultured for 24 h to allow the cells to adhere to the plate. After 24 h, the culture medium was changed to serum free medium supplemented with the samples at the indicated doses. Following culture with the samples for 48 h, MTT (0.5 mgmL-1) was added, and after 4 h of incubation at 37, 200 쩋L of DMSO was added to each well. The absorbance values of samples were measured at 540 nm against a background control using a 96-well plate reader. The THP-1 cells were seeded at a plating density of 5 × 104 cells/well and cultured overnight; the culture medium was then replaced with serum free medium along with the samples at the indicated doses. Following culture with the samples for 48 h, 10 쩋L of WST-1 was added to each well. The cells were then incubated at 37 for 4 h. The absorbance of the samples was measured at 450

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nm against a background control using a 96-well plate reader. The percentage of viable cells under each treatment condition was determined relative to the negative control. Vwdwlvwlfdo# Dqdo|vlv Each experiment was performed three times and the data are expressed as means and standard deviations. Statistical analysis was performed by Duncan’s multiple range tests using PASW 18.0 software. The level of statistical significance was set at p < 0.05. Furthermore, comparisons of total polyphenol content, DPPH and OH radical scavenging activities, nitrite scavenging ability, and cell proliferation were carried out with Pearson correlation tests at a p < 0.001 probability level.

Uhvxowv# dqg# Glvfxvvlrq Wrwdo# Sro|skhqrov# Phenolic compounds such as flavonoids, phenolic acids, and tannins are widely researched, naturally occurring antioxidant components of plants. These phenolic compounds, found in medicinal plants as well as fruits and vegetables, play important roles in preventing degenerative diseases, including inflammation, cancer, and arteriosclerosis, when they are consumed as part of the daily diet (Li et al., 2008; Schieber and Saldaña, 2009). Table 1 presents the extractable phenolic compound contents of potato extracts, which are expressed in gallic acid equivalents, respectively. The total phenolic contents (TPC) of the analyzed cultivars varied between 113.3 mg100 g-1 powder (‘Superior’) and 153.3 mg100 g-1 powder (‘Blue’). Individual cultivars differed significantly -1 in TPC. The highest TPC was in ‘Blue’ (153.3 mg100 g -1 powder), followed by ‘Jaseo’ (142.2 mg100 g powder), ‘Jasim’ (130.0 mg100 g-1 powder), ‘Red’ (122.2 mg100 -1 -1 g powder), ‘Rose’ (118.9 mg100 g powder), and ‘Har-1 young’ (116.7 mg100 g powder), while ‘Superior’ had the lowest TPC (113.3 mg100 g-1 powder). Lewis et al. (1998) Table 1. Total phenolic contents of extracts from various potato cultivars Cultivars

Polyphenol (mg100 g-1powder)

‘Superior’

113.3 ± 0.0f

‘Red’

122.2 ± 1.9d

‘Rose’

118.9 ± 3.8de

‘Haryoung’

116.7 ± 3.3ef

‘Blue’

153.3 ± 0.0a

‘Jaseo’

142.2 ± 1.9b

‘Jasim’ 130.0 ± 3.3c Each value represents mean ± SD of triplicate measurements. Values in a column with different letters are significantly different at p < 0.05.

Hye Lim Jang and Kyung Young Yoon

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found that cultivated potato tuber skins contained 2,000-5,000 쩋gg-1 FW phenolic acids, and tuber flesh contained lower concentrations ranging from 100-600 쩋g of phenolic acids. They also found that purple- and red-skinned tubers contained twice the concentration of phenolic acids as white-skinned tubers, which is in agreement with our results. The major phenolics in potato peels are chlorogenic acid, gallic acid, protocatechuic acid, caffeic acid, and quercetin (Rumbaoa et al., 2009). Cholorogenic acid is by far the most abundant phenolic component and may constitute up to 90% of the total phenolics (Friedman, 1997; Im et al., 2008). Other phenolic compounds in potatoes include ferulic acid and p-coumaric acid as well as small amounts of rutin, myricetin, kaempferol, naringenin, and other flavonoids (Nara et al., 2006; Reyes, 2005). Purple-fleshed potatoes also contain petunidinand malvidin-3-rutinoside-5glycosides acylated with p-coumaric acid and ferulic acid, while red-fleshed potatoes have pelargonidin- and peonidin-3-rultinoside-5-glycosides acylated with p-coumaric and ferulic acid (Reyes, 2005). One could expect that some potato cultivars including ‘Blue’ and ‘Jaseo’ would be more valuable as functional food materials due to their higher phenolic contents. In an earlier study, colored potatoes contained high amounts of phenolic compounds, and there was a positive linear correlation between total phenolic content and antioxidant activity (Lachman et al., 2009; Rumbaoa et al., 2009). This suggests that color fleshed potatoes, which contain higher levels of phenolics and flavonoids compared to white fleshed potatoes, might have high antioxidant properties. GSSK# Udglfdo# Vfdyhqjlqj# Dfwlylw| DPPH is a stable free radical that is widely used to test the free radical scavenging activities of various kinds of samples (Shin et al., 2008). The DPPH scavenging activities of all extracts increased according to increases in extract concentration (Table 2). The DPPH radical scavenging activity of the ‘Rose’ extract was higher than that of the other extracts at

all extract concentrations. At the concentration of 2,000 mgmL-1, the DPPH radical scavenging effects of ‘Superior’, ‘Red’, ‘Rose’, ‘Haryoung’, ‘Blue’, ‘Jaseo’, and ‘Jasim’ were 42.2, 57.4, 81.9, 59.0, 60.2, 78.6, and 69.4%, respectively. Kang et al. (1996) reported that radical scavenging activity is an index for the antioxidant effectiveness of phenolic compounds, and it increases with increasing extract concentration. Brown (2005) found that colored potatoes contained two-fold higher levels of phenolic acids compared to yellowfleshed potatoes. Due to the fact that colored varieties have 2-3 times higher antioxidant capacity than yellow varieties (Hejtmánková et al., 2009), which is in agreement with our results, the higher total phenol contents of colored potato extracts as compared to white fleshed potato extracts might explain the higher antioxidant properties of colored potatoes. These results show that colored potatoes, especially; ‘Rose’, ‘Jaseo’, and ‘Jasim’ are quite sufficient to be potential functional food materials or antioxidant sources and would therefore be preferred for use in the diet. K|gur{|o# Udglfdo# Vfdyhqjlqj# Dfwlylw|# Among the oxygen radicals, the hydroxyl radical is the most reactive, inducing severe damage to adjacent biomolecules in cells and causing cell death. Thus, the removal of hydroxyl radicals is very important for the protection of living systems (Yang et al., 2007). As shown in Fig. 1, all the extracts were capable of scavenging hydroxyl radicals in a concentration-dependent manner. ‘Rose’ had the highest activity at all extract concentrations except at 500 쩋gmL-1, and particularly showed about 55% scavenging activity at 2,000 쩋gmL-1. The activities of ‘Superior’, ‘Red’, ‘Haryoung’, ‘Blue’, ‘Jaseo’, and ‘Jasim’ were 26.5, 35.2, 32.3, 35.9, 35.9, -1 and 42.3%, respectively, at 2,000 쩋gmL ; all the colored potato extracts showed significantly stronger scavenging activities than the white fleshed potato extract (‘Superior’). Furthermore, the hydroxyl radical scavenging activity of the ‘Blue’ extract was twice that of the ‘Superior’ extract. Chu et

Table 2. DPPH radical scavenging activity (%) of extracts from various potato cultivars Cultivars

Concentration (˩gmL-1) 250

500

1000

2000

4.4 ± 0.4d

9.3 ± 2.3c

19.1 ± 2.3d

42.2 ± 1.4e

‘Red’

3.0 ± 2.0d

10.0 ± 1.3c

20.6 ± 0.7d

57.4 ± 1.3d

‘Rose’

15.9 ± 4.0a

28.4 ± 2.8a

49.7 ± 4.5a

81.9 ± 1.8a

6.3 ± 1.1cd

8.0 ± 1.5c

21.8 ± 1.0d

59.0 ± 1.7d

9.7 ± 2.8bc

29.1 ± 3.1a

42.3 ± 0.6b

60.2 ± 0.5d

21.1 ± 1.8b

46.1 ± 3.2ab

78.6 ± 2.8b

‘Superior’

‘Haryoung’ ‘Blue’ ‘Jaseo’

10.8 ± 0.8b

‘Jasim’ 10.1 ± 0.4b 19.1 ± 1.2b 34.6 ± 0.5c 69.4 ± 2.3c Each value represents mean ± SD of triplicate measurements. Values in a column with different letters are significantly different at p < 0.05.

Hort. Environ. Biotechnol. 53(2):175-181. 2012.

Fig. 1. Hydroxyl radical scavenging ability of extracts from various potato cultivars. Each bar represents mean ± SD of triplicate measurements. Values with different letters are significantly different at p < 0.05.

Fig. 2. Nitrite scavenging ability of extracts from various potato cultivars at pH 1.2. Each bar represents mean ± SD of triplicate measurements. Values with different letters are significantly different at p < 0.05.

Fig. 3. Effects of extracts from various potato cultivars on THP-1 cell proliferation. Each value is the mean ± SD of triplicate measurements. *Significant when compared to ‘Superior’ extract at p < 0.05. **Significant when compared to ‘Superior’ extract at p < 0.01. ***Significant when compared to ‘Superior’ extract at p < 0.001.

al. (2000) found that flavonoid or flavone extracts of potato skins showed 94% scavenging activity towards hydroxyl radicals, and almost complete inhibition of superoxide radicals. However, our results show lower scavenging activities toward hydroxyl radicals compared to these previous results because flesh extracts of potatoes generally contained lower

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amounts of polyphenols including flavonoids and flavones than skin extracts. Natural polyphenols are known for their significant oxygen radical scavenging properties in vivo and in vitro (Yang et al., 2007). In addition, Mau et al. (2005) anticipated that extracts with moderate to high radical scavenging abilities might possess some antimutagenic properties. The present results indicate that colored potatoes, containing high amounts of phenolics, are powerful free radical inhibitors and scavengers. Thus, purple and red-fleshed potatoes could be used as novel sources of natural antioxidants, providing added value to the food industry and human health as well as functional food material (Reyes et al., 2007). Qlwulwh# Vfdyhqjlqj# Delolw|# Nitrosamines are known to be potent human carcinogens when consumed in the diet or produced from endogenous biosynthesis in the body. Nitrosamines are formed by reactions of secondary amines with nitrosating agents under acidic conditions in the stomach. Therefore, it is very important to inhibit nitrosamine formation in order to prevent carcinogenicity (Shin et al., 2008). Generally, the inhibition of nitrosamine formation occurs by the degradation of nitrite itself, as well as by the nitrosation inhibition of secondary amines, by chemicals having reducing abilities (Kato et al., 1987). Fig. 2 shows the nitrite scavenging abilities of the extracts at pH 1.2, in which scavenging ability was positively correlated with extract concentration. ‘Blue’ had the highest NSA of all the samples under the same concentration. Some colored potato extracts had stronger NSA than the white fleshed potato, ‘Superior’, and some colored potato extracts had similar or slightly higher NSA than ‘Superior’; however, ‘Haryoung’ did not have NSA at any of the tested concentrations. The NSA values of ‘Superior’, ‘Red’, ‘Rose’, ‘Haryoung’, ‘Blue’, ‘Jaseo’, and ‘Jasim’ were 3.9, 4.3, 5.1, 0, 25.5, 15.2, -1 and 20.9%, respectively, at 2,000 쩋gmL . Phenolic compounds such as flavonoids, catechins, and tannins are reported to have high nitrite scavenging effects, and have even higher effects under conditions of low environmental pH (Kang et al., 1996; Mirivish et al., 1972). Our results show that when compared to the ‘Superior’ extract, the higher antioxidant activities of the ‘Blue’ and ‘Jasim’ extracts are in good accordance with their greater amounts of total phenolics. Dqwlsurolihudwlyh# Dfwlylwlhv# ri# Srwdwr# Fxowlyduv# rq# Fdqfhu# Fhoo# Olqhv To evaluate the potential of the potato cultivars as cancer preventive foods, we examined their antiproliferative activities against THP-1 cells and HepG2 cells. When THP-1 cells were treated with hot-water extracts from the various potato cultivars for 48 h, all extracts except for ‘Rose’ and ‘Haryoung’ showed higher antiproliferative activities compared to the ‘Superior’ extract (Fig. 3) at the concentration of 100

Hye Lim Jang and Kyung Young Yoon

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Table 3. Correlation coefficients among total phenolic content, free radical scavenging activity, nitrite scavenging ability, and cell cytotoxicity of potato cultivars

TPC DPPH OH

TPC

DPPH

OH

NSA

WST-1

1

0.339 1

0.808*

0.912**

-0.656

0.214

0.145

0.316

-0.241

0.417

1

0.794*

-0.518

-0.230

1

-0.791*

NSA WST-1

1

MTT

0.384 -0.533

MTT 1 TPC, total phenolic content; DPPH, DPPH radical scavenging activity; OH, OH radical scavenging activity; NSA, nitrite scavenging ability; WST-1, cytotoxicity on TPH-1 cells by WST-1 assay; MTT, cytotoxicity on HepG2 cells by MTT assay. *p < 0.05,**p < 0.01.

Fig. 4. Effects of extracts from various potato cultivars on HepG2 cell proliferation. Each value is the mean ± SD of triplicate measurements. *Significant when compared to ‘Superior’ extract at p < 0.05. ***Significant when compared to ‘Superior’ extract at p < 0.001.

쩋gmL-1. In particular, the ‘Jaseo’ and ‘Jasim’ extracts significantly inhibited THP-1 cell proliferation at the low con-1 centration of 30 쩋gmL . On the other hand, all extracts showed weak activities against HepG2 cell proliferation (Fig. 4). It was reported that ‘Jasim’ extracts showed moderate inhibition of proliferation against prostatic LNCap, renal ACHN, and leukemia MOLT-4F cells (Park et al., 2008). It is likely that the differences between the effects of the potato cultivars on THP-1 and HepG2 cell proliferation may be associated with cell-type specificity. Numerous articles have reported that polyphenol and flavonoid contents are related to anticarcinogenic effects on human cancer cells (Chu et al., 2000; Hayashi et al., 2006). Therefore, differences in activities between colored potatoes on cancer cell proliferation may be related to their contents of active compounds such as polyphenols and flavonoids. Based on these results, we can suggest that colored potatoes might have potential for cancer prevention. Fruuhodwlrq# Frhiilflhqwv# ehwzhhq# Dvvd|v Pearson correlation analysis revealed that the antioxidant content was correlated with antioxidant activity (Table 3),

and the best positive correlation was found between TPC and hydroxyl radical scavenging activity (r = 0.912, p < 0.01). In addition TPC had a strong positive correlation with OH radical scavenging activity (r = 0.808, p < 0.01). The NSA of samples showed a positive correlation with OH radical scavenging activity (r = 0.794, p < 0.05) and a negative correlation with cytotoxicity in TPH-1 cells (r = -0.791, p < 0.05). However, DPPH radical scavenging activity was not significantly correlated within any other assays. Furthermore, no dependency was observed between HepG2 cell cytotoxicity by MTT assay and other biological activity. Reddivari et al. (2007) reported that a significantly positive correlation was observed between total phenolics and antioxidant activity among specialty potato selections. Hejtmánková et al. (2009) also reported that the best positive correlation was observed between total anthocyanin content and antioxidant activity, and a good correlation was found between chlorogenic acid content and antioxidant activity. A high positive correlation between antioxidant activity and the total polyphenolic content of colored potatoes was found by Lachman et al. (2008) as well as Reyes (2005) and Reddivari et al. (2007). These results suggest that polyphenol content may be an important contributor to antioxidant and anticancer activity, and our results support this evidence. The results of this study demonstrate that the effects of the cultivars and the differences between white- and colorfleshed potatoes for total polyphenol content and antioxidant activity were found to be significant. The color-fleshed potatoes contained higher phenolic contents compared to the white-fleshed potato variety. Color-fleshed potatoes also showed high antioxidant activities in experimental analysis, and all extracts, except for the ‘Rose’ and ‘Haryoung’ extracts, showed higher antiproliferative activities against cancer cells compared to the ‘Superior’ extract. Therefore, color-fleshed potatoes have potential for use as food supplements and could be a promising source of beneficial antioxidants for human health.

Hort. Environ. Biotechnol. 53(2):175-181. 2012.

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