Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : January 22, 2018
Accepted : February 10, 2018
Published online : March 31, 2018

Original article

Analysis of anti-glycative components in Smallanthus sonchifolius (yacon)
Taiki Yamaguchi, Wakako Takabe, Masayuki Yagi, Yoshikazu Yonei
Anti-Aging Medical Research Center and Glycation Stress Research Center, Graduate School of Life and Medical Sciences,
Doshisha University, Kyoto, Japan

Abstract

Aim: Glycation, the non-enzymatic reaction between excess blood sugar and proteins, leads to multiple disorders,aging and inflammation of body organs and tissues via the formation and accumulation of advanced glycation end
products (AGEs). In this study, we investigated the yacon tuber’s inhibitory efficacy against the formation of AGEs
and analyzed the anti-glycation compounds in yacon.
Methods: Yacon tuber (Smallanthus sonchifolius) was divided into an edible part and a peel part and an extract
was prepared by hot water. Human serum albumin (HSA) glycation model were used to evaluate the efficacy of
extract against fluorescent AGE formation. We used a reversed phase high performance liquid chromatography(RP-HPLC) system to isolate the compounds in yacon tuber. Mass spectrometry was used for identification ofeffective compounds in yacon tuber.
Results: Compared to the edible part, the peel part extract (YPE) strongly inhibited fluorescent AGE formation. We
observed at least 4 anti-glycative compounds in YPE, however, every compound was shown to be less effective than
the whole YPE. Based on mass spectrometry data, we concluded that 3,4- or 3,5- dicaffeoylquinic acid, and 2, 3, 5or 2,4, 5- tricaffeoylaltraric acid were the principal anti-glycative compounds in yacon.
Conclusions: In yacon tuber, the peel part extract inhibited fluorescent AGE formation. We identified 4 compounds
as anti-glycative compounds.

KEY WORDS: glycation, fluorescent advanced glycation end products (AGEs), intermediates of AGEs, yacon(Smallanthus sonchifolius), tricaffeoylaltraric acid, dicaffeoylquinic acid,

Reducing sugar such as glucose, fructose, etc. is importantin life activity. On the other hand, reducing sugar causes
glycation, the non-enzymatic reaction between proteins andreducing sugar, and it forms advanced glycation end products(AGEs). Generation and accumulation of AGEs will cause
aging and inflammation in body organs and tissues. Nagai
et al. reported that glycation relates to complications fromdiabetes, lifestyle diseases, and age-related diseases 1).
To prevent the glycative stress from glycation, multiple
ideas have been studied such as I. Inhibition of the AGE
formation, II. Promoting degradation of AGEs and III.
Preventing the high blood glucose condition 2). In this study,
we are focusing on preventing the formation of AGEs.
Several lines of evidence, polyphenolsin plants showed astrong anti-glycation effect 3-6), and we have studied over 500
kinds of plants to evaluate their anti-glycative efficacy 7-11).
Yacon, Smallanthus sonchifolius, is a plant originallycultivated in the Andean region, and mainly the tuber iseaten 12). The yacon tuber contains rich polyphenol compounds
such as fructooligosaccharides, chlorogenic acid, caffeic acid,
3,4- or 3,5- dicaffeoylquinic acid (DCQA) and 2, 3, 5- or 2,4,5tricaffeoylaltraric acid (TCAA) 12-14). Fructooligosaccharides
are sugars found in plants but never in concentrations ashigh as in yacon tuber, soluble dietary fibers. Chlorogenic
acid has an antioxidant effect and it is included in potatoes,
apples, and tomatoes 15). DCQA has a strong and selective
α-glucosidase inhibitory activity 16 -18). TCAA has a strong
antioxidative activity and α-glucosidase inhibitory activity 14)
and to our knowledge, it has been identified only in yacon.
Overall, yacon root contains multiple compounds which have

Corresponding author: Wakako Takabe, PhD
Anti-Aging Medical Research Center and Glycative Stress Research Center,
Graduate School of Life and Medical Sciences, Doshisha University
1-3 TataraMiyakodani, Kyotanabe, Kyoto 610 - 0321, Japan
TEL & FAX: + 81-774 - 65 - 6382 eMail: wtakabe@mail.doshisha.ac.jp
Co-authors: Yamaguchi T, ctub2025@mail4.doshisha.ac.jp ;Yagi M, myagi@mail.doshisha.ac.jp ; Yonei Y, yyonei@mail.doshisha.ac.jp

Glycative Stress Research 2018; 5 (1): 036- 0 44(c) Society for Glycative Stress Research

Introduction_ 36 _Glycative Stress Researchsome health-promoting effects, such as the improvement in
the intestinal microflora balance 19-22) and inhibiting the highblood glucose condition due to its α-glucosidase inhibitory
activity 14).
In this study, we investigated the compounds effective
against glycation in yacon tubers.

Materials & Methods
Materials.

Yacon tuber was purchased from Minamiyamashiro
village in Kyoto, Japan in April, 2016. Human serum albumin(HSA) was purchased from Sigma-Aldrich (St. Louis, MO).
All other chemicals were analytical grade and obtained from
Wako Pure Chemical Industries (Osaka, Japan), SigmaAldrich (St. Louis, MO), and Dojindo (Kumamoto, Japan).

Preparation of yacon tuber extract.

Yacon tuber was divided into an edible part and a peel
part. Each sample was dried and ground, and then 2 g ofthe powdered samples were mixed with 40 mL of distilledwater. After incubation at 80°C for 75 minutes, the extracted
samples were centrifuged at 2,500 rpm (570 x g) for 10
minutes and filtered using filter paper. We named the extractfrom the edible part YEE (Yacon tuber edible part extract)
and the peel part YPE (Yacon tuber peel part extract).
Five mL of each extract was used for the measurementof solid content by evaporation, and then the appropriate
concentrations were adjusted with distilled water.

Preparation of glycated proteins.

The HSA glycation model 7, 8) was used to evaluate theeffect of YEE and YPE on glycation. Briefly, 25 μL of thesamples were added to 125 μL of 0.1 mol/L phosphate buffer
solution (pH 7.4), 25 μL of distilled water, 50 μL of 40 mg/
mL HSA, and 25 μL of 2.0 mol/L glucose. The reaction
mixture was incubated at 60°C for 4 0 hours (named A).
Distilled water was added instead of samples as a blank(named B). At the same time, using distilled water insteadof glucose was also prepared as a blank for each reaction(A’ = blank of sample, B’ = blank of distilled water). Insteadof samples, 1 mg/mL aminoguanidine (AG) 23) was used as apositive control.

Measurement of AGE-derived fluorescence.

AGE-derived fluorescence was measured as reported
previously 7, 8). Briefly, 200 μL of the reaction mixture wasused to measure fluorescence at an excitation wavelengthof 370 nm and an emission wavelength of 440 nm by a
Varioscan ® Flash microplate reader (Thermo Scientific,
Waltham, MA). The value was calculated using the equation
below.
Ratios of Fluorescent AGE formation [%] = 100 × (A – A’) /(B – B’)

Isolation of the glycation inhibitory compounds inyacon extract.

YPE was isolated using a reversed phase high performanceliquid chromatography (RP -HPLC) system (Shimadzu

Corporation, Kyoto, Japan), according to the protocol, butslightly modified from Takenaka’s report 12), described below.
Briefly, 100 μL of YPE were injected in RP-HPLC andfractionated every 0.5 minute. This operation was performed
twice, then these fractions were mixed together. Then samples
were evaporated by centrifugation evaporator (CC-105 Tomy,
Tokyo, Japan) and re-dissolved in 200 μL distilled water andused to determine the inhibitory effect of those fractions on
AGE-derived fluorescence formation.
HPLC condition is listed below.
Column: Cosmosil 5C18-MS (4.6 mmφ × 150 m ; Nacalaitesque,
Kyoto, Japan), Eluent: (Phase A) 10 mmol/L phosphate acid: acetonitrile (90 : 10), (Phase B) acetonitrile, Gradient: 0 →4 9. 5% B (0 → 30 min), Column temperature: 40°C, flow
rate: 1.0 mL/min, UV detection: 326 nm, injection volume:
100 μL

Analysis of glycation inhibitory compounds inyacon extract.

The glycation inhibitory compounds from YPE wereanalyzed by liquid chromatography-time-of -flight / mass
spectrometer [LC-QTOF/MS] with photo diode array (PDA).
The Analytical conditions are listed below.
Column: Wakosil II 5C18 RS (2.0 mmφ × 150 mm ; Wako),
Eluent: (Phase A) 0.1% formic acid, (Phase B) acetonitrile,
Gradient: 10 → 95% B (0 → 30 min), Column temperature:
40 °C, flow rate- 0.2 mL/min, Ionization method: ESI(negative mode), Capillary voltage: 3,000 V (negative mode),
Nebulizer gas: Nitrogen 1.6 bar, Drying gas flow rate: nitrogen
8.0 L/min, Drying gas temperature: 180 °C, Measurement
mass range: m/z 50 ~ 2,000, Measurement wavelength: 190~ 800 nm.

Purification of tricaffeoylaltraric acid fromyacon
extract.

Tricaffeoylaltraric acid (TCAA) in yacon was purified
from 6 g of dried powder of yacon tuber peel according to
the previously described method 24). The purity of TCAA
and the content of those in YEE and YPE were evaluated by
HPLC. The purified sample was used for further analysis.

Effect of yacon extract and tricaffeoylaltraric acidagainst intermediate of AGE formation.

Three kinds of AGE intermediates, 3-deoxyglucosone(3-DG), glyoxal (GO) and methylglyoxal (MGO) were
measured using a RP-HPLC system. Samples were prepared
as previously described 25). Briefly, 100 μL of HSA glycation
model reaction mixtures were mixed with 75 μL of 0.2
mmol/L phosphate buffer and 155 μL of distilled water.
Then, the samples were deproteinized using 170 μL of 6 %perchrolic acid. After centrifugation at 12,000 rpm (13,200x g) for 10 minutes, 4 00 μL of supernatant was immediately
neutralized with 350 μL of saturated sodium bicarbonate.
Then, 3-DG, GO and MGO were labeled with 50 μL of 1
mg/mL 2, 3-diaminonaphthalene for 24 hours at 4°C. Aftercentrifugation at 15,000 rpm (20,630 x g) for 10 minutes,
supernatants were analyzed by HPLC.
HPLC conditions are listed below.
Column: UnisonUK-Phenyl (3 mmφ x 75 mm; Imtakt Corp,
Kyoto, Japan), Eluent: 50 mmol/L phosphoric acid : acetonitrile= 89 :11, Column temperature: 40°C, flow rate: 1.0 mL/min,
UV detection: 268 nm, injection volume: 20 μL_ 37 _

Anti-Glycative Compound in Yacon Tuber.
experiments in order to identify effective compounds against
fluorescent AGE formation.
YPE’s 50% inhibition concentration (IC 50) against
fluorescent AGE formation was 0.093 mg/mL ( Fig. 1-b).
IC 50 against fluorescent AGE formation of AG, the positive
control, was 0.062 mg/mL (Fig. 1-c).

Statistics.

The statistical analysis was performed by Dunnett’s
multiple comparison test. Differences were consideredsignificant at p values less than 0.05.

Isolation of the glycation inhibitory compounds
from yacon extract.

Results

Evaluation of yacon extracts against fluorescent
AGE formation.

RP-HPLC was used to analyze the compounds in YPE
and the flow through was collected every 0.5 minute. Eachfraction was evaporated and re-dissolved in distilled water,then it was introduced into a HSA glycation model reaction
mixture in order to evaluate the fluorescent AGE formation( Fig. 2-a). From these results, several fractions showed strong
inhibitory efficacy against fluorescent AGE formation. Next,
we selected 4 peaks (#1~ 4) that have a strong effect andisolated the peaks by hand ( Fig. 2-b).These peaks were also
evaporated and re-dissolved in distilled water, then used
to measure the effect of those peaks on fluorescent AGE
formation ( Fig. 2-c). Compared to the reference, all 4 peaks
inhibited fluorescent AGE formation, especially peaks #3
and 4 showed a stronger effect than other peaks. However,each peak was less effective than the whole YPE.

The inhibitory efficacy against fluorescent AGEs of
YEE and YPE was evaluated using the HSA glycation
model ( Fig. 1-a). Ten % final concentration of YEE andYPE showed the inhibitory efficacy against fluorescent AGE
formation, and especially YPE showed a strong inhibitory
effect. Without glucose condition, YEE and YPE showed 3
times and twice higher fluorescent AGEs than the reference(water). This result suggested that YEE and YPE might haveauto fluorescence in our measurement condition. However,with glucose condition, YPE suppressed about 50% of thefluorescent AGE formation compared to the reference.
YEE showed a significant effect, but was less effective than
YPE. Therefore, we decided to use YPE for the following

b)

120
100

Glucose +Glucose -

＊＊

80
60

Fluorescent AGEs [% control]

Fluorescent AGEs [% control]

a)

＊＊

＊＊

YPE

AG

40
20
0
Ref

YEE

IC 50
0.093 mg/ml

0.02158

0.2158

2.158

Reaction Concentration [mg/mL]c)
Fluorescent AGEs [% control]

90
80
70
60
50
40
30
20
10
0

100
IC 50
0.062 mg/ml

80
60
40
20
0
0.01

0.05

0.1

Reaction Concentration [mg/mL]

Fig. 1. 1. Effect of yacon extracts and AG on the inhibition of fluorescent AGE formation.

a) YEE and YPE were introduced into glycation models containing 8 mg/mL HSA and 0.2 mol/L glucose as indicated concentrations of thesolid contents. After 40 h incubation at 60°C, fluorescent AGEs were measured by 370/440 nm (AG’s final concentration: 0.1 mg/mL). b)
Three different concentrations of YPE were used to determine its IC 50 against fluorescent AGE formation. c) Three different concentrationsof AG was used to determine its IC 50 against fluorescent AGE formation.** p < 0.01 vs ref. YEE, yacon tuber edible part extract. YPE, yacon
tuber peel part extract. HSA, human serum albumin. AGEs, advanced glycation end products. AG, aminoguanidine.

_ 38 _

Intensity [mV]a)2000000
1800000
1600000
1400000
1200000
1000000
800000600000400000200000
0

#4

140
120
100
80

#1

60
#2#3

40
20
0

0

5

10
15
Time [min]20

25

Fluorescent AGEs [% control]

Glycative Stress Research

YPE
Fluorescent AGEs
formationb)
14000000

Intensity [mV]

12000000
10000000

YPE

8000000#1

6000000#2

4000000#3

2000000#40- 2000000

c)

0

10

15

20

＊＊

Glucose +Glucose -25

Time [min]Fluorescent AGEs [% control]

120
100
＊＊

80

＊＊
＊＊

60

＊＊

＊＊

40
20
0
ref

#1

#2

#3

#4

YPE

AG

Fig. 2. Isolation of anti-glycative compounds in yacon extract using RP-HPLC system.

a) YPE were fractionated by RP-HPLC system. The fractions were added into a HSA glycation model at 60°C for 40 h, then we measured thefluorescent AGEs at 370/440 nm. HPLC condition: Column: Cosmosil 5C18-MS (4.6 mmφ × 150 m ; Nacalaitesque, Kyoto, Japan), Phase A:
10 mmol/L phosphate acid : acetonitrile (90 : 10), Phase B: acetonitrile, Gradient: 0 → 49.5% B (0 → 30 min), Column temperature: 4 0 °C,
flow rate: 1.0 mL/min, UV detection: 326 nm, injection volume: 100 μL. b) Verification of isolated peaks by RP-HPLC. c) Peaks #1~ 4 wereadded into the HSA glycation model. After 40 h of incubation at 60°C, fluorescent AGEs were measured by 370/440 nm.** p < 0.01 vs ref.
YPE, yacon tuber peel part extract. HSA, human serum albumin. AGEs, advanced glycation end products.

_ 39 _

Anti-Glycative Compound in Yacon Tuber.

Identification of glycation inhibitory compounds inyacon extract.

Purification of tricaffeoylaltraric acid in yacon
extract.

Next, we performed LC-QTOF/MS with PDA analyses
to identify those 4 effective anti-glycative compounds in
YPE. As shown in Table 1, m/z of those peaks were 533.09(peak #1), mixture of 515.12 and 533.09 (peak #2), 515.13(peak #3) and 695.13 (peak #4) at a negative mode. To
compare the HPLC chromatograms of these 4 peaks(Fig. 2-b) and previous report 12), we expected that thesecompounds are caffeoylaltraric acid or caffeoylquinic acid.
The comparison with chemical standards, we estimated thatthe peak #1: 2, 4- or 3, 5-dicaffeoylaltraric acid, peak # 2 isthe mixture of 3, 4 -dicaffeoylquinic acid and the isomer ofpeak #1, peak #3: 3, 5-dicaffeoylquinic acid and peak #4:
2, 3, 5- or 2, 4, 5- tricaffeoylaltraric acid (TCAA).

TCAA was purified from YPE and we validated its
purity by HPLC using the previously reported method ( Fig.
3 ) 12). Based on the result, one obvious peak is observed. Also,
we calculated the concentration of TCAA in YEE and YPE.
YEE contained about 0.002 mg and YPE contained about
0.023 mg TCAA in each 1 mg of solid content of YEE and
YPE. In addition, we also evaluated the efficacy of TCAA
against fluorescent AGE formation, and its IC 50 was 0.019
mg/mL (Fig. 4 ).

Table 1. The results of analyzing the glycation inhibitory compounds in yacon
extract using LC-QTOF/MS with PDA.

Peak #

m/z

Estimation of composition formula1533.09C 2 4 H 22 O 14

515.12

C 25 H 2 4 O 12

533.09C 2 4 H 22 O 14

515.13

C 25 H 2 4 O 12695.13

C 33 H 28 O 17

2-1
2-2
3
4

Peaks #1~4 were isolated from yacon peel extract and were analyzed by LC-QTOF/MS with PDA.
Analytical condition: Column: Wakosil-Ⅱ5C18 RS (2.0 mmφ × 150 mm ; Wako Pure Chemical
Industries, Osaka, Japan), Phase A: 0.1% formic acid, Phase B: acetonitrile Gradient: 10 → 95% B (0 →30 min), Column temperature: 4 0°C, flow rate: 0.2 mL/min, Ionization method: ESI (negative mode),
Capillary voltage: 3,000 V (negative mode), Nebulizer gas: Nitrogen 1.6 bar, Drying gas flow rate:
nitrogen 8.0 L/min , Drying gas temperature: 180°C, Measurement mass range: m/z 50 ~ 2,000,
Measurement wavelength: 190 ~ 800 nm.

TCAA 0.348 mg/mL

YPE

YEE
0

5

10

15

20

25

30

Time [min]Fig. 3. Comparison of HPLC chromatogram of yacon extract and tricaffeoylaltraric acid.

YEE, YPE, TCAA were analyzed by RP-HPLC. HPLC condition: Column: Cosmosil 5C18-MS (4.6 mmφ × 150
m ; Nacalaitesque, Kyoto, Japan), Phase A: 10 mmol/L phosphate acid : acetonitrile (90 : 10), Phase B: acetonitrile,
Gradient: 0 → 4 9.5% B (0 → 30 min), Column temperature: 40°C, flow rate: 1.0 mL/min, UV detection: 326 nm,
injection volume: 20 μL.
YEE, yacon tuber edible part extract. YPE, yacon tuber peel part extract. TCAA, tricaffeoylaltraric acid.

_ 40 _

Fluorescent AGEs [% control]

Glycative Stress Research

80

IC 50
0.019 [mg/mL]

70
60
50
40
30
20
10
0
0.035

0.007

0.07

Reaction Concentration [mg/mL]

Fig. 4. Effect of tricaffeoylaltraric acid on fluorescent AGE formation.

TCAA was used to determine the IC 50 against fluorescent AGE formation in HSA glycation models. After 4 0 h of incubation at 60 °C,
fluorescent AGEs were measured by 370/440 nm. Three different concentrations were used to determine IC 50 against fluorescent AGE
formation. TCAA, tricaffeoylaltraric acid. AGEs, advanced glycation end products. HSA, human serum albumin.

Effect of yacon extract and tricaffeoylaltraric acidagainst intermediate of AGE formation.

Finally, we also investigated the efficacy of YPE andTCAA on intermediate AGE (3-DG, GO, MGO) formationin HSA glycation reaction model. As shown in Fig. 5, both
YPE and TCAA inhibited all 3 intermediates formation.
YPE’s IC 50 against 3-DG, GO, MGO were 0.28, 0.046, 0.15
mg/mL, TCAA’s IC 50 against 3-DG, GO, MGO were 0.33,
0.011, 0.024 mg/mL, respectively.

Discussion

In this study, we investigated the anti-glycative
compounds in yacon tuber. First, we evaluated the YEE’s
and YPE’s inhibitory efficacy against fluorescent AGE
formation using HSA glycation model. YPE has a stronger
inhibitory efficacy against fluorescent AGE formation
than YEE ( Fig. 1-a). Thus, we further investigated in order
to identify the effective compounds against glycation in
YPE (Fig. 2-a). We selected 4 peaks (#1~ 4), especiallythose that are expected to have strong effect and evaluatedthe inhibition of fluorescent AGE formation using the
HSA glycation model. As shown in Fig. 2-c, peak #1~ 4
showed a strong inhibitory efficacy against fluorescent
AGE formation. However, each peak was less effective
than the entire YPE. These results suggested that multiple
compounds in yacon tubers contribute to those anti-glycative
effect.
Thus, next we tried to identify anti-glycative compounds
in YPE. From the Fig. 2-b, c and the result of structure
estimation by LC-QTOF/MS with PDA analyses, DCQA
and TCAA highly contribute to anti-glycation effect of YPE.
DCQA and TCAA are polyphenols and DCQA is reported
to be contained in coffee beans 26, 27), sweet potato’s stem andleaf 28), garland chrysanthemum 29), artemisia 30) and TCAA
is reported to be contained tuber, leaf and stem in yacon 12).

Based on the RP-HPLC analyses, YPE contains about ten
times the TCAA compared to YEE in each 1 mg of solid
content ( Fig. 3 ). These results indicate that the differencein the amount of TCAA between YPE and YEE may affecttheir anti-glycative efficacy.
Several lines of evidence indicate that polyphenols
have an anti-glycative efficacy 3-6). We performed the RPHPLC analyses detected at UV 326 nm which is the typicalabsorbance of polyphenols. Other than DCQA and TCAA,
every YEE peak was smaller than YPE peaks in thechromatograms ( Fig. 3 ). We also measured total polyphenol
content in yacon tubers using the Folin-Ciocalteu method,which is approved by the National Consumer Affairs Centerof Japan (NCAC). YPE contained at least 5 times theamount of polyphenols than YEE in the same solid content(data not shown). This difference may also affect their antiglycative efficacy.
Traditionally, intake of yacon tubers have been
recommended to diabetic patients 31-33). Especially,fructooligosaccharides which is abundantly existed in yacon
tuber are able to resist the hydrolysis of enzymes in the humanupper gastrointestinal tract and have a low caloric value 34).
Genta et al. reported that daily intake of yacon syrup obtained
from tuber ameliorated body weight, fasting serum insulin
and LDL cholesterol in human 33). Other than that, DCQA
and TCAA are reported to have an α-glucosidase inhibitory
activity 14, 16-18), which means that intake of yacon tuber may
contribute to suppressing increases in blood glucose level.
Preventing the high blood glucose condition is one of theways to prevent glycation. In addition, we demonstrated that
DCQA and TCAA in YPE have anti-glycative efficacy.
Overall, our findings indicate that anti-glycative effect ofyacon tuber itself may partially contribute to those beneficial
effects.
Furthermore, we demonstrated that YPE and TCAA havean inhibitory efficacy against all 3 kinds of intermediates of
AGE formation in a dose-dependent manner ( Fig. 5 ). Because
TCAA contains 0.023 mg in 1 mg of solid content of YPE( Fig. 3 ), compare to IC 50, TCAA in YPE may strongly_ 41 _

Anti-Glycative Compound in Yacon Tuber.

a)b)

3-DG [% control]

70
60

IC 50
0.28 [mg/mL]

3-DG [% control]

80

50
40
30
20
10

80
GO [% control]70600.21582.158
0.1079Reaction Concentration [mg/mL]

40
30
20

MGO [% control]

40
30
20

0.035
0.07
0.007
Reaction Concentration [mg/mL]

80

IC 50
0.15 [mg/mL]

IC 50
0.024 [mg/mL]

70

50
40
30
20
10
0

50

0

0.10790.21580.02158
Reaction Concentration [mg/mL]

MGO [% control]

70

IC 50
0.011 [mg/mL]

10

10

60

0.035
0.07
0.007
Reaction Concentration [mg/mL]

60

50

0

IC 50
0.33 [mg/mL]

70

IC 50
0.046 [mg/mL]
GO [% control]

0

90
80
70
60
50
40
30
20
10
0

60
50
40
30
20
10
0

0.21582.158
0.1079Reaction Concentration [mg/mL]

0.035
0.07
0.007
Reaction Concentration [mg/mL]

Fig. 5. Effect of yacon peel extract and tricaffeoylaltraric acid onintermediate of AGE formation.

YPE (a) and TCAA (b) were used to determine the inhibitory effect on the intermediates of AGE formation. RP-HPLC analyses were
performed to detect 3-DG (top), GO (middle) and MGO (bottom). All data were shown as the mean ± SD (n = 3).

HPLC condition: Column- UnisonUK: Phenyl ( 3 mmφ x 75 mm; Imtakt Corp, Kyoto, Japan), eluent: 50 mmol/L phosphoric acid : acetonitrile= 89 : 11, Column temperature: 40°C, flow rate: 1.0 mL/min, UV detection: 268 nm, injection volume: 20 μL.

contribute to the inhibition of GO and MGO formation, but
not 3-DG. It is reported that AGE intermediates such as
3-DG, GO, MGO are mediating AGE generation pathway 35).
Thus, to inhibit the formation of AGEs, intermediates leads
to inhibit the AGE formation.
AG is a specific inhibitor for glycation 23). IC 50 of AG
against the formation of fluorescent AGEs was 0.062 mg/
mL ( Fig. 1-c). In the previous report, AG’s IC 50 against
fluorescent AGE formation was 0.067 ~ 0.100 mg/mL 8, 9).
From the point of view of the inhibition of fluorescent
AGE formation, YPE has similar IC 50 (0.093 mg/mL) and

TCAA has smaller IC 5 0 (0.019 mg/mL) compared to AG.
While AG has shown the preventive effect of nephropathy,
retinopathy, and nerve disorder in an animal study 23, 36-38), it
will cause adverse effects such as anemia, hepatic disorderand vitamin B6 deficiency. For this reason, AG has not been
approved in Japan. In this study, we suggest that TCAA inyacon tuber will come to be used as a new specific inhibitor
against glycation. Furthermore, yacon peel is usuallydisposed of because it’s a non-edible part. Using the yacon
peels as a source of anti-glycative compounds, might lead toexpanding the agricultural resource utilization.

_ 42 _Glycative Stress Research

Conclusion

Yacon tuber peel extract (YPE) showed a stronger
inhibitory efficacy against fluorescent AGE formation
than the edible part yacon tuber extract (YEE). DCQA andTCAA highly contribute to YPE’s strong anti-glycation
effect. TCAA was able to inhibit not only the formation offluorescent AGEs, but AGE intermediates.

Acknowledgement

This work was partially supported by the JapaneseCouncil for Science, Technology and Innovation, SIP (Project
ID 14533567), “Technologies for creating next-generation
agriculture, forestry and fisheries” (funding agency: Biooriented Technology Research Advancement Institution,
NARO).

Conflict of Interest Statement

The authors claim no conflict of interest in this study.

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