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ABSTRACT
1. INTRODUCTION
2. MATERIALS AND METHODS2.1. Place of Performance
2.2. Raw material
2.3. Reagents
2.4. Equipment and materials
2.5. Analytical Methods
2.5.1. Determination of moisture and dry matter
2.5.2. Anthocyanins Analysis
2.5.2.1. Extraction and quantification of anthocyanins in alcoholic media.
2.5.2.2. Quantification of total anthocyanins aqueous extracts.
2.5.3. Quantification of phenolic compounds (NFs)2.5.4. Quantification of antioxidant activity (AOA)
2.6. Experimental methodology
2.6.1. Conditioning of the raw material
2.6.2. Quantification of anthocyanins, total phenolics and antioxidant capacity of purple sweet
potato peel
2.6.3. Evaluation of the stability of the dye extracts
2.6.3.1. Evaluation of the stability of the heat-treated extracts
2.6.3.2. Evaluation of stability during storage extracts
3. RESULTS AND DISCUSSION
3.1. Quantification of total anthocyanins, total phenolic antioxidant capacity and the raw
material
3.1.1. Anthocyanin content
3.1.2. Phenolic content
3.1.3. antioxidant activity
3.2. Evaluation of the stability of the dye extracts
3.2.1. Influence of temperature on the stability of the extracts
3.2.2. Evaluation of stability during storage extracts
4. CONCLUSIONS
5. REFERENCES
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Anthocyanins, phenolics and antioxidant activity in three varieties of shells
purple sweet potato(Ipomoea batatas (L.) Lam)
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ABSTRACT
In the present study we quantified the content of anthocyanins, phenolics and
antioxidant activity present in the peel of three varieties of purple sweet potato: Leg Widow
(PDV), Pachacamac (PCH) and Italian (ITA).
The anthocyanin content (ACNS) present in the skin of three varieties of purple sweetpotato were: 1.37, 1.10 and 1.01 mg equivalent Cy-3-glu / g (bh) for the varieties PDV, PCH
and ITA respectively. The total phenolic content (NFs) found were: 12.47, 10.99 and 12.45 mg
chlorogenic acid equivalent / g (bh) for varieties PDV, PCH and ITA respectively. The values of
antioxidant activity (AOA) found were: 7825, 7139.87 and 7790.90 g Trolox equivalent / g (bh)
for varieties PDV, PCH and ITA respectively. We found a high correlation between the content
of NFs and antioxidant activity (AOA) (r2 = 0.99) for the three varieties studied, no correlation
was found between the content of CNRs and AOA.
We also evaluated in concentrated aqueous extracts, stability of CNRs, NF and AOA
facing pasteurization conditions (85 C for 15 minutes) and storage (20 C for 45 days).
During the treatment there was an apparent pasteurization-crease and good stability for thecontent of the extracts evaluated CNRs. The content of NFs slightly declining (1-4%), being
higher in the AOA loss (8-19%) in all extracts tested.
During the storage was also observed an apparent increase and stability of CNRs, with
respect to a decrease FNs (between 14-20%), being May res AOA losses (23-27%) for the
different extracts of sweetpotato evaluated.
I. INTRODUCTION
As the new millennium, a new era in the field of food science and nutrition has become
increasingly present intensity. The interaction area food - health known as the "functional
foods". Functional foods are defined as "Any food in natural or processed, in addition topresenting its nutrient components contain additional compounds that promote health, physical
ability and mental state of a person" (Vasconcellos, 2001).
Currently, many of the compounds that tend to give the character functional foods have
not been fully identified or evaluated by the physiological functions that would lead in the
human body.
Phenolic compounds appear as part of this wide range of functional elements and in
recent years has given its strong relationship with the reduction of chronic diseases like cancer,
due to its high antioxidant activity. Some of these phenolic compounds besides having the
above properties are presented
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as useful substances for the food industry such as in the case of the pigments called
anthocyanins.
In the processing industry raw materials of plant origin, there is a lot of waste that have
not been exploited yet, by the ignorance of their functional properties and paradoxically, in the
majority of this waste is concentrated as much these chemical elements beneficial to health,
posing as a great potential to explore and exploit. Within the mentioned industrial waste themare sweet potato peels (including the purple), the content of phenolic compounds and good
quality of its pigments (anthocyanins) make it a good source to consider.
In the present research had the following objectives:
- Quantifying total anthocyanins, total phenolics and evaluate the antioxidant capacity in
the peel of three varieties of purple sweet potato.
- Studying the influence of heat treatment and the storage stability of anthocyanins,
phenolic compounds and antioxidant, in aqueous extracts of purple sweet potato peel.
II. MATERIALS AND
METHODS 2.1 Place of
Performance
This research was conducted in the laboratories of Biotechnology, Faculty of Food
Industry and the Institute of Biotechnology (IBT) of the Universidad Nacional Agraria La Molina
(UNALM), Industrial Biotechnology area.
2.2 Raw material
We used the peel of three varieties of purple sweet potato ( Ipomoea batatas (L.) lam):
Pachacamac (PCH), Leg Widow (PDV) and Italian Purple (ITA) program provided by the roots
and tubers of UNALM.
2.3 Reagents
The 37% hydrochloric acid, 96% ethanol, absolute methanol, potassium chloride,
sodium carbonate, anhydrous sodium acetate, sodium hydroxide and potassium phosphate
monobasic (all PA grade) were purchased from the firm MERCK. 2,2 diphenyl-1-picrylhydrazyl
(DPPH)), 6-hydroxy-2 ,5,7,8-tetramethyl-2-carboxylic acid (Trolox), Folin-cicocalteau 2N and
chlorogenic acid (all grade QP) were purchased from Sigma - Aldrich.
2.4 Equipment and materials
Magnetic stirrer (Barnstead / Thermolyne, USA) with shaking water bath (GFL,
Germany) spectrophotometer (Genesys 5 / Milton Roy, USA), analytical balance (A & D Co.
Ltd., Japan), potentiometer (Orion, USA) CRF (General Electric, USA), rotary evaporator
(Buchi, Germany). Blender (Oster) and tube shaker (WORK, Hungary). Necessary materials
were used for conducting the tests and analysis
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2.5 Analytical Methods
2.5.1 Determination of moisture and dry matter: Method was used gravimetric
percentage, consisting of dry matter in a stove at 105 C for 6-9 hours until constant weight.
The moisture content is the result of the difference of the initial and final weight expressed as a
percentage (AOAC, 1990).
2.5.2 Analysis of anthocyanins (ACNS)
a. Extraction and quantification of anthocyanins in alcoholic media:
Was performed following the method reported by Fuleki and Francis
(1968). Anthocyanins were expressed as mg of cyanidin 3 glucosideequivalent / g of fresh product, based on a standard curve of cyanidin-3-glucoside; used the molar extinction coefficient e = 20 941 L x mol-1 xcm-1 and the molecular weight of 449.2 gx mol-1. This method was usedfor quantification of the pigments in purple sweet potato peels.
b. Quantification of total anthocyanins in aqueous extracts: It carried
out following the methodology reported by Wrolstad (1976). Anthocyanins
were expressed as mg of cyanidin 3 glucoside equivalent / mL of extract,
we used the molar extinction coefficient e = 20 941 L x mol-1 x cm-1 and
molecular weight (MW) of 449.2 gx mol-1. This method was used for the
stability tests of the aqueous extracts.
2.5.3 Quantification of phenolic compounds (NF): Was performed following the
method of Swain and Hillis (1959). Phenolic compounds were expressed as chlorogenic acid
equivalent mg / g or ml of fresh sample extract, based on a standard curve of chlorogenic acid.
2.5.4 Quantification of antioxidant activity (AOA): Was performed following themethod of Brand-Williams et al. (1995). The results were expressed in mg Trolox Equivalent
/ g ml fresh sample or extract, based on a standard curve of trolox.
2.6. Experimental methodology
2.6.1. Conditioning of the raw material
The continued flow of operations for obtaining the potato shell shown in Figure 1.
2.6.2. Quantification of anthocyanins, total phenolics and antioxidant capacity in
the purple sweet potato peel
At this stage the total anthocyanins was quantified (ACNS), total phenolics (NFs) and
antioxidant activity (AOA) in the peel of three varieties of purple sweet potato: Leg widow
(PDV), Pachacamac (PCH) and Italian (ITA) , using the methods described in items 2.5.2 (a),
2.5.3 and 2.5.4. All analyzes were performed in triplicate.
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Figure 1. Operation flow used for conditioning of raw material
Purple SweetPotato
Water
WASH
SELECTION
BARE
Shell
Steam
SCALDING
T = 100 C,1min
FROZEN
T = -18 C 2
STORAGE
T = -18 C 2
Water + impurities
Sweet potatoesdamaged
Pulp
The results were statistically analyzed according to a completely randomized design
(DCA) and the treatment means were confronted by the comparison test of multiple means of
Duncan. To find the interrelation between the different characteristics evaluated, we performed
a linear regression analysis, using the Statgraphics - PLUS 4.
2.6.3. Evaluation of the stability of the dye extracts
To obtain extracts of the three varieties studied (PDV, PCH and ITA) was used in
alcohol extraction method (section 2.5.2 a). The extracts were concen-trated in vacuo at 50 C
until a concentration of 10 Brix (aqueous extract), then the pH was adjusted to a value of 3
0.2, using a solution of 0.1N HCl or 0.1N NaOH. Also prepared an extract of purple corn
anthocyanins (MM) from a commercial product powder (SA Extracts and Dyes), which was
used as reference for the evaluation of the
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stability of purple sweet potato extracts. For evaluation of the stability of the extracts was
performed by linear regression analysis using the Statgraphics-PLUS 4.
a) Evaluation of the stability of the extracts subjected to heat
treatment
Was placed in test tubes completely sealed 3 mL of each extract (PDV, PCH,
ITA and MM) and then subjected to heat treatment at 85 C in a water bath for
15 minutes taking into account different intermediate times (0, 2, 5 , 10 and 15
minutes). Immediately after each treatment the samples were placed in ice
water at 0 C. For each time was analyzed for total anthocyanins (item 2.5.2
b), total phenolics and antioxidant activity. Analyses were performed in
triplicate for each of the extracts.
b) Evaluation of stability during storage extracts
Were placed in test tubes (capacity of 8 cm3) 3 mL of each extract (PDV, PCH,
ITA and MM) and then be sealed. Subsequently were subjected to storage
under the following conditions: Temperature 20 C in the presence of oxygen
(the tubes had a headspace of 8 cm3 ) And low light, for 45 days taking into
account different intermediate times (0, 5, 15, 30 and 45 days). For each day
Storage Storage is analyzed for total anthocyanins (item 2.5.2 b), total
phenolics and antioxidant activity. Analyses were performed in triplicate for
each of the extracts.
III. RESULTS AND DISCUSSION
3.1. Quantification of total anthocyanins, total phenolic antioxidant capacity
and the raw material3.1.1. Anthocyanin content
Table 1 presents the results of anthocyanin content expressed on a dry basis and wet
basis. There is a higher content of pigments in the range PDV (1.37 mg / g bh), representing
20% and 26% compared to the variety PCH (1.10 mg / g bh) and ITA (1.01 mg / g bh )
respectively.
Box 1. Anthocyanins found in the shells of three varieties of sweet potato purple *
P DV P CH ITA
b. s b. h b. s b. h b. s b.h
5 .35 1 .37 4 .56 1 .10 4 .24 1.1
* Expressed as mg equivalent Cy-3-glucoside / g sample
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Expressed on a dry basis (db), the pigment content is between 424 and 535 mg CNRs /
100g. Yoshimoto et al. (1999) indicate that the outer (5mm thick) purple-fleshed sweet potato
(variety Ayamurasaki) is 1.4 times higher anthocyanin content than the inner portion, this gives
us an idea of the high concentration of anthocyanins in the peel. Cascon et al. (1984) mention
that several cultivars of purple-fleshed sweetpotato obtained in different regions of Brazil
anthocyanins vary from 100 mg to 430 mg / 100g (bs). These values correspond to the whole
root (peel and pulp).
Expressed on a wet basis (bh) anthocyanin content is between 101 and 137 mg of
CNRs / 100g shell. In radishes red and white pulp shell were encountered values between 39.3
and 185 mg CNRs / 100 g of shell, whereas the red pulp cultivars pigment content varies from
12.2 to 52 mg CNRs / 100 g roots. They have also been reported in potato cultivars Urenika
dwelling as a high pigment content, with an average of 183.6 and 507.8 mg CNRs / 100 g (bh)
in pulp and peel respectively (Lewis, 1996 cited by Rodriguez-Saona et al., 1998). Rodriguez-
Saona et al. (1998) found in red-fleshed potatoes concentrations of 28.4 mg CNRs / 100 g pulp
and 21.7 mg / 100 g shell (bh). It is observed that the anthocyanin content found in this work is
within the average of those obtained in other roots.
The results of the statistical analysis indicate significant differences (a = 0.05), on the
content of anthocyanins (bh) in the three varieties of purple sweet potato. Comparing the
Duncan test indicated that the content of anthocyanins (bh) in the range PDV was significantly
higher than in the PCH and ITA variety.
3.1.2. Phenolic content
Table 2 presents the results of the total phenolic content expressed on a dry basis and
wet basis. One can observe a higher phenolic content in the range PDV (12.47 mg / g bh) and
ITA (12.45 mg / g bh) that are 12% higher compared to the variety PCH (10.99 mg / g bh).
The phenolic compound concentration expressed on a dry basis obtained in purple
sweet potato peels are between 4.55% and 5.24%. Schmidt-Hebbel et al. (1969) reported
values of phenolic compounds in eight varieties of apples, which is between 0.7-ban and 1.42%
(db). Yan et al. (1999) indicate that the roots of yacon
Table 2. Total phenolic content found in three varieties of purple sweet potato
P DV P CH ITA
b. s b. h b. s. b. h b. s b.h
4 8.72 1 2.47 4 5.46 1 0.99 5 2.38 12.45
* Expressed as mg chlorogenic acid equivalent / g sample
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contain a substantial amount of phenolic compounds, about 3.8% (db). The latter figure would
be closer to the values obtained from potato peels.
Expressed on a wet basis phenolic values obtained in potato peels are between 1099
mg and 1247mg / 100g. Walter et al. (1979) reports values of total phenolic seven potato
cultivars (full root) which are Didos comprises between 14 and 51 mg / 100g.
Table 3 shows the total phenolic content for different plants and compared with the
results found in this work. It is noted that none of these
analyzed plant exceeds those from purple sweet potato peels evaluated.
Table 3. Comparisons of the total phenolic content of purple sweet potato peels and
other plant products
VegetableTotal phenolic
VegetableTotal phenolic
(Mg Ac. Clor / 100g) (Mg Ac. Clor / 100g)
C amote - ITA 1237 K umara - gold * 154.4
C amote - PCH 1084 P apa * 38.3
C amote - PDV 1215 P apa - red skin * 41.8
B rcoli * 8 3.1 C ebolla * 66.8
Za nahoria * 4 0.2 L echuga - red leaf * 182.0
C oliflor * 3 5.0 L echuga - heart * 4.24
Umara K - shell * 7 8.5 To kill * 8.28
*Source : Lister and Podivinsky (1998)
Rodriguez-Saona et al. (1998) evaluated the content of phenolic acids in the peel and
pulp of purple potatoes. Tubers peels showed a high proportion of free phenolic acids,
especially the chlorogenic acid and p-coumaric acid.
Phenolic acids are usually accumulated in the skin and are of much importance in the
defense mechanisms for infection of some plants (Friend et al., 1985; Ramamurthy et al., 1992
cited by Rodriguez-Saona et al. 1998). Yoshimoto et al. (1999) studied four varieties of sweet
potato (flesh white, yellow, orange and purple), finding a higher concentration of phenolic
compounds in the outer portion (5mm thick) compared to the inner portion, in all varieties. They
also found a higher content of phenolic compounds in purple variety.
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The results of the statistical analysis indicated that there were significant differences (a
= 0.05) in total phenolic content (bh) in the three varieties of purple sweet potato. The
comparison test of Duncan said phenolic content (bh) is in the range PDV as in the variety and
ITA respective significantly higher both in the variety to PCH.
3.1.3. Antioxidant activity
The results of certain antioxidant activity in the peel of three varieties of purple sweet
potato are presented in Figure 2. The variety of the PDV AOA (7825.46 mg Eq Trolox / g bh)
was 9% and 0.4% greater with regard to the variety PCH (7139.87 mg Eq Trolox / g bh) and
ITA (7790.90 mg Eq Trolox / g bh) respectively ; also had an AOA variety ITA 4% higher with
respect to the variety PCH. For comparison we determined the AOA in strawberry product,
according to the authors Wang et al., (1996) and Vinson et al., (2001), has a high antioxidant
capacity. It can be seen that potato peel had higher antioxidant activity than the cutter.
Cao et al. (1996) found a value calculated for antioxidant activity sweetpotato (Whole
root) which was 5 times lower than that obtained in strawberry (Wang et al., 1996) based on 11
times lower fresh and dry basis. Contrary to this work (see Figure 2) Strawberry (3039.31 mg
Trolox Eq / g bh) represents 61% less compared to the variety PDV and ITA and 57% less
compared to the variety PCH.
Figure 2. Antioxidant activity in the peel of three varieties of purple sweet potato
TroloxEqug/gmf
9000
7790.907825.46800
0 7139.87
7000
6000
5000
4000
3039.31
3000
2000
1000
0PDV PCH ITA Strawberry
Variety
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Cisneros-Cevallos (2002) mentions that the AOA-found in blueberry, plum and purple
sweet potatoes (whole) was 1784, 3244 and 3167 mg Equiv. Trolox / g bh respectively. By
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mentioned we can say that the purple sweet potato peels have high antioxidant activity against
DPPH free radical?.
The results of the statistical analysis indicated that there were significant differences (a
= 0.05) in antioxidant activity (bh) in the three varieties of purple sweet potato. The comparison
test indicated that the AOA Duncan (bh) is in the range PDV as in the range ITA and bothsignificantly higher than in the variety PCH.
Finally, we looked for the relationship between the content of anthocyanins and total
phenolic content versus antioxidant capacity to three shells of purple sweet potato varieties.
No relationship was found between the content of anthocyanins and AOA, on the
contrary, we found a good linear correlation between phenolic content and AOA, with r2 =
0.998. Prior et al. (1998) analyzed four different cultivars of species Vaccinium, and found a
linear correlation between the content slightly anthocyanin and AOA (r2 = 0.77) and a much
higher among the phenolic content and AOA (r2 = 0.85).
The disconnect between the content and the AOA CNRs may be due to the low ratio
found in the relationship CNRs / NFs, the ratios found for varieties ITA, PCH and PVD were
0.081, 0.102 and 0.113 respectively. Prior et al. (1998) found values between 0228 and 0608.
The ratios found in the present study indicate that there is less amount of anthocyanins in
relation to the total phenolic content, so that anthocyanins lesser influence on the amount AOA,
this feature to be influenced mainly by the total phenolic content present in the peel of three
varieties of sweet potato purple evaluated.
3.2 Evaluation of the stability of the dye extracts
Tempetatura 3.2.1 Influence on the stability of the extracts
The effect of heat treatment (85 C x 15 minutes) in the anthocyanin content ofconcentrated extracts of purple sweet potato peel and purple corn (MM) are presented in Figure
3. In which one can observe two phenomena: An apparent increase in concentration and high
stability in the ACNS purple sweet potato. In extracts of PDV, PCH and ITA was observed an
increase in color intensity to 2 minutes followed by a 15 minute stabilization up. The three
varieties showed an increase final, being for variety and variety PCH PDV 18% and range from
26% ITA, the GM had a 10% decrease in the anthocyanin content.
The thermal stability of anthocyanin structure varies with pH, presence of oxygen and
interactions with other system components. For example the methoxylation, glycosylation and
acylation confer a protective effect against thermal degradation (Jackman and Smith, 1992).
One of the factors that such stability should be explained first to intramolecular
acylation or copigmentation of anthocyanins, and Francis demonstrated by Bassa
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Figure 3. Effect of heat treatment of purple sweet potato extracts in
CNRs stability
R
etention(%)
13
0
12
0
11
0
10
0
90
80
7060
50PDV
40PCH
30 ITA
20MM
10
00 2 4 6 8 10 12 14 16
Time(minutes)
(1987) in sweet violet and further if these pigments is diacylated, as in the case of purple sweet
potato anthocyanins reported by Terehara et al. (1999). The diacylation further increases the
stability of the pigment to the monoacilacin (Rodriguez-Saona et al., 1998) diacylated
anthocyanins are stabilized by a stacking causal sandwich hidrofficas sado by interactions
between the aromatic residue of the acyl group and the positively charged pyrylium nucleus
(Goto, 1987 cited by Rodriguez-Saona et al., 1998). This prevents the addition of nucleophiles,
especially water, to the positions C-2 and C-4 of the anthocyanin pseudobases decreasing the
formation of which would lead to degradation in pigment (Brouillard, 1981; Goto and Kondo,
1991 referred to by Rodriguez-Saona et al., 1998).
The effect of heat treatment (85 C) in the total phenolic content is presented in Figure
4. It is observed that both PDV, PCH and ITA as MM, show similar behaviors and good stability.
PDV has the highest percentage of degradation (5%) followed ITA (3%), MM (2%) and finally
PCH (1%)
Martinez-Valverde et al. (2000) indicate that the content of chlorogenic acid (major
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phenolic compound) is affected by the heat treatment, a decrease was found in potato with
respect to a raw potato 43% by microwave cooking and baking 60% in water boiling. Skrede et
al.(2000) indicate that other thermal processes as the concentration resulting in a loss of 4% of
phenolic pasteurized juice blueberry. Degradation of phenolic acids in purple yam extracts
possibly led to the formation of other acids or phenolic compounds and a small percentage to
other compounds during heat treatment (Rodriguez de Sotillo et al., 1994). These changes
would not be discriminated against on the methodology used by the Folin-Ciocalteau method toquantify phenolic compounds derived except for some who have become reductive capacity
and could have formed in smaller amounts.
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Figure 4.Effect of treatment trmicode purple sweet potato extracts inNFs stability
R
etention(%)
100
90
80
70
60
50
40
PDV
30
PCH
ITA20
MM10
0
0 2 4 6 8 10 12 14 16Time(minutes)
The effect of heat treatment on the antioxidant activity of the extracts of purple sweet
potato 3 and GM are shown in Figure 5. A similar trend is observed in extracts of PDV and MM,
the first to suffer the biggest drop in the AOA of 19% while for the MM was 14%.
Figure 5. Effect of heat treatment of purple sweet potato extracts in the AOA
100
90
80
70
(%)60
reten
5040
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PDV30
PCH20
ITA
10MM
00 2 4 6 8 10 12 14
Time(minutes)
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From Figures 4 and 5 can be noted that given the tendency to follow the curves PDV
varieties, PCH and ITA decreased antioxidant capacity may be linked directly with NFs
degradation, but not so with the content of CNRs .
3.2.2. Evaluation of stability during storage extracts
The effect of storage on the anthocyanin content is presented in Figure 6. It can be
seen in the purple sweet potato varieties PCH, PDV ITA and an apparent increase of pigment,
while for the MM degradation occurred. The ACNS PDV varieties, PCH and ITA increased
approximately until day 15 of storage, then a marked stability maintained until day 45, with a
relative increase of anthocyanin content of 26%, 16% and 37% respectively. MM extract
suffered a degradation of 35% to 45 days of storage.
Figure 6. Effect of storage of purple sweet potato extracts on the stability of the CNRs
dad
140
130
120
110
100
90
(%)
80
retention70
60
PDV5040 PCH30 ITA20 MM100
0 5 10 15 20 25 30 35 40 45 50Time (days)
During storage there are four factors to consider: The light, oxygen, temperature and
water action. In the case of the purple sweet potato these factors did not exert any effect due to
the high stability of their CNRs which is attributed to its structure (intramolecular co-
pigmentation or acylation) and interactions with other compounds (polyphenols copigmentation
other intermolecular ). However, in the case of decreasing MM indicates the susceptibility of
their pigment to the action of these factors together (light, temperature, oxygen and water) due
to the simple structure posibiblemente presenting their anthocyanins (Jackman and Smith,
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1992 ) and the small concentration of phenolic extracts compared with those obtained from
purple sweet potato.
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The effect of storage at ambient conditions in FNs stability is shown in Figure 7. At day
45 NFs content for varieties PCH, PDV and ITA showed a decrease of 20%, 18% and 13%
respectively for the MM was down 9%. The purple corn NFs are more stable to these conditions
than those obtained from purple sweet potato.
Figure 7. Effect of storage of purple sweet potato extracts stability in
FNs
Retention
(%)
110
100
90
80
70
6
0
5
0
4
0
PDVPCH3
0
ITA
20
MM1
0
00 5 10 15 20 25 30 35 40 45 50
Time(days)
One of the main factors of degradation of NFs perhaps was the incidence of light on
the samples. Rodriguez de Sotillo et al. (1994) studied the stability of potato extract at 4 C
and 37 C in the dark at 25 C exposed to light for 7 days. They found no major changes in
the extracts left in the dark, while those exposed to light showed a total degradation of its main
phenolic component, chlorogenic acid, which apparently contributed to an increase in the
concentration of caffeic acid.
Oxygen could also be another factor degradation, intervening in the auto-oxidation of
phenolic compounds. Talcott and Howard (1999) indicate that a decrease in the content of
soluble phenolics is due to an increase in the oxygen incorporated in the samples.
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The effect of storage on the AOA is presented in Figure 8. There isa rapid decrease in the AOA at 5 for 4 days extracts, decreasing by 20%and 22% POV PCH and ITA, while in MM only decreased by 16%. Thefour curves show a similar trend. At day 45 of storage PDV, PCH suffereda decline of 22% and ITA of 23%, while the decrease in MM was 29%.
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Figure 8.Effect of storage of purple sweet potato extracts on the AOA
100
90
80
70
(%)60
retention50
PDV
40PCH
30 ITA
20MM
10
00 5 10 15 20 25 30 35 40 45 50
Time (days)
During storage there was a decline in the middle of NFs possibly by autoxidation
(Figure 7), the oxygen in the space of "head" would be responsible for this change. The
phenolic antioxidants act as rust as in this way, if the phenol has been oxidized loses itsantioxidant capacity (Ceballos-Casals, 2002). Photodegradation of phenol may also be involved
in the reduction of antioxidant capacity, because during the light exposure may have been
formed intermediates which could have caused the partial reduction of the AOA. None of the
tests showed a stable behavior of the first order.
IV. CONCLUSIONS
The highest concentration of CNRs variety found in the PDV (1.37 mg Eq. Cy-3 glu /
gm bh) followed variety PCH (1.10 mg Eq. Cy-3 glu / gm bh) and finally the variety ITA
(1.10 mg Eq. Cy-3 glu / gm bh).
The highest concentration of NFs are found in the variety PDV (12.47 mg Eq.
Ac.Clorog. / Gm bh) and ITA (12.45 mg Eq. Ac.Clorog. / Gm bh) followed variety PCH
(10.99 mg Eq. Ac . Clorog. / gm bh).
Most AOA was found in the variety PDV (7825.46 g Eq. Trolox / gm bh) then ITA
(7790.90 g Eq. Trolox / gm bh) and finally in the variety PCH (7139.87 g Eq. Trolox /
gm bh). Compared with the cutter (3039.31 g Eq. Trolox / gm bh) values obtained in
purple yam having high AOA.
We found a high correlation between NFs and AOA (r2 = 0.998) in the three varieties of
sweet potato purple, indicating a strong influence of NFs content in AOA. Not
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found between CNRs and AOA.
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During the heat treatment, the content of CNRs in PDV, PCH and ITA was increased
(16,18 and 26% respectively), showing greater stability, whereas in the case of MM
degradation was observed (10%) , the content of NFs suffered a slight degradation for
both PDV, PCH, ITA (5, 1 and 3% respectively) and MM (2%), the AOA experienced a
similar decline for PCH and ITA (8%) and even greater fall for MM (14%) and PDV
(19%).
During storage, the content of PDV varieties CNRs, PCH and ITA was increased (26,
16 and 37% respectively), showing a greater stability, whereas in the case of
degradation was observed in MM (35%), the NFs content in MM suffered less
degradation (9%) that the PDV, PCH and ITA (20, 18 and 13% respectively), the AOA
decreased PDV experienced (22%), PCH (22%) and ITA (23%) and higher still for MM
(29%).
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