Ipomea Batatas - Evaluation of Drying Methods on Antioxidant Activity, Total Phenolic

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Evaluation of Drying Methods on Antioxidant Activity, Total Phenolic

and Total Carotenoid Contents of Sweet Potato

( Ipomoea batatas (L.) Lam.) var. Tainong73

Predner Duvivier1, Pao-Chuan Hsieh

2, Po-Yung Lai

1, and Albert L. Charles

1

1. Department of Tropical Agriculture and International Cooperation, and 2. Department of Food Science,

National Pingtung University of Science and Technology, Pingtung, Taiwan.

ABSTRACT

This study analyzed the evaluation of the antioxidant activity (AOA), total

phenolics, total flavonoids, and total carotenoids of sweet potato ( Ipomoea batatas Lam.)

var. Tainong 73 during the drying process. Flesh and skin samples were submitted to

sun-drying, low-temperature drying (LTD) at 25°C, hot air drying (HAD) at 50

°C, or

HAD at 75ºC, and extracted with ethanol. Then, AOA was assessed by

2,2-diphenyl-1-picrylhydradzyl (DPPH); anti-oxidative potency in linoleic acid system

model (AOP), and 2,2’-Azino-di-[3-ethylbenzothiazoline-6-sulfonate] (ABTS) assays.

Skin samples showed, on average, higher AOA than the flesh. The AOA and

composition were higher in samples submitted to HAD at 50 or 75ºC for four or one day

than at lower temperatures for longer times. Stronger correlation was observed between

the AOA and phenolics than carotenoids content, suggesting that phenolics are the major

contributors to AOA of sweet potato var. Tainong 73.

Key words: antioxidant activity, phenolics, carotenoids, sweet potato, drying process

J. International Cooperation 3 (2) (September 2008): 73-86© 2008 International Cooperation and Development Fund



September 2008 J. International Cooperation74

Introduction

Food storage is a key factor of food

and nutrition security and food drying byheat is an old and common practice of

preserving food. It brings food water

activity to a level unfavorable for the

microorganisms’ development during

storage and facilitates food distribution

by reducing bulk volume. However,

thermal processing has long been

perceived to cause the loss of someheat-labile nutrients, thus lowering the

nutritional value of the food. Earlier

studies in selected legume sprouts and

seedlings indicated that thermal

processing significantly alters functionality

of legumes (Randhir and Shetty, 2005).

The suitability of a post harvest food

treatment depends on its effect on

nutritious and functional properties of the

food (Marc et al., 2004).

Sweet potato ( Ipomoea batatas Lam.)

is an easy-to-grow crop with good

adaptability to diverse environmental

conditions, high yielding ability and high

energy content (Ravindran et al., 1995).

It is suitable for organic food production

and other environmentally friendly

agricultural practices. It ranks fifth most

important food crop in terms of fresh

weight after rice, wheat, corn, and

cassava in developing countries where

95% of its annual production (more than

133 million tons) is concentrated (Centro

Internacional de Potato (CIP), 1998).

Some varieties have anti-carcinogenic

properties and/or antioxidant activity

(AOA) (Teow et al., 2007), which

categorizes the sweet potato as a

promising crop for global food security

(Scott, 1992).

The objective of this study was to

analyze the effects of four drying

processes on the AOA, total phenolic,

flavonoid, and carotenoid contents of the

Taiwanese sweet potato ( Ipomoea batatas

Lam.) var. Tainong 73 (TNG 73).

Materials and Methods

Materials

Freshly harvested sweet potato

tuberous roots were purchased from the

local market in Pingtung, Taiwan, spring

2007. DPPH and ABTS radicals, catechin,

Folin-Ciocalteu phenol’s reagent, gallic

acid (GA), hexahydrate aluminium

trichloride, linoleic acid, rutin, sodium

carbonate (Na2CO3), sodium hydroxide,

sodium nitrite, thiobarbituric acid (TBA),

trichloroacetic acid (TCA), and vitamin C

were purchased from Sigma Chemical Co.

(St. Louis, MO, USA). All other reagents

were either extra pure or of analytical

grade.

Experiment Design

The study was carried out according

to a 2 x 5 factorial experiment yielding

10 treatments in a completely randomized

design (CRD) with three replicates. One

factor consisted of two parts of the root



Duvivier, Hsieh, Lai, and Charles Evaluation of Drying Methods on

Antioxidant Activity

75

(the flesh and the skin), while the other

consisted of four drying processes

(sunlight, LTD at 25 °C, HAD at 50 °C,and HAD at 75 ºC), which were tested

against a fresh sample as control. The

response variables were DPPH free

radical scavenging activity (FRSA), AOP,

ABTS FRSA, total phenolics, total

flavonoids, and total carotenoids.

Sample Preparation

Samples were washed in tap water,

dried at room temperature, peeled, and

cut in small pieces (0.5 to 1 cm of

thickness). The sample dry mater (SDM)

was measured according to the

Association of Analytical Chemists

(AOAC, 1990). Water activity was

measured in an Aw Quick water activity

meter (Rotronic Instrument Corp.,Huntington, N.Y., U.S.A.). The function

of the desorption isotherm was established

using Excel software. The samples were

then divided into five parts. Four of them

were submitted to sun-drying, low

temperature drying (LTD) at 25 °C, HAD

at 50, or HAD at 75 ºC. The other one

served as control. A drying curve was

established in each drying process to

decide the end-point drying time. This

end-point was set at the time the drying

curve stabilized. The dried samples were

ground to a fine powder (Figure 1) using

a laboratory miller. The sample powders

were weighted and sealed in laminated

plastic bag and kept in desiccators until

extraction.

Figure 1. Color Appearance of the

Samples. A and B: entire

and cross section of fresh

roots, respectively; C, D, E,

F: powder of the flesh

submitted to sun-drying,low temperature drying at

25

C, hot air drying at

50

C, and hot air drying at

75

C respectively; G, H, I,

J: powder of the skin

submitted to sun-drying,

low temperature drying at

25

C, hot air drying at

50

C, and hot air drying at

75 C, respectively.




Preparation of the Crude Extracts

Sweet potato powder (4 ± 0.01 g)

was mixed with 40 ml ethanol in a 250

ml flask. The flask was then shaken at

100 rpm in dark for 24 h in a water bath

set at 25 ºC for complete extraction

(Auerbach and Gray, 1999; Huang et al.,

2004). The mixture was filtered through

Whatman no. 1 filter paper (Whatman

Inc., Clifton, NJ). The residue was

washed with an additional 40 ml ethanol.

The filtrate was evaporated to drynessusing a rotary evaporator model BUCHI

111 equipped with a water-bath BUCHI

461 (Switzerland) and a vacuum pump

EYELA A-3S (Tokyo, Japan). The dried

residue, referred to as crude extract, was

weighted, re-dissolved in ethanol to a

concentration of 10 mg/ml, and stored at

-20 ºC until analysis.

Carotenoids Extraction

Carotenoids were extracted

according to Teow et al. (2007). Briefly,

25 g fresh sample or 5 g powder were

mixed with 2 g Na2CO3, 1 g

diatomaceous earth, and 25 ml methanol.

A hexane–acetone (1:1 v/v) mixture (50

ml) was added and stirred for 2 h in thedark. The mixture was filtered through

Whatman no. 1 filter paper. The residue

was first washed twice with 25 ml

methanol, then once with 50 ml

hexane–acetone mixture. The extract was

combined in a 250 ml separatory funnel

and made up to volume with de-ionized

distilled water (ddH2O). The aqueous

phase was discarded and the upper layer

was transferred into a 50 ml volumetric

flask and made to volume (50 ml) with

hexane for analysis (Chandler and

Schwartz, 1998).

Determination of the Antioxidant

Activity (AOA)

The AOA was measured by DPPH,

AOP, and ABTS assays. DPPH assay was

conducted according to Molyneux (2004).

Absorbencies were monitored at 517 nm(A517) in a spectrophotometer Beckman

Coulter DU 730 UV/VIS and DPPH

FRSA was determined using the

following formula: DPPH FRSA (%) =

[(A0-Af )/A0]*100, where A0 is the blank

absorbance and Af , the test sample

absorbance. AOP assay was carried out

according to Jung et al. (2005).

Absorbencies were read in

spectrophotometer at 532 nm (A532)

against blank and the AOP (%) was

calculated as follow: AOP (%) = [1-(A532

sample/A532 blank)*100]. ABTS FRSA

was determined according to Teow et al.

(2007). Absorbencies were monitored at

734 nm (A734) in spectrophotometer.

Vitamin C was used as standard

(Bouayed et al., 2007). The ABTS FRSA

was expressed in mg vitamin C

equivalent (VCE) / 100 g SDM.

Determination of a Single Antioxidant

Activity Indicator

Many methods for evaluating total

AOA exist; however, no correlation has





77

been established among them. As yet, the

choice of the methods is done in

consideration of the available resources,

the analysis to be done, and its cost

(Arnao, Cano, and Acosta, 1999). No

absolute superiority of one in comparison

to other has been established. This lack of

correlation and hierarchy among the

different methods of analysis has posed a

serious problem in ranking food crops on

basis of total AOA. In this study, to

overcome this problem, a single AOAindicator was computed from the results

of three assays (DPPH, AOP, and ABTS).

It was referred to as AOA relative

desirability index (RDI) and

corresponded to an integrated criterion of

ranking on basis of the AOA evaluated

not only by one, but three variables. A

modified Gauss-Laplace normalization

formula was used to compute the RDI:

where k is a treatment, namely,

sun-drying, LTD at 25 °C, HAD at 50°C,

HAD at 75 ºC, or the control fresh

sample; j is a response variable used toevaluate the AOA, namely, DPPH FRSA,

AOP, or ABTS FRSA; X j,k is the value of

the response variable j for treatment k; X j

is the average value of the response

variable j for all sample treatments; σ j is

the standard deviation of the response

variable j for all sample treatments; C is a

constant chosen to avoid negative values

of RDI and make its lowest value equals

1.00. The treatment with the lowest RDI

was considered as the least desirable in

term of AOA, while the treatment with

the highest RDI was considered as the

most desirable one.

Total Phenolic and Total Flavonoid

Contents Assays

Total phenolic content was assayed

according to the method of Folin and

Ciocalteu (1927) as reported by Kim et

al. (2006) using GA as standard. The

results were expressed as mg GA

equivalent (GAE)/100 g sample fresh

weight (SFW). The total flavonoid

content was assessed by the aluminium

trichloride colorimetric method as

described in Marinova, Ribarova, and

Atanassova (2005) using catechin asstandard. The results were reported in mg

catechin equivalent (CE)/ 100 g SFW.

C

X X

RDI j j

jk j

+

−

=

∑=

3

3

1

,

σ

, Total Carotenoids Analysis

Total carotenoid content was

measured according to Gomes (2007).

The absorbance of the extract was read in

spectrophotometer at 450 nm and the

total carotenoid content was calculated

according to the following formula:

xLxW CT

250

450= x A 1000

,

where CT is the total carotenoid content

in μg β-carotene equivalent (BCE) /g

sample; A450, the absorbance of the

extract at 450 nm; L, the path-length of




the cuvette used in the spectrophotometer;

w, the initial amount (g) of sample

divided by the final volume (ml) of

extract obtained. The results for the dried

samples were then converted in μg

BCE/g SFW.

Statistical Analyses

The data were submitted to a

two-way analysis of variance according

to Kuehl (1999). The SAS (Statistical

Analysis System, v. 8.1; SAS InstituteInc., Cary, NC, USA) software was used.

Treatment effects were evaluated by F

test at p=0.05. The results were reported

as mean±SE. Means comparison was

done by Duncan multiple range test at α

level= 0.05. The relationship among the

different variables analyzed in this study

was measured by the Pearson correlation

coefficient (r). The relative fit goodness

of the three methods used to evaluate the

AOA was assessed by the coefficient of

determination, R 2, and the coefficient of

variation (CV). Higher is the R 2-value,

more accurate is the method, and lower

CV-value corresponds to higher precision.

Results

Drying Control

The water activity (aw) of the

samples during drying stabilized around

0.4. To reach this aw, the samples took 10

days in LTD at 25 °C, seven days in

sun-sun-drying, four days in HAD at 50

ºC, and one day in HAD at 75ºC. The

function of the desorption isotherm was

y=176.03x3-148.96x

2+50.3x, where y is

the water activity and x, the water content

of the samples. The coefficient of

determination was R 2= 0.972.

Effect of drying on Antioxidant Activity

of TNG73

The highest DPPH FRSA in flesh

samples was observed in samples

submitted to HAD at 75 ºC, followed by

the fresh ones, then the sun-dried ones

(Table 1). While the flesh samplessubmitted to HAD at 75 °C showed

higher DPPH FRSA than the fresh ones,

the loss of activity was low in those

sun-dried (2.82 %), moderate in those

submitted to HAD at 50 °C (13.37 %),

and high in those submitted to LTD at 25

°C (47.58 %). In the skin, fresh and

sun-dried samples were not significantly

different and showed the highest DPPHFRSA, followed by those submitted to

LTD at 25 °C, then those which were

submitted to HAD at 75 °C. The loss of

DPPH FRSA was lower than 15 % in all

cases. Flesh samples dried in sunlight and

those submitted to LTD at 25 ºC showed

lower AOP values than those dried with

hot air at 50 and 75 ºC. No significant

difference was observed between samples

dried in sunlight (10.09 % of loss of

activity) and those submitted to LTD at

25°C (16.95 % loss of activity). The loss

of activity in samples dried with hot air at

50 and 75 °C were 3.93 and 5.05 %,

respectively, with no significant

difference. In the skin, the loss of AOA

evaluated as AOP varied from 2.66 % in





79

sun-dried samples to 23.12 % in those

which were submitted to LTD at 25 °C.

No significant difference was observed

between fresh and sun-dried samples, and

between samples submitted to HAD at 50

°C and 75 °C in terms of AOP.

The highest ABTS FRSA of the

flesh was observed in the fresh samples

with 4882.24 mg VCE/100 g SDM. Theextent of decrease of activity during the

drying process was high (68.77% in

samples dried with hot air at 75 °C, and

exceeding 85 % in the other conditions).

In the skin samples, the same trend was

observed, but the extents of decrease of

the ABTS FRSA were lower (from 30.94

to 86.67 % in samples submitted to HAD

Table 1. Effect of the Drying Process on the Antioxidant Activity of Sweet Potato var.

Tainong 73

Treatment1

DPPH (%) A2

AOP (%)

B2

ABTS+23

C2

Flesh

Control 89.26±0.07b - 71.26±1.80a - 4882.24±0.00a -

Sun-drying 86.74±0.08c 2.82 64.07±0.00c 10.09 616.52±0.41c 87.37

LTD at 25ºC 46.79±0.39e 47.58 59.18±0.71c 16.95 616.04±1.75c 87.38HAD at 50ºC 77.33±0.00d 13.37 68.46±0.20b 3.93 569.68±0.00d 88.33

HAD at 75ºC 90.32±0.00a -1.19 67.66±0.00b 5.05 1524.60±1.82b 68.77

Skin

Control 94.96±0.14a - 82.64±0.00a - 4669.63±11.71a -

Sun-drying 94.06±0.08a 0.95 80.44±0.20a 2.66 1618.02±4.56d 65.35

LTD at 25ºC 90.59±0.04b 4.60 62.87±1.20c 23.12 1898.97±0.88c 59.33HAD at 50ºC 81.11±0.12d 14.59 73.65±0.92b 10.87 622.04±1.70e 86.67HAD at 75ºC 89.10±0.1b 6.17 74.85±0.60b 9.67 3224.73±0.00b 30.941LTD: low-temperature drying; HAD: hot air drying. Means with a same letter in a column are not

significantly different (p>0.05).2A, B and C are extent of decrease (%) of DPPH, AOP and ABTS, respectively, during the drying process,

with regard to the fresh samples values.3mg vitamin C equivalent /100 g dry weight.

at 75 °C and 50 °C, respectively). The

correlation parameters listed in Table 2

show that the pair-wise correlations

among the three analytical methods

(DPPH, AOP, and ABTS assays) were

positive (r>0) and significant (p<0.05),

but not high (0.37≤r ≤0.61).

According to the RDI, the fresh

samples of both the flesh and the skinwere the most desirable (Figure 2). In the

flesh, the second best result after fresh

samples was observed in samples

submitted to HAD at 75 °C, followed by

those sun-dried, then those dried with hot

air at 50 °C for four days. The lowest

RDI-value was observed in samples dried

at low temperature (25 °C) for 10 days.




Table 2. Matrix of Pearson Coefficients of Correlation (r) among Different

Variables Analyzed

Variables DPPH AOP ABTS TotalPhenolics

Totalflavonoids

Totalcaraotenoids

AOP 0.61**

ABTS 0.44* 0.37*

Total phenolics 0.40* 0.63** 0.78**

Total Flavonoids 0.36 NS

0.52** 0.31 NS

0.64**

Total carotenoids 0.21 NS

0.23 NS

0.80** 0.75** 0.16 NS

RDI 0.60* 0.55* 0.63* 0.45* 0.22 NS 0.38*

*,** Correlation significant (p<0.05) and (p<0.01), respectively. NScorrelation non-significant (p>0.05).

The RDI varied slightly among the skin

samples during the drying process (from

2.79 in samples submitted to HAD at 50

°C for 4 days to 3.14 in sun-dried

samples). However, even in the best case

of the skin samples dried in sunlight,

there was a substantial decrease of the

RDI to the extent of 23.97 %.

Effect of Drying on the Total

Carotenoids Content

The results of carotenoids contentare summarized in Table 3. Total

carotenoids content of flesh samples

varied from 2.19 μg BCE/g SFW in

samples dried at 75 ºC to 8.46 μg BCE

equivalent /g SFW in the fresh samples.

The decrease in carotenoid content during

the drying process reached 68.09 % in

samples submitted to LTD at 25°C to

Figure 2. Antioxidant Activity (AOA)

and Relative Desirability

Index (RDI) of Sweet

Potato var. Tainong 73. (□)

flesh and (■) skin samples

submitted to different drying

processes.





81

74.11 % in those dried at 75 °C. In

samples submitted to HAD at 50 °C and

sun-drying, the decrease was 69.98 and

71.51 %, respectively.

Total carotenoids content of skin

samples varied from 1.78 μg BCE/g SFW

(in sun-dried samples) to 4.76 μg BCE/g

SFW (fresh samples). The decrease

during the drying process reached 20.37

% in samples dried with hot air at 75 °C

to 62.61 % in sun drying. In drying at

25 and 50 °C, the decrease was 31.93 and26.05 %, respectively.

Effect of drying on the Total Phenolic

Content

The highest total phenolic contents

in the flesh were observed in fresh

samples, followed by those dried with hot

air at 50 and 75°C. The two latter drying

Table 3. Effects of the Drying Process on Total Carotenoid Contents of Tainong 731

Total Carotenoids (μg β-carotene equivalent/g SFW)

Treatment2 Flesh A

3Skin B

3

Fresh samples 8.46±0.01a - 4.76±0.01a -

Sun-drying 2.41±0.01d 71.51 1.78±0.01e 62.61

LTD at 25ºC 2.70±0.01b 68.09 3.24±0.01d 31.93

HAD at 50ºC 2.54±0.04c 69.98 3.52±0.05c 26.05

HAD at 75ºC 2.19±0.04e 74.11 3.79±0.04b 20.371 Means with a same letter in a column are not significantly different ( p>0.05).

2 LTD: low-temperature drying; HAD: hot air drying.

3 A and B are extent of decrease (%) of flesh and skin total carotenoids, respectively, during the drying

process based on fresh samples values.

temperatures did not show significant

difference (Table 4). Samples submitted

to sun-drying and LTD at 25 °C were not

significantly different and had lower total phenolics content.

In the skin, the highest content of

total phenolics was observed in the fresh

samples, followed by those dried with hot

water at 50 °C, then those dried at 75 °C.

The lowest content was observed in

sun-dried samples, followed by those

submitted to LTD at 25 °C. Skin sampleshad consistently higher total phenolics

content than flesh samples.

Effect of Drying on the Total Flavonoids

Content

The total flavonoid content followed

the same trend as the total phenolics, both

in the flesh and the skin during the drying




process. The highest contents were

observed in the fresh samples, followed

by those dried with hot air at 75 °C, then

those dried at 50 °C (Table 4). The

samples dried in sunlight had the lowest

content, followed by those dried in LTD

at 25 °C. Losses of flavonoids during the

drying process were consistently higher

in the flesh (14.32 to 53.56 %) than the

skin (4.26 to 44.86 %), suggesting that

high-temperature-short-time were better

than low-temperature-long-time drying

conditions.

Table 4. Effects of the Drying Process on the Total Phenolic and Total Flavonoid

Contents of Tainong 73

Treatment1

Total Phenolics2

A3

Total Flavonoids2

B3

Flesh

Fresh samples 243.02±0.32a - 42.25±0.09a -

Sun-drying 23.21±0.10c 90.95 19.62±0.07e 53.56

LTD at 25ºC 27.62±0.01c 88.63 21.78±0.17d 48.45

HAD at 50ºC 76.11±0.02b 68.68 34.45±0.02c 18.46

HAD at 75ºC 76.10±0.08b 68.68 36.20±0.02b 14.32

Skin

Fresh samples 258.95±0.67a - 104.25±0.12a -Sun-drying 74.16±0.05e 71.36 57.48±0.06e 44.86

LTD at 25ºC 94.81±0.28d 63.39 61.78±0.14d 40.74

HAD at 50ºC 185.03±24.35c 28.55 70.54±0.12c 32.34

HAD at 75ºC 237.48±1.11b 8.29 99.81±0.02b 4.26

1 LTD: low-temperature drying; HAD: hot air drying; means with a same letter in a column are notsignificantly different (p>0.05).

2 (mg catechin equivalent/100 g sample fresh weight).3 A and B are extent of decrease (%) of total phenolics and total flavonoids respectively, during the drying

process, with regard to the fresh samples values.

Correlation of AOA with Total Phenolics,

Total Flavonoids, and Total Carotenoids

Significant pair-wise correlations

were observed between total phenolics

and each one of the three AOA indicators(p<0.05) as indicated in Table 2. These

results agreed with Islam et al. (2003)

who reported significant correlation

between the AOA and the total phenolics

content of sweet potato leaves. However,

significant correlation was observed

between the AOA and total flavonoids

only in the AOP assay, and between AOA





83

and total carotenoids in ABTS assay. The

parameters of pair-wise correlations

involving total phenolics, total flavonoids,and total carotenoids indicated that the

drying process had a similar effect on the

various secondary metabolites studies.

Discussion

DPPH FRSA of fresh samples was

high (89.6 %) and similar to results of

some medicinal plants (Miliauskas,Venskutonis, and van Beek, 2004). The

pair-wise correlations among the three

methods used to evaluate the AOA were

low. Such low correlation is common

according to Molyneux (2004) and poses

a serious problem in ranking food

commodities for AOA. The relative

desirability index (RDI) indicated that

total phenolic, total flavonoid, and totalcarotenoid contents were higher in fresh

than dried samples. Similarly, Muchoki,

Imungi, and Lamuka (2007) observed

that heating and drying of vegetables lead

to substantial loss of antioxidants.

Rehman, Salariya, and Habib (2003)

reported that evaporation and

decomposition at elevated temperatures

results in loss of AOA. Larraruri,

Sanchez-Moreno, and Saura-Calixto

(1998) observed reduction of AOA by 28

% in the red grape pomace peels when

dried with hot air at 100oC. The RDI was

higher when the samples were dried at 75

ºC for 1 day in comparison to drying at

25 ºC for 10 days and 50 °C for 4 days.

On average, fresh skin samples had

higher DPPH FRSA and phenolic content

than the flesh. Similarly, Kondo et al.

(2002) reported total phenolics content

was higher in the skin than the flesh of

fruits. Teow et al. (2007) observed very

large variations in carotenoids content of

sweet potato (from 0.18 to 226 μg BCE

/g SFW). In views of their results,

Tainong 73 may be considered as a

low-carotenoids content variety. Though

statistically significant, the variation

among the drying processes was low. Theloss of carotenoids during the drying

process was higher in the flesh (68.09 to

74.11 %) than the skin samples (20.37 to

62.61 %). Those results suggested that

the drying process is an inefficient

storage method of the sweet potato

Tainong 73 in term of AOA retention.

However, drying is necessary in the food

industry to improve storage life, reduce

bulk volume, facilitate distribution, and

combat food insecurity. If the flesh of

sweet potato Tainong 73 is to be dried,

high- temperature-short-time method is

most suitable for preserving the

nutritional properties of the crop. It is

interesting that the sun-drying gave quite

good results, considering that sunlight is

the main and often the only source of

energy available to farmers for drying in

developing countries.

Conclusions

The AOA and phenolic compounds

were higher in the skin than the flesh

samples of Tainong 73. Since sweet




potato is usually peeled before cooking,

and the skin is considered a waste, the

skin of sweet potato Tainong 73 can

constitute a non-expensive source of

antioxidants in the food industry. The

correlations among the analytical

methods were poor, and the fit goodness

analysis did not establish any hierarchy

among them. However, using the relative

desirability index, AOA was higher in the

fresh samples. In this study, a high

temperatures short time conditions

resulted in increases in AOA, total

phenolics, flavonoids, and carotenoids.

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Ipomea Batatas - Evaluation of Drying Methods on Antioxidant Activity, Total Phenolic

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