Optimum Condition of Beta-Cyanin Colorant Production from Red Dragon Fruit (Hylocercus polyrhizus) Peels using Response Surface Methodology

Abstract

The extraction and drying processes used to produce red colorant from red dragon fruit peels were optimized to yield the highest beta-cyanin content. The types of solvents (deionized water and 80% ethanol), pH, extraction time and temperature were the independent variables in the extraction process. The amount of binding medium (acetylated oxidized starch and maltodextrin) and extract, inlet temperature and feed rate were the independent variables in the spray-drying process. Based on response surface methodology, Box-Behnaken and full factorial designs were used for the experiment, while beta-cyanin was determined as the response. Antioxidant activity of the colorant powder was also tested. The optimum extraction condition giving the highest beta-cyanin content was a pH of 5.5 at 40°C for 20 min extracted by deionized water. The optimum drying condition for the production of red colorant powder was 6% binding medium at a feed rate of 6 ml/min and an inlet temperature of 140 and 160°C for acetylated oxidized starch and maltodextrin, respectively. The experimental results following the response surface methodology corresponded well to the predicted values. The optimum drying conditions yielded a red colorant powder with antioxidant properties that could be used in food products.

Full text

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CMUJ NS Special Issue on Food and Applied Bioscience (2014) Vol.13(1)
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Optimum Condition of Beta-Cyanin Colorant Production
from Red Dragon Fruit (Hylocercus polyrhizus)
Peels using Response Surface Methodology
Pachamon Pichayajittipong and Siwatt Thaiudom*
School of Food Technology, Institute of Agricultural Technology, Suranaree
University of Technology, Nakhon Ratchasima 30000, Thailand
*Corresponding author. E-mail: thaiudom@sut.ac.th
ABSTRACT
The extraction and drying processes used to produce red colorant from
red dragon fruit peels were optimized to yield the highest beta-cyanin content.
The types of solvents (deionized water and 80% ethanol), pH, extraction time
and temperature were the independent variables in the extraction process. The
amount of binding medium (acetylated oxidized starch and maltodextrin) and
extract, inlet temperature and feed rate were the independent variables in the
spray-drying process. Based on response surface methodology, Box-Behnaken
and full factorial designs were used for the experiment, while beta-cyanin was
determined as the response. Antioxidant activity of the colorant powder was also
tested. The optimum extraction condition giving the highest beta-cyanin content
was a pH of 5.5 at 40°C for 20 min extracted by deionized water. The optimum
drying condition for the production of red colorant powder was 6% binding
medium at a feed rate of 6 ml/min and an inlet temperature of 140 and 160°C
for acetylated oxidized starch and maltodextrin, respectively. The experimental
results following the response surface methodology corresponded well to the
predicted values. The optimum drying conditions yielded a red colorant powder
with antioxidant properties that could be used in food products.
Keywords: Beta-cyanin, Spray drying, Extraction, Red dragon fruit, Optimum
condition
INTRODUCTION
Peels from red esh dragon fruit (Hylocereus polyrhizus), a byproduct of
consumption, are potentially useful to the food colorant industry because of an
abundance of betalains, with their red shades of color. Betalains are composed
of beta-cyanins and betaxanthins compounds, which have red and yellow color,
respectively. The beta-cyanins are more abundant than the betaxanthins in beta-
lains (Harivaindaran et al., 2008). Betalains are an antioxidant, like anthocyanins,
that can dissolve in water, but are very sensitive to pH and heat (Wybraniec and
Mizrahi, 2002; Wu et al., 2006). Thus, the extraction process of betalains is impor-
tant to maintaining the stability of sensitive pigments, such as beta-cyanins.
DOI: 10.12982/CMUJNS.2014.0051

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Encapsulation of these pigments by spray drying has been used to produce and
stabilize the colorants, because of its ability to yield a powder that preserves the
pigments. The colorants obtained from spray drying are of good quality – low
water activity, color stability, high antioxidant activity and lower cost (Cai and
Corke, 2000; Gharsallaoui et al., 2007). However, a ratio of binding medium such
as maltodextrin (MD) to beta-cyanin extract in spray drying had the largest effect
on the yield of beta-cyanin colorants from beet roots. The more maltodextrin
added, the less beta-cyanin content in the powder (Azeredo et al., 2007). In addi-
tion, the interaction between lower and higher dextrose equivalent maltodextrins
as binding medium seemed to retard the degradation of beta-cyanin color (Cai and
Corke, 2000).
Acetylated oxidized starch (AOS) is the other high potential binding medi-
um used in spray-drying encapsulation. Acetylated oxidized starch is a chemically
modied starch preventing an association of amylopectin and amylose, resulting
in less retrogradation when it is cooled or stored (Apeldoorn et al., 2001). These
attributes of acetylated oxidized starch are suitable for food or avor microen-
capsulation in order to prevent oxidation. However, no one has reported using
acetylated oxidized starch as a binding medium in spray-dry encapsulation.
Response surface methodology has been demonstrated to be a useful tool
for optimization in food innovation production. However, to our knowledge, there
is no information about the optimum condition of beta-cyanin colorant production
from peels of red dragon fruit, a waste product of fresh consumption. The main
objective of this study was to optimize the extraction and drying parameters for
yielding beta-cyanin from red dragon fruit peels and to determine the antioxidant
activity of the resultant natural red. The results of this study would be useful in
developing a novel and natural colorant powder as a functional food colorant that
could potentially replace synthetic food colorants.
MATERIALS AND METHODS
Materials
Fresh red dragon fruits were purchased from farms in Nakhon Ratchasima
Province in northeastern Thailand. Acetylated oxidized starch and maltodextrin
were obtained from Siam Modied Starch Inc., Thailand. All chemicals used were
of analytical grade.
Preparation of dragon fruit peels
The peels of fresh dragon fruits were washed and used as materials to pro-
duce the beta-cyanin extract. The peels were cut into 3x3 cm2 and then dried in
a tray dryer (tray dryer, TD372, New Way Manufacturing Co., Ltd., Thailand) at
55°C for 24 hr. The dried peels were ground and stored in sealed laminated plastic
bags at -20°C before use.

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Optimization condition of beta-cyanin extraction in dragon fruit peels
Dragon fruit peels were extracted in deionized water (DI water) or 80%
ethanol (EtOH) by varying the extract pH (X1) adjusted by 1M citric acid and
2M NaOH(aq), extraction temperature (X2) and duration of extraction (X3). The
ratio of peels to extraction solvent was xed at 6 g to 200 ml, respectively. The
mixes were made homogeneous by Vertex (Vortex-Genic1 Touch Mixer, Scientic
Industries, Inc., USA) and centrifuged (Legand Mach 1.6R, Sorvall, Germany)
at 10000xg, 4°C for 20 min. The supernatant after extraction was volumetrically
adjusted to 200 ml with solvents before analyzing the beta-cyanin content. The
experimental design was Box-Behnken with 15 treatments (Table 1). The extract
condition with the highest beta-cyanin content was selected to be the optimum
condition for extraction calculated and analyzed by response surface methodology.
Optimization condition of beta-cyanin colorant powder production
The extract that provided the highest beta-cyanin content from the extraction
process was mixed with acetylated oxidized starch or maltodextrin as a binding
medium in different ratios (Y1). The mixes were homogenized at 5,000 rpm for
10 min by single stage homogenizer (Homogenizer T50L, Sciencelab.com, Inc.,
USA). For spray drying, inlet temperature (Y2) and feed ow rate (Y3) were also
varied following 23 Factorial designs (Table 2). The optimum condition of spray
drying that provided the highest beta-cyanin content in the colorant powders was
determined and analyzed by response surface methodology.
Analysis of beta-cyanin content
Beta-cyanin content in the extract and in the colorant powders were analyzed
following methods of Wu et al. (2006) and Cai and Corke (2000), respectively.
The absorbance expressed at 537 nm was measured by spectrophotometer (Spec-
trophotometer UV-vis, Libra S22, Biochrom, UK).
Determination of total phenolic content
The total phenolic content in the extract and colorant powders was
determined using the Folin-Ciocalteu method following Bae and Suh (2007). The
absorbance was measured at 750 nm. Gallic acid was used as a reference standard
and the results were expressed as milligram gallic acid equivalent (mg GAE)/L of
extract and (mg/100 dry basis) of powder.
Antioxidant activity and reducing power of dragon fruit peel extract DPPH•
radical scavenging activity
The 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH•) of
the colorant powders was analyzed following Wu et al. (2006). McIlvaine buffer
(pH 5.6) and DPPH solution were used in this study. The absorbance was mea-
sured at 515 nm using UV-Vis spectrophotometer. Ethanol (80%) was used as a
blank solution and DPPH solution without test samples (3.9 ml of DPPH with 0.1
ml of 80% ethanol) accounted as the control.

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Table 1. Beta-cyanin content and total phenolic compounds in the extract of red dragon fruit peels in different extraction conditions.
Treatment pH Temp (ºC) Time (min) Beta-cyanin (mg/g dry sample) Total polyphenols (mg/100 gdry sample)
80%EtOH DI water 80%EtOH DI water
1 5.0 (0) 40 (-1) 20 (-1) 11.83 ± 1.05B, f 143.66 ± 5.95A, abc 434.53 ± 8.45A, g 358.73 ± 3.68B, c
2 5.0 (0) 85 (+1) 20 (-1) 42.62 ± 1.87B, c 131.98 ± 12.30A, de 517.74 ± 17.78A, bc 388.46 ± 5.70B, ab
3 5.0 (0) 40 (-1) 60 (+1) 8.73 ± 0.26B, h 147.14 ± 2.96A, ab 431.02 ± 15.61A, g 337.84 ± 5.83B, e
4 5.0 (0) 85 (+1) 60 (+1) 33.92 ± 1.30B, d 126.78 ± 3.05A, e 556.95 ± 7.31A, a 390.85 ± 14.72B, ab
54.5 (-1) 40 (-1) 40 (0) 10.26 ± 0.57B, g 147.81 ± 2.00A, ab 462.05 ± 22.91A, ef 353.41 ± 10.68B, cd
6 4.5 (-1) 85 (+1) 40 (0) 55.48 ± 0.89B, b 131.78 ± 2.91A, de 512.47 ± 15.23B, c 400.06 ± 23.17B, a
7 5.5 (+1) 40 (-1) 40 (0) 9.73 ± 0.22B, gh 149.11 ± 1.59A, a 434.60 ± 11.03A, g 360.82 ± 19.93B, c
8 5.5 (+1) 85 (+1) 40 (0) 60.47 ± 1.62B, a 118.79 ± 14.55A, f 535.02 ± 29.71A, b 357.84 ± 5.06B, c
9 4.5 (-1) 60 (0) 20 (-1) 12.67 ± 2.17B, f 141.55 ± 2.02A, abc 444.28 ± 31.49A, fg 381.09 ± 4.46B, b
10 4.5 (-1) 60 (0) 60 (+1) 15.80 ± 0.54B, e 140.43 ± 2.92A, bc 442.61 ± 12.12A, fg 392.31 ± 3.72B, ab
11 5.5 (+1) 60 (0) 20 (-1) 9.21 ± 0.33B, gh 147.18 ± 3.97A, ab 436.06 ± 9.97A, g 348.82 ± 20.86B, cde
12 5.5 (+1) 60 (0) 60 (+1) 16.13 ± 1.42B, e 137.94 ± 2.28A, cd 430.39 ± 8.09A, g 341.75 ± 4.63B, de
13 5.0 (0) 60 (0) 40 (0) 15.95 ± 0.47B, e 146.18 ± 1.41A, ab 482.01 ± 7.86A, de 353.75 ± 10.02B, cd
14 5.0 (0) 60 (0) 40 (0) 16.01 ± 0.56B, e 141.59 ± 4.51A, abc 483.88 ± 10.60A, d 350.30 ± 6.79B, cde
15 5.0 (0) 60 (0) 40 (0) 16.03 ± 0.28B, e 143.70 ± 1.83A, abc 434.75 ± 29.28A, g 342.10 ± 7.58B, de
Note: Least signicant difference with capital letter for comparison of means in the same row. Least signicant difference with small letter for comparison of means
in the same column.

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Table2. Beta-cyanin content and total phenols of colorant powders with different spray-drying conditions.
Treatment MS:Extract
(%w/w) Inlet Temp (۫C) Feed ow rate
(ml/min)
Beta-cyanin (mg/g dry sample) Total polyphenols (mg/100g dry sample)
MD AOS MD AOS
1 8 (+1) 160 (+1) 6 (-1) 52.53 ± 1.55 ns, c 51.63 ± 0.95 ns, d 545.82 ± 23.11 ns, f 529.62 ± 41.95 ns, d
2 8 (+1) 140 (-1) 6 (-1) 53.59 ± 1.08 B, c 54.91 ± 0.63 A, c 552.68 ± 24.20 ns, ef 545.86 ± 37.34 ns, cd
3 6 (-1) 160 (+1) 6 (-1) 69.12 ± 0.44 A, a 66.28 ± 1.58 B, b 742.90 ± 23.41 A, a 658.75 ± 24.31 B, a
4 8 (+1) 160 (+1) 12 (+1) 54.47 ± 1.18 ns, c 54.49 ± 0.83 ns, c 594.58 ± 22.82 ns, d 572.09 ± 50.71 ns, bc
56 (-1) 140 (-1) 12 (+1) 64.65 ± 2.17 B, b 66.90 ± 0.18 A, ab 712.26 ± 30.29 A, b 673.30 ± 18.02 B, a
6 8 (+1) 140 (-1) 12 (+1) 54.22 ± 1.72 A, c 50.72 ± 0.99 B, d 572.41 ± 16.90 ns, e 585.70 ± 37.53 ns, b
7 6 (-1) 160 (+1) 12 (+1) 68.23 ± 2.72 ns, a 66.88 ± 1.63 ns, ab 683.62 ± 21.18 ns, c 696.91 ± 60.47 ns, a
8 6 (-1) 140 (-1) 6 (-1) 64.85 ± 0.30 B, b 68.31 ± 1.72 A, a 715.22 ± 29.41 ns, b 686.98 ± 49.05 ns, a
Note: Least signicant difference with capital letter for comparison of means in the same row. Least signicant difference with small letter for comparison of means
in the same column. ns means not signicant.

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ABTS•+ assay
The 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) assay
(ABTS•+) was modied from Wu et al. (2006). Concisely, a colorant powder (in
grams) was diluted 100 X with the ABTS•+ solution to a total volume of 1 ml and
allowed to react for 6 min. Five different concentrations at 5 to 40 mg/ml were
determined. Absorbance was measured at 734 nm with different time intervals
by UV-Vis spectrophotometer. The percentage inhibition was calculated against
a control used as blank and 990 μl of PBS were added to these control samples
instead.
Ferric-ion reducing antioxidant power (FRAP)
The analytical measurement of FRAP was determined using a modied
method of Wootton-Beard et al. (2010). FRAP reagent was prepared from 300
mM acetate and glacial acetic acid buffer (pH 3.6), 20 mM ferric chloride and 10
mM 4,6-tripryridyls-triazine (TPTZ) in 40 mM HCl. These solutions were mixed
together in the ratio of 10:1:1. The FRAP assay was completed by warming 1
ml of deionized water to 37°C before adding 25 μl of sample solution and 1 ml
of reagent and then incubating at 37°C for 4 min. The sample solution was pre-
pared by dissolving 1.0 g of colorant powder with McIlvaine buffer (pH 5.6). The
determination was expressed as the absorbance at 593 nm. The total antioxidant
capacity of samples was determined against a standard (1000 μM ferrous sulphate)
of known FRAP value.
Statistical analysis
Analysis of variance and mean difference test were performed using Dun-
can’s New Multiple Range Test (DMRT) (SPSS version 12.0, SPSS Inc., Illinois,
USA). Response surface methodology was performed using Design-Expert version
8 (Stat-Ease Inc., Minneapolis, USA). Each experiment was run in three replicates
of each sample. A probability of 5% or less was accepted as statistically signi-
cant.
Table 3. Antioxidant activity of colorant powders.
Samples/standard ABTS.+ (IC50) DPPH. (IC50) FRAP (mmol
Fe2+/100 g)
Dragon fruit peel
extract with AOS
6.20 ± 0.87a
(mg GAE/100 ml)
11.52 ± 0.46a
(mg GAE/100 ml)
1.26 ± 0.32b
Dragon fruit peel
extract with MD
5.63 ± 0.94a
(mg GAE/100 ml)
11.24 ± 1.57a
(mg GAE/100 ml)
1.31 ± 0.41b
Ascorbic acid 4.44 ± 0.24b
(mg/100 ml)
4.94 ± 0.45b
(mg/100 ml)
1,280.93 ± 15.84a
Note: Least signicant difference with capital letter for comparison of means in the same row. Least
signicant difference with small letter for comparison of means in the same column.

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RESULTS
Optimum extracting condition of red dragon fruit peel extract
Extraction conditions of red dragon fruit peels for beta-cyanins and total
phenols are shown in Table 1. Beta-cyanin content in the peel extract with deion-
ized water was signicantly higher than that extracted by EtOH (p<0.05).
However, from using response surface methodology with stepwise regres-
sion analysis, we found that the condition of beta-cyanin extract followed equation
1 (R2 = 0.6856):
Beta-cyanin content (mg/g dry sample) =
-6.09015+26.44521X1+2.52394X2+1.21725X3
-0.33408X1X2-0.20307X1X3-4.52680×10-3X2X3-8.86370×10-
3
X22…....................… (1)
Equation 1 was differentiated to obtain the optimum condition of beta-cyanin
extraction. From the results, extraction with deionized water at pH 5.5 and 40°C
for 20 min yielded the most beta-cyanin (150.41 mg/g of dried peels) (Figure 1a-c).
Optimization condition of red colorant powder production from red dragon
fruit peel extracts
The extracts from the optimal condition were then mixed with acetylated
oxidized starch or maltodextrin following the ratio shown in Table 2. Both acetyl-
ated oxidized starch and maltodextrin could be used as binding medium or dry-
ing carrier, since they were both perfectly compatible with the dragon fruit peel
extracts. The mixtures were sprayed and dried in a spray dryer. Beta-cyanins, total
phenols and antioxidant activity of the powder from the drying condition were
determined. The results are shown in Table 2.
The results revealed that the different binding mediums signicantly affect-
ed beta-cyanin content and total phenols (Table 2). However, beta-cyanin content
in the colorant powder was lower than in the extract, in contrast with total phenols.
In order to obtain the optimum condition of colorant powder production using
spray drying, beta-cyanin content was chosen as the response of response surface
methodology analysis. The independent variables were the ratio of binding medi-
um to the extracts (Y1), inlet temperature of spray dryer (Y2) and feed ow rate
(Y3). Stepwise regression analysis was used to determine the equation of condi-
tions for colorant powders made from acetylated oxidized starch and maltodextrin
according to equation 2 (R2 = 0.9782) and 3 (R2 = 0.8259), respectively.
Beta-cyanin content-AOS (mg/g dry sample) =
-1.945+33.34833333Y1+0.739583333Y2
+16.41472222Y3-0.314083333Y1Y2-6.335Y1Y3-0.109013889Y2Y3
+0.041944444Y1Y2Y3…............................................. (2)

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Beta-cyanin content-MD (mg/g dry sample) =
303.4116667-72.41Y1-1.094583333Y2
-57.8Y3+0.331166667Y1Y2+16.42027778Y1Y3
+0.351486111Y2Y3-0.099680556Y1Y2Y3………................. (3)
To obtain the optimum condition of spray drying of colorant powder, equa-
tions 2 and 3 were differentiated. The results showed that the optimum condition
of colorants containing acetylated oxidized starch was using acetylated oxidized
starch at 6% (w/w) at a feed rate of 6 ml/min and inlet temperature of 140°C. For
maltodextrin, the optimum condition was similar, except the inlet temperature
was 160°C. From these conditions, we found that the beta-cyanin contents were
68.3 and 69.1 mg/g of dry peels for acetylated oxidized starch and maltodextrin,
respectively (Figure 2 and 3, respectively).
Figure 1. The effects of pH and Temperature at extraction time of 20 min (a),
pH and extraction time at temperature of 40°C (b), and extraction time
and temperature at pH of 5.5 (c) on beta-cyanin content in the extract.
(a) (b)
(c)

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Figure 2. The effects of the ratio of extract to acetylated oxidized starch and
inlet temperature at feed  ow rate of 6 ml/min (a), the ratio of extract
to acetylated oxidized starch and feed  ow rate at inlet temperature of
140°C (b), and inlet temperature and feed  ow rate at ratio of extract
to acetylated oxidized starch of 6%(w/w ((c) on beta-cyanin content in
colorant powders.
(a) (b)
(c)
Antioxidant activity of colorant powders
DPPH• radical scavenging activity, ABTS•+assay and Ferric-ion reducing
antioxidant power (FRAP) were used to analyze the antioxidant activity of the
colorant powders that were produced according to the optimum spray-drying
conditions mentioned previously. All antioxidant activity values of colorants
from acetylated oxidized starch and maltodextrin were not signi cantly different
(p<0.05) (Table 3). However, ABTS•+ and DPPH• of both colorants were less than
those of the standard sample (ascorbic acid) (p>0.05).

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DISCUSSION
Our results showed that beta-cyanins dissolved better in water than in EtOH,
as explained by Casteller et al. (2003); given their high polarity, they prefer to
dissolve in a more polar solvent such as water, than in a less polar solvent such
as EtOH. The other factor that affected beta-cyanins was the pH. Herbach et al.
(2006a) suggested that a pH of 4-6 least affected beta-cyanin stability. This might
be due to the isomerization of C-15 of betanin and betanidin, found as compounds
in beta-cyanins, in a high acidic condition (low pH) that could change betanin
and betanidin to isobetanin and isobetanidin, respectively. Both pigments have a
red-purple color. However, the color might be changed further from red-purple to
yellow of 14,15-dehydrobetanin or neobetanin under very high acidic conditions
or when hydrolysis occurred, converting betanin and betanidin to betalamic acid,
which also presented a yellow color (Strack, Vogt, and Schliemann, 2003; Herbach
et al., 2006a; Stintzing and Carle, 2007; Tsai, et al., 2010). Moreover, temperature
and extraction time also affected the beta-cyanin content (Wybraniec and Mizrahi,
2002; Castellar, et al., 2003; Wu et al., 2006; Harivaindaran et al., 2008; Meoreno
et al., 2008).
Figure 3. The effects of the ratio of extract to maltodextrin and inlet temperature
at feed  ow rate of 6 ml/min (a), the ratio of extract to maltodextrin and
feed  ow rate at inlet temperature of 160°C (b), and inlet temperature
and feed  ow rate at ratio of extract to maltodextrin of 6%(w/w) (c) on
beta-cyanin content in colorant powders.
(a) (b)
(c)

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However, from our results, a higher temperature and lower pH lowered
beta-cyanin content. This might be due to the degradation of beta-cyanins to
yellowish betalamic acid, colorless cyclo-dopa 5-O-β-glucoside, or reddish 12,
15-decarboxybetaninas mentioned previously (Strack, Vogt and Schliemann, 2003;
Herbach et al., 2006a; 2006b; Stintzing and Carle, 2007), resulting in less beta-
cyanin content in this studied extract. Moreover, Stintzing and Carle (2004) and
Meoreno et al. (2008) reported that initial pigment content, oxygen and aw also
affected the content of beta-cyanins.
Nevertheless, the results revealed that the optimum condition of beta-cyanin
extraction from red dragon peels did not give the highest total phenol content,
and the total phenol content inversely varied with beta-cyanin content. Phenolic
compounds found in red dragon fruit peels were not only beta-cyanins, but also
betaxanthins, ascorbic acid and beta-cyanins’ derivatives, such as betalamic acid,
cyclo-dopa 5-O-glycoside, neobetanin and betanidin (Stintzing and Carle, 2004;
Bellec et al., 2006; Herbach et al., 2006a). These might interfere with the results
of beta-cyanin content when reacted with gallic acid in Folin-Ciocalteu’s method
(Naczk and Shahidi, 2004; Prior et al., 2005; Rebecca et al., 2010). Wu et al.
(2006) explained this might be due to the unspecic site reaction of gallic acid
with such compounds. Thus, from our study, the optimum condition that gave the
highest beta-cyanin content was not the suitable condition that provided the highest
total phenols. Moreover, phenolic compounds dissolved in EtOH better than in
deionized water, due to their ability to dissolve in polar alcoholic solvents (Harjo,
Wibowo and NG, 2004; Naczk and Shahidi, 2004; Stalikas, 2007;).
Modied starches (acetylated oxidized starch and maltodextrin) were
selected as the binding medium in this study in order to increase the extract soluble
solid, reduce the effect of the browning reaction and neutralize the acidity of the
extracts (Cai and Corke, 2000; Saénz et al., 2009; Chik et al., 2011). In addition,
the powder from these binding media might entrap some functional ingredients
and antioxidant agents in a severe condition like spray drying. However, in this
study, beta-cyanins could not be completely shielded from degradation during
spray drying, especially from heat, which contributed to the change of beta-cya-
nins to betalamic acid and cyclo-dopa 5-O-β-glucoside (Stintzing and Carle, 2004;
Bellec et al., 2006; Herbach et al., 2006a), resulting in less beta-cyanin in the
powder than before spray drying.
The antioxidant activity of the colorant powders also decreased as a result
of spray drying. This result agreed with the studies of Kim et al. (2002), Wetwita-
yaklung et al. (2005), and Stratil et al. (2006). The decreased antioxidant activity
of the colorant powders might be due to the effect of the high temperature of spray
drying, which could change the chemical structures of beta-cyanins into their
derivatives, such as betanins (Pedreño and Escribano, 2001; Herbach et al., 2006a)
that are composed of imino and hydroxyl groups, with consequently less antioxi-
dant capacity (Wu et al., 2006). In addition, mixing binding mediums (acetylated
oxidized starch and maltodextrin) might inuence the antioxidant activity by
decreasing beta-cyanin content compared to the same weight of standard samples
used for this analysis.

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CONCLUSION
The optimum extraction conditions for high beta-cyanin content from drag-
on fruit peel were mixing deionized water at pH 5.5 and extracting at 40°C for
20 min. The optimum conditions of spray drying to produce red colorant powder
were mixing 6% (w/w) dragon fruit peel extract with acetylated oxidized starch
or maltodextrin, feeding the mix into a spray dryer at 6 ml/min and controlling
the inlet temperature at 140 and 160°C for acetylated oxidized starch and malto-
dextrin, respectively. The red colorant powder provided the highest beta-cyanin
content and showed the highest potential as an antioxidant-food colorant in the
food industry. Thus, red dragon fruit peels, typically considered a waste product of
fresh fruit consumption, offer potential as an economic, value-added, raw material
for food colorant production.
ACKNOWLEDGEMENTS
The authors are grateful for nancial support from the National Research
Council of Thailand, NRCT and Suranaree University of Technology under Grant
SUT3-305-53-24-14.
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