Effect of drying air temperature and chemical pretreatments on quality of dried chilli

International Food Research Journal 16: 441-454 (2009)
Effect of drying air temperature and chemical pretreatments on quality of
dried chilli
1*Wiriya, P., 2Paiboon, T. and 3Somchart, S.
1Department of Agro-Industry, Faculty of Agriculture, Ubon Ratchathani University, Ubon
Ratchathani, 34190, Thailand
2Faculty of Agro-Industry, Prince of Songkla University, Songkla, 90112, Thailand
3School of Energy, Environment and Materials, King Mongkut’s University of Technology
Thonburi, Bangkok, 10140, Thailand

Abstract: The quality of dried chilli (Capsicum annuum c.v. Huarou Yon) in terms of color
attributes and nutrients was studied using a lab-scale tray dryer in order to reduce the quality loss
caused by sun drying. Different drying temperatures from 50-70oC, and a two-stage temperature
regime (70oC and 50oC) were used to compare with the sun drying method. A one-temperature
regime provided low values of lightness, chroma and hue angle compared to sun drying. The
two-stage temperature provided bright–red colored dried chilli. Browning color of dried chilli
was observed due to non-enzymatic browning reaction as reducing sugar was decreased. Not
only did the Maillard reaction provide a dark-brown color, but thermal degradation and oxidation
of total phenolic compounds and ascorbic acid also provided an unacceptable color of dried
chilli. A drying temperature of 70oC and a two-stage temperature regime (70oC for 4 hours
followed by 50oC) in conjunction with soaking the chilli in different chemical pretreatments
were used to promote the color and nutrient preserving capacity. It was found that sodium
metabisulfite preserved color stability but not the nutritional compounds chilli was dried at an air
temperature of 70oC. Using sodium metabisulfite combined with calcium chloride provided the
best color attributes when two-stage temperatures of 70oC and 50oC were used.
Keywords: Chilli, drying, nonenzymatic browning reaction, anti-browning agent
______________________________________________________________________________

Introduction
throughout the producing countries. This

method takes more than 5 days, depending


The amount of chilli produced in the
on weather conditions, to obtain the required
world is 24 million tonnes (FAO, 2005). The
moisture content (4-11% db). Due to this
main production areas are located in Asia
long period of time and direct exposure to
with 16 million tonnes produced annually
air and light, low quality dried chilli is
(FAO, 2005), of which China produces more
commonly produced. This low quality
than 12 million tonnes. Thailand provides
includes red color fading, development of
18,200 tonnes of fresh chillies annually
browning pigment and loss of vitamin C and
(FAO, 2005). The main production area of
provitamin A (Osunde and Musa Makama,
chilli in Thailand is located in the northeast,
2007; Ergüne? and Tarhan, 2006; Ramesh,
particularly in the southern part of the
Wolf et al., 2001; Condori et al., 2001).
northeast, namely Ubon Ratchathani and


To improve dried chilli quality, some
Srisaket provinces. The conventional drying
mechanical and solar dryers have been
method for chilli is sun drying and this
introduced for drying chilli in order to
remains the most widely practiced method
decrease the drying time. (Vega-Gálvez et
? Corresponding author.
© All rights reserved
E-mail: wiriya@agri.ubu.ac.th
Fax: +66 4528 837

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442 Wiriya, P., Paiboon, T. and Somchart, S.

al., 2008; Tasirin et al., 2007; Kaleemullah

Moreover, it has been found that
and Kailappan, 2005; Doymaz and Pala,
using stepwise temperatures regimes, such
2002; Hossain and Bala, 2002). Most have
as cyclic or three-stage temperatures, during
used air temperatures of between 50-80oC.
drying can preserve the color and nutrients
It has been found that the higher
of food products (Davidson et al., 2003; Ho
temperatures resulted in reduced drying time
et al., 2002; Chua et al., 2000). However,
and an increase in the effective moisture
these methods, using drying air temperature
diffusivity (Kaleemullah and Kailappan,
of 20-50oC, lead to long drying periods. It
2005; Di Scala and Crapiste, 2007; Vega et
can lead to mold growth, particularly in food
al.,
2007).
However,
using
high
products with a waxy skin such as tomato or
temperatures for drying produces a low
chilli. Furthermore, Klieber (2000) observed
quality of chilli, with losses of volatile
a dark-brown red color chilli using both a
compounds, nutrients and color (Di Scala
heat pump dryer (40oC, 20%RH) and a hot
and Crapiste, 2008; Kaleemullah and
air dryer (60oC for 6 hr and then 40oC for 48
Kailappan, 2006).
hr). Using such a long period of drying can


The important reactions occurring
maintain moisture content of chilli at
during
drying
are
enzymatic
and
intermediate moisture levels resulting in a
nonenzymic browning reaction. Enzymatic
brown color. Such color instability and long
browning reaction can be prevented by
drying periods have caused concern for
pretreatment methods, such as blanching and
chilli drying.
chemical treatment, that bring about


Therefore, the objective of this study
inactivated enzyme activity. (Gupta et al.,
was to optimize chilli drying using different
2002; Hossain and Bala, 2002). On the other
drying air temperatures compared to sun
hand, the nonenzymatic reactions increase in
drying. Chemical pretreatments were also
rate at higher temperatures and at
used to obtain a good quality dried chilli in
intermediate levels of moisture content in
terms of nutritional values and organoleptic
the fruit (Manzocco et al., 2001; Klieber,
attributes.
2000; Sigge et al., 1999). This reaction is a

diffusion-controlled binary reaction between
Material and Methods
amino acid and reducing sugar, namely the

Maillard reaction. It produces color and
Raw material
flavor, which are features of quality change
Freshly harvested chilli (Capsicum
in a food product (Miao and Roos, 2006).
annuum c.v. Huarou Yon) was purchased
Not only do Maillard reactions cause brown
from a local farmer in Srisaket province.
or dark colors in dried food product, other
Fully ripened chilli of a purely red color was
reactions may also be involved such as
used, having an average moisture content
pigment degradation, chemical oxidation of
75.0 ± 0.192%wb, an average diameter of
phenols and ascorbic acid (Manzocco et al.,
0.544 ± 0.294 cm and an average length of
2001; Sigge et al., 1999). A number of
5.796 ± 0.681 cm. The fresh chilli was
researchers have used chemical solutions in
packed in plastic bags and stored in a
order to prevent non-enzyme browning
refrigerator at 7-10oC for 2-3 days before the
reaction at drying air temperatures of
experiment. The chilli was blanched using
between 55-65oC as a single-temperature
hot water at 90oC for 3 minutes (Gupta et
regime
(Vega-Gálvez
et
al.,
2008,
al., 2002), and then cooled in cold water and
Kaleemullah and Kailappan, 2006; Doymaz
drained on a perforated tray before the
and Pala, 2002).
experiment.
International Food Research Journal 16: 441-454

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Effect of drying air temperature and chemical pretreatments on quality of dried chilli 443






















1-Fan; 2-Electric-heaters; 3-Drying chamber; 4-Controller; 5-Drying tray
6-Temperature probe; 7,8,9- Thermocouples; 10-Digital balance

Figure 1. A schematic diagram of lab-scale tray dryer

Drying methods
conducted for 8 hr per day, starting at 08.30
Sun drying
a.m. and finishing at 16.30 p.m. Between
Sun drying was conducted at Ubon
450-500 g of chilli was processed for each
Ratchathani University by spreading freshly-
replication.
blanched chilli on a stainless-steel tray in a

single layer and exposed directly to sunlight.
Mechanical drying
The temperature of this sun drying method,
A laboratory tray dryer with a
between March and April 2008, was
chamber of 30×60×40 cm and one tray
between 26-53oC and relative humidity was
(20×50 cm) was used to dry chilli. The
15-69%
as
measured
by
a
temperature of the dryer was controlled by a
temperature/relative
humidity
logger
temperature controller with a magnetic
(HOBO, Model H14-001). The temperature
switch and a voltage regulator adjusting for
and humidity probe was placed on an empty
between 0-260V. The drying air was heated
tray besides a tray of chilli. The sun drying
using 4 electric 1.4 kW-heaters. The
method took 3-5 days to obtain the required
temperature of inlet air was measured by a
moisture content (9-11%db) depending on
temperature probe at the end of duct before
weather conditions. This method was
entering the drying chamber. A schematic
International Food Research Journal 16: 441-454

---

444 Wiriya, P., Paiboon, T. and Somchart, S.

diagram of the tray dryer is shown in Figure
at a temperature of 25 ± 1oC for 10 minutes
1. The drying air temperatures varied
using a mass ratio between the chilli and
between 50o, 60o, and 70oC recorded by the
chemical solution of 450-500 g: 2 litres.
data logger (PRESICA 2002) and measured

by a thermocouple type T, which was inside
Determination of moisture content and
the chamber at 3 positions (the front, the
water activity (aw)
middle and the end of the tray). The
The AOAC method (AOAC, 1990)
variations in the drying air temperature were
was used for determining moisture content
between 0.6-2.6 oC. Two-stage temperature
using the hot air oven at temperatures of
was obtained from the preliminary test,
103-105oC (BINDER, Model FED240-M).
which was 70 ± 1oC for 4 hours, at which
Water activity of the chilli was measured
moisture content of product was less than
using a Thermoconstanter (Novasina, Model
intermediate moisture levels (aw ‹ 0.75), and
PS200 S/N 9809020) calibrated standard
followed by 50±0.4oC until the required
sample with a known value (Range 0.11-
moisture content was reached. The air
0.99). The experimental data was obtained
velocity was controlled at 1.34 ± 0.88 m/s
using 3 replications.
(maximum capacity) and measured in nine

positions in the chamber by a vane
Color measurements
anemometer (DIGICON, Model DA-43)

Surface color measurement was
without humidity control. An approximate
conducted using the L* a* b* system
drying time was calculated, using the Page
(Universal HunterLab, Model 45/0 S/N CX-
model obtained from Phomkong, Dasook,
0413), calibrated to a standard white tile
Thammarak & Ekpong (2007), in order to
(L*=91.7,
a*=-1.16,
b*=1.06).
L*
obtain the required moisture content. The
corresponds to lightness, a* represents red
blanched chilli to be dried was spread on a
(+)/green (-) and b* refers to yellow (+)/blue
tray in a rectangular grid as a single layer.
(-). Ten measurements were conducted in
The experiment was carried out by using
each treatment using 5 chilli pods per one
450-500 g of chilli for each replication.
measurement. Chroma and Hue angle were

suggested to be more practical measures of
Chemical pretreatments
color (McGuire, 1992).
The blanched chilli was soaked in

different chemical solutions obtained from
Reducing sugar analysis
the literature data as follows: (a) 0.3 %

Reducing sugar was analyzed using
(w/w) sodium metabisulfite (NaMS) (Vega-
the Nelson-Somogyi method, which is
Gálvez et al., 2008); (b) 1% (w/w) ascorbic
suitable for food with low reducing sugar
acid (Son et al., 2001) ; (c) 0.3 % (w/w)
(Low, 1994). The concentration of reducing
sodium metabisulfite (NaMS) combined
sugar
was
obtained
using
a
with 1 % (w/w) citric acid ( modified from
spectrophotometer at 520 nm and a standard
Vega-Gálvez et al., 2008 and Son et al.,
curve of glucose at 0-200 µg/ml was used.
2001); (d) 0.3 % (w/w) sodium metabisulfite
The method of extraction followed the Lane-
(NaMS) combined with 1 % (w/w) calcium
Eynon method (AOAC, 1990) using 1 g of
chloride (CaCl2) (modified from Vega-
chilli. Three replications were conducted.
Gálvez et al., 2008 and Davoodi et al.,

2007); and (e) freshly-blanched chilli
Ascorbic acid analysis
without soaking was used as a control
L-ascorbic acid was analyzed using
sample. The soaking process was controlled
the 2,6-dichlorophenol indohenol titrimetric
International Food Research Journal 16: 441-454

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Effect of drying air temperature and chemical pretreatments on quality of dried chilli 445
method (AOAC, 1990). Five grams of both
significant difference test was applied for
fresh and dried chilli were mixed with 5%
multiple comparisons at the 95% confidence
dichloroacetic acid. In addition, 0.1 mg/ml
level.
of ascorbic acid solution was used as the

standard. The analysis was conducted in
Results and Discussion
three replications.


Effect of drying air temperature on chilli
Total phenolic compounds analysis
quality
Total phenolic compounds were
Dried chilli prepared from fresh-blanch
determined using the Folin-Ciocalteau
chilli without chemical pretreatment, using
reagent and gallic acid as a standard
different drying air temperatures, were
(Slinkard and Singleton, 1977). The
processed and compared to sun dried chilli.
extracted solution was obtained using 0.2 g
The moisture content of chilli obtained from
of chilli flesh mixed with 80% methanol at
the different conditions using the AOAC
200 rpm for 2 hours by using a shaking bath
method (AOAC, 1990) were 9.7-11.2% db
(GFL, Model 1083) at room temperature and
and water activities were 0.42-0.48. From
then centrifuged at 1500 rpm for 20 minutes
Figure 2, a lower value of lightness (L*) of
controlled at 25oC by using a refrigerated
dried chilli using drying air temperatures of
centrifuge (Universal, Model 32R). This was
50o, 60o, 70oC was observed compared with
followed by mixing 2 ml of the extract with
the sun drying method (P<0.05). However,
10 ml Folin-Ciocalteau reagent before
the two-stage drying method significantly
placing these in a dark cabinet for 1-8
improved the lightness of dried chilli
minutes. After adding 8 ml of 7.5% Na2CO3,
compared to other drying method, and this
the mixture was allowed to stand at room
method did not significantly differ from the
temperature for 2 hours before measuring
sun drying method. Nevertheless, different
the absorbance at 765 nm. Triplicate
drying air temperatures provided chroma
measurements were conducted for all sample
between 26.6-29.6 and these values did not
treatments. The results were expressed as
significantly differ from the sun drying
mg gallic acid/ 100 g dried chilli.
method (P>0.05). On the other hand, the

highest value of hue angle of chilli obtained
Experimental Design
from two-stage temperature was observed.
The effects of the drying air
In all cases, hue angle was commercially
temperatures and chemical pretreatment
acceptable in the range of 35-45 degrees on
methods were conducted using Randomized
the basis of chilli powder, which is a
Completed Design (RCD) with three
reddish-orange hue color (Osuna-Garcia and
replications. In the drying air temperature
Wall, 1998).
study, there were five treatments (sun
Since it is difficult to interpret three
drying, 50oC, 60oC, 70oC, 70oC + 50oC and
values separately, all criteria used for the
fresh chilli) and three replications. In the
evaluation of dried chilli quality were in
chemical pretreatment study, there were six
terms of its color attribute. It was observed
treatments (fresh chilli, fresh blanched chilli,
that the mechanical drying method using a
0.3% NaMS, 1% ascorbic acid, 0.3% NaMS
one-temperature regime provided a dark-red
with 1% citric acid, 0.3% NaMS with 1%
color in dried chilli, particularly at 70oC.
CalCl2) and three replications. ANOVA
These results agreed with the findings of
analysis using SPSS V.11.5 (Trial version)
Vega-Gálvez et al. (2008), Turhan et al.
was used to evaluate variances. The least-
(1997) and Lee et al. (1991) who have
International Food Research Journal 16: 441-454

---

446 Wiriya, P., Paiboon, T. and Somchart, S.

60.00


a
50.00


a
a
40.00
ab
ab

ab
a
x
b
e
d

b
b
b
r

I
n
30.00
b
l
o
b
o

C
b
b
c

c
20.00
d

L*

10.00
Chroma

Hue angle

0.00
Sun drying
50 °C
60 °C
70 °C
70 °C+50 °C
Fresh chilli

Figure 2. Color attributes of chilli using different drying air temperatures compared to sun
drying

suggested that using high temperatures for
temperatures were also monitored and
drying air results in a dark-brown color due
compared with the sun drying method. Table
to non-enzymatic browning reaction. On the
1 shows that the reducing sugar levels of the
other hand, using a two-stage temperature
chilli were between 4.99-5.26 mg/g dried
regime resulted in having a more pure light-
chilli and all drying methods were not
red color for dried chilli. Normally fruit and
significantly different but were significantly
vegetable drying occurs in the falling rate
lower than fresh chilli. Even though
period, thereby it can be treated as a purely
different drying air temperatures did not
diffusion-controlled
mass
transport
significantly affect reducing sugar, the
phenomenon (Wang and Brennan, 1995;
decrease in reducing sugar resulted in the
Simal et al., 1999). As a result, an internal
forming of browning compounds due to the
factor plays an important role for moisture
non-enzymatic browning reaction between
removal rather than external factors.
reducing sugar and amino acid (Lee at al,
According to the experiments, two-stage
1991). This result is compatible with the
temperature drying was initiated by a higher
decrease in lightness, chroma and hue angle
temperature
followed
by
the
low
compared to fresh-blanched chilli (L*= 33.8
temperature, thus a product tempering
± 1.1, C*=50.2 ± 1.02, H*=38.9 ± 1.5). The
period was obtained. During this period, the
total phenolic compounds of dried chilli
product temperature had an adequate enough
obtained
from
different
drying
air
high temperature for moisture diffusion from
temperatures did not significantly differ with
the center to the surface of product. Thus,
sun drying (P>0.05), except when a drying
moisture removal of chilli during drying can
air temperature of 60oC was used (Table 1).
still be obtained during the second stage of
The explanation could be that a long drying
drying
without
excessive
heating,
period using a low drying air temperature
particularly on the product surface, and this
(50oC and sun drying) resulted in an increase
prevents a dark brown color forming.
with the loss of phenolic compounds due to
Therefore, at a lower drying air temperature,
oxidation induced by the presence of oxygen
a better quality of chilli can be observed.
and light (von Elbe and Schwartz, 1996).
Nutrition compounds of dried chilli
This finding agrees with Erbay and Icier
obtained
from
different
drying
air
(2009) who using drying air temperatures of

International Food Research Journal 16: 441-454

---

Effect of drying air temperature and chemical pretreatments on quality of dried chilli 447
Table 1. Nutritional values of chilli at different drying air temperatures

Total phenolic
Reducing sugar
Ascorbic acid
compounds

Drying
(mg/g dried
(mg/100 g dried
(mg/100 g dried

method
chilli)
chilli)
chilli)
Sun drying
5.26±0.40b
35.76±2.11c
255.15±18.70c

50oC
4.99±0.88b
49.31±1.03b
253.84±28.52c

60oC
5.18±0.55b
45.20±4.51b
312.20±11.00b

70oC
5.26±0.38b
38.02±3.95c
266.84±11.66c

70oC+50oC
5.13±0.13b
39.02±1.72c
263.13±6.22c

Fresh chilli
6.51±0.67a
344.32±48.1a
468.29±10.9a

between 40-60oC for olive leaves drying.
16-17 hours compared to the one-
On the other hand, drying air temperatures
temperature regime. The loss of ascorbic
higher than 60oC (70oC and 70oC-50oC)
acid using the sun drying method was due to
provided a lower value of phenolic
oxidation as the dried chilli was exposed
compounds due to thermal degradation (von
directly to light and sun (Gregory, 1996).
Elbe and Schwartz, 1996). The optimum
Since the color of dried chilli is the
drying air temperature of 60oC for phenolic
main attribute for consumer acceptance, the
compounds retention was similar to Katsube
lightness, chroma and hue angle can be used
et al. (2009) who used the temperatures of
as major criteria for process optimisation
40-110oC for mulberry leaves drying. In all
(Vega-Gálvez et al., 2008, Doymaz and
treatments, decreases in the total phenolic
Pala, 2002; Sigge et al., 1999; Onsuna-
compounds were observed compared with
Garcia and Wall, 1998). It was found that
the fresh form (468± 10.9 mg/ 100 g dried
the two-stage temperature regime, using a
chilli).
temperature of 70oC for 4 hours and
The same results were found for
followed by 50oC until reaching the required
ascorbic acid in dried chilli. As drying air
moisture content, provided the highest
temperatures using a lab-scaled dryer
values of lightness, chroma and hue angle.
increased, decreases in ascorbic acid were
However, there were low values in terms of
noted (Table 1). The expected result agrees
ascorbic acid and phenolic compounds.
well with those of Vega-Gálvez et al. (2008)
Meanwhile, a drying air temperature at 70oC
and Di Scala and Crapiste (2007). Ascorbic
provided the lowest value of lightness and
acid was degraded by higher temperatures
chroma, and low values of ascorbic acid and
and
the
degradation
product
(L-
total phenolic compounds. Therefore, these
dehydroascorbic
acid,
DHAA)
could
two drying methods were selected to study
participate in Strecker degradation with
further their potential for color and nutrition
amino acid, producing a browning pigment
stability in chilli using a mechanical dryer in
(BeMiller and Whistler, 1996). Not only
conjunction with the use of chemical
does the high temperature of drying air
pretreatments.
affect the loss of ascorbic acid, but a long

period of drying time can also introduce a
Using chemical substances for color and
significant loss of ascorbic acid. From the
nutrients stability of dried chilli
experiments the sun drying method took 3-5
The fresh-blanched chilli were
days and a two-stage drying method took
treated with chemical substances, which
International Food Research Journal 16: 441-454

---

448 Wiriya, P., Paiboon, T. and Somchart, S.

60.00

a

50.00

a
a

40.00
a
a
a
a
a
x

e
b
d
bc
30.00
r

I
n
cd

cd
l
o
o
b
d
C
bc

d
cd
d
20.00

L*

10.00
Chroma

Hue angle

0.00
S
l 2

aM
aC
N
ontrol
itric acid
S +C
C
resh chil i
+C
F

S
scorbic acid
aM
A
N
aM
N

Figure 3. Color attributes of chilli treated with chemical substances using 70oC

60.00


a
50.00

a
a
a

40.00
a
a
x
a
b
a
e

d
c
c
c
r

I
n
30.00
l
o

o
d
C
b
b
b
bc
c

20.00

L*
10.00

Chroma

Hue angle
0.00

S
l 2
aM
aC
N
ontrol
itric acid
S +C
C

resh chil i
+C
F
S
scorbic acid
aM
A
N
aM

N

Figure 4. Color attributes of chilli treated with chemical substances using two-stage temperature


were 0.3 % NaMS, 1% ascorbic acid , 0.3
NaMS, improves lightness of dried chilli at
% NaMS combined with 1 % citric acid and
drying air temperature 70oC, but the
0.3 % NaMS combined with 1 % CaCl2.
lightness of dried chilli using two-stage
The moisture content of dried chilli, using
temperature was similar to untreated chilli
drying air temperature at 70oC and using a
(Figure 4). This suggests that NaMS inhibits
two-stage temperature regime was between
browning reaction by binding with the
9.1-10.3% db and 8.9-9.7% db respectively.
carbonyl group of reducing sugars and other
These values were not significantly different
compounds to retard the browning process
(P<0.05). The water activities of dried chilli
(Lindsay, 1996). Thus, the browning
obtained from these two drying methods
pigment can be minimized, resulting in a
pretreated with chemical substances were
bright color of dried chilli. This result agrees
between 0.39-0.43. Figure 3 shows that
with the findings of Sigge et al. (2001) and
using chemical pretreatments, in particular
Simal et al., (2005). On the other hand,

International Food Research Journal 16: 441-454

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Effect of drying air temperature and chemical pretreatments on quality of dried chilli 449
Table 2. Nutritional values of chilli soaking in chemical solutions at 70oC
Reducing
Total phenolic
sugar
Ascorbic acid
compounds
Chemical
(mg/g dried
(mg/100 g dried (mg/100 g dried
pretreatments
chilli)
chilli)
chilli)
NaMS
4.83±0.13c
44.26±1.48c
280.65±3.19c
NaMS + Citric acid
4.79±0.03c
48.28±1.16c
271.34±4.80c
Ascorbic acid
4.84±0.11c
72.25±13.69b
312.93±20.77b
NaMS + CaCl2
4.68±0.19c
42.01±2.04c
283.49±13.74c
Control
5.26±0.38b
38.02±3.95c
266.84±11.66c
Fresh chilli
6.51±0.67a
344.32±48.1a
468.29±10.9a


Table 3. Nutritional values of chilli soaking in chemical solutions at two-stage temperature
Total phenolic
Reducing sugar
Ascorbic acid
compounds
Chemical
(mg/g dried
(mg/100 g
(mg/100 g dried
pretreatments
chilli)
dried chilli)
chilli)
NaMS
4.91±0.14b
43.59±0.54cd
252.79±4.92c
NaMS+Citric acid
4.45±0.23cd
44.99±0.76c
269.85±6.61c
Ascorbic acid
4.91±0.11b
68.61±6.74b
299.00±7.88b
NaMS +CaCl2
4.52±0.07c
45.80±2.78c
316.61±30.66b
Control
4.11±0.22d
39.02±1.72d
263.13±6.22c
Fresh chilli
6.51±0.67a
344.32±48.1a
468.29±10.9a

using chemical pretreatments with two-stage
red color stability, as CaCl2 may react with
temperatures was found to produce similar
water molecules resulting in increased water
value of lightness compared with the non-
mobility and reduced drying time. Thus,
pretreated chilli (Figure 4). This was
thermal degradation and oxidation of
probably due to all chemical substances
carotenoid can be minimized along with
being degraded by thermal degradation due
using of NaMS as an inhibitor of browning
to the long period of two-stage temperature
reaction. This is compatible with the
regime.
Therefore,
using
a
lower
experiment when chilli soaked in NaMS
temperature in the second stage of drying
with CaCl2, reduced the drying time from
could be enough to retard browning color
8.7 to 7.5 hours and from 16.4 to 15 hours
occurring.
for 70oC and a two-stage temperature
From Figure 3 and 4, the highest
regime, respectively. These results agree
value of the Chroma of dried chilli using
with Davoodi et al. (2007) who suggested
NaMS combined with CaCl2 was observed
that calcium may be acting in some manner
at both 70oC and a two-stage temperature
to block the amino groups before entering
regime. As chroma presents the purity of
into the enzymatic browning reaction.
color, using NaMS combined CaCl2
However, it was found that the chemical
preserved a pure red color, in which
pretreatments did not significantly affect hue
carotenoid pigments could be retained.
angle when both 70oC and a two-stage
Adding of CaCl2 was found to improve the
temperature regime were used compared to
International Food Research Journal 16: 441-454

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450 Wiriya, P., Paiboon, T. and Somchart, S.

untreated and fresh chilli. The hue angles of
play a role for total phenolic degradation,
chilli using 70oC and a two-stage
such as thermal degradation or oxidation.
temperature
regime
with
chemical
Thus, browning pigment possibly develops
pretreatments were between 33-42 degrees,
as a product of these reactions induced by
which is a reddish-orange hue. Using
drying air at a high temperature. This
chemical pretreatments before drying
finding agrees with Erbay and Icier (2009)
provids the same reddish-orange color of
and Katsube et al. (2009).
chilli, but different saturation and lightness
As shown in Tables 2 and 3, using a
due to different degrees of browning
pretreatment method before drying could not
reaction and oxidation.
prevent the degradation of ascorbic acid
Reducing sugar content of dried
both at 70oC and a two-stage temperature
chilli obtained from different chemical
regime, with the exception of soaking in
pretreatments was similar (P<0.05) (Table 2)
ascorbic
acid
solution
which
was
using a drying air temperature of 70oC, but
significantly higher than other chemical
reducing sugar content were significantly
pretreatments and control. Generally,
decreased compared with the control
ascorbic acid is used for food ingredients as
(P>0.05). Meanwhile, using chemical
a reducing and antioxidation agent. This
substances with the two-stage drying
contradicted with these results, as the
temperature method significantly (P>0.05)
soaking of chilli in this solution was found
improve the amount of reducing sugar of
to lead to a darker color, even though the
dried chilli compared to the non-
amount of ascorbic acid was increased after
pretreatment method (Table 3). However,
the drying process. This can be explained in
the reducing sugar of dried chilli decreased
that ascorbic acid was oxidized by the high
compared to fresh chilli (6.5 mg/g dried
temperature of drying air leading to DHAA
chilli) in all cases. It is suggested that the
and a wide variety of carbonyl and other
degradation of the reducing sugar causes the
unsaturated compounds being formed
browning pigment to develop due to a
(Gregory, 1996). The breakdown products
Maillard reaction, and therefore a decrease
then participated in Strecker degradation
in lightness and chroma was observed.
with amino acids and further polymerized to
The total phenolic compounds of
form
melanoidins
or
nonnitrogenous
dried chilli obtained from 70oC and a two-
caramel-like pigments (Gregory, 1996). This
stage temperature regime were similar to the
result was similar to those Arroyo-LÓpez et
control (P<0.05), with the exception of using
al. (2008), who observed browning color
ascorbic acid and NaMS with CaCl2 (Tables
occurring during storage of cracked table
2 and 3). Most notably, the amount of total
olives when ascorbic acid was used between
phenolic compounds was higher than the sun
0.75- 1.5% (w/v). Therefore, using ascorbic
drying method (255 mg/ 100 g dried chilli)
acid does not improve the color stability of
and tray drying with non-pretreatment
dried chilli, but rather induces the
method, while the values decreased
development of browning for both 70oC and
compared to freshly-blanched chilli (468
the two-stage temperature. As discussed
mg/100 g dried chilli). It was observed that
above, the mechanism of browning pigment
using chemical pretreatments could not
developed during chilli drying involves
preserve total phenolic compounds, in spite
different reactions. It could be suggested that
of blanching that was conducted in order to
not only does the Maillard reaction cause
inhibit enzymatic browning reaction. It can
browning pigment, but also other reactions
be suggested that the other reactions also
International Food Research Journal 16: 441-454

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