Effect of Drying Conditions on Antioxidant Properties of Rosehip Fruits (Rosa canina sp.)

Abstract

The objective of this work was to investigate the influence of drying conditions on antioxidants contents and antioxidant activity of rosehips. Freshly harvested rosehips were dried under 3 air temperatures (50, 60 and 70 °C) at air flow rates of 0.5, 1.0 and 1.5 m s-1. The retention of total phenolics was best at 50 °C and 1.5 m s-1 air flow rate. For the retention of total carotenoids and antioxidant activity, the appropriate drying conditions were found to be 70 °C and 1.5 m s-1 air flow rate. For the highest retention of ascorbic acid, 60 °C drying temperature and 1.5 m s-1 air flow rate was determined to be appropriate.

Full text

Asian Journal of Chemistry Vol. 21, No. 2 (2009), 1061-1068
Effect of Drying Conditions on Antioxidant Properties of
Rosehip Fruits (Rosa canina sp.)
ILKAY KOCA*, NEBAHAT SULE USTUN and TURHAN KOYUNCU†
Department of Food Engineering, Faculty of Engineering
Ondokuz Mayis University, Samsun, Turkey
E-mail: itosun@omu.edu.tr
The objective of this work was to investigate the influence of drying
conditions on antioxidants contents and antioxidant activity of rosehips.
Freshly harvested rosehips were dried under 3 air temperatures (50, 60
and 70 ºC) at air flow rates of 0.5, 1.0 and 1.5 m s-1. The retention of
total phenolics was best at 50 ºC and 1.5 m s-1 air flow rate. For the
retention of total carotenoids and antioxidant activity, the appropriate
drying conditions were found to be 70 ºC and 1.5 m s-1 air flow rate. For
the highest retention of ascorbic acid, 60 ºC drying temperature and 1.5
m s-1 air flow rate was determined to be appropriate.
Key Words: Antioxidant activity, Ascorbic acid, Rosehip fruits.
INTRODUCTION
There is a much interest in the association between fruit and vegetable consum-
ption and human health. Because oxidative stress plays a significant role in most
disease processes and aging, the potential health benefits of fruits and vegetables
have been largely attributed to their potential antioxidant capacity1.
Rosehip fruits are one of the richest sources of antioxidant phytochemicals
encountered. In addition to ascorbic acid, rosehips are also rich in carotenoids and
phenolics2,3.
Rosehips have been used for the production of herbal tea, nectar and marmelade
in Turkey. Freezing, chilling or drying are the methods used for the storage of
rosehips before processing by the food industry. Freezing and chilling are the methods
used by food factories, drying is the method applied by people living at sunny regions.
There are many literatures aimed to investigate the health benefit effects4, compo-
sition5-7, antioxidant activity2,8 and the utilization9-12 of rosehips. But there is not
much work about the losses during processing rosehips into various products13-16.
Therefore, the objective of this work was to investigate the influence of the drying
conditions on antioxidant content and antioxidant activity of rosehips and to find
out the most suitable drying temperature and drying air flow rate.
†Department of Agricultural Machinery, Faculty of Agriculture, Ondokuz Mayis University, Samsun,
Turkey.

EXPERIMENTAL
The freshly harvested rosehips (Rosa canina sp.) were wholly dehydrated by
hot air drying technic using the dehydration system developed17 at 50, 60 and 70 ºC
with air flow rates of 0.5, 1.0 and 1.5 m s-1 to achieve moisture content of 10 %. The
dehydrated rosehips were put into sealable glass jars and were cooled. Before analysis,
the samples were divided into two pieces by using a mortar and they were sorted.
The samples which will be used for ascorbic acid determination were ground by
the mortar and the others were milled as can pass through 1 mm sieve by using
stainless steel mill. The average composition of fresh rosehip samples is given in
Table-1. The drying experiments and analyses were duplicated and results were
given as mean values.
TABL
E
-1
AVERAGE COMPOSITION OF FRESH ROSEHIP SAMPLES
Parameters Mean
pH 003.94
Dry matter (g 100 g-1) 038.28
Total sugar (g kg-1)* 222.67
Reducing sugar (g kg-1)* 205.82
Unreducing sugar (g kg-1)* 016.01
Total carotenoids (mg g-1)* 000.38
Ascorbic acid (mg g-1)* 024.96
Total phenolics (mg g-1)* 079.88
Antioxidant activity (FRAP value) (mmol g-1)* 009.22
*Dr
y
matter basis.
Determination of dry matter: Dry matter content was determined by heating
in a vacuum oven at 70 °C until a constant weight was obtained18.
Determination of total carotenoids: Total carotenoid determination was carried
out according to the method of Chan and Cavaletto19, with some modifications.
Three grams of the samples were extracted with a mixture of 50 mL acetone
and petroleum ether (1:1 by volume), by using a homogenizer (Controls, Milano-
Italy) and filtered under vacuum. The residue was extracted until the complete
exhaustion of colour (usually 4-5 extractions were enough) with acetone:petroleum
ether. The extracts were transferred to a seperatory funnel containing 25 mL of 10 %
KOH in methanol (w/v) and allowed to stand for 1 h in darkness. Partition was
achieved by adding 75 mL of petroleum ether and 100 mL of 20 % NaCl (w/v) and
mixing gently. The hypophasic layer was discarded. The epiphasic layer was washed
3 times with water, passed through anhydrous Na2SO4 and made up 250 mL with
petroleum ether. Absorption spectra in the visible region, 350-750 nm, were run with
a spectrophotometer (Jasco V-530, Japan). Total carotenoid values were calculated20
from the absorption maxima using an extinction coefficient of 2592 at 453 nm. The
results were expressed based on ß-carotene equivalents as mg g-1 dry matter.
1062 Koca et al. Asian J. Chem.

Determination of ascorbic acid: A sample of 3 g was weighed and homogen-
ized with metaphosphoric acid solution (5 %, w/v) until uniform consistency at
room temperature (20 ± 2 ºC), then centrifuged for 10 min at 3000 rpm and filtered
under vacuum in a volumetric flask. This procedure was repeated twice. The final
volume of the extracted solution was set at 100 mL with the metaphosphoric acid
solution. The supernatants were recovered and ascorbic acid immediately measured
spectrophotometrically by 2,6-dichlorophenolindophenol dye21 at 520 nm. L-Ascorbic
acid was used to prepare a standard solution (1 mg mL-1). The results were expressed
as mg g-1 dry matter.
Determination of total phenolics: A ground sample of 1 g weighed and phenolic
compounds were extracted with 20 mL of 80 % aqueous methanol for 1 h with
agitation (magnetic stirrer) at room temperature (20 ± 2 ºC) and filtered. The residue
was extracted again in the same way. The solution was diluted to volume with the
methanol. Sample extract was introduced in a 100 mL volumetric flask; 5 mL of
Folin Ciocalteau's reagent (Sigma Chemical Co., St. Louis, MO) were added and
mixed. The mixture was allowed to stand at room temperature for 5 min. A volume
of 10 mL of saturated sodium carbonate solution (7.5 %, w:v) was added to the
mixture and then mixed gently. A blank was also made by mixing water and the
reagents. The solution was brought to 100 mL with water. After allowing the mixture
to stand at room temperature for 0.5 h, the absorbance was read at 760 nm using the
spectrophotometer. The experiment was carried out in duplicate. The standard cali-
bration curve was plotted using catechin equivalent and the results expressed as,
miligrams per gram of dry matter22.
Determination of antioxidant activity: To measure antioxidant activity, an
aliquot of the acetone/methyl alcohol/water/formic acid (40:40:20:0.1) extracts of
rosehip samples were dried at 30 °C under vacuum, using an evaporator (Heidolph
4001, Germany) and redissolved in same volume of water23. Aqueous samples were
mixed with 0.95 mL of ferric-TPTZ reagent (prepared by mixing 300 mM acetate
buffer, pH 3.6, 10 mM 2,4,6-tripyridil-s-triazine in 40 mM HCl and 20 mM FeCl3
in the ratio of 10:1:1) and measured at 593 nm. FeSO4 was used as a standard and
the antioxidant activity was expressed as mmol g-1 FRAP of dry matter2.
RESULTS AND DISCUSSION
During dehydration of rosehips using different temperature and air flow rate,
the time to reach the same dry matter is given in Fig. 1.
As can be seen from Fig.1, the drying time of the samples changed due to air
flow rate. As expected, samples dried at 0.5 m s-1 air flow rate showed the highest
drying time and drying time decreased as the air flow rate increased. Also, drying
time increased as the temperature decreased. Similar results were reported by many
resarchers24-27. According to them, during constant rate period of dehydration, the
faster the air, the faster the rate of drying, but during the falling rate period, the
factors that control the rate of drying change. Initially the important factors are
Vol. 21, No. 2 (2009) Antioxidant Properties of Rosehip Fruits 1063

0
1000
2000
3000
4000
5000
6000
7000
50 60 70
Temperature (°C)
Drying ti
m
e(
m
in)
0.5 m/s
1.0 m/s
1.5 m/s
Fig. 1. Relation between air flow rate, drying temperature and drying time
similar to those in constant rate period, but gradually the rate of water movement
from the interior of the food becomes the controlling factor. So the effect of air
flow rate becomes unimportant. The drying times of samples dehydrated at 50 ºC
and all 3 air flow rates were higher than the others. The samples dried at 60 and 70 ºC
showed shorter drying times and as will be point out later, drying time significantly
affected the antioxidant matters and antioxidant activity.
At the drying temperatures of 60 and 70 °C, the ascorbic acid and total carotenoids
contents of the samples were close to each other, but at 50 °C, these values were
lower (Figs. 2 and 3). This could be attributed to the fact that the decrease of the
drying temperature resulted in the increase of drying time and hence, longer exposure
time to the drying air. Same result was found by Rodriguez-Amaya28 for carotenoids.
This was ascribed to the continuation of enzymatic activity. Carotene degradation
during drying has been attributed to its high sensitivity to oxidation. In a drying
process, the cumulative effect of time-temperature determines the total carotene
loss. In the absence of oxygen, formation of cis-isomers can also cause degradation
of carotene29. According to Suvarnakuta et al.26, carotene is degraded by free radical
0
0.05
0.10
0.15
0.20
50 60 70
Temperature (ºC)
Total carotenoids (
m
g/g)
0.5 m/s
1.0 m/s
1.5 m/s
Fig. 2. Influence of air flow rate and drying temperature on total carotenoids
1064 Koca et al. Asian J. Chem.

0
5
10
15
20
25
50 60 70
Temperature (°C)
A
sc
o
r
b
ic aci
d
(
m
g
/
g
)
0.5 m/s
1.0 m/s
1.5 m/s
Fig. 3. Influence of air flow rate and drying temperature on ascorbic acid
oxidation mechanism and the degree of oxidation depends on the heating time,
heating temperature and oxygen content.
Samples dehydrated at 50 ºC and 0.5 m s-1 air flow rate showed the lowest
value for total carotenoids as indicated in Fig. 2. The loss was 71.05 %. For all
drying temperatures used in this experiment, the samples dried at air flow rate of
1.5 m s-1 showed the lowest total carotenoids loss. Between the drying temperatures
and air flow rates studied, 70 ºC and 1.5 m s-1 caused the lowest (55.26 %) total
carotenoids loss.
As seen in Fig. 3, samples dehydrated at 50 °C and 0.5 m s-1 air flow rate
showed lower ascorbic acid content. For all the experimental drying temperatures,
samples dried at 1.5 m s-1 air flow rate gave much lower ascorbic acid loss, compared
to the other air flow rates. During drying, the ascorbic acid degradation was between
17.65-48.57 %. The lowest loss was determined for 60 °C and 1.5 m s-1, while the
highest loss was at 50 °C and 0.5 m s-1. According to Mrkìc et al.30 the ascorbic acid
content positively correlated with air flow rate. The present results are in agreement
with theirs. Ascorbic acid is easily oxidized and, if the oxidation process continues
beyond the stage of dehydroascorbic acid, it becomes irreversible31.
As shown in Fig. 4, the highest total phenolics content was obtained for the
samples dried at 50 °C, as the temperature raised, phenolic matter loss increased.
Similar results were reported by several resarchers32,33. Kyi et al.33 recorded that the
polyphenol degradation rate increased with increasing temperature and the concen-
tration of total polyphenol declined rapidly during drying because of the enzymatic
oxidation of polyphenols. The lowest total phenolics loss (32.86 %) was obtained
for the samples dried at 50 °C and 1.5 m s-1 air flow rate. For all the experimental
air flow rates, although the total phenolics loss of samples dried at 60 and 70 °C
seem close to each other, the highest loss was determined as 47.21 % for the samples
dried at 70 °C and 1.0 m s-1 air flow rate conditions.
The highest FRAP value was obtained for the samples dehydrated at 70 °C.
This means, total antioxidant activities of analyzed rosehip samples were affected
from ascorbic acid and total carotenoids, rather than total phenolics.
Vol. 21, No. 2 (2009) Antioxidant Properties of Rosehip Fruits 1065

0
10
20
30
40
50
60
50 60 70
Temperature (°C)
T
o
tal
p
h
e
n
o
lics (
m
g
/
g
)
0.5 m/s
1.0 m/s
1.5 m/s
Fig. 4. Influence of air flow rate and drying temperature on total phenolics
When FRAP values examined (Fig. 5), it is observed that, the rosehip samples
dehydrated at 70 °C and 1.5 m s-1 air flow rate gave the highest values (70.64 % loss),
whereas the samples dried at 60 °C and 0.5 m s-1 gave the lowest (87.26 % loss)
values. Drying time showed a negative effect on antioxidant contents and the anti-
oxidant activity decreased with increase in temperature. Hence, high temperature
short time prosess maximized the antioxidant activity of rosehips. This is consistent
with the data reported by Mrkìc et al.30 for broccoli. The negative effect of drying
time on antioxidant activity could be ascribed to its depleting effect on ascorbic
acid and total carotenoids contents.
0
0.5
1.0
1.5
2.0
2.5
3.0
50 60 70
Temperature (°C)
F
R
A
P(
m
m
o
l/
g
)
0.5 m/s
1.0 m/s
1.5 m/s
Fig. 5. Influence of air flow rate and drying temperature on FRAP value
Hot-air drying implies a thermal treatment and thermal degradation of polyphenols
is expected but the decomposition of polyphenols was proven to depend on the
food matrix and the processing conditions. Moreover, this process enhances or
depletes the antioxidant activity of products depending on the nature of the substrate.
During drying, oxidation reactions could also take place and polyphenols with an
intermediate oxidation state can exhibit a higher radical scavenging activity than
non-oxidized polyphenols. High temperature drying could further cause the formation
of Maillard reaction products that could act as pro- or antioxidants. These compounds
1066 Koca et al. Asian J. Chem.

have been shown to act as antioxidants in dried foodstuffs, individually or in synergism
with naturally occurring antioxidants, since synergistic effects between antioxidants
have been demonstrated30.
As can be seen from the Figs. 2-5, samples dried at 1.5 m s-1 air flow rate
showed the highest value of ascorbic acid, total carotenoids, total phenolics and anti-
oxidant activity, whereas the samples being dried at 0.5 m s-1 generally gave the
lowest values.
Conclusion
The obtained experimental data showed that, retention of ascorbic acid, total
carotenoids, total phenolics and antioxidant activity depended on drying temperature,
air flow rate and drying time related to these two factors. From the retention point
of view, 50 °C dehydrating temperature and 1.5 m s-1 air flow rate were found to be
the most suitable for drying rosehips in terms of total phenolics retention, whereas
70 °C and 1.5 m s-1 were found to be the most suitable dehydration conditions in
terms of the retention of total carotenoids and antioxidant activity.
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(Received: 15 December 2007; Accepted: 19 September 2008) AJC-6875
1068 Koca et al. Asian J. Chem.
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