Douglasb a Department of Chemical Engineering, King Mongkut’s University of Technology, Thonburi, Bangkok 10140, Thailand b Department of Chemical Engineering, University of Waterloo, Wa
Trang 1LWT 41 (2008) 1417–1424
Extraction of a-tocopherol and g-oryzanol from rice bran
Photchanathip Imsanguana, Amorn Roaysubtaweea, Ratsuda Boriraka,
Suwassa Pongamphaia, , Supaporn Douglasa, Peter L Douglasb a
Department of Chemical Engineering, King Mongkut’s University of Technology, Thonburi, Bangkok 10140, Thailand
b Department of Chemical Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 Received 15 May 2007; received in revised form 31 August 2007; accepted 31 August 2007
Abstract
The aim of this research was to study the effect of operating mode (continuous versus batch+continuous), temperature, pressure and solvent on a-tocopherol and g-oryzanol extraction from rice bran (Oryza sativa Linn.) and compare the efficiency of three extraction methods: SC-CO2 extraction, solvent extraction and soxhlet extraction Three sets of experiments were performed First, extraction using SC-CO2was performed over a range of temperatures and pressures (45–65 1C and at 38 and 48 MPa), and at a CO2flow rate of 0.45 mL/min The results showed that the best conditions for a-tocopherol extraction were 55 1C, 48 MPa in the batch+continuous mode For g-oryzanol, the best conditions were 65 1C, 48 MPa and in the continuous mode In the second set of experiments, solvent extraction using hexane and ethanol at 32 and 55–60 1C was studied The results showed that none of the solvents could extract a-tocopherol; however, ethanol at 55–60 1C was suitable for g-oryzanol extraction Finally, soxhlet extraction experiments using hexane for a-tocopherol and ethanol for g-oryzanol were also performed In summary, SC-CO2was found to be the best solvent for extracting both a-tocopherol and g-oryzanol from rice bran, because of its higher yields and extraction rate
r2007 Swiss Society of Food Science and Technology Published by Elsevier Ltd All rights reserved
Keywords: Rice bran; a-Tocopherol; g-Oryzanol; Supercritical carbon dioxide; Solvent extraction
1 Introduction
Rice (Oryza sativa Linn.) production is a significant crop
in Thailand resulting in significant amounts of rice bran
waste Rice bran contains many valuable substances
such as vitamin E (a-tocopherol and tocotrienol) and
g-oryzanol The major component of vitamin E in rice bran
is a-tocopherol which is an antioxidant and can lower the
risk of cancer formation and coronary heart diseases
prevent Alzheimer’s disease and allergies (Mervyn, 1994)
g-Oryzanol is a mixture of 10 ferulate esters of triterpene
alcohol (Zhimin et al., 2001) and can be used to reduce
blood cholesterol levels, treat nerve imbalance, as well as
an antioxidant and preservative (Murase & Iishima, 1963;
Rong, Ausman, & Nicholosi, 1994;Sasaki et al., 1990) The
major components of g-oryzanol in rice bran are
cycloar-tenyl ferulate, 24-methylene cycloartanyl ferulate and campestanyl ferulate (Zhimin et al., 2001) Since they are
so abundant in rice bran, this research focused on the extraction of a-tocopherol and g-oryzanol (cycloartenyl ferulate, 24-methylene cycloartanyl ferulate and campesta-nyl ferulate) from rice bran The chemical structures
of a-tocopherol and g-oryzanol are shown in Figs 1 and
2, respectively Currently, a-tocopherol and g-oryzanol are extracted from various sources such as wheat germ
supercritical carbon dioxide (SC-CO2), and rice bran oil
can find no reports in the literature describing the direct extraction of a-tocopherol or g-oryzanol from rice bran using supercritical carbon dioxide The literature does however contain studies on the extraction of these substances from rice bran oil (Noppamas, 2002) This then leads to the motivation for this research Carbon dioxide is the most commonly used supercritical solvent, because it
www.elsevier.com/locate/lwt
0023-6438/$34.00 r 2007 Swiss Society of Food Science and Technology Published by Elsevier Ltd All rights reserved.
doi: 10.1016/j.lwt.2007.08.028
Corresponding author Tel.: +66 24709221x208; fax: +66 24283534.
E-mail address: suwassa.pon@kmutt.ac.th (S Pongamphai).
Trang 2has a relatively low critical temperature and pressure
(31.1 1C and 7.39 MPa), toxic, flammable,
non-corrosive, inert and inexpensive
The most suitable extraction methods for the
extrac-tion of vitamin E (a-tocopherol) and g-oryzanol
(cycloartenyl ferulate, 24-methylene cycloartanyl ferulate
and campestanyl ferulate) from rice bran were studied and
the extraction efficiency and operating conditions were
determined
2 Materials and methods
2.1 Materials Bran from Suphanburi rice, which was grown at Chacherngsow, Thailand, was used in this work Carbon dioxide (99.95% purity) was supplied by Thai Industrial Gases (TIG), Thailand Methanol, acetonitrile, hexane and ethanol used in this work are of HPLC grade and were
Fig 1 The chemical structure of a-tocopherol ( Noppamas, 2002 ).
Fig 2 The chemical structures of g-oryzanol ( Zhimin & Samuel, 1999 ).
Trang 3procured from Merck Ltd., Thailand a-Tocopherol and
g-oryzanol standards were obtained from Sigma Chemical
Co., USA and Tsuno, Japan, respectively
2.2 Rice bran mean composition
Rice bran was analyzed for particle size, moisture and oil
content The particle size was measured using a Taylor
sieve The moisture content was determined using oven
drying at 110 1C for 2 h and the oil content was measured
using soxhlet extraction with hexane for 24 h (AOAC,
1995)
2.3 Extraction of a-tocopherol and g-oryzanol from rice
bran using SC-CO2
SC-CO2 extraction experiments were carried out in an
ISCO Model SFXTM 3560 laboratory extractor shown in
operation mode (continuous versus batch+continuous),
pressure (38 and 48 MPa) and temperature (45–65 1C)
2.3.1 Effect of operating mode
2.3.1.1 Continuous mode A 0.5 g of rice bran was placed
in the extraction vessel The flow rate of CO2 was set at
0.45 mL/min and allowed to flow continuously through
the extraction vessel for 7 h at a temperature of 55 1C
and a pressure of 48 MPa The extract was analyzed
using a Waters Corporation, Model #600-486-717
high-performance liquid chromatograph (HPLC) HPLC
ana-lysis was performed using symmetry C-18 column
(150 mm 3.9 mm i.d.) with mobile phase
acetonitrile:-methanol (90:10, v/v), flow rate of 1.5 mL/min and UV
detector of 295 nm
2.3.1.2 Batch+continuous mode Rice bran was placed in the extraction vessel and exposed to SC-CO2at 55 1C and
48 MPa for 1 h and then CO2was allowed to flow through the sample at a flow rate of 0.45 mL/min for 6 h
2.4 Extraction of a-tocopherol and g-oryzanol from rice bran using solvent extraction
A 1 g sample of rice bran was extracted using 100 mL of hexane at a rotating speed of 200 rpm and a temperature varying from 32 1C to about 55–60 1C for 24 h The extract was analyzed using an HPLC The hexane solvent was replaced with ethanol and the remainder of procedure and conditions are all the same as before
2.5 Extraction of a-tocopherol and g-oryzanol from rice bran using vacuum soxhlet extraction
A 3 g sample of rice bran was extracted in a soxhlet apparatus with 300 mL of hexane at temperatures varying from 65 to 70 1C and pressures varying from 500 to
550 mmHg for 24 h The extract was analyzed using an HPLC The hexane solvent was then replaced with ethanol and the remainder of the procedure and conditions are all the same as before
3 Results and discussion
3.1 Rice bran mean composition Bran from Suphanburi rice (O sativa Linn.) was used in this research Moisture and fat/oil content of rice bran were found to be 14.01% and 19.08% (w/w), respectively The
Fig 3 ISCO Model SFXTM3560 supercritical CO extractor.
Trang 4majority of rice bran particles were found to be 297–595 mm
in size as shown inTable 1
3.2 SC-CO2extraction
3.2.1 Effect of operating mode
A comparison of two methods of SC-CO2extraction, (i)
continuous mode (ii) batch+continuous mode, is shown in
The extraction was performed at 55 1C, 48 MPa and a CO2
flow rate of 0.45 mL/min The results show that the
extraction of a-tocopherol reached a maximum of both
continuous mode and batch+continuous mode operations
after which no additional extraction was observed; the
average extraction rate was 24.80 mg/kg (dry basis)/h
and 31.83 mg/kg (dry basis)/h, respectively and the
extrac-tion rate of g-oryzanol was 2322.79 and 2464.73 mg/kg/h,
respectively Fig 4 shows that batch+continuous mode
results in higher extraction rates than continuous
mode a-Tocopherol is found in a stable matrix form in
rice bran, so continuous mode is inadequate for high
a-tocopherol extraction Under batch+continuous mode,
CO2was confined inside extraction vessel for 1 h, thereby
increasing the CO2penetration into rice bran and increas-ing extraction resultincreas-ing in an increase in the a-tocopherol extraction On the other hand, Fig 5 shows a lower g-oryzanol extraction rate when batch+continuous mode was used
3.2.2 Effect of pressure SC-CO2 extraction was carried out at a constant temperature of 65 1C, a carbon dioxide flow rate of 0.45 mL/min and a pressure varying from 38 to 48 MPa The extraction results for a-tocopherol and g-oryzanol are shown inFigs 6 and 7, respectively Both figures indicate that when the pressure was increased, the extraction rate and yields increased This effect is expected since an increase in the pressure increases the density and solvent ability of supercritical fluid thereby allowing it to dissolve more solute
Table 1
Size distribution of rice bran particles
time (h) 0
20
40
60
80
100
120
140
7 5
4 3
Fig 4 Effect of operating mode on a-tocopherol extraction using
SC-CO 2 (T ¼ 55 1C, P ¼ 48 MPa, CO 2 flow rate ¼ 0.45 mL/min): (’)
continuous and (m) batch+continuous.
time (h) 0
2000 4000 6000 8000 10000 12000
6 5 3
2 1
Fig 5 Effect of operating mode on g-oryzanol extraction using SC-CO 2 (T ¼ 55 1C, P ¼ 48 MPa, CO 2 flow rate ¼ 0.45 mL/min): (’) continuous and (m) batch+continuous.
time (h) 0
20 40 60 80 100 120 140
7 6 4
3 2
Fig 6 Effect of pressure on a-tocopherol extraction using SC-CO 2 (T ¼ 65 1C, CO 2 flow rate ¼ 0.45 mL/min): (’) 38 MPa and (m) 48 MPa.
Trang 53.2.3 Effect of temperature
The effect of temperature on the extraction was studied
at a constant pressure of 48 MPa, using a CO2flow rate of
0.45 mL/min and at temperatures from 45 to 65 1C The
results of a-tocopherol and g-oryzanol extraction are
shown inFigs 8 and 9, respectively These figures indicate
that increasing extraction temperature results in increase
extraction rates This effect is also expected since increasing
the temperature decreases the viscosity and increases the
diffusivity resulting in an increased extraction rate
Based on the range of experimental conditions, the best
conditions for a-tocopherol extraction using supercritical
carbon dioxide were found to be 48 MPa, 55 1C, CO2flow
rate of 0.45 mL/min with batch+continuous mode and for
g-oryzanol extraction were found to be 48 MPa, 65 1C, CO
flow rate of 0.45 mL/min with continuous mode The extraction yields of a-tocopherol and g-oryzanol at these conditions were 127.33 and 11,371.79 mg/kg (dry basis), respectively
retention times of a-tocopherol and 3 of the 10 components
of g-oryzanol (cycloartenyl ferulate, 24-methylene cycloar-tanyl ferulate and campescycloar-tanyl ferulate) were identified and found to be 10.52, 21.58, 24.61 and 30.18 min, respectively The area under a particular peak in the chromatogram indicates the amount of that particular component in the rice bran extract
3.3 Solvent extraction The solvent extraction experiments were carried out at atmospheric pressure and at various temperatures Solvent extraction experiments showed neither ethanol nor hexane could extract a-tocopherol The results showed that this is because a-tocopherol is in a matrix form in rice bran, so extraction at low pressure (i.e atmospheric pressure) is inadequate for a-tocopherol extraction, because this pressure cannot eliminate the interferences from other molecules such as proteins and carbohydrates, that are non-soluble in organic solvents (Ruperez, Martın, Herrera,
& Barbas, 2001) Perhaps at elevated pressures and longer extraction times a-tocopherol might be extracted from rice bran The results of solvent extraction of g-oryzanol using hexane are shown in Fig 11 This figure shows that increasing temperature increases the quantity of g-oryzanol extracted Increasing temperature decreases the viscosity and increases the diffusivity of the solvent resulting in increasing extraction rate and yield In this work, the highest extraction yield of g-oryzanol was found to be 7349.25 mg/kg (dry basis) at temperatures between 55 and
60 1C The effect of solvent type on the extraction was
0
time (h) 0
2000
4000
6000
8000
10000
12000
7 6 5 4 3 2 1
Fig 7 Effect of pressure on g-oryzanol extraction using SC-CO 2
(T ¼ 65 1C, CO 2 flow rate ¼ 0.45 mL/min): (’) 38 MPa and (m) 48 MPa.
time (h) 0
20
40
60
80
100
120
140
4 3
Fig 8 Effect of temperature on a-tocopherol extraction using SC-CO 2
(P ¼ 48 MPa, CO 2 flow rate ¼ 0.45 mL/min): (K) 45 1C, (m) 55 1C and
(’) 65 1C.
time (h) 0
2000 4000 6000 8000 10000 12000
7 6 5 4 3 2
Fig 9 Effect of temperature on g-oryzanol extraction using SC-CO 2 (P ¼ 48 MPa, CO 2 flow rate ¼ 0.45 mL/min): (K) 45 1C, (m) 55 1C and (’) 65 1C.
Trang 6carried out at atmospheric pressure and temperature
of 55–60 1C Fig 12 shows the solvent extraction of g-oryzanol using both ethanol and hexane Ethanol was found to be a better solvent than hexane This is because g-oryzanol, which consists of triterpene alcohol or sterols and fururic acid, is a polar molecule (Zhimin & Samuel,
1999), so it is easily dissolved in ethanol, which is also
a polar molecule; extraction yield was 9414.02 mg/kg (dry basis)
3.4 Vacuum soxhlet extraction The effect of solvent type on the vacuum soxhlet extraction was carried out at pressures of 500–550 mmHg and temperatures of 65–70 1C The results showed that hexane and ethanol were the best solvents for a-tocopherol and g-oryzanol extraction, respectively This is because hexane and a-tocopherol are non-polar molecules, whereas ethanol and g-oryzanol are polar molecules Extraction yields of a-tocopherol and g-oryzanol were found to be 172.23 and 9808.79 mg/kg (dry basis), respectively More-over, the quantity of both substances using the vacuum soxhlet extraction was higher than that achieved using the solvent extraction The reasons being that the extraction temperature of the soxhlet extraction was higher than the solvent extraction, and the solvent used in soxhlet extraction can be evaporated and condensed in the same way as the steam distillation, so efficiency of the soxhlet extraction is higher than the solvent extraction (Pattira, Krisda, & Kittipong, 2003)
3.5 Extraction rate
increasing in the beginning of extraction, since there
is a lot of concentration gradient of substances in bulk fluid and interior of rice bran The extraction rate then
Fig 10 Chromatogram of the rice bran extract using SC-CO 2 (P ¼ 48 MPa, T ¼ 65 1C).
time (h) 0
2000
4000
6000
8000
10000
12000
Fig 12 Effect of solvent type on g-oryzanol extraction: (m) hexane and
(’) ethanol.
time (h) 0
2000
4000
6000
8000
10000
12000
Fig 11 Effect of temperature on g-oryzanol extraction using hexane: (m)
32 1C and (’) 55–60 1C.
Trang 7continually decreases due to the decreasing of
concentra-tion gradient of the solute in the solvent Finally, the
extraction process approaches equilibrium
3.6 Extraction efficiency
The comparison of three extraction methods, SC-CO2,
solvent and soxhlet extraction, is shown inFigs 13 and 14
for a-tocopherol and g-oryzanol, respectively The
extrac-tion efficiency of a-tocopherol for SC-CO2 and solvent
extraction were 73.93% and 0%, respectively, as compared
to soxhlet extraction For g-oryzanol, extraction yield of
SC-CO2 extraction is greater than the soxhlet extraction,
because soxhlet extraction time and temperature were
higher than that of SC-CO2extraction, so some g-oryzanol
was degraded Both figures indicated that SC-CO2
extrac-tion resulted in higher extracextrac-tion yields, lower extracextrac-tion time and avoided degradation of substances
4 Conclusions
The results indicated that the extraction of a-tocopherol and g-oryzanol from rice bran is successfully performed using SC-CO2 The extraction yields of a-tocopherol and g-oryzanol depend on the pressure and temperature during extraction The best conditions for a-tocopherol extraction were pressure
of 48 MPa, temperature of 55 1C and batch+continuous mode Extraction yield was 127.33 mg/kg (dry basis) For g-oryzanol extraction, the best conditions were pressure of
48 MPa, temperature of 65 1C in the continuous mode Extraction yield was 11,371.79 mg/kg (dry basis)
Neither ethanol nor hexane could extract a-tocopherol at atmospheric pressure but ethanol at 55–60 1C was found to
be best for extracting g-oryzanol For soxhlet extraction, hexane and ethanol were the best solvent for a-tocopherol and g-oryzanol extraction, respectively
Based on a comparison of three extraction methods (SC-CO2, solvent extraction and soxhlet), it was concluded that SC-CO2 extraction was the best extraction method for a-tocopherol and g-oryzanol extraction from rice bran Extraction using SC-CO2results in high yields and the highest extraction rates using a non-toxic solvent, CO2 Although a greater yield of a-tocopherol results from soxhlet extraction with hexane than SC-CO2, the extraction rate is significantly higher when using SC-CO2than hexane (31.83 mg/kg/h with SC-CO2 compared to 7.18 mg/kg/h with soxhlet) Since the SC-CO2 extraction time was much lower than the soxhlet extraction time (4 h compared to 24 h) at similar temperatures the possibility of thermal degradation is greatly reduced Acknowledgment
The authors gratefully acknowledge the financial sup-port from the Thailand Research Fund (TRF) through the Royal Golden Jubilee Ph.D Program (1.C.KT/47/G.1) References
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2000
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Fig 14 Comparison of extraction methods (SC-CO 2 extraction, solvent
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Trang 8Bachelor of Engineering, Department of Chemical Engineering, King
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