3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P69 TOCOPhEROL AND FATTy ACIDS CONTENTS
OF SELECTED ROMANIAN CEREAL GRAINS
CRISTIAn TUDOR MATEA, OCTAVIAn nEGREA,
IOAn HAS, SIMOnA IFRIM and COnSTAnTIn BELE
University of Agricultural Science and Veterinary Medicine,
R-400372,Cluj-Napoca, Romania,
a426401@yahoo.com
Introduction
Cereals grains are one of the main sources of tocopherols
(Ts) for humans 1 . These compounds are recognized for their
inhibition of lipid oxidation in biological systems and each
isomer shows , to a different extent, vitamin E activity in the
order α – T > β – T > γ – T > δ – T(ref. 2 ). The interest in the
relationship between Ts and fatty acids (FA) is outlined by
the fact that fats are carriers for Ts and they have at the same
time a prooxidant effect since they are susceptible to oxidation
3 .
The objective of this study is to determine the content
of tocopherols (α– , β + γ and δ–) and FA composition in
19 elected Romanian cereal grain varieties (wheat, maize
and oat).
Experimental
C e r e a l S a m p l e s
Cereal grain samples harvested in 2006 and 2007 were
obtained from Agricultural Research Institute Turda. The
samples included eight wheat, eight maize and three oat varieties
(var.). Samples from two replicates were chosen for analysis.
All samples were ground in a laboratory mill. Ground
samples were stored at –20 °C until extracted.
M e t h o d s
Total lipids (TL) were determined according to a routine
procedure 4.
The tocopherols were analysed using a Shimadzu VP
Series liquid chromatograph equipped with a degasser and a
fluorescence detector FR-10 AXL with excitation wavelength
of 290 nm and emission wavelength of 325 nm. Chromatographic
separation was performed on a Alltima RP C-18 column
(250 mm × 4,6 mm, 5 μm). The column was used at 40 °C.
The mobile phase was a mixture of acetonitrile and methanol
(50 : 50 , v/v) and eluted at a flow rate of 1.0 ml min –1 .
Sample treatment included saponification of 0.5 g cereal
flour in a Pyrex glass tube with 0.5 ml 50% KOH and a mixture
of 5 ml + 2 ml water in the presence of 0.1 g ascorbic
acid. The tube was transferred to a boiling water bath for
30 min. Then 6 ml of ethanol 50% was added to the cooled
tube. Unsaponified lipids were extracted by using three portions
(each 10 ml) of n-hexane: diethyl ether (7 : 3, v/v). After
separation of the phases, the organic layers were collected
in a separatory funnel. Organic extracts were washed three
times with water and then evaporated in a vacuum rotary evaporator
at 35 °C. The dried residue was extracted with 2 ml
methanol + 2 ml acetonitrile by mixing on a vortex mixer for
s726
2 min. The tocopherol contents were calculated from the peak
areas using standard curves of tocopherols (α – T, β – T, γ – T
and δ – T) obtained from Merck and Sigma.
FA were analyzed by gas-liquid chromatography (GLC)
with flame ionization detection (FID). The sample (1 μl) was
injected into gas-chromatograph, a Shimadzu GC-17 A series
equipped with a 30 m Alltech AT-WAX coated with polyethylene
glycol (0.25 mm I.D., 0.25 μm film thickness).The
oven temperature was programmed as follows : 70 °C for
2 min, then raised to 150 °C at 10 °C, held at 150 °C for a
further 3 min, then raised to 235 °C at 4 °C min –1 . The final
oven temperature was maintained for 5 min. The injector and
detector temperature was 260 °C. The carrier gas was helium
at a pressure of 147 kPa.
FA were converted to methyl esters by reaction with
boron trifluoride/methanol at 80 °C for 2 h in a Pyrex glass
tube. Esters were extracted twice with 1 ml n-hexane, the
extracts were combined, neutralized with sodium carbonate
and dried with anhydrous sodium sulfate and filtered. Finally
the filtrate was concentrated under a stream of nitrogen.
Table I
The content of tocopherols in different cereal grains
Cereal Tocopherols [mg 100 g –1 ] range
α β + γ δ
Wheat 0.77 0.23 –
0.64–0.98 0.16–0.31 –
Maize 0.26 0.96 0.08
0.16–0.34 0.75–1.21 0.05–0.12
Oat 0.31 0.03 –
0.27–0.37 0.02–0.04 –
Results
The means and ranges of tocopherols in different cereal
grains are shown in Table I.
α-tocopherol was the main isomer found among analysed
tocopherols in wheat and oat var. The content of α-T in
wheat var. was similar to that reported by other authors 1,5 .
Maize had the highest β + γ tocopherol content. Small quan-
Table II
Total lipids and fatty acid profiles of selected cereals
TL and fattyacids
[g 100 g –1 ] food
Wheat Maize Oat
TL 1.6 5.2 5.8
SFAs 1 0.17 0.55 0.74
MUFAs 2 0.18 1.32 1.80
PUFAs 3 – – –
Total cis 0.67 2.66 1.75
n-6 (as 18 : 2) 0.64 2.59 1.70
n-3 0.03 0.07 0.05
1 Saturated fatty acids
2 Monounsaturated fatty acids
3 Polyunsaturated fatty acids