Effects of Stir-Fry Cooking with Different
Edible Oils on the Phytochemical
Composition of Broccoli
DIEGO A. MORENO, CARMEN L´ OPEZ-BERENGUER, AND CRISTINA GARC´ ıA-VIGUERA
protect humans against cancer; they are rich sources of glucosinolates and posses a high content on flavonoids,
(potassium, sodium, calcium, magnesium, iron, manganese, zinc, and copper) in the edible portions of freshly
harvested broccoli (florets), which was subjected to stir-frying treatments, were evaluated. In the present work, the
stir-fry cooking experiments were carried out using different edible oils from plant origin (refined olive oil, extra
with extra virgin olive, soybean, peanut, or safflower oil did not reduce the total glucosinolate content of the cooked
broccoli compared with that of the uncooked sample. The vitamin C content of broccoli stir-fried with extra virgin
Keywords: Brassica oleracea, glucosinolate, minerals, phenolics, vitamin C
2003c; Anilakumar and others 2006). Food processing has the po-
1995; Severi and others 1997; Vallejo and others 2002, 2003d). The
methods for broccoli and other cruciferous vegetables for prepara-
tion by means of conventional cooking such as boiling, steaming,
microwaving, and pressure cooking reduce the intake of important
glucosinolates and phenolic compounds (McNaughton and Marks
2003; Vallejo and others 2003d; Verkerk and Dekker 2004).
The effect of cooking on glucosinolates has received a relatively
large amount of attention. Cooking reduces broccoli glucosinolate
levels by approximately 30% to 60%, depending on the method (for
example, conventional, microwave, high pressure), cooking inten-
sity (for example, temperature, time), and the type of compound
(Vallejo and others 2002, 2003d). On the other hand, total and in-
dividual glucosinolates measured in red cabbage after various mi-
crowave treatments showed higher levels of these compounds than
in the untreated vegetable (Verkerk and Dekker 2004).
Broccoli heads used to investigate the effect of the cooking treat-
ments on the texture and the antioxidant properties of this plant
food resulted in slight reductions in 2,2 diphenyl-1-picrylhydrazyl
(DPPH+) radical-scavenging activity with respect to fresh material
(Zhang and Hamauzu 2004; Lin and Chang 2005). On the contrary,
the phenolic content of broccoli was either reduced (Vallejo and
rassica species are very rich in health-promoting phytochemi-
MS 20060377 Submitted 7/10/2006, Accepted 10/17/2006. Authors are with
Espinardo, Murcia, Spain. Direct inquiries to author Moreno (E-mail:
ing or microwaving.
High-pressure boiling, steam cooking, microwaving, and low-
pressure boiling (conventional boiling) showed great differences in
their influence on the content of vitamin C in broccoli. Thus, clear
disadvantages were detected when cooking in a microwave due to
the high loss of vitamin C (40%). On the other hand, steaming had
cesses (Vallejo and others 2002).
Concerning mineral composition of plant foods, it is well known
and broccoli should be a mineral-rich plant food source (Huarte-
Mendicoa and others 1997; Severi and others 1997; Margen 2002;
(frying in an oven or in a pan deep frying) on the nutritive value of
vegetables revealed that after frying vegetable food, the content of
vitamins and minerals was nearly fully retained, while boiling and
Schnepf and Driskell 1994; Bognar 1998).
Therefore, the purpose of the present paper was to evaluate the
freshly harvested broccoli inflorescences.
Materials and Methods
Freshly harvested commercial broccoli inflorescences (Brassica
and sampled for 4 h before analysis. Broccoli heads were selected
at maturity or marketable stage (optimum quality heads of 130 ±
lected and transported to the laboratory, where the inedible parts
were removed using a sharp knife. The broccoli was cut into almost
and divided into portions (150 g). One portion was retained raw,
and others were cooked in triplicate with the different oils as de-
Processing treatments (stir-fry cooking)
Broccoli floret portions (150 g) were placed in the pan for stir-
frying once the ready-to-cook temperature of the corresponding
40 mL of edible oil was reached (ranging 125 to 140◦C) in a fry-
ing pan (EU certified 22 cm∅ non-stick ‘Silver’ VitrexTM, Zaragoza,
Spain), and were cooked for 3 min 30 s.
Edible oils for cooking were obtained from different sources
(Table 1). Uncooked and stir-fried broccoli florets were frozen us-
ing liquid nitrogen and kept at −80◦C, and then freeze-dried. The
material was subsequently ground into a fine powder and stored at
−80◦C for further phytochemical analysis. In all these treatments,
the cooking time was established previously by an informal testing
for stir-fried broccoli regarding sensory parameters and the desir-
able relatively short duration when cooking cruciferous vegetables
from a health perspective (Vallejo and others 2002; Rungapamestry
and others 2006).
Glucosinolate extraction and analysis
A modified previously reported procedure (Vallejo and others
2002, 2003a; Bennett and others 2004) was used for extraction of
glucosinolates. In brief, each freeze-dried sample (50 mg) was ex-
tracted in 1.5 mL polypropylene-capped microcentrifuge tubes us-
ing 1500 µL of 70% aqueous methanol, heated at 70◦C for 30 min
using a heating bath, with vortex mixing every 5 min, followed by
centrifugation (15 min, 17500 × g, 4◦C) to pellet insoluble mate-
rial. Subsamples (1000 µL) of each supernatant were taken. Solvent
multisolvent delivery system, in-line degasser, W717plus Autosam-
pler, and a W2996 Photodiode Array Detector at 227 nm, using a
Table 1---Characteristics of the edible oils used in the experiments
Type of commercial edible oil Brand name, company, city, countryNutritional lipid compositiona
Refined olive oil Carbonel, SOS Cu´ etara SA, Madrid, SpainSaturated 13
Extra virgin olive oil Olisone, LIDL Supermercados SA, Montcada i Rexac, Catalonia, Spain
Sunflower oilKoipesol, SOS Cu´ etara SA, Madrid, Spain
Soyabean oilSoy oil, Spectrum Organic Products Inc., Petaluma, Calif., U.S.A.
Peanut oilPlanters, Kraft Foods Global Inc., Glenview, Ill., U.S.A.
Safflower oilHollywood, The Hain Celestial Group, Inc., Melville, N.Y., U.S.A.
aNutritional lipid composition in the label (g/100 g).
Merck KGaA, Darmstadt, Germany) with a LiChroCART?4-4 guard
(A) and acetonitrile (B). Glucosinolates were eluted off the column
in 35 min. The flow rate was 1 mL/min in a linear gradient starting
with 1% B reaching 20% B in 30 min and 1% B at 40 min (Bennett
described intact glucosinolate LC-MS method, and quantified by
Sigma-Aldrich Chemie Gmbh, Steinheim, Germany) as standard.
Extraction and analysis of phenolic compounds
The extraction procedure has been previously described (Vallejo
and others 2003 c,d). Samples (20 µL) were analyzed on a Merck-
Hitachi liquid chromatograph equipped with a pump (L-6200) and
a UV-vis detector (L-7420) (Merck KgaA, Darmstadt, Germany).
Separations were achieved on a LiChroCart column (Merck KGaA,
ODS-18, 25 × 0.4 cm; 5 µm particle size). The mobile phase was
water:formic acid (95:5) (A) and methanol (B). The flow rate was
1 mL/min, and a linear gradient starting with 10% B, reaching 15%
B at 5 min, 30% B at 20 min, 50% B at 35 min, and 90% B at 40
min, was used. Chromatograms were recorded at 320 and 360 nm.
(5-caffeoyl-quinic acid, Sigma, St. Louis, Mo., U.S.A.), flavonoids
as quercetin 3-rutinoside (Sigma), and sinapic acid derivatives as
sinapinic acid (Sigma).
Extraction and analysis of vitamin C and minerals
Ascorbic acid (AA) and dehydroascorbic acid (DHAA) contents
were determined according to Vallejo and others (2002, 2003c).
HPLC analysis was achieved after derivatization of DHAA into
the fluorophore 3-(1,2-dihydroxyethyl)furo[3,4-b]-quinoxaline-1-
one (DFQ), with 1,2-phenylenediamine dihydrochloride (OPDA).
HPLC equipped with an L-4000 UV detector and an L-6000 pump.
Separations of DFQ and AA were achieved on a Kromasil 100 C-18
column (25 cm × 0.4 cm; 5 µm particle size; Tecnokroma, BCN,
Spain). The mobile phase was methanol:water (5:95) containing
5 mM cetrimide and 50 mM potassium dihydrogen phosphate at
pH 4.5. The flow rate was 0.9 mL/min, the detector wavelength was
initially set at 348 nm, and after elution of DFQ, it was manually
shifted to 261 nm for AA detection.
Mineral analysis was carried out after HNO3-HClO4(2:1) acid
digestion of the material. Calcium, magnesium, potassium, iron,
manganese, zinc, and copper concentrations were determined by
ICP-spectrometry (IRIS Intrepid II XDL?; Thermo Electron Corp.,
Franklin Mass., U.S.A.) in a dilution with LaCl3+ CsCl of the extract
aliquot, as reported elsewhere.
MS-DOS version of STATGRAPHICS Plus 7.0 version (StatPoint Inc.,
V.I., U.S.A.). The data shown are mean values (means ± SD) and the
significance of the differences was compared using the Duncan’s
Test, a multiple range test at 95% confidence level (P < 0.05).
Results and Discussion
Influence of stir-frying on glucosinolates
and phenolic compounds
The total intact glucosinolate contents (Figure 1) in stir-fried
broccoli florets were significantly reduced (P < 0.05) when using
refined olive oil (49% loss) and sunflower oil (37% loss) with respect
to the uncooked controls (43.22 mg/100 g wet basis), whereas the
altered when using extra virgin olive, soybean, peanut, or safflower
Figure 1---Total intact glucosinolates
in broccoli inflorescences cooked
(stir-fried) with different edible oils.
Values are mean ±SD (n = 3). Means
followed by the same letter are not
significantly different at P < 0.05,
according to Duncan’s test.
Table 2---Phenolics in stir-fried broccoli using different oils
Compound (mg/100 g wet basis)
Flavonoids Treatment (oil) Caffeoyl-quinic acid derivativesSinapic acid derivatives
Refined olive oil
Extra virgin olive oil
19.87 ± 4.75
13.65 ± 1.86
13.16 ± 3.10
18.89 ± 4.35
17.01 ± 4.38
18.44 ± 4.69
16.82 ± 1.82
118.78 ± 32.93 a(∗)
57.28 ± 39.23 b
59.47 ± 13.61 b
73.60 ± 22.53 ab
81.94 ± 21.97 ab
93.37 ± 9.06 ab
77.64 ± 7.35 ab
7.54 ± 1.84 a(∗∗)
2.35 ± 1.11 c
2.08 ± 0.38 c
3.33 ± 0.69 bc
4.50 ± 1.99 bc
5.33 ± 0.42 ab
4.21 ± 0.91 bc
Results represents means ± standard deviation, n = 3. Values followed by a different lowercase letter are significantly different from the uncooked control at
(∗) P < 0.05 and (∗∗) P < 0.01, according to Duncan’s test.
Previous findings on cooking cruciferous vegetables (Vallejo and
Oerlemans and others 2006; Rungapamestry and others 2006) by
other conventional methods such as steaming, boiling, and mi-
crowaving also reported losses of glucosinolate content. The broc-
coli thermal breakdown and/or the enzymatic degradation at high
temperatures (stir-frying at 125 to 130◦C on average) induced a
significant reduction of glucosinolates. However, depending on the
edible oil used, this degradation was different, but we could not
find any relationship between the cooking temperature (125◦C in
peanut oil; 130◦C extra virgin and refined olive oils; 135 to 140◦C
sunflower, soybean, and safflower oils) or the lipid composition of
the oils (Table 1) and the exerted effect on the glucosinolate levels
Regarding polyphenolic composition of broccoli florets, the data
in this study confirmed previously published data on profiling
tives (Vallejo and others 2002, 2003d). No significant reductions
(P > 0.05) of the caffeoyl-quinic acid derivatives were observed for
broccoli after stir-frying (Table 2). Flavonoids, more sensitive to the
effects of cooking, as demonstrated by other authors (Vallejo and
losses) when stir-frying broccoli florets with olive oils (refined and
< 40% (soybean oil), about 44% (safflower oil), about 55% (sun-
and others 2005), the high temperature conditions of the cook-
ing processes reduced the total phenols (flavonoids, sinapic, and
caffeoyl-quinic derivative contents). When refined and extra vir-
gin olive oils were used, the reductions of the total phenolics were
greater than during steaming (only 11% loss of total phenols), but
similar to the loss during high-pressure boiling (53% loss of total
80% loss total phenols) (Vallejo and others 2002, 2003d). Other au-
thors have observed the increased or reduced phenolic content of
broccoli depending on the type of cooking method: boiling, steam-
ing, or microwaving (Turkmen and others 2005).
The cooking method used in the present experiment, stir-frying,
gave data on reduction of the flavonoids and sinapic acid deriva-
tives of broccoli depending on the oil used. Nonetheless, the effect
was completely independent of the cooking temperature but not
of the type of oil, since edible oils from olive origin demonstrated
a negative effect on flavonoids and sinapic acid derivatives. This
prompts future studies of the different cooking treatments (tem-
perature compared with oil quality and composition) on phyto-
how limited (Vallejo and others 2003d; Zhang and Hamauzu 2004;
Moreno and others 2006). The differences in the analysis extrac-
Figure 2---Vitamin C (ascorbic acid
+ dehydroascorbic acid) in broccoli
florets after stir-fried cooking with
different edible oils. Values are
mean ± SD (n = 3). Means followed
by the same letter are not
significantly different at P < 0.01,
according to Duncan’s test.
Table 3---Minerals in stir-fried broccoli using different oils
(mg/100 g wet basis)
Copper TreatmentsIron ManganeseZinc PotassiumSodiumCalcium Magnesium
Refined olive oil
1.34 ± 0.04 c∗
1.79 ± 0.23 abc
1.48 ± 0.28 bc
2.02 ± 0.13 a
1.42 ± 0.09 bc
1.89 ± 0.28 ab
1.54 ± 0.06 abc
0.44 ± .01
0.42 ± 0.04
0.41 ± 0.06
0.46 ± 0.06
0.35 ± 0.02
0.45 ± 0.04
0.39 ± 0.02
0.88 ± 0.06
0.83 ± 0.09
0.83 ± 0.06
0.97 ± 0.08
1.07 ± 0.12
1.01 ± 0.13
1.03 ± 0.16
0.34 ± 0.03 c∗∗
0.74 ± 0.20 ab
0.42 ± 0.07 bc
1.03 ± 0.21 a
0.41 ± 0.05 bc
0.36 ±. 012 c
0.37 ± 0.03 c
399.91 ± 18.93 bc∗∗
345.33 ± 12.84 c
365.31 ± 19.16 bc
369.35 ± 7.61 bc
409.71 ± 7.51 ab
407.18 ± 19.06 ab
459.49 ± 18.12 a
33.63 ± 2.69
34.56 ± 0.47
31.07 ± 3.16
33.36 ± 1.22
34.40 ± 1.01
31.95 ± 4.13
36.12 ± 2.94
45.09 ± 2.57
41.98 ± 1.95
34.68 ± 3.16
43.97 ± 0.66
41.46 ± 1.90
45.99 ± 4.38
42.66 ± 2.21
26.56 ± 1.62
21.97 ± 0.17
21.52 ± 2.29
24.36 ± 0.34
21.93 ± 0.73
25.53 ± 2.19
24.65 ± 0.71
Results represents means ± standard deviation, n = 3. Values followed by a different lowercase letter are significantly different from the uncooked control at (∗) P < 0.05 and
(∗∗) P < 0.01, according to Duncan’s test.
tion and the cooking methods could be also part of the reason for
such reductions, where boiling, baking, and frying resulted in sig-
and Marks 2003; Sahlin and others 2004).
Effect of stir-frying on vitamin C and minerals
were significant (P < 0.01), and considerably high for peanut oil,
safflower oil, and soybean oil (40% to 48% loss) or refined olive oil
(80% loss). The content of vitamin C of the uncooked florets was
similar to previously reported concentrations in different broccoli
cultivars and breeding lines (62 to 122 mg/100 g wet basis; Vallejo
and others 2003a, 2003d), but stir-fry cooking induced significant
losses, reaching levels below half of the dietary recommendations
(Recommended Dietary Allowance [RDA] per portion size, for US
population; Margen 2002).
None of the cooked samples showed significantly lower concen-
trations of mineral than the uncooked controls (Table 3). The con-
tent of these nutrients in the cooked florets was in accordance with
the RDA per portion size (for U.S. population, also used in Canada;
Margen 2002) for human nutrition: potassium, calcium, magne-
sium, sodium, and zinc (10%); manganese (45%); iron (15% to 25%
The influence of mineral nutrients on fruits and vegetables in
the diet is crucial for human health and wellness, so, natural
S:Sensory&NutritiveQualitiesofFood Download full-text
mineral-rich foods like green leafy vegetables should turn out to be
a better strategy for improving nutrition than adding low bioavail-
able elements in supplements or salts (Agte and others 2000). With
that broccoli is a good source of potassium, sodium, calcium, mag-
nesium, copper, iron, zinc, and manganese (Agte and others 2000;
Margen 2002) after being cooked.
minerals, revealed different degrees of retention for these health-
presented the highest losses), whereas the response of glucosino-
lates and vitamin C was different (refined olive oil showed highest
loss, but extra virgin olive oil showed a good level of retention), but
order to improve our knowledge about the potential for improving
the density of phytochemicals (glucosinolates and phenolics) and
the human metabolism once ingested and digested.
he use of stir-frying as domestic or conventional cooking for
The authors wish to thank the CICYT National Programme for the
financial support of this work (AGL2005-00650). Part of this work
L´ opez-Berenguer was funded by a grant from Seneca Foundation–
Comunidad Aut´ onoma de la Regi´ on de Murcia (Spain). Diego A.
Moreno thanks the European Social Fund (ESF) and the Spanish
Ministerio de Educaci´ on y Ciencia for funding through a Ramon y
Cajal postdoctoral contract.
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