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Consumption of brown onions (Allium cepa var. cavalier and
var. destiny) moderately modulates blood lipids, haematological
and haemostatic variables in healthy pigs
Ewa Ostrowska
1
, Nicholas K. Gabler
1
, Sam J. Sterling
2
, Brendan G. Tatham
1
,
Rodney B. Jones
2
, David R. Eagling
2
, Mark Jois
3
and Frank R. Dunshea
1
*
1
Department of Primary Industries, Victorian Institute of Animal Science, 600 Sneydes Rd, Werribee,
VIC 3030, Australia
2
Department of Primary Industries, Institute for Horticultural Development, VIC 3176, Australia
3
La Trobe University, Bundoora, VIC 3083, Australia
(Received 9 June 2003 – Revised 11 September 2003 – Accepted 1 October 2003)
Although garlic and onions have long been associated with putative cardiovascular health benefits, the effects of different commercially
available onions and level of intake have not been studied. Therefore, the aim of the present study was to evaluate the potential health
benefits of raw onions using the pig as a biomedical model. Twenty-five female (Large White £ Landrace) pigs were used in a
(2 £ 2)þ1 factorial experiment. Pigs were fed a standard grower diet supplemented with 100 g tallow/kg with the addition of Allium
cepa var. cavalier or var. destiny at 0, 10 or 25 g/MJ digestible energy for 6 weeks. Overall, the consumption of onions resulted in sig-
nificant reductions in plasma triacylglycerol; however, the reductions were most pronounced in pigs fed destiny onions (– 26 %, P¼0·042).
Total plasma cholesterol and LDL:HDL ratios were not significantly different. Onion supplementation, regardless of the variety, resulted in
dose-dependent reductions in erythrocyte counts and Hb levels, while the white blood cell concentrations, particularly lymphocytes, were
increased in pigs that consumed onions. Furthermore, indices of blood clotting were largely unaffected by onion consumption. In con-
clusion, dietary supplementation with raw brown onions has moderate lipid-modulating and immunostimulatory properties. However,
daily onion intake . 25 g/MJ digestible energy could be detrimental to erythrocyte numbers.
Onions: Health: Lipid metabolism: Pig
There is an increasing amount of consumer interest and
research focused on various food products that offer a posi-
tive health benefit beyond basic nutrition (‘functional
foods’). Plants from the genus Allium, particularly onions
(A. cepa) and garlic (A. sativum), have been consumed
for their putative nutritional and health benefits for centu-
ries. Although the health functionality of garlic has been
reported extensively (Bordia & Verma, 1980; Ali &
Thomson, 1995; Dorant et al. 1995; Smith & Yang,
2000; Liu & Yeh, 2001; Slowing et al. 2001), very little
is known about the specific benefits of onion (Bordia &
Verma, 1980; Ali & Thomson, 1995; Dorant et al. 1995;
Ide et al. 1997; Smith & Yang, 2000; Slowing et al.
2001). Epidemiological studies have shown a correlation
between diets rich in onion and reduced risk of stomach
cancer in human subjects (You et al. 1989), as well as an
inverse relationship with mortality from CHD in man
(Hertog et al. 1993a,b). Compounds that have been impli-
cated in providing a number of health-promoting attributes
of onion include flavonoids, particularly the flavonol
quercetin and the organosulfur compounds such as cysteine
sulfoxides (CSO) (Price & Rhodes, 1997). S compounds
from garlic, and common to onion, have been shown to
reduce plasma total cholesterol, LDL-cholesterol and tria-
cylglycerol (TG) levels in human subjects and rodents
(Bordia & Verma, 1980; Chi, 1982; Chi et al. 1982;
Qureshi et al. 1983a,b; Slowing et al. 2001); flavonols
such as quercetin have also been shown to have lipid-mod-
ulating properties (Bok et al. 2002; Glasser et al. 2002).
In the absence of clinical studies on the effects of raw
onion consumption, the present study used a pig model
to characterise the functional properties of two onion
cultivars grown in different environments and agronomic
conditions. The pig is a good animal model for human
nutrition, because of the many similarities between pigs
and man in the anatomy and physiology of the digestive
(Book & Bustad, 1974; Swenson, 1977) and cardiovascular
(Martin, 1964; Lumb, 1966) systems. Furthermore,
the advantage of the pig in biomedical research is
the similarity in the major lipoprotein subclass of LDL
* Corresponding author: Professor Frank R. Dunshea, fax þ 61 39 742 0400, email Frank.Dunshea@dpi.vic.gov.au
Abbreviations: BW, body weight; CSO, cysteine sulfoxide; DE, digestible energy; TG, triacylglycerol; TXB
2
, thromboxane B
2
.
British Journal of Nutrition (2004), 91, 211–218 DOI: 10.1079/BJN20031036
q The Authors 2004
physico-chemical characteristics, albeit that the levels of
plasma lipids are lower in pigs than human subjects
(Chapman & Goldstein, 1976).
Materials and methods
Onions
Two varieties of onions commercially grown in the
Australian states of Tasmania (cool–temperate climate)
and Queensland (sub-tropical climate) were chosen for
the present study. Both varieties were brown onion.
A. cepa var. cavalier was grown in Gatton, Queensland
(approximately 1528 E, 288 S), while A. cepa var. destiny
was sourced from the Devonport region of Tasmania
(approximately 1458 E, 408 S). DM was determined in
triplicate by drying homogenised onion samples to a
constant weight in a force-draught oven at 1058C.
Animals and handling
All procedures were approved by the Victorian Institute of
Animal Science Animal Ethics Committee (Anonymous,
1997). Twenty-five female crossbred (Large White £
Landrace) pigs (initial body weight (BW) 41·5 (
SD 4·2)
kg) were placed in individual pens, blocked according to
initial live weight and allocated to one of five dietary treat-
ments, in a randomised block design. The blocks were
formed using the initial live weights of the pigs. Pigs
were fed approximately 90 –95 % of ad libitum intake
(1·67 MJ digestible energy (DE)/kg BW
0·75
) of a dry feed
formulated to contain 16·7 MJ DE/kg and 100 g tallow/kg
to simulate the saturated fatty acid content of a western
human diet. The energy intake from fat was about 3·6 MJ
or 21·5 %. The experimental diet (Table 1) was formulated
to be in excess of protein and lysine requirements for this
class of pigs (Dunshea et al. 1993). The amino acid content
relative to lysine was kept in excess of the amino acid bal-
ance proposed as ideal by the Standing Committee on
Agriculture (1987). A vitamin and mineral premix was
omitted from the diets as it contains antioxidants and
other compounds that could mask the effects exerted by
the onion. Pigs had access to water at all times.
The five experimental treatments consisted of a control
diet with no onion added, and a low (16 g/kg BW
0·75
or
10 g/MJ DE) and a high (40 g/kg BW
0·75
or 25 g/MJ DE)
dose of onion for each variety of onion. The amount of
onions fed to the pigs was set at levels that can be con-
sumed by human subjects, after normalisation for the com-
parative differences in energy intake between pigs and
human subjects. The low dose would be equivalent to
about half an onion per d and the high dose equivalent to
about one and a half large onions per d in human subjects.
Onions were stored at 48C, and diets were prepared daily to
maintain stability of the active compounds found in onions.
The loose outer epidermis of the onion was removed and
the onions were then chopped in half and homogenised
in a blender for approximately 2 min. The calculated
amount of the homogenate was weighed for each pig and
mixed together with the dry feed for 2 min until the feed
reached uniform consistency. Diets were fed within 1 h
of preparation, as the thiosulfinates (the product of the
breakdown of CSO when the onions are cut-up) are
highly unstable. Pigs were weighed once per week and
the amount of dry feed and onion adjusted according to
BW. Feed refusals were collected and recorded daily.
Blood collection and analysis
Blood samples were obtained from the jugular vein by
venepuncture before feeding (fasted) on two sequential
days after 4 and 6 weeks of treatment. Blood was also col-
lected from each pig 3 h post-feeding (postprandial), since
the absorption of dietary flavanols from onions in human
blood reaches peak values between 0·7 and 2·9 h after feed-
ing (Hollman et al. 1996, 1999; Aziz et al. 1998).
On the first sequential sampling day, blood was drawn
into EDTA, clot activator and sodium citrate vacutainer
tubes, which were dedicated for blood coagulation tests
(platelet count, prothrombin time, activated partial pro-
thrombin time and fibrinogen counts) and blood biochem-
istry assays (cholesterol, TG and glucose). Two blood
smears were prepared immediately for each pig, using
blood that contained EDTA as an anticoagulant, to deter-
mine the number of white blood cells, erythrocytes, eosino-
phils, segmented neutrophils, lymphocytes, monocytes and
basophils. Blood samples were placed on ice and trans-
ported for analysis (IDEXX Laboratories Pty Ltd, Mount
Waverley, Victoria, Australia). On the second day of
sampling, three blood samples were collected in vacutainer
tubes containing EDTA, heparin and without anticoagulant
respectively. Half of the blood collected into the EDTA
tube was immediately decanted after bleeding into a tube
that contained 10 m
M-indomethacin (final concentration)
for 11-dehydro-thromboxane B
2
(TXB
2
) assay. Plasma
was separated by centrifugation at 3000 rpm for 15 min
and stored at 2 208C until analysed. The rest of the
blood collected on the second day was used to determine
concentrations of plasma HDL-cholesterol (procedure no.
354L) and total cholesterol (procedure no. 401) using kit
reagents purchased from Sigma (Sigma-Aldrich Pty Ltd,
Sydney, Australia). To assess clotting capability of the
Table 1. Composition of experimental diets*
Ingredients g/kg
Wheat 679·0
Soyabean meal 91·4
Fish meal 45·7
Meat and bone meal 57·1
Blood meal 19·0
Tylan† 0·4
NaCl 1·8
Ca
2
PO
4
4·3
L-Lys hydrochloride 0·9
DL-Met 0·1
L-Thr 0·2
Tallow 100·0
* Diet was formulated to contain 16·7 MJ digestible energy, 177 g crude
protein (N £ 6·25) and 9·4 g available lysine/kg air-dry diet; raw
onions (Allium cepa) were mixed with the dry feed at 10 or 25 g/MJ
digestible energy.
† Tylosin phosphate 100 g/kg antibiotic (Elanco Animal Health, Mac-
quaire Park, NSW, Australia).
E. Ostrowska et al.212
blood, TXB
2
, a stable metabolite of thromboxane A
2
con-
centrations (catalogue no. 519501; Cayman Chemical Pty
Ltd, Crows Nest, NSW, Australia) were measured.
Cysteine sulfoxide and quercetin analyses
The analysis of CSO in raw onion tissue was carried out
with an HPLC methodology based on that of Yoo &
Pike (1998), with the exception that the samples were
frozen at 2 708C before extraction and 10 m
M-hydroxyl-
amine was added to the extraction solvent (i.e. 800 ml etha-
nol/l with 10 m
M-hydroxylamine). The level of acetic acid
in the mobile phase was increased to 6 ml/l. The mean con-
centration of CSO was calculated from analysis of ten
onions of each variety. For quercetin analysis, freeze-
dried onion powder from at least three separate onions
per treatment was hydrolysed in HCl at 908C for 2 h, and
total quercetin aglycone was assayed using HPLC accord-
ing to the method described by Hertog et al. (1992).
Statistical analyses
Data was analysed by ANOVA using GENSTAT for
Windows, version 4.1 (Payne et al. 1993). The results
are presented as mean values of the fasting samples and
3 h postprandial measurements taken at weeks 4 and 6.
Each mean value, as well as growth rate and average dry
feed intake, was initially analysed using a randomised
block design that included the types of onion and two
doses (10 and 25 g onions/MJ DE) with the control (no
onion) added. These initial results indicated that the
blood measurements could usefully be divided into two
groups. These were: (1) all blood measurements other
than lipid biochemistry measurements, where there was
no evidence of onion-type effects (P. 0·05); (2) lipid bio-
chemistry measurements, where there was often evidence
of onion-type effects (P, 0·05).
For lipid biochemistry measurements (Table 2), with the
exception of cholesterol, there was no evidence of any
difference between the 10 and 25 g onions/MJ DE doses
(P. 0·01). The results are thus tabulated as the means of
each type of onion as well as the mean of no onion. For
the haematology measurements (Table 3) the main effects
of two onion doses (0, 10 and 25 g onions/MJ DE) are
tabulated together with results of hypothesis tests for the
overall dose response and the linear component of this
response. A comparison of the onion type within 10 and
25 g onions/MJ DE dose levels is also presented. In
every analysis, a residual was used that allowed for the
effect of all five treatments, as well as a blocking effect.
Results showing the interactions between bleeding time
and week-to-week variation as well as effects of dietary
onions on oxidative capacity of serum are presented else-
where (NK Gabler, E Ostrowska, SJ Sterling, BG
Tatham, RB Jones, DR Eagling, M Jois and FR Dunshea,
unpublished results).
Results
The DM contents of the onions used in this study were 97·5
and 127·5 g/kg for cavalier and destiny varieties respect-
ively. Total CSO was 23 % higher in destiny than cavalier
onions, although this difference was not significant
(P¼0·16, Table 4). Of the three major CSO found in
onions, S-methyl-CSO and S-propyl-CSO were signifi-
cantly higher (P, 0·05) in destiny compared with cavalier
onions. Indeed, for the cavalier variety, S-propyl-CSO was
undetectable. S-propenyl-CSO was the major CSO found in
both onion varieties and there was no difference in S-pro-
penyl-CSO levels between the two varieties. The variety
destiny had a 38 % higher quercetin aglycone content
than cavalier (P, 0·05, Table 4).
All pigs offered onions remained in good health through-
out the experimental period. No signs of toxicity were
observed and onion consumption had no effect on growth
rate (830 v. 860 g/d for control and onion-supplemented
pigs respectively, P¼ 0·49) or feed intake (1816 v. 1807 g
DM/d respectively, P¼0·90). Overall, dietary onion
Table 2. The effect of two onion (Allium cepa) varieties on blood biochemistry*
(Mean values)
Onion variety Statistical significance of effect
Plasma concentration Control Cavalier Destiny
SED† Overall‡ Onion§
Cholesterol (mmol/l)k 2·71 2·52 2·44 0·13 0·15 0·073
Glucose (mmol/l)k 5·70 5·88 5·98 0·22 0·46 0·26
LDL (mmol/l)k{ 1·65 1·56 1·51 0·10 0·21 0·52
HDL (mmol/l)k 1·09 0·95 0·97 0·06 0·35 0·032
LDL:HDLk 1·54 1·66 1·57 0·08 0·32 0·15
TG (mmol/l)k 0·68 0·63 0·50 0·07 0·042 0·12
TG after (mmol/l)** 0·78 0·79 0·60 0·07 0·0067 0·18
TG before (mmol/l)†† 0·57 0·48 0·41 0·09 0·25 0·16
TG, triacylglycerol.
* For details of diets and procedures, see Table 1 and p. 212.
†
SED for control v. cavalier or destiny;forcavalier v. destiny and control v. pooled onion, multiply the SED by 0·817 and 0·888 respectively.
‡ P value for overall comparison of control v. cavalier v. destiny.
§ P value for comparison of control v. pooled onion.
k Mean of values taken in fasting and non-fasting states after 4 and 6 weeks of feeding (results were pooled across doses of each onion variety).
{ VLDL, intermediate-density lipoprotein and LDL concentration calculated by subtracting the HDL from total cholesterol concentration.
** Mean of values taken from non-fasting pigs after 4 and 6 weeks of onion feeding (results were pooled across doses of each onion variety).
†† Mean of values taken from fasting pigs after 4 and 6 weeks of onion feeding (results were pooled across doses of each onion variety).
Brown onions and haemostatic variables 213
supplementation tended to decrease circulating cholesterol
(2 9%, P¼0·073, Table 2). However, there was an inter-
action of onion dose £ type of onion, such that mean fast-
ing and postprandial plasma cholesterol measures were
decreased by 14 % at the low, but not at the high, intake
of cavalier onions, while plasma cholesterol was decreased
by 6 and 14 % (P¼0·009) at the low and the high intakes of
destiny onions respectively (mmol/l: control 2·71, low dose
of cavalier 2·29, high dose of cavalier 2·73, low dose of
destiny 2·55, high dose of destiny 2·33;
SED 0·15).
There was no apparent difference in plasma cholesterol
concentration between fasting and non-fasting states (2·53
v. 2·52 mmol/l respectively, P¼0·71). The mean HDL con-
centration was significantly lower (P¼0·032) in pigs that
consumed diets supplemented with onions, while LDL con-
centration was unaffected (P¼0·52). The LDL:HDL ratio
was unchanged by onion consumption (Table 2).
While overall plasma TG concentrations were not
significantly affected by dietary onion consumption
(Table 2), there was a significant (P, 0·001) interaction
in the response to different onion types and the nutritional
state of the pigs. Plasma TG concentrations were reduced
in the 3 h postprandial measurements for pigs fed destiny
but not cavalier onions (0·78 v. 0·79 and 0·60 mmol/l for
control, cavalier and destiny respectively, P¼0·0067).
Conversely, the TG concentrations were not significantly
different in fasting animals fed the different diets. There
was no difference in the plasma glucose concentrations
between pigs fed the different onion varieties or between
onion-fed and control pigs (Table 2).
The plasma erythrocyte number was reduced linearly in
response to the increased amount of onion in the diet
(P¼0·0004, Table 3). Consequently, mean Hb concen-
tration was decreased in a dose-dependent manner
(P¼0·046); however, the overall comparison of control
with low or high onion doses was not significantly different
(P¼0·13). The mean erythrocyte cell volume was higher
(P¼0·016) in pigs that consumed onions compared with
the control group.
Pigs that consumed low doses of onion, regardless of the
onion variety, had higher eosinophil, lymphocyte and total
white blood cell numbers (P¼0·034, P¼0·020 and
Table 3. The effect of onion (Allium cepa) dose on haematology and measures of immunity*
(Mean values)†
Dose (g/MJ DE) Statistical significance of effect
01025
SED‡ Linear§ Overallk
Erythrocytes (10
12
/l) 7·78 7·13 6·50 0·29 0·00040 0·0015
Hb (g/l) 134 131 124 4 0·046 0·13
MCV (fl) 53·6 55·9 59·8 2·0 0·0045 0·016
MCHC (pg) 17·3 18·1 19·2 0·8 0·028 0·083
PCV (l/l) 0·403 0·398 0·388 0·013 0·20 0·42
Basophils (10
9
/l) 0·38 0·34 0·38 0·06 0·82 0·80
Eosinophils (10
9
/l) 0·46 0·62 0·44 0·09 0·24 0·034
Lymphocyte activation{ 1·9 1·7 1·5 0·1 0·00081 0·0029
Lymphocytes (10
9
/l) 8·5 11·3 9·7 1·0 0·87 0·020
Monocytes (10
9
/l) 1·36 1·39 1·19 0·17 0·21 0·35
Neutrophil:lymphocyte ratio 0·61 0·43 0·49 0·08 0·39 0·068
Segmented neutrophils (10
9
/l) 5·1 4·6 4·4 0·4 0·096 0·23
WBC (10
9
/l) 15·7 18·3 16·1 1·1 0·46 0·016
DE, digestible energy; MCV, mean corpuscular volume; MCHC, mean corpuscular Hb concentration; PCV, packed cell volume; WBC, white blood cells.
* For details of diets and procedures, see Table 1 and p. 212.
† Mean of values taken in fasting and non-fasting states at 4 and 6 weeks of feeding (for each dose, results were pooled across both onion varieties).
‡
SED for control v. 10 or 25 g onion/MJ DE; for a comparison between 10 or 25 g onion/MJ DE, multiply the SED by 0·817.
§ P value for linear effect of dose of onion.
k P value for overall comparison of control v. 10 or 25 g onion/MJ DE.
{ Lymphocyte activation measured as slight (score 1), moderate (score 2) and high (score 3).
Table 4. Cysteine sulfoxide (CSO) and quercetin contents (mg/g fresh weight for Allium cepa var. cavalier and destiny)*
(Mean values and standard deviations for analysis of three onions picked at random)
Cavalier Destiny
Onion variety... Mean
SD Mean SD Statistical significance of effect: P
S-methyl-CSO 0·17 0·05 0·27 0·06 0·049
S-propenyl-CSO 0·71 0·17 0·72 0·16 0·92
S-propyl-CSO ND† 0·15 0·10 –
Total CSO 0·88 0·22 1·14 0·23 0·16
Quercetin 0·22 0·02 0·48 0·04 0·013
ND, not detected.
* For details of procedures, see p. 212.
† Detection limit about 0·07 mg/g; the DM contents for cavalier and destiny onions were 97·5 and 127·5 g/kg respectively.
E. Ostrowska et al.214
P¼0·016 respectively) compared with the control pigs
(Table 3). The lymphocyte activation decreased as the
dose of onion increased, resulting in a significant linear
effect (P¼0·00081). For all haematology measures there
was no difference in the response between the two onion
varieties (Table 3).
The effect of onion supplementation on measures of
blood clotting resulted in a small, but non-significant
(P¼0·15) increase in prothrombin time in pigs fed
onions, but no effect on activated partial prothrombin
time (Table 5). The blood fibrinogen concentration and pla-
telet number were unaffected by onion consumption. The
measures of blood coagulation were not affected by
onion variety (P. 0·10) with the exception of the mean
plasma TXB
2
concentration, which was significantly
higher (P¼0·030) in pigs fed cavalier but not destiny
onions compared with the control pigs.
Discussion
In general, consumption of raw brown onions was found to
moderately modulate blood lipids and haematological vari-
ables in healthy pigs, but the responses varied between the
two onion varieties and between doses of onions. In
addition, differences in the response to consumption of
onion were also evident between fasted and non-fasted
states. For example, the postprandial TG measurements
in pigs fed destiny onions were approximately 23 %
lower than in control pigs or the pigs fed cavalier
onions, while fasting measurements were not significantly
affected by onion consumption (Table 2). Postprandial
measurements of TG levels are useful, as they might
reveal a state of fat intolerance that cannot be detected
by the simple measurement of fasting plasma TG (Karpe,
1999). Therefore, these results suggest that the consump-
tion of destiny onions, at both doses investigated, resulted
in beneficial changes in plasma postprandial TG concen-
trations. This may lead to reduced risk of CHD and ather-
ogenesis (Zilversmit, 1979; Patsch et al. 1992).
Unlike TG, there was no significant difference between
fasting and postprandial measurement of plasma choles-
terol, which is in agreement with results from studies
with human subjects (Cohn et al. 1988). However,
onion consumption resulted in a 9 % lower plasma total
cholesterol concentration (mean fasting and postprandial
measurements) compared with the control group. There
was a more pronounced effect in pigs fed destiny onions,
where a linear decrease in plasma cholesterol in response
to dose was observed. The HDL-cholesterol fractions
were reduced in response to onion supplementation; how-
ever, the LDL:HDL ratio was unaffected. This suggests
that the removal of cholesterol from the circulation was
not enhanced, and it is likely that the cholesterol-lowering
action of destiny onions was due to a reduction in choles-
terol synthesis.
Despite similarities between pigs and human subjects,
there are some differences in lipoprotein metabolism that
must be considered. Pig blood contains lower cholesteryl
ester transfer protein activity and cholesteryl ester for-
mation than human subjects (Chapman, 1986) and treat-
ments that affect lipoprotein metabolism might have a
different impact on the levels of HDL in pigs than in
human subjects (Knipping et al. 1987). Second, LDL-
ApoB originates from VLDL catabolism in human sub-
jects, whereas it is synthesised de novo in pigs (Birchbauer
et al. 1992). Therefore, the extrapolation of these data to
adult human subjects should be treated with caution.
While the mechanisms responsible for the lowering of
lipid due to onion consumption are not clear, it has been
suggested that Allium compounds (possibly CSO and thio-
sulfinates) decrease synthesis or increase excretion of lipids
through the intestinal tract (Ali et al. 2000; Bok et al.
2002). Various garlic extracts have also been shown to
decrease the activities of NADPH-producing enzymes
and of fatty acid synthetase when fed to rats (Chi, 1982;
Chi et al. 1982), chickens (Qureshi et al. 1983b) and
pigs (Chi, 1982; Chi et al. 1982; Qureshi et al. 1983a,
1987). However, garlic extracts are generally more potent
than onion extracts. This is due to differences in the
levels and types of S compounds, which are present in
far lower concentrations in onions than in garlic. For
example, thiosulfinates are proposed to exist in garlic at
100 times the concentration found in onions (Mandon
et al. 2000).
In addition to the lipid-modulating effects of onion,
changes in blood cell counts were also evident. Raw
onion consumption reduced both erythrocyte numbers
and Hb concentrations (Table 3), although clinical anaemia
was not evident and the measures were within the normal
range for pigs (Pond & Houpt, 1978). Reductions in
Table 5. The effect of onion (Allium cepa) dose on coagulation profile of pig blood*
(Mean values)†
Onion variety Statistical significance of effect
Control Cavalier Destiny
SED‡ Overall§
APTT (s) 22·3 22·1 23·7 1·1 0·10
Fibrinogen (g/l) 1·02 0·95 0·98 0·08 0·68
PT (s) 13·9 14·1 14·4 0·2 0·15
TXB
2
(pg/ml) 19·8 23·2 19·6 1·9 0·030
Platelets (10
9
/l) 415 391 380 30 0·66
APTT, activated partial prothrombin time; PT, prothrombin time; TBX
2
, thromboxane B
2
.
* For details of diets and procedures, see Table 1 and p. 212.
† Mean of values taken in fasting and non-fasting states at 4 and 6 weeks of feeding.
‡
SED for control v. cavalier or destiny onion; for a comparison between onion varieties, multiply the SED by 0·817.
§ P value for overall comparison of control v. cavalier or destiny onion.
Brown onions and haemostatic variables 215
haematocritic measurements have also been observed in
placebo-controlled studies with human subjects using
encapsulated onion (Kalus et al. 2000; Mayer et al.
2001). Onion consumption has been shown to induce
acute haemolytic anaemia in sheep (Kirk & Bulgin,
1979), horses (Pierce et al. 1972), cattle (Rae, 1999; van
der Kolk, 2000), dogs (Spice, 1976) and cats (Kobayashi,
1981), largely due to the presence of onion disulfides:
these generate H
2
O
2
in the presence of Hb and glutathione
S-transferase within intact erythrocytes (Munday et al.
2003). It has been suggested that the resulting haemolysis
is of the oxidative type and occurred due to removal of
damaged erythrocytes by cells of the reticulo-endothelial
system (Munday et al. 2003). Although the erythrocyte
concentrations were decreased linearly by onion consump-
tion in the present study, there was a compensatory
increase in cell volume and the amount of Hb per cell,
which implies an increased O
2
-carrying capacity per eryth-
rocyte. The excessive consumption of onions should be
avoided, especially by individuals with anaemia or those
whose erythrocytes are unusually vulnerable to oxidative
damage (Munday et al. 2003).
Reductions in haematocritic measures appeared to
stimulate an immune response in the pigs as evident by
the increase in white blood cell numbers, mainly due to
increased lymphocyte concentrations in pigs that consumed
onions (Table 3). Moreover, blood from pigs fed onion-
supplemented diets exhibited decreased lymphocyte acti-
vation, which is often associated with reduced cholesterol
accumulation and the reduction in formation of athero-
sclerotic plaques (Hansson, 1994).
Surprisingly, the measures of clotting mechanisms such
as prothrombin time, activated partial prothrombin time,
platelet count and fibrinogen level were largely unaffected
by onion consumption (Table 5). Other studies that inves-
tigated the effects of garlic consumption have shown
increased bleeding and clotting times (Gadkari & Joshi,
1991). Similarly, raw juice from shoots of Welsh onion
(Allium fistulosum) fed to rats for 4 weeks at a dose of
2 g/kg per d significantly increased tail bleeding time and
lowered systolic blood pressure (Chen et al. 2000). How-
ever, as these authors pointed out, the green shoots of the
onion are more potent than the bulb.
Plasma TXB
2
was significantly increased in pigs fed
cavalier but not destiny onions (Table 5). Previous obser-
vations have shown that raw garlic extracts significantly
decrease rabbit serum TXB
2
levels, while onion extracts
were found to be ineffective (Ali et al. 1999). Similarly,
in human subjects, consumption of 70 g raw onion/d,
which is equivalent to the low dose of onion administered
to the pigs in the present study, had no effect on serum
TXB
2
levels after 7 d of consumption (Srivastava, 1989).
The differences across studies are possibly related to the
differences in the level and type of organosulfur com-
pounds in garlic and onion, and these are known to mediate
eicosanoid metabolism (Ali et al. 2000).
Many of the biochemical effects of dietary onion con-
sumption have been largely ascribed to CSO, which are
abundant in intact onion bulbs. Garlic bulbs contain
mainly allyl-CSO and to lesser extent S-methyl-CSO,
whereas S-propenyl-CSO is the predominant S compound
in onion (Keusgen et al. 2002). Analysis of CSO in the
onions used in the present study showed that there was
little difference in total CSO between the two onion var-
ieties, but destiny had significantly higher levels of
S-methyl-CSO and S-propyl-CSO than cavalier (Table 4).
Since S-methyl-
L-CSO was found to be one of the factors
responsible for suppressing hypercholesterolaemia in the
hepatoma-bearing rat (Komatsu et al. 1998), it is possible
that the differences between responses to different onion
treatments in the present study are due to these compounds.
Another possibility for the plasma lipid and haematological
changes could result from thiosulfinates, which are the pro-
ducts of enzymatic degradation of sulfoxide compounds
upon ingestion by human subjects and animals (Earl &
Smith, 1983). Finally, it is likely that changes observed in
the present study are due to a combination of S and flavonol
compounds found in onions, of which flavonols have also
been shown to be biologically active (Taucher et al. 1996).
Flavonols have been shown to affect cholesterol synthesis
and reduce thrombotic tendencies (O’Reilly et al. 2000;
Giugliano, 2000). Quercetin is the dominant flavonol in
onions, with levels up to 490 mg/kg fresh weight (Hollman
& Arts, 1994). The quercetin contents of both varieties of
onions fed to the pigs in the present study were in the
range reported in literature, but was significantly higher in
the destiny onions. Therefore, the variation in quercetin
levels may also be responsible for some of the health bene-
fits observed in the present study. Further work needs to be
conducted to elucidate the effect of different CSO and flavo-
noid compounds in onions to identify which are responsible
for the observed biological responses in the pig.
Conclusion
The present study has shown that onions have functional
properties with the ability to modify lipid metabolism and
stimulate the immune system. However, the differences in
the responses observed in the present study demonstrate
the complex interaction between the onion dose and type
of onion, which may be due to the differences in the
amount of active compounds. The identification of specific
compounds in different onion cultivars and agronomic
practices would lead to a better understanding of the phys-
iological responses to onion consumption. This would aid
the development of onion production systems that provide
an increased health benefit and the development of guide-
lines for the consumption of these compounds.
Acknowledgements
The authors would like to thank Lewis Lydon (Enzazaden
Australia Ltd, Narrowmine Research Station, Narrowmine,
NSW, Australia) for sourcing the onions and Michael
Imsic (IHD, Knoxfield, Victoria, Australia) for assistance
with the HPLC analysis.
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