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Avenanthramides and Phenolic Acids from Oats Are Bioavailable and Act Synergistically with Vitamin C to Enhance Hamster and Human LDL Resistance to Oxidation


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The intake of phenolic acids and related polyphenolic compounds has been inversely associated with the risk of heart disease, but limited information is available about their bioavailability or mechanisms of action. Polyphenolics, principally avenanthramides, and simple phenolic acids in oat bran phenol-rich powder were dissolved in HCl:H(2)O:methanol (1:19:80) and characterized by HPLC with electrochemical detection. The bioavailability of these oat phenolics was examined in BioF1B hamsters. Hamsters were gavaged with saline containing 0.25 g oat bran phenol-rich powder (40 micromol phenolics), and blood was collected between 20 and 120 min. Peak plasma concentrations of avenanthramides A and B, p-coumaric, p-hydroxybenzoic, vanillic, ferulic, sinapic, and syringic acids appeared at 40 min. Although absorbed oat phenolics did not enhance ex vivo resistance of LDL to Cu(2+)-induced oxidation, in vitro addition of ascorbic acid synergistically extended the lag time of the 60-min sample from 137 to 216 min (P < or = 0.05), unmasking the bioactivity of the oat phenolics from the oral dose. The antioxidant capability of oat phenolics to protect human LDL against oxidation induced by 10 micromol/L Cu(2+) was also determined in vitro. Oat phenolics from 0.52 to 1.95 micromol/L increased the lag time to LDL oxidation in a dose-dependent manner (P < or = 0.0001). Combining the oat phenolics with 5 micromol/L ascorbic acid extended the lag time in a synergistic fashion (P < or = 0.005). Thus, oat phenolics, including avenanthramides, are bioavailable in hamsters and interact synergistically with vitamin C to protect LDL during oxidation.
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Nutrient Metabolism
Avenanthramides and Phenolic Acids from Oats Are Bioavailable and Act
Synergistically with Vitamin C to Enhance Hamster and Human LDL
Resistance to Oxidation
Chung-Yen Chen, Paul E. Milbury, Ho-Kyung Kwak, F. William Collins,* Priscilla Samuel,
and Jeffrey B. Blumberg
Antioxidants Research Laboratory, Jean Mayer U.S. Department of Agriculture Human Nutrition Research
Center on Aging, Tufts University, Boston, MA; *Eastern Cereal and Oilseed Research Centre, Agriculture
and Agri-Food Canada, Ottawa, Canada; and
John Stuart Research Laboratories, The Quaker Oats
Company, Barrington, IL
ABSTRACT The intake of phenolic acids and related polyphenolic compounds has been inversely associated with
the risk of heart disease, but limited information is available about their bioavailability or mechanisms of action.
Polyphenolics, principally avenanthramides, and simple phenolic acids in oat bran phenol-rich powder were
dissolved in HCl:H
O:methanol (1:19:80) and characterized by HPLC with electrochemical detection. The bioavail-
ability of these oat phenolics was examined in BioF1B hamsters. Hamsters were gavaged with saline containing
0.25 g oat bran phenol-rich powder (40
mol phenolics), and blood was collected between 20 and 120 min. Peak
plasma concentrations of avenanthramides A and B, p-coumaric, p-hydroxybenzoic, vanillic, ferulic, sinapic, and
syringic acids appeared at 40 min. Although absorbed oat phenolics did not enhance ex vivo resistance of LDL to
-induced oxidation, in vitro addition of ascorbic acid synergistically extended the lag time of the 60-min
sample from 137 to 216 min (P 0.05), unmasking the bioactivity of the oat phenolics from the oral dose. The
antioxidant capability of oat phenolics to protect human LDL against oxidation induced by 10
mol/L Cu
also determined in vitro. Oat phenolics from 0.52 to 1.95
mol/L increased the lag time to LDL oxidation in a
dose-dependent manner (P 0.0001). Combining the oat phenolics with 5
mol/L ascorbic acid extended the lag
time in a synergistic fashion (P 0.005). Thus, oat phenolics, including avenanthramides, are bioavailable in
hamsters and interact synergistically with vitamin C to protect LDL during oxidation. J. Nutr. 134: 1459 –1466,
Studies showing an inverse association between the intake
of polyphenolic compounds, particularly flavonoids from fruits
and vegetables, and cardiovascular disease risk suggest that a
beneficial effect may be observed from other foods containing
these compounds (1–3). For example, polyphenolics have
been identified in several grains, including wheat, rice, corn,
and oats (4). These phytochemicals have a range of biological
activities, including antiatherosclerotic, anti-inflammatory,
and antioxidant effects (5). Similar to their actions in other
foods, simple phenolic acids and polyphenolic compounds
from oats (referred to here as oat phenolics) may serve as
potent antioxidants via scavenging reactive oxygen and nitro-
gen species and/or by chelating transition minerals both in
plants and in those animals that consume them (6).
Because most phenolics are located in the bran layer of
grains (7), oats (Avena sativa L.), which are normally con-
sumed as whole-grain cereal, could be a significant dietary
source of these compounds (8). Several oat phenolics have
been identified, including ferulic acid, caffeic acid, p-hydroxy-
benzoic acid, p-hydroxyphenylacetic acid, vanillic acid, proto-
catechuic acid, syringic acid, p-coumaric acid, sinapic acid,
tricin, apigenin, luteolin, kaempferol, and quercetin (9,10).
These oat phenolics are present as free or simple soluble esters
and, to a greater extent, as complex insoluble esters with
polysaccharides, proteins, or cell wall constituents (6,8). In
addition, Collins (11) isolated and characterized a group of
cinnamoylanthranilate alkaloid oat polyphenols, called ave-
nanthramides, which appear to be unique to oats.
The antioxidant capacity of oat phenolics was demon-
strated via in vitro studies (12–15). However, few studies have
explored the in vivo activity of oat phenolics. Hulless (“na-
Presented in part at Experimental Biology 02, April 2002, New Orleans, LA
[Chen, C.-Y., Milbury, P, O’Leary, J., Collins, F. W. & Blumberg, J. (2002)
Synergy between oat polyphenolics and
-tocopherol in prevention of LDL oxi-
dation. FASEB J. 16: A1106 (abs.)].
Supported by the U.S. Department of Agriculture (USDA) Agricultural Re-
search Service under Cooperative Agreement No. 58 –1950-00; the Agriculture
and Agri-Food Canada Matching Investment Initiative Program agreement No.
A01989, ECORC contribution No. 03–330; and The Quaker Oats Company. The
contents of this publication do not necessarily reflect the views or policies of the
USDA nor does mention of trade names, commercial products, or organizations
imply endorsement by the U.S. government.
To whom correspondence should be addressed.
0022-3166/04 $8.00 © 2004 American Society for Nutritional Sciences.
Manuscript received 9 December 2003. Initial review completed 29 January 2004. Revision accepted 1 March 2004.
ked) oats fed to cows resulted in a greater stability of their
milk against oxidative degradation (16). Similarly, carcasses of
broiler chickens fed oats or hulless oats had a lower content of
lipid peroxidation products (17,18). However, the antioxidant
capacity of serum was not affected in people consuming an oat
milk product (19).
To date, no studies have explored directly the bioavailabil-
ity of oat phenolics and their subsequent effect on antioxidant
activity. Therefore, we conducted this study with the following
goals: 1) to measure the bioavailability of oat phenolics using
a hamster model; 2) to determine the in vivo effect of absorbed
oat phenolics on the antioxidant capacity of hamsters; and 3)
to test in vitro the effect of oat phenolics on the resistance of
human LDL to oxidation and its potential interactions with
vitamin C in this system.
Chemicals and reagents. The following reagents were obtained
from Sigma Chemical: copper sulfate,
-tocopherol, sodium chloride,
p-hydroxybenzoic acid, syringic acid, p-coumaric acid, vanillin,
vanillic acid, ferulic acid, sinapic acid, sodium phosphate monobasic,
sodium phosphate dibasic, Folin Ciocalteus phenol reagent, and
-glucuronidase type H-2 (containing sulfatase). All organic sol-
vents, glacial acetic acid, ascorbic acid, and potassium bromide were
purchased from Fisher Scientic. Food-grade ascorbic acid was from
Mallinckrodt, and lithium hydroxide was from Fluka.
Production of oat bran phenol-rich powder. Oat bran was col-
lected from hulless oats passed 3 times through a Satake Rice Ma-
chine (type RMB, Satake Engineering). The nal weight removed
was 20% of the original hulless oats. The oat bran was extracted twice
with ethanol:water (80:20, v:v) for2hat35°C with continuous
agitation. The extraction slurry was centrifuged at 1250 g (Invert-
ing Filter Centrifuge, Model HF-600.1, Heinkel Filtering Systems, 5
mm-bag) to provide the supernatant. Food-grade ascorbic acid was
added to the supernatant as a processing aid preservative, but was
removed during late processing. The supernatant was vacuum con-
centrated (Alfa-Laval, Model 6 2) at 35 40°C to a thick oat bran
extract and then lyophilized (Virtis Model 50-SRC-6, Virtis) to an
oat bran phenol-rich powder and stored at 20°C until use.
Measurement of phenolics from oat bran phenol-rich powder.
Oat phenolics in oat bran phenol-rich powder were dissolved in
O:methanol (1:19:80). After centrifugation at 11,000 g for
10 min, an aliquot of the supernatant was dried under puried
nitrogen. The residue was reconstituted with the aqueous mobile
phase, and the oat phenolics prole was characterized by HPLC
equipped with electrochemical detection (ECD)
according to Mil-
bury (20). The quantity of individual oat phenolics was calculated
according to concentration curves constructed with authenticated
phenolic acid standards and with pure avenanthramide A and B.
Phenolic esters were not determined in this study. The total phenolic
content of the oat bran powder was also determined using the
Folin-Ciocalteu reaction against a gallic acid standard curve and
expressed as molar equivalents of gallic acid (21).
Animals. BioF1B strain Golden Syrian Hamsters (n 30; Bio-
Breeders), 1 y old, mean body weight 156.7 12.7 g, were housed in
cages with a 10-h:14-h light:dark cycle. Hamsters were used due to
the similarity of their lipoprotein metabolism to that of humans (22).
To increase lipoprotein formation for subsequent collection, hamsters
consumed ad libitum a nonpuried diet (Harlan) enriched with 10 g
coconut oil and 0.5 g cholesterol/100 g diet for 2 wk before the acute
oat phenolics feeding experiments (23).
After overnight food deprivation, 30 hamsters were randomly
assigned on the basis of their body weight into 6 time point groups:
0, 20, 40, 60, 80, and 120 min. A slurry with 250 mg oat bran
phenol-rich powder containing 40
mol phenolics (6.8 mg) was
delivered in 1.0 mL of 0.154 mol/L saline via stomach gavage to
hamsters anesthetized with Aerrane (Baxter). The same volume of
saline was given to hamsters in the baseline control group. The
estimated daily polyphenolic intake for a 70-kg body person is 14
mg/kg (24). We chose a dose of 45 mg/kg body weight (40
mol oat
phenolics/per hamster) because rodents consume 5 6 times more
food-based energy than humans on a body weight basis (25). Blood
samples from each hamster were collected into tubes containing
EDTA via orbital bleeding at selected time points. Plasma samples
were collected after whole blood was centrifuged at 1000 g for 15
min at 4°C. Two aliquots of plasma were stored at 80°C for
determination of oat phenolics and antioxidant capacity; the remain-
der was used immediately for analysis of LDL oxidation. This study
was approved by the Animal Care and Use Committee of the Jean
Mayer USDA Human Nutrition Research Center on Aging at Tufts
Analysis of plasma oat phenolics. Oat phenolics in plasma were
measured via HPLC-ECD (20). Briey, 20
L vitamin C-EDTA
(1.136 mmol ascorbic acid plus 3.42
mol EDTA in 1 mL of 0.4
mol/L NaH
) and 20
L glucuronidase were added to 200
plasma, and the mixture was incubated at 37°C for 45 min. Oat
phenolics were extracted with acetonitrile; the 500-
L supernatant
was removed after centrifugation at 14,000 g for 5 min, dried under
puried nitrogen, and reconstituted in 100
L of the aqueous HPLC
mobile phase. After centrifugation at 14,000 g for 5 min, the 50-
supernatant was injected into the HPLC for analysis of oat phenolics.
Quantication was accomplished using authenticated standards that
were spiked into human plasma and processed through the extraction
procedure. An internal standard was not used in this study to calcu-
late the recovery rate or for quantication; rather, spiked authenti-
cated standards were used in constructing standard curves that ac-
count for extraction losses. We observed an 80% recovery rate for the
internal standard (2,3,4-trihydroxyacetophenone), which has char-
acteristics similar but not identical to the oat phenolic compounds of
interest; the recovery rate did not always parallel the recovery rates of
authenticated oat phenolic standards during the extraction procedure
(data not shown).
Ex vivo antioxidant capacity of oat phenolics. Absorbed oat
phenolics were tested ex vivo to characterize their antioxidant effect
on the resistance of hamster LDL to Cu
-induced oxidation accord
ing to a slight modication of the method described by Esterbauer et
al. (26). Briey, LDL was separated from the plasma according to
Chung et al. (27) using a Beckman NVT-90 rotor in a Beckman
L8-mol/L centrifuge. Salt and EDTA were removed from the sample
using a PD-10 column (Amershan Pharmacia Biotech). LDL protein
was determined using a BCA protein assay kit (Pierce). Because LDL
content in hamster plasma is less than that found in human plasma,
91 nmol/L LDL was oxidized by 5
mol/L CuSO
with or without the
addition 5
mol/L ascorbic acid in a total volume of 1.0 mL phos-
phate buffer (pH 7.4). Formation of conjugated dienes was monitored
by absorbance at 234 nm at 37°C over 6 h using a Shimadzu UV1601
spectrophotometer equipped with a 6-position automated sample
changer. The results of the LDL oxidation were expressed as lag time
(dened as the intercept at the abscissa in the diene-time plot) (28).
The total antioxidant capacity of the plasma was measured with the
oxygen radical absorbance capacity (ORAC) assay according to a
slight modication of the method described by Huang et al. (29).
Synergistic relationship of oat phenolics and vitamin C in the in
vitro human LDL oxidation. Because the amount of LDL available
from hamsters is limited, human LDL was used to conrm the
observed synergistic relation between oat phenolics and vitamin C.
An added benet of using human LDL in this assay is the extension
of the results in an animal model to future applications for clinical
evaluations. Venous blood was obtained at 1400 h from nonfasting
healthy adult Caucasian women (n 6), 28 64 y old, with a mean
body weight of 63 15 kg, and plasma immediately separated after
centrifugation as described above. LDL samples from the rst 3
subjects were used to assess the dose-response relation of oat pheno-
lics and from the last 3 subjects for experiments on the interaction
between oat phenolics and vitamin C. All LDL experiments were
performed on 3 subjects in duplicate. The kinetics of LDL oxidation
Abbreviations used: C
, maximal concentration; ECD, electrochemical
detector; ORAC, oxygen radical absorbance capacity; pca, perchloric acid
treated; RT, retention time; TE, Trolox equivalent; T
, time to maximal concen
were monitored after the addition of 10
mol/L CuSO
to 182
nmol/L LDL protein in a total volume of 1.0 mL phosphate buffer
(pH, 7.4) and the formation of conjugated dienes monitored as
described above. An aliquot of oat phenolics in acidied methanol
was dried under nitrogen and redissolved in an equal volume of
phosphate buffer (pH 7.4) for testing in the assay. The lowest con-
centration of oat phenolics (0.52
mol/L) used in the in vitro LDL
oxidation experiment was selected because it consistently extended
the lag time. Additional concentrations of oat phenolics were se-
lected to reect the concentrations observed in the plasma from the
hamster study described above. Oat phenolics were incubated with
182 nmol/L LDL at 37°C for 30 min before initiation of oxidation.
When used in the assay, ascorbic acid was dissolved in PBS and added
to the reaction immediately before initiation of oxidation. The effect
of oat phenolics and ascorbic acid on the resistance of LDL against
oxidation was expressed as the lag time increase compared with the
lag time of LDL without the addition of oat phenolics or vitamin C.
Statistics. All results are reported as means SD. The Tukey-
Kramer honestly signicant difference (HSD) test was used after
signicant differences were obtained by one-way ANOVA in exper-
iments on plasma phenolics in hamsters, ex vivo and in vitro hamster
LDL oxidation, and in vitro human LDL oxidation. When variance
was unequal, Hartleys test (30) was used and data (including that for
ferulic and sinapic acids) were square roottransformed before
ANOVA. A paired t test was performed to determine the signicance
of the synergy between oat phenolics and vitamin C in human LDL
oxidation by comparing the observed lag time during their coincu-
bation with the expected (calculated) sums of values observed for oat
phenolics and vitamin C treatments alone. Differences with P 0.05
were considered signicant. The JMP IN 4 statistical software pack-
age (SAS Institute) was used to perform all statistical analyses.
The total polyphenolic content in the oat bran phenol-rich
powder was 162
mol gallic acid equivalents/g as determined
by the Folin-Ciocalteu method. As revealed by a typical
HPLC-ECD chromatogram, there were 30 peaks with de-
tectable redox potential (Fig. 1). We identied and quantied
9 phenolics in oat bran phenol-rich powder (in descending
order of concentration) as: avenanthramide A (2.50
avenanthramide B (1.97
mol/g), vanillin (2.40
p-coumaric acid (1.28
mol/g), ferulic acid (0.64
vanillic acid (0.53
mol/g), syringic acid (0.39
mol/g), si-
napic acid (0.25
mol/g), and p-hydroxybenzoic acid (0.03
mol/g). Although oats are rich in vitamin E (8,31), none was
detectable by our HPLC method in this oat bran phenol-rich
powder because most of tocopherols and tocotrienols are lo-
cated in the germ and endosperm (31), both of which were
eliminated by abrasion milling.
Although there were numerous compounds in oat bran
phenol-rich powder, avenanthramide A and B, vanillic acid,
syringic acid, p-coumaric acid, ferulic acid, sinapic acid, and
p-hydroxybenzoic acid (not shown in the chromatogram) were
bioavailable in hamsters (Figs. 2 and 3). In addition, 2 un-
known compounds in plasma were noted at a retention time
(RT) of 17.80 and 30.95 min. Comparing the ratio observed of
oat phenolic concentrations in oat bran phenol-rich powder
and plasma, the compounds syringic, ferulic, and p-hydroxy-
FIGURE 1 HPLC-ECD prole of phenolic acids and avenan-
thramides in oat bran phenol-rich powder identied by HPLC-ECD.
Labeled peaks are: (1) p-hydroxybenzoic acid, (2) vanillic acid, (3) sy-
ringic acid, (4) p-coumaric acid, (5) vanillin, (6) ferulic acid, (7) sinapic
acid, (8) avenanthramide A, (9) avenanthramide B.
FIGURE 2 HPLC-ECD chromatographs of hamster plasma sam-
ples obtained 40 min after administration of 0.25 g oat bran phenol-rich
powder in saline, containing 40
mol phenolics (gallic acid equivalents)
and immediately after gavage with saline (baseline). (A) The 420-mV
ECD trace. (B) The 560-mV ECD trace. Labeled peaks are: (a) 17.80-min
RT compound, (2) vanillic acid, (3) syringic acid, (4) p-coumaric acid, (b)
30.95-min RT compound, (6) ferulic acid, (7) sinapic acid.
benzoic acids possessed a similar bioavailability, whereas p-
coumaric acid had at least 10% greater bioavailability (Table
1). Among identied oat phenolics, avenanthramides were
found at the highest concentration in the oat bran phenol-rich
powder but the lowest concentration in hamster plasma.
On the basis of their pharmacokinetic prole, the maxi-
mum plasma concentrations (C
)ofp-hydroxybenzoic acid,
vanillic acid, sinapic acid, syringic acid, ferulic acid, and
p-coumaric acid ranged from 0.10 to 1.55
mol/L (Fig. 4). The
for avenanthramide A and B was 0.04 and 0.03
respectively (Fig. 4). The C
of these oat phenolics and the
compound identied at 30.95 min RT was reached at 40 min
). In contrast, the compound identied at 17.80 min RT
at 80 min. At 120 min, the plasma concentrations
of these 10 compounds did not differ from the baseline refer-
Absorbed oat phenolics did not change the resistance of
hamster LDL collected at 40 and 60 min against Cu
oxidation (Fig. 5). However, after 5
mol/L ascorbic acid was
added to the assay mixture, LDL collected at 60 min had a
58% longer lag time than that collected at baseline (216 and
137 min, respectively; P 0.05). The ORAC assay for total
antioxidant capacity, expressed as
mol/L Trolox equivalent
(TE), was measured in plasma (ORAC
) and protein-pre
cipitated, perchloric acidtreated plasma (ORAC
). Ab
sorbed oat phenolics did not change the ORAC
1243 and 7079 777
mol/L TE) or ORAC
123 and 1081 171
mol/L TE) in samples collected
at baseline and 40 min, respectively.
The antioxidant activity of oat phenolics in vitro was
apparent through a dose-dependent increase in the resistance
of human LDL against Cu
-induced oxidation (P 0.0001)
(Fig. 6). The lowest concentration of oat phenolics tested for
this effect was 0.52
mol/L gallic acid equivalents which
resulted in a lag time 9.6 1.7 min greater than that of the
control absent oat phenolics. Oat phenolics doses of 0.78, 1.3,
and 1.95
mol/L further extended the lag time by 12.8 2.1,
21.8 2.4, and 37.5 3.3 min, respectively. The addition of
ascorbic acid alone at 2.5 and 5.0
mol/L increased the lag
time by 11.8 2.6 and 46.3 3.5 min, respectively (Fig. 7).
A 1-fold synergy (i.e., an observed value twice the expected
value from additive calculation) was observed with oat phe-
nolics and the 5.0
mol/L ascorbic acid dose, but no such
interaction was found with the 2.5
mol/L dose (P 0.005).
In addition to their protein and micronutrient content,
whole grains contain an array of phytochemicals that may
contribute substantially to the total intake of dietary antioxi-
dants. Although typically consumed in lower quantities than
grains such as rice and wheat, oats are normally consumed as
a whole-grain cereal; thus, the antioxidant-rich portion of the
grain is retained. Among other potential health benets, these
constituents may contribute to the reduction in risk of cardio-
vascular disease associated with whole-grain intake as found in
several observational studies (3235). Interestingly, the anti-
oxidant capacity of oats had been recognized many years ago
with their use as additives in food and beverage products to
preserve their quality (36,37).
Using HPLC-ECD to analyze phenolics of oat bran phenol-
rich powder, we identied (in descending order of concentra-
tion) avenanthramide A and B, vanillin, ferulic acid, p-cou-
maric acid, vanillic acid, syringic acid, sinapic acid, and
p-hydroxybenzoic acid. These results are consistent with those
of Peterson et al. (9) and Daniels and Martin (10). However,
caffeic acid, protocatechuic acid, tricin, apigenin, luteolin,
FIGURE 3 HPLC-ECD chromatograph of avenanthramide A (peak
8) and B (peak 9) in hamster plasma obtained immediately after a
gavage with saline (baseline, lower trace) and 40 min after administra-
tion of 0.25 g oat bran phenol-rich powder in saline, containing 40
phenolics (gallic acid equivalents) (upper trace).
Relative bioavailability of 8 phenolics in hamsters fed 40
mol total phenolics of oat bran phenol-rich powder
Oat phenolics
Oral dose
Plasma C
Plasma C
/oral dose
Apparent relative
p-Coumaric acid 0.32 1.55 0.91 4.84 2.84 100
Sinapic acid 0.06 0.26 0.38 4.30 6.30 89.5
Syringic acid 0.10 0.38 0.25 3.80 2.50 78.5
p-Hydroxybenzoic acid 0.03 0.10 0.04 3.33 1.33 68.8
Ferulic acid 0.50 1.20 1.08 2.40 2.60 49.5
Vanillic acid 0.13 0.15 0.05 1.20 0.38 23.8
Avenanthramide A 0.63 0.04 0.03 0.06 0.05 1.3
Avenanthramide B 0.49 0.03 0.02 0.06 0.04 1.3
Oral dose is the absolute amount of each phenolic compound fed to each hamster.
Values are means SD, n 5.
The ratio of plasma C
/oral dose for p-coumaric acid was arbitrarily set at 100.
kaempferol, and quercetin were not found in the oat bran
phenol-rich powder by our HPLC-ECD method. We identied
2 of the 6 reported oat avenanthramides (11,15) by HPLC-
ECD using authenticated standards. Our chromatographic re-
sults suggest that there are numerous other antioxidant phy-
tochemicals in oat bran that remain to be identied and fully
characterized, such as phenolic esters (9). The absence of free
caffeic acid and some other oat phenolics from our material, in
contrast to reports by others (9,10), is likely due to the
different methods employed to isolate these compounds, in-
cluding factors such as extraction solvent, heating, and ester-
ase activity. As noted, the oat bran phenol-rich powder em-
ployed in our studies contained no vitamin E or other tocols as
detected by HPLC and reported by Peterson (31); thus, they
are not a source of the antioxidant activity noted in our
Oat phenolics from the oat bran phenol-rich powder were
found to be bioavailable in hamsters. Ji et al. (38) recently
reported that the dietary administration of a synthetic ave-
nanthramide had an antioxidant effect in selected tissues of
exercised rats. Vanillic, p-hydroxybenzoic, sinapic, ferulic, and
p-coumaric acids from other food sources were found previ-
ously to be bioavailable (3942), but our results appear to be
the rst to identify syringic acid and avenanthramides in
plasma and suggest their bioactivity. The T
of the phenolic
acids and avenanthramides in hamsters were reached at 40
min and essentially eliminated by 120 min. p-Coumaric acid
was the most bioavailable among the identied oat phenolics.
In contrast, although the polyphenolic avenanthramides had
the greatest concentration in the oat bran phenol-rich powder,
their apparent relative bioavailability was only 5% of the least
bioavailable phenolic acid (vanillic acid). Although p-cou-
maric acid is the most bioavailable phenolic acid, the apparent
relative bioavailabilities among phenolics might be inuenced
FIGURE 4 Time course of oat
phenolic compounds in the plasma of
hamsters administered 0.25 g oat bran
phenol-rich powder in saline contain-
ing 40
mol phenolics (gallic acid
equivalents). Values are mean SD, n
5. In panels I and J,
C is the area
under the ECD trace with time. Means
in each panel without a common letter
differ, P 0.05.
by the distribution and/or biotransformation of phenolic acids
in the hamsters. For example, vanillin was the richest phenolic
acid in oat bran phenol-rich powder, but none was observed in
plasma, possibly due to its conversion to vanillic acid in vivo
(43). Because the concentrations of the oat phenolics were
measured only in plasma, it is not possible to determine from
this study to what extent these compounds were distributed to
other tissues. The C
of the unidentied 17.80- and 30.95-
min RT compounds was achieved at 80 and 40 min, respec-
tively. The 17.80-min RT compound may be a metabolite
because its T
was substantially delayed relative to other oat
phenolics, and it was not present in baseline plasma. In addi-
tion to hepatic metabolism, the biotransformation of polyphe-
nolics by colonic microora was demonstrated (44 46). In
contrast, the 30.95-min RT compound was likely produced
endogenously because it was present, albeit at a lower concen-
tration, in the baseline plasma. The identication of these
compounds could not be achieved without authenticated stan-
dards by our HPLC-ECD method; therefore, an effort is un-
derway to identify these and other oat phenolic metabolites
using HPLC-MS.
In vitro studies of ferulic, syringic, and other phenolic acids
clearly reveal the capacity of these compounds to bind to LDL
and increase its resistance against oxidation (47,48). We eval-
uated the potential antioxidant activity of the oat phenolics
using an ex vivo hamster LDL oxidation model and found no
apparent change in the lag time after induction by Cu
. This
lack of an effect might be due to an inadequate concentration
of the oat phenolics in the plasma or to their biotransforma-
tion [hepatic phase 2 enzymes have been shown to reduce the
antioxidant capacity of polyphenolics relative to their parent
compounds (49,50)]. Although these results appear in contrast
to our in vitro results with oat phenolics in human LDL, it is
important to note that the ex vivo assay reects the action of
only those bioavailable oat phenolics that remain associated
with the LDL through its isolation process.
Despite no apparent change in the resistance of LDL to
oxidation ex vivo, the oat phenolics had a subtle action on the
lipoprotein that was indicated by their interaction with vita-
min C. When ascorbic acid was added in vitro, an increase in
the lag time was observed compared with its respective con-
trol. This increase was synergistic in nature, i.e., the lag time
was greater than the calculated additive effect of the antioxi-
dants, although the mechanism for such an interaction has yet
to be elucidated. This synergistic relationship is consistent
with that reported between isoavones and vitamin C on LDL
in vitro (51). Interestingly, the synergy appears only in LDL
collected at 60 min rather than at 40 min, the T
of most of
the oat phenolics. This time difference in action may be due to
an equilibration period between peak plasma and LDL con-
FIGURE 5 Lag time to Cu
-induced oxidation of hamster LDL
obtained at 0, 40, and 60 min after administration of 0.25 g oat bran
phenol-rich powder in saline, containing 40
mol phenolics (gallic acid
equivalents) without (A) or with (B)5
mol/L ascorbic acid added in
vitro. Values are means SD, n 5. Means in the same category
without a common letter differ, P 0.05.
FIGURE 6 Effect of oat phenolics on increased lag time to Cu
induced oxidation of human LDL in vitro;182
mol/L LDL was oxidized
by 10
mol/L Cu
with addition of oat phenolics. Lag time of control
(no added oat phenolics) was 49.3 3.7 min. Values are means SD,
n 3. Means without a common letter differ, P 0.0001.
FIGURE 7 The synergistic effect of oat phenolics and vitamin C
on the increased lag time of human LDL oxidation in vitro;182
LDL was oxidized by 10
mol/L Cu
with the addition of oat phenolics,
vitamin C, or oat phenolics and vitamin C combined. Values are means
SD, n 3. Means without a common letter differ, P 0.005. Lag time
of control (no added oat phenolics or ascorbic acid) (A) was 45.5 0.7
min and (B) 47.7 1.5 min. Open bar (oat phenolics) and hatched bar
(ascorbic acid) are stacked to illustrate expected values by calculation
of the additive effect of individual ingredients. Solid bar represents the
observed effect of oat phenolics ascorbic acid. The percentage value
above the solid bar indicates the observed synergistic increase of
combined antioxidants over expected calculated values of the individ-
ual ingredients.
centrations or the duration necessary for the oat phenolics to
bind and remodel LDL conformation.
The total antioxidant activity of plasma, assessed with the
ORAC assay, was not affected by absorbed oat phenolics in
hamsters. Although high doses of some avonoids were shown
to increase ORAC values (52), this assay may not be suf-
ciently sensitive to detect the changes obtained in this study
against the background antioxidant activity contributed by
protein, urate, and other redox constituents in plasma as
suggested by Ninfali and Aluigi (53).
In addition to the hamster model, we examined the inter-
action between the oat phenolics and vitamin C on human
LDL in vitro. Oat phenolics increased the resistance of human
LDL to oxidation in a dose-dependent fashion within concen-
trations that were achieved in hamsters. Whether these con-
centrations can be achieved and maintained in humans is not
known. A synergy between the oat phenolics and ascorbic acid
was evident at selected doses of the vitamin. These results are
consistent with the observation of a synergy between isoa-
vones and ascorbic acid as reported by Hwang et al. (51) who
found as much as a 5-fold increase in lag time over the
calculated effect. We also noted a synergy between vitamin E
and phenolic compounds from almond bran (54). The mech-
anism(s) for this interaction has not been established, al-
though a regeneration of vitamins C and E by polyphenolics
was proposed as contributing to this effect (51,55). Hwang et
al. (51) also suggested that polyphenolics may stabilize the
LDL particle structure via a dynamic interaction with its
apoprotein-B domain. Further, as suggested by the absence of
an effect with our low vitamin C concentration (2.5
ascorbic acid may also contribute to a synergy via its inhibition
of the decomposition of lipid peroxides and/or prevention of
binding to LDL.
We thank Jennifer OLeary and Ting-Huang Li for their excellent
technical assistance and Mark Andon for his valuable comments on
the manuscript.
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... Awareness of the nutritional and health benefits of oat continues to increase, especially since the discovery of phytoalexins such as avenanthramides (Collins 1989) in oat groats. These phenolic compounds are reported to possess antioxidant (Emmons and Peterson 1999) and cholesterol (LDL) lowering properties (Chen et al. 2004). Minimising losses to diseases will be critical in meeting projected increases in future global demand for cereals such as oat. ...
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... 4 Phenol contents of processed cheese containing 0, 1.00, 2.50, and 5.00% oat flour F I G U R E 1 Antioxidant activity of processed cheese samples contained 0, 1.00, 2.50 and 5.00% oat flour Cai et al., 2011;Chen et al., 2004). The AVA was considered as the key antioxidant agent in oats and confirmed the prevention of lipid oxidation in food stuffs (Singh et al., 2013). ...
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Four different levels (0, 1.00, 2.50, and 5.00%) of oat flour (OF) were used to produce processed cheese to assess their impact on the antioxidant activity, mineral contents, phenol contents, physicochemical, microstructure, and sensory properties of the resulting OF processed cheese. Dry matter and pH values of processed cheese increased with increasing OF. Meltability and oil separation of cheese decreased significantly (p ≤ .05) but increased during storage. The functionality of processed cheese increased with the addition of OF and samples with OF exhibited significantly (p ≤ .05) high levels of phenols, antioxidant activity, and mineral contents. Microstructure of processed cheese indicated that the samples with added OF had a dense protein network with lower interfaces, which affect the texture of cheese compared to control. In conclusion, the added proportions 1.00 or 2.50% of oat flour in processed cheese could be successfully used to improve functionality, health benefits and nutritional quality.
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... In particular, Avenanthramide (Avn), phenolic acid, and flavonoids are the most important phenolic compounds in oats. Phenolic compounds reportedly exhibit a variety of biological activities, such as anti-allergic, antioxidant, anti-inflammatory, and anti-carcinogenic activity [3,4]. The phenolic compounds AvnA, AvnB, and AvnC have been reported to have many anti-oxidant and anti-inflammatory properties, but their role in skin whitening is unknown. ...
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The pH-driven method is a green and efficient encapsulation technology to incorporate hydrophobic polyphenols. However, this method has never been used to prepare nanoparticles loaded with multiple polyphenols of different water solubility and chemical stability. In the present study, the pH-dependent water solubility and chemical stability of quercetin and avenanthramide 2c (AV 2c) were characterized to develop a novel two-step pH-driven method to co-load quercetin and AV 2c in sodium caseinate (NaCas) nanoparticles (Q-2c-N). Quercetin-loaded NaCas nanoparticles (QNN) were fabricated by increasing the mixture to pH 12.0, followed by acidification to pH 7.0. Subsequently, AV 2c was dissolved in the QNN dispersion that was further acidified to pH 6.0 to prepare Q-2c-N. The encapsulation efficiency of quercetin and AV 2c in the Q-2c-N was up to 94.3% and 80.6%, respectively, and remained stable in 21 days at 21 °C. Based on solubility, particle structure, zeta potential, and fluorescence spectroscopy assays, molecular binding between NaCas and deprotonated quercetin was critical to quercetin encapsulation during acidification to pH 7.0, and the gradual loss of AV 2c solubility during further pH adjustment to 6.0 enabled the embedment of AV 2c in QNN to form Q-2c-N with reduced particle size. Moreover, quercetin and AV 2c were almost molecularly distributed in Q-2c-N based on XRD patterns and FT-IR spectra. Co-loading quercetin and AV 2c in Q-2c-N significantly improved the bioaccessibility and Caco-2 cell monolayer uptake. The present study may be significant to the utilization of polyphenols with distinctly different physical properties.
Ophiocordyceps sinensis is a well-known entomogenous fungus with its fruiting bodies or cultural mycelium as food and herbal medicines in Asia. While metabolites which could responsible for its potent pharmaceutical effects has long remained to be elucidated. In this work, chemical investigation on the solid culture of O. sinensis strain LY34 led to the discovery of six digalactosyldiacylglycerols (DGDGS, 1–6) including one new. The structure of compound 1 was determined based on the comprehensive spectra analysis, including NMR, MSn, IR, and chemical derivatisation. Bioactivity studies showed a weak cytotoxicity of compounds 1–6 against 293 T cell and medium anti-inflammatory activity of compounds 1 and 2 on Raw 264.7 cell. The discovery of DGDGs in O. sinensis provides new insight into the pharmacologically active substances.
A field experiment was carried out at Al-Hamidhiya research station of the College of Agriculture - University of Anbar, located within 43.39 longitude, 33.44 latitude and 53 m heights above sea level during Winter seasons 2018-2019 and 2019-2020, with aim of studying the effect of levels of potassium fertilizer, nano and mineral zinc on the yield of three oat cultivars. The split-split-plot arrangement was used according to a randomized complete block design (RCBD) with three replications. The main plots included potassium concentrations (0, 6000, 3000 nm, and 6000 nm) mg K l ⁻¹ , while the subplot included zinc concentrations (0, 50 and 50 nm) mg Zn l ⁻¹ , while the cultivars were in the sub-sub plots (Hamel, Carrolup and Genzania). The results of the study indicate that the varieties differed significantly in all studied traits. Genzania cultivar outperformed in terms of grain yield (6.25 and 6.19 ton ha ⁻¹ ) and biological yield (16.37 and 16.26 ton ha ⁻¹ ) the two seasons, respectively. In addition, spraying zinc on the plant had a positive role in improving the yield and its components, as the treatment 50 mg Zn L ⁻¹ gave grain yield of 6.24 and 6.06 tons’ ha ⁻¹ for both seasons respectively, adding potassium improved the components of the yield, which was reflected in the yield in which the treatment 6000 nm mg K L ⁻¹ was superior with seed yield of 7.05 and 6.84 ton ha ⁻¹ for the two seasons respectively. Also, the two-way interaction between the concentrations of potassium and zinc, potassium and cultivars, and zinc and cultivars had a significant effect on most of the studied traits. The three-way interaction between the study factors had a significant effect on the studied traits, which was evident in seed yield, as the combination (Genzania sprayed with 3000nm K + 50 mg Zn L ⁻¹ ) gave the highest grain yield of 8.30 for the first season, while the plants of the variety Hamel sprayed with 6000nm K + 50 mg Zn L ⁻¹ gave the highest grain yield of 7.440 ton ha ⁻¹ for the second season.
Cereals are common staples for human nutrition. They include maize, rice, wheat, barley, sorghum, millets, oats, rye, and others. Phenolic antioxidants have been reported in cereals and legumes. The characteristic color of some cereals and grains is due to a specific class of phenolic compounds. Hydroxybenzoic acids, their derivatives, cinnamic acids, aldehydes, esters and alcohols, flavonoids, anthocyanins, and tannins have been reported in significant amounts in cereals and grains. The antioxidant properties of grains were due to the presence of these phenolic compounds, which play a significant antioxidants role, using their properties of radical scavenging and/or chelation of metals.
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The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is ∼1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 μM after the consumption of 10–100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.
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To test the feasibility of dry milling oats (Avena sativa L.) to concentrate antioxidant activity and phenolic antioxidants, groats were pearled for 5 to 180 s. These treatments removed <1 to 15% of the weight. The material obtained from short pearling times was mostly bran. Longer pearling times increased the amount of starchy endosperm in the pearlings. Antioxidant activity of 80% ethanol extracts, measured by β-carotene bleaching and by reduction of the free radical, 2,2-diphenyl-1-picrylhydrazyl, was highest in the short-pearling-time fractions and decreased as more endosperm tissue was included. Likewise, there was a decreasing concentration of total phenolics, determined colorimetrically, and of several simple phenolic acids, determined by high performance liquid chromatography, as more material was pearled from the groats. In contrast, concentrations of avenanthramides were not correlated with pearling time, indicating that they were more uniformly distributed in the groats.
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Cereal Chem. 76(6):902-906 Research was initiated to measure antioxidant activity of extracts from oat (Avena sativa L.) groats and hulls and the concentrations of phenolic substances that may contribute to antioxidant activity. Antioxidant activity of ethanolic extracts of four cultivars was evaluated by an in vitro assay that measures the inhibition of coupled autoxidation of linoleic acid and β-carotene. Total phenolic content was determined using Folin and Ciocalteau's phenol reagent and was expressed as gallic acid equivalents. Phenolic compounds were separated by reversed-phase HPLC and detected at 290 nm. Peaks were identified by comparing retention times and spectra with known standards and verified with internal standards. Groats had significantly higher antioxidant activity than hulls. For two cultivars, total phenolic content was similar in groats and hulls, whereas one cultivar had higher and another lower total phenolic content in groats than hulls. Ten phenolic compounds were separated and identified in extracts, and one flavan-3-ol and three avenanthramides were tentatively identified. The con- centrations of many of these compounds differed among cultivars and between fractions. In general, caffeic acid and the avenanthramides were predominantly found in groats, whereas many of the other phenolics were present in greater concentrations in hulls.
The aim of this review, a summary of the putative biological actions of flavonoids, was to obtain a further understanding of the reported beneficial health effects of these substances. Flavonoids occur naturally in fruit, vegetables, and beverages such as tea and wine. Research in the field of flavonoids has increased since the discovery of the French paradox,ie, the low cardiovascular mortality rate observed in Mediterranean populations in association with red wine consumption and a high saturated fat intake. Several other potential beneficial properties of flavonoids have since been ascertained. We review the different groups of known flavonoids, the probable mechanisms by which they act, and the potential clinical applications of these fascinating natural substances.
Broiler chickens were fed starter diets containing 0, 250 or 500 g kg−1 naked oat and, from 29 to 40 d of age, grower diets with 0, 250, 500 or 750 g kg−1 naked oat. All diets included an enteric antibiotic and water-miscible forms of vitamins A, D, E and K. Broiler performance, as evaluated by weight gain and feed:gain ratio, was as good as or better than the corn-soy control diet with up to 500 g kg−1 naked oat in the starter diets. A starter-by-grower diet interaction showed that weight gain was independent of oat level in the grower diet of birds previously fed naked oat, but gain was impaired by higher levels of oat following an oat-free starter diet. Carcass quality improved with increasing oat level in the starter diet by a decrease in abdominal fat and a decrease in oxidation of thigh meat lipids. Key words: Oat (naked), growth, carcass fat, broiler chicken
Objective. —To examine prospectively the relationship between dietary fiber and risk of coronary heart disease.Design. —Cohort study.Setting. —In 1986, a total of 43 757 US male health professionals 40 to 75 years of age and free from diagnosed cardiovascular disease and diabetes completed a detailed 131 -item dietary questionnaire used to measure usual intake of total dietary fiber and specific food sources of fiber.Main Outcome Measure. —Fatal and nonfatal myocardial infarction (Ml).Results. —During 6 years of follow-up, we documented 734 cases of Ml (229 were fatal coronary heart disease). The age-adjusted relative risk (RR) for total Ml was 0.59 (95% confidence interval [CI], 0.46 to 0.76) among men in the highest quintile of total dietary fiber intake (median, 28.9 g/d) compared with men in the lowest quartile (median, 12.4 g/d). The inverse association was strongest for fatal coronary disease (RR, 0.45; 95% CI, 0.28 to 0.72). After controlling for smoking, physical activity and other known nondietary cardiovascular risk factors, dietary saturated fat, vitamin E, total energy intake, and alcohol intake, the RRs were only modestly attenuated. A 10-g increase in total dietary fiber corresponded to an RR for total Ml of 0.81 (95% CI, 0.70 to 0.93). Within the three main food contributors to total fiber intake (vegetable, fruit, and cereal), cereal fiber was most strongly associated with a reduced risk of total Ml (RR, 071; 95% CI, 0.55 to 0.91 for each 10-g increase in cereal fiber per day).Conclusions. —Our results suggest an inverse association between fiber intake and Ml. These results support current national dietary guidelines to increase dietary fiber intake and suggest that fiber, independent of fat intake, is an important dietary component for the prevention of coronary disease.(JAMA. 1996;275:447-451)
Cereal Chem. 72(l):21-24 To determine the stability of tocols (vitamin E) in oat products under envelopes than in jars at room temperature, indicating that air may be various storage conditions, several oat products were stored in jars at involved in the degradation process. a-Tocopherol and a-tocotrienol -24° C or in jars or envelopes at room temperature for up to seven months. decreased faster than the other homologues during room temperature At approximately monthly intervals, products were ground and tocols storage in envelopes, indicating differential stabilities. Analysis of hand- were extracted with methanol and analyzed by high-performance liquid dissected fractions indicated that the germ was the location for most chromatography. Tocols were stable for seven months in all products of the a- and y-tocopherol. Tocotrienols were concentrated in the endo- in jars at -24° C. At room temperature, all tocols degraded in all processed sperm and absent from the germ. products, but were stable in undried groats. Tocols degraded faster in Tocols (vitamin E) occur in at least eight naturally occurring forms, a-,(x -, ,-y-, and 8-tocopherol and a-, ,8-, By-, and 6-tocotrienol (Barnes 1983a). These tocols are physiologically active in allevi- ating symptoms of vitamin E deficiency. Vitamin E is an important antioxidant and free radical scavenger, and its presence has been linked to prevention of chronic disease and premature ageing, cancer, cardiovascular disease, and stroke (Packer and Fuchs 1993). Recently, several reports have implicated tocotrienols as cholesterol synthesis inhibitors (Qureshi et al 1986, Pearce et al 1992, Wang et al 1993).
Fractionation of methanolic extracts of oat groats and hulls by anion-exchange chromatography revealed the presence of a series of anionic, substituted cinnamic acid conjugates, trivially named avenanthramides. Two-dimensional thin-layer chromatography (TLC) showed groat extracts contain more than 25 distinct avenanthramides, while hull extracts contained about 20. Some 15 were common to both groat and hull preparations. The substances were purified by repeated column chromatography on Sephadex LH-20, using TLC to monitor purity, and crystallized from aqueous acetone. The complete structures of 10 avenanthramides have been elucidated using 1H and 13C nuclear magnetic resonance (NMR), mass spectroscopy (MS), ultraviolet absorption spectroscopy (UV), and hydrolytic techniques and confirmed by total synthesis. The physicochemical properties, potential biological activity, and distribution within the oat grain are discussed.