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Food Safety and Toxicology
Impact of red versus white meat consumption in a prudent or Western dietary pattern on the oxidative status in a pig model Sophie Goethals, Els Vossen, Joris Michiels, Lynn Vanhaecke, John Van Camp, Thomas Van Hecke, and Stefaan De Smet J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.9b00559 • Publication Date (Web): 23 Apr 2019 Downloaded from http://pubs.acs.org on April 24, 2019
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Journal of Agricultural and Food Chemistry
Impact of red versus white meat consumption in a prudent or Western dietary pattern on the oxidative status in a pig model Sophie Goethals1,2,3, Els Vossen1, Joris Michiels1, Lynn Vanhaecke2,4, John Van Camp3, Thomas Van Hecke1, Stefaan De Smet1*
1 Laboratory
for Animal Nutrition and Animal Product Quality, Department of Animal Sciences
and Aquatic Ecology, Ghent University, Coupure Links 653, B-9000, Ghent, Belgium
2 Laboratory
of Chemical Analysis, Department of Veterinary Public Health and Food Safety,
Ghent University, Salisburylaan 133, B-9820, Merelbeke, Belgium
3 Research
Group Food Chemistry and Human Nutrition, Department of Food Safety and Food
Quality, Ghent University, Coupure Links 653, B-9000, Ghent, Belgium
4
Institute for Global Food Security, School of Biological Sciences, Queen’s University,
University Road, Belfast, BT7 1NN, Northern Ireland, United Kingdom
* Corresponding author: email:
[email protected], phone: +32 9 264 90 03
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Abstract
2
Human diets contain a complex mixture of antioxidants and pro-oxidants that contribute to the
3
body’s oxidative status. In this study, 32 pigs were fed chicken versus red & processed meat in
4
the context of a prudent or Western dietary pattern for four weeks, to investigate their oxidative
5
status. Lipid oxidation products (malondialdehyde, 4-hydroxy-2-nonenal and hexanal) were
6
higher in the chicken versus red & processed meat diets (1.7- to 8.3-fold) and subsequent in
7
vitro (1.3- to 1.9-fold) and in vivo (1.4 to 3-fold) digests (P < 0.001), which was presumably
8
related to the higher polyunsaturated fatty acid content in chicken meat and/or the added
9
antioxidants in processed meat. However, diet only had a marginal or no effect on the systemic
10
oxidative status as determined by plasma oxygen radical absorbance capacity,
11
malondialdehyde, glutathione and glutathione peroxidase activity in blood and organs, except
12
for α-tocopherol, which was higher after the consumption of the chicken-Western diet. In
13
conclusion, in contrast to the hypothesis, the consumption of chicken compared to red &
14
processed meat resulted in higher concentrations of lipid oxidation products in the pig intestinal
15
contents, however, this was not reflected in the body’s oxidative status.
16 17
Keywords: red meat, oxidative stress, pigs, malondialdehyde, 4-hydroxy-2-nonenal
18
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Introduction
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Several large-scale epidemiological studies have associated a high consumption of red and
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especially processed meat with a higher risk of developing various chronic diseases 1. As
22
opposed to red and processed meat, no such associations have been reported for the
23
consumption of poultry meat 2. In addition, higher consumption of foods such as whole grains
24
and fruits and vegetables have been linked with lower risks for chronic diseases 3, 4 . However,
25
foods are usually not consumed separately and higher intakes of certain foods are often
26
associated with lower intakes of other foods. Furthermore, the cumulative and interactive
27
effects of multiple components in the diet may attenuate or exert stronger effects than the sum
28
of the single components 5. The 2015 Dietary Guidelines Advisory Committee identified a
29
healthy diet as a diet high in fruits and vegetables, whole grains, low- or nonfat dairy, seafood,
30
legumes and nuts and low in red and processed meat, sugar-sweetened foods and drinks and
31
refined grains 6. The dietary guidelines in Western Europe and Unites States carry this same
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central message, however, despite the recommendations, a Western diet characterized by high
33
amounts of red and processed meat, refined grains, sweets, sugar drinks and fried food is still
34
very popular in these countries.
35
Iron plays a central role in the human body since it exerts various physiological functions such
36
as oxygen transport, DNA synthesis and electron transport. Although dietary iron intake is
37
important in the prevention of anemia, the intake of high heme iron levels by high red meat
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consumption is hypothesized to stimulate the formation of oxidation products. An imbalance
39
between reactive oxygen species and antioxidant defense is defined as oxidative stress and is a
40
common factor in many pathological conditions 7. Iron is able to initiate and catalyze the Fenton
41
reaction in the presence of hydrogen peroxide, through which reactive oxygen species such as
42
hydroxyl radicals are formed. These reactive oxygen species are highly unstable and can initiate
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further oxidative chain reactions affecting polyunsaturated fatty acids (PUFA) and proteins, 3 ACS Paragon Plus Environment
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resulting in the formation of oxidized proteins and lipid oxidation products, of which some are
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potentially harmful 8. Oxidation of n-6 PUFA leads to the specific formation of 4-hydroxy-2-
46
nonenal (4-HNE) and hexanal, whereas malondialdehyde (MDA) originates from both the
47
oxidation of n-3 or n-6 PUFA. Previous studies demonstrated the formation of lipid and/or
48
protein oxidation products during the digestion of red meat 9, 10. However, not only meat, but
49
also other dietary compounds are important sources of pro- and antioxidants, able to affect the
50
extent of oxidation during the digestion of meals. Several in vitro and in vivo digestion
51
experiments with red meat already demonstrated antioxidant effects of multiple herbs, spices,
52
fruits, vegetables and beverages
53
formation of oxidation products during meat digestion is influenced by the dietary context in
54
which meat is consumed. For example, Bastide et al. (2016) already concluded that the
55
epidemiological link between red meat consumption and colorectal cancer depended on the
56
ratio of heme iron to antioxidants in the diet
57
addressed the need to compare meat consumption included in a healthy versus unhealthy dietary
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pattern 15.
59
Pigs offer a valuable model for human nutritional studies. Pigs and humans share many
60
anatomical and physiological similarities related to the gastrointestinal tract resulting in similar
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nutritional requirements and digestive and metabolic processes 16. Furthermore, the ability of
62
feeding a strictly controlled diet for several weeks and invasive sampling is a great advantage
63
of using a pig model over a human intervention trial. Previously, (mini)pigs have been used to
64
investigate the effect of meat-based diets albeit in combination with fruits and vegetables on
65
oxidation 17, 18. These studies concluded that the supplementation of fruits and vegetables could
66
mitigate oxidation compared to the diets lacking fruits and vegetables. However, to the best of
67
our knowledge, the relevance of meat consumption as part of a typical Western-style diet or a
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realistic healthy diet and its contribution to oxidative stress has not been investigated yet.
11-13.
Therefore, the rationale of the present study is that the
14.
The review of Turner et al. (2017) also
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Therefore, the aim of the present study was to determine the impact of meat on the oxidative
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status in the context of either a prudent diet, conform current dietary guidelines, or a Western
71
diet, representing the average dietary intake of the Belgian population. In this study, it was
72
hypothesized that the consumption of red meat compared to chicken meat would lead to more
73
oxidation products during digestion, and that this effect would depend on the dietary context of
74
meat consumption. To that end, a four-week pig feeding study investigating meat type (red &
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processed meat, both associated with chronic diseases, versus chicken meat as control meat)
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and background diet (prudent versus Western background diet) was performed using a 2×2
77
factorial design comprising of the following four diets: chicken-prudent, red&processed-
78
prudent, chicken-Western and red&processed-Western. The oxidative status was measured in
79
blood and organ tissues, and formation of lipid and protein oxidation products during in vitro
80
and in vivo digestion of the diets was assessed. The in vitro digestion was performed to compare
81
the in vitro results with the in vivo study.
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Materials and methods
83
Chemicals. All enzymes used in the in vitro digestion of the diets, namely α-amylase from
84
porcine pancreas (~50 U/mg), mucin from porcine stomach type II, pepsin from porcine gastric
85
mucosa (> 250 U/mg solid), lipase from porcine pancreas type II (10-400 U/mg protein),
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pancreatin from porcine pancreas (8 × USP specifications) and porcine bile extract as well as
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reagents used in the analytical procedures such as Trolox, 1-fluoro-2,4-dinitrobenzene,
88
NADPH,
89
dinitrophenylhydrazine (DNPH), 4-HNE, hexanal and 1,3-cyclohexanedione were purchased
90
from
91
amidinopropane)dihydrochloride (AAPH) was purchased from Acros Organics (Geel,
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Belgium).
2-thiobarbituric
Sigma
Aldrich
acid
(Diegem,
(TBA),
1,1,3,3-tetramethoxypropane
Belgium).
The
radical
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initiator
(TMP),
2,4-
2,2’azobis(2-
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Diet formulation. Table 1 demonstrates the formulation of the four diets that were formulated
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to provide similar daily intakes of metabolizable energy and an equal meat intake per day. More
95
than 90 food items (such as fruits, vegetables, bread, potatoes, rice and milk) and different
96
methods of preparation (raw, cooking, grilling, frying) were used to mimic the diversity and
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nutrient levels of complex human diets. A detailed list of ingredients is provided in
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Supplemental Table S1. The amount of meat was based on the results from the Belgian Food
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Consumption Survey 2004, that reported a daily intake of 291 g of ‘meat, fish, eggs and meat
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alternatives’ at the 97.5 percentile of the Belgian population older than 15 years 19. Combined
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with the other food items, this fraction of meat corresponded to 21.5% of the total energy of the
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diets. The mixture of red & processed meat contained 62% fresh meat (mainly pork and beef)
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and 38% red processed meat (mainly cooked ham, filet de sax, salami and smoked bacon),
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which is a proportion based on the Belgian Food Consumption Survey 2004. Chicken thighs
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and breasts made up the chicken meat. To obtain isocaloric meat fractions in the diets, chicken
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skin was added to chicken meat resulting in a final fat percentage of 9.6% in both meat types.
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The meat was collected from local supermarkets, slaughterhouses and meat processing plants.
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The raw meat from both meat types was prepared in a similar way by either baking (70%) or
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vacuum cooking (30%) and were stored (3-4 weeks) at -20 °C before addition to the background
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diets. The formulation of the Western background diet was based on the average food intake of
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the Belgian population and characterized by high amounts of refined grains, desserts and sweets
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19.
113
guidelines of the Flemish active food guide pyramid (applied in the period 2005-2017) and was
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characterized by high amounts of fruits, vegetables, whole grains and dairy products
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Nubel databank, containing the nutrient composition of more than 3678 food items, was used
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to design the diets and to estimate their nutritional value 21. All food items were mixed to avoid
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selection of particular food items by the piglets and to obtain homogenous diets. Because of the
On the other hand, the prudent background diet was formulated based on the dietary
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The
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substantial volume (2000 kg in total), the food items of the background diets were collected
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from local supermarkets and were prepared over several weeks and stored at -20 °C. After
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collection and preparation, the food items were allocated to subgroups such as fruits, vegetables,
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fats & sweets, whole grains and refined grains. Within each subgroup, the frozen food items
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were grounded through a 10 mm plate equipped Omega T-12 grinder, carefully mixed using a
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concrete mixer and immediately stored at -20 °C. Finally, the four diets were made in 20 batches
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of 100 kg per batch by mixing the subgroups according to the tailored proportions in the diets.
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The meat fractions were added last. The resulting homogenous feed mixtures were divided in
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meal portions of 500 g to 1 kg and stored at -20 °C (with a maximum storage time of 3 months)
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until feeding. The temperature of the diets remained below 2 °C during the whole preparation
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process. Aliquots of the background diets, meat and final diets were taken randomly during the
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final preparation step and were stored at -20°C until the end of the feeding trial. Right after the
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trial, the feed aliquots were stored at -80°C until analysis to take eventual oxidation of the diets
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during storage at -20°C into account. All diet analyses were performed in duplicate on two
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randomly selected feed aliquots.
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Dietary characteristics. The pH was recorded and dry matter, crude protein and crude fat
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content were analyzed according to ISO 1442-1973, ISO 937-1978 and ISO 1444-1973
135
methods, respectively. Gross energy was determined with an adiabatic bomb calorimeter
136
(PARR 1261). Fatty acids were measured according to Raes et al. (2001) 22. Briefly, lipids were
137
extracted using chloroform/methanol (2/1; v/v) followed by methylation and gas
138
chromatography to separate the fatty acid methyl esters. From the fatty acid composition, the
139
peroxidizability index was calculated as an indication for its susceptibility to lipid peroxidation
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23.
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extraction in respectively acetone/H2O/HCl 12M (40/4/1) and acetone/H2O (40/5) according to
142
Hornsey (1956) 24.
Total heme and nitroso-heme were determined colorimetrically in the meat following its
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In vitro digestion. The four diets were subjected to an in vitro digestion protocol as previously
144
described by Van Hecke et al. (2014) to better characterise the diets in terms of susceptibility
145
to oxidation during digestion
146
with several enzymatic digestion buffers: 6 mL saliva (5 min), 12 mL gastric juice (2 h),
147
followed by 2 mL bicarbonate buffer (1 M, pH 8.0), 12 mL duodenal juice and 6 mL bile juice
148
(2 h). After the last incubation step, samples were homogenized with an Ultra Turrax (13500
149
rpm) and aliquots of 1 mL were stored at -80 °C. Incubations were performed in quadruplicate
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at 37 °C and for each diet, the four in vitro digest samples were used as replicates in further
151
analysis.
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Study design and animals. The experimental protocol was approved by the Ghent University
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Ethical Committee at the Faculty of Veterinary Medicine (EC 2016/26). Thirty-two castrated
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male piglets (Topigs×Piétrain) of three weeks old and originating from eight litters were
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purchased from a local commercial farm and allocated to eight pens. Each dietary treatment
156
was repeated in two pens (n = 8 pigs per diet) and each diet was given to one of the piglets of
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each litter. On arrival, all piglets were fed a commercial pre-starter diet ad libitum for one week.
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Thereafter, the dietary treatments were gradually introduced during one week, after which the
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piglets were subjected to the dietary treatments for four weeks. The piglets were weighed twice
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a week and the average body weight at the start of the experimental feeding period did not differ
161
significantly between the treatment groups (7.00 ± 0.88 kg). During the experimental feeding
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period, piglets were fed fresh meals at room temperature three times a day (8, 12, 18 h) during
163
30 min ad libitum. An individual feeding system was used to record their individual feed intake
164
per meal. Water was always available ad libitum. Piglets were sampled at the end of the four-
165
week feeding period, though due to practical reasons, euthanasia and sampling was spread over
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four consecutive days. Each day, two piglets from each dietary treatment were slaughtered,
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starting with the heaviest piglets. Two hours after receiving a last meal, piglets were euthanized
25.
In short, diet samples (4.5 g) were incubated consecutively
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by intramuscular injection of xylazine (20 mg/mL, 0.1 mL/kg bodyweight) and intraperitoneal
169
injection of pentobarbital (60 mg/mL, 0.8 mL/kg bodyweight) followed by exsanguination.
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Postprandial blood samples were taken from the jugular vein just before exsanguination and
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collected in heparin tubes. Plasma and red blood cells were separated by centrifugation (1000
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G, 15 min) and stored at -80 °C. Subsequently, all small and large intestinal contents were
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collected separately, the pH was measured and the contents were gently mixed and stored at -
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80 °C. Organs (heart, liver (lobus hepatis dexter medialis), kidney) and tissue segments of
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ileum, proximal and distal colon were removed, weighted and gently rinsed with 0.9% NaCl
176
solution. A 10 cm2 segment of the ileum, proximal and distal colon tissue was scraped to collect
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mucosa. The organs and intestinal mucosae were chopped and homogenized before storage at
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-80 °C. All analyses on these biological samples were performed in duplicate. Before the
179
analysis of thiobarbituric acid reactive substances (TBARS) and glutathione peroxidase (GSH-
180
Px) activity in organs and mucosae, buffered aqueous extracts were made by adding a 1% Triton
181
X-100 phosphate buffer (pH 7; 50 mM) in a 1/10 (w/v) proportion to the organs and mucosae,
182
followed by homogenization (Ultra Turrax, 13500 rpm), centrifugation (13800 G, 15 min, 4
183
°C) and subsequent filtration over glass wool.
184
Antioxidant capacity. The hydrophilic oxygen radical absorbance capacity (ORAC) of the
185
diets and plasma was measured fluorimetrically (excitation at 485 nm and emission at 520 nm)
186
and results were reported as µmol Trolox Equivalents (TE) per g diet and per mL plasma 26.
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Alpha-tocopherol in the diets, heart, liver, kidney and plasma was extracted with ethanol and
188
hexane and quantified by reversed-phase HPLC and UV detection (292 nm)
189
Concentrations of α-tocopherol (µg α-tocopherol/g sample) were determined by comparing the
190
peak areas with a standard curve of α-tocopherol (0 – 15 µg/mL). Levels of reduced glutathione
191
(GSH) and oxidized glutathione (GSSG) were determined in lysed erythrocytes and liver tissue
192
using HPLC separation and UV detection (365 nm) 29, 30. Results were expressed as area under
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the curve/g or mL sample. The GSH-Px activity was measured in plasma and buffered aqueous
194
extracts from organs and gastrointestinal tissues 31. The oxidation of NADPH was measured
195
colorimetrically (340 nm) and recorded over time. One unit of GSH-Px activity was defined as
196
the amount of sample (g) required to oxidize of NADPH per min at 25 °C.
197
Oxidation products. Total MDA concentrations in plasma and in buffered aqueous extracts of
198
heart, liver, kidney and intestinal mucosae were analysed as TBARS according to the method
199
of Grotto et al. (2007) with slight modifications
200
reaction steps involving alkaline hydrolysis, acid deproteinization, derivatization with TBA and
201
extraction with 1-butanol. The absorbance of the carbonyl-TBA complexes was measured
202
colorimetrically at 532 nm, quantified using a standard curve with TMP (0 – 30 nmol/ml) and
203
expressed as nmol MDA-equivalents/g sample. Because of the complexity of the diets, a more
204
specific HPLC method was applied to determine free reactive MDA in the diets, in vitro digests
205
and intestinal contents according to Mendes et al. (2009) 33. The samples were extracted with
206
trichloroacetic acid (7.5%) and derivatized with DNPH. In case of the in vitro digests, the
207
resulting MDA-DNPH hydrazine was subsequently separated by HPLC analysis, whereas for
208
the diets and the intestinal contents, the MDA-DNPH was first concentrated through extraction
209
with pentane, followed by evaporation to dryness with N2 and resolved in 1 mL acetonitrile/H2O
210
(1/1, v/v) prior to HPLC analysis and UV/VIS detection (310 nm). Standard solutions (0 – 20
211
nmol/ml) were made with TMP and results were expressed as nmol MDA/g sample.
212
Levels of 4-HNE and hexanal were analyzed in the diets, in vitro digests and intestinal contents
213
after formation of their fluorescent derivatives with 1,3-cyclohexanedione through HPLC as
214
described previously
215
those obtained from the standard curves of 4-HNE (0 – 2 nmol/mL) and hexanal (0 – 40
216
nmol/mL) and results were provided in nmol/g sample.
12.
32.
TBARS were determined after several
Concentrations were determined by comparing the peak areas with
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Protein carbonyl compounds (PCC) concentrations, indicating the extent of protein oxidation,
218
were measured colorimetrically in diets, in vitro digests and small intestinal contents following
219
their covalent reaction with DNPH according to Ganhão et al. (2010) 34. PCC was not measured
220
in the colonic contents because of the high digestion rate of dietary protein and the interference
221
with bacterial protein. The carbonyl concentration (nmol DNPH/mg protein) was calculated
222
from the absorbance at 280 nm and 370 nm of the samples using the equation below 35: 𝐶ℎ𝑦𝑑𝑟𝑎𝑧𝑜𝑛𝑒
223
𝐶𝑝𝑟𝑜𝑡𝑒𝑖𝑛
=
𝐴370 𝜀ℎ𝑦𝑑𝑟𝑎𝑧𝑜𝑛𝑒, 370 × (𝐴280 ― 𝐴370 × 0.43)
× 106
224
Where εhydrazone,370 is 22000 M-1 cm-1 and the carbonyl concentrations obtained from the blanks
225
were subtracted from the contribution obtained from the corresponding treated sample.
226
Statistical analyses. Data are presented as means ± SD, unless otherwise indicated. Data
227
normality and homoscedasticity were verified using Kolmogorov-Smirnov and modified-
228
Levene’s test in SAS enterprise guide 7. If assumptions were met, a mixed model ANOVA
229
procedure was used with meat, background diet and meat×background diet as fixed effects and
230
litter, pen and euthanization day as random effects (if applicable). Tukey-adjusted post hoc tests
231
were performed for all pairwise comparisons. If one of the assumptions for the use of ANOVA
232
was violated, the non-parametric independent-samples Kruskal-Wallis test with pairwise
233
multiple comparisons was performed using SPSS Statistics 25. P values < 0.05 were considered
234
statistically significant.
235
Results
236
Diet characterization. The analyzed nutritional composition of the diets presented in Table 2
237
was similar to the formulated nutritional values estimated according to the Nubel nutrient
238
database
239
protein content, higher fat content, more SFA, less MUFA and a higher n-6/n-3 fatty acid ratio
240
compared to the prudent diets. A similar crude fat content of 9.6 g/100 g in both meat types was
241
obtained by adding 9% of chicken skin (45% crude fat) to chicken meat (6% crude fat).
21
(Supplemental Table S2). The Western diets had a higher energy density, similar
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Compared to the red & processed meat, the cooked chicken meat contained lower proportions
243
of SFA and higher proportions of n-6 PUFA, a higher n-6/n-3 PUFA ratio and higher
244
peroxidizability index. Total heme was 3.5-fold higher in red & processed meat than in chicken
245
meat. Approximately 10% of total heme in red & processed meat was nitrosylated, whereas
246
chicken meat contained very low amounts of nitroso-heme. No clear differences in ORAC
247
values were observed between the four diets. The α-tocopherol concentration of the Western
248
background diet was 2-fold higher compared to the prudent background diet, whereas the meat
249
types had similar α-tocopherol contents. A 30% higher α-tocopherol level was found in the
250
chicken-Western diet compared to the other diets, indicating a loss of α-tocopherol through the
251
combination of the red & processed meat and the Western background diet. Cooked chicken
252
meat contained approximately 4-fold more 4-HNE, 11-fold more hexanal and 4-fold more
253
MDA compared to red & processed meat. The concentrations of hexanal and MDA in the
254
background diets were considerably lower compared to those in the meat, except for 4-HNE
255
where the concentrations in the red & processed meat were comparable to those in the
256
background diets. The concentrations of lipid oxidation products in the diets corresponded to
257
the combined fractions of lipid oxidation products in the meat and background diets, resulting
258
in higher levels of lipid oxidation products in the diets containing chicken meat. The amount of
259
PCC was comparable between the chicken-prudent, red&processed-prudent and chicken-
260
Western diet, but slightly higher in the red&processed-Western diet.
261
In vitro digestion. The differences in lipid oxidation products in the diets were reflected in the
262
in vitro digests, as shown in Table 2. The concentrations of PCC in the in vitro digests were
263
slightly higher after the digestion of the red & processed meat diets compared to the chicken
264
diets.
265
Animal performance. The average daily energy intake of the pigs did not differ significantly
266
between the four treatment groups, as illustrated in Figure 1. Since the meat fraction represented
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an equal energy percentage in the four diets, the piglets consumed an equal amount of meat per
268
day, as intended. However, because of the lower energy density of the prudent background diet,
269
the average daily feed intake of the prudent diets (1268 ± 204 g/day) was higher (P = 0.001)
270
compared to the Western diets (905 ± 81 g/day). In the second week of the experimental feeding
271
period, there was a drop in feed intake and concomitant stagnation of body weight gain,
272
regardless of dietary treatment. During this drop in feed intake, pigs presented loose stools but
273
most of them recovered within 3-5 days. Nonetheless, two pigs fed the chicken-Western diet
274
still suffered from diarrhea at the day of euthanasia, therefore, their colonic contents could not
275
be collected. Pigs receiving the prudent diets (312 ± 91 g/day) had a higher body weight gain
276
compared to those fed the Western diets (239 ± 55 g/day, P = 0.026), whereas meat consumption
277
did not significantly affect body weight. Additionally, the liver tissue weight per kg body weight
278
was 10% higher for pigs fed the prudent diets (P = 0.010), whereas the weight of heart and
279
kidney was not significantly affected. The pH of the intestinal digest samples did not differ
280
significantly among the dietary treatments (data not shown).
281
Oxidation products in intestinal contents. The concentrations of lipid oxidation products and
282
protein carbonyl compounds in small intestine and colonic contents are demonstrated in Figure
283
2. Lipid oxidation products were 1.4- to 3-fold higher in the intestinal contents of the pigs fed
284
chicken meat compared to pigs fed red & processed meat diets (P < 0.001). The concentration
285
of hexanal was higher in the small intestinal content when chicken meat was consumed in
286
combination with the prudent vs. Western background diet (P = 0.038). Significantly higher
287
PCC concentrations were found in the small intestinal content of piglets consuming red &
288
processed meat in the Western vs. the prudent background diet (P = 0.010).
289
α-Tocopherol. As illustrated in Figure 3, highest α-tocopherol concentrations were found in
290
pigs fed the chicken-Western diet.
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Oxidative status. The mean values and statistics of the analyzed parameters for the oxidative
292
status are summarized in Table 3. No significant interaction effect of meat type and background
293
diet was observed in the analyzed parameters. The ORAC values in plasma of pigs fed chicken
294
meat tended to be slightly higher compared to those fed red & processed meat, irrespective of
295
the background diet. The MDA concentrations were only significantly different in kidney, with
296
slightly higher concentrations in kidneys following chicken meat consumption compared to red
297
& processed meat (P = 0.014). Pigs fed the Western diets had higher GSH-Px activity in heart
298
(+ 9%, P = 0.029) and showed a trend to be higher in kidney (+ 10%, P = 0.055) compared to
299
the prudent diets. On the other hand, pigs on the red & processed meat diets tended to have
300
higher GSH-Px activity in the liver (+ 15%, P = 0.070) compared to those fed the chicken diets.
301
No significant differences were observed for GSH-Px activity in plasma or in the intestinal
302
mucosae at three different locations. However, GSSG levels tended to be higher (+ 24%, P =
303
0.057) in erythrocytes of pigs fed red & processed meat diets compared to the chicken diets,
304
whereas the type of meat had no effect on GSH levels. In liver on the other hand, GSH levels
305
tended to be influenced by the background diet, with slightly higher levels in pigs fed the
306
prudent diets compared to the Western diets (P = 0.081), whereas no significant differences
307
were observed for liver GSSG levels between the treatment groups.
308
Discussion
309
Although oxidative reactions are the basis of numerous biochemical pathways, oxidative stress
310
has been linked to several pathological conditions and chronic diseases. Therefore, the role of
311
dietary oxidation products as external factors of oxidative stress and the related health risks has
312
become a subject of great interest. The aim of the present study was to investigate the effect of
313
meat sources that have been linked with chronic diseases (red & processed meat) versus chicken
314
meat as control in a complex dietary context (Western or prudent) on the oxidative status in
315
pigs following a four-week experimental feeding period. Most studies investigating the impact
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316
of meat on oxidation during digestion used (semi-)purified diets and levels of meat or meat-
317
derived compounds above common intake levels 15. To the best of our knowledge, the present
318
study is unique in its kind as it used a great diversity of whole foods and a lower meat fraction
319
corresponding to the upper intake level of a Western diet.
320
We hypothesized that the consumption of red meat would lead to more oxidation products
321
during digestion compared to chicken meat because of the catalyzing effect of iron in the Fenton
322
reaction. In contrast, we found higher levels of lipid oxidation products in the chicken-based
323
diets and subsequent digests. The results of the in vitro and in vivo digests correlated well,
324
however, the oxidation products in the digests reflected the differences in the diets. In
325
agreement with the hypothesis, the results of previously reported in vitro and in vivo
326
experiments showed lower MDA levels throughout the digestion of chicken compared to beef
327
and/or pork
328
susceptibility of red meat to oxidation. However, Steppeler et al. (2016) indicated that the
329
amount of unsaturated fatty acids and not the iron content was the most important factor in the
330
formation of aldehydes during in vitro digestion of cooked meat and salmon loin, that both
331
comprised of similar fat contents but different fatty acid profiles
332
content and fatty acid profile was also previously demonstrated upon digestion of meat or heme
333
iron supplemented with different types of oils or by adding different proportions of lard to meat
334
10, 37, 38.
335
added chicken skin, which led to a considerable proportion of n-6 PUFA. In contrast, in their
336
in vitro digestions, Van Hecke et al. (2014) normalized the fatty acid composition of chicken,
337
pork and beef meat by adding lard, which might offer a possible explanation for the different
338
results obtained 9. In the present study, the undigested cooked chicken meat was already more
339
oxidized compared to the red & processed meat. Besides differences in heme iron and fatty acid
340
profile, a range of other factors such as differences in the endogenous antioxidant capacity and
9, 10, 13.
In these studies, heme iron was mostly held responsible for the higher
36.
The importance of fat
The chicken meat in the present study consisted of a mixture of breasts, thighs and
15 ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
Page 16 of 33
39,
341
in the ability of heme proteins from different animal species to promote lipid oxidation
342
processing methods and storage conditions could have played a role. The study of Rhee et al.
343
(1994) demonstrated that among raw muscles from different animal species, beef was most
344
susceptible to lipid oxidation during storage at -20°C, whereas cooking drastically changed the
345
susceptibility of meat during storage resulting in significantly higher levels of TBARS in
346
chicken thigh compared to beef, pork and chicken breast 40. Although storage time in the present
347
study was equal for all meat fractions, a different oxidative susceptibility during storage could
348
be involved. In addition, also the added antioxidants such as nitrite salt in processed meat could
349
have reduced the amount of lipid oxidation products in the red & processed meat 9.
350
The majority of lipid oxidation products in the diets originated from the meat and hence, the
351
background diet did not affect lipid oxidation product concentrations in the diets and digestion
352
as distinctly as expected. The prudent diet contained considerable amounts of compounds that
353
could lower the oxidative load in the diets or during digestion of meat 17, 41. However, neither
354
α-tocopherol concentrations nor ORAC values were higher in the prudent diets compared to the
355
Western diets. Nevertheless, care should be taken in the interpretation of ORAC values since
356
this method has been criticized regarding its biological relevance, its selective activity against
357
particular radicals and the contribution of the protein fraction to the antioxidant capacity. In
358
addition, feeding the piglets a mixture of many ingredients always including a certain fraction
359
of protective compounds could have attenuated the adverse effects of a Western dietary pattern.
360
Indeed, in order to prevent postprandial oxidative stress, Prior (2007) concluded that
361
antioxidant containing foods should be consumed in each meal, which was the case in this study
362
42.
363
aspects of a dietary pattern, e.g. portion size, temporal distribution of intake, variety etc.
364
PCC were higher in the small intestinal contents of pigs fed the red&processed-Western diet
365
compared to the red&processed-prudent diet. The susceptibility to protein oxidation is
In this regard, next to the dietary composition, future studies should also consider additional
16 ACS Paragon Plus Environment
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Journal of Agricultural and Food Chemistry
366
primarily affected by the protein content and amino acid composition, but importantly, also
367
lipid oxidation processes are involved 43. Protein and lipid oxidation are interrelated since both
368
lipids and proteins could be targets of ROS and because secondary lipid oxidation products can
369
interact with the amino acid residues of proteins. Also, PCC can be formed during the Maillard-
370
mediated pathway, in which reducing sugars react with the δ-amino group of alkaline amino
371
acids 43. Possibly, this reaction pathway could have contributed to the higher PCC measured in
372
the digests of the red&processed-Western diet. The evaluation of more specific protein
373
oxidation products and further studies on this Maillard-mediated pathway will aid to elucidate
374
this hypothesis. Additionally, the nature and action of antioxidants can also contribute to the
375
outcome of PCC and the inconsistency with the results for lipid oxidation products in this study.
376
Similar to our results, the studies of Delosière et al. (2016) and Raes et al. (2015) investigating
377
the antioxidant potential of fruits and vegetables and a number of well-known antioxidants
378
(carnosic acid, quercetin and α-tocopherol) during digestion, also found varying results
379
comparing antioxidant effects on lipid and protein oxidation 41, 44.
380
The α-tocopherol concentrations (the major vitamin E component) in plasma and organs
381
reflected the dietary α-tocopherol levels, being 30% higher in the chicken-Western diet
382
compared to the other diets. The two-fold higher α-tocopherol concentrations in the Western
383
background diet compared to the prudent background diet was probably due to the high (vitamin
384
E rich) fat content of the Western diet. Indeed, in two large food consumption surveys in
385
Belgium and Ireland, the food group ‘fats and oils’ was identified as the main source of dietary
386
vitamin E intake, followed by vegetable intake 45, 46. Although both meat types had similar α-
387
tocopherol concentrations in this study, the combination of red & processed meat with the
388
Western background diet resulted in lower α-tocopherol levels in the red&processed-Western
389
diet compared to the chicken-Western diet. This loss could possibly be explained by the
390
catalyzing effect of heme iron on oxidation but was unexpected since more lipid oxidation
17 ACS Paragon Plus Environment
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391
products were present in the chicken meat. However, no clear antioxidant effect of the higher
392
α-tocopherol concentration in the chicken-Western diet could be observed in the oxidative
393
stress parameters measured in organs, in contrast to what was expected as α-tocopherol is
394
known to influence cellular responses to oxidative stress. On the other hand, the α-tocopherol
395
concentrations in the present diets corresponded to a daily intake of 11.6 – 16.6 mg/day for
396
humans (calculated with a theoretical daily energy intake of 2500 kcal), which is close to the
397
European Food Safety Authority adequate intake levels (13 mg/day for men 47) and the usual
398
vitamin E intake in the Belgian population (14 mg/day in men
399
concentrations used in experimental studies that clearly demonstrate a protective effect of α-
400
tocopherol on oxidative stress markers, involve much higher doses of vitamin E
401
supplementation such as 67 mg/day in diabetic patients and 200 mg/kg body weight per day in
402
rats 48, 49.
403
Recent reviews demonstrate involvement of dietary PCC and lipid oxidation products in
404
oxidation markers in blood, urine or organs
405
containing chicken meat had considerably more lipid oxidation products in the present study,
406
an increase in oxidative stress was expected in pigs on chicken-based diets. However, only renal
407
MDA was higher in pigs fed chicken meat compared to those fed red & processed meat. The
408
increased GSH-Px activity in heart tissue could indicate a higher need for antioxidant action
409
due to the Western background diet. In accordance, a lower erythrocyte GSH-Px activity
410
together with a higher blood total antioxidant capacity was previously indicative for a beneficial
411
oxidative status in pigs fed strawberries compared to other fruits
412
(2018) demonstrated a higher total antioxidant status and higher GSH-Px activity in duodenum
413
and colon mucosae of pigs after the addition of polyphenols to the control diet
414
apparent inconsistencies emphasize the existence of different antioxidant mechanisms in
415
different organs and emphasize that a proper interpretation of the oxidative status requires the
43, 50.
45).
The α-tocopherol
Since the diets and intestinal contents
18 ACS Paragon Plus Environment
51.
Contrary, Chedea et al.
52.
These
Page 19 of 33
Journal of Agricultural and Food Chemistry
416
analysis of multiple parameters. The rather inconsistent effects of the different diets on the
417
measured parameters for the oxidative status (ORAC, α-tocopherol, MDA, GSH-Px, levels of
418
GSH and GSSG), hampers a straightforward conclusion about the body’s antioxidant status.
419
Previously, dietary factors such as resistant starch and polyphenols, characteristic for a prudent
420
diet, or sucrose, highly present in Western diets, have been demonstrated to attenuate or
421
stimulate, respectively, MDA formation in colon mucosae or kidney tissue
422
the present study, a mitigating or stimulating effect on lipid oxidation could not be attributed to
423
those dietary compounds. Despite the close contact with the digests containing different lipid
424
oxidation concentrations, no effect was observed at the level of the intestinal mucosae in terms
425
of MDA concentrations or GSH-Px activity. In contrast, feeding pigs oxidized soybean oil
426
(resulting in 270 – 414 nmol MDA/g oxidized diet versus 6.6 nmol MDA/g unoxidized diet)
427
increased the concentrations of MDA in the mucosal samples from the jejunum 55, while more
428
oxidized diets (approximately 75 nmol MDA/g diet versus 45 nmol MDA/g diet) also yielded
429
higher MDA concentrations in colonic mucosae in rats 10. However, the concentrations of lipid
430
oxidation products in the present study (with MDA levels below 5 nmol MDA/g diet) were
431
relatively low compared to the MDA levels in the studies mentioned above. Furthermore, the
432
concentrations of 4-HNE in this study (up to 0.63 nmol/g diet and up to 1.53 ± 0.48 nmol/g
433
intestinal content) were also at the lower end compared to the cytotoxic concentration ranges
434
of 4-HNE as documented by Esterbauer et al. (1991) 8. In addition, besides the concentration
435
of oxidation products in the diets and intestinal lumen, other factors such as bioavailability, the
436
antioxidant defense system and barrier functionality of the intestinal mucosa, transit time and
437
changes in microbiota could be involved in the oxidative status of the intestinal mucosae.
438
In conclusion, the hypothesis that red & processed meat consumption stimulates oxidation
439
during digestion to a greater extent compared to chicken meat could not be confirmed. In
440
contrast, chicken meat was more susceptible to lipid oxidation as observed already in the diets 19 ACS Paragon Plus Environment
52-54.
However, in
Journal of Agricultural and Food Chemistry
441
as such, and in the in vitro and in vivo digests. Not only heme iron, but other factors such as the
442
fatty acid composition, the antioxidants in processed meat or other differences in the
443
endogenous antioxidant capacity of the meat will have influenced the oxidative susceptibility
444
during preparation, storage and subsequent digestion. Marginal differences between the two
445
background diets were observed regarding oxidation product formation during digestion. In
446
contrast to the hypothesis, little interaction effects were observed between meat type and
447
background diet. The systemic oxidative status was not or only minimally affected by the
448
background diet and meat type. More in vivo studies on the interaction of separate foods and
449
dietary patterns on oxidation phenomena are warranted.
450
ABBREVIATIONS USED
451
4-hydroxy-2-nonenal (4-HNE); 2,2’azobis(2-amidinopropane)dihydrochloride (AAPH); 2,4-
452
dinitrophenylhydrazine (DNPH); reduced glutathione (GSH); glutathione peroxidase (GSH-
453
Px); oxidized glutathione (GSSG); malondialdehyde (MDA); oxygen radical absorbance
454
capacity (ORAC); polyunsaturated fatty acids (PUFA); 2-thiobarbituric acid (TBA);
455
thiobarbituric acid reactive substances (TBARS); Trolox Equivalents (TE); 1,1,3,3-
456
tetramethoxypropane (TMP)
457
ACKNOWLEDGEMENTS
458
The authors thank C. Lachat for his input in the formulation of the diets and S. Coolsaet, D.
459
Baeyens, E. Claeys and A. Ovyn for their practical assistance during the preparation of the
460
diets, sampling of the piglets and laboratory analyses.
461
FUNDING
462
This research was funded by the Flanders Research Foundation (FWO) project G011615N.
463
SUPPORTING INFORMATION DESCRIPTION
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464
Detailed list of food items used to compose the four diets (Supplementary Table S1) and
465
Formulated and analyzed composition of the four diets (Supplementary Table S2). This material
466
is available free of charge via the Internet at http://pubs.acs.org.
21 ACS Paragon Plus Environment
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467 468 469
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Table 1 Formulation of the four diets expressed in g/kg (fresh weight basis) and energy percentage (E%) prudent chicken R&P
Western chicken R&P
prudent chicken R&P
197
21.5
g/kg red (62%) & red processed meat (38%) chicken meat cereal products and potatoes fruits and vegetables dairy products and eggs butter and cooking fats fats and sweets R&P = red & processed meat
145 304 299 243 8.62 0.51
145
E% 197 199 173 143 14.3 275
304 299 243 8.62 0.51
Western chicken R&P
21.5 45.6 10.4 15.1 7.06 0.33
199 173 143 14.3 275
45.6 10.4 15.1 7.06 0.33
21.5 23.4 4.50 12.7 8.54 29.4
Table 2 Characteristics of the four diets, meat and background diets separately diets prudent chicken R&P
meat Western chicken R&P
chicken
background diet R&P
prudent
Western
gross energy, kcal/kg 1263 1265 1743 1726 pH 5.83 5.39 5.69 5.28 dry matter, g/100 g 26.0 26.1 30.9 31.2 37.4 36.2 23.5 30.6 crude protein, g/100 g 6.44 6.35 7.61 6.97 26.2 21.7 3.55 2.96 crude fat, g/100 g 3.13 3.47 6.24 6.76 9.61 9.59 2.28 5.87 proportion of energy from fat, % 22.5 24.9 32.5 35.6 SFA, g/100 g FA 31.6 35.6 37.0 38.2 29.7 38.3 32.5 40.0 MUFA, g/100 g FA 44.0 42.2 38.6 38.8 42.6 41.8 45.9 37.8 PUFA, g/100 g FA 21.2 19.5 21.6 20.2 26.1 17.7 20.1 21.0 linoleic acid, g/100 g FA 17.4 15.4 19.0 17.3 22.4 13.9 15.1 18.0 total n-6 PUFA, g/100 g FA 18.2 16.2 19.6 17.9 23.8 15.3 15.8 18.5 α-linolenic acid, g/100 g FA 2.74 2.89 1.87 1.98 1.93 2.03 3.77 2.20 total n-3 PUFA, g/100 g FA 3.00 3.29 2.05 2.28 2.25 2.44 4.22 2.52 ratio n-6/n-3 FA 6.08 4.94 9.57 7.93 10.6 6.26 3.8 7.33 peroxidizability indexb 25.9 24.6 24.8 23.8 31.3 22.6 26.1 24.8 total heme, mg hematin/kg meat 42.8 149 nitroso-heme, mg hematin/kg meat 17.8 40.4 ORAC (µmol Trolox equivalent/g) 10.2 8.96 9.50 9.29 11.58 12.89 8.77 8.38 α-tocopherol (mg/kg) 7.92 8.03 11.6 8.02 6.38 6.50 5.59 11.3 oxidation products in diet before digestion 4-hydroxy-2-nonenal (nmol/g) 0.63 0.32 0.55 0.28 1.34 0.32 0.41 0.30 hexanal (nmol/g) 11.1 1.5 12.3 1.3 46.4 4.36 1.24 0.99 malondialdehyde (nmol/g) 2.56 1.22 4.04 2.74 19.1 4.46 0.52 0.42 PCC (nmol DNPH fixed/mg protein) 5.00 5.38 5.19 6.45 oxidation products after in vitro digestion 4-hydroxy-2-nonenal (nmol/mL) 0.65 0.32 0.60 0.34 hexanal (nmol/mL) 1.69 1.19 1.63 1.28 malondialdehyde (nmol/mL) 1.11 0.51 1.24 0.75 PCC (nmol DNPH fixed/mg protein) 7.65 8.77 7.51 8.99 - = not analyzed; R&P = red & processed meat; FA = fatty acids; SFA = saturated fatty acids; MUFA = monounsaturated fatty acids; PUFA = polyunsaturated fatty acids; Total n-6 PUFA = C18:2,n-6 + C18:3,n-6 + C20:2,n-6 + C20:3,n-6 + C20:4,n-6 + C22:4,n-6 + C22:5,n-6; Total n-3 PUFA = C18:3,n-3 + C20:3,n-3 + C20:4,n-3 + C20:5,n-3 + C22:5,n-3 + C22:6,n-3; PCC = protein carbonyl compounds; ORAC = Oxygen Radical Absorbance Capacity; DNPH = 2,4-dinitrophenylhydrazine. b Peroxidizability index (Hu et al., 1989) was calculated as follows: (% dienoic x 1) + (% trienoic x 2) + (% tetraenoic x 3) + (% pentaenoic x 4) + (% hexaenoic x 5).
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Table 3 Parameters for the oxidative status in blood and organ tissues of pigs following four weeks on the dietary treatments (n = 8 per diet) prudent chicken R&P ORAC plasma* TBARS plasma* liver heart kidney* mucosa of ileum* mucosa of proximal colon* mucosa of distal colon* GSH-Px activity plasma* liver* heart* kidney* mucosa of ileum mucosa of proximal colon mucosa of distal colon reduced glutathione red blood cells liver oxidized glutathione
Western chicken R&P
SEM
Pback
P-values Pmeat
µmol TE/mL
12.8
11.5
12.4
11.1
0.45
0.910
0.060
nmol ME/mL nmol ME/g nmol ME/g nmol ME/g nmol ME/g
9.11 184 68.2 59.5 63.2
9.31 221 71.1 57.9 56.8
8.70 174 68.8 63.5 44.4
9.35 175 68.9 58.3 46.7
0.42 7.67 1.66 0.82 3.45
0.692 0.115 0.797 0.274 0.110
0.485 0.270 0.646 0.014 1.000
nmol ME/g nmol ME/g
30.7 39.9
31.8 40.7
29.3 38.2
24.9 35.1
1.27 0.96
0.155
0.429
0.123
0.406
µmol/min.mL µmol/min.g µmol/min.g µmol/min.g µmol/min.g µmol/min.g µmol/min.g
2.25 3.89 0.64 4.01 2.02 3.13 2.40
2.27 4.62 0.67 3.76 2.12 3.68 2.62
2.40 4.06 0.74 4.48 2.20 4.24 2.41
2.28 4.72 0.70 4.15 2.28 3.82 2.29
0.06 0.19 0.02 0.12 0.11 0.24 0.11
0.970 0.821 0.029 0.055 0.452 0.176 0.671
0.792 0.070 0.763 0.187 0.678 0.892 0.791
AUC×105/mL
2.66
2.82
2.75
2.58
0.10
0.768
0.979
AUC×105/g
4.39
5.40
3.24
4.17
0.31
0.081
0.145
0.699 0.057 3.51 4.57 3.28 4.39 0.29 0.291 0.792 liver* AUC×104/g 2.11 2.98 1.92 1.69 0.27 R&P = red & processed meat, ORAC = Oxygen Radical Absorbance Capacity, TBARS = Thiobarbituric acid reactive substances, ME = malondialdehyde equivalents, TE = Trolox equivalent, GSH-Px = glutathione peroxidase, AUC = area under the curve, SEM = standard error of the mean, Pback = P-value of the fixed factor background diet, Pmeat = P-value of the fixed factor meat. Data of parameters with an asterisk (*) were analyzed with non-parametric statistical tests. P-values ≤ 0.05 are highlighted in bold, P-values between 0.05 and 0.10 are highlighted in italic. P-values for the interaction term meat×background diet were not included since they were not significant. red blood cells
AUC×104/mL
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Journal of Agricultural and Food Chemistry
Figure 1 Feed intake in g/day, kcal/day and body weight during the experimental feeding period (n = 8 per diet) Figure 2 Lipid oxidation products (4-hydroxy-2-nonenal, hexanal and malondialdehyde) and protein carbonyl compounds in small intestinal (N = 32) and colonic (N = 30) contents. Bars with different superscripts differ significantly (p < 0.05) among dietary treatments within the same compartment of the intestinal tract. The error bars illustrate standard deviations. Samples with an asterisk (*) were analyzed using non-parametric statistical tests. DNPH= 2,4-dinitrophenylhydrazine. Figure 3 Alpha-tocopherol concentrations in plasma (N = 32) and organs (liver, heart and kidney, N = 32) of pigs following four weeks on the dietary treatments. Bars with different superscripts differ significantly (p < 0.05) among dietary treatments within the same type of sample. The error bars illustrate standard deviations. Samples with an asterisk (*) were analyzed using non-parametric statistical tests.
Feed intake (g/day)
2000 1600 1200 800 400 0
Feed intake (kcal/day)
2500 2000 1500 1000 500 0
Body weight (kg)
20 15 10 5 0 0
10
20
30
Time (days) chicken-prudent chicken-Western
red&processed-prudent red&processed-Western
Figure 1
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Journal of Agricultural and Food Chemistry
hexanal
4-hydroxy-2-nonenal
a
3
a ab
2
b
b
1
ab
nmol/g
nmol/g
3
a ab
b
0
a
2
bc
c
b c
c
1
Colonic content*
protein carbonyl compounds a
ab a
(nmol DNPH fixed/mg protein)
12 a
6
c
bc
b
b
3 0
Colonic content*
Small intestinal content
Colonic content
Small intestinal content
malondialdehyde
nmol/g
ab
0 Small intestinal content*
9
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a
12 ab
8
b
ab
4 0 Small intestinal content*
Figure 2
α-tocopherol a
14 12
µg/g sample
a 10 b
8 6 4 2
b
b a
ab
b b
b
a ab
b b
ab
b
0 Plasma* chicken-prudent
Liver
Heart
red&processed-prudent
chicken-Western
Figure 3
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Kidney* red&processed-Western
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Journal of Agricultural and Food Chemistry
GRAFIC FOR TABLE OF CONTENTS
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