INTRODUCTION
The
wild boar (Sus scrofa scrofa) has favourable
meat characteristics compared to the domestic pig particularly regarding the
fat and cholesterol content (Morán et
al., 2019; Russo et al., 2017). The high quality of meat from wild
boars is the consequence of several factors, including genetics, crossbreeding,
rearing systems and processing conditions (Morán et
al., 2019). Within the factors encompassed by the rearing system, feed
composition seems to be key to influencing wild boar product quality (Morán et al., 2019).
Quercus spp.
acorns form an important part of the diet of free-living wild boar (Sus scrofa
s.) in their native European habitat (Mikulka
et al., 2018). Meat products obtained under these ecological conditions
command higher prices in markets due to high nutritional value and particular
sensory properties desired by consumers, and they are considered a significant
source of healthy food (Russo et al., 2017). Some studies of Iberian
pigs fed on grass and acorns reported increased meat tenderness and taste
(Rodríguez-Estévez et al., 2008). These
quality characteristics are mainly attributed to the high consumption of
acorns, which are rich in oleic acid (Rey et al., 2006; Tejerina et
al., 2018).
In Chile, wild boars are raised for commercial purposes in
confinement conditions and these animals are mainly fed diets based on
corn, soybean meal and wheat (Skewes & Morales, 2006). The final meat
products are also distributed to higher priced markets due to their believed
attributes similar to those explained above, even when their chemical
characteristics have not been documented.
Quercus genus trees
can also be found in Chile; however, their fruits have not been reported to be
part of the wild boar production diet, and thus there is not much information
on what effects this acorn intake could have on wild boar meat characteristics.
The present
study was designed to test the hypothesis that the addition of acorns to the
diet of wild boars increases the level of monounsaturated and polyunsaturated
fatty acids in their meat, as well as the improvement of cholesterol and
sensory characteristics.
MATERIALS AND METHODS
Location and
facilities
Healthy and
pure wild boars (male and females) were selected from a Chilean commercial
farm, located in the county of Chillan, 36°34’S 72°06’W, 118 m above sea level,
with an annual mean precipitation of 1034 mm and annual mean temperature of 14
°C, with a maximum mean for the hottest month (January) of 28.8 °C and a
minimum mean for the coldest month (July) of 3.5 °C. Animals were kept in
outdoor pens with 8 m2 per animal, wooden feeders on the ground
(providing linear access of 0.3 m per animal), a sucking drinker for every 15
animals, a soil-covered floor, a hay bed for refuge, and community housing of 6
m2.
Feeding and
management
The animals
were initially subjected to similar nutritional and health management until
reaching a live weight of 40 kg. The amount of feed given daily to experimental
animals was equivalent to 4.1% of their live weight and was adjusted every 15
days. The feedstuff contained corn, soybean meal and wheat, and its nutritional
value was determined based on proximal chemical analysis and fatty acid
composition using gas chromatography.
Animals were
randomly assigned to three experimental groups of six animals (4♀ and
2♂), which were housed together for five days until the start of the
trial. Each group received the following feedstuff daily for 60 days:
- Control
group: commercial ration (4.1% live weight)
- 20% group:
80% w/w commercial feed+ 20% w/w fresh acorns.
- 40% group:
60% w/w commercial feed + 40% w/w fresh acorns.
The acorns
were collected directly from the ground under Q. robur trees from the county of Chillan
and then kept dry at room temperature in a barn.
Animals were
stunned and slaughtered at a local slaughterhouse at the end of the trial at a
live weight of 55.3 kg (±2.57 kg). In the slaughterhouse, carcass weight (CW)
and backfat thickness (BT) at the level of the last rib were taken. Samples of Longissimus lumborum muscle (LL) at the
level of the L1 to L4 lumbar vertebra were taken at cutting (24 hours after
slaughter), weighed, vacuum-packed in low-oxygen permeable bags and kept frozen
at –18 °C ± 2 °C until analysis. Analyses were carried out within three weeks
of slaughter.
Chemical
analysis
Chemical analysis
were performed on 100 g samples of the feedstuff,
acorns, and meat (n=3). The moisture of the samples was immediately determined
by drying at 103 ºC ± 2 ºC until constant weight. The total intramuscular fat
was measured by Soxhlet extraction, Crude protein was measured by the Kjeldahl method, Fibre was analysed by Weende method, and
the Ash was measured gravimetrically by burning samples (AOAC, 1990).
Fatty acids
Samples of
muscle were divided into three equal portions (n=18) for each experimental group.
The fat extraction was performed according to Bligh & Dyer (1959) and
Lumley & Colwell (1991). In brief, 20 g of sample were extracted by a solvent
composed of methanol, chloroform and water (80:50:32). The fat was concentrated
in the chloroform layer. The chloroform phase was removed by evaporation and
500 µL of n-hexane was added to the extract, which was then stored at –18 ºC ± 2 °C until analysis.
Transmethylation was carried out according to ISO: 5509:1978. This was calculated for 1 g oil or fat in 10 ml of
hexane, to which 0.5 ml 2 mol-1 Na2OH4 in
methanol was added and stirred for 20 s. After phase separation, the
supernatant was collected for subsequent gas chromatography analysis. The fatty
acid profile was determined in a gas chromatograph (Clarus 600 Perkin Elmer®,
USA) equipped with a flame ionization detector (FID). A capillary column
SP-2560™ (Sigma-Aldrich Co., USA) of 100 m × 0.25 mm × 0.25 µm film were used.
Helium was used as the carrier gas at 1.0 ml/min and inlet pressure of 15 psi,
and the method of injection was split (100:1). The injector temperature was
fixed at 250 ºC
and the detector was fixed at 260 ºC. The sample volume injected was 1.0 µl.
The oven temperature was programmed to increase from 140 ºC (held for 5 min) to 240 ºC (held for 15 min) at
4 ºC/min. Fatty acids were identified by comparing the retention times of the
chromatograph peaks with those of the methyl esters from a mixture prepared
with a standard 37 component FAME Mix (Sigma-Aldrich Co., USA).
Cholesterol
Cholesterol
extraction was performed by direct saponification of KOH 2% in ethanol (Mazalli Saldanha & Bragagnolo
et al., 2003) with subsequent chromatographic analysis (n=18) in the following conditions:
the injector temperature was fixed at 270 ºC and the detector was fixed at 300 ºC. The sample volume
injected was 1.0 µl. The oven temperature was programmed to increase from 160 ºC (held for 1 min) to 300 ºC (held for 7 min) at
10 ºC/min. Cholesterol was quantified by the standard internal method using 5
alpha cholestane (Supelco Analytical, Bellefonte, PA,
USA) as the reference.
Sensory panel
The day
before the test, the samples were thawed at 4 °C ± 2 °C over 24 h. Subsequently, each sample was sealed with aluminium foil and was cooked in a pre-heated oven (FAGOR
Innovation Class A) at 200 °C
to achieve an internal temperature of 70 ºC. Subsequently, the specimens were wrapped
in aluminium foil to avoid drying and were used for
the sensory analysis. A panel of six members was selected and trained according
to ISO 3972:1991 and ISO 8586-1:1993 standards. A total of four tasting
sessions were performed in which each assessor evaluated the six samples coded
using random three-digit numbers. The order of presentation of the samples and
the first-order and carry-over effect were blocked (MacFie
et al., 1989). The assessors conducted a descriptive sensory analysis to
evaluate the flavour, juiciness and tenderness in the
cooked meat using a hybrid hedonic scale described by Villanueva et al.
(2005).
Analyses were
performed in the Animal Nutrition and Meat quality laboratory of the
Agricultural Research Institute (INIA Remehue),
Osorno, Chile.
Statistical
analysis
The data were
analysed as a completely randomised
design using the general linear model (GLM) procedure contained in SAS
Statistical Package v 8.01 (SAS Institute, 2001). Before the statistical
analysis, percentage of fatty acids was arcsin
transformed when necessary to fulfil the population normality and homogeneity
assumptions. The comparative analysis between means was conducted using the
Duncan test.
RESULTS AND DISCUSSION
Carcass,
chemical and fatty acids composition of diets
With respect
to type of diet consumed, no differences for carcass weight (CW) and backfat
thickness (BT) were observed between the control group and the wild boars fed
with 20% acorns. The CW found were 37.6, 40.1 and 44.6 kg, and BT of 11.8, 14.0
and 15.6 mm for wild boars fed with commercial feed, 20% acorns, and 40% acorns
respectively. These values were higher than those reported by Daza et al. (2007) in Iberian pigs, which is
probably due to higher crude fat content found in acorns during this
experiment. A significant correlation coefficient between carcass weight and
backfat thickness was found (r =
0.69; P ≤ 0.01).
The acorns
had low protein content, and were relatively high in oleic acid content (C18:1 n-9). The commercial feed had a
relatively high proportion of linoleic acid (C18:2n-6) in accordance with data from Rey et al. (2006) and a
higher amount of protein than that provided by the fresh acorns (15.6% vs. 5.6%
respectively). Acorns have a higher content of crude fat, net energy, and
metabolizable energy when compared with commercial feeds. The fresh acorns had
the highest MUFA, PUFA, and n6:n3 ratio
(Table 1).
Table 1. Analysed composition of feed (g/100g) and fatty acid (mg/100 mg) composition of the experimental diet groups
|
Nutrient composition
|
Feedstuff
|
Fresh acorns
|
P*
|
|
Moisture (g/100 g)
|
14b
|
32.4a
|
0.0017
|
|
Crude protein
(g/100 g)
|
15.6a
|
5.6b
|
0.0001
|
|
Crude fat (g/100 g)
|
3.3b
|
5a
|
0.002
|
|
Fibre (g/100 g)
|
6.8a
|
5.6b
|
0.013
|
|
Ash (g/100 g)
|
3.7a
|
2.7b
|
0.010
|
|
Net energy (Mcal/kg)
|
1.73b
|
1.85a
|
0.09
|
|
Metabolisable energy (Mcal/kg)
|
2.9b
|
3.13a
|
0.011
|
|
Value D
|
80b
|
88a
|
0.0012
|
|
Fatty acid profile
mg/100 mg
|
|
|
|
|
C 14:0
|
18.16a
|
0.12b
|
0.0032
|
|
C16:0
|
|
17.48
|
nsA
|
|
C 16:1n-9
|
1.18
|
1.7
|
ns
|
|
C 16:1n-7
|
|
0.16
|
|
|
C 17:0
|
|
0.05
|
|
|
C18:0
|
|
1.72
|
|
|
C18:1n-9
|
18.39b
|
27.3a
|
0.0016
|
|
C18:1n-7
|
0.75b
|
5.84a
|
0.0031
|
|
C18:2n-6
|
57.7a
|
39.1b
|
0.009
|
|
C 20:0
|
3.51b
|
4.58a
|
0.0001
|
|
C18:3 n-3
|
|
1.65
|
|
|
C 20:2
|
19.75a
|
0.06b
|
0.0001
|
|
SFAB
|
|
23.9
|
|
|
MUFAC
|
19.1b
|
35.01a
|
0.0001
|
|
PUFAD
|
61.2a
|
40.8b
|
0.0001
|
|
n6:n3E
|
16.4b
|
23.7a
|
0.001
|
|
P:SF
|
3.1a
|
1.7b
|
0.001
|
|
Ans: not significant
|
|
BƩ Saturated fatty acids: C14+C16+C17+C18+C20
|
|
CƩ Monounsaturated fatty acids: C16:1+C18:1n-9+C18:1n-7
|
|
DƩ Polyunsaturated fatty acids: C18:2n-6+C18:3n-3+C20:2
|
|
En-6:n-3: Fatty acids ratio
|
|
FP:S: Polyunsaturated: Saturated fatty acids ratio
|
*The p-value correspond to Student t test between feedstuff and fresh
acorn
Fatty acid
profile in muscle
Wild boars
fed with acorns had a significantly lower proportion (P= 0.0001) of C 16:0 than those fed only with commercial feed
(Table 2). However, no differences in C 14:0, C 16:1n-9, C 16:1n-7,
and C 20:3n-3 were detected among the groups. Similar results have been
described before in Iberian pigs fed with acorns and grass (Carrapiso
et al., 2020; Rey et al., 2006). However, there is no information
available about the effects of acorns or combinations of acorn and commercial
feed diets in confinement. According to the results of the present study, acorn
intake significantly modified the proportion of saturated fatty acids (SFA) of
the muscle. Wild boars raised with acorns had significantly (P= 0.0001) higher proportions of C18:1 n-9 in Longissimus lumborum (LL) muscle than the control group. Similar
results were found in C18:2 n-6,
C18:3 n-3, and MUFA. This effect is
more marked in diets with 40% acorns. Consequently, the group fed with 40%
acorns was a better indicator of the feeding background. It has been reported
that during winter commercial pigs reared outdoors (5 °C) had a reduced
proportion of SFA when compared with pigs fed indoors (22°C) (Bee Guex & Herzog, 2004). This differs from the present
study, where the average of temperatures between outdoors and indoors was not
as marked (17°C). Other studies showed that grass intake also increases the
proportion of C18:3 n-3 in the
backfat and intramuscular neural lipids in pigs fed with acorns and grass (Rey et
al., 2006). In this study, the proportion of C18:3 n-3 in LL can be attributed to the high content of linolenic acid
in acorns. According to the results of this experiment, it seems that the
content of fatty acids in the muscle is very sensitive to small variations in
dietary fat composition. This evidence indicates the importance of the acorn
diets on the quality of final products in wild boar meat. Ayuso
et al. (2020) found that eating acorns produced a higher C18:3 n-3 compared with commercial feed in
Iberian pigs, and Karolyi et al. (2007) found similar results in Black
Slovenian pigs.
In addition,
it is of interest to observe that the proportion of polar lipids such as C 22:6n-3
in LL was also increased (P= 0.0001)
by the acorns, but not by the commercial feed. This fatty acid, C 22:6n-3,
can reduce the risk of human cardiovascular disease (Morán
et al., 2019).
The P/S ratio
(Table 2) in LL ranged from 0.33 in the control group to 0.39 in 40% acorn diet
(P= 0.0001). For optimal health, the
P/S ratio of meat should be at least 0.4 (Batorska et al., 2018). Studies of meat
from the wild boars recorded the P/S ratio at a level of 0.50 (Batorska et al., 2018). The study concluded that the
P/S ratio was related to a high content of C18:2 n-6 (15.5–24.7 g 100 g−1), the origin of which is
associated with chestnuts, acorns, corn, and potatoes (Batorska
et al., 2018).
Cholesterol
in muscle
The
cholesterol content showed significant differences between groups (Table 2),
being lower for the wild boars fed with acorns, and with the highest value
found in the control group fed with commercial feed (P= 0.0001). Lui et al. (2007) reported a low content of
cholesterol in wild boars (29.6 mg/100 g), which was far from the 80 mg/100 g
found in domestic pigs by Sudom et al. (2001).
The cholesterol contents of the present study are low compared to those
reported for wild boars (48.1 to 63.8 mg/100 g) by Russo et al. (2017)
or by other studies on wild boars in Chile (Skewes et al., 2009). These
results coincide with those of other researchers who associated the consumption
of diets rich in MUFA with reductions in cholesterol and triglycerides (Márquez
Contreras et al., 2018).
Sensory
characteristics
In this
study, the hedonic scale reflected a higher perception by consumers of meat
sensory characteristics. The sensory panel detected differences (P≥0.05) in the flavour,
tenderness and juiciness between groups (Table 2). A positive relationship was
observed between the percentages of MUFA and PUFA with the attributes flavour, tenderness and juiciness. This is explained by the
fact that meat from animals fed with acorns was perceived as juicier and more
tender by a sensory panel. Tartrakoon et al.
(2016) reported that SFA and MUFA have a positive influence on the flavour, tenderness and juiciness of the meat. Similarly, Aaslyng & Meinert (2017)
reported a strong relationship between sensory characteristics such as flavour with the type and amount of fatty acids in meat,
especially C18:1 n-9, and in Iberian
dry-cured loins, Soto et al. (2008) found a significant difference in flavour
in pigs reared with free access to acorns (Quercus
spp.) and grass. These studies are all in agreement with the acorn impact
observed in the present experiment.
Table 2. Fatty acid
composition (mg/100 mg), cholesterol and sensory characteristics of L.
lumborum muscle from wild boars fed the experimental diets.
|
Control
|
20%
|
40%
|
R2
|
|
C 14:0
|
1.17
|
1.21
|
1.22
|
0.632
|
|
C 16:0
|
24.56a
|
23.11b
|
23.51b
|
0.553
|
|
C 16:1n-9
|
0.4
|
0.41
|
0.42
|
0.712
|
|
C 16:1n-7
|
2.43
|
2.58
|
2.69
|
0.643
|
|
C 17:0
|
0.25b
|
0.32a
|
0.33a
|
0.783
|
|
C 17:1
|
0.21b
|
0.28a
|
0.29a
|
0.641
|
|
C 18:0
|
11.73b
|
11.9ab
|
12.1a
|
0.893
|
|
C 18:1n-9
|
40.3b
|
41a
|
41.1a
|
0.857
|
|
C 18:1n-7
|
2.59b
|
3.01a
|
3.11a
|
0.735
|
|
C 18:2n-6
|
12.5b
|
12.9b
|
13.1a
|
0.884
|
|
C18:3n-3
|
0.46b
|
0.5a
|
0.51a
|
0.865
|
|
C 18:4n-3
|
0.05c
|
0.08b
|
0.1a
|
0.873
|
|
C 20:0
|
0.17b
|
0.18ab
|
0.19a
|
0.842
|
|
C 20:1
|
0.82b
|
0.84a
|
0.84a
|
0.786
|
|
C 20:2
|
0.53b
|
0.53b
|
0.57a
|
0.768
|
|
C 20:3n-6
|
0.12c
|
0.14b
|
0.15a
|
0.850
|
|
C 20:3n-3
|
0.08
|
0.09
|
0.09
|
0.794
|
|
C 20:4n-6
|
0.03c
|
0.14b
|
0.19a
|
0.725
|
|
C 22:6n-3
|
0.1b
|
0.11a
|
0.12a
|
0.639
|
|
C 23:0
|
0.72c
|
0.84b
|
1.03a
|
0.747
|
|
C 24:1
|
0.09b
|
0.1b
|
0.16a
|
0.759
|
|
SFAA
|
37.54b
|
38.13a
|
38.77a
|
0.825
|
|
MUFAB
|
47.3b
|
48.03a
|
48.11a
|
0.769
|
|
PUFAC
|
14.06c
|
14.43b
|
14.47a
|
0.758
|
|
n6: n3D
|
19.96b
|
19.92b
|
20.76a
|
0.807
|
|
P:SE
|
0.33c
|
0.38b
|
0.39a
|
0.811
|
|
Cholesterol
|
23.9a
|
21.6b
|
22.2b
|
0.732
|
|
Flavour
|
4.99c
|
5.04b
|
5.33a
|
0.620
|
|
Tenderness
|
4.43c
|
5.05b
|
5.22a
|
0.812
|
|
Juiceness
|
4.4c
|
4.71b
|
5a
|
0.849
|
|
AƩ Saturated fatty acids: C14+C16+C17+C18+C20
|
|
BƩ Monounsaturated fatty acids: C16:1+C18:1n-9+C18:1n-7
|
|
CƩ Polyunsaturated fatty acids: C18:2n-6+C18:3n-3+C20:2
|
|
Dn-6:n-3: Fatty acids ratio
|
|
EP:S: Polyunsaturated: Saturated fatty acids ratio
|
* Values with different superscript are
significantly different using the Duncan test (P < 0.05).
CONCLUSIONS
The wild boar
L. lumborum muscle from the three
groups had a fatty acid profile that was quite variable, as expected in animals
on a controlled diet. LL muscles of the wild boar control group showed a higher
composition of C 16:0 fatty acid and cholesterol, and lower MUFA, PUFA, n6:
n3, and P/S ratio than those wild boar groups fed with acorns. As a
consequence, the meat of wild boars fed with acorns was superior with regard to
nutritional factors and sensory characteristics. In order to understand the
role of acorn diets on wild boar meat quality in Chile, further studies are
recommended on specific parameters such as HDL cholesterol in the meat, because
the findings of this study indicate that these could be well-received by
consumers.
ACKNOWLEDGEMENTS
The authors
thank the JABALICHILE for the financing part of this study. The authors would
also like to acknowledge Professor Nestor Mendoza of the Department of Bromatology,
University of Concepcion, and Ms Nelly Delgado of the
Agricultural Research Institute (INIA Remehue) for
their collaboration in the present study.
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Author contribution
Conception
and design of research: PGFA, RMP, OSR;
data analysis and interpretation: PGFA, RMP, OSR; redaction of the manuscript:
PGFA, RMP, OSR.
Conflict of interests
The authors
declare no conflict of interests.
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, Rodrigo Morales Pavez **