AABArchives Animal BreedingAABArch. Anim. Breed.2363-9822Copernicus GmbHGöttingen, Germany10.5194/aab-58-159-2015Concentration of three branched-chain fatty acids in adipose tissue
does not affect meat sensory traits in crossbred and purebred German
“Merinolandschaf” lambsSchillerK. F.katja.schiller@uni-hohenheim.dePreussS.KaffarnikS.VetterW.RodehutscordM.BennewitzJ.Institute of Animal Science, University of Hohenheim,
Stuttgart, GermanyInstitute of Food Chemistry, University of Hohenheim,
Stuttgart, GermanyK. F. Schiller (katja.schiller@uni-hohenheim.de)1591638January201513March201530March2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://aab.copernicus.org/articles/58/159/2015/aab-58-159-2015.htmlThe full text article is available as a PDF file from https://aab.copernicus.org/articles/58/159/2015/aab-58-159-2015.pdf
Intense sheep odour and flavour in lamb is often associated with
lower consumer acceptance. Branched-chain fatty acids (BCFAs) are suggested
as possible reasons. Therefore, muscle and subcutaneous adipose tissue
samples of 98 lamb chops were analysed for three BCFAs (4-methyloctanoic,
4-ethyloctanoic and 4-methylnonanoic fatty acid). Samples were derived from
a previous study, in which lambs were raised and fattened under intensive
conditions and tested for sensory quality. BCFA contents of fat extracts
from muscle tissue were very low and quantification was not possible. In
subcutaneous adipose tissue different concentrations of BCFA and
differences between crosses were detected. The sex of lambs had a significant
influence. The BCFA correlations were significant, while correlations between
BCFA of adipose tissue and sensory traits were not significant. Therefore, it
seems likely that BCFA concentrations were too low and/or other substances
are involved in causing the lamb flavour detected through sensory analysis.
Introduction
“Merinolandschaf” (ML) represent a widespread sheep breed in Germany. In order to
improve growth performance of fattening lambs, F1-crossbreeding obtained
from mating ML ewes with a meat-type terminal-sire breed is frequently
performed. The choice of the sire line is of fundamental importance for
optimizing F1-crossing systems to provide the best possible quality.
Typical sheep odour and flavour is often associated with an unpleasant smell
and therefore lower consumer acceptance of sheep products such as lamb (Prescott et al., 2001; Rhee and Ziprin, 1996; Wong et al., 1975). For lamb production,
choosing a certain terminal-sire
breed would be a rather simple and practicable opportunity to achieve better
consumer acceptance if this reduced species-specific odour and flavour.
In the sensory analysis of Henseler et al. (2014), differences
in lamb flavour between crosses were detected. Since feeding conditions were
comparable for the crosses, a genetic influence of crossing was assumed.
The branched-chain fatty acids (BCFAs) 4-methyloctanoic acid (4-Me-8:0), 4-methylnonanoic acid (4-Me-9:0) (Wong et al., 1975) and
4-ethyloctanoic acid (4-Et-8:0) (Ha and Lindsay, 1990) were
thought to be mainly responsible for species-related flavour.
Prescott et al. (2001) mentioned 4-Me-8:0, in particular, as a
strong candidate. The authors reported that an increase in BCFA content in
meat, reached by adding different amounts of 4-Me-8:0 and 4-Me-9:0, resulted in decreased acceptance
of the meat on the part of consumers. As medium-chain fatty acids might have a
more decisive role than longer chained fatty acids in sensory analysis, due
to their higher volatility, we focused on three medium-sized BCFAs, namely
4-Me-8:0, 4-Me-9:0 and 4-Et-8:0.
Crosses, cross abbreviations (abbrev.), number (n) of muscle tissue
samples (MEAT), number of subcutaneous adipose tissue samples (FAT) per
cross and sex and concentrations of 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0
(ng mg-1)
in subcutaneous adipose tissue of different crosses of sheep.
* ML is “Merinolandschaf”; ** German blackheaded mutton sheep is “Deutsches Schwarzköpfiges
Fleischschaf”; a,b,c,d within a column and same effect (cross or sex), values with different superscript letters (a-d) differ significantly at P≤0.05.
Feed was found to have a strong impact on the concentrations of BCFA in lamb
tissue. According to Duncan and Garton (1978),
carbohydrate-rich feed (barley-based) results in higher BCFA concentrations
in subcutaneous adipose tissue than grass feeding. Busboom
et al. (1981) reported higher BCFA concentrations for high- compared to low-energy diets. For pasture feeding, lower concentrations of 4-Me-8:0 and
4-Me-9:0 were reported compared to concentrate feeding
(Priolo et al., 2001; Young et al., 2003). Similar
results were reported for other BCFAs, such as 4-Me-10:0, 4-Me-12:0 and 4-Me-14:0
(Miller et al., 1986), even though only low amounts of BCFA
could be found in plants (Diedrich and Henschel, 1990).
BCFAs are formed mainly from microbial metabolism in the rumen
(Chilliard et al., 2003). Through this
fermentation, acetate, propionate and butyrate are produced, and, especially
at high propionate concentrations, BCFA formation increases (Lindsay, 1996).
The aim of the present study was to investigate the occurrence and
concentrations of the branched-chain fatty acids 4-Me-8:0, 4-Me-9:0 and
4-Et-8:0 in five different F1-crossbreeds and purebred ML. Intense feeding
conditions were chosen because BCFA concentrations were expected to be
higher than for pasture feeding and feeding differences could be minimized.
A further aim was to investigate the relationship between the branched-chain fatty acids tested and several sensory traits.
Material and methodsAnimals and sensory data set
The tissues analysed were from chops of the 10/11th rib obtained from
98 lambs. All lambs were purebred ML or F1-crossbred lambs which were
produced to test five meat-type terminal-sire breeds (Charolais, Ile de
France, German blackheaded mutton sheep, Suffolk and Texel) on ML ewes. Crosses
and cross abbreviations are listed in Table 1. Intensive feeding conditions
were chosen. Lambs were raised on seven farms until weaning at a body weight (BW) of 17 kg with free access to concentrate (soy- and barley-based) and
roughage. Fattening was centralized and took place in group housing with
200–300 g hay day-1 per animal and concentrate ad libitum. Lambs were slaughtered at 43.14±3.78 kg body weight and at an age of 102–161 days. After slaughter the
carcasses were chilled to 1–3 ∘C and dissected; adipose and muscle
tissue of the chops were separated and frozen (-20∘C) 48 h post mortem. To ensure enough sample
material for analysis, lambs needed to weigh at least 36 kg at slaughter
and show medium fat coverage. Lambs were chosen at random from animals fulfilling these
criteria. All samples were homogenized after 222–530 days
of storage (disperser Ultra Turrax T18-10, IKA Werke, Staufen,
Germany), and muscle tissue was lyophilized (freeze dryer Gamma 1-20 LMC2, Martin
Christ, Osterode, Germany) at 2.6 mbar for 72 h. Samples were frozen
(-20∘C) until preparation for analysis.
In a previous study, chops of the same animals as used for this study were
tested for their sensory meat quality (Henseler et al.,
2014). The traits tested were overall appraisal, lamb flavour, flavour
quality, odour, juiciness and tenderness. Traits were evaluated by a trained
sensory panel of 21 persons of different sex and ages. Fifteen sensory tests were conducted on 15 days; a duplicate was
included in every test for every tester. The chops tested were 2 cm thick and unseasoned, and subcutaneous
fat was removed. They were grilled on a contact grill at 170 ∘C and subsequently left to simmer for 2:20 min wrapped in aluminium foil. For tasting, the
chops were sliced in 0.7 cm broad sections, and the inner and outer sections were
discarded. The data set of the sensory analysis was used for determining
possible relations between BCFA concentrations and sensory traits.
Analysis of BCFA
The fat extracts of raw muscle tissue of musculuslongissimus thoracis et lumborum and subcutaneous adipose tissue
of the same chop (without bones) were analysed separately. The preparation
of the samples was undertaken according to the method of
Kaffarnik et al. (2014).
Subcutaneous fat samples were directly transesterified to result in fatty
acid methyl esters (FAMEs).
The fat of muscle tissue samples (dried homogenized muscle tissue,
subcutaneous fat removed) was extracted by means of a Soxtherm apparatus
(Kaffarnik et al., 2014). The
sample extracts were concentrated to 10 mL, and an aliquot was used for the
formation of FAMEs. FAMEs were analysed by gas chromatography coupled with
mass spectrometry in selected ion monitoring mode (GC–MS-SIM).
Quantification was performed using the internal standards undecenoic acid
methyl ester (11:1n-1) and tetradecanoic acid ethyl ester (14:0). The limit of
detection was 1.1–1.4 ng g-1, and the limit of quantification was 3.6–4.8 pg
(Kaffarnik et al., 2014).
Additionally, it was tested whether lyophilization had any influence on the
results. For this purpose, 1.43 g fresh muscle tissue was pulverized and
mixed with sodium sulfate (ratio 2.6:1); the remaining procedure was as described above.
For another test three adipose tissue samples were lyophilized. The dry
samples and their condensates, derived from the drying process, were directly
esterified and analysed.
Statistical analysis
The concentrations of BCFA found were recorded for each chop and analysed using
the following statistical model:
yijk=μ+Cj+SEXk+Cj⋅SEXk+eijk,
where y… is the amount of BCFA of lamb i (ng mg-1),
Cj is the fixed effect of cross j and SEXk is the fixed effect of sex
k. Cj⋅ SEXk represents the interaction of crossj and SEXk. The
model was fitted using the MIXED procedure of SAS (9.2, SAS Inst. Inc.,
Cary, NC). For the calculation of correlation, data of subcutaneous adipose
tissue and the sensory analysis from Henseler et al. (2014)
were used.
ResultsMuscle tissue
Muscle tissue samples from 17 lambs showed concentrations below the limit of
quantification or below the limit of detection for all three BCFAs investigated
(data not shown). This was also valid for the non-lyophilized fresh muscle
tissue tested. Due to these results the amount of samples was limited to 17
because a sample with BCFA sufficient for
quantification was not expected to be found. Losses in BCFA concentration arising from lyophilization
under the conditions applied were not detectable. In collected fatty
condensates, developed during lyophilization, no BCFAs were detectable.
Adipose tissue
Significant differences between crosses were detected for all three fatty acids tested (shown in Table 1). Concentrations of 4-Me-8:0 ranged between
56.9 and 103.0 ng mg-1, while those of 4-Et-8:0 (13.3–19.7 ng mg-1) and for 4-Me-9:0
(17.3–46.6 ng mg-1) were lower. Only CH and SK showed significant differences
in 4-Me-8:0 and 4-Me-9:0 concentrations compared to ML. For 4-Me-9:0, two groups
were distinguishable, with CH, SK and SU having significantly higher values.
For 4-Et-8:0, none of the crosses tested showed significant differences
compared to purebred ML. A significant (P≤0.001) influence of sex was
identified for concentrations of 4-Me-8:0 and 4-Me-9:0 but not for 4-Et-8:0
(Table 1). The cross–sex interaction effect was significant for 4-Me-8:0
and 4-Me-9:0 at P≤0.05. These interaction effects resulted in scaling effects,
i.e. the differences between the crosses and between sexes varied numerically but
without a re-ranking. For 4-Et-8:0, the interaction effect was not
significant.
Correlation coefficients of concentrations of the fatty acids 4-Me-8:0,
4-Et-8:0 and 4-Me-9:0 (ng mg-1) in sheep subcutaneous adipose tissue and
six sensory traits (Henseler et al., 2014).
Correlations of BCFA concentrations and sensory analysis
Significant (P≤0.01) correlations were detected between the BCFAs tested
(see Table 2), indicating, in particular, that concentrations of 4-Me-8:0 and
4-Me-9:0 are closely related. Correlations between the amounts of BCFAs in
adipose tissue and the sensory traits were not significant.
Discussion
The quantification of the fat extracts of muscle tissue (MEAT) samples turned out to
be more problematic than for subcutaneous adipose tissue (FAT).
Quantification for MEAT was not possible, while for corresponding FAT from
the same individual quantification was possible. FAT samples showed
analysable results despite the concentration of injection being lower than for
MEAT. Brennand and Lindsay (1992) reported
higher concentrations of 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0 in FAT than in
MEAT, which supports the results of the present study. Miller et al. (1986)
reported lower levels of other BCFAs (4-Me-10:0, 4-Me-12:0 and 4-Me-14:0) in
MEAT than in FAT, partly below the limit of quantification.
For all three BCFAs, significant differences between specific crosses were
detected. The smallest differences were detected for 4-Et-8:0.
Busboom et al. (1981) tested several BCFAs (4-Me-10:0 until
4-Me-17:0 and 4-Me-17:1) and reported small and nonsignificant breed effects.
Also, Duckett and Kuber (2001) determined that breed or the breed of
terminal sire seems to have a minor impact on the intensity of lamb flavour. Apart
from the detected breed effects in the present study, a highly significant
(P≤0.001) influence of sex was detected for two of the BCFAs investigated (Table 1). This is supported by results in Watkins et
al. (2010), who detected influences of sex and age for 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0.
The influence of age at slaughter was tested but was not significant in the
present study, most likely because age variation was low.
As summarized by Young and Braggins (1998), it seems probable
that other substances, such as phenols and sulfur-containing compounds, could
play a role besides BCFA for the lamb or sheep-like odour and flavour. According
to Resconi et al. (2010), lamb flavour in
grilled loins is related to the concentration of heptan-2-one and
oct-1-en-3-one. Priolo et al. (2001) suggested that
3-methylindole (skatole), in addition to its own flavour, might increase the perception
of sheep-like flavour caused by BCFA. Another factor might be the
concentration of linoleic and α-linolenic acid, which, according to
Sañudo et al. (2000),
influence lamb flavour intensity. The presence of some of the substances
mentioned might explain the results of Henseler
et al. (2014), where lamb flavour was noticed by the sensory panel although
BCFA levels detected in the present study were very low in fat extracts of
muscle tissue.
A lack of significant results concerning correlations could be due to other substances besides the three BCFAs tested being involved in lamb flavour. Another possibility would be a different fatty acid composition
in subcutaneous as opposed to intramuscular fat as observed for some fatty acids
and reviewed by Wood et al. (2008). Differences in the fatty acid composition of subcutaneous and
intramuscular fat with regard to BCFA remain unclear but might be an
interesting objective for further studies.
Conclusions
Differences in concentrations of 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0 were
detected in subcutaneous adipose tissue of different crosses. For fat
extracts from muscle tissue, concentrations of the fatty acids investigated could not be quantified. In adipose tissue samples significant correlations
were found between BCFAs. Correlations between the amount of BCFAs in
adipose tissue and meat sensory traits were not significant, possibly
because of other substances involved or differences in the fatty acid
composition of intramuscular fat and adipose tissue.
Acknowledgements
The authors thank the laboratory teams of the Institute of Animal Science
and the Institute of Food Chemistry of the University of Hohenheim. K. F. Schiller
was supported by the H. Wilhelm Schaumann Stiftung, Hamburg, Germany.
Edited by: K. Wimmers
Reviewed by: two anonymous referees
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