Concentration of three branched-chain fatty acids in adipose tissue does not affect meat sensory traits in crossbred and purebred German "Merinolandschaf" lambs

Abstract

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.

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K. F. Schiller1, S. Preuss1, S. Kaffarnik2, W. Vetter2, M. Rodehutscord1, and J. Bennewitz1

1Institute of Animal Science, University of Hohenheim, Stuttgart, Germany

2Institute of Food Chemistry, University of Hohenheim, Stuttgart, Germany

Correspondence to: K. F. Schiller ([email protected])

Received: 8 January 2015 Revised: 13 March 2015 Accepted: 30 March 2015 Published: 24 April 2015

Abstract. Intense sheep odour and avour 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 quantication was not possible. In subcutaneous adipose tissue different concentrations of BCFA and differences between crosses were detected. The sex of lambs had a signicant inuence. The BCFA correlations were signicant, while correlations between BCFA of adipose tissue and sensory traits were not signicant. Therefore, it seems likely that BCFA concentrations were too low and/or other substances are involved in causing the lamb avour detected through sensory analysis.

1 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 avour 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-specic odour and avour. In the sensory analysis of Henseler et al. (2014), differences in lamb avour between crosses were detected.Since feeding conditions were comparable for the crosses,

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Concentration of three branched-chain fatty acids in adipose tissue does not affect meat sensory traits in crossbred and purebred German Merinolandschaf lambs

a genetic inuence 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 avour.Prescott et al. (2001) mentioned 4-Me-8:0, in particular, as a strong candidate. The authors reported that an increase inBCFA 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.

Feed was found to have a strong impact on the concentrations of BCFA in lamb tissue. According to Duncan andGarton (1978), carbohydrate-rich feed (barley-based) results in higher BCFA concentrations in subcutaneous adipose tissue than grass feeding. Busboom et al. (1981) reported higher

Published by Copernicus Publications on behalf of the Leibniz Institute for Farm Animal Biology.

160 K. F. Schiller et al.: Concentrations of branched chain fatty acids in lambs

Table 1. 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 mg1) in subcutaneous adipose tissue of different crosses of sheep.

Cross/sex abbrev. n 4-Me-8:0 (ng mg1) 4-Et-8:0 (ng mg1) 4-Me-9:0 (ng mg1)

MEAT FAT LSmean SE LSmean SE LSmean SE

Charolais ML CH 4 14 103.0

c 13.1 19.7b 2.3 46.6b 9.3 Ile de France ML IF 3 18 67.0

a,b 11.6 19.4b 2.1 18.7a 8.2 ML ML ML 3 15 57.3

a 12.7 15.4a,b 2.3 18.3a 9.0 German blackheaded mutton sheep ML SK 2 18 99.1

b,c 11.6 18.4a,b 2.1 44.6b 8.3 Suffolk ML SU 3 16 87.9

a,b,c 12.3 13.3a 2.2 46.6b 8.7 Texel ML TX 2 17 56.9

a 12.0 18.2a,b 2.1 17.3a 8.5 Male m 8 44 99.7a 7.4 15.5a 1.3 48.5a 5.3 Female f 9 54 57.3b 6.7 18.3a 1.2 15.6b 4.8

ML is Merinolandschaf; German blackheaded mutton sheep is Deutsches Schwarzkpges Fleischschaf; a,b,c,d within a column and same effect (cross or sex), values with different superscript letters (a-d) differ signicantly at P 0.05.

trate ad libitum. Lambs were slaughtered at 43.14 3.78 kg

body weight and at an age of 102161 days. After slaughter the carcasses were chilled to 13 C and dissected; adipose and muscle tissue of the chops were separated and frozen (20 C) 48 h post mortem. To ensure enough sample ma

terial for analysis, lambs needed to weigh at least 36 kg at slaughter and show medium fat coverage. Lambs were chosen at random from animals fullling these criteria. All samples were homogenized after 222530 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 avour, avour 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.

2.2 Analysis of BCFA

The fat extracts of raw muscle tissue of musculus longissimus 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 sam-

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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 ve 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.

2 Material and methods

2.1 Animals 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 ve 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 200300 g hay day1 per animal and concen-

K. F. Schiller et al.: Concentrations of branched chain fatty acids in lambs 161

ples were directly transesteried 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 (GCMS-SIM). Quantication 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 1.11.4 ng g1,

and the limit of quantication was 3.64.8 pg (Kaffarnik et al., 2014).

Additionally, it was tested whether lyophilization had any inuence 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 esteried and analysed.

2.3 Statistical analysis

The concentrations of BCFA found were recorded for each chop and analysed using the following statistical model:

yijk = + Cj + SEXk + Cj SEXk + eijk, (1) where y... is the amount of BCFA of lamb i (ng mg1), Cj is the xed effect of cross j and SEXk is the xed effect of sex k. Cj SEXk represents the interaction of crossj and SEXk.

The model was tted 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.

3 Results

3.1 Muscle tissue

Muscle tissue samples from 17 lambs showed concentrations below the limit of quantication 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 sufcient for quantication 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.

3.2 Adipose tissue

Signicant 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 mg1,

Table 2. Correlation coefcients of concentrations of the fatty acids 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0 (ng mg1) in sheep subcutaneous adipose tissue and six sensory traits (Henseler et al., 2014).

4-Me-8:0 4-Et-8:0 4-Me-9:0

4-Me-8:0 14-Et-8:0 0.335 14-Me-9:0 0.878 0.080 1

Overall appraisal 0.156 0.044 0.045

Lamb avour 0.005 0.072 0.073

Flavour quality 0.088 0.058 0.026

Odour 0.104 0.060 0.012

Juiciness 0.034 0.097 0.128

Tenderness 0.189 0.037 0.144

Signicant at P 0.01.

while those of 4-Et-8:0 (13.319.7 ng mg1) and for 4-Me-9:0 (17.346.6 ng mg1) were lower. Only CH and SK showed signicant 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 signicantly higher values. For 4-Et-8:0, none of the crosses tested showed signicant differences compared to purebred ML. A signicant (P 0.001) inuence of sex was identied for

concentrations of 4-Me-8:0 and 4-Me-9:0 but not for 4-Et-8:0 (Table 1). The crosssex interaction effect was signi-cant for 4-Me-8:0 and 4-Me-9:0 at P 0.05. These inter

action 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 signicant.

3.3 Correlations of BCFA concentrations and sensory analysis

Signicant (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 signicant.

4 Discussion

The quantication of the fat extracts of muscle tissue (MEAT) samples turned out to be more problematic than for subcutaneous adipose tissue (FAT). Quantication for MEAT was not possible, while for corresponding FAT from the same individual quantication 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

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162 K. F. Schiller et al.: Concentrations of branched chain fatty acids in lambs

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 quantication.

For all three BCFAs, signicant differences between specic 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 nonsignicant 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 avour. Apart from the detected breed effects in the present study, a highly signicant (P 0.001) inuence of

sex was detected for two of the BCFAs investigated (Table 1).

This is supported by results in Watkins et al. (2010), who detected inuences of sex and age for 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0. The inuence of age at slaughter was tested but was not signicant 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 avour. According to Resconi et al. (2010), lamb avour 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 avour, might increase the perception of sheep-like avour caused by BCFA. Another factor might be the concentration of linoleic and -linolenic acid, which, according to Saudo et al. (2000), inuence lamb avour intensity. The presence of some of the substances mentioned might explain the results of Henseler et al. (2014), where lamb avour 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 signicant results concerning correlations could be due to other substances besides the three BCFAs tested being involved in lamb avour. 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.

5 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 quantied.In adipose tissue samples signicant correlations were found between BCFAs. Correlations between the amount of BCFAs in adipose tissue and meat sensory traits were not signicant, 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. WimmersReviewed by: two anonymous referees

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