Meat Science 100 (2015) 97–109

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Identification of sensory attributes, instrumental and chemical measurements important for consumer acceptability of grilled lamb Longissimus lumborum O.R. Oltra a,b,1, L.J. Farmer a,b,⁎,1, A.W. Gordon a, B.W. Moss a,b,1, J. Birnie c, D.J. Devlin a, E.L.C. Tolland a, I.J. Tollerton a, A.M. Beattie a, J.T. Kennedy a, D. Farrell a a b c

Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, UK Consorcio Lechero, Antonio Matta 1266, Osorno 5960900, Chile Dunbia, Granville Industrial Estate, Dungannon, Co., Tyrone BT70 1NJ, UK

a r t i c l e

i n f o

Article history: Received 6 June 2014 Received in revised form 10 September 2014 Accepted 15 September 2014 Available online 28 September 2014 Keywords: Lamb Sensory Preference mapping Consumer

a b s t r a c t In this study, important eating quality attributes that influence consumer liking for grilled lamb loin have been identified using preference mapping techniques. The eating quality attributes identified as driving the consumer liking of lamb loin steaks were “tenderness”, “sweet flavour”, “meaty aftertaste”, “roast lamb flavour” and “roast lamb aftertaste”. In contrast, the texture attribute “rubbery” and the flavour attributes “bitter flavour” and “bitter aftertaste” had a negative influence on consumer perceptions. Associations were observed between eating quality and a number of instrumental and chemical measurements. Warner Bratzler Shear Force showed an association with “rubbery” texture and a negative association with “tenderness” and consumer liking scores. The compounds, glucose, glucose-6-phosphate, inosine, inosine monophosphate and adenosine monophosphate were associated with the attributes, “sweet flavour”, “meaty aftertaste”, “roast lamb flavour”, “roast lamb aftertaste” and with consumer scores for liking of lamb which is probably caused by the role some of these compounds play as precursors of flavour and as taste compounds. © 2014 Published by Elsevier Ltd.

1. Introduction Sensory quality is a fundamental issue for consumer satisfaction for meat products. However, a very low correspondence between quality expectation and quality experience has been reported (Grunert, 2006; Grunert, Bredahl, & Brunso, 2004). This gives ample scope for improving eating quality to meet consumer expectations. To achieve this, knowledge of those eating quality attributes of meat that really matter to consumers is essential. Lamb eating quality can be influenced by a range of pre- and postslaughter factors (Saňudo, Muela, & Campo, 2013; Xiong, Ho, & Shahidi, 1999). Acceptability of lamb can also depend on regional or cultural factors and can differ between countries (Dransfield et al., 1984; Oliver et al., 2006; Saňudo et al., 1998). Approaches to investigate the importance of the different eating quality attributes of meat have involved the use of marketing tools such (Thompson, Gee, et al., 2005) as surveys (Verbeke & Viaene, 1999), ⁎ Corresponding author at: Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, UK. Tel.: +44 28 90255342. E-mail address: [email protected] (L.J. Farmer). 1 Previously, Queen's University Belfast, University Road, Belfast BT7 1NN, UK.

http://dx.doi.org/10.1016/j.meatsci.2014.09.007 0309-1740/© 2014 Published by Elsevier Ltd.

sensory techniques using consumers (Hopkins, Hegarty, Walker, & Pethick, 2006; Oliver et al., 2006; Thompson, Gee, et al., 2005) or trained sensory panels (Jeremiah, Tong, & Gibson, 1998; Prescott, Young, & O'Neill, 2001; Saňudo et al., 2000). While tenderness has traditionally been the primary concern of retailers (Huffman et al., 1996), sensory studies have provided evidence that flavour as well as tenderness is very important for consumer overall acceptability (Font I Furnols et al., 2009; Thompson, Hopkins, et al., 2005). However, the connection between consumer scores, sensory profiling attributes, and meat quality measurements remains unclear. Preference mapping (Greenhoff & MacFie, 1994) can help elucidate differences in consumer preferences but this method has been little used to evaluate consumer acceptability of fresh meat. Schmidt et al. (2010) have used preference mapping to study the effect of cooking temperatures in beef steaks while Prescott et al. (2001) evaluated beef to which selected flavour compounds were added to simulate lamb. In the research reported herein, groups of lamb carcases were selected to give as wide a variation in eating quality as possible. Preference mapping was used to identify the eating quality attributes that drive consumer preferences for grilled lamb and the relationship of these attributes with instrumental and chemical analyses.

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2. Materials and methods 2.1. Animals and sampling Fourteen experimental groups of sheep (n = 289 in total) were selected from commercial production and processing regimes (Table 1). The aim was to select 14 groups of animals which would be expected to provide loin meat with high, medium and low tenderness and with a range of flavour characteristics. It was not the aim of this study to compare the effects of the different treatments and production methods were not controlled. The animals were obtained from local farms and the farmers provided basic information to the meat plant on the final feeding regime (Table 1); all treatments were reared on grass until weaning. They were slaughtered in two different abattoirs (in Wales and Northern Ireland) on five occasions. In Abattoir A, the carcasses were slow chilled at 10 °C for 10 h and then the temperature dropped to 2 °C for the next 14 h. In Abattoir B, the carcases were electrically stimulated with high voltage (800 V at ca. 30 min postslaughter), fast chilled at 1 °C for 4 h and then stored at 2 °C for the next 20 h. In both abattoirs, the carcasses were boned out at 24 h after slaughter and the muscle Longissimus lumborum was removed, vacuum packed and aged in a chill room (2 °C) for the ageing time assigned to each experimental group (Table 1). After ageing, samples for sarcomere length were taken and the samples were blast frozen and stored at −20 °C until the analyses were conducted. The whole lamb loins were thawed for 12 h at 4 °C. The Longissimus lumborum was excised from the fat and accompanying muscles and cut into small steaks of 25 mm thick and a maximum of 50 mm long × 25 mm wide. The LD samples from the 14 experimental groups were used for sensory profiling panels and seven groups were selected to conduct consumer panels and analysis for Warner Bratzler Shear Force (WBSF), fatty acids and flavour precursors.

2.2. Sensory profiling panels Nine panellists (5 females and 4 males) were used to assess the samples from the Longissimus lumborum. The training of the panellists was adapted from the 4 step training system used by Labbe, Rytz, and Hugi (2004). The training was conducted in 5 sessions of 2 h each (10 h in total) and the sessions were conducted twice a week. The panellists developed a list of 48 profiling attributes for grilled lamb loin, together with definitions for these attributes (Table 2), using

animals from the same experimental groups as those subsequently assessed. The lamb loin steaks were grilled using a Silesia Clam Shell Grill (York, UK). The plate temperature was 180 °C, with the heat equally distributed between bottom and top plates. The lamb steaks were placed on the bottom plate and cooked for 30 s before the top plate was lowered. The steaks were cooked for a total of 4 min 30 s, then the samples were placed on a cardboard plate and left to equilibrate for 2 min before serving. This cooking time gave steaks cooked to a “well-done” endpoint or an internal temperature of 80 °C, which matches the preferences of most Northern Irish consumers (L.J. Farmer, unpublished data). In beef, this liking for “well-done” meat has been shown to have a little effect on consumer scores (Farmer, Devlin, et al., 2009). The assessors scored each attribute on a 100 mm linescale, anchored with terms such as “not intense” (0) to “extremely intense” (100). The assessors were instructed that any attribute that was not detected should be marked as zero on this scale. The assessors had a list of attribute descriptors and definitions available together with water for rinsing their palate. Panels were conducted over three sessions conducted on separate days within the same week. At each session, the panellists were presented with 14 samples in two batches over a period of 2 h. The samples were presented in a Latin square design and the experimental design and data recording were conducted using Fizz software (Biosystemes, Dijon, France).

2.3. Consumer panels Samples from the seven experimental groups selected from the sensory profiling data were presented to 120 consumers using the same cooking method described for the sensory profiling panels. All the consumers that participated in the panels were residents of Northern Ireland and were members of sport clubs, charity groups and/or parent associations. They included 63 females and 54 males (and three consumers who failed to answer this question). They were at least 15 years of age with a spread of ages up to 65 or more, and included people with a range of household incomes and occupations. Two consecutive panels with 20 consumers were conducted on each of three evenings. The consumers assessed a ‘starter’ sample (not analysed) and then one sample from each of the seven groups selected presented in a Latin square design, recording scores on a 100 mm line scale on paper forms for liking of appearance, liking of aroma, liking of flavour, liking of texture and overall liking anchored by the terms “dislike

Table 1 Experimental groups of animals selected according to the pre and post-slaughter factors included in the study. Exp group

1 2 3 4 5 6 7 8 9 10 11 12 13 14 a b c

Pre-slaughter and post-slaughter factors Sex

Age (months)

Dieta

Ageing (days)

Electrical stimulation

Chilling regime

Abattoir and month of slaughterb

Number of animals

Castrated male Castrated male Female — high fat coverc Female Entire male Castrated male Entire male Castrated male Female Castrated male Female — high fat coverc Entire male Entire male Entire male

4 to 8 4 to 8 4 to 8 4 to 8 4 to 8 N12 4 to 8 4 to 8 N12 4 to 8 4 to 8 4 to 8 b4 4 to 8

Grass/concentrate Grass/concentrate Grass Grass Grass Concentrate Concentrate Grass/concentrate Concentrate Grass Grass Grass/salt marsh Grass/milk Grass/concentrate

4 14 14 14 14 4 4 4 4 14 14 4 4 7

High voltage High voltage High voltage None None None High voltage None None None None High voltage High voltage None

Fast Fast Fast Slow Slow Fast Fast Fast Slow Fast Fast Fast Fast Slow

B-July B-July B-July A-July A-July B-May B-May B-July A-June B-July B-July B-July B-July A-September

21 21 21 21 21 21 21 21 21 21 21 21 16 21

Diet as reported by the farmer. Sheep for this experiment were slaughtered on two occasions at abattoir A and three occasions at abattoir B. High fat cover (classification 3H–4L European Commission Regulation, EC No 1249/2008).

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Table 2 Definitions of the sensory profiling descriptors for the lamb grilled steaks panels. Descriptor

Abbreviation

Definitions

Intensity aroma Char grilled aroma Roast lamb aroma Roast beef aroma Liver aroma Pork aroma Piggy aroma Buttery aroma Oily aroma Fatty aroma Caramel on bottom external appearance Juicy external appearance Pink internal appearance Brown internal appearance Juicy internal appearance Open internal appearance Connective tissue int. appearance Intensity flavour Char grilled flavour Roast lamb flavour Beefy flavour Pork flavour Liver flavour Bloody flavour Fatty flavour Bitter flavour Salty flavour Sour flavour Sweet flavour Tenderness texture Rubbery texture Chewy texture Lumpy on chewing texture Melts in the mouth texture Crumbly texture Spongy texture Intensity aftertaste Meaty aftertaste Roast lamb aftertaste Liver aftertaste Bloody aftertaste Oily aftertaste Lactic aftertaste Sour aftertaste Bitter aftertaste Salty aftertaste Sweet aftertaste Dry aftertaste

IntensityAr CharGrillAr RoastLambAr RBeefAr LiverAr PorkAr PiggyAr ButteryAr OilyAr FattyAr CaramAp JuicyAp PinkAp BrownAp JuicyAp OpenAp ConnectAp IntensityF CharGrillF RLambF BeefyF PorkF LiverF BloodyF FattyF BitterF SaltyF SourF SweetF TenderT RubberyT ChewyT LumpyT MeltsT CrumblyT SpongyF IntensityAT MeatyAT RLambAT LiverAT BloodyAT OilyAT LacicAT SourAT BitterAT SaltyAT SweetAT DryAT

First Impact of aroma strength Aroma of barbeque Aroma of roast lamb, whole joint, well done, just out of oven Aroma of roast beef, whole joint, well done, just out of oven Aroma of cooked fried Liver Aroma of roast pork just out of the oven Aroma reminiscent of pig slurry Aroma of warm melted butter Aroma of new vegetable oil Aroma of cooked lamb fat Toffee colour Shiny surface, liquid juices around the meat Pink colour of undercooked meat Brown colour of cooked meat Liquid juices inside the meat after cutting Space between fibres Gristle or connective tissue inside the meat after cutting First impact of flavour strength in the mouth Flavour reminiscent of meat burnt on a bbq Flavour of roast lamb, whole joint, well done, just out of oven Flavour of roast beef, whole joint, well done, just out of oven Flavour of roast pork just out of the oven Flavour reminiscent of cooked liver Flavour reminiscent of iron and metallic Flavour of cooked lamb fat Flavour reminiscent of burnt caramel Salt flavour in the mouth Sour flavour in the mouth Salt flavour in the mouth Soft and easy to chew before swallow Sample springs back on initial chewing Sample has to be chewed many times before swallowing Sample forms lumps in mouth on chewing Sample dissolves in mouth with little chewing Sample separates after chewing Soft and springy in mouth First impact of aftertaste strength Flavour reminiscent of roast cooked meat Flavour of roast lamb, whole joint, well done, just out of oven Flavour reminiscent of cooked liver Flavour reminiscent of iron and metallic Flavour of new vegetable oil Flavour reminiscent of milk Sour flavour in the mouth Flavour reminiscent of burnt caramel Salt flavour in the mouth Sweet flavour in the mount Dryness in mouth

extremely” (0) and “like extremely” (100). The panellists also completed a questionnaire which included 18 questions on demographic information and consumer behaviour, including composition of household, attitudes to red meat consumption, frequency of consumption of lamb, buying and cooking practices and satisfaction with eating experience. The consumer preference data were managed using the software FIZZ Forms by Biosystemes. 2.4. Instrumental measurements Instrumental measurements were conducted on samples from the seven experimental groups selected for the consumer panels, after the ageing time assigned to each group, except for sugar and nucleotide analyses which were conducted for only six of these seven experimental groups due to shortage of sample from Group 13. Sarcomere length was measured 48 h after slaughter using a laser diffraction technique, as described by Cross et al. (1981). Warner Bratzler Shear Force (WBSF) measurements were performed on 6 sample cores (13 mm diameter × 25 mm length) obtained from chilled steaks which were cooked at 75 °C for 50 min in a water bath (Grant, model Y28, Cambridge, England), using a texture analyser (Instron

model 3366, Bucks, UK) connected to a computer running the software Bluehill2 (version 2.5, High Wycombe, UK). 2.5. Chemical analysis The lean muscle from one loin steak (ca. 20 g) was homogenised and fatty acid profiles were determined on a one gramme subsample using a two-step saponification and methylation procedure (O'Fallon, Busboom, Nelson, & Gaskins, 2007). Analysis was conducted by gas chromatography (Varian-Chrompack CP-3800, Walton on Thames, UK) fitted with a flame ionisation detector and a BPX70 120 m × 0.32 mm column. The column oven was programmed from 50 °C to 120 °C at 20 °C/min holding for 0.1 min, then from 120 °C to 180 °C at 2 °C/min holding for 0.1 min and finally from 180 °C to 225 °C at 4 °C/min holding for 40 min. An aliquot of fatty acid methyl esters (1 μl) was injected using a split injection ratio of 25:1 and the injector temperature was programmed from 50 °C to 250 °C at 200 °C/min. The carrier gas used was helium at a constant flow rate of 1 ml/min and the detector temperature was 260 °C. Fatty acids were identified by comparing their retention times with fatty acid methyl ester standards (Sigma-Aldrich, Poole, UK).

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Total fat was obtained from 3 g of lean meat by extraction with diethyl ether following digestion with hydrochloric acid (British Standard 4401-4, 1970 Method B). Sugars, nucleotides and related compounds were extracted from duplicate samples (3 g of lean meat) which were placed in a 50 ml plastic centrifuge tube (Labcon, USA) together with 6 ml of perchloric acid solution (0.6 M). Rhamnose (10 mM) and cytidine (10 mM), in 0.5 ml of deionised water, were added as internal standards (Sigma, Poole, UK). Deionised water (1 ml) was added to the tubes and the mixture was homogenised (13,000 rpm) using an Ultraturrax blender (IKA-Verke model T-25, Staufen Germany) for 1 min, or until a smooth homogenate was obtained without heat generation. The tubes were then centrifuged (Mistral 3000i, London, UK) at 1800 rpm for 20 min. The supernatant was removed and its pH adjusted to pH 7 using a potassium hydroxide solution (5 M and then 0.5 M, added dropwise). The potassium perchlorate formed was removed by centrifugation at 1800 rpm for 20 min. The final “aqueous meat extract” was stored at − 80 °C until required for sugar and nucleotide measurements. Inosine monophosphate (IMP), adenosine monophosphate (AMP), inosine and hypoxanthine (μmol/g of tissue) were determined by analysis of the aqueous meat extract by reverse phase HPLC. The HPLC system (Thermo Separation Products, Manchester, UK) was equipped with a degasser (model SCM1100), Chromquest 4.2 software and a variable wavelength detector (SpectraSYSTEM UV1000, Thermo Separation Products, Manchester, UK). A HyPurity Aquastar column (5 μm particle size, 190 Å pore size, 150 × 4.6 mm i.d.; Thermo Electron Corporation, Manchester, UK) connected to a Phenomenex Securityguard guard column with a C18 3 × 4 mm ID cartridge was used for separation. An injection of sample extract (20 μl) was eluted with an isocratic mobile phase KH2PO4 (50 mM) prepared with HPLC grade water, pH adjusted to 2.5 by dropwise addition of hydrochloric acid (0.5 M) and filtered using 0.2 μm cellulose nitrate membrane filters (Whatman) prior to use. The flow rate was 1 ml min−1 with a total run time of 30 min and UV detection at 254 nm. Glucose, ribose, glucose-6-phosphate and ribose-5-phosphate were determined on the aqueous meat extract. One 2 ml aliquot was placed in 50 ml centrifuge tubes, diluted with 3 ml sodium carbonate buffer (50 mM, containing MgCl2 0.5 mM) at pH 9.3 and shaken for 3 min with a mixture of 1:1 (w/w) Dowex SOWX4-400 and WGR-2 resin (3 g; Sigma). The resins were removed by centrifugation for 20 min at 1800 g (centrifuge Mistral 3000i) and this first supernatant (A) was transferred to 1.8 ml screw cap glass vials. To 2 ml of the second sample was added 3 ml of sodium carbonate buffer containing alkaline phosphatase enzyme (Sigma) at a concentration of 0.55 units/ml buffer. The tubes were placed in an incubator (C25K New Brunswick Scientific Edison, New Jersey, USA) at 39 °C for 120 min. After incubation, the resins were added to the tubes, shaken and centrifuged as described above and the second supernatant (B) was transferred to vials. Both supernatant samples were analysed by ion chromatography (model DX500; Dionex Corp., Camberley, Surrey, UK) equipped with an AS50 autosampler, a GS50 gradient pump and an ED50 pulsed electrochemical detector with a gold electrode and an Ag/AgCl reference electrode. The sugars were separated and analysed on a CarboPac PA1 anion-exchange analytical column (Dionex P/N 35391; 250 × 4 mm i.d.) preceded by a similar guard column (Dionex P/N 43096; 4 × 50 mm). The wave form parameters used were as follows: (wave form = 0.00 s: 0.05 mV, 0.20 s: integration = begin, 0.40 s: integration = end, 0.41 s: 0.06 mV, 0.60 s: 0.06 mV, 0.61 s: −0.15 mV, 1 s: − 0.15 mV). The system was controlled by a HPLC Chromoleon software (Windows version, 6.30). The two eluents, I: deionised water prepared using a water purification unit (Elgastat option 4, Elga Labwater, UK) and II: 200 mM NaOH in deionised water were prepared as specified by the Dionex Corporation Document No. 032626 (Revision 07 March 2004). The elution programme for separation of sugars was: 0–15 min, I (10%): II (90%), 0.7 ml min− 1. The injection volume was 25 μl. From the analysis of the samples

extracted with and without enzyme (samples A and B) the glucose phosphates and ribose phosphates were determined by the difference between the total glucose and ribose in samples A and B. The analytical results for sugars and ribonucleotides and related compounds were corrected for recoveries determined from the internal standard and expressed as μmoles sugar/g tissue (lean meat). Recoveries for glucose, ribose, glucose phosphate and ribose phosphate were 102%, 81%, 86% and 68% respectively while those for IMP, AMP, inosine and hypoxanthine were 92%, 89%, 90% and 85%, respectively. 2.6. Statistical analysis The profiling data for all 14 experimental groups were analysed as linear mixed models by Random Effect Model (REML). Animal was fitted as a random effect and a factorial arrangement of panellist × product as fixed effects. Principal component analysis (PCA) was used to select seven experimental groups for the consumer panels. Assessors whose responses differed from the majority were omitted from the analysis, where their removal removed or reduced the significance of the assessor × group interaction. Attributes where P N 0.25 in the REML analysis were excluded from the PCA. The profiling data from the seven experimental groups selected were reanalysed by REML to select the profiling descriptors that were used in the preference mapping analysis. The consumer data were analysed by analysis of variance (ANOVA) to identify preference differences between experimental groups. Hierarchical Cluster Analysis was conducted to group the consumers into three different clusters depending on their preference similarities. At each step in the cluster analysis the method of complete linkage was used to group units together to form the different cluster groups. The matrix of similarities was generated using the Euclidean method. Cluster groups were also characterized using the demographic information surveyed, while Chi-squared (X2) analysis was used to determine differences between them. Consumers who had failed to answer one or more question were omitted from this analysis. The effect of experimental group and these three cluster groups on the consumer liking scores were analysed using a linear mixed model by REML. The data from instrumental and chemical analysis were analysed by ANOVA to examine the differences between the experimental groups. Internal preference mapping (Greenhoff & MacFie, 1994) was conducted on the seven selected groups using the liking scores for appearance, aroma, flavour, texture and overall liking, obtained from all consumers who had fully completed the assessment and the sensory profiling scores. Again, attributes where P N 0.25 in the REML were excluded from the preference map. External preference mapping using a vector model (Greenhoff & MacFie, 1994) was conducted using the same sensory profiling and consumer scores together with the instrumental and chemical analysis data (only six groups for sugar and nucleotides). All statistical analyses were conducted using the software GenStat 11th edition (VSN, Hemel, UK). 3. Results and discussion 3.1. Sensory profiling panels and selection of seven groups used for further analysis The sensory attributes that received the highest scores were intensity of aroma, caramelised external appearance, juicy external and internal appearance, brown internal appearance, intensity of flavour, roast lamb flavour, tenderness and dry aftertaste. These reflect the attributes which form the most marked characteristics of grilled lamb and include aspects of appearance, texture, aroma and flavour. However, the assessors identified a total of 48 descriptors (Table 2), of which eight showed statistically significant differences (P b 0.05) between the 14

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Table 3 Predicted means (REML) of the intensity scores for the sensory attributes of grilled lamb LD steaks from 14 experimental groups. Descriptorp

1q

2

3q

4q

5

6

7q

8q

9

10

11q

12

13q

14

P

SED

IntensityAr CharGrillAr RoastLambAr LiverAr OilyArr FattyAr CaramAp JuicyAp BrownApr JuicyAp OpenApr ConnectAp IntensityF CharGrillF RLambFr BeefyF LiverF FattyF BitterFr SweetFr TenderTr RubberyTr ChewyT LumpyT MeltsT CrumblyT IntensityAT MeatyATr RLambATr LiverAT BitterATr DryAT

36.8 18.2 26.0 11.5 3.5 6.5 35.6 40.9 23.1 31.5 13.0 13.2 32.5 11.5 31.4bcde 3.3 11.7 5.4 3.0ab 1.6a 40.0bc 6.8ab 15.4a 10.2 21.4bc 12.5 23.7 16.9 21.2abcd 6.3 3.2 30.5

42.8 25.9 24.9 11.0 3.3 9.0 40.5 40.6 29.9 22.4 14.0 12.2 34.8 8.7 36.0ef 2.9 12.0 9.3 3.6abc 1.8a 56.0cd 4.7ab 12.2a 9.1 32.4c 14.4 34.9 20.3 28.2d 6.3 3.1 23.3

38.0 23.3 30.4 7.6 4.1 10.4 37.0 41.9 31.4 27.0 27.3 12.2 41.2 14.1 42.3f 2.9 11.2 5.4 1.9ab 2.7ab 58.6d 2.9a 9.2a 4.6 36.9c 16.3 27.7 23.5 25.8cd 3.7 2.1 23.9

28.5 13.5 22.7 6.6 4.4 5.8 34.3 32.8 24.7 19.0 17.8 12.9 40.9 10.7 25.0abcd 2.6 12.8 5.5 3.3abc 1.6a 41.4bcd 6.8ab 21.4a 10.7 22.2bc 9.7 28.4 20.7 25.6bcd 9.4 2.2 32.9

29.3 18.9 16.9 8.2 6.1 9.4 34.1 40.1 20.9 23.4 21.0 12.1 41.2 10.5 30.5bcde 3.3 10.4 8.1 3.4abc 2.1a 43.9bcd 7.0ab 23.6a 11.9 24.1bc 8.2 24.5 17.3 20.9abcd 8.4 2.5 27.0

25.2 10.8 15.9 6.3 4.5 7.5 31.5 30.9 26.9 22.7 21.7 24.2 39.0 7.6 21.1ab 4.5 7.5 8.3 10.8de 1.4a 14.0a 35.2d 63.4b 25.3 4.6a 2.0 25.1 15.5 15.4a 6.5 4.6 31.1

28.6 12.4 17.4 10.5 4.8 8.7 37.8 45.3 23.9 35.4 33.3 9.8 40.7 6.8 21.3ab 4.7 14.0 11.9 14.6e 1.5a 45.4bcd 8.6ab 19.5a 13.2 21.9bc 5.5 30.5 17.0 15.2a 11.4 7.9 26.5

30.1 17.2 17.8 4.5 7.7 6.9 36.4 28.4 23.4 22.6 24.9 15.6 32.2 9.4 22.8abc 3.3 9.6 7.4 3.2ab 1.5a 38.5b 15.3bc 25.4a 15.1 15.0ab 10.0 24.1 15.8 18.3ab 4.8 4.1 27.1

34.2 19.3 15.2 7.2 2.9 5.3 54.5 31.8 42.7 14.7 11.7 23.9 38.8 10.2 16.0a 10.8 13.2 8.6 8.3cd 1.5a 16.4a 26.2cd 54.2b 13.8 3.5a 9.2 21.7 17.2 14.5a 6.1 3.0 41.1

34.3 14.6 19.7 5.3 4.8 8.0 41.4 41.0 19.7 25.0 21.5 12.6 40.4 14.5 32.2cdef 4.5 12.4 11.9 1.2a 4.2b 42.0bcd 11.5ab 19.9a 9.3 22.7bc 13.0 31.8 18.2 21.5abcd 4.4 1.4 30.1

33.8 20.8 22.8 6.4 4.3 5.9 39.4 45.4 29.0 33.6 29.8 13.2 39.2 11.9 31.0bcde 4.4 7.9 6.5 3.1ab 2.1a 47.0bcd 7.4ab 19.6a 12.2 24.7bc 7.8 29.8 17.0 24.3bcd 5.0 2.1 30.5

33.6 15.5 20.7 7.9 4.5 5.8 38.1 41.2 27.4 29.9 23.7 13.2 35.3 7.2 28.5bcde 5.2 13.6 7.9 3.5abc 2.7ab 44.0bcd 6.0ab 19.5a 9.9 28.4bc 12.2 23.3 18.4 19.6abc 5.1 3.3 30.7

31.8 24.6 19.9 8.0 2.7 6.8 37.8 38.7 22.9 22.7 15.0 9.4 41.6 13.0 34.4def 6.0 6.2 9.5 4.1abc 4.2b 58.5d 5.8ab 10.7a 8.7 26.5bc 12.4 29.9 26.5 26.5cd 5.6 2.5 25.1

27.0 14.5 21.7 6.8 5.0 7.9 31.5 38.0 24.3 29.4 23.9 9.4 35.7 9.3 21.0ab 3.6 13.8 8.2 6.4bcd 1.8a 50.5bcd 5.7ab 13.5a 7.3 27.7bc 11.4 23.7 17.1 21.5abcd 7.4 1.2 25.1

0.504 0.462 0.678 0.476 0.426 0.867 0.899 0.694 0.057 0.686 0.172 0.120 0.677 0.922 0.020 0.052 0.878 0.439 b0.001 0.010 b0.001 b0.001 b0.001 0.146 0.012 0.738 0.476 0.537 0.015 0.434 0.171 0.532

5.06 4.24 4.97 3.60 1.40 2.71 10.25 8.50 4.69 8.14 7.90 5.34 4.77 4.41 5.14 2.28 5.27 2.92 2.54 1.02 8.56 5.83 8.71 5.86 7.75 5.98 4.27 4.06 3.82 2.80 1.83 6.91

a,b,c… Numbers in the same row which do not share a common superscript are significantly different (P b 0.05). p Explanation of abbreviations for descriptors may be found in Table 2. Data is presented for those attributes where P b 0.25 for either the analysis of 14 or seven treatments or where one or more scores exceeded 10; 16 descriptors listed in Table 1 are omitted. q Experimental groups selected for further analysis (n = 7). r These attributes were used for external preference mapping with seven experimental groups. The statistical analyses for seven treatments only gave the following values for P and SED: OilyAr, P = 0.242; 1.553; BrownAp, P = 0.087, 3.207; OpenAp, P = 0.084, 7.589; RLambF, P = 0.130, 5.356; BitterF, P b 0.001, 2.085; SweetF, P = 0.012, 0.935; TenderT, P = 0.112, 7.424; RubberyT, P = 0.140, 4.279; MeatyAT, P + 0.179, 3.822; RLambAT, P = 0.215, 3.926; BitterAT, P = 0.208, 2.144.

1

T2

T9

T1

T13 T3

0.5

RLambAT RLambF

BrownAp

T4

ConnectAp BeefyF

T10 PC2 7.0%

T12

-1

MeltsT TenderT

T5 SweetF

T11 -0.5

T6 ChewyT RubberyT 1

0 0

0.5

T8

T14

LumpyT

-0.5

BitterAT

BitterF

OpenAp T7

-1 PC1 81.5%

Fig. 1. Principal component analysis of selected sensory profiling attributes (P b 0.25) for lamb LD steaks (PC1/PC2, 88% of the variation). T1–T14 = experimental groups; Abbreviations: Ap = appearance; F = flavour; T = texture, AT = aftertaste.

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experimental groups with a further two approaching significance (Table 3). Most significant were the differences in tenderness, rubbery and chewy textures (P b 0.001) which highlighted the significant difference between Experimental Groups 6 and 9 and the rest. The remaining significant attributes included bitter flavour (P b 0.001), roast lamb flavour, roast lamb aftertaste, sweet flavour and melts in the mouth texture (all P b 0.05) while beefy flavour and brown internal appearance approached significance. The attributes, roast lamb flavour and aftertaste scored twice as high for lamb from some groups (3, 13) than others (6, 7, 8, 9). Principal component analysis (PCA) was conducted on the sensory profiling attributes for all 14 experimental groups, excluding those attributes for which P N 0.25 (Fig. 1). Principal Component 1 (PC1) accounted for 81% of the total variation, while PC2 accounted for 7% of the variation. PC1 showed separation between the texture descriptors, with tenderness at one extreme and chewy and rubbery at the other. This dimension primarily separated Experimental Groups 6 and 9 from the remaining groups. These lamb samples were from the two older groups of sheep, both more than 12 months in age, and the greater toughness of this lamb dominated PC1. PC2 showed some separation between the descriptors brown appearance and open appearance, with Experimental Groups 7 and 6 most associated with open appearance. Based on the distribution of the experimental groups in the PCA plot (Fig. 1) and the REML analysis of the sensory profiling data, seven groups were selected for consumer and instrumental/chemical analyses. Groups 6 and 9 were excluded because they were so extremely different from the rest of the experimental groups that they would have caused the consumer panels to focus only on the large differences in tenderness and to ignore the more subtle differences between the other groups. From the remaining 12 groups, Experimental Groups 1, 3, 4, 7, 8, 11 and 13 were selected to give a wide range of sensory qualities for further analysis. 3.2. Eating quality attributes that determine consumer liking for lamb Consumer panel scores showed statistically significant differences (P b 0.001) between the seven selected experimental groups for all the liking scores (Table 4). Experimental Groups 7 and 8 consistently obtained the lowest liking scores for all the attributes. Of the remaining experimental groups, Group 3 had the best score for overall liking and tended to have the highest score for the other attributes. Internal preference maps (Figs. 2 and 3), where the principal components are based on the individual consumer scores for overall liking, show that the closest experimental groups to the mean consumers' overall liking vector were Groups 3, 11 and 13, while in the opposite direction to the overall liking are Groups 7 and 8. Groups 3, 11 and 13 are ewe lambs or very young male lambs, and their association with overall liking is not unexpected. The consumers' overall liking was located very close to liking of texture, liking of flavour, liking of aroma and liking of appearance and also to the flavour profiling attributes, tenderness, sweet flavour, meaty aftertaste, roast lamb flavour and aftertaste. To understand consumer liking, it is important not only to identify the descriptors that the consumers like, but also to consider the descriptors that they dislike, because these descriptors may be responsible for

consumers' grievances. In this case, rubbery texture, bitter flavour and aftertaste and oily aroma were identified in the opposite direction to the vector for the consumers' overall liking. These preference maps show clearly that both flavour and texture attributes contribute to overall liking for lamb. A preference mapping study conducted with Japanese and New Zealand lamb consumers, using meat to which skatole and branched chain fatty acids had been added, reported similar findings (Prescott et al., 2001); the preferences of both consumer groups were related to sweet flavour, while sour flavour appeared in the opposite direction. The results obtained in the present study also seemed to be in agreement with an internal preference mapping study conducted for drycured ham, where the preferences of consumers appeared to be closely related to sweet flavour (Pham et al., 2008) and with a study conducted in lamb (Karamichou, Richardson, Nute, Wood, & Bishop, 2007), where the flavour attribute “bitter” was negatively correlated with “overall liking”, “lamb flavour” and “sweet flavour”, while being positively correlated with “rancid flavour”. Amongst the texture attributes, tenderness was closely associated with the consumer scores for overall liking (Figs. 2 and 3), while the descriptor, rubbery texture, was found opposite. These results are again similar to those reported elsewhere (Pham et al., 2008). The responses to demographic and behavioural questions by the 120 consumers are presented in Table 5. These data show that the consumers included a spread of gender, age and socioeconomic group. Regular consumption of lamb was a prerequisite of participation and most did so, but there were 5 people who claimed to rarely or never eat red meat and 11 who never ate lamb. The opinions on the favoured cooking endpoint confirmed previous findings on Northern Irish beef consumers (L.J Farmer, unpublished findings): 51 of the 120 consumers preferred their lamb “well-done” while a further 32 liked it “medium to welldone”. Only half the people were always or almost always satisfied with the eating quality of lamb, if purchased in a restaurant but this proportion rose to more than two thirds if the lamb was cooked in the home. Interestingly, when asked after the panel which sensory attribute had been most important, 59 responded “tenderness” and 48, “flavour”, which supports the observations based on the internal preference maps above. 3.3. Cluster group preferences and demographic characteristics Euclidian cluster analysis showed that 93% of the consumers fitted in one of three consumer cluster groups identified with 70% similarity in the overall liking scores for lamb loin steak. Fig. 4 shows that there are marked differences in the pattern of mean liking scores of each of these three cluster groups for each of the seven treatments; REML analysis shows that there was a very highly significant interaction (P b 0.001) between cluster group and treatment for all these attributes. Cluster Group (CG)1 had the fewest consumers (n = 8) and showed the most extreme views, though this was at least partly due to the small number of consumers. However, CG1 actively disliked Groups 7 and 8 for both flavour and texture, with scores less than 50 (Fig. 4), and significantly (P b 0.05) less than all other treatments except Group 11 for flavour liking. CG2 was the largest cluster (70 consumers) and liked

Table 4 Means of the consumer liking scores (0 to 100) for the attributes examined in the consumer panels of the lamb LD steaks. Experimental groups

Liking of appearance Liking of aroma Liking of flavour Liking of texture Overall liking

1

3

4

7

8

11

13

63.3b 60.4c 59.4c 61.2b 61.3c

64.3b 62.2c 64.8d 67.6c 65.5d

62.2b 60.6c 61.9cd 61.1b 61.1c

57.7a 51.9a 46.8a 50.2a 47.9a

58.0a 55.8b 53.1b 48.0 a 50.8b

62.3b 60.9c 63.4d 62.7bc 62.1c

62.8b 60.0c 64.1d 65.6c 63.7cd

Within a row, means with common superscripts are not significantly different (P N 0.05)

SEM

P

1.198 1.199 1.504 1.642 1.513

b0.001 b0.001 b0.001 b0.001 b0.001

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103

Fig. 2. Internal preference map of LD grilled lamb steaks for overall liking (PC1/PC2, 47% of variation). ● = consumers; → = preference vectors; experimental groups encircled; CG1 to CG3 = cluster Groups 1–3; Abbreviations: L = liking; Ar = aroma; Ap = appearance; T = texture; F = flavour; RLamb = roast lamb.

most of the samples, with all receiving scores of greater than 50 for all attributes (Fig. 4). CG3 (34 consumers) scored most of the samples moderately, but disliked Experimental Group 7 and, to a lesser extent, Group 8. Group 7 received especially low scores from CG3 for liking of flavour; there was a significant difference (P b 0.05) between the scores for Group 7 and all the remaining groups except Group 1. Experimental Group 7 comprised entire males and it is possible that CG3 may have been especially sensitive to any resulting off-flavour. In the internal preference maps (Figs. 2 and 3), the overall liking of all the cluster groups was strongly correlated with PC1 and was associated with tenderness, sweet flavour, roast lamb flavour and aftertaste and the lack of bitter flavour and aftertaste, oily aroma and rubbery texture. Analysis of the three cluster groups showed that only one of the 18 demographic and purchasing behaviour questions showed significant differences between them (P b 0.05). When asked “how frequently do you buy lamb and freeze it to cook it later”, the number of answers for “sometimes” was highest for Cluster Groups 1 and 2 (63% and 61%, respectively) compared with Cluster Group 3 (31%). This result would appear to be coincidental. Thus, the primary differentiator between cluster groups is their liking for the sensory attributes of the different

lamb samples and not demographic or behavioural factors. This supports the findings of Grunert (2006), who reported that under controlled conditions, as for the consumer panel conducted in this experiment, consumers base their preferences on the sensory characteristics of the product. However, if the consumers are exposed to more information, such as price, brand and quality claims, there is evidence that that demographic characteristics such age and sex can be important factors for the consumers' preferences (Guinard, 2002).

3.4. Instrumental analyses Sarcomere length was significantly different between the seven selected experimental groups (Table 6). However, the differences are small and there is no evidence that fast chilling the carcasses from Experimental Groups 8 and 11 without the application of electrical stimulation was successful in producing cold shortening of the muscular fibres, as described by others (Pouliot et al., 2012; Savell, Mueller, & Baird, 2005). This was confirmed by the absence of statistically significant differences in WBSF between the seven experimental groups

Fig. 3. Internal preference map of LD grilled lamb steaks for overall liking (PC1/PC3, 47% of variation). ● = consumers; → = preference vector; experimental groups encircled; CG1 to CG3 = cluster Groups 1–3; Abbreviations: L = liking; Ar = aroma; Ap = appearance; T = texture; F = flavour; RLamb = roast lamb.

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Table 5 Answers to demographic and behavioural questions by consumers. Question

Answers and number of consumer responses

Age group

15–24

25–34

35–44

45–54

55–64

65+

7

6

22

32

20

33

Gender

male

female

53

No answer 0 No answer

64

3

A

B

C1

C2

D

E

Your own occupation* (if retired please mark your former occupation)

16

19

34

10

12

24

5

Occupation* of the main household earner (if retired mark former occupation)

19

24

36

19

10

8

4

How many children (16 years old or less) normally live in your household?

Which of the following best categorizes your household income?

None

1

2

3

83

19

14

4

Below £15,000 per year

Between £15,000 & £35,000 per year

18 Which one of the following statements applies to you?

I enjoy red meat. It’s an important part of my diet

How often do you eat lamb (in any form such as chops , roasts, stews, casseroles, kebabs, BBQ, etc)?

Daily

When you eat lamb what level of cooking do you prefer?

Blue

41

31 I do eat some red meat although truthfully I wouldn’t worry me if I didn’t 26

2 or 3 times a week

2

0

23

Butcher

47

31

59

Above £55,000 per year

5

No answer

11 Well done

32

5

No answer

1 Never

45

Other

No answer

1

I rarely/ never eat red meat

Medium well

28 Farm shop

Never

0

Monthly

Medium

7

Supermarket

Which of the following apply in your household?

Fort– nightly

Medium rare

No answer

11

Weekly

6

Rare

0 Where do you normally buy lamb?

59 I like red meat well enough. It’s a regular part of my diet 47

4 or 5 times a week

1

Between £35,000 & £55,000 per year

No answer

1 No answer

51 Do not buy lamb

2

2 No answer

6

Sometimes

1

Frequently

No answer

a) Buy fresh lamb and cook from fresh

14

59

43

b) Buy fresh lamb and freeze for cooking later**

43

57

11

4 9

c) Buy frozen lamb for cooking later

74

32

2

12

Always

Almost always

Some of the time

Almost never

Never

Do not eat lamb in a restaurant/at home

No answer

f you eat meat in a restaurant how often do you have an excellent eating experience?

4

47

30

5

7

26

1

If you eat lamb at home how often do you have an excellent eating experience?

20

62

27

3

2

6

0

And for completion after the consumer panel: Who normally buys lamb for your household

Yourself

Spouse

68 What was most important when you ate the lamb during tonight’s taste panel?

Aroma 1

Child

34

Parent

1 Tenderness 59

Other

11 Juiciness 11

No answer

4 Flavour 48

2 No answer 1

*NRS social grade (Anon, 2006): Class A: Doctor, barrister, lecturer, banker, company director, etc.; Class B: Teacher, accountant, librarian, middle manager, solicitor, etc.; Class C1: Junior civil servant, sales person, police officer, nurse, farmer, supervisor, etc.; Class C2: Machinist, electrician, carpenter, plumber, bricklayer, etc.; Class D: Manual worker, shop worker, machine tool operator, apprentice, farm labourer; Class E: Not currently in paid employment, casual labourer, student, homemaker, etc.

(Table 6) and the fact that Groups 8 and 11 were not significantly less tender than other treatments (Table 3). 3.5. Chemical analyses The total intramuscular fat content of the lean LD muscle ranged from 1.4% to 3.2% (Table 7), which is similar to that reported elsewhere (Priolo, Micol, Agabriel, Prache, & Dransfield, 2002). The highest total fat content in muscle occurred in Experimental Groups 4, 3 and 11, all

of which were ewe lambs, while the lowest intramuscular fat was in the lamb from Group 7, which were entire males. The quantities of the fatty acids were expressed in mg per grammes of tissue to facilitate analysis of the effect on the eating quality (Table 7). The MUFA, USFA and SFA follow the same trend as the total fat, as did the amounts of important fatty acids such as C18:1c9, C:16 and C:18. This is to be expected as these classes of fatty acids are especially abundant in the neutral intramuscular fat (Enser, Hallett, Hewitt, Fursey, & Wood, 1996). There were significant differences (P b 0.05) in the

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Overall Liking

80

Mean score

105

60 40 20 0

Liking of appearance

Mean score

80 60 40 20 0

Liking of aroma

Mean score

80 60 40 20 0

Liking of flavour

Mean score

80 60 40 20 0

Liking of texture

Mean score

80 60 40 20 0 1

2

3

1 3 4 7 8 11 13 Cluster Group and Experimental Group Fig. 4. Mean scores for each cluster group (CG1-3) for Liking attributes for seven selected experimental groups. Cluster group × experimental group interaction was very highly significant (P b 0.001) for all attributes.

Table 6 Means of sarcomere length (μm) and Warner Bratzler shear force (WBSF, N cm−2) of the seven experimental groups selected for the consumer panels of the LD lamb steaks. Instrumental analysis

Sarcomere length WBSF

Experimental groups 1

3

4

7

8

11

13

1.82ab 22.8

1.84ab 20.0

1.79a 20.0

1.85ab 18.7

1.93c 25.3

1.87ab 25.1

1.88bc 24.9

Values within a row that do not carry a common superscript are significantly different (P b 0.05).

SEM

P

0.036 20.0

0.050 0.165

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Table 7 Means of fatty acid profile and groups of fatty acids (mg/g of tissue) for the seven experimental groups selected for the consumer panels of the LD lamb steaks. Fatty acids

Experimental groups

C14:0 C14:1c C15:0 C15:1c C16:0 C16:1t C16:1c C17:0 C17:1c C18:0 C18:1t9 C18:1t11 C18:1c9 C18:1c11 C18:2t9:12 C18:2c9:121 C18:3c2 CLAc9:t11 CLAc10:t12 C20:4n-6 C20:5n-3 C22:5n-3 C22:6n-3 Total n-3 PUFA Total n-6 PUFA Ratio n-6/n-3 Total PUFA3 Total MUFA4 Total USFA5 Total SAF6 Total fat

1

3

4

7

8

11

13

0.78ab 0.03 0.07a 0.07abcde 4.40ab 0.09abc 0.25a 0.21ab 0.173a 3.32abc 0.05 0.68a 7.09ab 0.16 0.02a 0.85 0.48a 0.27 0.02 0.26 0.19 0.12 0.02abc 0.80a 1.11 1.35abc 1.91 7.76a 9.68ab 8.78ab 19.61a

1.09ac 0.03 0.12b 0.06abcfg 5.21ac 0.09ab 0.29ab 0.20ab 0.192a 3.67abd 0.06 1.18bc 7.45ab 0.16 0.02a 0.92 0.56a 0.33 0.02 0.25 0.24 0.17 0.02ab 0.98a 1.17 1.21ab 2.15 8.17ab 10.32ab 10.29ac 22.32ab

1.01a 0.03 0.11b 0.07adefg 7.58d 0.12a 0.39bc 0.28a 0.297b 5.49e 0.09 1.21b 12.31c 0.23 0.08b 1.17 0.59a 0.38 0.08 0.27 0.19 0.14 0.03ac 0.95a 1.44 1.57ac 2.39 13.32c 15.72c 14.47d 32.15c

0.42b 0.02 0.04a 0.03a 3.07b 0.06c 0.19a 0.09c 0.107a 2.04c 0.12 0.74ad 4.96a 0.22 0.03a 1.21 0.17b 0.26 0.02 0.16 0.12 0.04 0.01b 0.33b 1.37 4.07d 1.7 5.53a 7.23a 5.66b 14.11a

0.77ab 0.03 0.08ab 0.05abdf 4.08ab 0.08bc 0.22a 0.14bc 0.16a 2.94acd 0.05 0.79acd 5.86a 0.15 0.02a 0.83 0.39ab 0.20 0.02 0.23 0.16 0.12 0.02abc 0.69ab 1.06 1.59c 1.74 6.45a 8.19a 8.02ab 17.37a

1.42c 0.04 0.12b 0.09ceg 6.89cd 0.13a 0.44c 0.22ab 0.28b 4.18ae 0.08 1.15bcd 9.82bc 0.19 0.03a 0.97 0.62a 0.33 0.04 0.25 0.24 0.17 0.04c 1.07a 1.22 1.13b 2.29 10.86bc 13.16bc 12.83cd 27.75bc

0.89a 0.03 0.07a 0.08bcdefg 4.00ab 0.07bc 0.25a 0.16bc 0.14a 2.55bcd 0.05 0.87abcd 5.47a 0.13 0.02a 0.65 0.38ab 0.25 0.02 0.19 0.17 0.14 0.04ac 0.73ab 0.85 1.14b 1.57 6.09a 7.66a 7.68ab 16.62a

P

SEM

b0.001 0.559 0.004 0.028 b0.001 0.009 0.004 0.011 b0.001 b0.001 0.411 0.043 b0.001 0.128 0.015 0.254 0.011 0.133 0.098 0.647 0.246 0.051 0.023 0.024 0.49 b0.001 0.546 b0.001 b0.001 b0.001 b0.001

0.146 0.006 0.015 0.013 0.715 0.017 0.052 0.031 0.030 0.533 0.027 0.147 1.050 1.050 0.007 0.174 0.091 0.049 0.017 0.051 0.051 0.051 0.051 0.255 0.267 0.116 0.507 0.997 1.252 1.162 3.020

1 = linoleic acid; 2 = linolenic acid; 3 = polyunsaturated 4 = monounsaturated fatty acids; 5 = unsaturated fatty acids;6 = saturated fatty acids; Values within a row that do not carry a common superscript are significantly different (P b 0.050).

concentration of linolenic acid (C18:3), omega 3 (n − 3) (P b 0.05) and in the ratio n − 6/n − 3 (P b 0.001). These results were as expected (Saňudo et al., 2000), who reported that high levels of 18:2 are related to the feeding of cereal-based concentrates. Experimental Group 7 had the highest ratio of n − 6/n − 3 fatty acids, the lowest levels of linolenic acid and n − 3 fatty acids (Table 7), were also the leanest and had the highest proportion of 18:2 (8.6%). These results are consistent with the fact that Group 7 was entire males fed, according to the farmer, on “concentrates only” (Table 1). Group 7 also had the highest ratio of n − 6/n − 3 fatty acids; at 4.07 the n − 6/n − 3 ratio is only just above the recommended value of 4 or less (Enser, 2001). The concentrations of the sugars, glucose, glucose-6-phosphate (G6P) and ribose found in the lamb meat (Table 8) were lower than those reported for beef by ourselves (Oltra, 2010) and others (Koutsidis et al., 2008a,b; Lawrie, 1998). The concentrations of

Table 8 Means of sugars, nucleotides and related compounds (μmoles/g of fresh weight lamb) for the seven experimental groups selected for the consumer panels of LD lamb steaks. Precursors

AMP IMP Hypoxanthine Inosine Glucose Ribose G6P R5P

Experimental groups 1

3

4

7

8

11

0.35b 4.48c 0.40a 3.65ab 3.45abc 0.19a 2.14a 0.15ab

0.62c 3.22a 0.26b 5.12c 3.53abd 0.16ab 6.66b 0.11ac

0.56d 3.16a 0.21b 4.01a 3.79acd 0.22a 3.19a 0.14ab

0.25e 0.13d 3.20c 2.99d 3.25a 0.19a 3.81a 0.18b

0.15a 2.80b 0.30ab 3.30bd 1.73e 0.10b 3.80a 0.05c

0.12a 3.07ab 0.25b 4.77c 4.19bcd 0.21a 5.98b 0.11ac

SEM

P

0.011 0.118 0.043 0.134 0.313 0.027 0.642 0.022

b0.001 b0.001 b0.001 b0.001 b0.001 0.042 b0.001 0.015

AMP = adenosine monophosphate, IMP = inosine monophosphate; R5P = ribose 5 phosphate; G6P = glucose 6 phosphate; values within a row that do not carry a common superscript are significantly different.

hypoxanthine, IMP, and AMP were higher than those reported for beef by Koutsidis et al. (2008a,b) but in the same range as those found in our laboratory (Oltra, 2010). In contrast, the levels of inosine were higher in lamb than the levels reported for beef (Koutsidis et al., 2008a,b; Oltra, 2010). The concentrations of G6P and inosine found in lamb in the current experiment are higher than those reported for pork by Meinert et al. (2009). In the current experiment, significant differences in sugars, nucleotides and related compounds were observed between the experimental groups with Group 8 having only half the concentration of glucose and ribose than other experimental groups, and Groups 3 and 11 being especially high in G6P. Despite the fact that the experimental groups differed in diet and ageing time, there was no consistent relationship with treatment. These were not controlled treatments and, presumably, other factors must also influence the concentrations of these compounds. 3.6. Relationship between the profiling descriptors, consumer liking and instrumental and chemical analyses External preference mapping, where the principal components are based on the sensory profiling scores, was used to view associations between the consumer liking, the profiling descriptors and the instrumental/chemical measurements. Figs. 5 and 6 show the external preference maps for PC1 versus PC2 and PC1 versus PC3 of the lamb steaks. As shown using internal preference mapping (Figs. 2 and 3), the consumer scores for overall liking were associated with sweet flavour, meaty aftertaste, roast lamb flavour, roast lamb aftertaste and tenderness (Figs. 5 and 6). Despite the absence of significant differences between experimental groups (Table 6), WBSF was associated with the texture descriptor rubbery, and was located opposite to the overall liking, liking of texture and tenderness in the external preference map (Figs. 5 and 6). This

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107

Fig. 5. External preference map relating sensory profiling attributes for LD grilled lamb steaks to consumer liking scores and data from instrumental and chemical analyses (PC1/PC2, 83% of variation). → = preference vector; T1, T3, T4, T7, T8, T11, T13 = experimental groups 1, 3, 4, 7, 8, 11, 13; CG1 to CG3 = cluster Groups 1–3; Abbreviations: L = liking of attribute; Ar = aroma; Ap = appearance; T = texture; F = flavour; RLamb = roast lamb; sarcomere = sarcomere length; n − 3 = omega 3 fatty acid; n − 6 = omega 6 fatty acid; SFA = total saturated fatty acids; USFA = total unsaturated fatty acids; MUFA = monounsaturated fatty acids; n − 6/n − 3 = ratio omega 6/omega 3.

relationship with acceptability of texture has been previously reported by many (for example, Platter et al., 2003; Wheeler, Shackelford, & Koohmaraie, 1999). In contrast, sarcomere length occupied a narrow range and was unrelated to any important texture attributes. Total fat, together with SFA, USFA, MUFA and PUFA showed a little correlation with PC1 and PC2 but were correlated with PC3 in the PCA of all attributes (Figs. 5 and 6). These fatty acid classes did not show an association with any of the consumer liking scores. These results agree with those reported previously for beef, which showed that total fat content is not a key driver for consumer's overall acceptability of grilled beef (Oltra, Farmer, Moss, Gordon, & Birnie, 2010). However, total fat was associated with an absence of bitter flavour and higher scores for brown appearance (Figs. 5 and 6). It may be speculated that a sample with higher moisture and lower fat contents may give more surface evaporation during cooking and, therefore, a reduced surface cooking temperature which could reduce the browning occurring on the meat surface (Oltra et al., 2010).

A negative association was observed (Fig. 5) between consumer liking and the n − 6/n − 3 ratio, linoleic acid (C18:2; n − 6), and the n − 6 fatty acids which were located opposite to the consumer scores for liking and associated with the attributes bitter flavour and aftertaste and, to a lesser extent, oily aroma. Several studies have related content of n − 6 fatty acids, and specifically linoleic acid (C18:2), with scores for acceptability of lamb (Fisher et al., 2000; Saňudo et al., 2000). These reports have shown differences in the acceptability between meat from animals fed diets based on grass (rich in C18:3/n − 3), and animals fed diets based on concentrates (rich in C18:6/n − 6). Some authors have suggested that this difference is due to the fact that the meat from pasture-fed animals, which are rich in C18:3 fatty acids but also fatsoluble antioxidants like carotene and tocopherol, may be more protected from oxidation and yield lesser quantities of aldehydes than meat from concentrate-fed animals which is rich in 18:2 fatty acids and low antioxidants (Resconi et al., 2010; Young, Berdagué, Viallon, RoussetAkrim, & Theriez, 1997). In addition, the effect on acceptability

Fig. 6. External preference map relating the sensory profiling attributes for LD grilled lamb steaks to consumer liking score and data from instrumental and chemical analyses (PC1/PC3, 65% of Variation). → = preference vector; T1, T3, T4, T7, T8, T11, T13 = experimental groups 1, 3, 4, 7, 8, 11, 13; CG1 to CG3 = cluster Groups 1–3; L = liking of attribute; A = aroma; App = appearance; T = texture; F = flavour; RLamb = roast lamb; sarcomere = sarcomere length; n − 3 = omega 3 fatty acid; n − 6 = omega 6 fatty acid; SFA = total saturated fatty acids; USFA = total unsaturated fatty acids; MUFA = monounsaturated fatty acids; n − 6/n − 3 = ratio omega 6/omega 3.

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depends on the past experience of the consumers (Saňudo et al., 2000); while increased levels of 18:0 and 18:3 were associated with increased flavour and odour intensity for all consumers, this resulted in increased acceptability scores for British consumers, accustomed to eating grassfed lamb, and lower scores for Spanish consumers, who normally eat concentrate-fed lamb. Group 7, which was the only one of the seven selected groups fed only with concentrates, was located opposite to the consumers' overall liking in the preference map, and close to the attributes bitter flavour and aftertaste and oily aroma, n − 6/n − 3 ratio, n − 6 and linoleic acid concentrations. Similar results have been reported recently for beef (Oltra, Farmer, Moss, Gordon, & Birnie, 2009). However, in this instance, Group 7 was also the only experimental group comprising entire males and it is possible that the perceived bitter flavour may also have been influenced by this fact. Lamb meat from entire males is often regarded as having an off-flavour (which can be influenced by diet) and has been associated with a number of compounds including branch chain fatty acids, indoles and phenols (Brennand & Lindsay, 1992; Watkins et al., 2014; Young et al., 1997). The concentrations of glucose, AMP and inosine and to a lesser extent glucose-6-phosphate and IMP seemed to be closely associated with the flavour attributes, sweet flavour, meaty aftertaste, roast lamb flavour and aftertaste in the overall PCA (Figs. 5 and 6). Hypoxanthine was inversely associated with these profiling attributes and positively associated with bitter flavour and bitter aftertaste. Ribose and R5P were little associated with profiling attributes. Reducing sugars and ribonucleotides are known to be associated with flavour formation in meat and may be formed by ATP breakdown in post-mortem muscle. The amount of hypoxanthine, ribose and inosine has been shown to increase, while the amount of IMP decreases, during the ageing of beef (Koutsidis et al., 2008a). Ribose has been strongly associated with roasted and meaty aromas produced by the Maillard reaction, and has also been reported to decrease the formation of lipid oxidation products (Farmer, Hagan, & Paraskevas, 1999). In the external preference maps from the current study (Figs. 5–6), the association observed between AMP, IMP, sweet flavour, meaty aftertaste and roast lamb flavour and aftertaste and consumer's overall liking, might be explained by the relationship between these nucleotides as precursors of ribose and the participation of this sugar in the formation of meaty aroma compounds. IMP and related compounds also contribute to the fifth taste of umami (deliciousness) and it is possible that they are exerting their effect through this role. The mechanism for these compounds to contribute to lamb flavour justifies further study. While ribose has been shown to be important for flavour formation in chicken (Aliani & Farmer, 2005a,b), it has been proposed (Farmer, Kennedy, & Hagan, 2009) that, in red meats, glucose and glucose-6phosphate may have equal or more importance for roasted and meaty aromas than the 5-carbon reducing sugars, ribose and ribose-5phosphate, due to their higher concentrations. Glucose and G6P have also been related to the formation of meaty aromas in pork (Meinert, Schafer, Bjergegaard, Aaslyng, & Bredie, 2009). In the current study, the external preference map of lamb steaks (Figs. 5–6) showed an association between the descriptor sweet flavour, roast lamb flavour and aftertaste, liking of flavour and the sugars, glucose and G6P. This agrees with findings reported previously for beef (Oltra et al., 2010) that there is a link between the flavour precursors in the raw lamb, the sensory quality and the acceptability to consumers.

4. Conclusions The texture and flavour eating quality attributes identified as driving the consumer liking of lamb loin steaks were sweet flavour, meaty aftertaste, roast lamb flavour and aftertaste and tenderness. In contrast, the texture attribute rubbery and the attributes bitter flavour and aftertaste had a negative influence on the consumer perceptions of lamb. Further analysis of the liking of the 120 consumers by cluster

analysis showed that these clusters were differentiated by their sensory preferences and not by demographic factors. Associations were observed between a number of instrumental and chemical measurements and eating quality. WBSF showed an association with rubbery texture and a negative association with tenderness and consumer liking scores. An apparent relationship was observed between the proportion of n − 6 fatty acids and the attribute bitter flavour, which may be an indirect effect related to the lower antioxidant content and higher n − 6 fatty acids of concentrate diets. The compounds glucose and glucose-6-phosphate, inosine, IMP, and AMP were positively related to the attributes, sweet flavour, meaty aftertaste, roast lamb flavour and aftertaste and to consumer scores for liking of lamb. This may be explained by the role of these compounds in the generation of flavour precursors and volatiles and/or for taste. Conflict of interest There is no conflict of interest. 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