Flavour perception of oxidation in beef M.M. Campo * , G.R. Nute, S.I. Hughes, M. Enser, J.D. Wood, R.I. Richardson Division of Farm Animal Science, University of Bristol, Langford, Bristol BS40 5DU, UK Received 28 February 2005; received in revised form 10 July 2005; accepted 21 July 2005 Abstract Lipid oxidation is a major factor in meat quality. In order to relate human perceptions of lipid oxidation, as determined by a trained taste panel, to a chemical measurement of oxidation, we studied meat from animals with a wide range of potential oxidation through differences in their PUFA composition and by displaying the meat in high oxygen modified atmosphere packs for varying lengths of time. Meat was obtained from 73 Angus- and Charolais-cross steers from different trials that had been raised on 10 different diets: grass silage (high in C18:3, n-3), cereal concentrate (high in C18:2, n-6), three diets with 3% added fat consisting of three levels of protected lipid supplement (high in C18:2, n-6 and C18:3, n-3, ratio 1:1), a control with Megalac Ò (relatively saturated), three diets with three levels of inclusion of protected fish oil (high in C20:5 n-3 and C22:6 n-3) plus a constant amount of unprotected fish oil and a final diet with an unprotected fish oil control. The longissimus dorsi muscle was excised from the left carcass side, aged vacuum packaged for 10–13 days depending on the projects and frozen for less than eight months. TBARS and sensory analyses were performed on steaks displayed for 0, 4 or 9 days under simulated retail conditions, exposed to light in modified atmosphere packaging (CO 2 :O 2 ; 25:75). Meat oxidation increased throughout display for each of the diets, as shown by a rise in TBARS values. This increase was not linear, differences between 0 and 4 days of display were smaller than between 4 and 9 days of display. The lowest TBARS and lowest increment occurred in the two control diets and the grass-fed animals, probably due to the more saturated fat of meat from animals fed the control diets and the higher content of vitamin E. Sensory attributes were also influenced by time of display. Positive attributes, such as beef flavour or overall liking, decreased throughout display, whereas negative attributes, such as abnormal and rancid flavours, increased. The correlations between sensory and analytical attributes were high. TBARS were a good predictor of the perception of rancidity (SpearmanÕs rho = 0.84). Panellist preferences were related to the presence of beef flavour (rho = 0.93) and to the absence of abnormal (rho = 0.88) and rancid flavours (rho = 0.83). Under the experimental conditions used, a TBARS value of around 2 could be con- sidered the limiting threshold for the acceptability of oxidised beef. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Beef; Oxidation; Flavour; MAP 1. Introduction Lipid oxidation is a major cause of deterioration in meat quality (Gray & Pearson, 1987; Gray, Gomaa, & Buckley, 1996). It limits the storage or shelf life of meat exposed to oxygen under conditions where microbial spoilage is pre- vented or reduced such as refrigeration or freezing. The products of fatty acid oxidation produce off-flavours and odours usually described as rancid (Gray & Pearson, 1994). Lipid oxidation in muscle systems is initiated at the membrane level in the phospholipid fractions as a free-radical autocatalytic chain mechanism (Labuza, 1971) in which prooxidants interact with unsaturated fatty acids resulting in the generation of free radicals and prop- agation of the oxidative chain (Ashgar, Gray, Buckley, Pearson, & Booren, 1988). The relationship of rancidity to flavour is unclear. As rancid flavours develop there is a loss of desirable flavour notes. However, most studies of rancidity rely on chemical assay methods that determine the fatty acid breakdown 0309-1740/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.07.015 * Corresponding author. Present address: Department of Animal Production and Food Technology, University of Zaragoza, C/Miguel Servet 177, 50013-Zaragoza, Spain. Tel.: +34 976 761600; fax: +34 976 761590. E-mail address: [email protected](M.M. Campo). www.elsevier.com/locate/meatsci Meat Science 72 (2006) 303–311 MEAT SCIENCE
Transcript
www.elsevier.com/locate/meatsci
Meat Science 72 (2006) 303–311
MEATSCIENCE
Flavour perception of oxidation in beef
M.M. Campo *, G.R. Nute, S.I. Hughes, M. Enser, J.D. Wood, R.I. Richardson
Division of Farm Animal Science, University of Bristol, Langford, Bristol BS40 5DU, UK
Received 28 February 2005; received in revised form 10 July 2005; accepted 21 July 2005
Abstract
Lipid oxidation is a major factor in meat quality. In order to relate human perceptions of lipid oxidation, as determined by a trainedtaste panel, to a chemical measurement of oxidation, we studied meat from animals with a wide range of potential oxidation throughdifferences in their PUFA composition and by displaying the meat in high oxygen modified atmosphere packs for varying lengths of time.Meat was obtained from 73 Angus- and Charolais-cross steers from different trials that had been raised on 10 different diets: grass silage(high in C18:3, n-3), cereal concentrate (high in C18:2, n-6), three diets with 3% added fat consisting of three levels of protected lipidsupplement (high in C18:2, n-6 and C18:3, n-3, ratio 1:1), a control with Megalac� (relatively saturated), three diets with three levelsof inclusion of protected fish oil (high in C20:5 n-3 and C22:6 n-3) plus a constant amount of unprotected fish oil and a final diet withan unprotected fish oil control. The longissimus dorsi muscle was excised from the left carcass side, aged vacuum packaged for 10–13days depending on the projects and frozen for less than eight months. TBARS and sensory analyses were performed on steaks displayedfor 0, 4 or 9 days under simulated retail conditions, exposed to light in modified atmosphere packaging (CO2:O2; 25:75). Meat oxidationincreased throughout display for each of the diets, as shown by a rise in TBARS values. This increase was not linear, differences between0 and 4 days of display were smaller than between 4 and 9 days of display. The lowest TBARS and lowest increment occurred in the twocontrol diets and the grass-fed animals, probably due to the more saturated fat of meat from animals fed the control diets and the highercontent of vitamin E. Sensory attributes were also influenced by time of display. Positive attributes, such as beef flavour or overall liking,decreased throughout display, whereas negative attributes, such as abnormal and rancid flavours, increased.
The correlations between sensory and analytical attributes were high. TBARS were a good predictor of the perception of rancidity(Spearman�s rho = 0.84). Panellist preferences were related to the presence of beef flavour (rho = 0.93) and to the absence of abnormal(rho = �0.88) and rancid flavours (rho = �0.83). Under the experimental conditions used, a TBARS value of around 2 could be con-sidered the limiting threshold for the acceptability of oxidised beef.� 2005 Elsevier Ltd. All rights reserved.
Keywords: Beef; Oxidation; Flavour; MAP
1. Introduction
Lipid oxidation is a major cause of deterioration in meatquality (Gray & Pearson, 1987; Gray, Gomaa, & Buckley,1996). It limits the storage or shelf life of meat exposed tooxygen under conditions where microbial spoilage is pre-vented or reduced such as refrigeration or freezing. The
0309-1740/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.meatsci.2005.07.015
* Corresponding author. Present address: Department of AnimalProduction and Food Technology, University of Zaragoza, C/MiguelServet 177, 50013-Zaragoza, Spain. Tel.: +34 976 761600; fax: +34 976761590.
products of fatty acid oxidation produce off-flavours andodours usually described as rancid (Gray & Pearson,1994). Lipid oxidation in muscle systems is initiated atthe membrane level in the phospholipid fractions as afree-radical autocatalytic chain mechanism (Labuza,1971) in which prooxidants interact with unsaturated fattyacids resulting in the generation of free radicals and prop-agation of the oxidative chain (Ashgar, Gray, Buckley,Pearson, & Booren, 1988).
The relationship of rancidity to flavour is unclear. Asrancid flavours develop there is a loss of desirable flavournotes. However, most studies of rancidity rely on chemicalassay methods that determine the fatty acid breakdown
304 M.M. Campo et al. / Meat Science 72 (2006) 303–311
products, mainly because they are objective, cheap and ra-pid compared with organoleptic assessment. The disadvan-tage of such methods is that they measure one amongstmany contributors to the rancid flavour, such as hexanal,or secondary breakdown products that do not contributeto flavour, such as the widely used determination of mal-ondialdehyde by the thiobarbituric acid reaction (TBARS)(Tarladgis, Watts, Younathan, & Dugan, 1960). Several at-tempts have been made to determine the threshold in sen-sory perception of oxidation in relation to that assessedchemically. Tarladgis et al. (1960) suggested that oxidationwas perceived at TBARS in the range of 0.5–1.0 in pork.Greene and Cumuze (1981) found that oxidized flavourin beef was detected over a broad range of TBARS from0.6 tp 2.0 indicating a big variation in the threshold ofthe panellists. The latter were inexperienced, resembling or-dinary consumers, and the correlations between TBARSand consumers taste were low. Furthermore, as the authorsacknowledged, threshold does not indicate acceptability.
In order to investigate further the relationship betweenflavour and rancidity, assessed chemically and by a tastepanel, we have studied beef from a wide range of produc-tion systems in order to obtain differences in susceptibilityto oxidation. Since the susceptibility to oxidation of a fattyacid is related to the number of double bonds it contains,this was achieved through differences in the muscle contentof long chain polyunsaturated fatty acids (PUFA).
In order to limit possible effects of microbial growth onflavour the meat was packed in a modified atmosphere(MAP) of oxygen and carbon dioxide (Gill, 1996). Thishad two practical aspects: the high oxygen stimulated lipidoxidation (Renerre, 1990) although maintaining the myo-globin in its oxygenated form decreased its activity as aprooxidant (Anton, Gatellier, & Renerre, 1993). Further-more, MAP is widely used commercially as a way ofincreasing the shelf life of meat whilst maintaining a desir-able bright red colour.
The aim of this work was to assess the limit of rancidityin beef by relating sensory perception by a taste panel to
Table 1Fatty acid (FA) composition (% by weight of total fatty acids) of intramusculadifferent diets
Cont PLS PLS1 PLS2 PLS3
Saturated FA NL 50.9 48.1 48.3 46.0Saturated FA PL 36.1 36.1 35.9 35.7Monounsaturated FANL 43.7 43.3 42.0 43.1Monounsaturated FA PL 26.9 15.3 12.7 12.4Polyunsaturated FA NL 2.0 4.9 6.1 7.1Polyunsaturated FA PL 31.3 43.4 46.4 47.1
Cont PLS: control protected lipid supplement; PLS: Protected lipid supplemeCont PFO: control protected fish oil; PFO: Protected fish oil.Conc: concentrate.1, 2, 3 = three different levels of inclusion of either PLS or PFO in the diet.
simple chemical measurements, using meat conditioned inMAP from animals fed diets with different fatty acidcomposition.
2. Material and methods
2.1. Animals
Meat was obtained from 73 Angus- and Charolais-crosssteers from different trials that had been raised on 10 differ-ent diets: grass silage (high in C18:3, n-3), cereal concen-trate (high in C18:2, n-6), three diets with 3% added fatconsisting of three levels of protected lipid supplement(high in C18:2, n-6 and C18:3, n-3, ratio 1:1) (PLS), a con-trol with Megalac� (relatively saturated) (contPLS), threediets with three levels of inclusion of protected fish oil (highin C20:5, n-3 and C22:6, n-3) plus a constant amount ofunprotected fish oil (PFO) and an unprotected fish oil con-trol (contPFO). The PLS diet was composed of soya beans,linseed and sunflower oils, and the PFO supplement com-prised soya beans and tuna oil, together with 350 IU vita-min E/kg concentrate in both supplements. Lipids of PLSand PFO diets were prepared as in Scott, Cook, and Mills(1971), protected from ruminal biohydrogenation byencapsulating them in a matrix of rumen inert protein.Grass and concentrate-fed animals were slaughtered at 19months (Richardson, Nute, Wood, Scollan, & Warren,2004), PLS animals at 20 months (Scollan, Enser, Gulati,Richardson, & Wood, 2003) and PFO animals at 24months (Scollan et al., 2004).
As a result of the fatty acid composition of the differentdiets we obtained meat with very different fatty acid com-position, especially long chain polyunsaturated fatty acids(Table 1).
2.2. Sampling
Forty-eight hours after slaughter, the left side loin ofeach animal was separated from the carcass, vacuum
r fat in the neutral (NL) and phospholipids (PL) fractions in steers fed 10
Beef Flavour associated with cooked beefAbnormal Abnormal flavour not found in cooked beefRancid Rancid flavour found in the meatGreasy Flavour associated with oilBloody Flavour associated with blood or raw beefMetallic Flavour associated with meat tasteLivery Flavour associated with liverBitter Bitter tasteSweet Sweet tasteFishy Flavour associated with fishAcidic Sour tasteCardboard Flavour associated with wet cardboard and staleVegetable Flavour associated with vegetablesGrassy Flavour associated with fresh grassDairy Flavour associated with dairy productsOverall liking Hedonic liking from the panellists
M.M. Campo et al. / Meat Science 72 (2006) 303–311 305
packaged and kept at 1 �C. Loins of grass- and concen-trate-fed animals were stored vacuum packaged for an ex-tra 8 days until reaching 10 days of conditioning, whereasloins from the rest of the diets were kept for 11 days untilreaching 13 days of conditioning according to the protocolsof their respective projects. Then, 2-cm thick steaks werecut from each loin, vacuum packaged, frozen and kept at�18 �C until the trial started.
TBARS and sensory analyses were performed on steaksdisplayed for 0, 4 or 9 days under simulated retail condi-tions in modified atmosphere packaging (MAP). After fro-zen storage, samples were thawed at 1 �C for 24 h. Theywere transferred onto a polystyrene tray, covered by per-meable film and enclosed in a plastic transparent bagimpermeable to oxygen. Top web was a polyester(20 lm)/polyethylene (50 lm) laminate with O2, N2, CO2
transmission rates of <4.0, 16.3 and 12.0 cm3 m�2 day�1
respectively at 25 �C and 0% RH and water vapour of<5.0 g m�2 day�1 at 38 �C and 90% RH. The atmosphereof the bag was modified to contain CO2:O2 in the ratio25:75. Samples were displayed for 4 or 9 days at 4 �C underlights (700 lux at the surface of the meat 16 h on) until ana-lysed. Samples at 0 days of display were not displayed inMAP and were analysed immediately the vacuum was bro-ken after thawing to avoid oxidation. These were consid-ered as control samples.
2.3. TBARS
Thiobarbituric acid reactive substances (TBARS) wereanalysed by the steam distillation method of Tarladgiset al. (1960) and expressed as mg of malonaldehyde perkg of lean muscle.
2.4. Sensory analysis
Immediately after breaking the vacuum or MAP pack-aging, steaks for sensory analysis were grilled under pre-heated conventional Tricity low-level grills, one grill pertreatment and turned every 3 min for homogeneous cook-ing until the internal centre temperature reached 74 �Cmeasured by a hand-held digital thermometer. Uniform cu-boids were cut, wrapped in randomly coded aluminium foiland kept at 60 �C until the tasting was performed. Sensoryassessments were performed by nine assessors who hadbeen selected and trained in accordance with the BritishStandard Institution method for the selection, trainingand monitoring of assessors (BS7667/ISO8586-1, 1993)and had received further training specifically related tomeat. The taste panel performed the trial under controlledconditions, in booths with red lights to mask colour differ-ences. The assessors used direct entry into a computerisedsensory assessment programme to record their results.Each assessor was given the list of sensory descriptorsand the definition of these words, which had been agreedto by them at previous training sessions used to developa consensus or fixed choice sensory profile (BS5929/ISO
11035; 1994). Panellists were presented with three samplesat a time, comparing meat within animal that had been dis-played for 0, 4 and 9 days. Within each panel and betweenpanels the order of tasting was rotated for each assessorusing a 3 · 3 (incomplete) Latin-Square design. After atraining period composed of two sessions of different sam-ples in which sensory descriptors were defined (Table 2),panellists rated beef, abnormal, greasy, bloody, livery,metallic, bitter, sweet, rancid, fishy, acidic, cardboard, veg-etable, grassy and dairy flavours as well as the hedonicoverall liking on an unstructured line scale with anchorpoints at each end where 0 meant no flavour or dislike ex-tremely, and 100 meant very intense flavour or like extre-mely. The hedonic scale served as an indication ofpreference by the panel, but it cannot be used to infer con-sumer acceptance since the results are based on nine asses-sors who cannot be longer considered as typical consumersbecause of the training they have received in meatassessment.
2.5. Statistical analysis
Statistical analysis of panel data was by analysis of var-iance (Genstat 5 Release 3.1). Each diet was analysed sep-arately with conditioning time and assessor as factors andpanel treated as a block structure. Paired comparisons be-tween mean values for conditioning time were assessed posthoc using the least significant difference procedure. Spear-man�s rho correlations were performed on the diet by con-ditioning time sample means (sample means for nineassessors) by SPSS 12.0.
3. Results and discussion
Fig. 1 shows the TBARS number of meat from animalson each of the diets. No oxidation was observed at 0 daysof display, a logical observation since the meat had beenkept vacuum packed and the entire loin was used. At 4days of display in MAP, all samples reached TBARS
Fig. 1. TBARS number (mg malonaldehyde/kg muscle) of samples from animals fed 10 different diets after display in MAP for 0, 4 or 9 days. Standarddeviation bars are indicated.
306 M.M. Campo et al. / Meat Science 72 (2006) 303–311
values under 1.1 except those from animals fed concen-trates, which showed an average value over 4.5. Concen-trate diet was purely cereal and straw, which would havevery low vitamin E content (Richardson et al., 2004) mak-ing these samples oxidatively unstable. TBARS also in-creases in meat that has been previously frozen, due todamages in some cellular structures thus encouraging oxi-
Table 3Effect of display time on significance of differences in sensory attributes for ea
n.s. = not significant; * = p 6 0.05; ** = p 6 0.01; *** = p 6 0.001.Cont PLS : control protected lipid supplement; PLS: Protected lipid supplemeCont PFO: control protected fish oil; PFO: Protected fish oil.Conc: concentrate.1, 2, 3 = three different levels of inclusion of either PLS or PFO in the diet.
dation. After 9 days of display in MAP, only animals fedthe control diets contPLS and contPFO, plus grass-fed ani-mals, had TBARS values under 2, probably due to thehigher proportion of saturated fatty acids in the meat fromanimals fed the control diets and the higher content ofvitamin E in the grass-fed animals (Richardson et al.,2004) acting as a natural antioxidant (Gatellier, Hamelin,
M.M. Campo et al. / Meat Science 72 (2006) 303–311 307
Durand, & Renerre, 2001). Those diets with the highervalues at 4 days showed the higher values at 9 days ofdisplay. However, the increment was not linear, differencesbetween 0 and 4 days of display were smaller than between4 and 9 days of display, as expected since lipid oxidation isa free-radical autocatalytic chain reaction (Rhee, 1988).The greater the inclusion of protected PUFA in the diet,the higher the TBARS value obtained, especially observed
Table 4Taste panel results for flavour sensory attributes that are statistically significa
Display Days Diet
Cont PLS PLS1 PLS2 PLS
Beef 0 26.5 c 25.5 b 26.1 c 26.34 22.5 b 22.3 b 17.5 b 19.99 17.1 a 10.8 a 7.8 a 10.1sed 1.60 1.57 3.27 2.79
Abnormal 0 11.7 a 10.7 a 15.0 a 12.64 23.1 b 19.5 b 27.9 b 22.39 34.0 c 42.4 c 51.1 c 45.3
2.91 2.65 5.33 5.74
Rancid 0 1.2 a 1.3 a 1.7 a 1.34 5.4 a 4.9 a 11.0 b 8.09 14.2 b 17.8 b 21.3 c 18.0
3.06 3.98 3.97 2.90
Greasy/oily 0 11.4 a 12.9 a 15.0 a 12.14 18.2 ab 17.3 ab 22.1 ab 20.89 23.6 b 28.1 b 32.4 b 33.3
4.21 2.05 5.18 6.24
Bloody 0 8.7 b 9.3 b 9.7 b 7.84 1.7 a 1.6 a 1.7 a 2.19 2.8 a 1.6 a 1.5 a 1.2
2.69 2.06 3.20 2.54
Metallic 0 7.8 b 6.3 8.9 b 10.14 3.7 a 5.1 3.3 a 2.79 3.8 a 5.3 2.8 a 3.2
1.54 1.47 2.03 2.72
Livery 0 7.1 b 7.9 b 8.5 b 9.34 3.1 a 2.8 a 2.4 a 2.89 2.6 a 1.9 a 1.8 a 1.2
1.20 1.87 2.50 2.06
Bitter 0 2.9 4.7 ab 4.0 4.54 2.5 3.3 a 4.7 4.49 3.6 8.1 b 6.3 5.8
0.96 1.72 1.23 1.08
Sweet 0 5.13 6.7 b 5.4 5.24 6.9 6.0 ab 5.2 5.49 5.3 3.6 a 2.1 5.0
Overall liking 0 26.8 c 29.4 b 25.6 c 27.54 19.9 b 22.6 b 14.6 b 19.69 15.9 a 8.6 a 5.7 a 8.3
1.91 4.35 3.33 3.21
a, b, c: Different letters within column and descriptor represent differences bet
in the PFO diets where an extra level of inclusion of pro-tected lipid fish oil in the diet gave meat with a higherTBARS value, coincidentally with a higher proportion ofn-3 PUFA in the intramuscular fat (Table 1). In PLS diets,the oxidation of the meat did not increase from PLS2 toPLS3 because there was only a minor increase in unsatu-rated FA deposition in the muscle over PLS2 althoughthe protected lipid in the diet was 25% higher. Thus, these
nt
3 Cont PFO PFO1 PFO2 PFO3 Grass Conc
c 24.9 b 22.7 b 23.6 b 25.2 c 25.5 b 25.2 bb 23.4 a 21.2 b 19.7 b 20.4 b 18.6 ab 12.1 aa 16.3 a 14.1 a 12.4 a 9.8 a 14.4 a 7.7 a
2.32 1.53 1.47 2.32 3.57 2.81
a 13.6 a 17.3 a 13.5 a 13.7 a 12.8 a 18.2 aa 16.4 a 16.1 a 20.5 b 22.4 b 24.1 ab 38.0 bb 31.6 b 36.3 b 39.7 c 49.5 c 31.2 b 53.7 c
3.59 3.00 3.09 3.01 5.92 6.52
a 1.7 a 1.5 a 2.0 a 1.2 a 0.9 a 1.3 ab 4.3 a 4.3 ab 5.2 a 6.9 a 5.3 ab 9.5 bc 12.7 b 11.4 b 18.5 b 19.0 b 12.1 b 21.4 c
3.12 3.73 4.39 5.05 3.84 4.09
a 15.6 13.2 12.2 a 12.5 a 10.9 a 10.9 aa 17.0 15.1 19.5 b 17.9 a 13.9 a 22.5 bb 22.3 20.9 17.6 c 21.1 b 22.1 b 27.1 b
2.85 3.37 3.64 3.91 3.62 5.68
b 7.4 6.0 b 10.0 b 6.3 10.9 b 8.8a 3.2 3.5 ab 4.0 ab 2.0 1.6 a 1.8a 2.7 1.6 a 2.1 a 3.6 2.5 a 2.1
2.48 1.33 2.86 2.27 3.30 2.96
b 5.9 11.4 8.2 b 5.5 5.6 4.3a 3.3 4.6 4.3 ab 2.9 5.4 2.8a 5.4 4.9 2.6 a 6.4 4.0 4.4
1.37 2.91 2.03 1.70 2.01 1.27
b 8.7 b 10.4 b 9.4 b 10.9 b 9.3 b 3.6a 2.4 a 3.4 a 2.9 a 2.8 a 2.6 a 2.6a 1.6 a 2.8 a 3.3 a 2.1 a 2.1 a 2.8
2.40 1.70 1.98 1.58 1.86 0.97
4.2 3.9 3.6 a 3.9 a 3.3 3.0 a2.6 3.9 5.0 ab 3.7 a 2.9 3.9 a5.4 6.3 7.9 b 9.7 b 4.4 8.8 b1.70 1.20 1.52 2.16 1.39 2.25
5.1 5.8 4.4 5.5 a 5.0 5.94.7 7.7 10.1 7.5 a 7.8 6.09.2 10.9 7.5 16.5 b 5.5 11.43.43 2.92 1.77 3.68 2.36 1.95
c 26.7 b 21.6 b 24.4 b 27.2 c 25.2 b 26.2 bb 23.2 b 19.9 b 18.3 a 19.4 b 16.7 a 10.6 aa 13.7 a 11.9 a 10.2 a 7.0 a 11.9 a 6.05 a
3.45 2.83 2.63 2.95 4.12 3.44
ween display times, p 6 0.05.
308 M.M. Campo et al. / Meat Science 72 (2006) 303–311
samples provided a wide range of objective oxidation mea-surement to compare with the sensory analysis.
Significance of the effect of display time within diet onthe perception of sensory attributes is shown in Table 3.Display had a big influence on the perception of beef,abnormal, rancid and overall liking, the only four attri-butes with a significant effect in each diet. Livery flavourwas also highly influenced by display, and, to a lesser ex-tent, greasy, bloody and metallic flavours, although somediets did not show statistically significant differences. How-ever, no influence of display was observed for fishy, card-board, vegetable, grassy or dairy flavours, in any of thediets studied.
Sensory attributes behaved differently throughout dis-play (Table 4). Beef flavour decreased as display time in-creased. Although all diets showed similar values for beefflavour at 0 days of display, in meat cooked after breakingthe vacuum in the packaging, the biggest reduction oc-curred in those diets with the biggest values of oxidation,
Table 5Spearman�s correlations between TBARS and sensory attributes (n = 216)
especially PLS2, PLS3, PFO3 and concentrate-fed animals.In general, the decrease in strength of beef flavour wasmore pronounced between 4 and 9 days of display than be-tween 0 and 4 days. The degradation of sulphur-containingamino acids and aroma compounds has been associatedwith a loss of �meatiness� (Drumm & Spanier, 1991; Spa-nier, Edwards, & Dupuy, 1988).
Abnormal flavour behaved in the opposite way to beefflavour, with values increasing throughout display. Thehigher values at 9 days of display corresponded to concen-trate-fed animals followed by PLS2, PFO3 and PLS3 diets.Concentrate and PLS2 also showed the highest abnormalflavour values after 4 days of display. MacDonald, Gray,and Kakuda (1980) stated that off-flavour formation couldbe predicted from the TBARS values during the first 7 daysof storage, maybe as a consequence of the autoxidation ofmembrane phospholipids (St. Angelo et al., 1987), a majorcomponent of warmed-over flavour (WOF), one of themost studied off-flavours in the literature.
cid Greasy Bloody Metallic
4*** 0.70*** �0.60*** �0.36***
9*** �0.69*** 0.51*** 0.20**
2*** 0.71*** �0.52*** �0.22**
0.73*** �0.58*** �0.28***
– �0.51*** �0.24***
– 0.35***
–
Cardboard Vegetable Grassy Dairy Overall liking
0.06 0.23** �0.23** 0.35*** �0.84***
�0.01 �0.15* 0.33*** �0.20** 0.93***
�0.01 0.15* �0.31*** 0.24*** �0.88***
0.03 0.21** �0.34*** 0.36*** �0.83***
�0.01 0.09 �0.15* 0.33*** �0.69***
�0.09 �0.28*** 0.10 �0.30*** 0.52***
�0.11 �0.13 0.05 �0.24*** 0.18**
�0.10 �0.17* 0.13 �0.38*** 0.52***
�0.17* �0.02 �0.33*** 0.08 �0.42***
�0.05 �0.09 �0.03 0.13 0.24***
�0.02 �0.07 �0.08 0.02 �0.03
�0.13 0.06 �0.10 0.08 �0.34***
– 0.20** �0.08 �0.07 �0.03– 0.02 0.08 �0.15*
– �0.02 0.33***
– �0.22**
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Rancid flavour followed a similar tendency to abnormalflavour, increasing with display especially between 4 and 9days. The significance of the effect of display was moreimportant in those diets with a high content of unsaturatedfatty acids in the muscle, concentrate, PLS2 and PLS3. Val-ues at day 0 of display were almost null indicating the ab-sence of lipid induced oxidation during the frozen storageunder vacuum conditions. However, values at 4 or 9 daysof display were lower than those found for abnormal fla-vour which would indicate that rancid was an abnormalflavour, but not the only one detected by panellists.
Greasy/oily notes rose throughout display, although theincrease was not significant in cont PFO and PFO1 diets.Nevertheless, the increase in perception was less than thatfound for abnormal flavour. Bloody, metallic and liveryfollowed a similar tendency, values decreasing with display,although the intensity of their perception was not high.Bloody and metallic have been associated with uncondi-tioned meat. Samples used in this experiment had, at least,10 days of conditioning at the moment of tasting, whichagrees with those low values found from 0 days of display.Bitter was only influenced by display in four out of the 10diets studied. Even for these diets, values were very low,although they showed a tendency to increase with display.Since peptides have been associated with this taste (Spanieret al., 1988), it seems logical that this increase with ageingarises from proteolysis occurring during this period with anincrease in the amount of free peptides.
None of the other parameters studied showed an impor-tant influence of display time on their perception. Poste,Willemot, Butler, and Patterson (1986) could not clearlyestablish that a taste panel could differentiate between
y = 0.0349x2 - 2.1482x + 34.704
R2 = 0.7084
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30
beef
ran
cid
35
y = 1.0896x - 2.5681
R2 = 0.8637
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30
Beef
Ove
rall
likin
g
35
Fig. 2. Relationship between rancid, beef, abnormal flavour and overal
WOF and other types of autoxidative changes, as card-board can be considered. However, Byrne et al. (2001)found a good association between fish and cardboard fla-vours for detecting WOF. We have not found this relation-ship, perhaps because fresh beef is not normally associatedwith such off-flavour, although TBARS are also highly re-lated to WOF (St. Angelo, Crippen, Dupuy, & James,.1990; Stapelfeldt, Bjørn, Skovgaard, Skibsted, & Bertelsen,1992) or because cardboard taste disappears when oxidisedrancidity notes dominate the flavour profile (Johnsen & Ci-ville, 1986). Green notes have been associated with thepresence of hexanal, a volatile aldehyde deriving from theoxidation of n-6 fatty acids, however no differences werefound in grassy flavour. Maybe, as found by Byrne et al.(2001) in WOF, the aroma of hexanal was masked by otherstrong flavours such as rancid in the present meat samples.
Spearman�s correlations between TBARS and sensoryattributes are shown in Table 5. Although few high corre-lations between sensory perceptions and instrumental mea-surements have been reported, beef, abnormal, rancid andoverall acceptability showed correlations over 0.7 withTBARS, positively for abnormal and rancid and negativelyfor beef and overall liking. Most of the correlations werehighly significant due to the high number of observations.However it was very clear that abnormal flavour(rho = �0.87***) and rancid (rho = �0.79***) were asso-ciated with decreased beef perception. Overall liking washighly related to the perception of beef flavour(rho = 0.93) and to the absence of abnormal(rho = �0.88***) and rancid (rho = �0.83***) flavours.The presence of rancid flavour was highly correlated tothe presence of greasy flavour (rho = 0.73***), which was
y = 0.0247x2 - 1.48x + 27.164
R2 = 0.6987
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40
Rancid
Ove
rall
likin
g
y = -0.0138x2 + 2.0102x + 11.244
R2 = 0.7662
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40
Rancid
Ab
no
rmal
fla
vou
r
l liking over the period of display (j 0 days; 4 days; r 9 days).
310 M.M. Campo et al. / Meat Science 72 (2006) 303–311
associated to a decrease in acceptability (rho = �0.69***).Fig. 2 shows the development of these four attributesthroughout display in relation to each others. Except foroverall liking and beef, whose best regression was linear,sigmoidal curves were the best fitting for the relationshipbetween rancid and beef, abnormal flavour or overallliking.
The perception of rancid and beef flavour in relation toTBARS also followed a sigmoidal curve as the best fit(Fig. 3). The higher the TBARS the more rancidity andthe less beef flavour were perceived sensorially. From theinitial point of perception, rancidity increased rapidly untilit reached either a saturation point or an adaptation from
y = 0
0
5
10
15
20
25
30
35
40
0 2 4 6TBA
Ran
cid
y = -0.0359x3 +
0
5
10
15
20
25
30
35
40
0 2 4 6TBA
Bee
f
0 2 4 60
5
10
15
20
25
30
35
40
TBARS = 2.28
Fig. 3. Relationship between TBARS, rancid and beef flavour
the panellist, where a higher oxidation in terms of TBARScould not be perceived as such. From a TBARS value pointover 8, the sensitivity of the technique may not be as accu-rate as at lower values. The crossing point of those twocurves, TBARS of 2.28, indicates the TBARS value fromwhich the perception of rancidity overpowers beef flavour.This could be considered as the limiting threshold foracceptability of oxidation in beef. It is not far from themaximum value reported by Greene and Cumuze (1981)whose threshold for oxidised flavour perception ranged be-tween 0.6 and 2.0. This range was wider than 0.5–1.0 foundby Tarladgis et al. (1960) in pork. Obviously, thresholds de-pend upon experience and sensitivity of panellists, but it
.0553x3 - 1.122x2 + 7.3962x + 2.3204
R2 = 0.6224
8 10 12RS
14
0.8276x2 - 6.2937x + 24.475
R2 = 0.6773
8 10 12RS
14
8 10 12 14
rancid
beef
over the period of display (j 0 days; 4 days; r 9 days).
M.M. Campo et al. / Meat Science 72 (2006) 303–311 311
seems clear that oxidation is perceived differently in beefthan in pork and that a TBARS value of 1.0 seems toolow for the rejection of beef. This would have implied highrancid or abnormal scores in most of the diets at 4 days ofdisplay, and that was not the case in this work.
4. Conclusions
It is difficult to value the limiting point at which beef canbe rejected due to lipid oxidation, based on sensory percep-tions. Perceptions will depend upon personal thresholds,which can vary due to experience, among other factors.But thresholds indicate the point from which stimuli canbe perceived, not necessarily from which the stimuli mayproduce rejection of the product. Clearly, oxidation pro-vokes deterioration on beef flavour throughout display inatmospheres enriched in oxygen and this deteriorationcan be closely related to TBARS. The point of TBARS va-lue of 2 could be considered the limiting point from whererancid flavour overpowers beef flavour, and therefore, tobe considered as the maximum level for positive sensoryperception of beef. From that point onwards, we can ex-pect beef to be rejected due to a strong sensory perceptionof lipid oxidation.
Acknowledgement
This research was supported by a Marie Curie Fellow-ship of the European Union programme Quality of Lifeunder contract number QLK1-CT-1999-51147. Authorswish to thank Anne Baker for technical assistance andAnglo Beef Processors, Masterfoods, Meat and LivestockCommission and Sainsbury�s and MCyT, Programa Ra-mon y Cajal, for financial support.
References
Anton, M., Gatellier, P., & Renerre, M. (1993). Relationships betweenmyoglobin and microsomal lipid oxidation: Influence of muscle typeand time post-mortem. In Proceedings of the 39th International
Congress of Meat Science and Technology, Calgary, Canada (pp.389–392).
Ashgar, A., Gray, J. I., Buckley, D. J., Pearson, A. M., & Booren, A. M.(1988). Perspectives on warmed-over flavor. Food Technology, 42,102–108.
Byrne, D. V., Bredie, W. L. P., Bak, L. S., Bertelsen, G., Martens, H., &Martens, M. (2001). Sensory and chemical analysis of cooked porcinemeat patties in relation to warmed-over flavour and pre-slaughterstress. Meat Science, 59, 229–249.
Drumm, T. D., & Spanier, A. M. (1991). Changes in the content of lipidautoxidation and sulfur-containing compounds in cooked beef duringstorage. Journal of Agriculture and Food Chemistry, 39, 336–343.
Gill, C. O. (1996). Extending the storage life of raw chilled meats. Meat
Science, 43, S99–S109.Gatellier, P., Hamelin, C., Durand, Y., & Renerre, M. (2001). Effect of
dietary vitamin E supplementation on colour stability and lipidoxidation of air- and modified atmosphere-packaged beef. Meat
Science, 59, 133–140.Gray, J. I., Gomaa, E. A., & Buckley, D. J. (1996). Oxidative quality and
shelf life of meats. Meat Science, 43, S11–S123.
Gray, J. L., & Pearson, A. M. (1987). Rancidity and warmed-over flavour.In A. M. Pearson & T. R. Dutson (Eds.). Advances in meat research (3,pp. 221–270). Amsterdam: Elsevier.
Gray, J. L., & Pearson, A. M. (1994). Lipid-derived off-flavours in meat-formation and inhibition. In F. Shahidi (Ed.), Flavour of meat and
meat products (pp. 116–143). London: Blackie Academic.Greene, B. E., & Cumuze, T. H. (1981). Relationship between TBA
numbers and inexperienced panellists� assessments of oxidized flavor incooked beef. Journal of Food Science, 47, 52–54, 58.
ISO (1993). Sensory analysis- General guidance for the selection, trainingand monitoring of assessors. Part 1: selected assessors. InternationalOrganization for Standardization, ISO, 8586-1, Geneve, Switzerland.26pp.
ISO (1994). Sensory analysis- Identification and selection of descriptorsfor establishing a sensory profile by a multidimensional approach.International Organization for Standardization, ISO, 11035, Geneve,Switzerland. 26pp.
Johnsen, P. B., & Civille, G. V. (1986). A standardized lexicon of meatWOF descriptors. Journal of Sensory Studies, 7, 99–104.
Labuza, T. P. (1971). Kinetics of lipid oxidation in foods. CRC Critical
Reviews of Food Technology, 2, 355–404.MacDonald, B., Gray, J. I., & Kakuda, Y. (1980). Role of nitrite in
cured meat flavour: chemical analysis. Journal of Food Science, 45,889–892.
Poste, L. M., Willemot, C., Butler, G., & Patterson, C. (1986). Sensoryaroma scores and TBA values as indices of warmed-over flavour inpork. Journal of Food Science, 51(4), 886–888.
Renerre, M. (1990). Review: factors involved in the discoloration of beefmeat. International Journal of Food Science and Technology, 25,613–630.
Rhee, K. S. (1988). Enzymatic and nonenzymatic catalysis of lipidoxidation in muscle foods. Food Technology, 42, 127–132.
Richardson, R. I., Nute, G. R., Wood, J. D., Scollan, N. D., &Warren, H.E. (2004). Effects of breed, diet and age on shelf life, muscle vitamin Eand eating quality of beef. In Proceedings of the British Society of
Animal Science 84, York, UK.Scollan, N. D., Enser, M., Gulati, S. K., Richardson, I., & Wood, J. D.
(2003). Effects of including a ruminally protected lipid supplement inthe diet on the fatty acid composition of beef muscle. British Journal ofNutrition, 90, 709–716.
Scollan, N., Enser, M, Richardson, R. I., Gulati, S., Hallett, K.G., &Nute, G.R., et al. (2004). The effects of ruminally-protected dietarylipid on the lipid composition and quality of beef muscle. InProceedings 50th International Congress of Meat Science and Technol-
ogy (2.50), Helsinki, Finland.Scott, T. W., Cook, L. J., & Mills, S. C. (1971). Protection of
dietary polyunsaturated fatty acids against microbial degradationin ruminants. Journal of the American Oil Chemists Society, 48,358–364.
Spanier, A. M., Edwards, J. V., & Dupuy, H. P. (1988). The warmed-overflavor process in beef: a study of meat proteins and peptides. FoodTechnology, 6, 110–118.
St. Angelo, A. J., Vercellotti, J. R., Legendre, M. G., Vinnet, C. H., Kuan,J. W., James, C. Jr.,, et al. (1987). Chemical and instrumental analysesof warmed-over flavor in beef. Journal of Food Science, 52(3),1163–1168.
St. Angelo, A. J., Crippen, K. L., Dupuy, H. P., & James, C. Jr., (1990).Chemical and sensory studies of antioxidation-treated beef. Journal ofFood Science, 55, 1501–1539.
Stapelfeldt, H., Bjørn, H., Skovgaard, I. M., Skibsted, L. H., & Bertelsen,G. (1992). Warmed-over flavour in cooked sliced beef. Chemicalanalysis in relation to sensory evaluation. Zeitschrift Lebensmittel-
Utersuchung and Forschung, 195, 203–208.Tarladgis, B. G., Watts, B. M., Younathan, M. T., & Dugan, L. (1960). A
distillation method for the quantitative determination of malonalde-hyde in rancid foods. Journal of the American Oil Chemist�s Society, 37,44–48.
