beef quality attributes as affected by increasing the intramuscular levels of vitamin e and omega-3...
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Meat Science xxx (2011) xxx–xxx
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Beef quality attributes as affected by increasing the intramuscular levels of vitamin Eand omega-3 fatty acids
Manuel Juárez a,⁎, Michael E.R. Dugan a, Noelia Aldai a, John A. Basarab b, Vern S. Baron a,Tim A. McAllister c, Jennifer L. Aalhus a
a Agriculture and Agri-Food Canada, Lacombe Research Centre, 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1b Alberta Agriculture and Rural Development, Lacombe Research Centre, 6000 C & E Trail, Lacombe, AB, Canada T4L 1W1c Agriculture and Agri-Food Canada, Research Centre, 5403-1st Ave. S. Lethbridge, AB, Canada T1J 4B1
⁎ Corresponding author at: Agriculture and Agri-FooCentre, 6000 C & E Trail, Lacombe, Alberta, Canada T4L
E-mail address: [email protected] (M. Juáre
0309-1740/$ – see front matter. Crown Copyright © 20doi:10.1016/j.meatsci.2011.11.010
Please cite this article as: Juárez, M., et al., Bfatty acids, Meat Science (2011), doi:10.101
a b s t r a c t
a r t i c l e i n f oArticle history:Received 15 April 2011Received in revised form 2 June 2011Accepted 2 November 2011Available online xxxx
Keywords:FlaxseedLinseedMeat qualityOxidationTocopherol
In order to investigate the effects of increasing beef n-3 fatty acid content and the protective effects ofvitamin E antioxidant activity on meat quality characteristics, 80 feedlot steers were fed 4 different diets(control, high vitamin E, 10% ground flaxseed or high vitamin E–10% ground flaxseed). While dietary treat-ments had no effect (P>0.05) on meat composition or tenderness values, the increase in oxidation productswas lower (P=0.046) in meat from vitamin E supplemented steers and higher (P=0.006) in meat fromflaxseed fed animals. The increase in α-tocopherol tissue levels (Pb0.001) in meat from animals fed flaxseedand increased dietary vitamin E resulted in the lowest drip loss values (P=0.013). As expected, display timehad a large effect on retail traits in both steaks and patties (Pb0.001). While retail traits of steaks were notaffected by the dietary treatments (P>0.05), feeding flaxseed decreased (Pb0.05) ground beef retail scores,which were not corrected by higher levels of dietary vitamin E. Finally, although no effect (P>0.05) wasobserved among treatments for sensory attributes in steaks, the correlations of a combined n-3:α-tocopherolratio against retail and sensory attributes (Pb0.05) suggest that increased n-3 fatty acids levels requireincreased dietary antioxidants, such as vitamin E to avoid negative effects on meat quality from a loss inoxidative stability.
Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved.
1. Introduction
Lipid peroxidation in meat is an important factor limiting both thequality of meat and its consumer acceptability (Aalhus & Dugan,2004). Peroxidation of lipids in meat becomes apparent to consumersby the development of rancid odours or flavours, and “warmed-over”flavour in previously cooked meats. Oxidation of meat pigments isrecognisable by the development of brown discolouration replacingthe normally acceptable bright cherry red colour. Typical lipid perox-idation in meat involves the phospholipid fraction (Frankel, 1998),located in the membranes and containing over 40% polyunsaturatedfatty acids (PUFA). Due to their high level of unsaturation and theirproximity to the haeme catalysts of the mitochondria and micro-somes, they are susceptible to oxidation.
Despite the numerous known deleterious quality changes associatedwith oxidation of PUFA (Wood et al., 2004), there is considerable interestalong the meat value chain in enhancing the PUFA content of meat sothat niche products with health label claims can be marketed (Juárez etal., 2010; Ruxton, Reed, Simpson, & Millington, 2004). In this regard,
d Canada, Lacombe Research1W1. Tel.: +1 4037828118.z).
11 Published by Elsevier Ltd. All righ
eef quality attributes as affec6/j.meatsci.2011.11.010
dietary flax supplementation has been used by several authors in orderto increase omega-3 (n-3) fatty acid content in beef (e.g. Bartoň,Marounek, Kudrna, Bureš, & Zahrádková, 2007; Juárez et al., 2011;Raes, De Smet, Balcaen, Claeys, & Demeyer, 2003; Scollan et al., 2001).However, as expected, some side-effects on meat quality, includingearly development of off-flavour and off-colour, have been reported(LaBrune, Reinhardt, Dikeman, & Drouillard, 2008). Consequently,increasing lipid stability by addition of elevated levels of antioxidantcompounds could be a means of overcoming this problem, as observedin pork (Rey et al., 2001). Thus, vitamin E iswidely used as an antioxidantin biological systems, and its accumulation in muscle has been shown tohave a positive impact on colour and lipid stability of fresh and frozenbeef (Liu, Lanari, & Schaefer, 1995).
The present study was undertaken to elucidate the effects of in-creasing beef total n-3 content and the protective effect of vitamin Eantioxidant activity on meat quality characteristics.
2. Material and methods
Experimental design, animal handling, dietary treatments, slaughterprocess and sampling were previously reported by Juárez et al. (2011).Briefly, 80 feedlot steers were housed in 8 feedlot pens (2 pens per die-tary treatment, 10 steers per pen, n=20 steers per dietary treatment)
ts reserved.
ted by increasing the intramuscular levels of vitamin E and omega-3
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and fed ad libitum. Steers (381±7.10 kg) were stratified by weight andassigned to one of four diets in a 2×2 factorial experiment, with twolevels of dietary vitamin E, with or without flaxseed: control(451 IU dl-α-tocopheryl acetate·head−1·day−1), high vitamin E(1051 dl-α-tocopheryl IU·head−1·day−1), flaxseed (10% groundflaxseed substituted for steam-rolled barley) and flaxseed–vitamin E(10% flaxseed and 1051 IU dl-α-tocopheryl acetate·head−1·day−1).Steers were on trial for 129±3.2 days and finished to 571±7.1 kg.
Steers were slaughtered at the Lacombe Research Centre in groupsof 16, which included the two heaviest animals per pen per slaughterdate, and all animals were slaughtered within 35 days. At slaughter theleft longissimus thoracis (LT; rib-eye) temperature and pH at 45 min(Hannah HI9025C pH metre, Hannah Instruments, Mississauga, ON,Canada, equipped with an Orion Ingold electrode, Udorf, Switzerland)and 24 h, 24 h colour (Minolta CM2002; Minolta Canada Inc.,Mississauga, ON, Canada) (CIE, 1978) were measured posterior to thegrade site as described in Aldai et al. (2010). The left loin primal wasremoved from the carcass and one steak with the fat cap on from theposterior end (near the grade site) was removed and frozen(−80 °C) for subsequent fatty acid determination. The primal wasthen trimmed of subcutaneous fat and overlying muscles.Approximately 200 g of subcutaneous fat and 800 g of lean werelabelled, individually vacuum packaged (Ultravac Model UV2100;Koch Instruments, Kansas City, MO, USA) and placed in a cooler at2 °C for 6 days, for subsequent analysis. Another steak (25 mm)was re-moved from the posterior end of the LT, finely comminuted (RobotCoupe Blixir BX3; Robot Coupe USA Inc., Ridgeland, MS, USA) andsamples (approximately 20 g) were placed into pre-labelled sterilesample whirl-pak bags (Fisher Scientific, Mississauga, ON, Canada) andstored at−80 °C for α-tocopherol level determination. Muscle levels ofα-tocopherol were determined on the grind using normal phase HPLCwith tocopherol acetate as an internal standard (Katsanidis & Addis,1999), adapted for fluorescence detection (Hewavitharana, Lanari, &Becu, 2004). The remaining portion of the LT was labelled, vacuumpackaged and stored in the cooler for 6 days, for subsequentmeat qualityanalysis.
2.1. Meat quality analysis
Following a 6 day ageing period,five steaks (25 mmthickness)wereremoved from the LT muscle. The first steak was placed on a grill(Garland Grill ED30B; Condon Barr Food Equipment Ltd., Edmonton,AB, Canada) preheated to approximately 210 °C to an internal temper-ature of 35.5 °C, turned and cooked to a final temperature of 71 °C(Hewlett Packard HP34970A Data Logger; Hewlett Packard Co., Boise,ID, USA). Steaks were placed into polyethylene bags, sealed and imme-diately immersed in icewater to prevent further cooking. Cooked steakswere immediately transferred to a cooler and allowed to stand for a24 h period. The following day, final steak weight was recorded fordetermination of cook loss and six 1.9 cm cores were removed parallelto the fibre grain and peak shear force was determined on each coreperpendicular to the fibre grain using a TA-XT Plus Texture Analyzerequipped with a Warner–Bratzler shear head at a crosshead speedof 20 cm min−1 and a 30 kg load cell using Texture Exponent 32Software (Texture Technologies Corp., Hamilton, MA, USA). Peakshear force was expressed as the average of the 6 cores. The secondand third steaks were individually vacuum packaged and frozen at−35 °C until sensory evaluation. The fourth steak was placed into apolystyrene tray with a dri-loc pad (UZ Soaker Ultra Zap Pads,Paper Pak Industries Washington, GA, USA), over-wrapped withoxygen permeable film (8000 ml·m−2·24 h−1 vitafilm choicewrap, Goodyear Canada Inc., Toronto, ON, Canada) and displayed inretail case at 1 °C for retail evaluation after 0, 1, 2 and 3 days, asdescribed by Nassu et al. (submitted for publication). Following a20 min period of exposure to atmospheric oxygen, objective colourmeasurements were collected across the fifth steak. To determine
Please cite this article as: Juárez, M., et al., Beef quality attributes as affecfatty acids, Meat Science (2011), doi:10.1016/j.meatsci.2011.11.010
drip-loss, the steak was then pre-weighed, and stored on a polysty-rene over-wrapped tray with a dri-loc pad for 4 days at 2 °C, andthen a final steakweight was recorded, as described in Aldai et al. (2010).
The remaining portion of the LTwas trimmed of all overlying connec-tive tissue and ground three times (Butcher Boy Meat Grinder ModelTCA22; Lasar Manufacturing Co., Los Angeles, CA, USA). Grind (100 g)was used to determine the proximate composition, as described byAldai et al. (2010).
At 6 days after slaughter, the stored lean and subcutaneous fat wasground two times (Butcher Boy Meat Grinder Model TCA22, initiallywith a 0.48-cm grind plate followed by a 0.32-cm grind plate; LasarManufacturing Co., Los Angeles, CA, USA) to achieve an 80/20 lean tofat grind. A sub-sample (~50 g) was finely comminuted with a robotcoupe and concentrations of thiobarbituric acid reactive substances(TBARS) (0 days in retail) were determined as described by Nielsen,Sorensen, Skibsted, and Bertelsen (1997). Briefly, after grinding thesample (10 g), it was mixed with 30 mL 7.5% trichloroacetic acid andfiltered with Whatman #4 filter (Whatman, Maidstone, UK). Thefiltrate (2.5 mL) was mixed with the 2.5 mL of thiobarbituric acidsolution (20 mM) and after heating at 100 °C for 40 min the absor-bance was measured at 532 nm. The concentration (mg·kg−1meat)was calculated by comparison with standard solutions. An additional50 g of grind was placed on pre-labelled over-wrapped polystyrenetray (8000 ml/m2· per 24 h vitafilm choice wrap; Goodyear CanadaInc., Toronto, ON, Canada), and placed in a retail display case todetermine 3 day TBARS content. The increase in TBARS between days0 and 3 (ΔTBARS) was then calculated. The remaining grind was usedto form a 140 g patty (11.5 cm diameter×0.63 cm thick) using a singlepatty hamburger press (Cabelas, Sydney, NE, USA). Patties were placedonto pre-labelled polystyrene trays, over-wrapped and placed intodisplay case for retail evaluation at 0, 1, 2 and 3 days.
Intramuscular lipids were analysed as previously reported byJuárez et al. (2011). The concentration of n-3 fatty acids (% totalfatty acids) was used to calculate the combined n-3:α-tocopherolratio.
2.2. Retail and sensory evaluation
All samples were placed into a fan assisted, horizontal (chest type)retail display case (Hill Refrigeration of Canada Ltd., Barrie, ON) underfluorescent room lighting (GE deluxe cool white), supplemented withincandescent lighting directly above the display case (GE clear coolbeam 150W/120 V spaced 91.5 cm apart) resulting in an intensity of1076 lx at the meat surface for 12 h per day (Jeremiah & Gibson,2001). On each specific display time (0, 1, 2 and 3 days) three objectivecolour measurements were collected across both the steak and patties.Following objective colour measurements, the same steaks and pattieswere subjectively evaluated for retail appearance, lean colour score andpercent surface discolouration by 8 trained panellists using an 8-pointhedonic (1=extremely undesirable and 8=extremely desirable), an8-point descriptive (1=white and 8=extremely dark red) and a7-point descriptive (1=0% and 7=100% discolouration) scales,respectively.
Taste panel steaks were removed from the freezer and placed in arefrigerator to thaw for 24 h. Steaks were grilled and prepared forsensory analysis as described by Aldai et al. (2010). Attribute ratingsfrom panellists were electronically collected with Compusense 5, re-lease 4.6 computer software (Compusense Inc., Guelph, ON, Canada)using an eight point descriptive scale for initial and overall tenderness(8=extremely tender; 1=extremely tough), initial and sustainablejuiciness (8=extremely juicy; 1=extremely dry), beef flavour inten-sity (8=extremely intense; 1=extremely bland), off-flavour intensity(8=no off-flavour; 1=extremely intense off-flavour) and amount ofconnective tissue (8=none detected; 1=abundant). Flavourdesirability and overall palatability were rated on an eight point he-donic scale, (8=extremely desirable; 1=extremely undesirable).
ted by increasing the intramuscular levels of vitamin E and omega-3
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2.3. Statistical analysis
Statistical analyses were conducted using the MIXED procedure ofSAS (SAS, 2003). The model included the fixed effects of diet (flax/noflax) and vitamin E (normal/enhanced), as well as the diet×vitamin Einteraction, and kill as a random effect. For retail evaluation traits, daywas included in the model as a fixed effect, with no interaction(P>0.05) observed between day and any of the dietary treatments.Hence, linear and quadratic contrasts were conducted to furtherexplore the effects of day on retail evaluation traits. Treatmentmeans were determined using the LSMEANS option and separatedusing an F-test protected LSD (P≤0.05). Correlation coefficients ofthe combined n-3:α-tocopherol ratio against retail and sensory attri-butes were also determined.
3. Results and discussion
3.1. Meat composition
Temperature and pH, as well as LT composition values (moisture,fat and protein content) were similar (P>0.05) among dietarytreatments (Table 1), as observed in previous studies when flaxwas in-cluded in beef cattle diets (Noci, French, Monahan, & Moloney, 2007;Scollan et al., 2001). While flaxseed supplementation had no effect(P>0.05) on colour traits, colour measurements at the grade siteshowed lower chroma (P=0.012) and hue (P=0.005) values inmeat from vitamin E supplemented steers. Several studies have alsoreported positive effects of dietary vitamin E supplementation in re-ducing the oxidation of lipids and myoglobin in beef (Liu et al., 1995;Lynch, Kerry, Buckley, Faustman, & Morrissey, 1999; Robbins et al.,2003).
Some authors (e.g.Maddock et al., 2006) have reported an increasein tenderness with increasing dietary flaxseed content. Oxidisingconditions in post-mortem muscle have been reported to inactivate ormodify the activity of the calpain system (Harris, Huff-Lonergan,Lonergan, Jones, & Rankins, 2001), and it has been suggested that
Table 1Effect of dietary vitamin E (VitE) and flaxseed (Flax) on beef quality traits.
Diet
No VitE–No Flax VitE–No Flax No
pH and temperature, °CpH, 45 min 6.77 6.75 6.7Temperature, 45 min 39.7 39.6 39.9pH, 24 h 5.59 5.59 5.6Temperature, 24 h 4.00 3.79 3.9
Proximate analysis, %Moisture (g·100 g−1 meat) 72.4 72.1 71.7Fat (g·100 g−1 meat) 5.56 6.04 6.2Protein (g·100 g−1 meat) 21.2 21.0 21.1
Objective colour measurements, 24 hL* 37.4 37.4 37.8Chroma 22.7 22.1 22.9Hue 24.6 24.0 24.4
Texture and drip lossShear, kg 5.99 5.47 5.4Drip loss, mg·g−1 meat 40.7a 39.6a 43.7
α-Tocopherol and n-3:α-tocopherol ratioα-Tocopherol, μg·g−1 meat 2.03 3.16 2.2n-3:α-Tocopherol ratio, %:μg·g−1 0.50 0.37 0.9
Malonaldehyde, mg·kg−1 meatΔTBARS (3 days) 0.42 0.22 0.64
a,bDifferent letters indicate statistical difference (P≤0.05); TBARS: thiobarbituric acid react
Please cite this article as: Juárez, M., et al., Beef quality attributes as affecfatty acids, Meat Science (2011), doi:10.1016/j.meatsci.2011.11.010
increasing the level of antioxidants in meat may improve tenderness(Huff Lonergan, Zhang, & Lonergan, 2010). The results from the presentstudy showed no effect on tenderness (P>0.05) either on a typicalCanadian barley-based or a high α-linolenic (flaxseed) diet when thelevels of dietary vitamin E increased from 451 to 1051 IU dl-α-tocopheryl·head−1·day−1.
Meat from steers fed flaxseed and high levels of vitamin E had thelowest (P=0.013) drip loss values, which is positive from a meatquality perspective. α-Tocopherol preserves the integrity of musclecell membranes, inhibiting the passage of sarcoplasmic fluid, as wellas acting as a radical-quenching antioxidant, thereby preventingdrip loss and the oxidation of membrane phospholipids duringstorage (Asghar et al., 1991; Faustman, Chan, Schaefer, & Havens,1998; Gray, Gomaa, & Buckley, 1996).
As expected, increases in α-tocopherol levels (Pb0.001) wereobserved in meat from vitamin E and vitamin E plus flaxseedsupplemented steers, while including flaxseed in the diet resultedin greater n-3:α-tocopherol ratios (Pb0.001), as a consequence ofthe increase in n-3 fatty acids (Juárez et al., 2011). Both dietarytreatments had an effect on TBARS (ΔTBARS) increases. Specifically,the increase between 0 and 3 days of ageing was lower (P=0.046)in meat from vitamin E supplemented steers and higher (P=0.006) in meat from flaxseed fed steers. Realini, Duckett, Brito,Dalla Rizza, and De Mattos (2004) also reported higherα-tocopherol levels and lower TBARS values in steaks and groundbeef from pasture and concentrate-fed beef cattle supplementedwith vitamin E. Increasing the n-3 content in meat has beenshown to result in higher levels of oxidation due to the highersusceptibility of the PUFA (Wood et al., 2004).
3.2. Retail evaluation
In steaks, the appearance (Pb0.001) scores, L* (P=0.024) andchroma (Pb0.001) values linearly decreased, and lean colour anddiscolouration surface, as well as hue values, linearly increased(Pb0.001) from day 0 to day 3 for all groups (Table 2). Similar effects
SEM P value
VitE–Flax Flax–VitE VitE Flax VitE Flax
8 6.8 0.031 0.054 0.531 0.11439.4 0.252 0.084 0.976 0.126
0 5.61 0.016 0.091 0.982 0.1459 4.02 0.384 0.494 0.403 0.367
71.8 0.413 0.699 0.139 0.5997 6.23 0.493 0.579 0.257 0.516
21.2 0.151 0.318 0.888 0.305
36.9 0.778 0.319 0.829 0.37121.1 0.649 0.012 0.391 0.21523.6 0.328 0.005 0.292 0.630
6 5.89 0.495 0.888 0.874 0.169a 34.9b 1.812 0.002 0.556 0.013
5 3.25 0.130 b0.001 0.237 0.6245 0.83 0.083 0.078 b0.001 0.941
0.49 0.135 0.046 0.006 0.809
ive substances.
ted by increasing the intramuscular levels of vitamin E and omega-3
Table 2Effect of days on retail on evaluation characteristics of beef muscle and patties (20%fat).
Day SEM P value
0 1 2 3 Linear Quadratic
SteakAppearance 7.66 7.11 6.59 5.79 0.064 b0.001 0.084Lean colour 5.00 5.00 5.00 5.17 0.017 b0.001 0.004Discolouration surface 1.01 1.25 1.72 2.15 0.098 b0.001 0.223L* 42.1 41.5 41.6 41.3 0.191 0.024 0.470Chroma 24.0 23.1 22.9 22.8 0.294 b0.001 0.086Hue 36.1 36.3 36.7 37.2 0.167 b0.001 0.314
PattyAppearance 6.71 6.11 5.33 4.40 0.318 b0.001 0.046Lean colour 4.41 4.62 4.83 4.52 0.242 0.056 b0.001Discolouration surface 1.00 1.19 1.58 3.11 0.087 b0.001 b0.001L* 55.1 53.6 54.0 53.7 1.368 0.025 0.092Chroma 24.6 21.0 20.0 19.7 0.387 b0.001 b0.001Hue 44.3 50.0 52.8 55.6 0.860 b0.001 b0.001
Appearance (1=extremely undesirable and 8=extremely desirable), lean colourscore (1=white and 8=extremely dark red) and percent surface discolouration(1=0% and 7=100% discolouration).
4 M. Juárez et al. / Meat Science xxx (2011) xxx–xxx
were observed for ground beef, with the exception of a quadratic effect(Pb0.001) on lean colour, due to a decrease after 3 days of ageing. Theextent and rate of oxygen diffusion into the meat surface has beenreported to increase during ageing due to continuous inactivation ofoxygen-consuming enzymes (Lindahl, Karlsson, Lundström, &Andersen, 2006; Tikk, Lindahl, Karlsson, & Andersen, 2008).
Dietary addition of either vitamin E or flaxseed (Table 3) did notaffect (P>0.05) any of the subjective or objective retail attributes insteaks, although effects have been observed following extended ageingtimes (Nassu et al., submitted for publication). In high-fat products(patties), several interactions between both treatments were observed.The scores for patty appearance decreased (P=0.043) when flaxseedwas included in the diet, and vitamin E supplementation did notshow any protective effect. Lean colour scores increased (Pb0.001)and L* values decreased (P=0.030) when vitamin E was added tothe control diet, but the opposite effect was observed in patties fromflaxseed fed steers. Furthermore, patty hue values increased(P=0.041) with the inclusion of both flaxseed and vitamin E in thediet and patty surface discolouration increased (P=0.003) with flax-seed inclusion in the diets. Previous studies (Houben & van Dijk,2001; LaBrune et al., 2008; Realini et al., 2004) have reported shorterretail display life of steaks with higher n-3 content (from flaxseed
Table 3Effect of dietary vitamin E (VitE) and flaxseed (Flax) on evaluation characteristics of beef m
Diet
No VitE–No Flax VitE–No Flax No VitE–Fl
SteakAppearance 6.84 6.8 6.76Lean colour 5 5.06 5.05Discolouration surface 1.5 1.54 1.59L* 41.5 41.4 41.7Chroma 23.3 23.5 23.0Hue 36.5 36.4 37.0
PattyAppearance 5.69ab 5.88a 5.57bc
Lean colour 4.57b 4.85a 4.57b
Discolouration surface 1.64 1.51 1.81L* 54.1ab 53.5b 54.0ab
Chroma 21.2 21.2 21.7Hue 50.5b 50.1b 50.7ab
a,b,cDifferent letters indicate statistical difference (P≤0.05); appearance (1=extremely unddark red) and percent surface discolouration (1=0% and 7=100% discolouration).
Please cite this article as: Juárez, M., et al., Beef quality attributes as affecfatty acids, Meat Science (2011), doi:10.1016/j.meatsci.2011.11.010
diets) and higher lipid stability of beef during retail display after sup-plementing feedlot cattle with vitamin E. The fact that these effectswere observed in patties only is explained by the fact that, in groundbeef, cellular integrity has been disrupted, the PUFA concentration isincreased at the same time antioxidant concentration is diluted andthe exposure of the tissues to oxygen increases (Hultin, 1988).
Only steaks were used for sensory evaluation and no effect oftreatments (P>0.05) was observed in any of the studied sensoryattributes (Table 4). Some authors have reported decreases injuiciness scores (Maddock et al., 2006) and increases in off-flavour(LaBrune et al., 2008) when n-3 content is increased through theinclusion of flaxseed in the diet. Other studies have also reported anincrease in overall liking scores in meat from cattle given flaxseeddiets (Vatansever et al., 2000), but most studies have shown a declinewith decreases in panellist preferences for meat from animals feddiets high in unsaturated fatty acids (e.g. Campo et al., 2006) due tothe increase in oxidation products (Yang et al., 2002). Increasingα-tocopherol levels has been reported to increase lipid stability and re-duce off-flavour development in beef (Delmore, Schmidt, Tatum, Sofos,& Smith, 1998; Yang et al., 2002). The lack of an effect in the presentstudy may be due to the initial levels of vitamin E in the control diet(451 IU dl-α-tocopheryl acetate·head−1·day−1). This dietary level ofvitamin E is within the norm used by Canadian feedlot producers andseems to be sufficient to counteract any potential negative effect onlean beef palatability resulting from an increase in n-3 fatty acids inflaxseed supplemented diets.
3.3. n-3:α-Tocopherol ratio as an indicator of lipid oxidation
Numerous studies have compared the effects of different dietarylevels of vitamin E or n-3 sources, reporting decreases in oxidationlevels when vitamin E is increased in the diet and greater oxidationvalues in meat from animals fed n-3 enhanced diets (e.g. Bartoň etal., 2007; Lee, Panjono, Kang, Kim, & Park, 2008; Noci et al., 2007;Raes et al., 2004). Both treatments (dietary vitamin E and flaxseed)are known to have opposite effects on meat colour and lipid stabilityand in the present study this was demonstrated in patties but not insteaks. Finding effects in patties likely relates to their higher suscepti-bility to oxidation, while the lack of effects in steaks may relate moreto the limited changes seen coupled with natural variation betweenanimals in both n-3 and vitamin E content. Hence we were interestedin determining if correlation analysis between beef quality traits andthe n-3:α-tocopherol ratio would provide a more sensitive measureof the effects of increasing beef n-3 content and the protective effectof vitamin E on meat quality characteristics.
uscle and patties (20% fat).
SEM P value
ax Flax–VitE VitE Flax VitE Flax
6.75 0.110 0.718 0.313 0.8015.05 0.030 0.072 0.122 0.2461.5 0.170 0.735 0.761 0.398
41.8 0.330 0.982 0.211 0.67023.1 0.510 0.592 0.069 0.75336.5 0.290 0.050 0.083 0.382
5.42c 0.550 0.808 b0.001 0.0434.40c 0.420 0.455 b0.001 b0.0011.92 0.150 0.959 0.003 0.221
55.0a 2.370 0.570 0.049 0.03021.3 0.670 0.109 0.071 0.25651.5a 1.490 0.518 0.014 0.041
esirable and 8=extremely desirable), lean colour score (1=white and 8=extremely
ted by increasing the intramuscular levels of vitamin E and omega-3
Table 4Effect of dietary vitamin E (VitE) and flaxseed (Flax) on beef sensory characteristics.
Diet SEM P value
No VitE–No Flax VitE–No Flax No VitE–Flax Flax–VitE VitE Flax VitE Flax
Initialtenderness
5.65 6.04 5.92 6.16 0.372 0.288 0.503 0.811
Initial juiciness 5.70 5.89 5.87 5.88 0.174 0.438 0.545 0.478Beef flavour intensity 5.08 5.16 5.35 5.28 0.131 0.973 0.078 0.510Off-flavour intensity 7.34 7.36 7.10 7.31 0.126 0.365 0.241 0.447Amount connective tissue 7.46 7.49 7.58 7.51 0.135 0.892 0.550 0.650Overall tenderness 6.01 6.22 6.15 6.42 0.292 0.302 0.456 0.910Sustained juiciness 5.55 5.63 5.61 5.68 0.114 0.444 0.564 0.988
Initial and overall tenderness (8=extremely tender; 1=extremely tough), initial and sustainable juiciness (8=extremely juicy; 1=extremely dry), beef flavour intensity(8=extremely intense; 1=extremely bland), off-flavour intensity (8=no off-flavour; 1=extremely intense off-flavour) and amount of connective tissue (8=none detected;1=abundant).
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Several significant relationships (Pb0.05) were observed betweenthe n-3:α-tocopherol ratio and retail characteristics of steaks. Ap-pearance and hue were negatively correlated with this ratio (r=−0.154 and −0.268, respectively), while discolouration surface andchroma were positively correlated to this ratio (r=0.216 and 0.142,respectively). And as would be expected, similar negative correlationswere also observed between the n-3:α-tocopherol ratio and chromaand L* values in patties (−0.143 and −0.193, respectively), togetherwith a positive correlation with lean colour (0.176). Results showhow higher levels of n-3 fatty acids and lower α-tocopherol tissuelevels lead to an increase in negative retail characteristics, and clearlydemonstrated the sensitivity of correlation analysis. In an extensivereview, Faustman, Sun, Mancini, and Suman (2010) reported thelink between myoglobin and lipid oxidation. The conversion ofoxymyoglobin to metmyoglobin and the oxidation of unsaturatedfatty acids seem to generate products that can further acceleratetheir oxidation in a reciprocal manner. As observed in the presentstudy, Chan, Faustman, and Decker (1997) reported that as thedegree of fatty acid unsaturation increased, and the presence of α-tocopherol decreased, the oxidation of both lipid and oxymyoglobinincreased. α-Tocopherol functions as a lipid-soluble chain-breakingantioxidant in cell membranes, effectively controlling lipid oxidationand, indirectly, colour deterioration (Faustman & Wang, 2000).
Consistent with the enhanced sensitivity for finding differences inretail characteristics of steaks, all the sensory traits were negativelycorrelated with the calculated n-3:α-tocopherol ratio (Pb0.05;r=0.260 to 0.374). Therefore, increasing the concentration of n-3fatty acids, while decreasing the α-tocopherol level in beef, leads totougher, less juicy and flavoured and with greater off-flavourintensity meat. All these changes indicate a lower palatability andacceptability, leading to a poorer eating experience. Therefore, feed-ing animals with more unsaturated fatty acids to increase the n-3polyunsaturated fatty acid content increases the susceptibility of themeat to oxidation and concomitant increases in dietary vitamin Eare therefore necessary to prevent flavour deterioration due to lipidoxidation (Wood & Enser, 1997).
4. Conclusions
The increase in oxidation values observed in meat from flaxseedfed steers resulted in lower scores during the retail display of patties(20% fat), which were not corrected by higher levels of dietaryvitamin E supplementation. Therefore, the only clear effect observedfrom increasing vitamin E in the diet was a decrease in drip loss.However, correlation analysis using the n-3:α-tocopherol ratioindicated that a balance between the desired increase in unsaturatedfatty acids and the levels of endogenous antioxidants is necessary toavoid negative effects on beef colour and palatability.
Please cite this article as: Juárez, M., et al., Beef quality attributes as affecfatty acids, Meat Science (2011), doi:10.1016/j.meatsci.2011.11.010
Acknowledgments
Dr. M. Juárez acknowledges the receipt of a NSERC fellowshipfunded through the AAFC ABIP-FOBI programme. Dr. N. Aldaiacknowledges the receipt of a research contract from the 7th EuropeanCommunity Programme (Marie Curie International Outgoing Fellow-ship). The skilled assistance of the Beef Unit and Meat Processing staffat the Lacombe Research Centre is sincerely appreciated. The authorsalso wish to thank the dedicated technical assistance of Ivy Larsen,Lorna Gibson, Fran Costello, Christine Burbidge-Boyd, Rhona Thackerand Kathy Roxburgh.
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