Sensory profiling of textural properties of meat from dairy cows exposed to a compensatory finishing strategy

Meat Science 87 (2011) 73–80

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Meat Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m e a t s c i

Sensory profiling of textural properties of meat from dairy cows exposed to a compensatory finishing strategy Margrethe Therkildsen a,⁎, Sandra Stolzenbach b, Derek V. Byrne b a b

Department of Food Science, Faculty of Agricultural Science, Aarhus University, PO box 50, DK-8830 Tjele, Denmark Department of Food Science, Sensory Science, Faculty of Life Science, University of Copenhagen, Rolighedsvej 30, DK-1958, Frederiksberg C, Denmark

a r t i c l e

i n f o

Article history: Received 25 June 2010 Received in revised form 31 August 2010 Accepted 2 September 2010 Keywords: Cull dairy cows Sensory profiling Carcass quality Texture

a b s t r a c t A compensatory finishing strategy was evaluated to improve the quality of meat from dairy cows. The experiment included ten pairs of Holstein Friesian dairy cows. Each pair was the progeny of the same sire, in the same parity, and approximately at the same number of days in lactation before entering the experiment. Within each pair, one cow was allocated to a compensatory finishing strategy, dried off for 4 days, and further restricted in energy intake for another 17 days followed by 6 weeks of ad libitum feeding. The strategy improved the sensory texture and flavour of both M. longissimus dorsi (LD) and M. semimembranosus (SM). This was supported by lower shear force in both muscles (P b 0.02). The effect can be ascribed to various factors; in LD an increased amount of IMF plays a significant role, whereas in SM an increased protein turnover is suggested to be the dominating factor. © 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved.

1. Introduction Meat from dairy cows often has the reputation of being very tough, and coming from older animals. Nevertheless, in countries where milk production plays a major role in the cattle industry, as in Denmark, the optimisation of milk production involves a continuous focus on the best potential of dairy cows, and thus a continuous exchange of the animals to improve the herd. In Danish dairy production, the exchange percentage is around 34–38% per year (Jørgensen, Martin, & Slot, 2010), and the average dairy cow has around 2 lactations before slaughter (Jørgensen et al., 2010). Therefore there is a general interest in improving the meat quality of these slaughter cows, in order to improve the value of the meat from the animals when removed from the herd, and thus increase the total output of the dairy production. In several studies with young animals, it has been shown that it is possible to manipulate meat quality through feeding strategy (Aberle, Reeves, Judge, Hunsley, & Perry, 1981; Allingham, Harper, & Hunter, 1998; Purchas, Burnham, & Morris, 2002; Therkildsen, Melchior Larsen, Bang, & Vestergaard, 2002). One of the possible linkages is stimulation of muscle protein turnover in the live animal, which affects the potential for tenderness development post mortem (Koohmaraie, Kent, Shackelford, Veiseth, & Wheeler, 2002). Recently, it was shown that utilisation of a compensatory growth strategy in young dairy bull calves leads to an optimisation of muscle protein degradation 5–8 weeks after change to ad libitum feeding (Therkildsen,

⁎ Corresponding author. Tel.: +45 89 99 12 40; fax: +45 89 99 15 64. E-mail address: [email protected] (M. Therkildsen).

2005), and that slaughter at that time improves the tenderness of some muscles, but not others (Therkildsen, Houbak, & Byrne, 2008). In the lactating dairy cow, most of the absorbed nutrients are directed towards milk production, whereas muscle tissue is expected to have much lower priority. However, in the beginning of the lactation, protein degradation in muscle tissue will be high in order to release amino acids for milk production (McNamara, 2004), whereas later in the lactation where the absorbed nutrients support the milk production, protein degradation in the muscle tissue is expected to be at a minimum. This low protein degradation may explain why meat from dairy cows is often experienced as tough. Our hypothesis is that if the protein turnover in the muscle tissue from dairy cows could be increased through increased nutrient availability, there would be a better potential for tenderness development post mortem. Finishing feeding of culled dry cows has previously mostly been studied from the perspective of the effect on performance and slaughter quality and especially in beef cows (Cranwell, Unruh, Brethour, & Simms, 1996; Sawyer, Mathis, & Davis, 2004) and less so with focus on meat quality and dairy cows (Vestergaard et al., 2007). Lately, Vestergaard et al. (2007) showed that finishing feeding of dried-off dairy cows for either 2 or 4 months resulted in larger muscles, increased fatness, improved overall carcass quality, a reduced shear force value (Pb 0.06) and overall high eating quality as the meat flavour was significantly improved (P b 0.001), and the sensorial evaluated tenderness tended to be improved (Pb 0.16). In that study, the finishing-fed dairy cows were compared with dairy cows which were dried off for 7 days before slaughter. This procedure may actually have stimulated protein breakdown in the semi-fasted cows, which may have improved the tenderness of the meat, as seen in experiments with feeding below maintenance (McDonagh, Fernandez, & Oddy, 1999).

0309-1740/$ – see front matter © 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2010.09.005

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The aim of the present experiment was to improve the meat quality of dairy cows through introduction of a compensatory feeding strategy following a drying-off period. The effect of the compensatory growth strategy on meat quality was studied in terms of carcass quality traits, technological quality traits and sensory profiling of two muscles; M. longissimus dorsi (LD) and M. semimembranosus (SM), in order to extend the knowledge of mechanisms involved in the textural improvements of different muscles. The effect of feeding strategy on the muscle protein composition and the expression and activity of the calpain system will be presented in Houbak & Therkildsen (in manuscript). 2. Materials and methods The experiment was conducted according to the Danish Ministry of Justice law no. 382 (June 10, 1987), Act no. 726 (September 9, 1993) concerning experiments with animals and care of experimental animals. 2.1. Animals and feeding strategy Twenty Holstein Friesian dairy cows from the dairy herd at the Faculty of Agricultural Science, Aarhus University, were used (see Table 1). The 20 dairy cows constituted 10 pairs, each pair was the progeny of the same sire, in the same parity, from 1 to 4, and approximately the same number of days post-calving when entering the experiment, on average 264 days post-calving. Within each pair of cows, one was allocated to a compensatory feeding strategy (COMP) and the other acted as a control (CONT). The cows allocated to the COMP strategy were dried off for 4 days on barley straw and water, followed by 17 days with restricted energy and protein intake offered as free access to a total, mixed ration (TMR) with a metabolic energy content of 11.8 MJ/kg DM and 81 g digestible crude protein/kg DM. Following this 3 week restriction period, the COMP cows were offered free access to a high energy TMR with a metabolic energy content of 13.8 MJ/kg DM and 104 g digestible crude protein/kg DM for 6 weeks. The composition of the rations offered during the restriction period and the compensation period is given in Table 2. At the end of the 6week period, the cows were slaughtered. The CONT cows did not enter the experiment before the day of slaughter, thus they were slaughtered while still in lactation, and at the same time as the COMP cow in the pair. The composition of the ration fed to cows in lactation can be seen in Table 2. The cows were housed in tie stalls. They were weighed twice when entering the experiment, and the COMP cows were also weighed after the 3-week restriction period and again at slaughter. Likewise, the COMP cows were ultrasound-scanned at the last rib when entering the experiment, after 3 weeks and just prior to slaughter, in order to estimate the area of LD. The ultrasound scanning was done with Aloka SSD-500 and a UST-5024 N-3.5 probe (Simonsen & Weel, Denmark). 2.2. Slaughter procedure All cows were slaughtered at the experimental slaughterhouse at the Faculty of Agricultural Science, Aarhus University. Two pairs were

Table 1 Experimental design of feeding strategies. 20 cows Feeding CONT (10 cows) Parity 1 2 3 4 (3 cows) (4 cows) (2 cows) (1 cow) Ageing 7 14 7 14 7 14 7 14

COMP (10 cows) 1 2 3 4 (3 cows) (4 cows) (2 cows) (1 cow) 7 14 7 14 7 14 7 14

Table 2 Composition of diets fed to CONT cows prior to slaughter and COMP cows in the 9-week finishing period. CONT diet fed Restriction diet Finishing diet in lactation 5–21 days 22–63 days Ingredients (percent of feed) Barley straw Maize silage Clover grass silage Rapeseed cake Barley Sugar beet molasses Minerals and vitamins

3.6 35.4 40.1 10.8 5.7 3.7 0.7

Calculated chemical composition Net energy content (SFU/kg)a 0.48 14.1 Metabolic energy (MJ/kg DM)b Digestible crude protein (g/kg DM)b 109 a b

37.6 22.1 25.1 6.7 3.5 4.3 0.7

10.0 47.4

0.39 11.8 81

0.57 13.8 104

14.9 23.3 3.7 0.7

SFU—Scandinavian feed units. DM—dry matter.

slaughtered each day, thus there were 5 slaughter days. At the day of slaughter, the cows were transported to the slaughterhouse (500 m), stunned by captive bolt pistol, hung and bled. Within 10 min following slaughter, the left side M. semitendinosis (ST) was excised, trimmed for fat and weighed. The carcasses were split and weighed, and the carcass length was measured from the middle of the posterior edge of the first rib to the anterior edge of the symphysis pubis. The weights of liver, heart, kidney and kidney fat were recorded. pH was measured in LD at the last rib 45 min post mortem with a PHM201 pH meter (Radiometer, Denmark) equipped with Metrohm probe type glass electrode WOC (Metrohm, Switzerland). The electrode was calibrated in pH 4.01 and 7.00 IUPAC buffers equilibrated to 35 °C. The carcasses were chilled at 10 °C until 12 h after slaughter of the last cow (thus from 12 to 15 h at 10 °C), whereupon the temperature in the cold room was decreased to 2 °C. In the cold room, the carcasses were classified according to the EUROP scale for conformation, fatness and colour (Commission Regulation EC 1249/2008). Forty-eight hours post mortem, the carcasses were weighed, and pH48 was measured as described previously, however, at this time the electrode was calibrated in buffers equilibrated to 3 °C. SM were cut from both sides, trimmed of fat and weighed, vacuum-packed and aged for either 7 or 14 days post mortem at 3 °C before storage at −20 °C. The ageing time was switched between the carcass sides. Likewise, the LD from the 5th to 1st lumbar vertebra from both sides was removed, vacuum-packed and aged for 7 days at 3 °C before storage at −20 °C as described for the SM. In addition, from each side the LD was removed from the 10th thoracic vertebra to the 13th thoracic vertebra, and used as follows from the cranial direction: left side: 7 cm for Warner Bratzler shear force (WBsf) aged 2 days, and 7 cm for WBsf aged 7 days; right side: 7 cm used for determination of intramuscular fat (IMF), myofibrillar fragmentation index (MFI) on days 2, 7 and 14, and for colour and drip loss determination, and 7 cm for WBsf aged 14 days. The samples were vacuum-packed and aged as described at 3 °C before storage at −20 °C (Warner Bratzler shear force) or frozen in liquid nitrogen and stored at −80 °C until further analysis (MFI). 2.3. Determination of drip loss and colour Drip loss was measured on approximately 100 g of LD muscle removed 48 h post mortem using the plastic bag method described by Honikel (1998). Colour was measured on the LD sample removed 48 h post mortem using a Minolta Chroma Meter CR-300 (Osaka, Japan) calibrated against a white tile (L* = 92.30, a* = 0.32 and b* = 0.33). Samples were allowed to bloom for 1 h at 3 °C prior to the measurements. The parameters L*, a* and b*, representing lightness, redness and yellowness, were measured on five sites of each steak and the average presented.

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2.4. Sensory evaluation The sensory evaluation of the SM and LD was performed at the sensory laboratory of the University of Copenhagen, Faculty of Life Science, Frederiksberg, Denmark and at the Danish Meat Research Institute, Roskilde, Denmark, respectively. Each sensory panel consisted of 8 persons. In general, the sample preparation of SM and LD prior to the sensory profiling differed, but the sensory profiling was identically performed. The sensory profiling of SM was more comprehensive, as the sample set included samples aged for 7 and 14 days, while the sensory profiling of LD included samples aged 7 days. Further, the vocabulary was more detailed in the sensory profiling of SM than LD. 2.4.1. Sample preparation Prior to cooking, the SM and LD muscles were taken from the freezer and placed at 4 °C for approximately 44 h and 20 h, respectively, to enable gradual thawing. From the SM two roasts were cut parallel to each other from the proximal end of the SM and placed in preheated ovens (Bosch HBN 245 A; Robert Bosch A/S, Ballerup, Denmark) at 160 °C, until a core temperature of 60 °C was reached. Each panellist received three slices of 4 mm in thickness. The LD muscles were sliced into 21 mm thick steaks, placed on a roasting pan (155 °C) and heated for 8–9 min while being turned every second minute. The core temperatures were monitored and varied between 62 and 65 °C. Each LD steak was cut with a template equivalent to 5 cm width; two panellists got half of the cut beefsteak corresponding to a sample of 2.5 cm width. The border of fat was removed before serving. All the samples were served on preheated plates covered with aluminium to ensure that the samples were kept warm. 2.4.2. Descriptive sensory vocabulary development and profiling Prior to the sensory profiling, the sensory panels participated in the development of a sensory vocabulary to describe and discriminate the effects of the design variables on the textural characteristics of the beef. The panel evaluating the SM samples was trained with reference to the texture profile method (Meilgaard, Civille, & Carr, 1999; ISO 11036, 11036, 1994), while the vocabulary development for the LD samples was based on ISO 8586-1 (1993) and ASTM STP758 (1981). The training resulted in a vocabulary (Table 3) developed via collaboration between the panel leader and the panelists (Byrne, Bredie, & Martens, 1999; Byrne et al., 2001; Byrne, O'Sullivan, Dijksterhuis, Bredie, & Martens, 2001). The sensory, descriptive profiling was carried out by the same trained panel as utilised in the vocabulary development. The sensory profiling of the SM and LD was done according to ISO 11036, 11036 (1994) and Meilgaard et al. (1999). The sample presentation order was randomised within the sensory profiling days. 15 cm unstructured line scales anchored to the left with ‘none’ and to the right with ‘very much’ (Meilgaard et al., 1999) were used. Quantitative data were collected using the FIZZ Network data acquisition software (BIOSYSTEMS, Couternon, France).

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Table 3 List of sensory terms with definitions derived for sensory profiling of beef samples.

Odour 1. 2. 3. Appearance 4. 5. 6. 7. 8. 9. Flavour 10.

Termc

Definition with reference materialsd

Fresh cooked beef-Ob Sour/fresh-Ob Liver-Ob

Odour associated with Oven-cooked beef meat with no surface browning Fresh, sour, natural yoghurt Cooked beef liver

Surface exudate-Aa Read area-Aa Brown/grey-Aa,b Redness-Aa Connective tissue-Aa Overall-Aa

11.

Fresh cooked beef-Fa,b Beef fat-Fa

12. 13. 14.

Liver-Fa,b Sour/fresh-Fa,b Off flavour-Fb

15.

Overall-Fa

Texture 16.

Springiness-TXa

17.

Tenderness-TXa,b

18.

Juiciness-TXa,b

19. 20.

Fattiness-TXa Cohesiveness-TXa

21.

Hardness-TXa,b

22. 23. 24. 25

Crunchiness-TXa Fibrousness-TXa,b Crumbliness-TXa,b Chewiness-TXa

26.

Mastication remnants-TXa Overall-TXa

27.

Amount of visible exudate on sample surface and on the plate Area of red colour developed during roasting Area of brown/grey colour developed during roasting Degree of red in the red area Easiness to tear apart the connective tissue Liking of appearance Aromatic taste sensation associated with Oven-cooked beef meat with no surface browning Fat from oven-cooked beef meat with no surface browning Cooked beef liver (metallic) Fresh, sour, natural yoghurt Flavour that is non-related to oven-cooked beef meat with no surface browning Liking of flavour Texture associated with Springiness after chewing half through the sample and releasing the pressure Easiness with which the meat is divided into fine particles during mastication Amount of juice released from the sample during mastication Fatty feeling in the palate during mastication Degree of deformation before the structure is broken Force required to bite completely through the sample in first bite Sound of crunchiness Amount of fibres appearing during mastication Amount of fine particles during mastication Length of time required to masticate a solid product into a state ready for swallowing Remaining remnant when the sample is ready to swallow Liking of texture

Mouth feeling Fatty mouth feeling after mastication of 28. Fatty mouthcoathing-MFa the sample 29. Metallic-MFa Metallic mount feeling after mastication of the sample a 30. Astringent-MF Degree of astringency after mastication of the sample 31. Overall-MFa Liking of mouth feeling Overall liking 32. Overall impressiona Liking of sample a

2.5. Instrumental and chemical measurements

Sensory terms used in the sensory profiling of SM. Sensory terms used in the sensory profiling of LD. Suffix to sensory terms indicates method of assessment by panelists: -A; appearance, -O; odour, -F; flavour, -TX; texture, -MF; mouth feeling. d Definitions of sensory terms as derived during vocabulary development. b c

2.5.1. Intramuscular fat The amount of intramuscular fat in LD and SM was determined by ether extraction (method NMKL 131:1989, Q481/Q7003), performed by Steins Laboratorium A/S, Holstebro, Denmark as described in Hansen, Therkildsen, and Byrne (2006). 2.5.2. Myofibrillar fragmentation index The MFI was measured according to Culler, Parrish, Smith, and Cross (1978), with minor modifications as described in Therkildsen et al. (2002).

2.5.3. Warner Bratzler shear force The determination of Warner Bratzler shear force was done as described in Hansen et al. (2006) according to the procedure described by Honikel (1998).

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2.6. Data analysis The production, instrumental and chemical data were analysed using a mixed model (SAS® System, 1996). The live weight characteristics, slaughter characteristics and intramuscular fat were analysed with the fixed effects of feeding strategy (COMP vs. CONT) and parity (1, 2, 3 and 4), whereas the analysis of the variables that were measured at different ageing times (MFI and WBsf) was carried out with day included in the model as a repeated measurement. For the sensory data, the sensory raw data were initially preprocessed to correct for variation in panellist and sensory replications using Generalised Procrustes Analysis (GPA; Gower, 1975) in Matlab 6.5 (MathWorks Inc., USA). Afterwards, data were averaged over panellists and sensory replicates. All sensory analyses were performed using Unscrambler Software, Version 9.7 (CAMO ASA, Trondheim, Norway). A Principal Component Analysis (PCA) was established to achieve an overview of the sensory sample variation. Next, the sensory data was forwarded Quantitative ANOVA Partial Least Squares Regression (APLSR) to visualise and determine structure and the degree of feeding strategies, lactations and ageing contribution to the variation in the sensory data (Martens & Martens, 2000). PC1 shows the main source of variation, and PC2 shows the next most important source of variation etc. To derive significance indications, regression coefficients were analysed by jack-knifing, which is based on crossvalidation (Martens & Martens, 2001). To determine the predictive ability of the sensory data for IMF, Partial Least Squares Regression (PLSR) was performed (Martens & Martens, 2000). Thus, it was investigated if IMF comes into play in the sensory perception of the textural changes. Since each LD sample was assessed only once by each panellist, it was not possible to pre-process the sensory raw data to correct for panellists and sensory replicate variation by GPA. Otherwise, the data were analysed in the same way for both the SM and LD data.

3. Results 3.1. Growth and slaughter quality characteristics The COMP cows had a very high daily gain as soon as they were dried off. Even though the daily intake of metabolic energy was restricted to 77.6% of what they ate in the finishing 6 weeks period, they had a weight increase of 44 kg over the 3-week restriction period. In the final finishing period, the COMP cows increased their live weight by 63 kg, making the daily gain in the total finishing period of 9 weeks 1.698 kg per day (Table 4). The ultrasound scanning of the LD of the COMP cows also reflected the weight gain with an increase in the area of LD of 11% from 45.2 cm2 when entering the experiment to 50.2 cm2 at slaughter. The increased live weight had a marked effect on the slaughter quality characteristics; a 49 kg heavier carcass (P b 0.02), improved dressing percentage (42.7 vs 46.6%, P b 0.04), 11% and 15% increase in the weight of SM and heart, respectively, with no significant effect on ST, liver and kidney (Table 5). The increased dressing percentage during the finishing period reflects a net gain of

Table 4 Age, live weight and growth rate of dairy cows slaughtered in lactation (CONT) or after a 9-week compensatory feeding strategy (COMP). Feeding strategy

CONT

COMP

SEM

P-value

Age at start, days Weight at start, kg Weight end of restriction period, kg Age at slaughter, d Weight at slaughter, kg Daily gain in finishing period, kg/day

1494 631

1462 574 618 1526 681 1698

131 28

0.87 0.07

131 23

0.87 0.13

1494 631

Table 5 Slaughter characteristics, conformation, colour and drip loss of dairy cows slaughtered in lactation (CONT) or after a 9-week compensatory feeding strategy (COMP). Feeding strategy

CONT

COMP

SEM

P-value

Carcass weight, kg Dressing percentage, % Carcass length, cm Weight ST, kg Weight SM, kg Heart, kg Liver, kg Kidney, kg Kidney fat, kg pH45 Temp45 pH48 Temp48 EUROP conformation EUROP fatness Colour score Minolta colour L* a* b* Drip loss, %

272 42.7 147.6 2.0 4.0 2.4 10.6 1.6 3.6 6.56 37.0 5.62 1.77 1.4 2.3 3.4

321 46.6 147.4 1.9 4.5 2.8 11.6 1.8 8.9 6.68 37.6 5.57 1.86 2.7 3.9 3.2

12 1.3 1.9 0.2 0.1 0.1 0.5 0.1 1.5 0.04 0.33 0.04 0.06 0.19 0.22 0.21

0.02 0.04 0.96 0.78 0.04 0.007 0.18 0.10 0.005 0.03 0.19 0.37 0.29 0.001 0.001 0.51

36.4 23.1 11.2 3.04

37.6 23.8 12.0 2.63

0.73 0.47 0.32 0.30

0.26 0.30 0.08 0.35

76 kg or 1.2 kg per day, calculated as the difference between carcass weight at the end and beginning of the experiment, with the assumption that the dressing percentage is 42.7% when the COMP cows enter the experiment. In addition, finishing feeding had a large effect on the deposition of fat, thus the amount of kidney fat increased by 146% (P b 0.005), and the EUROP fatness score increased by 1.6 units (P b 0.001), with two COMP cows classified with fatness score 5, and one CONT cow classified with fatness score 1. At the same time, the EUROP conformation score was improved by 1.3 units (P b 0.001), whereas no effect was seen neither on the visual evaluation of colour nor on the Minolta-assessed colour traits, L*, a* and b*. Likewise, finishing feeding had no effect on drip loss. pH measured in the LD 45 min after slaughter showed a higher pH in the COMP cows compared with the CONT cows (P b 0.03) (Table 5), whereas there was no difference in the ultimate pH (48 h) or temperatures measured after 45 min and 48 h. Only a few of the registered and measured traits were affected by the parity, although this conclusion should take into account the unbalanced distribution of cows in the 4 parity groups (see Table 1). Not surprisingly, the carcass length increased from parity 1 to 2 (P b 0.02) with no further increase over the following parities. Likewise there was an increase in weight of liver (P b 0.01) and kidneys (P b 0.02) over the parities, whereas there was no effect on the heart, the muscles (SM and ST) or the carcass weight. 3.2. Intramuscular fat The amount of intramuscular fat was measured in SM and LD, and showed a very different response to the compensatory finishing strategy. Thus in LD, the amount of IMF increased from 3.7% in the CONT cows to 7.9% in the COMP cows (P b 0.001), whereas in SM the amount of IMF was within the range 2–3%, with no significant difference between the feeding strategies (Table 6). Overall, the PLSR analysis revealed that IMF has multidimensional contribution. In the SM samples, juiciness-TX (P b 0.001), fattiness-TX (P b 0.001), cohesiveness-TX (P b 0.05), crunchiness-TX (P b 0.01), crumbliness-TX (P b 0.001), mastication remnant-TX (P b 0.001) and overall positive texture (P b 0.05) were significantly, positively related to/and predicted by IMF. However, crumbliness seemed to be the strongest. In respect to the LD samples, crumbliness (P b 0.001) and tenderness (P b 0.001) were found to be significantly, positively

Table 6 Myofibrillar fragmentation index (MFI) of M. longissimus dorsi (LD) and Warner Bratzler shear force (WBsf) and percentage of intramuscular fat (IMF) of M. longissimus dorsi (LD) and M. semimembranosus (SM) of dairy cows slaughtered in lactation (CONT) or after a 9-week compensatory finishing strategy (COMP). Feeding strategy

CONT

COMP

MFI LD, day 2 MFI LD, day 7 MFI LD, day 14 WBsf LD, day 2 WBsf LD, day 7 WBsf LD, day 14 IMF LD, % WBsf SM, day 7 WBsf SM, day 14 IMF SM, %

48 106 130 9.1 7.4 6.4 3.65 5.6 5.0 2.13

48 105 127 6.7 4.9 4.7 7.87 4.1 4.4 2.62

SEM 6.0

0.66

Feeding 0.81

0.02

0.62 0.36

0.001 0.02

0.47

0.44

Day 0.001

0.001

0.63

correlated to IMF, while hardness (P b 0.001), juiciness (P b 0.05) and fibrousness (P b 0.05) were significantly, negatively correlated to IMF (figure not shown). 3.3. WBSF and MFI characteristics The texture characteristic of SM was assessed with WBsf of meat aged 7 and 14 days (Table 6). Ageing of this muscle for more than 7 days had no effect on the shear force, as the shear force after 7 days of ageing was already fairly low, especially in SM from COMP cows, which had a significantly lower WBsf than SM from CONT cows (P b 0.02). An adjustment for the numerical difference in IMF between the feeding strategies had no influence on the positive effect of the finishing feeding. The instrumentally measured texture of LD was described partly by MFI and partly by WBsf of meat aged 2, 7 and 14 days (Table 6). The ageing showed the expected effect with increased MFI (P b 0.001) and lowered WBsf (P b 0.002) with time post mortem. There was no effect of feeding strategy on the MFI, whereas WBsf was significantly lower in LD from COMP cows (P b 0.02) at all times post mortem. However, if the WBsf was adjusted for the difference in IMF in the two feeding strategies, the difference between the strategies disappeared. 3.4. Sensory profiling of SM The PCA plot showed a clear discrimination of sensory modalities (not shown). The texture was separated into tenderness and hardness dimensions. Further, a discrimination of appearance/visual terms such as redness and brownness dimension was observed. A clear association of increased overall preference with tenderness-TX, juiciness-TX, beef meatiness-F, overall flavour and redness-A was found. An APLSR model (Fig. 1) was performed to investigate which design factors (feeding strategy, lactation, and ageing) were involved in this discrimination. It was found that all design factors were significantly described and discriminated by at least one of the sensory terms. Overall, the sensory terms were considered reliable since all of them except for surface exudate-A, sour/fresh-F, juicinessTX, fibrous-TX and metallic-MF significantly differentiated between the treatments and thus appeared to have utilisation in the description of the sensory variation in the samples. The texture was optimised using the compensatory feeding strategy. It was confirmed as COMP significantly increased overall impression (P b 0.05) supported by significantly positive correlation to overall texture (P b 0.01) and fatty mouthcoating (P b 0.05). Opposite, CONT was significantly positively correlated to springiness-TX (P b 0.01) and cohesiveness-TX (P b 0.05), which are regarded as negative aspects of sensory texture. The lactations influenced texture and flavour, as two lactations significantly improved the texture and flavour, whereas 3 lactations or more had a significantly negative effect on the texture and flavour.

Principal Component 2 (Y-explained variance 11%)

M. Therkildsen et al. / Meat Science 87 (2011) 73–80

77

1.0 Tenderness-TX

0.5

14 days of ageing Connective_tissue-A

1 lactation Beef_fat-F Overall_impression Overall-TX COMP feeding Fatty_mouthcoathing-MF 2 lactations Fattiness-A Redness-ASour/fresh-F

0.0

Liver-F Crumbliness-TX Brown/grey-A Mastication_remnants-TX

Fibrousness-TX Metallic-MF

Overall-F

Springiness-TX

Red_area-A Juiciness-TX Surface_exudate-A Overall_A

-0.5

CONT feeding Cohesiveness-TX Crunchiness-TX Chewiness-TX

Fresh_cooked_beef-F

3+ lactations

Hardness-TX Astringent-MF

7 days of ageing

-1.0 -1.0

-0.5

0.0

0.5

1.0

Principal Component 1 (Y-explained variance 25%) Fig. 1. SM; APLSR correlation loadings plot of PC1 versus PC2. The design variables: feeding strategy (CONT, COMP), parity (1, 2, 3+) and ageing (7 days, 14 days) in the X-matrix and the sensory terms in the Y-matrix. -A: Appearance, -F: Flavour, -TX: Texture, -MF: Mount feeling.

Overall, a shift in sensory characteristic of the beef was observed after 2 lactations. The effect of ageing was found to be conflicting with regard to texture and flavour, since 14 days of ageing resulted in improved tenderness (non-significant) compared to 7 days of ageing (this observation was especially clear in PC2 versus PC3, not shown), while the flavour and appearance were more associated to beef meat, when the beef had aged for 7 days. This was interpreted since 7 days of ageing was significantly, positively correlated with red area-A (P b 0.05), redness-A (P b 0.05), overall appearance (P b 0.05), beef meat-F (P b 0.001), overall flavour (P b 0.001) and overall liking (P b 0.01), whereas 14 days of ageing was significantly, positively correlated to brown/grey-A (P b 0.01), connective tissue-A (P b 0.001) and liver-F (P b 0.05). Further, 14 days of ageing was significantly, positively correlated to the texture terms springiness-TX (P b 0.05) and crumbliness-TX (P b 0.01). 3.5. Sensory profiling of LD The PCA plot spanned the variation of the texture across PC1, and the flavour aspects were differentiated across PC2 (not shown). Tenderness-TX, juiciness-TX, crumbliness-TX and fresh cooked beef-O/F were closely related to each other and negatively covaried with a group of sensory terms containing hardness-TX, fibrousness-TX, liver-O and off flavour-F. The APLSR model (Fig. 2) revealed that all design variables were significantly described and discriminated by at least one of the sensory terms. However, only the sensory terms fresh cooked beef-F, hardness-TX, juiciness-TX, crumbliness-TX and tenderness-TX significantly differentiated the treatments. The APLSR model displayed the same trends as found for the SM with regard to textural changes and flavour. Thus, COMP was significantly, positively correlated to tenderness-TX (P b 0.001), crumbliness-TX (P b 0.001), juiciness-TX (P b 0.05) and fresh cooked beef-F (P b 0.001). Also, the parity influenced texture and flavour in a similar direction as observed for the SM i.e. a significant positive correlation to tenderness-TX (P b 0.01), crumbliness-TX (P b 0.05), juiciness-TX (P b 0.05) and fresh cooked beef-F (P b 0.01) for two lactations.

Principal Component 2 (Y-explained variance 9%)

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1.0 3+ lactations Brown/grey-A

COMP feeding

0.5 Hardness-TX Fibrousness-TX Liver-O

Fresh_cooked-beef-F Fresh_cooked-beef-O

0.0

2 lactations

Crumbliness-TX Juiciness-TX Tenderness-TX

Sour/fresh-O

Off-flavour-F

-0.5

Vestergaard et al. (2007), an increased weight of SM of 11% whereas the weight of ST did not respond to the compensatory finishing strategy. In contrast to previous studies on finishing feeding of cull cows (Cranwell et al., 1996; Franco et al., 2009; Vestergaard et al., 2007), the compensatory finishing strategy had no effect on the colour traits L*, a* and b* measured on LD. Likewise drip loss was unaffected by feeding strategy. This partly agrees with Franco et al. (2009), who found improved WHC after one month, but not two months of finishing. Thus in general, the finishing feeding had positive effects on the carcass, i.e. improved EUROP conformation, increased carcass weight with no negative effect on the technological quality traits.

1 lactation

CONT feeding

4.2. Sensory and textural changes Liver-F Sour/fresh-F

-1.0 -1.0

-0.5

0.0

0.5

1.0

Principal Component 1 (Y-explained variance 74%) Fig. 2. LD; APLSR correlation loadings plot of PC1 versus PC2. The design variables: feeding strategy (CONT, COMP) and parity (1, 2, 3+) in the X-matrix and the sensory terms in the Y-matrix. -O: Odour, -A: Appearance, -F: Flavour, -TX: Texture.

4. Discussion 4.1. Effect of compensatory finishing strategy on live weight and carcass characteristics The compensatory finishing strategy, which was introduced to the dairy cows on the COMP strategy, was planned to restrict the cows' energy intake for a 3-week period followed by a 6-week period with a high energy intake to stimulate compensatory growth and muscle protein turnover in favour of later sensory tenderness development. The length of the 6-week period was chosen on the basis of the results generated in Therkildsen (2005), which showed maximal protein degradation in young bulls after 5–8 weeks of ad libitum feeding following a 3-month restriction period. The true necessary length of both restriction and finishing period of full-grown dairy cows to actually induce compensatory response has not been studied, however, the design used was chosen in order to minimise the total length of the finishing period of the cows making the strategy attractive to dairy producers. The effect of the restriction period on live weight gain cannot be calculated, because of an expected, simultaneous change in gut-fill in the short period. The very large gain of 44 kg over the 3 weeks restriction period do suggest both changes in gut-fill as well as carcass gain, and thus that the cows already at this stage compensate for limited nutrient availability to muscle tissue during lactation. The overall daily and net gains in the full 9-weeks period are similar to results observed on finishing beef cows (Matulis, McKeith, Faulkner, Berger, & George, 1987; Schnell, Belk, Tatum, Miller, & Smith, 1997) and above the results observed in dairy cows (Allen et al., 2009; Franco, Bispo, Gonzalez, Vazquez, & Moreno, 2009; Vestergaard et al., 2007), but similar to the gain of dairy cows finished for 68 days after a 10-day dry-off period (Jones & Macleod, 1981). The high daily gain in the 9-week finishing period improved financially important factors such as dressing percentage and EUROP conformation to a similar degree as seen by Vestergaard et al. (2007), although the dressing percentage did not reach the same level seen in other studies, i.e. above 50% (Allen et al., 2009; Schnell et al., 1997). However, the dressing percentage very much depends on diet and genetic background (Andersen, Ingvartsen, & Klastrup, 1984; Raux, Teissier, Bonnemaire, & Dumont, 1987), which may explain the differences. The net gain of the carcass was reflected in an increased area of LD of 11%, similar to the gain of dairy cows finished for 2 months in

The sensory changes caused by the different treatments were significantly described and differentiated by the developed vocabularies. Thus, these terms were applicable to differentiate the sensory characteristics of the beef. This high degree of applicability for sample description and discrimination is an indication of panellist agreement on the sensory terms (Byrne, O'Sullivan, et al., 2001). However, the sensory changes were dependent on whether the feeding strategy, lactations or ageing were considered. 4.2.1. Textural changes in the beef in relation to feeding strategy The compensatory finishing strategy improved the textural properties of both SM and LD. The compensatory finishing strategy had a multidimensional effect, since it affected the appearance, odour, flavour and texture of the meat. However, in the SM and LD samples, the feeding strategy was best differentiated by texture with hardness being the most influential. The impact of hardness was also confirmed in the separate analysis only including the sensory texture terms. This observation is comparable with Tornberg et al. (1985), who studied the pattern of mastication of meat and concluded that the number of chewing cycles was the best single indicator of the impression of the texture of the meat. As the number of chewing cycles and hardness are both evidence of chewing resistance of meat, these studies are in agreement. Commonality in the textural effects on SM and LD were found. However, the evidence of changes in the texture was stronger in the LD samples, since significant effects were found for increased tenderness, crumbliness and juiciness. Therkildsen (2005) demonstrated that compensatory growth is associated with increased muscle protein turnover and that muscle protein degradation exceeds the level in continuously ad libitum-fed bulls when restricted-fed bulls are exposed to ad libitum feeding again. Thus the improved tenderness of the meat from the COMP cows could be a result of increased protein degradation at the time of slaughter, which means a better potential for tenderness development post mortem. An effect of compensatory growth strategy on textural changes in bulls has earlier been demonstrated by Hansen et al. (2006). Here the texture of SM samples from young bulls fed ad libitum for 20 weeks following a 3month restriction period was significantly improved by the compensatory growth strategy. However, Hansen et al. (2006) found the opposite effect on LD, as LD samples were evaluated as having better textural properties when the young bulls had been exposed to ad libitum feeding. In a similar study with young bulls (Therkildsen et al., 2008), where the bulls were slaughtered at a time with maximal protein degradation corresponding to 6 weeks after change to ad libitum feeding, a positive effect was also seen on the tenderness of SM compared with continuously ad libitum-fed bulls, whereas the tenderness of LD was superior in bulls fed ad libitum continuously. In both Hansen et al. (2006) and Therkildsen et al. (2008), the amount of intramuscular fat in LD was higher in the continuously ad libitumfed bulls compared with the compensatory-fed bulls no matter if the bulls were slaughtered after 6 weeks (0.90% vs. 1.56% IMF) or 20 weeks of ad libitum feeding (2.13% vs 2.87% IMF). In the present

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experiment, the amount of IMF in LD was much higher from compensatory-finished cows compared with cows slaughtered in lactation. Thus, the various effects of a compensatory finishing strategy in the tenderness of LD in young bulls and full-grown cows could probably be ascribed to the effect of the finishing strategy on intramuscular fat. This is supported by the disappearance of the treatment effect when the shear force data were corrected for the amount of intramuscular fat and by the fact that no difference was observed in MFI between the treatments in the present study. In contrast, there was no significant difference in the amount of intramuscular fat in SM measured in Therkildsen et al. (2008) and in the present study, but there was a positive effect of the compensatory finishing strategy on the tenderness characteristics in these studies as well as in Hansen et al. (2006). This suggests that there are variations between muscles in response to strategies which in general stimulate muscle protein turnover as suggested in Therkildsen et al. (2008), which relates to location in the carcass, amount of connective tissue, intramuscular fat, fibre type composition and maturity. In cows, SM compared with LD is characterised as having more collagen measured both as total and insoluble collagen (4.63 and 3.57 vs 3.21 and 2.62 μg OH-proline/mg dry matter) (Jurie et al., 2007). Finishing feeding with a high energy ratio has been shown to increase the amount of soluble collagen in LD even in mature cows (Cranwell et al., 1996; Miller, Cross, Crouse, & Jenkins, 1987), which is known to be a contributing factor to meat tenderness. Thus the positive effect of compensatory finishing strategy on the tenderness of LD and SM in the present study could mainly be ascribed to the effect of IMF in LD and probably collagen and myofibrillar protein turnover in SM. The compensatory finishing strategy decreased the Warner Bratzler shear force in both muscles, which is similar to results seen in LD from Holstein Friesian cull cows (Franco et al., 2009) and Angus and Hereford cull cows (Matulis et al., 1987) after 56 days of finishing feeding, whereas the effect of either 2 or 4 months of finishing feeding in the study by Vestergaard et al. (2007) only decreased shear force marginally (5.93 vs 5.68 and 5.13 kg, respectively). The lack of effect in the last study could be ascribed to the comparison with cows which were dried off for one week and then slaughtered, as this may have caused increased protein degradation in the muscles. 4.2.2. Flavour changes in the beef in relation to feeding strategy Overall, the compensatory finishing strategy has a positive impact on flavour development in both SM and LD compared with meat from the cows slaughtered in lactation. In respect to SM, the flavour was improved in meat from COMP cows indicated by a positive correlation to flavour of beef meat and beef fat as well as fresh, sour and overall flavour. Further, compensatory finishing resulted in a lower degree of liver flavour in the SM samples. However, none of the flavour sensory terms differed significantly between the feeding strategies. In the study by Hansen et al. (2006), the variance of the flavour was not described in the experiment indicating that the flavour was not differentiated by the feeding strategies. The flavour impact from compensatory finishing strategy was greater in the LD samples resulting in significantly increased fresh meat flavour. The CONT feeding resulted in off-flavour and liver flavour, but this observation was non-significant. The perceived flavour of liver is in accordance with the perceived odour of liver, which tended (P = 0.085) to be related to the CONT cows. In an earlier study, liver flavour has also been associated with off-flavour (Hansen et al., 2006). Improved flavour in response to finishing feeding of culled cows has been found in other studies (Boleman, Miller, Buyck, Cross, & Savell, 1996; Vestergaard et al., 2007). 4.2.3. Sensory changes in the beef in relation to ageing The greatest differentiation due to ageing of the SM samples was observed in beef meat flavour, and 7 days of ageing was significantly,

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positively correlated to it. In contrast, Hansen et al. (2006) found no effect of ageing in SM, but improved flavour of LD with increased ageing. Gorraiz, Beriain, Chasco, and Insausti (2002) found increased flavour characteristics of LD and also increased levels of volatile compounds related to flavour with increased ageing from 2 to 7 days. However, Monsón, Sañudo, and Sierra (2005) saw very few changes in the beef flavour of LD aged either 1, 3, 7, 14, 21 or 35 days, but found a major increase in bitter flavour after 21 days of ageing. Thus some effect of ageing on flavour attributes has been demonstrated, and this may vary between muscles, which could be related to the content of IMF. In respect to the SM muscles, the appearance was affected by ageing of the beef meat, with extended ageing (14 days) resulting in a significant, positive correlation to brown/grey appearance. The texture was improved with extended ageing. However, this finding was not significant in the APLSR model, whereas significant shear force and MFI results indicated improved tenderness of LD with increased ageing, but no change in the shear force of SM aged either 7 or 14 days. A positive effect of prolonged ageing from 7 to 14 days was previously seen in Therkildsen et al. (2008) on the tenderness of LD and SM, whereas in Hansen et al. (2006), only SM responded to prolonged ageing. This variation between studies and muscles most probably relates to the tenderness per se of the meat, i.e. the meat can already be so tender that the methods used cannot measure further improvement with extended ageing. This was demonstrated in Franco et al. (2009), where minimum shear force of LD was achieved after 7 and 14 days of ageing depending on the length of the finishing feeding, which affected the initial shear force, i.e. 8.00 kg/cm2 for two months of finishing feeding and 10.61 kg/cm2 for one month of finishing feeding. The results generated in the present study suggest that muscles respond differently to ageing, and that some muscles do not benefit from extended ageing when factors such as tenderness, flavour and appearance are taken into account. 5. Conclusions The meat quality of culled dairy cows can be improved by introduction of a compensatory finishing strategy with three weeks of restriction including the period of drying off followed by six weeks of ad libitum feeding. This strategy will improve financially important traits such as slaughter weight, dressing percentage, EUROP conformation and amount of intramuscular fat as well as the sensory optimised texture and flavour of the meat. The improved tenderness can be ascribed to various factors depending on the muscle, thus in LD, the increased amount of IMF plays a significant role, whereas in SM, an increased protein turnover as a result of compensatory growth is suggested to be the dominating factor leading to improved tenderness. Acknowledgements The authors wish to thank Jens Askov Jensen, Lars Gildberg, Mogens Vestergaard, Marianne Rasmussen, Anne-Grete Dyrvig Petersen and Aase Karin Sørensen, Faculty of Agricultural Sciences, Aarhus University for their assistance during sampling, sample analysis and critical review of the manuscript, and Stine Hansen and Judith Henning, Faculty of Life Science, University of Copenhagen and Danish Meat Research Institute, Roskilde for assistance during the sensory profiling. The authors also wish to acknowledge the financial support from the Ministry of Food, Agriculture and Fisheries and the Danish Livestock and Meat Board through the FØTEK 4 programme. References Aberle, E. D., Reeves, E. S., Judge, M. D., Hunsley, R. E., & Perry, T. W. (1981). Palatability and muscle characteristics of cattle with controlled weight gain: Time on a high energy diet. Journal of Animal Science, 52, 757−763. Allen, J. D., Ahola, J. K., Chahine, M., Szasz, J. I., Hunt, C. W., Schneider, C. S., et al. (2009). Effect of preslaughter feeding and ractopamine hydrochloride supplementation on

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