Very fast chilling of beef: effects on meat quality

Meat Science 59 (2001) 31–37 www.elsevier.com/locate/meatsci

Very fast chilling of beef: effects on meat quality W. Van Moeseke 1, S. De Smet *, E. Claeys, D. Demeyer Ghent University, Faculty of Agricultural and Applied Biological Sciences, Department of Animal Production, Proefhoevestraat 10, 9090 Melle, Belgium Received 4 August 2000; accepted 4 February 2001

Abstract The effect of very fast chilling (VFC) of beef on several meat quality parameters was studied in semitendinous samples of three young bulls of the Belgian Blue breed. Left carcass sides were chilled conventionally. The semitendinosus of the right carcass sides were hot boned at approximately 50 min post mortem and cut longitudinally in two equal pieces. Packed in plastic bags, one piece was chilled very fast using a brine solution (3.4% NaCl, 2 C), whereas the other was chilled in a freezer ( 20/ 25 C, 3 m/s). The very fast chilling treatments lasted until 5 h post mortem. Samples were further chilled in a refrigerator (2 C) until 24 h post mortem. Sub-samples for meat quality measurements were taken and frozen at 18 C after an ageing period of 1, 4 and 11 days at 2 C. In three of the six cases, a core temperature of 0 C was achieved within 5 h post mortem [VFC condition; In the other cases, the VFC condition was nearly met. The brine chilling treatment in this study resulted in a higher cooling rate compared with the freezer treatment, and concomitantly in more pronounced effects. VFC resulted in increased concentrations of water extractable calcium and higher pH values at 5 h post mortem. These factors could be expected to activate the calpains and to accelerate proteolysis. This could not be confirmed by our results. Cold shortening occurred and sarcomere lengths were reduced by more than 30% in the VFC treatment compared with conventional chilling. This was reflected in much higher shear force values for the VFC samples. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Very fast chilling; Beef; Meat quality

1. Introduction From a sanitary point of view, meat has to be chilled as soon as possible after slaughter (Honikel, 1998b). The rate of chilling is very critical; too slow or too fast chilling of beef can result in an inferior meat quality (Joseph, 1994). It has been suggested that very fast chilling (VFC) of beef allows producing meat of high eating quality (Bowling, Dutson, Smith, & Savell, 1987). Low temperatures, obtained by very fast chilling, bring about a considerable release of calcium from the sarcoplasmic reticulum to the myofibrils, and this very early post mortem (Jaime, Beltran, Cena, Lopez-Lorenzo, &

* Corresponding author. Tel.: +32-9-264-90-03;Fax: +32-9-26490-99. 1 Present address: Ministry of Traders, Small Enterprises and Agriculture, Directorate of Animal Health and Animal Product Quality, S. Bolivarlaan 30, 1000 Brussel, Belgium. E-mail address: [email protected] (S. DeSmet).

Roncales, 1992). It was hypothesised that this early supply of free calcium, together with a high muscle pH, could result in an advanced and increased activation of calpains and therefore in an intense tenderisation, capable of overcoming toughness caused by cold shortening. An acceptable tenderness level for VFC beef was found after 7 days instead of 14 days of conventional chilling (Honikel, 1998b). Jaime, Beltran, Cena, LopezLorenzo, and Roncales (1989) also found that an early post mortem conditioning of longissimus dorsi from lambs of different age at low ( < 10 C) and high temperatures (>20 C) caused muscles to shorten, which resulted in meat toughening except for a very low temperature treatment at 0 C. Yet, for many years it has been shown that rapid chilling of pre-rigor bovine muscles leads to contraction of the myofibrillar structure (cold shortening), that affects the mechanical strength of the product and therefore its tenderness (Marsh & Leet, 1966). Demeyer, Steen, and Claeys (1998) concluded from preliminary experiments that VFC resulted in higher shear force values due to cold shortening compared with conventional chilling.

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Any VFC procedure with beef carcasses requires the meat to be removed from the carcass as soon as possible after slaughter and reduced to a size enabling a rapid temperature fall (Taylor, Richardson, & Fisher, 1998). However, there is no clear definition of very fast chilling. It was defined as the achievement of a temperature of 0 C within 4 h post mortem (Dransfield, 1998), 1 C within 5 h post mortem (Joseph, 1996) and 0 C within 5 h post mortem (Honikel, 1998a,b). The latter and most recent definition of VFC was used in our experiments, aiming at investigating different chilling regimes to reach the VFC condition and to examine the effects on the quality properties of beef. Special attention was given to tenderness and sarcomere lengths.

semitendinosus muscle in a plastic bag in an ordinary ice bath or in a brine solution was not successful in obtaining the VFC condition. Neither was chilling of a longitudinally split semitendinosus muscle in an ice bath. Therefore, the ice bath was provided with a continual cooler and a stirrer, and the semitendinosus muscles were cut longitudinally in two pieces. Pieces were packed in plastic bags for the VFC treatments. One piece was chilled in a 3.4% salt solution in the above mentioned bath. A temperature of 2 C (approximately the boundary for meat freezing) was kept up during the VFC treatment period. The second piece was chilled in a freezer ( 20/ 25 C), so that surface freezing would prevent cold shortening. 2.3. Meat quality measurements

2. Materials and methods 2.1. Animals and slaughtering Three young bulls of the Belgian Blue breed were used, of which two were of the double-muscled conformation. Mean age at slaughter and carcass weight were 17 months and 649 kg, respectively. Bulls were slaughtered in the abattoir of our department after captive bolt stunning and pithing. The semitendinosus muscle of the right carcass side was hot boned at approximately 50 (S.D. 11) min post mortem and immediately subjected to one of the very fast chilling regimes until 5 h post mortem. Due to some variation in the time of hot boning, the duration of the VFC treatment was not fully standardised. The VFC muscles were subsequently stored at 2 C for 19 h. The left carcass side was chilled conventionally (CC) at 2 C until 24 h post mortem and served as the control treatment. 2.2. Chilling regimes Chilling regimes were drawn up according to simulations with the BeefChil Model program (Schofield & Gibbs, 1998). This program models heat transfer in one dimension through a beef carcass, using information and knowledge about the thermal properties and the process conditions. The model assumes a surface heat transfer coefficient of 5 W/m2 K for slow air chilling (air speed < 1.5 m/s) and a coefficient of 50 W/m2 K for fast air chilling (air speed >3 m/s). Immersion of muscles in a brine solution to lower the freezing point is equalled with spray chilling of carcasses with cold water (surface heat transfer coefficient of 850 W/m2 K). Meat has a conductivity coefficient of 0.49 W/m  C (Phillips, 1997). This means that the heat transfer of meat is the limiting factor for chilling rate, and that the diameter of the muscles has to be restricted to achieve the VFC condition. In preparatory experiments, chilling of a complete

From the installation of the VFC regime until 24 h post mortem, the temperature at the surface of the muscle, at a depth of 2 cm and in the core of the muscle was continuously registered with an Escort Junior temperature logger (Tech Innovators, New Lynn, New Zealand). At 1, 5 and 24 h post mortem, pH was determined in fivefold using a Knick Portamess 654 pH meter (Knick, Berlin, Germany) equipped with an Ingold Xerolyt electrode (Mettler-Toledo, Greifensee, Switzerland). At 24 h post mortem, five slices (approximate thickness 2.5 cm) were taken from the semitendinosus samples, vacuum packed and frozen at 18 C after storage at 2 C until 1, 4 and 11 days post mortem. From the abdominal to the dorsal extremity, the samples were used for shear force determination (1, 4 and 11 days of ageing), for taste panel evaluation and for other laboratory measurements (water extractable calcium, SDS-PAGE, calpain and calpastatin activity and sarcomere length). One sample was immediately wrapped in a thin polyethylene film to avoid dehydration and was used for the determination of the CIELAB colour co-ordinates in triplicate after a 30 min blooming time with a Hunterlab MiniScan device (D65 light source, 10 standard observer, 45 /0 geometry, 1 in. light surface, white standard; Hunter, Reston, USA). Shear force measurements were carried out on samples aged for 1, 4 or 11 days. After overnight thawing, samples were heated at 75 C for 60 min and cooled in running tap water. Shear force was measured on cylindrical cores (diameter 1.27 cm, n=20) taken parallel to and sheared perpendicular to the fibre direction using a Lloyd Texture Analyser TA500 (50 N load cell, speed 200 mm/min; Lloyd Instruments, Hampshire, England) equipped with a triangular Warner Bratzler shear. Sarcomere length was measured on sub-samples of about 2 g taken at three different places in one of the slices used for shear force determination. For the mea-

W. Van Moeseke et al. / Meat Science 59 (2001) 31–37

surements at 1 and 5 h post mortem, a sub-sample was taken at one end to limit damage to our cooling regime. The sub-samples were fixed in 2.5% glutaraldehyde. Laser diffraction was used as described by Vandendriessche, Buts, Claeys, Dendooven, and Demeyer (1984). Taste panel tenderness was evaluated on an 8-point rating scale (1=extremely tender; 8=extremely tough) by staff members of the department. The panel members were trained in two sessions, using psoas and sternomandibularis muscle samples as reference. The meat samples were standardised (221cm) and grilled for 2 min on a two side contact grill (Philips HD4431 or SEB 1308.02). 2.4. Chemical analyses Water extractable calcium was determined as described by Nakamura (1973). Five grams of minced meat was homogenised with an ultra turrax in 2 mg% iodoacetic acid to inhibit glycolysis during extraction, and centrifuged for 10 min at 4000 t/min. A quantity of HclO4 was added to the supernatant to a final concentration of 0.6 M and centrifuged for 10 min at 4000 t/min. Calcium was determined on a mixture of 4 ml of the supernatant and 1 ml of LaCl3 (0.5 M) using a Varian Atomic Absorption Spectrophotometer AA175 at 422.7 nm. The concentration was expressed as mg Ca2+ per gram of meat. Calpains were extracted and assessed by a slight modification of the method described by Uytterhaegen, Claeys, and Demeyer (1992). A semi-quantitative determination of myofibrillar proteins by SDS-PAGE (8% slab gels) using BSA as internal standard was carried out according to Claeys, Uytterhaegen, Buts, and Demeyer (1995). 2.5. Statistical analyses Due to the low number of animals and the large variability between them, data are mentioned in the tables per animal and no statistics were applied. Only for the variables sarcomere length and shear force, paired t-tests were performed across sampling times comparing conventionally chilled and very fast chilled (brine or freezer) samples.

3. Results and discussion Several definitions have been applied in literature for the VFC temperature condition. We used the definition of Jaime, Beltran, Cena, and Roncales (1993), recently also used by Honikel (1998b): reach 0 C in the core of the muscle within 5 h post mortem. In our study, the VFC condition was achieved in three of the six cases

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with semitendinosus samples that were hot boned and cut longitudinally chilling in a freezer or in a continuously cooled salt solution (Fig. 1). In the other cases, the VFC condition was nearly achieved. It has to be stressed that exactly localising the centre of the muscle for registering the core temperature is difficult, which might partly explain the differences in temperature evolution between samples. Superficial freezing occurred in the freezer regime but not in the brine chilling regime. Nevertheless, the temperature decrease in the brine chilled samples was faster compared with the freezer samples. A sample diameter of approximately 8 cm was estimated to be the upper limit for obtaining the VFC condition in our chilling regimes. At 5 h post mortem, pH was significantly higher in four out of five VFC cases (Table 1). At one day post mortem, pH values were not different anymore between chilling regimes for two of the three animals. Trevisani, Claeys, and Demeyer (1998a) also found a lower pH fall for VFC samples early post mortem, with differences lost after 24 h. In most but not all cases water extractable calcium increased at a faster rate post mortem in VFC samples compared with control samples in the first 5 h post mortem (Table 1). Independently of the chilling regime, the amount of water extractable calcium increased until approximately 4 days, at which time the amounts levelled off between the chilling regimes ( 15 ppm). It should be mentioned that the method used determines the overall water extractable calcium and not exclusively the cytoplasmic ‘free’ calcium. So these values are only indicative, since membranes may be disrupted by the extraction procedure (Trevisani, Claeys, & Demeyer, 1998). Higher free calcium concentrations after very fast chilling were also reported by Jaime et al. (1992) for lamb longissimus dorsi, and by Beltran, Tomas, and Roncales (1998) and Steen, Claeys, and Demeyer (1998) in beef. On the other hand, Trevisani, Loschi, and Severini (1998) reported that water extractable calcium concentrations at 5 and 24 h were not influenced by VFC, in agreement with the findings of Claeys, Demeyer, and Van de Voorde (1998) and with some of the experiments reported by Demeyer et al. (1998). Results of the calpain and calpastatin activities were very variable and difficult to interpret (data not given). At 24 h post mortem, the m-calpain activity appeared to be lower for the VFC samples compared with the CC samples. This could mean that proteolysis was onset earlier in the VFC treatment. No clear differences between chilling regimes were found for m-calpain activity. The calpastatin activities at 4 and 11 days post mortem were slightly lower for almost all of the VFC samples. Trevisani, Claeys, and Demeyer (1998) found no significant differences for calpain 1 between VFC and CC at different times post mortem. Beltran and Roncales (1998) concluded that m-calpain activity in the

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Fig. 1. Temperature of the very fast and conventionally chilled semitendinosus samples from 1 to 5 h post mortem.

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W. Van Moeseke et al. / Meat Science 59 (2001) 31–37 Table 1 Water extractable calcium concentration and pH value according to chilling regime and time post mortem (pm) Animal

Chilling regimea

Calcium concentration (ppm)

pH

1 h pm

5 h pm

24 h pm

4 days pm

1 h pm

5 h pm

24 h pm

1

CC B F

10.0 8.9 11.0

10.9 17.0 8.2

12.3 19.5 15.9

16.0 15.4 15.8

6.84 6.69 6.69

5.52 6.04 6.11

5.46 5.45 5.48

2

CC B F

10.3 8.5 9.8

11.6 10.8 9.6

13.1 11.5 13.3

15.9 15.8 14.2

6.70 6.54 6.54

5.87 6.28

5.67 5.57 5.69

3

CC B F

5.6 5.8 5.4

7.4 10.3 7.5

13.6 12.7 12.8

13.2 15.0 13.5

6.93 6.94 6.87

6.08 6.11 6.27

5.56 5.68 5.71

a

CC, conventional chilling; B, brine chilling; F, freezer.

sternomandibularis muscle decreased faster in VFC samples, when a core temperature of 0 C was reached. The effect of changes in muscle proteolytic enzyme activities was checked by analysing the protein degradation pattern using SDS-PAGE. There were no apparent differences between chilling regimes for troponin-T and 30 kDa, indicator proteins for proteolysis in relation to tenderness (Buts, Claeys, & Demeyer, 1987). The concentration of creatine phosphokinase at 4 and 11 days post mortem was clearly lower for the VFC than for the CC samples. This indicates a less pronounced denaturation of this sarcoplasmic protein (Claeys et al., 1995) and fits with the higher pH values at 5 h post mortem (Uytterhaegen et al., 1994). In summary, our data do not show much evidence for an increased rate of proteolysis due to very fast chilling. Cold shortening is recognised as a major determinant of tenderness in both beef and lamb. The VFC samples in our study had clearly undergone severe cold shortening (Table 2). Changes in the length of the semitendinosus were even visible by eye: in animal 3, where changes were most prominent, the length of the samples was  32 cm before the brine chilling treatment and  17 cm afterwards. Trevisani, Claeys, and Demeyer (1998) prevented cold shortening through superficial freezing. In our study, only the muscle sample of animal 2 that had undergone the freezer regime was shortened to a more limited extent. Superficial freezing probably did not occur in the muscle samples of the other two animals because of a too early removal of the sample or a too low air speed in the freezer. This resulted, together with the brine chilled samples, in severe cold shortening. Troy and Vidal (1998) found no shortening in very fast chilled longissimus lumborum (5 h, 27 C) due to superficial freezing. Beltran et al. (1998) studied VFC (liquid nitrogen, 70 C) of beef longissimus thoracis on the bone, and also could prevent shortening due to this kind of muscle restraint. However, restraining muscles

does not always result in normal sarcomere lengths. Steen et al. (1998) found a sarcomere length reduction of 22% for muscle samples attached at only the extremities to a small wooden board by means of four nails. Taylor, Richardson, and Perry (1998) chilled unrestrained sternomandibularis samples very fast and obtained sarcomere lengths lower than 1.1 mm, whereas the sarcomere length of the CC muscle was  1.8 mm. These results are in agreement with ours. As a consequence of the severe muscle shortening and the absence of a clear effect on proteolysis, very fast chilling did increase meat toughness (Table 3). Shear force values as well as taste panel scores clearly indicated higher meat toughness. In agreement with the lower sarcomere length in the brine chilled samples, shear force values and taste panel scores of these samples were highest. Ageing was not able to counteract the initial increase in toughness due to muscle shortening. Only in the freezer sample of animal 2, that underwent Table 2 Sarcomere length according to chilling regime and time post mortem (pm)a Animal

Chilling regimeb

1 h pm

5 h pm

11 days pm

1

CC B F

1.92 1.67 1.78

2.03 1.70 1.15

2.07 1.26 1.33

2

CC B F

1.97 1.85 1.88

2.22 1.16 1.98

2.24 1.60 1.88

3

CC B F

2.01 1.99 1.95

2.07 1.30 1.20

1.94 1.18 1.67

a Across sampling times the differences in sarcomere length between CC and B and between CC and F were significant at P<0.01 (paired ttest). b CC, conventional chilling; B, brine chilling,; F, freezer.

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Table 3 Shear force values after 1, 4 and 11 days of ageing, taste panel score for tenderness (11 days ageing) and colour co-ordinates according to chilling regimea Animal

Chilling regimeb

1

CC B F CC B F CC B F

2

3

a b

Shear force (N)

Taste panel score

1 day

4 days

11 days

114.4 124.8 51.9 124.8 70.5 36.6 112.7 72.0

43.0 117.0 104.4 31.8 123.0 54.6 29.5 103.3 79.2

34.0 98.0 97.3 41.5 97.5 44.5 31.2 66.3 57.7

2.5 6.6 6.3 4.9 7.7 5.3 4.0 6.4 6.1

Colour co-ordinates L*

a*

b*

47.7 36.8 37.4 44.1 33.5 36.0 40.8 38.7 36.6

13.9 12.5 13.6 18.0 16.4 16.7 16.8 13.3 14.2

16.7 15.8 15.2 19.4 16.0 16.7 16.3 13.0 13.9

Across sampling times the differences in shear force between CC and B and between CC and F were significant at P<0.01 (paired t-test). CC, conventional chilling; B, brine chilling; F, freezer.

limited shortening because of prominent superficial freezing, shear force after 11 days of ageing was of the same magnitude as for the CC sample. Hence, only if cold shortening can be avoided very fast chilling can be expected to yield an equal tenderness level (Trevisani, Claeys, & Demeyer, 1998; Trevisani, Loschi, & Severini, 1998). Regarding the effect of very fast chilling on meat colour co-ordinates of M. semitendinosus samples, significant differences were found between four of the six VFC samples and their respective control samples (Table 3). The L*, a* and b* values were always lower for the VFC samples. These results confirm those of Trevisani, Claeys, and Demeyer (1998), but the differences they found were not as pronounced. VFC consequently results in somewhat darker meat, a finding probably related to the muscle shortening.

4. Conclusions Very fast chilled beef samples were undoubtedly much tougher than CC samples as a result of muscle shortening. Our results do not support the hypothesis of improved tenderness by VFC due to a more pronounced proteolysis. Rigorous restraining by superficial freezing may be the only outcome for obtaining meat of acceptable tenderness in case of hot boning and VFC.

Acknowledgements The first author received a specialisation grant of the Flemish Institute for Stimulation of the Scientific/Technological Research in the Industry. The assistance of the scientific and technical personnel of the department in

slaughtering, sampling and laboratory analyses is greatly acknowledged.

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