Effect of rigor temperature and frozen storage on functional properties of hot-boned manufacturing beef

PII:

Meat Science, Vol. 49, No. 2, 233-241, 1998 CC 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0309-1740/98 s19.oo+o.oo

so309-1740(97)00134-4

ELSEVIER

Rigor Temperature and Frozen Storage on Functional Properties of Hot-boned Manufacturing Beef M. M. Farouk* Mirinz Food Technology (Received

6 March

and Research

1997; revised version

& J. E. Swan

(Inc.), PO Box 617, Hamilton,

received

12 July 1997; accepted

New Zealand 8 November

1997)

ABSTRACT Within 45min post-mortem, 10mm thick strips of semitendinosus muscle from both unstimulated and high voltage stimulated heifer sides were held at 0, 5, IO.25 and 35” C for 24 hr, during which they entered rigor. Half the samples were frozen and stored at -20°C for one month. The pH, sarcomere length, drip, total (TPS), myojibrillar (MPS) and sarcoplasmic (SPS) protein solubilities, and Hunter L*, a* and b* values were determined at 24 hr and on thawed samples. Electrical stimulation did not significantly affect any of the parameters measured. The ultimate pH of samples entering rigor at 10 and 25°C was lower (p
INTRODUCTION Because

of the processing

and energy

efficiencies

of hot boning,

an increasing

amount

of

beef (especially that destined for manufacturing purposes) produced in export oriented countries such as New Zealand and Australia is processed this way. For example, about 40% of New Zealand’s beef (representing 252 800.0 tonnes of bone-in meat) is hot boned (NZMPB, 1997). The common practice in New Zealand plants is to bone out carcasses within 45 min of slaughter, before they go into rigor. At this time meat that would reach a *To whom correspondence should e-mail: [email protected]

be addressed.

Fax:

233

+(64)

7 854 8550;

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M. M. Farouk. J. E. Swan

normal pHu would still be in a pre-rigor state even if electrical stunning, electrical immobilization and/or electrical stimulation (low or high voltage) has been used. The meat is then packed into cartons and frozen to - 18°C within 2472 hr of slaughter. The frozen meat may be held for a long period between production and use in the importing countries. In plants using electrical stimulation, the boxed hot-boned meat could go into rigor at a higher temperature than if stimulation is not used. All these processing and storage practices could affect the functional properties of the boxed meat. Previous studies have shown that rigor temperature affects the functional properties of muscle proteins (Penny, 1977; Honikel et al., 1986; Fernandez et al., 1994; Olsson et al., 1994; Simmons et al., 1996). However, most of these studies were directed towards table rather than manufacturing meat. The present study was designed to investigate the combined effect of rigor temperature, electrical stimulation, and frozen storage on the functional properties of semitendinosus muscle, which is processed as manufacturing meat in New Zealand (NZMPB, 1991).

MATERIALS

AND

METHODS

Sample preparation Heifers were captive bolt stunned and processed, with no electrical immobilisation or stimulation, at a commercial abattoir. Carcasses were halved. One side was electrically stimulated (high voltage-alternating polarity pulses, 15 pulses see-‘, 1130volts peak, 12Os), the other side was not stimulated. The semitendinosus muscle from each side was removed approximately 45min after slaughter and immediately sliced across the fibres into 10 mm thick cuts (weight range for all trials, 73-140 g). The muscles were sliced this thin and in this orientation to give uniform slices and achieve a fast rate of temperature equilibration. Two slices from each muscle (four per animal) were weighed and then sealed separately in a 24Ox300mm vacuum bag (Tuf-Flex Barrier Packaging, Trigon Plastics Ltd., Hamilton, New Zealand) without vacuum and submerged in water baths at 0, 5, 10, 25 and 35°C. After 24 hr, the drip from each slice was determined. One slice from each treatment was used for pH, protein solubility, colour, cook loss and NMR Tl determinations (24 hr time) and samples for sarcomere length determination were immediately frozen at -20°C. The second slice from each treatment was sealed (non vacuum) in a 225 x 375 mm polythene bag and kept at -20°C for one month. The slices were thawed for 14 hr at 10°C and analysed as described for the 24 hr slices. pH measurement The temperature of samples from each treatment were brought to the same level by holding at room temperature. pH was measured by an Ingold spear electrode (John Morris Scientific Ltd., New Zealand) inserted directly into the samples at two different locations, then measuring the pH with a 230A Orion pH meter (Orion Research Inc., Boston, MA). The mean of the two readings was recorded. Measuring sarcomere length Sarcomere lengths were determined in samples that had been stored frozen at -20°C for 3 months and thawed at 4°C for 3 hr. Sarcomere lengths were determined by microscopic measurement of single fibres (Simmons et al., 1996). Images of the myofibrils were produced with phase contrast light microscopy (Wild Leitz, Germany), digitized and stored

Treatment of hot-boned beef

235

on VHS video tape and the sarcomere length calculated using an image analysis software package (Matrox Inspector V 1.71). Drip and thaw drip loss

After being held at the required temperature for 24 hr, slices were carefully removed from their bags, gently blotted with a paper towel and reweighed. For thawed slices drip in the package was carefully poured off and the meat gently blotted with a paper towel and reweighed. Weight loss from the fresh meat slices during 24 hr holding (drip loss) and from frozen meat slices following thawing (thaw drip loss) was expressed as percentage of weight before immersion in the water bath and freezing, respectively. Colour measurements

After thaw or thaw drip determinations were completed, a 10 mm thick x 40 mm wide x 80mm long slice (across the fibre) of meat from each treatment was placed on a white polystyrene tray, overwrapped with high clarity d-film [stated oxygen permeability > 2000 ml m-’ atm-’ 24 hr-’ at 25°C W. R. Grace (N.Z.) Ltd, New Zealand] and kept in the dark for 4 hr at 3°C. Three measurements were taken through the film at different locations, with a Hunter Lab Miniscan (model MS/S-4000S, Hunter Associates Laboratory, Inc., Reston, VA) with a D65 illuminant at lo”. The meter was standardized with a light trap, then with white and pink tiles wrapped with d-film. Hunter L*, a* and b* values for the pink tile were 77.7, 21.8 and 5.4, respectively. Hue angle was calculated as tan-’ (b*/a*) (Liu et al., 1996). Cook yield, cook loss and total moisture loss

Cook yield (weight after cooking/raw meat weight) of the samples used for drip and colour measurements was determined as described by Bernthal et af. (1989). Duplicate 5g samples of ground muscle were weighed into corex centrifuge tubes, placed in a water bath filled with Whiterex oil (Mobil Co., New Zealand) at 100°C. After 15 min, the juice was drained off and the meat gently blotted with a paper towel and reweighed. Percentage cook loss was calculated as lOO-% cook yield. Total moisture loss for each treatment was determined as: Total moisture loss = % drip + % thaw drip + % cook loss of frozen samples Protein solubility measurements

Procedures described in Helander (1957) were modified and used to determine protein solubility. To determine total soluble protein, 2 g of razor minced meat was weighed into a centrifuge tube, 20ml of ice-cold 1.1 M potassium iodide in 0.1 M phosphate buffer (pH 7.4) added and the meat and buffer homogenized on ice for 20s using an Ultra-Turrax (Lab Supply Pierce, Auckland, New Zealand) at highest speed. The contents were centrifuged (6000 x g, 15 min, 4°C) and the protein content in the supernatant determined by the Biuret method (Bergmeyer et al., 1974). To determine sarcoplasmic protein, a second sample of mince was subjected to the same extraction procedure, using 0.025 M phosphate buffer (pH 7.4). Myofibrillar protein was calculated as the difference between total soluble protein and sarcoplasmic protein. Tests were done in duplicate and the means expressed as percentage (g/100 g) of meat.

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NMR relaxation times (Tl) of meat water The proton Tl of meat samples was measured on a Bruker AC-200 NMR spectrometer at 200 MHz using an MAS probe. Samples were packed in 7 mm ZrOz rotors and spun at 500Hz. The spin-lattice relaxation (Tl) was measured using an inversion recovery sequence (RD-18&tau-90-FID). A recovery delay of 8 s was used with variable delay times of 0.01, 0.05, 0.1, 0.5, 1, 5, 10, 20 and 40s. Statistical analysis A split plot design was used, with stimulation as the main plot and rigor temperature the subplot. Data were analysed using the Genstat (1993) statistical software package. All comparisons were based on the significance of two- and three-factor interactions for stimulation (electrically stimulated or non-simulated), rigor temperature (0, 5, 10, 25 and 35°C) and storage condition (fresh, 24 hr post-mortem and -20°C for onemonth). The data were analysed for trends (linear and quadratic). The experiment was replicated four times on different days.

RESULTS

AND

DISCUSSION

Electrical stimulation Early post-mortem electrical stimulation of carcasses reduces the possibility of cold and thaw shortening (Chrystall and Devine, 1978). The high voltage electrical stimulation used in this trial did not significantly affect the factors measured (pH,, sarcomere length, protein solubility, drip losses, colour, cook yield and NMR Tl values), and there was no interaction between electrical stimulation and the other factors used (rigor temperature, storage condition). Therefore, all data were averaged over electrical stimulation. Previous studies have also found that electrical stimulation does not affect the various functional properties of meat (Whiting et al., 1981; Rashid et al., 1983). When stimulated and unstimulated meat entered rigor at the same temperature, the effect of a rapid development of rigor (as induced by electrical stimulation) on protein functionality (as measured by protein solubility, WHC, Hunter colour, NMR T 1) was reduced or completely eliminated. Thus, the effect of electrical stimulation on meat functionality only becomes apparent when muscles go into rigor at different temperatures post mortem. PH At 45 min post mortem, the pH values of stimulated and non-stimulated muscles were 5& 6.1 and 646.9 respectively, however all meat reached an ultimate pH value of 5.47 to 5.54, indicating, glycogen levels were normal and glycolysis was complete in all muscles. Muscles held at 10 and 25°C had significantly lower ultimate pH values than muscles held at 0, 5 and 35°C (Table I), which had similar ultimate pH values. The small difference in pH may be due to differences in the time glycolysis was completed at these temperatures [Bendall, 1972; Jeacocke, 1977). Sarcomere length Previous studies have shown that the degree of muscle fibre shortening is temperature dependent; and that shortening increases with decreasing pre-rigor storage temperature

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TABLE 1

Effect of Rigor Temperature on the Ultimate pH and Sarcomere Length of Beef Semitendinosus Averaged Across Stimulation and Storage Condition Rigor temperature 0

5 10 25 35 S.E.D.

(“C)

PH

5.54 5.53 5.47 5.47 5.52 0.01

Sarcomere length (pm)

169 1.84 1.71 1.75 1.82 0.41

S.E.D. Standard error of difference between means. (Locker and Hagyard, 1963; Honikel et al., 1986; Olsson et al., 1994). In the present study sarcomere lengths from samples held at various rigor temperatures were not significantly different (p> O-05) (Table l), although shortening tended to increase with decreasing temperature except at 5°C. Few studies have been published on the sarcomere length of m. semitendinosus, fewer studies still have examined sarcomere length for this muscle at temperatures similar to those used in our study. Herring et al. (1965) reported sarcomere length values ranging between 1.61.8 and 1.9-2.1 pm for pre-rigor excised m. semitendinosus held at 1 and 5°C respectively. These values support our data in which sarcomere lengths averaged 1.69 and 1.84pm for samples held at the same two temperatures. The type of muscle used in the present study (m. semitendinosus) and the length of time the samples were held before sarcomeres were measured, coupled with the way the samples were prepared (cut orientation, thickness, rapid temperature equilibration), may have contributed to the lack of significant temperature effect on sarcomere length. m. semitendinosus (ST) contains a greater proportion of white fibres compared to many other muscles (sternomandibularis, longhimus, semimembranosus, biceps femoris and psoas major) that have been used in studies involving sarcomere length measurements (Hertzman et al., 1993; Olsson et al., 1994). Red fibres are known to cold shorten much more than white fibres (Cornforth et al., 1980). Muscles with a high content of white fibres also reach constant shortening and isometric tension faster than muscles with a high red fibre content (Busch et al., 1972; Hertzman et al., 1993). It is also known that the rate of glycolysis is accelerated by muscle excision and storage below 10°C (Herring et al., 1965; Bendall, 1972; Jeacocke, 1977). These factors, coupled with the fact that the sarcomere length of the ST increases with aging (Jeremiah and Martin, 1978); and the observation that a wide range of sarcomere lengths can be obtained by manipulating the rate of glycolysis (Smulders et al., 1990), may explain the lack of significant difference in sarcomere length in this present study. In fact Smulders et al. (1990) suggest that in addition to cooling rate and degree of rigor onset, another factor may allow rapid cooling of muscles without shortening. Further studies are needed to confirm the effect of these factors, on muscle shortening in ST muscles. Moisture loss Rigor temperature and frozen storage affected @ < 0.01) the amount of exudate (drip and thaw drip) from the raw muscles (Fig. 1) Drip from thawed muscle was significantly (p < 0.01) greater than drip collected from similar muscle during the first 24 hr post mortem, before freezing. It is known that frozen storage increases drip (Farouk and Price,

238

M. M. Farouk, J. E. Swan

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temperature

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on the moisture loss of beef m. semitendinosus 24 hr post mortem (m). Total moisture loss, (V) is the % drip + % thaw drip + % cook loss of frozen samples.

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239

1994). The amount of drip collected at 24 hr post mortem and after frozen storage tended to increase (p
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Treatment of hot-boned beef

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24 hr post

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M. M. Farouk, J. E. Swan

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Incubation temperature (C) Fig. 4. Effect of rigor temperature on the meat water NMR Tl relaxation time of beef m. semitendinosus 24 hr post mortem (a) and after one month at -20°C (w). temperatures. This reduced capacity becoming evident after 1 month of frozen storage. On prolonged storage, enzyme activity may tend to decrease so metmyoglobin content will increase. Yellowness (Hunter b* values) increased (p < 0.001) with rigor temperature and decreased (p < 0.001) with frozen storage (Fig. 2). The effect of frozen storage on yellowness has also been reported for lamb (Farouk and Price, 1994). Hue angle was affected by rigor temperature and frozen storage (p
Treatment of hot-boned beef

243

(data not shown), and values were consistent on their own (Fig. 3) and when compared to those reported in the literature. Samples entering rigor at 35°C had a significantly (p < 0.001) lower total protein solubility than samples entering rigor at the lower temperatures (Fig. 3). Penny (1977) and Fernandez et al. (1994) have reported similar observations. Between 0 and 25°C rigor temperature had no significant (p > 0.05) effect on total soluble protein content. Samples that had entered rigor at 0 to 10°C and were then stored frozen had higher @ < 0.05) total protein solubility levels than the corresponding fresh samples (Fig. 3). Proteolysis during frozen storage may have increased the total protein solubility (Davey and Gilbert, 1968). Both myofibrillar and sarcoplasmic protein solubilities were affected by rigor temperature and frozen storage (JJ
244

M. M. Farouk. J. E. Swan

were shorter in frozen meat samples than in fresh (Fig. 5). The decrease in Tl relaxation time might be due to changes in protein as a result of denaturation or aggregation (Blanshard and Derbyshire, 1975; Hills er at., 1989; Beauvallet and Renou, 1992). This decrease in Tl also implies that water molecule mobility increased, because the amount of free water increased with an increase in rigor temperature. Protein denaturation with increased rigor temperature reduces the water binding ability of the muscle protein, thus increasing the amount of free water in the muscle (Blanshard and Derbyshire, 1975; Ouali et al., 1988). Borowiak et al. (1986) reported that PSE muscles, which have highly denatured proteins, have shorter Tl relaxation times than normal muscles. Other observations Samples entering rigor at 35°C had a strong dairy odour. An exploratory trial was done to further investigate the cause of the odour. A sample of head space from one trial was analysed using a GCMS (Fisons MD800; BPX 5, 30 m x O-25 mm x 1 pm thick column), and the microbial loading on selective media of drip from the sample determined. As only exploratory trials were done, procedures and data for the GCMS and microbiological analysis are not included in this paper. Compounds identified included dimethyl sulphide, dimethyl disulphide, butanol, hexane, ethanethioic acid, 5 methylester, 3 methyl heptane, cyclopropane pentyl, octane and branched chain hydrocarbons. Low levels of lactic acid producing microorganisms were present in the drip.

CONCLUSIONS

AND

IMPLICATIONS

Electrical stimulation accelerated glycolysis but did not affect the protein characteristics studied, when stimulated and non-stimulated samples entered rigor at the same temperature. This suggests that the temperature at which a muscle goes into rigor has a stronger effect on functional properties than the rate at which rigor is achieved. Myofibrillar proteins, particularly myosin, are often thought to be responsible for changes in the functional properties of meat. However, our data (Fig. 3) indicate that at temperatures below 35”C, sarcoplasmic rather than myofibrillar proteins were more susceptible to denaturation, as determined by solubility measurements. At these temperatures, sarcoplasmic protein solubility decreased with rigor temperature and frozen storage, whereas myofibrillar protein solubility increased. There was a significant (p < 0.05) negative correlation between soluble sarcoplasmic proteins and percent drip loss (r = -0.9) and Hue angle (r = -0.84); but no significant correlation between myofibrillar protein solubility and any of the parameters measured. This suggests that within the range of rigor temperatures used in the present study, sarcoplasmic protein denaturation and/or the effect of their precipitation on myofibrillar proteins may be good indicators of the functional properties of muscles with increasing rigor temperature, between 0 and 25°C. The effect of myofibrillar proteins denaturation is apparent only when the rigor temperature was as high as 35°C (Fig. 3). The effect of rigor temperature on sarcoplasmic protein solubility was supported by the data on Tl relaxation times (Fig. 4). There was a significant positive correlation (r = 0.91, p < O-05) between Tl relaxation times and soluble sarcoplasmic proteins, but there was no significant correlation between Tl and other protein solubilities measured. It is assumed that either the Tl times were a direct reflection of the denaturation and/or aggregation of sarcoplasmic proteins or that the data may be reflecting subtle changes in myofibrillar proteins (which solubility measurements would not detect) as well as the apparent changes The high negative correlation @ < 0.05) in properties of the sarcoplasmic proteins.

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245

between Tl and drip losses (I = -0.91) and Tl and hue angle (r = -0.7) suggest that Tl values may be a good indicator of the state of muscle proteins, water and colour. It also indicates that solid state NMR could be used to predict PSE meat and to follow changes in meat during freezing and frozen storage. Data from this study indicate the following. Within current practices in New Zealand hot boning plants, damage to the functional properties of manufacturing meat that will undergo short term frozen storage can be minimized if the muscles are prevented from going into rigor at high temperatures. The temperature/pH combination at time of rigor could be more important in determining the functional properties of the muscle protein than the rate at which rigor was achieved. For fresh meat and meat stored frozen for a short time, the sarcoplasmic proteins appear to be good indicators of the functional properties of muscles that go into rigor at temperatures between 0 to 25°C. The decrease in functional properties with long-term frozen storage may start with the denaturation and/or aggregation of sarcoplasmic proteins before it extends to myofibrillar proteins. The NMR spin-lattice relaxation (Tl) of muscle water may be a good way to measure functional properties of meat in addition to using measurements of protein solubilities. Hue angle may be a better indicator of the colour in fresh meat or meat after short-term frozen storage than Hunter a* and b* values. Further work is needed to see if the effects reported in this paper are observed for other muscle types, and whether the sample surface-to-volume ratio and cut orientation or muscle fibre axis orientation influences the observations. Whether samples held at 35°C often develop a dairy odour and if so, what is the cause of this odour.

ACKNOWLEDGEMENTS The research was supported by the New Zealand Foundation for Research, Science and Technology. The statistical analyses were carried out by Dr John Waller of New Zealand Pastoral Agriculture Research Institute Ltd.; Dr Roger Meder of the New Zealand Forest Research Institute Ltd. assisted with the NMR measurements. Technical support was provided by Shashi Prasad and Michael Agnew of MIRINZ Analytical Section, Guillaume Le Roux of MIRINZ Microbiology Section and Klaus Putzfeld, visiting student from Fachhochschule Lipppe, Germany.

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