ABSTRACT

HOW TO MEASURE THE WATER-HOLDING CAPACITY OF MEAT? RECOMMENDATION OF STANDARDIZED METHODS

K.O. Honikel Federal Centre for Meat Research, Kulmbach

Federal Republic of Germany

129

In principle, water-holding capacity (WHC) is defined as the ability of meat to hold all or part of its own water. There exist, however, no reference unit nor reference procedures for measuring WHC which have been adopted in general in meat science or technology. Therefore a wide varie­ty of methods are used, due to the fact that meat is handled and processed in a variety of ways. Also the meaning of WHC may vary. People who slaughter, chill, transport and sell fresh meat understand by WHC the weight or drip loss of carcasses or cuts. Consumers and processors of "ready to eat" meat understand by WHC its cooking loss. The present work illustrates that the WHC measured as drip loss does not allow conclusions about the cooking loss of fresh meat. Two standardized procedures for drip loss and cooking loss determination will be recommended after the factors that influence these WHC determinations are evaluated.

INTRODUCTION

Muscles of live animals contain 70 - 75 % water which is bound primarily to the muscle proteins within the muscle cell. The high pH of about 7.0 in the muscle cell and its physiological salt concentration allows the muscle proteins to bind about 90 % of the water intracellularly.

This ability of muscles we call water-holding capacity (WHC). After the death of the animal the pH of normal beef and pork muscle starts to fall to its ultimate value of about pH 5.5. This pH fall reduces the ability of the muscle proteins to hold the water tightly. The WHC of the muscles decreases (Hamm, 1972). Additionally the velocity of the pH fall in

combination with the temperature of the muscle during this time influences WHC. Slow pH fall and rapid temperature decrease induces cold shortening with an enhanced drip loss, whereas slow pH fall at very low chilling rates causes rigor shortening again with an increased drip loss (Honikel et al., 1986). Fast glycolyzing muscles at prevailing high temperatures result in

PSE muscles with a rapid release of exudate from the meat (Honikel and Kim, 1985; Honikel, 1986).

So besides pH itself, the temperature/time/pH conditions in muscles in the first hours post mortem influence WHC. Drip loss of meat is effec­ted by all these factors, the cooking loss, however, is effected primarily

P. V. Tarrant et al. (eds.), Evaluation and Control of Meat Quality in Pigs© ECSC, EEC, EAEC, Brussels-Luxembourg 1987

130

by the pH of the meat. Also,cooking loss is greatly effected by the

conditions of cooking (Bendall and Restall, 1983; Kopp and Bonnet, 1985).

As different factors influence drip and cooking loss it cannot be

expected that drip loss results allow reliable conclusions about cooking

loss and vice versa. Therefore separate methods must be used.

In this paper the factors that influence drip and cooking loss will

be described and taking these into account two standardized procedures

will be recommended.

FACTORS WHICH INFLUENCE DRIP AND COOKING LOSS

As mentioned above, the pH of the meat influences WHC. Furthermore

the WHC depends on the muscle type and the degree of marbling. Also the

species of animal influences the WHC of the meat due to variations in

the muscle composition and structure. In addition to these factors

the drip loss depends on

1) size and shape of the sample. The surface to weight ratio is important for the amount of drip released. A larger surface area per weight unit

increases the drip loss per unit time.

2) treatment during conditioning period. As mentioned above, rapid chilling

of prerigor muscles may lead to cold shortening and very slow chilling

may lead to rigor shortening as is shown in Fig. 1.

The shortening of sarcomeres was at a minimum when muscles were

chilled to 10 - 15°C within the prerigor period i.e. at pH values above

6.0. The drip loss released from these muscles within 7 days of storage

(Fig. 2) coincided, with respect to the minimum of drip loss and shape

of curves, with the sarcomere shortening in Fig. 1. There was indeed a

linear relationship between final sarcomere length and drip loss of pork

and beef muscles as shown in Fig. 3. As also mentioned above, PSE conditions are induced by a rapid

pH fall at prevailing high temperatures. Results are presented in Fig. 4

for drip loss in slices of M. long. dorsi taken from a pig carcass

with a pHI value of 6.0 and subjected to different chilling conditions. One pair of slices was stored and slowly chilled simulating PSE condi­

tions, the other pair was chilled rather rapidly thus avoiding PSE

conditions and simulating normal meat quality.

131

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20 / \ / \ / '" ro

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0 4 8 12 16 20 24 28 32 36°C

temperature

Fig. 1 Influence of temperature on the shortening of sarcomeres in prerigor pork muscles

Pieces of slaughterfresh M. mastoideus were stored at 0° to 35°C between 45 min and 24 hours post mortem. After 24 hours the sarcomere length was measured according to Voyle (1971) and the degree of shortening calculated by comparison with the sarcomere length of the muscle before incubation. For each temperature a different muscle sample was taken.

The "PSE" conditions lead (Fig. 4 )to rapid release of juice within the

first 24 hours, whereas the "normal" muscle slices had little drip at the

first day increasing between day land 5. After 17 days of storage the

difference in drip loss has been diminished. Therefore drip loss of meat depends also on

3) the time of measurement post mortem and on

4) the length of time of measurement. The drip loss also depends on

5) the chilling temperature of the meat after the ultimate pH is reached. Storage at 4°C results in a higher drip loss than storage at O°C.

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7

6

5 III

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muscle temperature at 0-24 hours

BAFF Ho 1983

Fig. 2 Drip loss of pork muscles stored at the various temperatures indicated on the abcissa during the first day post mortem and subse­quently stored at O°C. Cubes (about 50 g weight) of M. mastoideus obtained within 45 min post mortem with pH values between 6.3 and 6.5 were stored during the first day post mortem at 0° to 35°C. After 24 hours all samples were kept in a chilling room at O°C. At 1, 3, 6 and 7 days post mortem (indicated on the right hand of the Figure) the drip loss was determined. The exact procedure is described in the text. For each temperature a sample from a different carcass was taken.

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final sarcomere length

Fig. 3 Relationship between drip loss and final sarcomere length in pork M. mastoideus and beef M. sternomandibularis. Drip loss was determined between day 1 and 7 post mortem as described in Fig. 2. Sarcomere length were determined according to Voyle (1971)

20

18

o 2 4 6 8 10 12 14 16 Days of storage

Fig. 4 Influence of temperature on the drip loss of slaughterfresh M. long. dorsi of pork with a pHI of 6.0 Slices of M. long. dorsi were obtained within 45 min post mortem with a pH of 6.0. Two slices were stored at 38°C between 45 min and 2 hours, at 35°C between 2 and 3 hours and at 33°C between 3 and 4 hours post mortem. They were then stored at ooe until day 17. These were designated as "PSE conditions". Two further adjacent slices of the same muscle were incubated at 20°C between 45 min and 4 hours post mortem. Then the temperature was reduced to ooe and the slices stored until day 17. These were designated as "normal conditions". Drip loss was measured at the days indicated and was carried out as described below in the recommended procedure. The figures between the curves are the difference in drip loss in percent.

133

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Finally the drip loss of meat samples depends on 6) the rrethod of packaging used in the experirrent.

Surface tight (heat shrunk) vacuum packaging releases less exudate from the meat during storage than vacuum packaging with vacuum holes at the corners of the meat sample.In both cases the amount of drip released differs from measurements in plastic pouches or boxes under atmospheric pressure.

The above mentioned influence of pH on drip loss is shown in Fig. 5.

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6.5 6.4 6.3 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5(pH) Ultimate pH

Fig. 5 Influence of ultimate pH value on the drip loss of M. mastoideus of pork. Samples were stored at 15°C to 25°C at then at O°C up to day 7, when the drip samples had pH1 values above 6.2. Drip described in FTg. 2.

the first day post mortem, loss was measured. All muscle loss was determined as

The relationship between ultimate pH of meat and drip loss was not linear. In these experiments neither shortening nor conditions associated

with the development of PSE existed. There was little pH influence above pH 6.0. Below this pH there was a sharp increase in drip loss.

The cooking loss of meat, however, had a linear relationship to pH not only in the prerigor (Honikel et al., 1981) but also in the postrigor

state as shown in Fig. 6.

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6.7 6.5 6.3 6.1 5.9 5.7 post ngor

Fig. 6 Influence of the ultimate pH on cooking loss in M. mastoideus of pork.

5.5 pH

Samples were taken from the carcass at the first day post mortem. Between day 2 and 7 the temperature of storage was O°C. Cooking loss was measured 7 days post mortem.

Cooking loss was determined as described in the recommended proce­dures in the text but due to the size of M. mastoideus the slices weighed about 50 g.

Besides on pH the cooking loss depends on

1) the final temperature of heating.

135

In Fig. 7 the meat samples were heated to the indicated internal tempera­

ture and chilled immediately afterwards. In Fig. 7 again the influence

of pH is shown. Furthermore Fig. 7 shows that in PSE and normal meat

between 65°C and about 85°C the release of fluid was faster in PSE muscles,

whereas at 55°C and 100°C the differences in cooking loss were virtually

non exi stant.

136

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Fig. 7 Cooking loss of M. long. dorsi heated to different final temperatures. Muscles of varying qualities and ultimate pH values were studied. Cooking loss was determined as described in the recommended procedure in the text with the exception that the slices at 20°C were put into a boiling water bath and taken off the bath immediately after the prescribed final temperature was reached.

PSE muscles had a pHI of 5.6, normal muscles (N) had a pH, of 6.3 and DFD had a pH, of 6.5. Samples were taken from the carcass after 24 hours and stored for a week at O°C.

In the meantime we have confirmed this in a number of experiments. So

cooking loss depends on

2) the meat condition at certain final temperatures of heating;

the cooking loss also depends on

3) the velocity of heating (Fig. 8).

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40

39

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34 0 4 8 12 16 20 24 28 32 36

11 VE'locity of hE'oting (sE'c/OC)

Fig. 8 Cooking loss of M. mastoideus of pork with an ultimate pH of 5.8 after 3 days post mortem,heated with different velocities.

Samples of 50 g weight as described in Fig. 6 were heated from 20°

137

to 90°C. Between 20 and 55°C the heating rate was 5 sec/DC (or 12°C/min) in all cases. From 55° to 90°C the velocities indicated were chosen with a constant (linear) temperature increase. At the moment 90°C was reached in the centre, the samples were put in tap water.

The faster the velocity of heating the lower is the cooking loss (Kopp

and Bonnet, 1985).

4) The length of heating after reaching the final temperature influences

WHC. Longer heating time increases the loss of fluid (Bouton and

Harris, 1972). Connective tissue is gelatinized and released from the

meat.

5) Size, shape, marbling and composition of the meat also influence cooking loss. The surface/weight ratio is important. Meat with a considerable

fat content releases fat as well as watery fluid which often increases

total loss. Marbling of meat covering some muscle tissue may reduce

cooking loss. Contrary to drip loss which increases with time of storage (see Fig. 2

and 4) cooking loss does not change with the time of storage.

138

Fig. 9 shows that between day 1 and 8 post mortem there was no change in cooking loss. Fig. 9 also shows that neither cold (5°C during the

first day) nor rigor shortening (35°C) had any influence on cooking loss.

50

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~ A • 0

Ul 0 Ul 0 30 • rl

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Days post ITOrtem

Fig. 9 Cooking loss of M. mastoideus of pork at different times post mortem.

The samples were taken from the carcass within 45 min post mortem and stored unti 1 24 hours at 5°C (e), 20°C (D) and 35°C (/).). Between day 1 and 8 they were stored at O°C. The pH of all samples was 5.6 at the time of measurement. Cooking loss was determined as described in Fig. 6.

Due to the different factors that influence drip loss and cooking loss

a good relationship between both methods of detecting WHC cannot be

expected, when the pH of the samples is uniform. This is shown in Fig. 10.

Whereas the drip loss in these 36 samples of M. long. dorsi of pork with

a final pH of 5.5 - 5.6 varied from 1 to 17 percent i.e. a 17 fold

increase, the cooking loss of these samples with few exceptions was

between 35 and 45 percent i.e. a 1.3 fold increase.

Having considered the different factors that influence drip loss and

cooking loss, and the poor relationship that exists between these

properties of meat, we recommend that the following procedures are

adapted as standard practice.

139

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Fig_ 10 Relationship between drip and cooking loss in M. long. dorsi of pork.

The ultimate pH of all samples was 5.5 - 5.6. The recommended procedures described in the text were applied. Drip loss was measured between day 1 and 3. Cooking loss was determined immediately afterwards.

RECOMMENDED PROCEDURES Within the framework of the CEC Beef Production Programme, the

working group on Meat Quality published (Boccard et a1., 1981) procedures

140

for measuring meat colour, tenderness by instrumental methods, sensory assessment, and chemical analysis. The present recommended procedures

for measuring the drip loss and cooking loss of intact muscular tissue

are an extension of that work. Both methods of measuring water-holding

capacity are of paramount interest to meat scientists and technologists.

Where it is necessary to carry out both measurements on the same

piece of muscle, cooking loss measurement will succeed drip loss deter­mination.

The methods are described for transverse slices of M. long. dorsi as

this is the most widely used muscle. Other muscles may be assessed in a

similar manner but care should be taken in these cases to note the muscle fibre direction and to report it in the description of the method.

MEASUREMENT OF DRIP LOSS Before carrying out the experiment the following data should be

measured or known: pH of the sample, the time post mortem, and type and age of the animal. Knowledge of conditioning temperatures and/or sarcomere

length could be helpful.

A slice, 2.5 cm thick, of M. long. dorsi sampled between the 8th

thoracic and first lumbar vertebra with a freshly cut surface should

be taken for measurement. Associated adipose tissue or parts of M. spinalis

and M. multifidus dorsi should be removed. The facies should stay around

the muscle. The temperature of the room during cutting should be similar

to the temperature of the meat. The muscle should be weighed as accurately

as appropriate in a plastic pouch (the weight is usually between 70 and

100 g) in which the slice may suspended by means of a net or a thread.

The plastic pouch is sealed under atmospheric pressure. The samples

are stored at 0° to 4°C for at least 48 hours. The time of storage must

be stated in the method's description. The pouches should hang in such

a way that the exudate dripping from the meat does not stay in contact

with the meat. At the end of the experiment the muscle is taken from

the pouch, dried gently with an absorbing tissue and reweighed. During

the weighing care must be taken that no condensation of water vapour

at the cold surface occurs. The drip loss is expressed as the weight

loss in mg/g original weight of meat or percent of original weight.

Finally the pH of the muscle chould be measured again.

After drip loss evaluation the sample can be used immediately for cooking loss measurements. If there is a delay before measuring cooking

loss the sample must be wrapped to avoid drying of the surface.

DETERMINATION OF COOKING LOSS

The sample remaining after drip loss measurement, of known weight

141

and pH, is placed in a thin walled polyethylene bag (the bag must be water­

proof and withstand 75°C) and sealed under moderate vacuum. The vacuum

must be applied in order to remove air layers or air pockets between meat

and wall of the bag. Furthermore during subsequent heating the meat must

be completely immersed in water. With air pockets in the pouch part of the

meat may be above the water level and that is not acceptable. If the bag is not sealed, care must be taken that the wall of the bag

touches the meat surface in order to allow optimum heat flow. The mouth

of the bag must remain above the water level. Glass beads or similar

devices should be put at the bottom of the bag in order to keep all meat

surfaces immersed in the bath.

The properly sealed bag is placed in a water bath at preferably 75°C

(other temperatures may be used, if necessary) where it will stay for

30 minutes. The pack is then placed for 40 min in running tap water

(about 15°C) after which time the meat is taken from the bag, mopped dry

and weighed. The heating loss will be expressed as g cooking loss/g initial

weight (before cooking) or as percent heating loss.

In some experiments the measurement of drip loss may be unnecessary.

In this case the sample may be used directly for cooking loss measurement

after preparing it as described above for drip loss.

There are experiments in which the "history" of the meat is not known

to the researcher. In this case it may be advantageous to measure the

moisture content of meat and relate the loss to total moisture content

or if appropriate to dry matter. Method of moisture determination is

described by Boccard et al. (1981). Also the expression of g cooking loss/g

protein is possible.

After measurement of cooking loss the sample can be used for

tenderness measurements and sensory assessment according to the method

described by Boccard et al. (1981).

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CCNCLUDING REMARKS

Adoption of these nethods will nean that in the future the wide

variety of ways for neasuring WHC can 1:e reduced to a necessary minimum.

Drip loss and cooking loss neasurerrents are of pararrount interest to

research in neat science and technology. Considering the distinct

factors that influence the different nethods, we recOInTend the use of

these two nethods as they are nost closely related to the cOInTercial

and consurrer uses of neat.

REFERENCES

Bendall, J.R. and Restall, D.J., 1983. The cooking of single Jl'!YOfi1:ers, small Jl'!YOfibre l::undles, and muscle strips of teef M. psoas and M. sternomandihllaris fruscles at varying heating rates and tenperatures. Meat Sci. 8, 93-117.

Boccard, R., Buchter, L., Casteels, E., Cosentino, E., Dransfield, E., Hood, D.E., Joseph, R.L., MacDougall, D.B., Rhodes, D.N., Schon, 1., Tin1:ergen, B. J. and Touraille, C., 1981. Procedures for neasur ing neat quality characteristics in teef production experiments. Livestock Production Sci. 8, 385-397.

Bouton, P.E. and Harris, P.v., 1972. A corrparison of some objective nethods used to assess neat tenderness. J. Food Sci. 37, 218-221.

Hanm, R., 1972. Kolloidchernie des Fleisches. P. Parey Verlag, Berlin und Harnhlrg.

Honikel, K.O., Hamid, A., Fischer, C. and Hamn, R., 1981. Influence of post nortem changes in l:xJvine muscle on the water-holding capacity of teef. Post nogtern storage of muscle at various tenperatures 1:et~n 00 and 30 C. J. Food Sci. 46, 23-25 and p 31.

Honikel, K.O., 1986. Chilling of pig muscles early post nortern and neat quality. In: Evaluation and Control of Meat Quality in Pigs, EC Seminar, Dublin, NOV, 1985.

Honikel, K.O. and Kim, C.J., 1985. Uber die Ursachen der Entstehung von PSE-Schweinefleisch. Fleischwirtschaft 65, 1125-1131.

Honikel, K.O., Kim, C.J., Roncales, P. and Harrm, R., 1986. Sarcorrere shortening of prerigor muscles and its influence on drip loss. Meat Sci. in press.

Kopp, J. and Bonnet, M., 1985. Effects of cooking nethods on neat quality. In: The long-term definition of neat quality: Controlling the variability of quality in teef, veal, pigrreat and lamb, (ed. G. Harrington). Corrmission of the European Corrm.mities, Luxembourg, p. 105.

Voyle, C.A., 1971. Sarcorrere length and neat quality. Proc. 17th European Meeting of Meat Research Workers, Bristol, p 95-97.