Tenderising in M. longissimus dorsi of beef, veal, rabbit, lamb and pork

Meat Science 5 (1980-81) 139-147

TENDERISING IN M. LONGISS1MUS DORSI OF BEEF, VEAL, RABBIT, LAMB AND PORK

E. DRANSFIELD,R. C. D. JONES & H. J. H. MACF1E Agricultural Research Council, Meat Research Institute, Langford, Bristol, BS18 7DY, Great Britain (Received: 13 November, 1979)

SUMMARY

The decrease in toughness of M. longissimus dorsi with storage time at 1 °C was effectively described by an exponential decay equation. The average rate constant for beef, veal and rabbit was 0.17 whilst that for lamb was 0.21 and that for pork, 0.40 days- 1. However, the rate constants were not significantly different due to variations both within muscles and between animals. On average, 50% of the tenderising occurred in 2 days for pork and in 4.2 days for beef, veal and rabbit, and 80 % in 4"9 and9"5 days, respectively. At the completion of tenderising, beef and rabbit were the toughest andpork the most tender, whilst the greatest tenderising occurred in beef and lamb.

INTRODUCTION

Chilled storage of meat has long been recognised to increase tenderness which Bate-Smith (1948) suggested resulted from the proteolytic action of cathepsins. During conditioning of beef, changes have been observed in sarcoplasmic proteins (Sharp, 1963), actomyosin (Penny, 1968; Goll, 1970) and connective tissue (Kruggel & Field, 1971), but research workers have concentrated on myofibrillar fragmentation in the region of the Z-disc (Stromer & Goll, 1967; Davey & Dickson, 1970) because such fragmentation is also related to loss of toughness (MacBride & Parrish, 1977; Jeremiah & Martin, 1978; Penny & Dransfield, 1979). Similar qualitative changes also occur in rabbit (Suzuki et al., 1975) pork (Penny, 1976) and chicken (Samejima & Wolfe, 1976). Proteolysis is less in pig and sheep than in rabbit or lamb (Zender et al., 1958; Radouco-Thomas et al., 1959) but greater in rabbit than in beef (Sharp, 1963). Histological evidence has shown that the Z-disc is more labile in pig and rabbit than in beef(Henderson et al., 1970). However, tenderising in these species has not been investigated adequately because toughness is affected by 139 Meat Science 0309-1740/81/0005-0139/$02.50 © Applied Science Publishers Ltd, England, 1981 Printed in Great Britain

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E. DRANSFIELD, R. C. D. JONES, H. J. H. MAcFIE

many factors and some of them may be dominant in meat cooked before complete rigor development (Dransfield & Rhodes, 1975), a time when some myofibrillar weakening occurs (Jeremiah & Martin, 1978). In this paper, tenderising in different species is compared using a c o m m o n exponential decay equation. EXPERIMENTAL

All animals were stunned, bled and dressed conventionally. Carcasses were chilled slowly to avoid cold-shortening and the toughness of the M. Iongissimus dorsi (LD) was measured after the pH had fallen to 5.8 or, if higher, to the ultimate pH. LD was chosen because it is a large, economically important muscle used frequently in research.

/~eef Carcasses (hot carcass weights from 217 to 280kg) from six 20-month-old Hereford Friesian cross heifers were split and the sides hung at 16 °. Core samples of LD were taken from the l l t h to 13th rib region and the pH was measured intermittently until it had fallen to 6-0; this took about 8 h, when the temperature in the deep L D had fallen to 26 °C. One side from each carcass was then chilled at 0 °C with an air speed of 1 m/s until 20 h after stunning, when a 9 cm section of LD, posterior to the 11 th rib, was removed. The section of LD was cut into three slices and each slice was bisected. The six pieces, each weighing between 70 and 110 g, were packed under vacuum and stored at 0-1 °C. Ultimate pH's ranged from 5-5 to 5-7. Veal Carcasses (weighing 84 to 103 kg ) from eight Friesian and Hereford cross calves, slaughtered in a commercial abattoir, were held at 6 °C for between 3 and 5 h and then placed in a chiller set at 2 °C with an air speed of 0-2 to 0.6 m/s. The temperature of the deep L D (2nd rib) reached 10°C 18h after stunning and 5°C 20 to 24h after stunning when the pH ranged from 5.5 to 5.6. An 8 cm joint from one side of each carcass, posterior to the 6th rib, was removed and brought (at 0 °C) to the Meat Research Institute. The L D was removed, bisected longitudinally and again transversely, giving four pieces weighing 70 to 80 g, which were packed under vacuum. Lamb Carcasses, weighing 15.5 to 19 kg, from six Dorset lambs, were held at ambient temperature (about 15 °C) for 4 h and then placed in a chiller with air at 0 °C and a velocity o f 1 m/s--conditions which avoid cold-shortening (Dransfield, unpublished observations)--24h after stunning, when the pH was between 5.6 and 5-7. LD's from each carcass were removed and cut transversely into four pieces, weighing 70 to 100 g, which were packed under vacuum.

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eol'k Twelve pork weight gilt carcasses (from Large White or Large White cross-bred pigs) were chosen at random from a day's kill at a local abattoir. Carcasses were held at ambient temperature for between 1 and 3 h and chilled overnight. Between 18 and 20 h after slaughter, one loin section from the 5th rib to the last lumbar vertebra was removed and transported to the Meat Research Institute. Ultimate pH's of LD, measured 24h after stunning, range from 5-5 to 6.3 (mean 5-75). Each LD was cut transversely into ten pieces of equal length and weighing between 70 and 100 g.

Rabbit Two groups of four New Zealand White cross rabbits were electrically stunned, bled, skinned and eviscerated. Carcasses from one group were held at 15 °C for 16 h whilst those from the second group were held at 15 °C for 4 h when the pH of the L D was within 0-1 unit of the value at 24h. Both muscles were removed from each carcass, cut transversely into three sections, each weighing 45 g (the length of the sections increased as the muscle tapered towards the anterior end). The remainder, about 10g, of the anterior part of the LD was used for the determination of pH which ranged from 5-9 to 6-8 (mean 6.1) between rabbits at 20h after stunning.

Sarcomere lengths Sarcomere lengths, measured by optical diffraction (Voyle, 1971), averaged 1-7/~m and did not differ significantly between types of meat. Sarcomere lengths were similar to those of excised beef muscles held at 10°C for 24h (Dransfield, 1977). The largest range in sarcomere length (0.5/~m) was found in pork LD. Severe cold-shortening was avoided since this ted to irregular decrease in toughness with time (Penny & Dra'nsfield, 1979) and constants could not be determined accurately.

Storage and heating Clearly, it was important to measure toughness initially as early as possible after stunning. However, because of the combined effects of falling pH and muscle shortening on toughness (Dransfield & Rhodes, 1975), meat was not heated prerigor. Initial samples were heated as near as possible to the time when the ultimate pH was reached which, in practice, meant 24 h after stunning for beef, 30 h for veal, 28 h for lamb, 20 h for pork and as early as 5 h for rabbit. All pieces were stored at 0 to 1 °C. To obtain a rapid increase in temperature and thereby limit further conditioning in meat during cooking, the vacuum packed samples, chosen at random, were immersed in water at 80°C immediately after removal from the cold room. A temperature of 80 °C was chosen because we have found that the first yield force (see section below on toughness measurements) changed least between 75 °C and 85 °C, similar to that found by Davey & Gilbert (1974). Because the geometry and weight o f the samples inevitably varied between

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Fig. 1. Heating and cooling of samples from beef, lamb, rabbit, veal and pork. Samples of LD were heated in water at 80 °C and subsequently cooled in running tap water. Temperature was monitored at the centre of the meat. species, the time o f heating was adjusted accordingly. The heating and cooling profiles at the centre o f the samples are shown in Fig. 1. Variation within species was slight; the largest variation was in rabbit where the time taken to reach 75 °C varied, at most, f r o m 7 min in the anterior, to 15 min in the posterior, sections.

Toughness measurements T o u g h n e s s was measured instrumentally on blocks cut f r o m the heated samples so that the cross-section, at right angles to the direction o f muscle fibres, was 1 x 1 cm. Blocks were compressed at right angles to the direction o f fibres between 1 c m wide Volodkevich-type jaws m o u n t e d in an I n s t r o n materials testing machine. A complete f o r c e - d e f o r m a t i o n curve was recorded and the toughness values measured as the average first yield force (shear force) for six c o m p r e s s i o n s (Rhodes et al., 1972).

Analysis The relationship between toughness and time was analysed using the e q u a t i o n : F, = Fo~ + ( F o -- Fo~)e -k' or, by rearranging, 2-303 k =--log(F t

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Fig. 2. Tenderising in M. Iongissimus dorsi from beef, veal, rabbit, lamb and pork. T o u g h n e s s values are the mean, limits of the vertical bars represent two standard errors of the mean, with the n u m b e r of animals shown in parentheses. The curve is the best least squares fit to a first order kinetic model (see section in the text headed Analysis).

where Fo, F, and F~o are the toughness values at time zero (stunning), time t after stunning and at the completion of conditioning, respectively and k is the rate constant. In practice, F, was measured at times between 1 (or in rabbit, 0.25) and 28 days and the parameters Fo~, (Fo - F~) and k were uniquely estimated with statistical confidence values (Dransfield et al., 1980).

RESULTS

The relationships between average toughness values and time of storage, together with calculated decay curves for each type of meat, are shown in Fig. 2. Variability between animals (represented by a vertical bar) was large, being highest for beef and lowest for lamb and veal. Variability between lambs and pigs decreased with time (Fig. 2). We believe the model to be a good one since the toughness values scattered evenly about the calculated curves and the model accounted for 96, 96, 99 and 91

144

E. DRANSFIELD, R. C. D. JONES, H. J. H. MAcFIE TABLE 1 PARAMETERS FOR TENDERISING OF M. Iongissimus dorsi FROM FOUR SPECIES

Type o f meat

Number o f animals

Beef Veal Rabbit Lamb Pork

6 8 8 6 12

Rate constant, k (days- 1) 0.16 0.17 0-17 0.21 0"38

Total change in toughness, F o - Fo~ (kg)

(0.04) (0.03) (0-06) (0-05) (0.11)

6-2 3-1 3-0 6-0 4-4

Toughness at completion o f conditioning, F~ (kg)

(0.6) (0.2) (0-5) (0-5) (0-6)

5-8 4-4 5-4 4.3 5.3

(0.5) (0.2) (0.4) (0.3) (0.3)

Parameters, with standard errors in parenthesis, were calculated according to the model Ft = F~o + Foo)e-k' from measurements of toughness (F,) at time t after stunning, during storage at 1°C for up to 28 days. (F o -

of the variation in toughness with time for lamb, beef, veal and rabbit, respectively. The model was least effective with pork, when it accounted for only 66 ~o of the variation in toughness with time. The parameters oftenderising defined by the model are given in Table I. The rate constants of the five meats did not differ significantly and had a c o m m o n value of 0-21 d a y s - 1. Whilst the error tended to increase with increasing rate constant, rabbit - - a n d particularly p o r k - - s h o w e d the greatest variation in rate constant. This high variation led to the non-significant differences since, on average, pork tenderised twice as fast as beef, veal or rabbit. Variations in pH accounted for only 13 ~o (by linear correlation) o f the variation in the rate constant of rabbit, whilst in pork t/3 U')

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variations in pH and sarcomere length together accounted for 64 ~ of the variation in the rate constant. A corollary of an exponential decay equation is that for a given rate constant, the proportion of tenderising remaining is dependent only on the duration of storage (Fig. 3). For a rate constant of 0.21 d a y s - 1, 50 ~ o f the tenderising occurs in 3 days and 80 ~o in 8 days. Beef and lamb tenderised twice as much as veal or rabbit. F r o m 24h to the completion of conditioning (Table 1), toughness decreased in beef and lamb by 5 kg which is equivalent to about three points on an eight-point taste panel tenderness scale. This supports trade experience of ageing beef and lamb but not veal or pork, even though there is little difference in rate of conditioning. After the completion of tenderising, lamb and veal were more tender than beef, rabbit and pork.

DISCUSSION

Use o f an exponential decay equation enables us to compare the rate of tenderising obtained in different laboratories since the rate constant is independent of both the method and the period of measurement. In beef M. Iongissimus dorsi, a value of 0.29 _+ 0-09 days-a was calculated from measurements using the Ottawa texture measuring instrument (Jeremiah & Martin, 1 9 7 8 ) a n d 0 - 0 7 _ 0-06 days-x from taste panel assessments (Deatherage & Harsham, 1947). In pork, the use of the Volodkevich compressive test gave a value of 0-34 days-1 (Buchter & Zeuthen, 1971) whilst the Warner-Bratzler shear test gave 0-47 _ 0.40 days-a (Gould et al., 1965). Therefore, the rate constants and their high variabilities, particularly in pork, are similar to the values obtained in this work. Beef and veal exhibited identical rates of tenderising, showing that the differences in connective tissue contribute little, if anything, to the rate o f conditioning. The differences did, however, contribute substantially to toughness and to the amount of tenderising. Beef was one-and-a-half times tougher than veal and tenderised twice as much. More tenderising has often been reported in meat which is tough because o f differences in animal maturity (Bouton & Harris, 1972), breed and sex (Purchas, 1972), although the rate of tenderising is unaffected by sex, fatness or colour (Martin et al., 1971). The rate of tenderising of beef M. sternomanidubularis was the same (calculated as 0-19 + 0.03 days -a from Davey & Gilbert, 1976) as that of the M. longissimus dorsi used in the present work and similar to that of the M. psoas major and M. semitendinosus used in previous work (Dransfield et al., 1980), showing that the total amount of collagen has little influence on the rate constant. The rate of proteolysis, measured as liberated free amino groups, in beef M. bicepsfemoris was also the same as in M. Iongissimus dorsi (Field et al., 1971). The rate of tenderising was not significantly different between the species studied here, although pork was exceptionally variable. This contradicts the differences in

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E. DRANSFIELD, R. C. D. JONES, H. J. H. MAcFIE

autolysis of beef, lamb, rabbit and pig (Zender et al., 1958; Radouco-Thomas et al., 1959; Sharp, 1963) and the lability of the Z-disc in beef, rabbit and pig meat (Henderson et al., 1970). Although none of this evidence was analysed statistically, it would appear that the differences in autolysis and lability of the Z-disc in raw meat are obscured by variations in other factors influencing toughness after cooking. In avian meat, however, the much higher rate of tenderising (calculated as 5-23 _ 1.68 days- 1 from Yamamoto & Samejima, 1977; Sayre, 1970) is compatible with the fast myofibrillar degradation (Samejima & Wolfe, 1976). The average tenderising rate of porcine M. Iongissimus dorsi, reported here, was twice that for bovine LD, but the difference was not significant. We have made a limited study on tenderising rates of bovine M. semitendinosus (k = 0-20 days- 1 with standard error 0-04days - l , for 9 animals) and porcine St (k = 0.52 +_ 0.08 days, 1, for 7 animals). The difference between these common rates was significant (P < 0.01, using the Behrens test which allows different variances), confirming that pork tenderises about twice as fast as beef when stored at 1 °C. Although it was not the intention here to study pH, variations from 5.5 to 6.8 occurred in rabbit but accounted for little of the variation in rate of tenderising. A similar small pH effect was shown in the activity of endogenous protease in rabbit, which decreased only marginally over the same pH range (Drabikowski et al., 1977). The effect of pH on autolysis and fragmentation in pork (Sharp, 1963) and on proteoloysis in beef homogenates (Penny & Ferguson-Pryce, 1979) was much more pronounced. REFERENCES BATE-SMITH, E. C. (1948). Adv. Fd. Res., l, 1. BOUTON, P. E. & HARRIS, P. V. (1972). J. Food Sci., 37, 539. BUCHTER, L. & ZEUTHEN, P. (1971). Proc. 2nd Inst. Syrup. Conditions and Meat Quality o f Pigs, Wageningen, The Netherlands, p. 247. DAVEY, C. L. & DICKSON, M. R. (1970). J. FoodSci., 35, 56. DAVEY, C. L. & GILBERT, K. V. (1974). J. Sci. Food Agric., 25, 931. DAVEY, C. L. & GILBERT, K. V. (1976). J. Sci. Agric., 27, 244. DEATHERAGE, F. E. & HARSHAM, A. (1947). Food Res., 12, 164. DRABIKOWSKI, W., GORECKA, A. & JAKUBIEC-PUKA,A. (1977). Inst. J. Biochem., 8, 61. DRANSFIELD, E. (1977). J. Sci. Food Agric., 28, 833. DRANSFIELD, E,, JONES, R. C. D. & MACFIE, H. J. H. (1980). Meat Sci., 5, 131. DRANSFIELD, E. & RHODES, D. N. (1975). J. Sci. Food Agric., 26, 483. FIELD, R. A., RILEY, M. L. & CHANG, Y. O. (1971). J. Food Sci., 36, 611. GOLL, D. E. (1970). Thephysiology and biochemistry o f muscle as afood. Vol. 2. University of Wisconsin Press, Madison, p. 255. GOULD, P. F., BRATZLER, L. J. & MAGEE, W. T. (1965). Food TechnoL, 19, 248. HENDERSON, D. W., GOLL, D. E. & STROMER, M. H. (1970). Am. J. Anal., 228, 117. JEREMIAH, L. E. & MARTIN, A. H. (1978). Meat Sci., 2, 169. KRUGGEL, W. C. & FIELD, R. A. (1971). J. FoodSci., 36, 1114. MACBRIDE, M. A. & PARRmH, F. C. (1977). J. FoodSci., 32, 1621. MARTIN, A. H., FREDEEN, H. T. & WEISS, G. M. (1971). J. FoodSci., 36, 619. PENNY, I. F. (1968). J. Sci. FoodAgric., 19, 518. PENNY, I. F. (1976). J. Sci. FoodAgric., 27, 1147.

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