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The Effects of Pre- and Post-rigor High-intensity Ultrasound Treatment on Aspects of Lamb Tenderness
Article No. fs970361
Lebensm.-Wiss. u.-Technol., 31, 334–338 (1998)
The Effects of Pre- and Post-rigor High-intensity Ultrasound Treatment on Aspects of Lamb Tenderness James Gerard Lyng*, Paul Allen and Brian McKenna J. G. Lyng, P. Allen: Teagasc, National Food Centre, Dunsinea, Castleknock, Dublin 15 (Ireland) B. McKenna: Department of Food Science and Faculty of Agriculture, University College Dublin, Belfield, Dublin 4 (Ireland) (Received June 11, 1997; accepted December 12, 1997)
Lamb longissimus thoracis et lumborum muscles were excised by either hot or cold boning, cut into steaks and sonicated using a 20-kHz ultrasonic probe placed at intervals on the meat surface for 15-s periods to expose the entire surface of the meat to 62 W/cm2 of ultrasound. The influence of the ultrasound treatment was assessed on peak load bite-force tenderometry values, sensory characteristics, solubility of collagen and myofibrillar proteolysis using SDS–PAGE. Bite-force tenderometry, sensory analysis and collagen solubility all showed no effect due to ultrasound treatment. SDS–PAGE also revealed no apparent difference between ultrasound-treated and control samples either in the numbers of bands evident on gels or in the rate of appearance/ disappearance of the characteristic bands of ageing, suggesting no influence on myofibrillar proteolysis due to the ultrasound treatment.
©1998 Academic Press Keywords: high intensity ultrasound; lamb tenderness; SDS–PAGE; bite force tenderometry; sensory analysis; collagen solubility
Introduction A tenderizing role for high-intensity ultrasound (HIU) has been suggested by a number of workers (1–5). The effect of sonication on extracted collagenous and myofibrillar proteins has also been published (6, 7). Roncales ´ et al. (7) reported ultrasonic destabilization of lamb liver lysosomal membranes and activation of proteolysis in extracted lamb longissimus thoracis et lumborum (LTL) muscle fibres sonicated in solution. Nishihara and Doty (6) reported degradation in extracted collagen macromolecules sonicated in solution with high-intensity sound in the acoustic region, and Stagni and de Bernard (8) reported HIU disruption of isolated lysosomes; both findings if observed in whole meat could lead to improved tenderness. Extensive physical disruption of myofibrillar proteins, enhanced myofibrillar proteolysis or connective tissue disruption in whole meat could lead to a role for HIU in guaranteeing tender meat and upgrading of cheaper cuts. Apart from reports of physical disruption by Dolatowski (2, 9), Zayas and Orlova (10) and Sajas and Gorbatow (1), the authors have come across no relevant literature reporting a dramatic effect on meat tenderness from high-intensity low-frequency ultrasound. The treatment of beef steaks using ultrasound *To whom correspondence should be addressed.
baths did not improve meat tenderness (11), nor did a more powerful direct application with an ultrasound probe (12). Roncales ´ et al. (7) found that the sonication of extracted lamb muscle fibres activated proteolysis but did not obtain similar results in beef muscle fibres (Roncales, ´ personal communication), raising the possibility that lamb muscle is more susceptible to disruption by HIU. This work assesses the effects of HIU treatments comparable to those of Roncales ´ et al. (7) although on whole lamb LTL as opposed to isolated lamb LTL myofibrils. As in the study by Roncales ´ et al. (7) the muscles were exposed to 20 kHz HIU at 2 and 24 h post mortem (PM). The present study does not aim to be a direct comparison with the work of Roncales ´ et al. (7). It is more a continuation, investigating whether detectable changes in structural and textural aspects of whole lamb tenderness [as measured by peak load biteforce tenderometry (PLBFT), sensory analysis, SDS– PAGE and soluble collagen content] would be observed in intact lamb exposed to an HIU similar treatment to that used by Roncales ´ et al. (7). Another objective was to determine whether lamb was more susceptible to HIU treatment than beef treated in a similar fashion (12). The effects of both pre- and postrigor treatment with HIU were assessed, in case time of treatment in relation to rigor development was critical. However, experiments were not designed to compare hot boning (HB) and cold boning (CB) as animal differences and time of treatment were confounded.
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Table 1
Summary of ANOVA results for bite-force tenderometry data for lamb muscle Ultrasound treatment time post mortem (days) Type of boning
Cold Hot
Other factors
1
3
7
Animal
Conditioning
NS NS
NS NS
NS NS
** NS
* **
NS, not significant; *P <0.05; **P<0.01.
Materials and Methods Experimental material Eight lambs were slaughtered and their LTL muscles excised, four carcasses at 2 h PM (HB) and four at 24 h PM (CB). Muscles were cut into 11 steaks, 2.5 cm thick. HB steaks were held at 13–15 °C for 24 h, then aged at 2–4 °C; CB steaks were aged at 2–4 °C.
Ultrasound treatment As described by Lyng et al. (12), steaks from one side of each animal were sonicated with an ultrasound probe (Heat Systems Model XL 2020, frequency 20 kHz) which was repeatedly lowered on to one surface of the steak (on average 10 times per steak) for 15-s periods, exposing the meat to 63 W/cm2 ultrasound. The steaks from the other side were used as untreated controls. HB steaks were treated immediately after boning; CB steaks at 24 h PM. All steaks were then aged in vacuum packs for 1, 3 or 7 days before being either frozen (–25 °C) or immediately analysed. Only muscles of normal ultimate pH (5.5–5.8) were used for these experiments.
methods outlined previously by Lyng et al. (11, 12) (i.e. the technique described by Etlinger et al. (16) and modified by Wang (17) for the extraction and by Greaser et al. (18) for SDS–PAGE).
Collagen analysis Total collagen (TC) and soluble collagen (SC) content were determined (in triplicate) on a single steak using the method of Hill (19) and Bergman and Loxley (20) and a factor of 7.14 was employed to convert hydroxyproline to collagen (21).
Statistical analysis Data analysis was by a generalized least-squares procedure (22) and experimental design was a randomized block with possible differences along the length of a muscle being blocked across. As in a previous study by Lyng et al. (12) experiments were designed to compare differences between ultrasound-treated steaks and controls and not the effect of hot vs. cold boning.
Bite-force tenderometry Three steaks per animal side were sampled for PLBFT measurements and one steak of the three was frozen (–25 °C), on either day 1, 3 or 7 PM, for analysis. As in previous studies by Lyng et al. (11, 12) the methods of Boccard et al. (13) were employed in sample preparation, and a Volodkevich jaw (14) was used in PLBFT measurements.
(a)
Peak load bite force (N/cm2)
100 80 60 40 20 0
Sensory analysis Four steaks in total per animal side were taken for sensory analysis, two on either day 1 or 7 PM. On the appropriate PM day samples were frozen (–25 °C) for analysis. Sensory analysis was in accordance with American Meat Science Association guidelines (15), using six trained panellists.
(b)
Peak load bite force (N/cm2)
100 80 60 40 20 0
SDS–PAGE Three steaks from each animal side were sampled for SDS–PAGE analysis and one steak was sampled on day 1, 3 or 7 PM. Extraction of myofibrillar proteins was by
3 7 1 Post-mortem assessment time (days)
3 7 1 Post-mortem assessment time (days)
Fig. 1 Bite-force tenderometry results for sonicated lamb longissimus thoracis et lumborum (a) cold boned (b) hot boned. ( ) = unsonicated controls; (F) = 15 s at 62 W/cm2
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Table 2
Pearson correlation coefficients for sensory tenderness scores and Volodkevich peak load values Post-treatment time Day 1
Type of boning
Correlation coefficient
Significance
Correlation coefficient
Significance
–0.712 +0.028 –0.484
* NS NS
–0.530 –0.723 –0.563
NS * *
Cold Hot Pooleda aPooled,
Day 7
cold and hot boned. NS, not significant; *P < 0.05.
Results
samples even after 7-days ageing, though this finding could be due to animal differences.
Bite-force tenderometry Ageing improved PLBFT for both HB and CB lamb (P < 0.05) (Table 1). CB animals differed in tenderness (P < 0.01) but not HB animals (P ³ 0.05). HIU treatment did not affect (P ³ 0.05) tenderness of the CB or HB steaks after 1, 3 or 7 days ageing. Although the experiment was not designed to compare hot and cold boning, it can be seen from Fig. 1 that HB samples appeared to have higher PLBFT values than CB (a) Tenderness Overall appearance
Chewiness
Overall texture
Moistness
Overall acceptability
Meat flavour Overall flavour
Sensory analysis Sensory analysis tenderness scores for CB day 1 and CB and HB day 7 were negatively correlated with PLBFT measurements. The same was true when CB and HB data were pooled together (Table 2). Correlation coefficients for CB day 1, HB day 7 and overall day 7 were significant (P < 0.05) while the overall coefficient for day 1 did not reach significance (P < 0.10). Results for sensory analysis are illustrated in star diagrams (the centre of the circle is the lowest possible score and the circumference is the highest) (Fig. 2a, b). Within post-treatment times for both CB and HB LTL, HIU did not affect (P ³ 0.05) tenderness or any other attribute and for this reason the results of the ANOVA are summarized only for conditioning (Table 3). For HB LTL, ageing markedly improved (P < 0.05) all attributes except overall flavour which showed a slight improvement (P < 0.10). For CB samples, only tenderness, overall acceptability and chewiness improved significantly (P < 0.05) while the improvement in overall texture did not reach formal significance (P < 0.10).
(b) Tenderness Overall appearance
SDS–PAGE SDS–PAGE gels revealed no apparent difference between control and HIU-treated samples in rates of appearance/disappearance of bands or indeed in the numbers of bands present (Fig. 3). Bands in the 28–32-kDa region increased in intensity on ageing whereas there was an intensity decrease in bands in the region of 33–36 kDa. A number of bands also appeared in the 93–100-kDa region after 7 days of ageing.
Chewiness
Overall texture
Moistness
Meat flavour
Overall acceptability Overall flavour
Fig. 2 Sensory analysis results for sonicated lamb longissimus thoracis et lumborum (a) cold boned (b) hot boned. (–e–) = Control 1 day post mortem; (–s–) = sonicated 1 day post mortem; (–––) = control 7 days post mortem; (–G–) = sonicated 7 days post mortem
Collagen analysis SC content was not affected (P ³ 0.05) by HIU in either CB or HB lamb LTL (Table 4). CB animals differed (P < 0.05) in SC content but HB animals did not P ³ 0.05); TC contents of both CB and HB samples showed significant variation between animals (P < 0.05).
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Table 3
Significance of ageing for 7 days on sensory attributes of lamb longissimus thoracis et lumborum Sensory attribute
Boning type Cold Hot
Tenderness
Overall texture
Overall flavour
Overall appearance
Overall acceptability
Moistness/ juiciness
Meat flavour intensity
Chewiness
** ***
NS ***
NS NS
NS ***
* ***
NS ***
NS **
* ***
NS, not significant; *P <0.05; **P<0.01; ***P<0.001.
Discussion Similarities exist between treatment methodologies employed in this work on whole meat and in that on isolated myofibrillar bundles by Roncales ´ et al. (7). These authors removed small groups of LTL fibres (2 cm 3 0.5 mm approximately), immersed them in an extraction buffer and sonicated them with 56 or 62 W of ultrasound for different time periods [30 s–3 min (56 W) and 10–40 s (62 W)]. The fibres had been obtained at 2 or 24 h PM. Proteolytic effects observed by Roncales ´ et al. (8) due to HIU treatment in the early phases of meat ageing were virtually independent of time or intensity of treatment. In the present work, SDS–PAGE results in whole lamb LTL showed no similarities to the findings of Roncales ´ et al. (7). No decrease in intensity of an 87-kDa band with simultaneous appearance of an 83-kDa band was obtained in HIU-treated whole lamb and in addition no increase in the numbers of bands in the 30-kDa region was observed. The lack of an effect on proteolysis, despite similar post-treatment times, intensities and durations of treatment to those employed by Roncales ´ et al. (7), suggests that mechanical constraints in whole meat prevented free vibration of the myofibrillar proteins or kDa C1
S1
C3
S3
C7
S7
93–100 kDa 66
45 36
33–35 kDa
29 24
28–32 kDa
20 14.2
Fig. 3 15% SDS–PAGE of hot boned lamb longissimus thoracis et lumborum myofibrillar proteins following sonication. kDa, marker molecular weight; (C), control; (S) sonicated; (1,3,7), assessment time post mortem days
Table 4
decreased the intensity of the sonic waves transversing the meat, with insufficient HIU reaching the targets. This implies that different sonication conditions (i.e. higher intensities, longer treatment times, different frequencies etc.) would be necessary to produce similar effects to those observed by Roncales ´ et al. (7), if indeed it is possible to reproduce this effect in whole meat samples. PLBFT measurements showed no effect (P > 0.05) from HIU treatment at any of the post-treatment assessment times. This would suggest that had any myofibrillar disruption or indeed influence on the myofibrillar or collagenous components occurred they were not of sufficient magnitude to influence tenderness in the lamb as assessed by this method. Similar findings were made in fresh beef by Lyng et al. (11, 12) and, although such findings would seem to be in conflict with the work of Zayas and Orlova (10), Sajas and Gorbatow (1), Dolatowski (2) and Smith et al. (3), these other reports were all on meat sonicated in the presence of saline/brine (as discussed by Lyng et al. (11)) and indeed the work of Smith et al. (3) found a significant increase in the toughness of meat sonicated for one of the longer HIU exposure times and this in itself was not explained by the authors. No effects on the total or soluble collagen components of lamb were observed in agreement with earlier findings on beef (11, 12). This would again seem to contradict reports by Roberts (5) and Sullivan (4), although this experimental work is not directly comparable with the former owing to differences in durations and intensities of treatment. In conclusion, the method of ultrasound application used in the present study did not improve tenderness of entire HB or CB lamb LTL up to 7 days PM, nor was there any indication that it would shorten the ageing time required to reach final tenderness. No evidence was found to suggest that lamb muscle is more susceptible to disruption by this method of ultrasound application than beef. However, this is not an exhaustive study and a considerable amount of further investigation is necessary before a definitive conclusion can be made regarding the potential of ultrasound as a meat tenderizer.
Total and soluble collagen content of sonicated and control lamb muscle samples Soluble collagen (%)
Boning type Cold Hot
Total collagen (mg/g fresh weight)
Control
Sonicated
SED1
Significance1
18.8 17.4
19.8 17.5
2.541 0.972
NS NS
SED, standard error of the difference; NS, not significant.
337
Control 4.3 3.89
Sonicated
SED
Significance
4.24 3.75
0.322 0.286
NS NS
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References 1 SAJAS, J. F. AND GORBATOW, W. M. The use of ultrasonics in meat technology. Fleischwirtsch, 58, 1009–1021 (1978) 2 DOLATOWSKI, Z. J. Ultrasonics 3. Influence of ultrasonics on the production technology and quality of cooked hams. Fleischwirtsch, 69, 106–111 (1989) 3 SMITH, N. B., CANNON, J. E., NOVAKOFSKI, J. E., MCKEITH, F. K. AND O’BRIEN, W. D. J. Tenderisation of semitendinosus muscle using high intensity ultrasound. Ultrasonics Symposium, 1371–1373 (1991) 4 SULLIVAN, C. A sound investment. Chemistry and Industry, May, 365 (1992) 5 ROBERTS, R. T. High intensity ultrasonics. In: JOHNSTON, D. E., KNIGHT, M. K. AND LEDWARD, D. A. (Eds), The Chemistry of Muscle-based Foods. Cambridge: Royal Society of Chemistry, pp. 287–297 (1992) 6 NISHIHARA, T. AND DOTY, P. The sonic fragmentation of collagen macromolecules. Proceedings of the National Academy of Science (USA), 44, 411–417 (1958) ´ , P., CENA, P., BELTRAN, A. AND JAMIE, I. 7 RONCALES Ultrasonication of lamb skeletal muscle fibres enhances postmortem proteolysis. Zeitschrift fur ¨ LebensmittelUntersuchung und-Forschung, 196, 339–342 (1993) 8 STAGNI, N. AND DE BERNARD, B. Lysomal enzyme activity in rat and beef skeletal muscle. Biochimica et Biophysica Acta, 170, 129–139 (1968) 9 DOLATOWSKI, Z. J. Ultrasonics 2. Influence of ultrasonics on the ultrastructure of muscle tissue during curing. Fleischwirtsch, 68, 1301–1303 (1988) 10 ZAYAS, Y. F. AND ORLOVA, T. N. The application of ultrasonic vibrations for tenderization of meat. Izvestia vysshykh unhebnykh zavedeniy, 4, 54–56 (1970) 11 LYNG, J. G., ALLEN, P. AND MCKENNA, B. The influence of high intensity ultrasound baths on aspects of beef tenderness. The Journal of Muscle Foods, 8, 237–249 (1997) 12 LYNG, J. G., ALLEN, P. AND MCKENNA, B. The effect on aspects of beef tenderness of pre- and post rigor exposure to a high intensity ultrasound probe. Submitted to Journal of the Science of Food and Agriculture, 78 (1998)
13 BOCCARD, R., BUCHTER, L., CASTEELS, E., COSENTINO, E., DRANSFIELD, E., HOOD, D. E., JOSEPH, R. L., MACDOUGALL, D. B., RHODES, D. N., SCHON, I., TINBERGEN, B. J. AND TOURAILLE, C. Procedures for measuring meat quality characteristics in beef production experiments. Report of a working group in the Commission of the European Communities (CEC) beef production research programme. Livestock Production Science, 8, 385–397 (1981) 14 VOLODKEVICH, N. N. Apparatus for measurements of chewing resistance or tenderness of foodstuffs. Food Research, 3, 221–225 (1938) 15 CROSS, H. R., BERNHOLDT, H. F., DIKEMAN, M. E., GREENE, B. E., MOODY, W. G. AND STAGGS, R. L. Guidelines for Cookery and Sensory Evaluation of Meat. Chicago: American Meat Science Association and National Livestock and Meat Board, pp. 1–25 (1978) 16 ETLINGER, J. D., ZAK, R. AND FISCHMAN, D. A. Compositional studies of myofibrils from rabbit striated muscle. Journal of Cell Biology, 68, 123–141 (1976) 17 WANG, K. Purification of titin and nebulin. Methods in Enzymology, 85, 264–274 (1982) 18 GREASER, M. L., YATES, L. D., KRZYWICKI, K. AND ROELKE, D. Electrophoretic methods for the separation and identification of muscle proteins. Proceedings of the Reciprocal Meat Conference, 36, 87–91 (1983) 19 HILL, F. The solubility of intramuscular collagen. Journal of Food Science, 31, 161–166 (1966) 20 BERGMAN, I. AND LOXLEY, R. Two improved and simplified methods for the spectrophotometric determination of hydroxyproline. Analytical Chemistry, 35, 1961–1965 (1963) 21 YOUNG, O. A., BRAGGINS, T. J. AND BARKER, G. J. The effects of collagen characteristics on sensory assessment and shear values of cooked sheep semimembranosus muscles. ICoMST, 38, 455–458 (1992) 22 Systat Inc. Statistics. In: Intelligent Software for Statistics and Graphics. Illinois: Systac Inc., Version Dos 5.03 (1990)
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The Effects of Pre- and Post-rigor High-intensity Ultrasound Treatment on Aspects of Lamb Tenderness James Gerard Lyng*, Paul Allen and Brian McKenna J. G. Lyng, P. Allen: Teagasc, National Food Centre, Dunsinea, Castleknock, Dublin 15 (Ireland) B. McKenna: Department of Food Science and Faculty of Agriculture, University College Dublin, Belfield, Dublin 4 (Ireland) (Received June 11, 1997; accepted December 12, 1997)
Lamb longissimus thoracis et lumborum muscles were excised by either hot or cold boning, cut into steaks and sonicated using a 20-kHz ultrasonic probe placed at intervals on the meat surface for 15-s periods to expose the entire surface of the meat to 62 W/cm2 of ultrasound. The influence of the ultrasound treatment was assessed on peak load bite-force tenderometry values, sensory characteristics, solubility of collagen and myofibrillar proteolysis using SDS–PAGE. Bite-force tenderometry, sensory analysis and collagen solubility all showed no effect due to ultrasound treatment. SDS–PAGE also revealed no apparent difference between ultrasound-treated and control samples either in the numbers of bands evident on gels or in the rate of appearance/ disappearance of the characteristic bands of ageing, suggesting no influence on myofibrillar proteolysis due to the ultrasound treatment.
©1998 Academic Press Keywords: high intensity ultrasound; lamb tenderness; SDS–PAGE; bite force tenderometry; sensory analysis; collagen solubility
Introduction A tenderizing role for high-intensity ultrasound (HIU) has been suggested by a number of workers (1–5). The effect of sonication on extracted collagenous and myofibrillar proteins has also been published (6, 7). Roncales ´ et al. (7) reported ultrasonic destabilization of lamb liver lysosomal membranes and activation of proteolysis in extracted lamb longissimus thoracis et lumborum (LTL) muscle fibres sonicated in solution. Nishihara and Doty (6) reported degradation in extracted collagen macromolecules sonicated in solution with high-intensity sound in the acoustic region, and Stagni and de Bernard (8) reported HIU disruption of isolated lysosomes; both findings if observed in whole meat could lead to improved tenderness. Extensive physical disruption of myofibrillar proteins, enhanced myofibrillar proteolysis or connective tissue disruption in whole meat could lead to a role for HIU in guaranteeing tender meat and upgrading of cheaper cuts. Apart from reports of physical disruption by Dolatowski (2, 9), Zayas and Orlova (10) and Sajas and Gorbatow (1), the authors have come across no relevant literature reporting a dramatic effect on meat tenderness from high-intensity low-frequency ultrasound. The treatment of beef steaks using ultrasound *To whom correspondence should be addressed.
baths did not improve meat tenderness (11), nor did a more powerful direct application with an ultrasound probe (12). Roncales ´ et al. (7) found that the sonication of extracted lamb muscle fibres activated proteolysis but did not obtain similar results in beef muscle fibres (Roncales, ´ personal communication), raising the possibility that lamb muscle is more susceptible to disruption by HIU. This work assesses the effects of HIU treatments comparable to those of Roncales ´ et al. (7) although on whole lamb LTL as opposed to isolated lamb LTL myofibrils. As in the study by Roncales ´ et al. (7) the muscles were exposed to 20 kHz HIU at 2 and 24 h post mortem (PM). The present study does not aim to be a direct comparison with the work of Roncales ´ et al. (7). It is more a continuation, investigating whether detectable changes in structural and textural aspects of whole lamb tenderness [as measured by peak load biteforce tenderometry (PLBFT), sensory analysis, SDS– PAGE and soluble collagen content] would be observed in intact lamb exposed to an HIU similar treatment to that used by Roncales ´ et al. (7). Another objective was to determine whether lamb was more susceptible to HIU treatment than beef treated in a similar fashion (12). The effects of both pre- and postrigor treatment with HIU were assessed, in case time of treatment in relation to rigor development was critical. However, experiments were not designed to compare hot boning (HB) and cold boning (CB) as animal differences and time of treatment were confounded.
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Table 1
Summary of ANOVA results for bite-force tenderometry data for lamb muscle Ultrasound treatment time post mortem (days) Type of boning
Cold Hot
Other factors
1
3
7
Animal
Conditioning
NS NS
NS NS
NS NS
** NS
* **
NS, not significant; *P <0.05; **P<0.01.
Materials and Methods Experimental material Eight lambs were slaughtered and their LTL muscles excised, four carcasses at 2 h PM (HB) and four at 24 h PM (CB). Muscles were cut into 11 steaks, 2.5 cm thick. HB steaks were held at 13–15 °C for 24 h, then aged at 2–4 °C; CB steaks were aged at 2–4 °C.
Ultrasound treatment As described by Lyng et al. (12), steaks from one side of each animal were sonicated with an ultrasound probe (Heat Systems Model XL 2020, frequency 20 kHz) which was repeatedly lowered on to one surface of the steak (on average 10 times per steak) for 15-s periods, exposing the meat to 63 W/cm2 ultrasound. The steaks from the other side were used as untreated controls. HB steaks were treated immediately after boning; CB steaks at 24 h PM. All steaks were then aged in vacuum packs for 1, 3 or 7 days before being either frozen (–25 °C) or immediately analysed. Only muscles of normal ultimate pH (5.5–5.8) were used for these experiments.
methods outlined previously by Lyng et al. (11, 12) (i.e. the technique described by Etlinger et al. (16) and modified by Wang (17) for the extraction and by Greaser et al. (18) for SDS–PAGE).
Collagen analysis Total collagen (TC) and soluble collagen (SC) content were determined (in triplicate) on a single steak using the method of Hill (19) and Bergman and Loxley (20) and a factor of 7.14 was employed to convert hydroxyproline to collagen (21).
Statistical analysis Data analysis was by a generalized least-squares procedure (22) and experimental design was a randomized block with possible differences along the length of a muscle being blocked across. As in a previous study by Lyng et al. (12) experiments were designed to compare differences between ultrasound-treated steaks and controls and not the effect of hot vs. cold boning.
Bite-force tenderometry Three steaks per animal side were sampled for PLBFT measurements and one steak of the three was frozen (–25 °C), on either day 1, 3 or 7 PM, for analysis. As in previous studies by Lyng et al. (11, 12) the methods of Boccard et al. (13) were employed in sample preparation, and a Volodkevich jaw (14) was used in PLBFT measurements.
(a)
Peak load bite force (N/cm2)
100 80 60 40 20 0
Sensory analysis Four steaks in total per animal side were taken for sensory analysis, two on either day 1 or 7 PM. On the appropriate PM day samples were frozen (–25 °C) for analysis. Sensory analysis was in accordance with American Meat Science Association guidelines (15), using six trained panellists.
(b)
Peak load bite force (N/cm2)
100 80 60 40 20 0
SDS–PAGE Three steaks from each animal side were sampled for SDS–PAGE analysis and one steak was sampled on day 1, 3 or 7 PM. Extraction of myofibrillar proteins was by
3 7 1 Post-mortem assessment time (days)
3 7 1 Post-mortem assessment time (days)
Fig. 1 Bite-force tenderometry results for sonicated lamb longissimus thoracis et lumborum (a) cold boned (b) hot boned. ( ) = unsonicated controls; (F) = 15 s at 62 W/cm2
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Table 2
Pearson correlation coefficients for sensory tenderness scores and Volodkevich peak load values Post-treatment time Day 1
Type of boning
Correlation coefficient
Significance
Correlation coefficient
Significance
–0.712 +0.028 –0.484
* NS NS
–0.530 –0.723 –0.563
NS * *
Cold Hot Pooleda aPooled,
Day 7
cold and hot boned. NS, not significant; *P < 0.05.
Results
samples even after 7-days ageing, though this finding could be due to animal differences.
Bite-force tenderometry Ageing improved PLBFT for both HB and CB lamb (P < 0.05) (Table 1). CB animals differed in tenderness (P < 0.01) but not HB animals (P ³ 0.05). HIU treatment did not affect (P ³ 0.05) tenderness of the CB or HB steaks after 1, 3 or 7 days ageing. Although the experiment was not designed to compare hot and cold boning, it can be seen from Fig. 1 that HB samples appeared to have higher PLBFT values than CB (a) Tenderness Overall appearance
Chewiness
Overall texture
Moistness
Overall acceptability
Meat flavour Overall flavour
Sensory analysis Sensory analysis tenderness scores for CB day 1 and CB and HB day 7 were negatively correlated with PLBFT measurements. The same was true when CB and HB data were pooled together (Table 2). Correlation coefficients for CB day 1, HB day 7 and overall day 7 were significant (P < 0.05) while the overall coefficient for day 1 did not reach significance (P < 0.10). Results for sensory analysis are illustrated in star diagrams (the centre of the circle is the lowest possible score and the circumference is the highest) (Fig. 2a, b). Within post-treatment times for both CB and HB LTL, HIU did not affect (P ³ 0.05) tenderness or any other attribute and for this reason the results of the ANOVA are summarized only for conditioning (Table 3). For HB LTL, ageing markedly improved (P < 0.05) all attributes except overall flavour which showed a slight improvement (P < 0.10). For CB samples, only tenderness, overall acceptability and chewiness improved significantly (P < 0.05) while the improvement in overall texture did not reach formal significance (P < 0.10).
(b) Tenderness Overall appearance
SDS–PAGE SDS–PAGE gels revealed no apparent difference between control and HIU-treated samples in rates of appearance/disappearance of bands or indeed in the numbers of bands present (Fig. 3). Bands in the 28–32-kDa region increased in intensity on ageing whereas there was an intensity decrease in bands in the region of 33–36 kDa. A number of bands also appeared in the 93–100-kDa region after 7 days of ageing.
Chewiness
Overall texture
Moistness
Meat flavour
Overall acceptability Overall flavour
Fig. 2 Sensory analysis results for sonicated lamb longissimus thoracis et lumborum (a) cold boned (b) hot boned. (–e–) = Control 1 day post mortem; (–s–) = sonicated 1 day post mortem; (–––) = control 7 days post mortem; (–G–) = sonicated 7 days post mortem
Collagen analysis SC content was not affected (P ³ 0.05) by HIU in either CB or HB lamb LTL (Table 4). CB animals differed (P < 0.05) in SC content but HB animals did not P ³ 0.05); TC contents of both CB and HB samples showed significant variation between animals (P < 0.05).
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Table 3
Significance of ageing for 7 days on sensory attributes of lamb longissimus thoracis et lumborum Sensory attribute
Boning type Cold Hot
Tenderness
Overall texture
Overall flavour
Overall appearance
Overall acceptability
Moistness/ juiciness
Meat flavour intensity
Chewiness
** ***
NS ***
NS NS
NS ***
* ***
NS ***
NS **
* ***
NS, not significant; *P <0.05; **P<0.01; ***P<0.001.
Discussion Similarities exist between treatment methodologies employed in this work on whole meat and in that on isolated myofibrillar bundles by Roncales ´ et al. (7). These authors removed small groups of LTL fibres (2 cm 3 0.5 mm approximately), immersed them in an extraction buffer and sonicated them with 56 or 62 W of ultrasound for different time periods [30 s–3 min (56 W) and 10–40 s (62 W)]. The fibres had been obtained at 2 or 24 h PM. Proteolytic effects observed by Roncales ´ et al. (8) due to HIU treatment in the early phases of meat ageing were virtually independent of time or intensity of treatment. In the present work, SDS–PAGE results in whole lamb LTL showed no similarities to the findings of Roncales ´ et al. (7). No decrease in intensity of an 87-kDa band with simultaneous appearance of an 83-kDa band was obtained in HIU-treated whole lamb and in addition no increase in the numbers of bands in the 30-kDa region was observed. The lack of an effect on proteolysis, despite similar post-treatment times, intensities and durations of treatment to those employed by Roncales ´ et al. (7), suggests that mechanical constraints in whole meat prevented free vibration of the myofibrillar proteins or kDa C1
S1
C3
S3
C7
S7
93–100 kDa 66
45 36
33–35 kDa
29 24
28–32 kDa
20 14.2
Fig. 3 15% SDS–PAGE of hot boned lamb longissimus thoracis et lumborum myofibrillar proteins following sonication. kDa, marker molecular weight; (C), control; (S) sonicated; (1,3,7), assessment time post mortem days
Table 4
decreased the intensity of the sonic waves transversing the meat, with insufficient HIU reaching the targets. This implies that different sonication conditions (i.e. higher intensities, longer treatment times, different frequencies etc.) would be necessary to produce similar effects to those observed by Roncales ´ et al. (7), if indeed it is possible to reproduce this effect in whole meat samples. PLBFT measurements showed no effect (P > 0.05) from HIU treatment at any of the post-treatment assessment times. This would suggest that had any myofibrillar disruption or indeed influence on the myofibrillar or collagenous components occurred they were not of sufficient magnitude to influence tenderness in the lamb as assessed by this method. Similar findings were made in fresh beef by Lyng et al. (11, 12) and, although such findings would seem to be in conflict with the work of Zayas and Orlova (10), Sajas and Gorbatow (1), Dolatowski (2) and Smith et al. (3), these other reports were all on meat sonicated in the presence of saline/brine (as discussed by Lyng et al. (11)) and indeed the work of Smith et al. (3) found a significant increase in the toughness of meat sonicated for one of the longer HIU exposure times and this in itself was not explained by the authors. No effects on the total or soluble collagen components of lamb were observed in agreement with earlier findings on beef (11, 12). This would again seem to contradict reports by Roberts (5) and Sullivan (4), although this experimental work is not directly comparable with the former owing to differences in durations and intensities of treatment. In conclusion, the method of ultrasound application used in the present study did not improve tenderness of entire HB or CB lamb LTL up to 7 days PM, nor was there any indication that it would shorten the ageing time required to reach final tenderness. No evidence was found to suggest that lamb muscle is more susceptible to disruption by this method of ultrasound application than beef. However, this is not an exhaustive study and a considerable amount of further investigation is necessary before a definitive conclusion can be made regarding the potential of ultrasound as a meat tenderizer.
Total and soluble collagen content of sonicated and control lamb muscle samples Soluble collagen (%)
Boning type Cold Hot
Total collagen (mg/g fresh weight)
Control
Sonicated
SED1
Significance1
18.8 17.4
19.8 17.5
2.541 0.972
NS NS
SED, standard error of the difference; NS, not significant.
337
Control 4.3 3.89
Sonicated
SED
Significance
4.24 3.75
0.322 0.286
NS NS
lwt/vol. 31 (1998) No. 4
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