Test du système MSA pour prédire la qualité de la viande bovine irlandaise

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Prédiction de la qualité sensorielle de la viande bovine (tendreté, jutosité, flaveur, appréciation globale) en république d’Irlande à l’aide du système australien MSA (Meat Standards Australia)

Un programme de recherche a été mis en place pour tester le système « Meat standards Australia » (MSA) en république irlandaise. Cet article décrit les résultats de ce programme. Il a été préalablement publié en 2013 dans l’ouvrage « Developments in beef meat quality » édité par JD Wood qui résume les travaux qui ont été présentés lors de la « Langford Food Industy Conference » en juin 2012.

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INTRODUCTION

Beef is an important yet relatively expensive component in the diet of most consumers. The eating quality, or palatability, of beef, particularly tenderness, is therefore important to consumers. The palatability of beef is mainly a function of its flavour, juiciness, and tenderness. The consumer can assess none of these characteristics when purchasing beef. The EUROP beef carcass classification scheme (EC Regulation no. 1249/2008) uses visually assessed conformation and external fat cover as a means of sorting carcasses into classes for price reporting purposes. These are used by the industry to pay producers and for trading carcasses but conformation and fatness mainly affect the saleable yield of the carcass and have little or no relationship with palatability. In the absence of cues about eating quality, consumers select beef according to the redness of the meat (Mannion et al., 2000), which has little correlation with tenderness or juiciness.

There is considerable variation in quality, particularly tenderness at point of sale even for relatively homogeneous groups of animals and consistent post slaughter handling (Maher et al., 2004). A negative experience will affect a consumer’s willingness to purchase beef from the same source. The palatability of beef is a function of production, cut, processing, value adding and cooking method used to prepare the meat for consumption (Thompson, 2002). Increasing consumer confidence in the palatability of beef therefore requires all links in the meat production chain to work together to consistently produce beef with good palatability. This can be done by having blueprints for all sections of the industry to follow. In Australia the industry representative body, Meat and Livestock Australia, went a step further and developed a model, the MSA grading model, which predicts palatability of individual cuts from all the live animal and post slaughter factors that are known to affect it.

The voluntary MSA grading has been implemented in Australia for many years and its usage is increasing annually. The model was devised using Australian consumers rating the palatability of Australian beef samples and is based on a very large database covering all the important live animal and post slaughter factors (Polkinghorne et al., 2008). If such a model could be applied to Irish beef and Irish consumers it would offer the Irish industry the possibility of marketing beef of guaranteed eating quality. A project was therefore undertaken to test the model on Irish beef and Irish consumers and to check how well the model accounted for certain factors that are important to the Irish industry, since it is well known that there are differences between the Australian and Irish industries in the breeds and feeding systems used and in some of the post slaughter practices.

To fulfil the objective of thoroughly testing the MSA model in an Irish context, a series of experiments were carried out. Firstly a comparative study of Irish and Australian beef and consumers was completed then experiments were undertaken to test the effect of a range of post slaughter factors on predicted palatability scores.

 

I. TESTING THE MSA MODEL ON IRISH BEEF AND IRISH CONSUMERS

Samples from five muscles were taken from 18 Irish heifer carcasses and frozen. Samples from the same cuts from Australian animals matched as closely as possible to the Irish heifers for breed type, weight and age were frozen and shipped to Teagasc, Ashtown. The Irish and Australian beef samples were grilled or roasted and tasted by Irish consumers according to the MSA protocols. Consumers scored each sample (0-100) for tenderness, juiciness, flavour and overall acceptability and rated each sample as “unsatisfactory” (2-star), “good everyday eating quality” (3-star), “better than everyday eating quality” (4-star) or “premium eating quality” (5-star). Figure 1 shows the percentage falling into these quality categories for each cut. Not surprisingly, most of the fillet samples were rated as either 4-star or 5-star and most of the round samples were either 2-star or 3-star. The striploin samples were almost equally distributed across the quality categories which is a cause for concern, given that this is one of the most popular steaks with consumers.

The scores for the individual attributes were converted to overall meat quality scores (MQS, 0-100) using MSA weightings. These were then compared with the scores predicted by the MSA model. The results (Table 1) show how well the model works for Irish beef and Irish consumers.

For all attributes there was a wide range of scores and a mean score between 55 and 59%. The mean deviations of the actual scores from those predicted by the model (MQSDIFF) ranged from -2.1 for roasted rump samples to 12.3 for grilled rump samples. The latter suggests the model has a positive bias for this cut x cooking method combination (i.e. model predicts higher scores than the actual scores), though for all other cut x cooking method combinations and for all samples combined (see Table 1) the mean deviations were not different from zero, suggesting no bias.

Table 1: Summary statistics for meat quality attributes for a homogenous group of heifers (All samples, n=103)

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Figure 1: Percentage of different cuts falling into each quality category

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II. TESTING THE MODEL ON A COMMERCIAL SAMPLE

Three cuts (striploin, rump and topside) were taken from 16 steers varying in breed, weight, conformation and fatness slaughtered under factory conditions and prepared according to MSA guidelines. The samples were grilled and presented to consumers for assessment following the MSA protocols. The actual scores were compared with those predicted by the MSA model. These predicted scores proved to be a more conservative estimate of meat quality than the actual consumer scores for the striploin, rump and topside. For all three muscles the actual score was higher than the predicted score (Table 2). For the striploin the underestimation was greater than for the other two cuts (15% vs 11%).

Table 2: Actual and predicted scores for grilled samples of three cuts from commercial steers

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III. TESTING FACTORS IN THE MODEL

III.1. Effect of low voltage stimulation (LVES) and ageing on goodness of fit of the model

Low voltage stimulation had no effect on the MQS for any muscle. Ageing improved the MQS for all muscles. Mean deviations of actual Irish consumer scores from those predicted by the model are shown in Table 3 for carcasses that were either simulated or not and aged for 14 or 28 days. Deviations were large (greater than 10 units) for non-stimulated 14 day aged grilled outside round with the model underestimating the consumer scores for non-stimulated samples at both ageing times. This resulted in a significant effect of ageing time on the goodness of fit of the model.  The effect of stimulation on the goodness of fit of the model was non-significant.

Table 3: Mean differences between actual and predicted MQS for four grilled cuts at two ageing times and for stimulated (LVES) or non-stimulated carcasses (NON)

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III.2. Effect of sex, breed and high voltage stimulation (HVES) on goodness of fit of the model

HVES improved the MQS of the striploin but not for other cuts. Sex did not affect MQS of any muscles. The only effect of breed on MQS was a higher score for eye of round samples from Charolais carcasses. This was unaccounted for by the model, resulting in a significant deviation in the MQS of 10.4. There was also a significant deviation for the MQS score of non-stimulated striploin samples, though this was only 4.81. The model accounted quite well for the effects of sex (heifers v steers).

Table 4: Mean differences between actual and predicted MQS for three cuts from two breeds and two sexes

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III.3. Effect of hanging method and low voltage stimulation (LVES) on goodness of fit of the model

Aitch bone hanging improved the MQS for the striploin but not for the topside or eye of round cuts. LVES improved the MQS only for the eye of round. The largest deviation of the actual consumer scores from those predicted by the model was for the stimulated aitch bone hung samples, although this was not significant. The effect of hanging method was accounted for well by the model for all muscles while the stimulation effect on the goodness of fit of the model was significant only for the eye of round.

Table 5: Mean differences between actual and predicted MQS for three cuts from stimulated and non-stimulated carcasses hung by the Achilles tendon or the aitch bone

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OVERALL CONCLUSIONS

The MSA palatability model predicted Irish consumer scores of Irish beef at least as well as Australian consumer scores of Australian beef. Irish consumers seem to score beef in a similar way to Australian consumers, though there were some differences in the relative importance of tenderness and juiciness. In general the model accounted for the main factors that are known to affect meat quality and are commonly used by Irish processors but there were some significant deviations which suggest that the model could be optimised for use in the Irish industry. The Irish industry could use the model to sort carcasses and cuts into quality classes thereby reducing the variability within classes and allowing for a quality guarantee to consumers. There is evidence that consumers are willing to pay more for better quality beef (Lyford et al., 2010). The MSA grading model could also be used as a management tool, for instance to identify carcasses or cuts that would benefit from longer ageing times. The model has also been tested in Northern Ireland, France and will soon be tested in Poland, raising the possibility of the databases being combined to generate a European model for predicting palatability.

 

References:

Maher S.C., Mullen A.M., Moloney A.P., Buckely D.J., Kerry J.P. (2004). Quantifying the extent of variation in the eating quality traits of the M. longissimus dorsi and M. semimembranosus of conventionally processed Irish beef. Meat Science, 66, 351-360.
Lyford C. Thompson J. M., Polkinghorne R., Miller M., Nishimura T. Neath K., Allen P., Belasco E. (2010). Is willingness to pay (WTP) for beef quality grades affected by consumer demographics and meat consumption preferences?. Australian Agribusiness Review, 18, 1-17.
Mannion M., Cowan C., Gannon M. (2000). Factors associated with perceived quality influencing beef consumption in Ireland. British Food Journal, 102, 195-210.
Polkinghorne R., Thompson J. M., Watson R., Gee A., Porter M. (2008). Evolution of the Meat Standards Australia Model (MSA) beef grading system. Australian Journal of experimental Agriculture, 48, 1351-1359.
Thompson J. (2002). Managing meat tenderness. Meat Science. 62, 295-308.

 

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