Abstract:
153 Does nutrition affect the eating quality of beef? D. Perry1, A.F. Egan2, D.M. Ferguson3, V.H. Oddy1 and J.M. Thompson2 1 2 3 CRC for the Cattle and Beef Industry, NSW Agriculture, Armidale NSW 2351 Animal Science, University of New England, Armidale NSW 2351 Food Science Australia, Brisbane Qld 4170 Summary In this paper we have discussed the results of two major studies of the effect of finishing nutrition on the quality of beef, and the relationship between marbling and palatability as determined by Australian consumers in testing by Meat Standards Australia. Grain finishing of cattle resulted in a small but consistent increase in both tenderness, measured objectively, and palatability. Increasing intramuscular fat content increased the probability of a higher MSA grade, as assessed by consumers, which in turn was correlated with increased juiciness and/or flavour, rather than with tenderness. from consumer research conducted by Meat Standards Australia (MSA). Material and methods The core cattle project of the Beef CRC The data presented in this paper come from the straightbreeding program, which has been described in detail by Robinson (1995). Briefly, it involved purebred Angus, Hereford, Shorthorn, Murray Grey, Brahman, Belmont Red and Santa Gertrudis steers and heifers which, after weaning, were grown out (backgrounded) on pasture prior to finishing on either pasture or in a feedlot. The British breed animals were all backgrounded and finished on the New England Tablelands of NSW. Animals from the tropically adapted breeds were born in Queensland and, postweaning, divided into two groups within sire, one of which was backgrounded and finished in Queensland (northern) and the other on the New England Tablelands (southern). Cattle from both pasture and feedlot finishing regimens, from both environments, were grown out to three slaughter weights (400 kg, 520 kg, and 600 kg) to produce carcases suitable for the domestic, Korean and Japanese markets, respectively. In an attempt to minimise preslaughter stress cattle were not handled for 3 days prior to trucking. Cattle were slaughtered through commercial abattoirs and most carcases were electrically stimulated using low or high voltage. The tenderness of the meat was assessed objectively by measuring the Warner Bratzler shear force (peak force) and the compression values on cooked samples from the striploin (M. longissimus dorsi, LD) at 1 day postmortem (Bouton et al. 1972). Intramuscular fat percent was measured in the LD of northern animals by solvent extraction (AOAC 1990), and in southern animals by near infrared spectrophotometry using a prediction equation based on solvent extraction. Comparison of the two methods showed no consistent bias. Introduction Consumer studies have clearly identified consistency of eating quality of beef as a problem in Australia. In this regard tenderness, and its effect on overall palatability, is the major factor in consumer dissatisfaction, although juiciness and flavour also contribute to palatability. The nutritional and environmental history of an animal may have an important impact on the intrinsic eating quality of the meat. This can be a direct effect on the muscle tissue, for example on the connective tissue matrix. It can also result from differences in intramuscular fat content which is an important trait that is affected by grain versus pasture finishing, the level of nutrition and by the age of an animal at a particular slaughter weight. Intramuscular fat content (marbling) is important in the beef grading schemes of both Japan and the USA (USDA 1989). Under adverse environmental conditions these effects may be accentuated. The contrast between finishing cattle on extensive pasture systems and finishing cattle in a feedlot using a grain based ration, is an example of differing environments which might affect intrinsic meat quality. This paper presents data on the tenderness and palatability of grain vs. pasture fed beef, derived from the research program of the Cooperative Research Centre for the Cattle and Beef Industry (Beef CRC) and Recent Advances in Animal Nutrition in Australia, Volume 12 (1999) 154 Perry, D. et al. The effect of nutrition during the finishing phase of growth on the objective tenderness (peak force and compression) and intramuscular fat percentage of the LD was tested using a model with stimulation, finishing regimen, market, breed, location and the interactions between feed, market category, location, and breed fitted as fixed effects. Sire, herd of origin and kill (within market, location and feed) were fitted as random effects. Non significant interactions (P>0.05) and age at slaughter if P>0.05 were sequentially deleted. The analyses for both the measures of tenderness were run with and without the intramuscular fat percentage of the LD as a covariate, to test the effect of intramuscular fat on any relationship between the fixed effects and tenderness. Data were available for 4126 animals. These analyses were repeated on the data available from the subset of animals tested by MSA. score with the distribution of animals between the MSA palatability grades, as assessed by the consumer taste panels, and between AUSMEAT marbling scores and the sensory dimensions for tenderness, juiciness and flavour within the MSA grades. Results The effect of finishing nutrition on tenderness and intramuscular fat Figure 1 shows least square means for compression for grain and pasture finishing regimens, within market category, adjusted for breed, location (northern vs. southern), sire, herd of origin and day of kill (within market, location and feed). At each market weight the animals finished on grain had 0.19 (� 0.03) kg lower mean values for compression (were more tender) than those finished on pasture (P <0.001). Table 1 presents least square means for tenderness measurements and chemical fat percentage for each feed x location sub group, adjusted for stimulation, breed, market, sire and kill within finish, market and location. Grain finished animals had 0.30 (� 0.12) kg lower peak force and 0.19 (� 0.04) kg lower compression values than equivalent animals finished on pasture (P<0.05). Peak force and compression measurements for northern finished cattle were higher than for those finished in the south (P<0.001). Within market category, age at slaughter significantly affected peak force (P<0.05) but not compression (P>0.05). The magnitude of the age effect was small (0.1kg per 100 days of age), but it reduced the significance of the feed effect from 0.009 (Table 1) to 0.08, and the magnitude of the effect to 0.2 kg (� 0.12). Age at slaughter did not alter the effect of feed and location on compression. When adjusted for intramuscular fat percentage, the magnitude of the difference between pasture and grain finished animals was reduced to 0.16 kg (P<0.001) for compression and 0.21 kg (P>0.05) for shear force. Intramuscular fat itself was 1 � 0.117 % higher in grain fed compared to pasture fed carcases (P<0.001). Meat Standards Australia The palatability of the meat from a subset of the animals, from both feeding regimens and both locations described above, has been determined using the consumer testing protocol developed by Meat Standards Australia (Polkinghorne et al. 1999). The data presented here are for striploins aged for 14 days and grilled according to standard MSA procedures. For each animal a total of 10 consumers were asked to evaluate the tenderness, juiciness and flavour and overall liking of cooked steaks , using a 100point scale for each attribute. These results were then combined into a single meat quality score using weightings of 0.4, 0.1, 0.2 and 0.3 for tenderness, juiciness, flavour and overall liking, respectively. The 10 consumer scores were then clipped of the highest and lowest 20% and averaged to produce a CMQ4 score, where the higher the score the more palatable the meat. The effect of nutrition during the finishing phase of growth on this CMQ4 score was analysed as described above for objective measurements. Using data on grilled striploins from the MSA database (Polkinghorne et al.1999), which includes commercial as well as CRC animals, separate analyses were done on the association of AUSMEAT marbling 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 D K M arket category Grain Pasture Compression (kg) J Figure 1 Compression least square means (kg) for pasture vs. grain finished animals, within D (Domestic), K (Korean) and J (Japanese) market categories. Does nutrition affect the eating quality of beef? 155 Compression values decreased by 0.03 kg and peak force decreased by 0.09 kg for each increase of 1% in intramuscular fat (P<0.001). The above analyses were repeated on the subset of animals tested using consumer taste panels by MSA. Table 2 shows predicted means for palatability and chemical fat for this subset of animals tested (n = 1373), adjusted for the same terms as the data in Table 1. There was no significant effect of finishing regimen (grain vs. pasture) on peak force (P>0.05), but there was a difference between peak force measurements from northern and southern animals (P<0.05). With compression the reverse was the case. Pasture fed animals had higher compression values (tougher) than grain fed animals (P<0.001), with northern and southern finished animals having similar values within each feeding regimen (P>0.05). This effect of feed on compression was similar to that found in the larger data set. Age at slaughter within market had an effect on compression but not on peak force. However the magnitude of the effect was small (0.01 kg per 100 days Table 1 increase in age) and adjusting for age had no effect on the significance levels of either feed or location on compression. The objective measurements refer to samples which were tested one day postmortem whilst the sensory results refer to samples tested after ageing these samples for 14 days. Therefore the latter includes effects for the inherent tenderness of the sample, plus the changes that occurred during ageing. The palatability scores (CMQ4) were lower for pasture fed animals than grain fed animals when they were finished in the north, but there was no difference for those finished in the south. This pattern was similar irrespective of whether the measurements were adjusted for chemical fat. For every 100 days increase in age at slaughter the CMQ4 decreased by 0.5 (P<0.05). If not adjusted for age within market category, the interaction between feed and location was not significant (P = 0.075). Animals finished in the south had higher palatability scores than those finished in the north. Peak force, compression and chemical fat in the striploin for cattle finished on pasture or grain in two environments (n = 4126). Location Northern Southern Significance (P) Feed effect Location effect Peak force (kg) Grain Pasture Compression (kg) Grain Pasture Chemical fat (%) Grain Pasture 3.85 � 0.301 2.92 � 0.373 4.67 � 0.192 3.48 � 0.214 0.001 NS 1.72 � 0.079 1.98 � 0.095 1.56 � 0.042 1.73 � 0.051 0.001 0.03 6.10 � 0.221 6.46 � 0.275 3.34 � 0.144 3.66 � 0.159 0.009 0.001 Table 2 Objective tenderness, palatability (CMQ4 score) and chemical fat determinations of meat from the LD muscle for the subset of cattle tested by MSA (n = 1373). Location Northern Southern Feed effect Significance (P) Location effect Feed x location effect Peak force (kg) Grain Pasture Compression (kg) Grain Pasture CMQ4 Grain Pasture Chemical fat (%) Grain Pasture 3.63 � 0.232 3.10 � 0.303 3.78 � 0.163 2.80 � 0.294 NS 0.001 NS 52.10 � 2.06 46.30 � 1.40 59.30 � 2.67 61.10 � 2.41 NS 0.001 0.001 1.67 � 0.023 1.85 � 0.030 1.67 � 0.016 1.80 � 0.027 0.001 NS NS 5.89 � 0.427 6.51 � 0.598 4.54 � 0.310 4.74 � 0.597 NS 0.02 NS 156 Perry, D. et al. The effect of marbling on palatability MSA consumer research has provided data on the role of marbling fat in the palatability of beef as evaluated by Australian consumers. Table 3 shows the effect of AUSMEAT marbling score on the distribution of animals between the MSA grades as assessed by the consumer taste panels. The meat was from low Bos indicus content carcases which had been hung by the Achilles tendon and aged for 14 days prior to cooking as a grill and served to consumers. A higher marbling score increased the probability of a striploin being assessed as being in a higher grade (CMQ4 score was increased). Table 4 shows correlations between marbling score and the sensory attributes of steaks from the striploin, within the different MSA grades. There appeared to be no relationship with tenderness but the correlation coefficients between marbling and both juiciness and flavour increased from nograde to the 5star category. Discussion The results of the CRC program show that, as determined by objective measurements on 4126 animals, the meat of cattle finished on grain was slightly but significantly more tender than that of equivalent animals finished on pasture. This effect could have been caused by an increase in intramuscular fat content, a direct effect of diet on the muscle tissue, or to a combination of both. However the difference in intramuscular fat for the two Table 3 The effect of marbling score on the distribution of animals between the MSA grades assigned by the consumer taste panels. AUS_MEAT marbling score MSA Grade 5_star 4_star 3_star No grade 0 2 23 39 37 1 5 32 42 21 2 8 56 27 9 3 20 53 13 13 finishing regimens did not account for all of the pasture versus grain effect on shear force, and had little impact on compression values. Published studies suggest a direct effect on connective tissue, whereby feeding highenerg y, intensive, diets increases the solubility during cooking of heatlabile connective tissue (Miller 1994). If this were so, differences in compression values (which largely reflect the connective tissue component of meat toughness) between feeding regimens should be consistent within environments. This was the case in this study. It should also be kept in mind that the two different feeding regimens almost certainly result in differences in growth rate, particularly when pasture conditions are poor, which may in turn affect the structure of collagen within muscles, and the relationship between the connective tissue matrix and the myofibres. This in turn would affect meat tenderness. This may explain the significant effect of location of finishing on tenderness, with the meat from animals finished in the south being more tender than that of animals finished in the north. Consumers also found southern finished beef more palatable than northern finished product when assessing 14 day aged LD steaks. However they distinguished between grain and grass finished product only in northern finished animals, where the difference between growth rates on pasture and grain could be expected to be greater than in the more benign southern environment. In this smaller data set the difference between compression values for northern and southern finished animals, evident in the larger data set, was not apparent, but the difference in compression between grain and grass finishing systems was similar for both locations. The relationship between intramuscular fat content and tenderness has been widely studied but no consistent relationship has been established. Its role in the palatability of meat has been discussed by Savell and Cross (1988) and Miller (1994). Most studies have been done in the USA and these show that increasing marbling decreases the variability in the palatability of beef. At the marbling scores found in Australian product (AUSMEAT score 03, intramuscular fat below 7%), intramuscular fat content probably explains only a minor proportion of the variation in tenderness. The MSA data presented here show that as marbling increased the palatability of the meat increased, although even at the higher levels of marbling approximately ten percent Table 4 Correlations between AUS_MEAT marbling score and consumer sensory score, within MSA grades, for grilled striploin steaks aged for 14 days. Sensory attribute MSA Grade 5-star 4-star 3-star No grade Tenderness _ 0.18 0.02 0.04 0.08 Juiciness 0.36 0.20 0.12 0.09 Flavour 0.24 0.20 0.11 0.09 No. of cattle 167 1322 1646 1007 Does nutrition affect the eating quality of beef? 157 of the steaks tested failed to grade as satisfactory. Therefore whilst marbling improves palatability it is not a guarantee, and a proportion of failures can still occur. The MSA data also show that as MSA grade increased the correlation between marbling and the meat quality attributes of juiciness and flavour increased, but that between marbling and tenderness remained close to zero. These studies show small but consistent benefits in improved tenderness and increased palatability result from grain finishing, especially if the pasture finishing alternative were under adverse conditions. However it is not possible to say whether the benefits were due directly to difference in feed and its effect on intramuscular fat or muscle structure, or a consequence of other changes induced by differences in feed, such as higher or consistent growth rates. The effect of age within market category on tenderness traits was not consistent between the data sets studied here and did not account for all of the feed or location effects. The effect of growth path on meat quality is being investigated by the CRC, but it is not a simple question. Overall growth rate from birth to slaughter must be compared with growth rates and set backs during distinct periods of an animals growth path, such as during the periods of pre and postweaning, backgrounding and finishing. 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Agriculture Marketing Service, USDA, Washington D.C. 158 Perry, D. et al.