Sources of variation in subcutaneous fat colour of beef carcasses.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 18 SOURCES OF VARIATION IN SUBCUTANEOUS FAT COLOUR OF BEEF CARCASSES P.J. WALKER*, R.D. WARNER** and C.G. WINFIELD** SUMMARY Yellow fat in beef carcasses incurs price penalties in many domestic and export markets. Sources of variation in subcutaneous fat colour of beef carcasses was investigated by objective measurements on 622 carcasses of various classes of Fat colour was subjectively assessed using a six point photographic cattle. colour chart . The majority of carcasses sampled (80.6%) had creamy-white to cream fat. The objective measurement of the yellowness of the subcutaneous fat (b* value) explained 46% of variation in subjective fat colour scores (r *=0.46, r.s.d.=5.35; P<O.OOl). Multiple regression analysis of the results for British breeds of cattle showed significant effects of nutrition, age and sex and interactions between sex x age and age x hot carcass weight on the b* value of the subcutaneous fat (P<0.001 for all). Grassfed cattle and milk vealers had The subcutaneous fat of female cattle was yellower fat than feedlot cattle. Aged cattle (8 yellower than that of steers across all age categories. Breed also influenced the b* value of permanent incisors) had yellower fat. the subcutaneous fat (P<O.OOl) - dairy cattle breeds had yellower fat than British and European breeds. INTRODUCTION One of the most important characteristics of beef to consumers is its appearance (Naumann et al. 1966) and fat colour is an important parameter. Yellow fat in beef carcasses is less acceptable for both the domestic and export markets than whiter fat and generally such carcasses are sold on the lower priced, manufacturing beef market. The Japanese market in particular Factors affecting specifies a requirement for white fat in Australian beef. fat colour include diet, inheritance, age, carcass fat depot, chilling regime and processing technique (Morgan and Everitt 1969). Yellowness of fat is due to the presence of carotenoid pigments within adipocytes or to certain diseases. Beta-carotene, a major precursor of vitamin A, is the main contributing carotenoid pigment in beef fat although trace amounts of alpha-carotene and The greater the concentration of xanthophylls have also been found. carotenoids in the fat, the more intense is the yellow colouring (Morgan and Everitt 1969). Many studies of fat colour have used subjective assessment of fat colour or laboratory methods to measure carotenoid concentration in a sample of excised Advances in the technology of colour instruments have recently produced fat. portable reflectance chromameters which measure in the three dimensional CIEL*a*b* colour space as recommended by CIE (1978). L* represents the surface lightness/darkness, a*, the redness/greenness and b*, the yellowness/blueness. Thus, the b*- value is considered the ideal objective measurement of the yellowness of a fat surface. The aim of measurement sources of Australian this project was to quantify the relationship between objective and subjective assessment of fat colour and also to investigate the variation in subcutaneous fat colour of beef carcasses processed in abattoirs. * 'Rosevale', RMB A493, Learmonth, Vic. 3350. ** Animal Research Institute, Dept. of Agriculture & Rural Affairs, Werribee, Vic. 3030, 416 Proc. Aust. Soc. Anim. Prod. Vol. 18 MATERIALS AND ME!I!HODS Data was collected from 622 beef carcasses over the autumn/winter period during eleven visits to five Victorian abattoirs which ranged from small domestic meatworks to large export works. Measurements of subcutaneous fat colour were taken in the CIE-L*a*b* colour space using a Minolta CR200 chromameter at the Triplicate P8 site, the site used for fat depth measurement (AUS-MEAT 1987). measurements were taken on the hot carcass following the carcass wash and the average recorded. All data analyses used b* values as it is known to measure All carcasses were given a subjective fat colour score using the yellowness. 6-point photographic colour chart developed in Western Australia (Paul Frapple Areas of fat exhibiting blood per-s. comm.) where &white and 6=very yellow. splash, bruising or air bubbles and carcasses with a fat depth less than three millimetres at the P8 site were excluded from measurement. Carcasses were chosen from abattoir consignments of cattle to ensure the following four nutritional groups were represented in the sample; domestic feedlot beef (70 - 100 days on grain, destined for domestic market), export feedlot beef (greater than 100 days on grain, destined for Japanese market), grassfed beef (off autumn/winter pastures of southern Australia) and milk Breed was vealers. Breed, weight, sex, and dentition were also recorded, assessed visually prior to removal of the hide and classed as either British beef breeds and their crosses (Br), Channel Island dairy breeds and their crosses VW I other dairy breeds and their crosses excluding Channel Island breeds (OD) or European beef breeds and their crosses with British beef breeds Dentition categories were recorded as an estimate of th age of the animal and were consistent with AUS-MEAT definitions as follows; no permanent incisors with four or less mandibular molars (O/4), no permanent incisors and five mandibular molars (O/5), one to seven permanent incisors (l-7) and eight permanent incisors (8). w l Linear regression was used to analyse the relationship between the subjective fat colour scores and objective measurements of b* values. The majority of carcasses sampled were British breeds, thus a stepwise multiple regression was performed on the b* values to assess the effects of breed, dentition, sex, hot carcass weight and nutritional background and the interactions for this subset The effect of breed on b* value was analysed using multiple of data. regression on the full data set. RESULTS Approximately equal numbers of castrates (51.3%) and females (48.7%) were surveyed and most of the cattle (87%) were British breeds. Pasture fed cattle (63.2% of total) were represented in all dentition categories and hot carcass weights were predominantly in the range of 190-250 kg. Some confounding occurred in the sample between categories as follows; many older male cattle and cattle on grain for more than 100 days had carcasses with hot weights in excess of 300 kg, most carcasses in dentition category 8 were female while most carcasses in dentition category l-7 were male, domestic feedlot cattle were all in dentition category O/5 whereas the export feedlot cattle were in dentition category O/5 or l-7 and milk vealers were only represented in dentition category O/4. This confounding is typical of the categories of cattle slaughtered in Victoria, thus, although the analysis must be reported carefully, the results remain meaningful. The mean b* value the subjective fat (80.6%) fell into few carcasses had (Table 1). was 11.24 (S*-51.59) and explained 46% of the variation in colour scores (r* = 0.46 P<O,OOl; Table 1). Most carcasses fat colour scores 2 and 3 (creamy-white to cream) and very a fat colour score of 5 or more (yellow to very yellow) The multiple regression analysis of the b* value for British breeds of cattle 417 Proc. Aust. Soc. Anim, Prod. Vol. 18 showed significant effects of nutritional category, dentition, sex and the interactions hot carcass weight x dentition and sex x dentition (P<O.OOl for The model accounted for 63% (r*) of the variation in fat yellowness. all). The regression coefficient of b* value on hot carcass weight (kg), was 0.05 In addition, breed had a significant effect on the b* value (8-e. = 0.02). (P<O.OOl) in the analysis of the full data set. Table 1 Mean and variance for the CIE-b* values for each fat colour score and the coefficients and standard errors for the regression equation of b* values on fat colour scores. Feedlot cattle had lower b* values than he grassfed or milk vealer categories (domestic feedlot =8-l, export feedlot =4.2, grass-fed =13.8, milk vealers =9-O). For the British breeds of cattle, predicted b* values were similar between the dentition categories O/4, O/5 and 2-7 but were higher for cattle with eight incisors for both sexes (Table 2). The mean carcass weights were lower for females for all dentition categories with significantly lower mean carcass weights for females in dentition category 8 (Table 2). The predicted b* value for female cattle was 3.0-3.1 units higher than for steers up to dentition category 2-7 whereas for cattle in dentition category 8, the difference was only 1.0 unit (Table 2). For dentition category 2-7, the b* value of dairy breeds of cattle was higher than for the British breeds or European breeds (Br = 8.5, CI = 17.4, OD = 15.1, E = 11.5) and for cattle in dentition category 8, the differences between breeds were similar although the b* value was higher (Br= 20.7, CI= 28.1, OD= 24.1, E= 11.1). Table 2 Predicted b* values, mean hot carcass weight (HCW) and number of carcasses (n) for the interaction between sex and dentition categories for British breeds. This study provides new objective information on the range in subcutaneous fat colour of beef carcasses from grass-fed and grain-fed cattle and milk vealers 418 Proc. Aust. Soc. Anim. Prod. Vol. 18 slaughtered in Victoria during that the majority of carcasses fat or fat colour scores 2 and carcasses with scores 1-3 (b* = l-2 (b* = l-11), most carcasses the autumn/winter period. The results showed sampled had relatively creamy-white to creamy 3 (b*= 3-15). As the domestic market accepts 1-18) and.the Japanese market accepts scores of would not have been discounted for fat colour. The amount of variation in the subjective assessment of subcutaneous fat colour score, which was explained by objective measurement, was lower than expected This could have been caused by inaccuracies in the subjective W2 = 0.46). Murray et al. (1989) reported a high colour assessment system used. correlation (r = 0.96) between chromameter measurements and subjective meatcolour using a 5-point scale. Most of the carcasses having extremely yellow fat occured in aged cattle of the dairy breeds as findings in other studies have shown (Morgan et al. 1969). This study does indicate the presence of very yellow fat in aged cattle as evidenced by the fat colour of Channel Island, British and other dairy breeds with 8 Female cattle had yellower fat than castrates for the permanent incisors. British breed cattle across all dentition categories which disagrees with Morgan et al. (1969) who found negligible fat colour difference between sexes. The effect of feeding grain, for finishing cattle, has been reported to reduce yellow colour in the fat as a result of the low beta-carotene content of grain (Forrest 1981; Hidiroglou et al. 1987). Our results confirmed this as whiter fat was recorded in British breed cattle in the grain fed categories when compared with those of the grassfed category at the same age as indicated by dentition, Longer periods of grain feeding have been shown to cause continual reduction in yellow fat colour (Dinius and Cross 1978) up to at least 112 days in the feedlot (Forrest 1981). This effect was noted in the whiter fat of export feedlot cattle (in the feedlot for more than 100 days) compared with domestic feedlot cattle, The potential for reducing the yellowness of beef fat through dietary manipulation in the weeks/months pre-slaughter warrants further investigation under local conditions. It is particularly relevant for expanding export markets in Japan and the Pacific rim. The research was funded by AUS-MEAT and carried out in conjunction with the Victorian Department of Agriculture and Rural Affairs, The assistance of Chris Ball, Colin Boord and the abattoirs involved in the work is gratefully acknowledged. AUS-MEAT (1987). AUS-MEAT Language, July edition, p. 15. CIE (Commission Internationale d'Eclairage) (1978). Supplement no.2 to CIE publication no.15 (1971), Paris. DINIUS, D.A. and CROSS, H.R. (1978). J. Anim. Sci. 47: 1109. FORREST, R-J. (1981)Can. J. Anim. Sci. 61: 575. HIDIRIGLOU, N., MCDOUGALL L-R, and JOHNSON, D-D. (1987). Meat Sci. 20:195. 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