ReviewColour of bovine subcutaneous adipose tissue: A review of contributory factors, associations with carcass and meat quality and its potential utility in authentication of dietary history
Introduction
The colour of bovine subcutaneous (sc) adipose tissue (carcass fat) is an important component of beef carcass quality (Wood & Fisher, 1997) and thus, beef carcass grading systems (Walker et al., 1990, Price, 1995, UNECE, 2004), in the United States, Canada, Australia and Japan. This is due to the variability of bovine carcass fat colour, allied to the consumer expectation of consistency in the colour of bovine fat, if present on retail cuts (Price, 1995). Crouse, Cross, and Seideman (1984) stated that in the United States, the colour of both lean and fat were becoming increasingly important in quality grading, a phenomenon that was a reflection of consumer tastes. In a recent survey of 900 individuals in Japan, Korea, Taiwan, Hong Kong and Mexico, it was reported that 80% of respondents favoured beef with white or light amber coloured fat (Anonymous, 2007). In most beef markets, excessive yellowness in bovine carcass fat colour is undesirable (Walker et al., 1990; Yang, Larsen, & Tume, 1992) and may incite a good deal of consumer purchase resistance, commensurate with a perception that yellow colour in this tissue necessarily indicates that an animal was in a diseased state at the time of slaughter (Anonymous, 1993). Negative perceptions of the quality of meat from carcasses with yellow fat also abound, with a widespread belief that carcasses with such fat necessarily come from older animals and hence, produce less tender meat (Anonymous, 1993).
Beef production systems represent the combined and interacting effects of genotype, gender, age at slaughter and nutrition before slaughter (Moloney, Mooney, Kerry, & Troy, 2001b). Since feed costs are a major component of total variable costs in beef production systems, the temperate maritime climate in much of North-Western Europe, Britain and Ireland, conducive to pasture production and utilisation (Lee, 1988) ensures that grazed and conserved grass is an important source of feed for ruminants, including cattle, as it represents a renewable and relatively cheap source of feed (O’Riordan and O’Kiely, 1996). Pasture-based beef production is also commonplace in countries such as New Zealand (West et al., 1997) , Australia (Lanari, Rablin, Brewster, Yang, & Tume, 2000), Mexico (Izaguirre & Miyasaka, 2001) and Argentina (Pensel et al., 2000; Gómez & Rosso, 2002). In contrast, in regions such as southern Europe, where permanent grasslands are subject to severe moisture stress (Lee, 1988), cattle production does not rely to such a large extent on grass as a source of feed (Gigli & Iacurto, 1995).
Cattle produced in such diverse situations exhibit contrasting carcass fat colour. Consumer perceptions of what constitutes a ‘normal’ carcass fat colour may reflect regional variation in beef production practices. Consumers in Mediterranean Europe perceive beef that has ‘white’ or ‘pale’ adipose tissue to be of superior quality (Anonymous, 1999), a perception that is replicated in beef markets of North-East Asia (Morris et al., 1997, Barton and Pleasants, 1993), including Japan (Muramoto, Nakanishi, Shibata, & Aikawa, 2003) as well as the United States (Wood & Fisher, 1997).
However, yellow fat is positively associated with traditional, grass-based beef production (Wood & Fisher, 1997) and is perceived as a positive quality criterion which is more “ecologically favourable” and can influence consumer purchase decisions (Schwarz, Augustini, & Kirchgessner, 1997). Healthy cattle that are reared on pasture or which consume green leafy forage accumulate carotenoids in their adipose tissue which results in the tissue acquiring a yellow colour (Morgan and Everitt, 1969, Yang et al., 1992, Strachan et al., 1993). It is widely accepted that grass feeding can impart positive and beneficial effects on beef quality from a nutritional perspective, particularly in relation to the fatty acid profile (French et al., 2000b; Moloney et al., 2001b) and antioxidant content, with the latter also improving certain aspects of meat quality (Wood & Enser, 1997). In this regard, potential exists for using fat colour or carotenoid concentration as an indicator of dietary history from which inferences regarding nutritional and meat quality can be drawn and authentication of grass-feeding accomplished (Priolo, Prache, Micol, & Agabriel, 2002; Prache et al., 2002).
Management strategies to reduce carotenoid concentrations and thus yellow colour in bovine sc adipose tissue, in line with consumer expectations in certain markets, have employed use of grain-finishing of pasture-reared cattle (Forrest, 1981; Strachan et al., 1993; Morris et al., 1997). However, although several sources of variation in colour of bovine carcass fat are known, limited definitive information is available regarding the underlying mechanisms that control changes in this aspect of adipose tissue appearance and quality. Hence, this review aims to summarise current knowledge regarding (i) factors that affect bovine carcass fat colour, (ii) strategies to reduce yellow colour, (iii) associations between carcass fat colour and meat quality, to acknowledge the potential valuable role that carcass fat colour could play in authentication of beef.
Section snippets
Effects of production system and management practices on bovine fat colour
Beef production systems depend on climatological and socio-economic factors which frequently dictate management practices and decisions, and thus are a composite of combined and interacting factors that relate intrinsically to the biology of the bovine such as its breed, gender, age at slaughter and carcass weight and fatness as well as extrinsic nutritional and environmental factors. Many of these factors will be discussed individually in the present review.
Several studies have been conducted
Intrinsic biological factors that affect bovine carcass fat colour
Fat colour in the bovine is influenced by many intrinsic factors which include breed, gender and age (Table 1). Moreover, differences exist between ruminant species such as cattle and sheep with respect to their ability to absorb and deposit carotenoids, with consequent effects on carcass fat colour. Goodwin (1954) categorised mammals on the basis of their ability to selectively absorb carotenoids. Group (a) mammals accumulate carotenes and xanthophylls in their adipose tissue without
Carotenoid chemistry, structure and physiological purpose in plants
Fresh and conserved pasture swards and other green forages contain chemical compounds called carotenoids that cause yellow colour to develop in the fat of bovines when such forages are eaten regularly. The main pigment responsible is β-carotene, and to a lesser extent lutein (Morgan & Everitt, 1968; Strachan et al., 1993).The carotenoids are a family of chemical compounds which possess a variety of distinctive yellow and orange colours. Chemically, they are classified as tetraterpenoids, with
Stability of carotenoids in the rumen
While reviewing carotenoids for ruminants, Nozière et al. (2006) commented that the extent of carotenoid degradation by microorganisms in the rumen remains uncertain because of the varying results, mostly with β-carotene, from both in vivo and in vitro studies and most likely attributable to the form in which carotenoids were delivered, whether in purified form or in forages. Several anomalous observations emerge from the study conducted by Yang et al. (1992). Firstly, cattle had the highest
Underlying mechanisms and factors affecting colour changes in bovine sc adipose tissue
Having considered the compounds that are responsible for colour in bovine sc adipose tissue, their basic chemistry, origins, and challenges that they may face in the pre-absorption environment of the rumen, a further discussion of actual and hypothetical mechanisms contributing to changes, especially reductions, in bovine sc adipose tissue colour could be reinforced by consideration of current knowledge regarding the nature of this tissue, the dynamic changes it undergoes as well as the nature
Nutritional effects on fatty acids and antioxidant profiles of beef
Meat quality encompasses appearance, eating (sensory) quality and also nutritional quality. Bovine diet and nutritional effects influence fat colour but also affect aspects of meat quality. There remains a perception that beef is a ‘high fat’ food with a high proportion of saturated fatty acids (SFA) (Moloney et al., 2001b). However, due to improved breeding, management and butchery techniques over recent decades the fat content of beef is frequently 5% or less and less than half of the fatty
Conclusions
It is likely that the optimum finishing time on grain will be influenced by local perceptions of what constitutes an ‘acceptable’ colour. The length of time required to achieve an acceptable carcass fat colour, whatever that might be, is likely to depend on the age, gender and genotype of the animals, the extent of yellow colour prior to grain feeding, the rate of turnover of carotenoids in adipose tissue (although it is not known whether this occurs) and critically also the diet.
The amount of
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