Meat serves as a great source of protein and essential nutrients, and as a result, the consumption of beef has been steadily increasing. When consumers make the decision to purchase beef in the market, they primarily consider the quality of the beef, including factors such as color, marbling, texture, and freshness. Hanwoo, a native Korean breed, has been nurtured, transported, and even utilized in religious ceremonies within Korean culture for over 5,000 years (Chung et al., 2018). Korean consumers have consistently exhibited a preference for Hanwoo beef over imported beef, because of its juiciness and flavor. To control the quality of Hanwoo beef in Korea, the Korea Institute for Animal Products Quality Evaluation (KAPE) plays a crucial role in grading the quality and yield of beef before it is distributed. According to KAPE’s criteria, beef is classified into different quality grades (QG) and yield grades (YG) (Gajaweera et al., 2020). The QG of beef are determined based on the marbling score (ranging from 1 = devoid, to 9 = abundant), lean meat color (ranging from 1 = very bright red, to 7 = very dark red), fat color (ranging from 1 = creamy white, to 7 = yellow), firmness and texture of the lean meat (ranging from 1 = firm, to 5 = soft), and maturity (ranging from 1 = youthful, to 9 = mature) observed in the exposed longissimus thoracis muscle at the 13th rib interface. The lowest grade from each parameter is determined for final QG, and if the maturity score is 8 or 9, the final grade is further downgraded by one grade (Figure S1; KAPE, 2023).

Fat color, specifically the color of bovine subcutaneous adipose tissue (carcass fat), holds significant importance in beef carcass grading, not only in Korea but also in countries such as Japan, Canada, Australia, and the United States (UNECE, 2004). When purchasing beef, many consumers consider the fat color and tend to have a lower preference for beef with yellow carcass fat (Piao et al., 2015). In the grading system, carcasses with a yellowish color of carcass fat are classified as lower QG (QG 1 or 2) compared to those with creamy white fat (QG 1++ or 1+). Consequently, the lower quality grade attributed to beef with yellow carcass fat has a significant economic impact, affecting the income of beef producers in Korea and globally.

The yellow color of carcass fat can be influenced by various extrinsic and intrinsic factors, including breed, gender, age, fatness, growth rate, diet, carotene content, and supplementation (Dunne et al., 2009). In terms of intrinsic factors, older cattle tend to exhibit more yellow carcass fat, while females tend to have a yellower carcass fat color compared to steers (Dunne et al., 2009). Among the extrinsic factors, a higher concentration of carotenoids in feedstuffs such as forages and certain concentrates has been correlated with the presence of yellow carcass fat. Zhou et al. (1993) reported a positive relationship between the yellowness of carcass fat and the total carotenoid concentration in beef (r = 0.79; P < 0.01), with carotenoid concentrations ranging from 0.2 to 1.4 μg/g in beef corresponding to Commission Internationale de l´Eclairage (CIE) b* values of 6 to 18. Furthermore, beef produced from forage-based diets tends to have yellower-colored fat and contains higher proportions of beneficial nutrients such as omega-3 fatty acids and carotenoids (Umberger et al., 2002). Consequently, in the study, 23% of the participants expressed a willingness to pay a premium for beef with yellow fat due to their preference for it (Umberger et al., 2002). Nevertheless, the majority of consumers still believe that yellow fat may be an indicator of inferior meat quality. Therefore, there still exists a question regarding whether beef with yellow carcass fat truly exhibits lower meat quality and is considered negatively for consumption.

In this study, 20 cattle with either white or yellow carcass fat were collected in Korea. The objective was to identify the parameters that influence the yellowness of carcass fat and examine the relationship between meat quality and the color of carcass fat. This research was intended to be presented as a specific case study involving cattle from a distinct breed (Hanwoo) and market under a specific grading system in Korea.

Carcass fat refers to the layer of fat situated between the skin and the meat, on the outside of the muscle. It is typically removed from beef prior to sale due to its perceived inferiority compared to other types of fat. Nonetheless, the color of carcass fat remains a crucial factor in determining the high-quality grade of beef in Korea. According to KEPA, carcass fat color grade is assessed on a scale ranging from white (No. 1) to yellow (No. 7). It has been observed that when the carcass receives a fat color grade over No. 6, it negatively impacts the final QG However, as carcass fat is typically removed during the processing of fresh beef cuts or meat products in Korea, it is hard to influence consumer perception directly. Consequently, at the point of the producer, there may be questions regarding the significance of carcass fat color as a determining factor for the QG.

Several factors influence the occurrence of yellow carcass fat, including species, age, diet, and sex (Mare et al., 2013). However, in this study, there was no significant correlation between carcass fat color grade and carcass properties such as QG, marbling, YG, age, maturity, and carcass weight (Table 1). Among the factors examined, only the β-carotene content in carcass fat exhibited a notable coefficient value, with a correlation of r = 0.540 (P < 0.05) and ρ = 0.591 (P < 0.01). The yellow group of carcass fat displayed carotenoid levels ranging from 0.44 to 1.11 μg/g (Figure 2). The content of carotenoids in carcass fat can be influenced by various factors. A diet rich in α-tocopherol and polyunsaturated fatty acids (PUFA) has been shown to improve the absorption of carotenoids (Yang et al., 2002). Conversely, supplementation of vitamin A has been found to decrease carotenoid concentrations in plasma, subsequently reducing the concentration in adipose tissues (Knight et al., 1996). Additionally, consistent dietary patterns have been identified as the primary influencer of color and carotenoid levels in carcass fat, suggesting that variations in tissue size may not be the sole contributing factor (Dunne et al., 2009). When adipogenesis is suppressed due to factors such as lactation or feed restriction, carotenoids consumed through feed tend to accumulate in adipose tissue (Swanson, 1989). Meanwhile, the production of fatter carcasses through grain-feeding, which results in increased fat deposition in major fat depots, may dilute the carotenoid content in tissues (Noziere et al., 2006). In particular, in Korea, Hanwoo cattle is commonly raised using a total mixed ration (TMR)-feeding strategy and rice straw to accumulate lipids in intramuscular fat and address the issue of limited pasture resources (Kang et al., 2022).

Furthermore, carotenoid pigments in tissues have been considered as biomarkers of grass-feeding (Prache et al., 2003). The fatty acid composition of muscle and carcass fat from grass-fed cattle exhibits decreased levels of SFA and increased levels of w-3 PUFA (Dannenberger et al., 2004). Similar to previous study (Dannenberger et al., 2004), our study also found a strong negative correlation between the yellowness of carcass fat and SFA (r = −0.737, P < 0.01) as well as the w-6 to w-3 fatty acid ratio (r = −0.505, P < 0.05) (Figure 3). However, there was no association observed between the yellowness of carcass fat and UFA in both carcass fat and meat (Figure 3). Also, it has been generally reported that the fatty acid composition of meat and fat obtained from grass-fed cattle is characterized by low levels of oleic acid and MUFA (Nogoy et al., 2022). Surprisingly, in this study, the fat of the yellow group exhibited significantly higher levels of oleic acid and MUFA compared to the normal group (Table 3). It was found that grain-fed animals had higher proportions of MUFA (Moholisa et al., 2018). This finding contradicts the hypothesis that the yellow group, characterized by high carotenoid contents, is solely attributed to grass-feeding. According to Cooke et al. (2004), the exposure of animals to different levels of exercise can also influence the effects of grass- and grain-feeding on fat color changes. Previous studies have also reported that diet can impact meat color, particularly when animals are raised outdoors (Bidner et al., 1986; Morris et al., 1997; Muir et al., 1998). However, in another study in which all animals were housed indoors, the effect of diet on meat color was not observed (Cooke et al., 2004). Considering that most beef production systems involve varying proportions of grass and grain at different stages of production, it is difficult to attribute the carotenoid contents observed in the yellow group to a single specific factor. It is possible that an environment conducive to carotenoid absorption was established within these samples; however, further research is necessary to fully elucidate the underlying factors.

Interestingly, the diet of the yellow group showed a higher presence of probiotics (Table S1). Previous research by Mun et al. (2013) has demonstrated that supplementation of probiotics in the diet of Hanwoo steers can increase the content of oleic acid and decrease myristic acid levels in meat. Probiotics are live microorganisms believed to confer beneficial effects on the health of the host animal, including improved digestion and immune function (Uyeno et al., 2015). While limited research exists on the specific impact of probiotics on the color of carcass fat in beef, it is possible that they could indirectly influence fat color by enhancing nutrient absorption and metabolism in the animal. Studies have suggested that probiotics can improve the composition of the gut microbiota in animals, leading to enhanced nutrient utilization and absorption (Kowalski et al., 2009; Qiao et al., 2009). Consequently, this could potentially increase the deposition of carotenoids and other yellow pigments in adipose tissue. However, the current evidence supporting the effect of probiotics on carcass fat color in beef is limited and inconsistent. Further research is necessary to comprehensively understand the relationship between probiotics, gut microbiota, and carcass fat color in beef.

In previous studies, the relationship between meat quality and yellow carcass fat has been explored. For instance, it was reported that feeding pasture to cattle resulted in beef with yellow carcass fat, as well as higher eicosenoic acid and lower w-6 to w-3 fatty acid ratio in intramuscular fat. However, no significant difference in beef yellowness was observed (Varela et al., 2004), consistent with the findings of French et al. (2000). Shemeis et al. (1994) evaluated meat quality based on the age of cattle and found that meat from mature cattle exhibited higher yellowness in carcass fat and tended to have tougher tenderness. However, no significant differences were observed in meat color, dry matter, and intramuscular fat percentage. In contrast to these previous studies, the current study collected carcass fat and meat samples as the normal and yellow groups from 20 cattle with similar carcass performance, to evaluate the differences in meat quality. The results revealed no significant differences in proximate composition, shear force, even meat color between the normal and yellow groups. However, the yellow group only exhibited higher levels of eicosenoic acid in the meat (P < 0.05), which aligns with the findings of Varela et al. (2004). Eicosenoic acid, also known as 20:1, is a MUFA commonly found in beef and other animal fats. It contributes to the sensory qualities of beef by providing a mild, buttery taste and enhancing the overall richness of the meat (Song and Hwang, 2023). Additionally, dietary MUFA have been associated with reduced serum cholesterol levels and a lower risk of coronary heart disease (Nogoy et al., 2022). Therefore, the higher eicosenoic acid content in meat with yellow carcass fat could be considered an advantage.

The results suggest that the yellowness of carcass fat in beef is primarily influenced by carotenoid content in carcass fat than other factors. There were no significant differences in meat qualities, including physicochemical properties and intramuscular fatty acid composition, between beef in normal and yellow groups. On the contrary, beef in yellow groups showed higher MUFA, positively affecting human health and consumption. It means that beef with a yellow carcass fat can be considered normal beef in terms of meat quality. Also, these results can present a new perspective on the beef grading system in Korea and provide an alternative approach that could benefit the economic interests of Korean cattle producers. However, the study highlights the complexity of factors contributing to the color of carcass fat and calls for further research to better understand the underlying mechanisms and potential effects of probiotics and other factors on carcass fat color in beef production.