The role of marbling in the eating experience of beef is well established. Earlier research has shown that differences in marbling can explain between 24 and 34% of the variation in sensory panel ratings for juiciness, tenderness, flavor, and overall palatability (Smith et al., 1985). Emerson et al. (2013) reported that increasing degree of marbling resulted in greater juiciness, tenderness, meaty/brothy flavor, and buttery/beef fat flavor. Emerson et al. (2013) also demonstrated that marbling accounts for 40 and 23% of the variation in tenderness as evaluated by Warner-Bratzler shear force analysis and trained sensory panels, respectively.

Numerous branded beef programs have developed their product specifications to include stringent marbling requirements in an effort to ensure their customers have an enjoyable eating experience. For a beef carcass to qualify for a United States Department of Agriculture (USDA) grade or certified USDA beef program, based on marbling, at least 1 side must have the minimum suggested marbling for that respective grade or certification. Visual evaluation of the amount and distribution of intramuscular fat (marbling) located in the cut surface at the 12th to 13th rib Longissimus muscle (LL) interface provides the means for determining marbling scores ranging from the highest amount, Abundant, to the lowest amount, Practically Devoid based on the current USDA grading standards (USDA, 2017). The 12th to 13th rib interface is the point where marbling score is determined, however, previous research has shown that the amount of marbling throughout a carcass can vary depending on specific anatomical location (Doty and Pierce, 1961; Lawrie, 1961; Blumer et al., 1962). The variation of marbling is of greatest concern in the high-value steak cuts from the beef rib and loin (Smith et al., 1987; Smith et al., 2008) where more precise measures of eating quality potential could improve the merchandising value of those items. Within these primals, marbling variation can lead to potential problems with eating consistency (Smith et al., 1987; Platter et al., 2005; Smith et al., 2008), especially if the marbling score at one anatomical location is significantly lower than the marbling score at the 12th–13th rib interface. Furthermore, dimension of steaks can play a role in merchandising and consumer acceptability (Dunn et al., 2000; Sweeter et al., 2005; Bass et al., 2009). In order for beef purveyors to ensure they are providing a high–quality and consistent eating experience, it is important to understand how marbling score and other quality attributes can vary based on anatomical location. There are no contemporary objective empirical data to precisely describe the potential variation of marbling in high-value beef subprimals which may influence the eating experience or possibly allow for alternative merchandising strategies of those subprimals. The objectives of this experiment were to determine, using a USDA approved camera grading system, how marbling score, texture, and distribution, as well as, loin eye area, length, and width vary in strip loin samples from different anatomical locations.

Meat samples were obtained from a federally inspected beef processing facility; therefore, Institutional Animal Care and Use Committee approval was unnecessary.

Data characterizing the 6 samples from the beef strip loin are presented in Table 1. In the present study, the samples from the 13th thoracic vertebrae (location 1) and second lumbar vertebrae (location three) had the highest (P < 0.05) mean marbling scores. Samples from the fifth lumbar vertebrae (location six) had the lowest (P < 0.05) mean marbling score. Mean marbling score declined by 61 degrees from anterior (location 1) to posterior (location 6). Similarly, previous studies have shown that marbling score varies within the rib and loin depending on anatomical location; however, a consistent pattern has not been determined (Doty and Pierce, 1961; Lawrie, 1961; Blumer et al., 1962; Cook et al., 1964; Cross et al., 1975; Faucitano et al., 2004). Within the ninth to 11th rib region, Blumer et al. (1962) reported that marbling varied from 2/3 to 2 2/3 of a USDA marbling score. In contrast to the present study, Cook et al. (1964) evaluated the marbling score of samples taken from the 13th thoracic vertebra to the 5th lumbar vertebra and determined that marbling score was similar for each anatomical position with the exception of the sample from the 1st lumbar vertebra, of which had a lower marbling score. It is commonly accepted that an animal tends to deposit fat from anterior to posterior. However, it has not been previously documented how marbling score varies within the strip loin using a USDA-approved camera-grading system. Previous studies utilized human grading that would allow for more subjectivity and possibly more variation (Ockerman and Cahill, 1969; Moore et al., 2010) which may have resulted in the Cook et al. (1964) study failing to find differences between several of the different anatomical locations. With the results from this study and previous studies it is clear that marbling score does vary with anatomical location of the LL but the degree to this variation is not consistent between studies. Although carcasses were originally selected to determine how marbling score varied within the range of Modest⁰⁰ to Modest³⁰ to limit the variation of the marbling within the subprimals, the additional day of aging and chilling between selection and fabrication, as well as the use of 2 different cameras, led to an average marbling score of Modest⁶⁵ for the first location when evaluated in the meat laboratory environment (Table 1). It is known that as carcass chill time increases, the susceptibility for fat deposits to solidify increases thereby allowing for a greater amount of marbling to be observed (Johnson et al., 1985). Furthermore, some level of variation is allowed within camera grading systems (USDA, 2006) and therefore can possibly explain some of the variation observed in the current study.

Similar to marbling score, the texture of marbling can also vary depending on the anatomical location of the sample (Cross et al., 1975). Texture of marbling is defined as the actual size or coarseness of the intramuscular fat deposit (Cross et al., 1975). Several premium beef programs utilize marbling texture specifications (USDA, 2018) as a perceived quality measure. Moody et al. (1970) determined that a group of beef rib primals with finely textured marbling were classified by the Warner-Bratzler shear force method as more tender than the group of beef ribs with coarsely textured marbling. More recent research indicated a greater beef intensity and juiciness from beef strip loin steaks with coarser marbling (Vierck et al., 2018). In the present study, the texture of marbling was reported as marbling size (mm²) as reported by the CVS cold camera (Table 1). The mean marbling size was greatest (P < 0.05) in samples from the third and fourth lumbar vertebrae (locations 4 and 5) and least (P < 0.05) in the samples from the 13th thoracic vertebrae (location 1). Cross et al. (1975) observed that samples with lower marbling scores had finer textured marbling while samples in the higher marbling groups such as “moderately abundant” or “abundant” had coarser textured marbling. In the present study there was no clear relationship between marbling size (texture) and marbling score. Although there was a significant correlation of pooled individual location for marbling score and marbling size (P < 0.001), however, the simple correlation coefficient of r = 0.19 is rather weak (Fig. 1). In addition to marbling amount, the CVS cold camera measures the size and distribution of each individual piece of marbling and is capable of reporting an average marbling size (Mafi et al., 2014). The authors postulate that extremely large pieces of marbling could have increased the average marbling size of samples measured, as was observed in the pooled data reported in Table 2, to a degree that is unrepresentative of the entire respective sample. This could explain the lack of a stronger relationship between marbling size and marbling score.

In addition to marbling score and size, the CVS camera quantified marbling distribution in terms of distance (millimeters). Marbling distance was reported as an average measurement of distance, measured by the camera system, between each fleck of marbling within a sample (Table 1). A lower numerical value for marbling distance indicates a smaller distance between each individual piece of marbling within a sample. Marbling distance was lowest (P < 0.05) for the samples from the second lumbar vertebra (location 3) and was greatest (P < 0.05) for the samples from the 5th lumbar vertebra (location 6). Marbling distribution was the most uniform in samples taken from the middle of the strip loin and marbling distribution became more variable in samples from the ends of the strip loin. Similar to the present study, Cook et al. (1964) noted that marbling uniformity decreased toward the muscle extremities; however, in reality, the 13th vertebra (location 1) is rather a mid-point of the full LL, yet an extremity of the thoracic portion of that muscle. In contrast, Cook et al. (1964) reported that samples from the 10th to 13th thoracic region exhibited the most uniformly distributed marbling pattern. Breidenstein et al. (1968) noted that marbling distribution score increased as marbling score increased which indicated a more uniform distribution of marbling in samples with a higher marbling score. In the current study, as marbling score increased from the sixth to third sample locations (5th to second lumbar vertebrae, respectively), marbling distance became smaller indicating a more uniform marbling distribution in samples with a higher marbling score.

Table 1 contains the means for LL steak sample surface area, length, and width for samples from each anatomical position. Muscle area and width was largest (P < 0.05) for the samples from the most anterior position and decreased (P < 0.05) as the samples became more posterior suggesting a slight conical dimensionality of the muscle. Samples from the most posterior location of the strip loin were the longest (P < 0.05) and had a significantly smaller area than the more anterior locations. These measurements help depict how the overall shape of samples from a strip loin change moving from anterior to posterior considering the length of the strip loin steak and surface area continued to decrease, suggesting a smaller steak dimension. Samples from the most anterior location are more circular in shape while samples from the posterior positions are more oblong or rectangular in shape. Steaks from the more posterior region would thereby need to be cut thicker to obtain the same portion weight as steaks from the anterior section. The shape of a steak from the strip loin, in addition to the amount and distribution of marbling within the LL of the strip loin, can have marketing implications for a foodservice distributor or retail meat merchandiser. Bass et al. (2009) identified that LL area between 89.7 and 102.6 cm² to have a predicted probability of acceptance of 0.80 among surveyed professional culinarians; the current research observed smaller LL areas than the Bass et al. (2009) study from location 2 through 5. Dunn et al. (2000), however, observed surface area of steaks between 77 and 97 to be ideal for cooking time and tenderness in a foodservice setting. Leick et al. (2011) observed that thickness of steak was the greatest trait of importance, of those evaluated, to consumers when selecting LL steaks. Sweeter et al. (2005) found no preferences among steaks from different LL areas but rather suggest that a retail consumer exists for the wide range of LL areas observed in the beef industry.