Consumers’ willingness to pay for beef is closely linked to eating satisfaction, which is influenced by overall palatability. Recent studies have reaffirmed that the key components of beef palatability are tenderness, juiciness, and flavor (O’Quinn et al., 2018; Smith and Carpenter, 1974). These attributes significantly impact consumer preferences and their willingness to pay more for higher-quality meat (Lyford et al., 2010; Polkinghorne and Thompson, 2010). Beef tenderness has been widely recognized as a major determinant of overall eating satisfaction and consumer acceptability (Miller et al., 2001; Shackelford et al., 2001; Miller, 2020). The cooking method and muscle used can influence beef tenderness (Nair et al., 2019; Vierck et al., 2021). Typically, it is recommended to cook tough muscles at relatively low temperatures in moist environments (with humidity) for a long time to improve tenderness. Such moist heat cooking methods can reduce the amount of cooking loss (Rowe and Kerth, 2013), improve collagen solubility (Dominguez-Hernandez et al., 2018), and directly impact juiciness (Maughan et al., 2012). In addition to tenderness, beef flavor can be equally or even more important than tenderness for overall consumer eating satisfaction (O’Quinn et al., 2018; Felderhoff et al., 2020; Miller, 2020), and can be influenced by many factors, including the cooking method (Miller et al., 2022). Further, Vierck et al. (2021) demonstrated that different dry heat finishing cookery methods following a moist heat preparation method significantly impact the flavor profile and consumer ratings of beef strip loin steaks, including tenderness.

One cooking method gaining popularity in the food service industry is sous vide, which involves vacuum sealing raw meat in a heat-stable package and immersing it in a water bath under controlled temperatures for an extended period (Schellekens, 1996). Sous vide cooking offers numerous advantages over conventional cooking methods, including precise temperature control, potential cost savings in labor and materials, and reduced cooking loss (Baldwin, 2012; James and Yang, 2012; Roldán et al., 2014; Alahakoon et al., 2018; Ismail et al., 2022; Thathsarani et al., 2022). Additionally, several studies have demonstrated that the combination of low-temperature and extended-time use in sous vide can improve the tenderness and different sensory attributes of low-value or tougher meat cuts (Mortensen et al., 2012; Christensen et al., 2013; Sun et al., 2019; Bhat et al., 2020; Naqvi et al., 2021b; Naqvi et al., 2021c; Gámbaro et al., 2023). Typical sous vide processing temperatures range from 50°C to 65°C (Ismail et al., 2022). At these temperatures, collagen in meat begins to denature, converting it into gelatin, which may contribute to the increased tenderness (Baldwin, 2012). However, the effects of sous vide cooking on tenderness and collagen solubility vary based on the specific muscle used and the temperature–time combination (Baldwin, 2012; Purslow, 2018; Ismail et al., 2022). In addition to its culinary benefits, sous vide cooking is advantageous for enhancing the shelf life of cooked meat products by reducing microbial loads and limiting the risk of contamination after thermal processing (Baldwin, 2012; Bıyıklı et al., 2020; Yang et al., 2020; Haghighi et al., 2021; Ismail et al., 2022; Thathsarani et al., 2022).

In the U.S., the Food Safety and Inspection Service (FSIS) provides cooking guidelines for the safe production of ready-to-eat meat and poultry products in Appendix A (FSIS, 2021). When low temperatures are used, long dwell times are usually needed to achieve the lethality of certain pathogenic microorganisms (FSIS, 2021). Biceps femoris is a leaner and less tender muscle located in the beef round (Stolowski et al., 2006) and is typically cooked using slow, moist heat cooking. However, there are only limited studies that have examined the impact of different sous vide temperature and time treatment combinations on the palatability of biceps femoris. Therefore, the objective of this study was to evaluate the palatability characteristics of beef biceps femoris following different sous vide temperature and time combinations. We hypothesized that increasing sous vide cooking temperature while reducing dwell time would maintain the palatability of beef biceps femoris steaks. This will enable food service processors to optimize cooking parameters without compromising the eating experience.

Several studies have evaluated the effect of sous vide cooking on physicochemical and sensory characteristics of beef (Mortensen et al., 2012; Christensen et al., 2013; Alahakoon et al., 2018; Ismail et al., 2019; Naqvi et al., 2021a; Naqvi et al., 2021b; Naqvi et al., 2021c; Gámbaro et al., 2023). These studies have shown that sous vide cooking meat at low temperatures for an extended time could improve the sensory attributes of lower-quality meat muscles. However, results can vary with the cooking parameters (temperature and time) and the meat cut used. The current study assessed sensory characteristics, including cooking loss, internal cooked color, WBSF, and trained sensory evaluations of beef biceps femoris following sous vide cooking.

Cooking loss is of great economic importance to the food service industry since it indicates a reduction in yield and loss of moisture, which can change the textural quality of meat (Purslow et al., 2016). During cooking, the water-holding capacity of proteins decreases due to protein degradation, which can result in water being expelled from the muscle (Lepetit et al., 2000; Kondjoyan et al., 2013). Slow-cooking conditions, such as sous vide, can minimize fluid loss, as meat is cooked in moist conditions (James and Yang, 2012; Roldán et al., 2014). As treatment temperature and time increased, an increase in percent cooking loss was observed in the current study (Figure 1). These results are in agreement with previous studies that have also shown that, as the temperature and cooking time increase, the cooking loss percentage could also increase (Vaudagna et al., 2002; García-Segovia et al., 2007; Christensen et al., 2011; Roldán et al., 2013; Ismail et al., 2019; Naqvi et al., 2021b; Naqvi et al., 2021c). For example, Naqvi et al. (2021c) evaluated the effect of sous vide cooking temperature (55°C, 65°C or 75°C) and time (1 h, 8 h, or 18 h) on cooking loss of beef biceps femoris and reported that as cooking temperature and time increased, cooking loss increased. Similarly, in the current study, samples from treatment 1A, cooked at the lowest temperature and with the shortest dwell time at that temperature, had lower (P < 0.05) cooking loss compared with all other treatments. On the other hand, samples from treatment 2C, cooked at the highest temperature and for the longest dwell time, had the greatest (P < 0.05) cooking loss.

The internal color of cooked beef is an indicator of its degree of doneness, which is dependent on the highest internal temperature reached (Baldwin, 2012; Ismail et al., 2022). Myoglobin is the main protein responsible for both fresh and cooked meat color (Suman et al., 2016). The brown color formed in cooked meat results from myoglobin denaturation due to an increase in temperature. In general, during sous vide cooking, the cooking temperature will play a more prominent role than the cooking time when evaluating the changes in color (Ismail et al., 2022). In the current study, the a* (redness) and b* (yellowness) values of cooked steaks were influenced by treatment, whereas L* values (lightness) were not affected by the treatments evaluated (Table 2). On the contrary, previous studies have reported either an increase or a decrease in L* values of sous vide cooked meat with different cooking temperatures and times (García-Segovia et al., 2007; Roldán et al., 2013; Alahakoon et al., 2018). For example, Alahakoon et al. (2018) observed a decrease in L* value of beef deep pectoralis samples when temperature increased (60, 65, and 70°C), whereas an increase in L* value was observed when cooking time increased (24, 48, and 72 h) within the same temperature. This difference in L* observed between our study and previous studies might be due to the difference in the muscle type, which could be more influential than cooking time or temperature (Ismail et al., 2022).

In the current study, the internal cooked redness (a*) of samples cooked at the highest temperature was lower than those cooked at the lowest temperature. Additionally, internal a* values of samples cooked at 56.1°C decreased as treatment dwell time increased (Table 2). Typically, when the temperature rises, myoglobin denaturation increases (King and Whyte, 2006). However, the thermal denaturation rate also depends on the myoglobin redox form (Hunt et al., 1999). Since the internal cooked color of vacuum-packaged steaks was evaluated in the current study, myoglobin in the steak interior could be in the deoxymyoglobin form (the predominant redox form in vacuum-packaged meat) during the thermal processing, which is the least sensitive among the myoglobin redox forms to heat denaturation (Hunt et al., 1999; King and Whyte, 2006). This could lead to the higher a* values observed in steaks cooked at 56.1°C compared to 61.7°C. Even at 61.7°C, there was relatively high redness because while myoglobin denaturation starts at 55°C, deoxymyoglobin is not fully denatured until 75°C (Hunt et al., 1999). In agreement with these results, Ismail et al. (2019) reported that beef semitendinosus steaks sous vide cooked for a shorter time (6 h) at a lower temperature (60°C) had a higher internal surface redness than those samples cooked at the same temperature for 12 h or at higher temperatures (65°C, 70°C, and 75°C). Furthermore, Gámbaro et al. (2023) evaluated the interior color of beef hind shank sous vide cooked at different temperatures (55°C and 65°C) and times (5 h, 8 h, 12 h, and 24 h). These authors reported that the a* values of samples cooked at 55°C decreased with an increase in cooking time and were higher than all samples cooked at 65°C, regardless of the cooking time (Gámbaro et al., 2023). Similar observations were also reported by Vaudagna et al. (2002) for beef semitendinosus sous vide cooked at 50°C, 60°C, or 65°C up to 390 min, and Roldán et al. (2013) for lamb loins sous vide cooked at 60°C, 70°C, or 80°C for 6 h, 12 h, or 24 h; however, these studies showed no significant changes in the redness of samples held for a longer time at the same temperature, which could be due to the different muscles used.

The WBSF values of steaks were similar regardless of the cooking treatment, even though there were some numerical differences between the treatments in the current study (Figure 2). This lack of statistical difference could be due to the relatively large variation within samples (standard deviation ranged from 0.7 to 1.3) for the biceps femoris muscle. One of the key advantages of sous vide cooking is the improvement in tenderness of low-value tougher muscle cuts (Alahakoon et al., 2018; Ismail et al., 2019). Several previous studies have found significant changes in WBSF values of beef muscles depending on cooking temperature and time (Vaudagna et al., 2002; Christensen et al., 2013; Alahakoon et al., 2018; Ismail et al., 2019; Bhat et al., 2020; Naqvi et al., 2021a; Naqvi et al., 2021b; Naqvi et al., 2021c; Karki et al., 2022; Gámbaro et al., 2023). This improvement is attributed to the breakdown of connective tissue as a result of protein denaturation or collagen solubilization caused by prolonged heating (Dominguez-Hernandez et al., 2018).

Beef palatability is of great importance when evaluating cooking methods, and it is generally attributed to juiciness, tenderness, and flavor (Smith and Carpenter, 1974). In this study, trained panelists assessed the intensity of beef flavor, tenderness, juiciness, and the presence of sour and metallic flavors in beef samples. The results indicated that the different treatments did not significantly affect the intensity of beef, sour, and metallic flavors in the steaks. The similar scores in flavor attributes across treatments could be attributed to the low-temperature moist cooking method, which likely does not induce substantial differences in flavor profiles compared to dry heat methods (Miller et al., 2019; Vierck et al, 2021). Furthermore, all products in this study were of the same quality grade (USDA Choice) and were uniformly wet-aged. Similarly, Naqvi et al. (2021b) evaluated the beef flavor and metallic flavor of biceps femoris steaks sous vide cooked at 65°C for 8 h or 12 h using trained panels and reported no differences between the treatments.

Tenderness is of great importance in overall eating satisfaction and consumers’ acceptability of beef (Miller et al., 2001; Shackelford et al., 2001). In the current study, the highest tenderness score was for samples from treatment 1C (56.1°C and 240 min), which agrees with the WBSF results. Likewise, Naqvi et al. (2021b) observed an increased tenderness rating of beef samples cooked for 12 h compared to those cooked for 8 h at 65°C. Mortensen et al. (2012) also reported an increase in tenderness scores with longer cook time (3 h, 6 h, 9 h, or 12 h) for semitendinosus from young Holstein bulls (12–13 months) sous vide cooked at different temperatures (56°C, 58°C, and 60°C) with the highest rating observed for those samples cooked at 56°C for 12 h. Additionally, Gámbaro et al. (2023) reported that the tenderness scores within the same temperature increased as cooking time (5 h, 8 h, 12 h, or 24 h) increased, with samples cooked for 24 h at 55°C and 65°C having the highest rating. However, there was no difference in tenderness within a temperature in the current study, and differences between results could be due to differences in the beef cuts used (shank vs. biceps femoris in the current study) and the cooking conditions.

Juiciness is an essential sensory attribute positively correlated with consumer preference, and it is defined as the sensation produced by meats with higher levels of juices (Maughan et al., 2012). Similar to the tenderness scores, there were only minor differences in the juiciness among the treatments, with samples from treatment 1C (56.1°C and 240 min) having the highest score. However, the juiciness score from the treatment 1C samples was statistically different only from the 2A (61.7°C and 8 min) samples. This contrasts with the cooking loss results (Figure 1), in which an increase in cooking loss was observed as the treatment temperature and time increased. These results, where perceived juiciness increased as perceived tenderness increased, could be due to the halo effect of tenderness and the correlation between these sensory attributes (Miller, 2020). Similarly, Naqvi et al. (2021b) found no differences in the juiciness rating of beef biceps femoris samples cooked at 65°C for 8 h or 12 h. On the other hand, Gámbaro et al. (2023) observed a numerical increase in juiciness when cooking time increased for those samples cooked at 55°C. However, samples cooked at 65°C had lower juiciness scores than those cooked at 55°C.

Cooking loss, tenderness, and flavor are critical factors when evaluating different sous vide cooking temperatures and times. In the current study, the cooking loss increased while the internal surface redness decreased with an increase in sous vide temperature and time. There was no difference in WBSF between the treatments, whereas samples from treatment 1C (56.1°C and 240 min) had higher perceived tenderness scores than treatment 2A (61.7°C and 8 min) samples. Moreover, no off-flavor (sour or metallic) was detected with any cooking temperature–time combinations. These results suggest that sous vide processors could alter the cooking temperatures without negatively affecting palatability. However, it is essential to consider the cooking loss associated with temperature–time combinations. Overall, the result of this study provides food service processors an option to have flexibility in cooking times, allowing them to optimize production efficiency and energy usage. Although this study focused on biceps femoris, future studies should investigate other tough, low-value muscles, and explore additional cooking time-temperature combinations.