Slice shear force is a reference method for beef texture analysis. Using an angle adjustable cutting box could increase its accuracy for research purposes. The results from different locations within the longissimus muscle show a high correlation with Warner-Bratzler shear force methodology and high potential adaptability for different muscles.
Research indicates the fibre angle of the longissimus muscle can vary, depending upon location within a steak and throughout the muscle. Instead of using the original fixed 45 ° or 90 ° cutting angle for testing shear force, a variable angle cutting box can be adjusted so the angles of the knives correspond to the fibre angle of each sample. Within 2 min after cooking to an internal temperature of 71 °C on an open-hearth grill set at 210 °C, a 1 cm by 5 cm core is cut from the steak, parallel to muscle fibre direction, using 2 knife blades set 1 cm apart. This warm core is then subjected to the Slice Shear Force protocol (SSF) to evaluate meat texture. The use of the variable angle cutting box and the SSF protocol provides an accurate representation of the maximal shear force, as the slice and muscle fibres are consistently parallel. Therefore, the variable angle cutting box, in conjunction with the SSF protocol, can be used as a high-throughput technique to accurately evaluate meat tenderness in different locations of the longissimus muscle and, potentially, in other muscles.
Tenderness is one of the most important quality attributes in meat1. Inconsistency in beef tenderness has been identified as one of the major problems facing the beef industry2. The Warner-Bratzler shear force (WBSF) test, characterized by a triangular hole in a precisely machined shear plate, is the most widespread method used to indicate meat sensory tenderness3,4, as it is the instrumental method that arguably has shown the best correlation with sensory panel scores for meat toughness5. However, the slice shear force protocol (SSF) has become an important technique for analyzing muscle texture and tenderness6, as an alternative to the standard WBSF protocol7. It is beneficial in instances where rapid analysis or a high number of samples need to be processed. For the SSF, only one core is taken from the steak when it is still warm, versus the multiple cores (3-6) taken from the steak usually after 24 hr of refrigeration for the WBSF6. From this one slice, the SSF analyzes the average texture of the whole steak8, as it has been found that tenderness varies between the lateral to medial sides of the steak9, with the center and middle of steaks having the best representation for average WBSF. The downfall to the SSF is that, within a steak, from the lateral to medial sides, there is variation in the shear force values9; however, by consistently using the sizing box to make 5 cm sections, it may reduce variability that could come from using different sections of the steak. However, since some steaks are different sizes, a 5 cm slice may occur in different locations on the steak, which could then affect shear force values10.
On the other hand, the original cutting box designed to obtain the section to be analyzed in the SSF protocol allows only 2 fixed angles, 45 ° and 90 °; however, muscle fibre orientation changes within steaks, and within the muscle11. Shackelford and Wheeler12 stated that the average longissimus angle was 43.8 °, which was close to 45 ° and therefore deemed appropriate when samples were always collected from the same location. However, Derington et al.11 reported a range in the angle of the fibres along the longissimus muscle between 33.1 ° and 53.9 °. Thus, when, for research purposes, several steaks from the same animal need to be analyzed, assigning all fibre angles to either 45 ° or 90 ° potentially reduces accuracy. The use of a variable angle cutting box may provide a more accurate depiction of maximal shear force, as having the capacity to measure and adjust the cutting angle allows for the slice to consistently run parallel with the muscle fibres.
1. Steak Collection
2. Cooking Procedure
3. Angle Adjusting and Sample Preparation
4. Shear Force Analysis
Thirty-one finished commercial beef steers were slaughtered and their carcasses (528 – 601 kg) were split. In order to create variability in tenderness, right sides were immediately stored at 2 °C, while the left sides were held at 10 °C for 3 hr and then at 2 °C. The longissimus muscles from right and left sides were removed 24 hr after slaughter. Samples from the right sides (“TOUGH” treatment) were analyzed that day, while samples from the left side (“TENDER” treatment) were aged for 6 d before being analyzed. Two paired steaks were fabricated from the anterior (5th-6th thoracic vertebrae), middle (12th-13th thoracic vertebrae) and posterior (4th-5th lumbar vertebrae) portions of the right and left longissimus muscles. By sampling two steaks adjacent to one another and performing both the reference WBSF and SSF on the same steak we are able to compare the angle adjustable SSF to the WBSF reference material. Steaks were cooked as described in the preceding procedures. Following a balanced design, each pair of steaks were split into two halves, one medial and one lateral. The medial half of one steak and the lateral half of the second one were used to prepare slices using the angle adjustable cutting box and analyzed with the slice shear force (SSF) protocol. The remaining half steaks were placed in individual plastic bags, submerged in an ice bath to arrest cooking and refrigerated at 4 °C overnight for preparation of 1.9 cm cylindrical cores and analyzed using the reference Warner-Bratzler shear force method (WBSF).
According to the results (n = 372), shear force method × muscle location or steak location interactions were not significant (P > 0.05). This means that, regardless of the differences in absolute values from each method, the differences observed among treatments or locations were similar when either method was used to evaluate tenderness in cooked beef. Furthermore, no interactions (P > 0.05) were observed with the treatments (tough vs. tender). For the angle adjustable SSF method (Figure 2), differences were observed among muscle location (P < 0.05). The toughest steaks were those sampled from the middle section of the longissimus muscle. Anterior steaks were the most tender samples and posterior samples were intermediate. The same effect was observed in samples analyzed using the reference WBSF method (Figure 3). Both Janz et al.10 and Henrickson and Mjoseth13 showed similar results, reporting greatest shear force values in the middle area of the longissimus muscle, lowest in the anterior area and intermediate in the posterior area. Janz et al.10 explained these intramuscular differences on factors such as cooling rates, pH decline along the loin, muscle fibre angles and tensions during carcass hanging.
Similar to the study of Shackelford et al.6 which compared a fixed angle slice shear force to a standard WBSF, the results for the adjustable angle slice shear force were also compared to the standard WBSF in the present study. The coefficient of variation (Table 1) is a measure of the variability among samples within each method, and the overall coefficient of variation in this experiment was similar for both methods, regardless of the location along the muscle or within the steak. However, the coefficient of variation for WBSF was consistent between tender and tough samples (23-28%), while for SSF variability ranged from 13.6 for tough samples to 34.2% for tender samples. Thus, more variability was observed for the values from the angle adjustable cutting box in the tender sample, while WBSF shear force resulted in more variability in the tough samples.
After comparing the coefficients of variation, the next step was to determine the correlation (r) between the values obtained by the different methodologies (Table 2). Thus, a high correlation (P < 0.001) was observed between the values from both methodologies (overall 0.75), being highest (0.84) in the lateral samples from the anterior end and lowest (0.63) in the medial samples from the posterior end. These results are much higher than those reported by Derington et al.11, which ranged between 0.38 and 0.62. This may indicate an advantage of the angle adjustable compared to the original 45 ° cutting box, particularly when sampling occurs along the longissumus muscle, or from the medial rather that the lateral end of steaks.
Figure 1. Original design of the angle-adjustable cutting box for slice shear force analysis.
Figure 2. Slice shear force values (angle adjustable box) for steaks from three different locations within the LT muscle (n = 186).
Figure 3. Shear force values (WBSF) for steaks from three different locations within the LT muscle (n = 186). Anterior (5th-6th thoracic vertebrae); Middle (12th-13th thoracic vertebrae); Posterior (4th-5th lumbar vertebrae) a,b,cDifferent letters indicate significant differences (P < 0.05).
Side | Locations within Loin | Locations within Steak | ||||||
Overall | Left (Tender1) | Right (Tough2) | Anterior | Middle | Posterior | Lateral | Medial | |
Warner BratzlerShear Force | 38.5 | 28.6 | 23.1 | 39.9 | 36.6 | 37.7 | 39.1 | 37.7 |
Slice Shear Force | 34.9 | 34.2 | 13.6 | 37.1 | 31.4 | 34.7 | 35.7 | 34.1 |
Table 1. Coefficients of variation (%) for Warner-Bratzler and angle adjustable cutting box slice shear force values (n = 372). Anterior (5th-6th thoracic vertebrae); Middle (12th-13th thoracic vertebrae); Posterior (4th-5th lumbar vertebrae) 1Tender: carcasses held at 10 °C for 3 hr post-mortem and then stored at 2 °C and meat aged for 6 days; 2Tough: carcasses stored at 2 °C immediately post-mortem and meat aged for 24 hr.
Warner-Bratzler Shear Force | |||||||
Anterior | Middle | Posterior | |||||
Overall | Lateral | Medial | Lateral | Medial | Lateral | Medial | |
Slice Shear Force | 0.751 | 0.843 | 0.763 | 0.693 | 0.777 | 0.758 | 0.634 |
P value | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 |
Table 2. Coefficients of variation (%) for Warner-Bratzler and angle adjustable cutting box slice shear force values (n = 372). Anterior (5th-6th thoracic vertebrae); Middle (12th-13th thoracic vertebrae); Posterior (4th-5th lumbar vertebrae) 1Tender: carcasses held at 10 °C for 3 hr post-mortem and then stored at 2 °C and meat aged for 6 days; 2Tough: carcasses stored at 2 °C immediately post-mortem and meat aged for 24 hr.
The angle adjustable box ensures the SSF blade always shears muscle fibres at a true perpendicular angle, rather than approximately perpendicular which could happen with a fixed 45 ° angle cut8. The application of the variable angle cutting box allows for more accurate depictions of the maximal shear force in a sample, and it is on this basis of improving objective quality analysis techniques that the variable angle cutting box was developed. Furthermore, the wide range of angles presented by the angle adjustable box (30 ° to 60 °) allows for the preparation of samples from muscles other than the longissimus for SSF analysis. However, the double bladed knife, set 1 cm apart, may have some flex in the blade which may alter the thickness of the slice, and therefore the shear force. To ensure the variation is reduced, the knives should be as short as possible (5 to 7 cm) and very sharp. Then, one blade must be consistently rested along the edge of the knife gap and a slight sawing motion should be used to obtain a more consistent slice. The extra step of adjusting the angle and the training required to obtain repeatable sections from different steaks are drawbacks for the application of the angle adjustable box in an industrial environment (e.g. commercial abattoir). However, in a research environment, preparation of a single, angle adjusted slice may require less time than the multiple cores (normally 6-8) prepared for WBSF.
Before using the cutting box, there are a few steps that are important and more critical than others, such as the packaging of the samples. Fresh samples prior to cooking should be covered, preferably with a piece of plastic to prevent sample dehydration. Before vacuum packaged samples,are stored the seal should be inspected to ensure the vacuum has not been broken, and resealed if necessary. Ageing time is one of the most important factors contributing to the variability in meat tenderness14 and must be considered in the design of experiments. Freezing the samples may be necessary, but frozen-thawed samples usually have lower shear force values than chilled meat15. After storage and prior to cooking, it is important that the temperature probes are inserted into the middle of the steaks, equidistant from the cooking surfaces. This will prevent the steak from rapidly cooking on one side, and then very slowly cooking on the other side. If the internal temperature appears to be changing at a different rate than other steaks (either too fast or too slow), reposition the probe to a more central position. Also, for temperature probe placement, attempt to avoid locations that are not representative of the whole steak, such as areas with fat or connective tissue deposits, thickness inconsistencies, or areas that appear to have muscle fibre separation.
Cooking procedures may also have a significant impact on final tenderness7. Thus, the proposed method, electric grill at 210 °C is a typical dry-heat method used to cook the samples. Using a double “clam grill” may reduce the cooking time, but the moisture loss may be greater due to the extra pressure from the top grill, leading to reduced tenderness. Another option is cooking for a fixed time, instead of to an endpoint temperature. Belt-grills and conveyor ovens can be used and they may easily be combined with the SSF protocol16. However, the thickness of the steaks needs to be controlled, as large variations in endpoint temperature may cause inconsistent tenderness values17. Due to the nature of working with a non-homogenous tissue such as meat, structural differences amongst the samples may result in different steak depths despite care and attention when cutting. Other authors use moist cooking, such as water bath methods18. This usually results in longer cooking times at lower temperatures, increasing the tenderness of meat with high connective tissue content7. Therefore, the cooking method utilized to prepare the meat prior to tenderness evaluation needs to be carefully chosen according to the type of meat and the goals of the experiment.
Finally, when analyzing the SSF of the sample, very different values can be obtained. Authors can find values from <10 kg in extremely tender meat with tenderness enhancement treatments or very long ageing periods, to >50 kg in samples with high collagen content, cold shortening or extremely short ageing periods. If tough samples are expected in an experiment, the load cell for the texture analyzer should be 100 kg instead of 50 kg, as reported in the present study, or values from very tough samples will not be accurately recorded. However, using load cells with higher peak values would result in reduced precision. If the goal is merely to classify tender and tough meat, the 50 kg load cell may be sufficient, as any sample over that value would be considered extremely tough.
The authors have nothing to disclose.
This study was part of the Agriculture and Agri-Food Canada A-Base project “Development of high-throughput techniques for meat samples to reduce the phenomic gap for multivariate quality traits in marker assisted selection”. The skilled assistance of the Beef Unit and Meat Processing staff at the Lacombe Research Centre are sincerely appreciated. The authors also wish to thank the dedicated technical assistance of Christine Burbidge-Boyd, Fran Costello, Glynnis Croken and Rhona Thacker.
Name of equipment | Company | Catalogue number |
Vacuum Packager | Koch Equipment, Kansas City, MO, USA | Model UV2100 |
Vacuum bags | Winpak Ltd., Winnipeg, MB, Canada | |
Thermocouples and Scanning Device | Agilent / Hewlett Packard, Santa Clara, CA, USA | 34970A Data Acquisition Switch Unit |
Grill | Garland Commercial Ranges Ltd., Mississauga, ON, Canada | Model ED-30-B |
Crisco Vegetable Shortening | The J.M. Smucker Company, Orrville, OH, USA | |
Sample sizing box | G-R Manufacturing Co., Manhattan, KS, USA | |
Angle adjustable box | Innovation Centre, Red Deer College, Red Deer, AB, Canada | |
Texture Analyzer Machine | Texture Technologies, Hamilton, MA, USA | Model TA-XT Plus |
Load Cell, 50 kg | Texture Technologies, Hamilton, MA, USA | TA-XT Plus |
USDA Warner-Bratzler knife w/guillotine block | Texture Technologies, Hamilton, MA, USA | TA-7 |
Flat rectangle Blade for Slice Shear Force | Texture Technologies, Hamilton, MA, USA | TA-7C |