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Microbial safety issues related to mechanically tenderized beef have become prevalent, resulting in new labeling regulations for mechanically tenderized raw or partially cooked beef products. These products must bear labels to include validated cooking instructions, with specifications for minimum internal temperatures, to ensure that they are fully cooked. However, validation of cooking instructions for individual steak cuts of different sizes and weights is costly and time consuming. The objective of this study was to utilize predictive modeling techniques to determine safe cooking times for various mechanically tenderized steaks, cooked to an internal temperature of 70 to 71°C. A total of 162 steaks of various types (top round, knuckle, strip loin, top sirloin, sirloin cap, tri-tip, ribeye, flap, and flank), thicknesses (1.27, 2.54, and 3.81 cm), and weights (113 to 567 g) were used. Prior to cooking, samples were needle-tenderized, cut, vacuum-packaged, and refrigerated. Steak dimensions (width, thickness, and length) were measured prior to each cooking experiment. Samples were cooked on a flat-top-grill until they reached an internal temperature of 70 to 71°C, and the time taken to reach that temperature was defined as the Experimental Safe Cooking Time (ESCT). A thermocouple, attached to a data logger, recorded the steak-center temperature every 10 s. The time-temperature profiles obtained were used to determine the rate of temperature increase (RTI). Data generated through the experiments was used for model development and determination of predicted safe cooking time (PSCT) for steaks. The thickness, weight, and RTI of the steaks were identified as factors that had a 60% or higher correlation with the ESCT. Prediction accuracy of the regression model was 79%, with no significant differences (
Consumers, to a large extent, judge the palatability and quality of meat products based on their tenderness (
The popularity of tenderized beef products, however, has been accompanied by serious food safety concerns. Mechanical tenderization, which involves blade-or needle-piercing, could lead to increased transfer of surface pathogenic bacteria such as,
Predictive modeling, which incorporates mathematics, statistics, engineering, chemistry, and biology to study various processing parameters, can provide quick and inexpensive testing of “what if” scenarios in meat processing, thereby reducing production or experimental costs (
Various beef subprimals (UDSA Choice or higher grades) were delivered to the Robert M. Kerr Food and Agricultural Products Center (FAPC) at the Oklahoma State University (Stillwater, OK) by Performance Food Group (PFG, Richmond, VA). The subprimals were obtained by PFG from multiple beef processing plants in the US and originated from fed cattle, with a yield grade of 3 or higher. Prior to shipping to FAPC, subprimals were wet aged, vacuum packaged, and stored at refrigerated temperature (4 to 5°C). The subprimals were mechanically tenderized by passing once through a needle tenderizer (Ross TC700M-I, Ross Industries, Midland, VA) at the FAPC Meat Pilot Plant. Samples were placed in such a way that the external carcass surface faced downward when passed through the tenderizer. After tenderization, the subprimals (Institutional Meat Purchase Specifications item numbers in
Institutional Meat Purchase Specifications item numbers for the subprimals used for steak cuts
Subprimal | IMPS1 number |
Beef round knuckle-cap off | 167A |
Beef eye of round | 171C |
Beef ribeye roll-lip on-boneless | 112A |
Beef chuck-shoulder clod-top blade | 114D |
Beef round-top inside | 168 |
Beef loin-bottom sirloin butt-flap-boneless | 185A |
Beef loin-tops sirloin butt-boneless | 184 |
Beef loin-bottom sirloin butt-tri-tip-boneless | 185D |
Beef loin-bottom sirloin butt-ball tip-boneless | 185B |
Beef plate-outside skirt | 121C |
Beef flank-flank steak | 193 |
1IMPS = Institutional Meat Purchase Specifications.
Comparison of experimental safe cooking times and predicted safe cooking times of beef top round and knuckle steaks with uniform thickness (cm) and varying weights (g)
Round | ||||||
Top round | Knuckle | |||||
Thickness, cm | Weight, g | ESCT1, min | PSCT2, min | Weight, g | ESCT1, min | PSCT2, min |
1.27 | 170 | 4.27 ± 0.90a | 4.10 ± 0.20 | 170 | 6.88 ± 0.68a | 6.76 ± 0.29 |
227 | 5.23 ± 0.36a | 4.83 ± 0.16 | 198 | 8.21 ± 0.91a | 6.93 ± 0.11 | |
283 | 4.38 ± 0.53a | 5.75 ± 0.40 | 283 | 6.66 ± 0.86a | 7.93 ± 0.13 | |
2.54 | 170 | 11.94 ± 0.69b | 11.15 ± 0.20 | 113 | 11.66 ± 0.44b | 11.82 ± 0.41 |
227 | 12.33 ± 1.36b | 12.73 ± 0.58 | 170 | 15.16 ± 0.44b | 12.63 ± 0.65 | |
283 | 14.16 ± 3.92b | 13.48 ± 0.57 | 255 | 15.22 ± 1.07b | 13.80 ± 0.48 | |
3.81 | 170 | 23.11 ± 0.67c | 16.93 ± 0.35 | |||
227 | 18.05 ± 0.51c | 17.01 ± 0.33 | ||||
283 | 19.50 ± 0.33c | 18.02 ± 0.54 |
a–cLetters provide evidence of significant difference, where different letters represent statistical significance (P < 0.01) between ESCT values for a particular steak cut in the same column.
1ESCT = Experimental safe cooking time: cooking time (min) required by a steak to reach an internal temperature of 70 to 71 °C.
2PSCT = Predicted safe cooking time: cooking time (min) predicted by the model that would be required by a steak to reach an internal temperature of 70 to 71 °C. The values for ESCT and PSCT are expressed as the mean ± SD for 3 independent cooking experiments of a particular steak cut, with a given weight and thickness.
Comparison of experimental safe cooking times and predicted safe cooking times of beef top sirloin, sirloin cap, and tri-tip steaks with uniform thickness (cm) and varying weights (g)
Loin | |||||||||
Top sirloin | Sirloin cap | Tri-tip | |||||||
Thickness, cm | Weight, g | ESCT1, min | PSCT2, min | Weight, g | ESCT1, min | PSCT2, min | Weight, g | ESCT1, min | PSCT2, min |
1.27 | 142 | 4.29 ± 0.09a | 4.03 ± 0.10 | 170 | 6.55 ± 0.54a | 6.16 ± 0.51 | 170 | 10.16 ± 0.93a | 8.95 ± 0.17 |
283 | 6.43 ± 0.41a | 5.75 ± 0.22 | |||||||
2.54 | 142 | 9.38 ± 0.25b | 12.38 ± 0.15 | 198 | 19.21 ± 0.87b | 17.49 ± 0.05 | |||
170 | 12.60 ± 0.86b | 12.50 ± 0.26 | 198 | 13.72 ± 0.57b | 12.07 ± 0.51 | ||||
198 | 11.49 ± 0.74b | 12.61 ± 0.02 | |||||||
255 | 11.5 ± 0.19b | 13.78 ± 0.11 | |||||||
3.81 | 170 | 16.38 ± 0.95c | 16.38 ± 0.36 | 227 | 14.60 ± 0.69b | 16.99 ± 1.40 | |||
198 | 18.00 ± 0.35c | 17.45 ± 0.02 |
a–cLetters provide evidence of significant difference, where different letters represent statistical significance (
1ESCT = Experimental safe cooking time: cooking time (min) required by a steak to reach an internal temperature of 70 to 71°C.
2PSCT = Predicted safe cooking time: cooking time (min) predicted by the model that would be required by a steak to reach an internal temperature of 70 to 71°C. The values for ESCT and PSCT are expressed as the mean ± SD for three independent cooking experiments of a particular steak cut, with a given weight and thickness.
Comparison of experimental safe cooking times and predicted safe cooking times of beef ribeye steaks with uniform thickness (cm) and varying weights (g)
Rib | |||
Ribeye | |||
Thickness, cm | Weight, g | ESCT1, min | PSCT2, min |
1.27 | 113 | 2.22 ± 0.69a | 4.62 ± 0.60 |
170 | 4.27 ± 0.82a | 5.01 ± 0.12 | |
227 | 5.49 ± 1.08a | 5.36 ± 0.15 | |
2.54 | 283 | 10.83 ± 0.33b | 16.22 ± 0.06 |
340 | 15.50 ± 1.89b | 17.11 ± 0.29 | |
3.81 | 397 | 19.50 ± 1.89c | 22.10 ± 0.97 |
454 | 21.5 ± 1.45c | 23.61 ± 0.21 |
a–cLetters provide evidence of significant difference, where different letters represent statistical significance (
1ESCT = Experimental safe cooking time: cooking time (min) required by a steak to reach an internal temperature of 70 to 71°C.
2PSCT = Predicted safe cooking time: cooking time (min) predicted by the model that would be required by a steak to reach an internal temperature of 70 to 71°C. The values for ESCT and PSCT are expressed as the mean ± SD for three independent cooking experiments of a particular steak cut, with a given weight and thickness.
Comparison of experimental safe cooking times and predicted safe cooking times of beef strip loin, flap, and flanks steaks with uniform thickness (cm) and varying weights (g)
Strip loin | Flap | Flank | |||||||
Thickness, cm | Weight, g | ESCT1, min | PSCT2, min | Weight, g | ESCT1, min | PSCT2, min | Weight, g | ESCT1, min | PSCT2, min |
1.27 | 113 | 5.00 ± 0.86a | 4.21 ± 0.32 | 113 | 11.22 ± 0.83a | 14.17 ± 0.65 | 170 | 15.99 ± 0.16a | 14.41 ± 0.33 |
142 | 3.78 ± 1.10a | 4.41 ± 0.20 | 142 | 11.10 ± 0.95a | 14.33 ± 0.13 | 227 | 17.60 ± 0.10a | 15.63 ± 0.41 | |
170 | 5.77 ± 0.47a | 4.64 ± 0.03 | 170 | 18.10 ± 1.44b | 14.58 ± 0.11 | 283 | 18.22 ± 1.60a | 16.23 ± 0.13 | |
227 | 19.77 ± 0.50b | 15.82 ± 0.32 | 340 | 17.11 ± 0.25a | 16.57 ± 0.27 | ||||
2.54 | 227 | 17.16 ± 0.57b | 19.92 ± 0.16 | 283 | 25.55 ± 0.60c | 20.98 ± 0.39 | |||
255 | 16.72 ± 2.21b | 20.31 ± 0.23 | |||||||
283 | 21.72 ± 1.54b | 20.31 ± 0.15 | |||||||
3.81 | 340 | 26.10 ± 2.61c | 23.58 ± 0.17 | ||||||
394 | 25.46 ± 0.46c,d | 25.02 ± 0.54 | |||||||
454 | 27.06 ± 0.92c,d | 25.90 ± 0.25 | |||||||
567 | 30.11 ± 0.03d | 27.42 ± 0.76 |
a–dLetters provide evidence of significant difference, where different letters represent statistical significance (
1ESCT = Experimental safe cooking time: cooking time (min) required by a steak to reach an internal temperature of 70 to 71°C.
2PSCT = Predicted safe cooking time: cooking time (min) predicted by the model that would be required by a steak to reach an internal temperature of 70 to 71°C. The values for ESCT and PSCT are expressed as the mean ± SD for three independent cooking experiments of a particular steak cut, with a given weight and thickness.
Prior to each cooking experiment, steak dimensions (cm) and weights (g) were recorded. Steaks were measured for thickness (cm), width (cm), and length (cm), using the sliding vernier calipers (Starrett 86405180, MSC Industrial, Melville, NY), following the method described by
Experimental safe cooking time (ESCT) was defined as the cooking time required by a steak to reach an internal temperature of 70 to 71°C. Steak cooking temperature was chosen based on the recommendations of USDA-FSIS guidelines for a well-cooked, mechanically tenderized steak (
The rate of temperature increase (RTI), i.e., the rate at which the steak temperature increased with time, was calculated for each steak cut through linear fitting of the time-temperature profiles, obtained from the cooking experiments. The linear fit was statistically validated using regression coefficient (
The model was built using correlation and regression analyses and checked using multicollinearity. Association between the steak parameters (length, width, thickness, and weight), RTI, and ESCT was examined through the Pearson’s correlation statistics to identify the most influential factors for ESCT. The factors with a correlation coefficient (σ) of 0.60 or higher (at
Stepwise regression can be performed using any of the following 3 procedures: forward selection, backward elimination, or both (
To ensure that there was no inter-correlation between the prediction variables, which could result in false elevation of prediction accuracy, a multicollinearity check was performed using the variance inflation factor (
Precision and consistency were maintained throughout the experiments. The assumptions made by
Each experiment, where the experimental unit was an individual steak cut of a given weight and thickness, was repeated 3 times. The ESCT was used to determine PSCT and both were expressed as the mean ± standard deviation of the replicate values. Data were analyzed using one-way analysis of variance, where the Tukey-Kramer-honest significant difference test was used to obtain the means of ESCT for a given steak cut of a particular thickness and weight. Significant differences (
The ESCT for each steak cut, of a given weight and thickness, are presented in
The RTI was determined through linear fitting of the time-temperature profiles, obtained from the cooking experiments (
a-b. Rate of temperature increase (°C/min) during cooking of beef (a) top round and (b) knuckle steaks of varying thickness (cm). c-e Rate of temperature increase (°C/min) during cooking of beef (c) top sirloin, (d) sirloin cap and (e) tri-tip steaks of varying thickness (cm). f. Rate of temperature increase (°C/min) during cooking of beef (f) ribeye steaks of varying thickness (cm). g–i. Rate of temperature increase (°C/min) during cooking of beef (g) strip loin, (h) flank and (i) flap steaks of varying thickness (cm).
The results of correlation analyses are shown in
Selection of variables, to be included in the prediction model, based on correlation coefficient between the steak variables and the experimental safe cooking times
Steak variables | Correlation coefficient1 | 95% Confidence interval2 | |
Weight | +0.61 | 0.49 – 0.69 | 0.0001 |
Length | -0.07 | -0.22 – 0.84 | 0.3700 |
Width | -0.18 | -0.33 – (-0.03) | 0.0200 |
Thickness | +0.68 | 0.59 – 0.75 | 0.0001 |
RTI3 | -0.78 | -0.83 – (-0.71) | 0.0001 |
1Correlation was checked between steak parameters and ESCT (
2Confidence interval for each correlation coefficient indicates that 95% of the coefficient values will be included in that range.
3RTI = Rate of temperature increase (°C/min): the rate at which the steak temperature increased with time while cooking.
A regression coefficient (
The relationship between PSCT and ESCT is illustrated in
Linear relationship between experimental and predicted safe cooking times for different steak cuts, indicated by regression coefficient (
Experimental safe cooking times and RTI were found to be dependent on the thickness and type of steak cuts. However, for model building, correlation analyses revealed that the thickness, weight and RTI were highly correlated with ESCT. Furthermore, variance inflation factor showed that these factors were not inter-correlated which prevented the false elevation of model accuracy. The regression model built with these factors was robust in predicting cooking time to attain a safe internal temperature for various steak cuts. Overall, no significant differences (
The authors declare that there is no conflict of interest.
The authors would like to acknowledge the support of Brad Morgan and Performance Food Group (Richmond, VA). We also wish to thank Kyle Flynn for his assistance with meat fabrication.