Factors associated with surface iridescence in fresh beef.

The objective of this study was to investigate factors associated with surface iridescence in fresh beef. Eight muscles were evaluated for occurrence of surface iridescence: Biceps femoris (BF), Gluteus medius (GM), Longissimus lumborum (LD), Psoas major (PM), Rectus femoris (RF), Semimembranosus (SM), Semitendinosus (ST), and Tensor fasciae latae (TF). Incidence of surface iridescence was 91% for ST, 34% for SM, 27% for LD, 20% for GM, 12% for RF, 9% for BF, 8% for TF, and 6% for PM (P<0.05). Factors associated with surface iridescence in the ST were further examined because iridescence was observed to a much higher degree in the ST as compared with other muscles evaluated. Greater ST surface iridescence was associated with larger ribeye areas, more youthful lean maturity scores, higher L(∗), a(∗) and b(∗) colorimeter values, lower ultimate pH values, and faster cooking (P<0.05).

A survey of beef muscle color and pH.

The objectives of this study were to define a beef carcass population in terms of muscle color, ultimate pH, and electrical impedance; to determine the relationships among color, pH, and impedance and with other carcasses characteristics; and to determine the effect of packing plant, breed type, and sex class on these variables. One thousand beef carcasses were selected at three packing plants to match the breed type, sex class, marbling score, dark-cutting discount, overall maturity, carcass weight, and yield grade distributions reported for the U.S. beef carcass population by the 1995 National Beef Quality Audit. Data collected on these carcasses included USDA quality and yield grade data and measurements of muscle color (L*, a*, b*), muscle pH, and electrical impedance of the longissimus muscle. About one-half (53.1%) of the carcasses fell within a muscle pH range of 5.40 to 5.49, and 81.3% of the carcasses fell within a longissimus muscle pH range of 5.40 to 5.59. A longissimus muscle pH of 5.87 was the approximate cut-off between normal and dark-cutting carcasses. Frequency distributions indicated that L* values were normally distributed, whereas a* and b* values were abnormally distributed (skewed because of a longer tail for lower values, a tail corresponding with dark-cutting carcasses). Electrical impedance was highly variable among carcasses but was not highly related to any other variable measured. Color measurements (L*, a*, b*) were correlated (P < 0.05) with lean maturity score (-.58, -.31, and -.43, respectively) and with muscle pH (-.40, -.58, and -.56, respectively). In addition, fat thickness was correlated with muscle pH and color (P < 0.05). There was a threshold at approximately .76 cm fat thickness, below which carcasses had higher muscle pH values and lower colorimeter readings. Steer carcasses (L* = 39.62, a* = 25.20, and b* = 11.03) had slightly higher colorimeter readings (P < 0.05) than heifer carcasses (L* = 39.20, a* = 24.78, and b* = 10.80) even though muscle pH was not different between steer and heifer carcasses. Dairy-type carcasses (pH = 5.59, L* = 37.56, a* = 23.40, and b* = 9.68) had higher muscle pH values and lower colorimeter readings than either native-type (pH = 5.50, L* = 39.55, a* = 25.13, and b* = 11.00) or Brahman-type (pH = 5.46, L* = 39.75, a* = 25.17, and b* = 11.05) carcasses (P < 0.05).

Using measurements of muscle color, pH, and electrical impedance to augment the current USDA beef quality grading standards and improve the accuracy and precision of sorting carcasses into palatability groups.

This research was conducted to determine whether objective measures of muscle color, muscle pH, and(or) electrical impedance are useful in segregating palatable beef from unpalatable beef, and to determine whether the current USDA quality grading standards for beef carcasses could be revised to improve their effectiveness at distinguishing palatable from unpalatable beef. One hundred beef carcasses were selected from packing plants in Texas, Illinois, and Ohio to represent the full range of muscle color observed in the U.S. beef carcass population. Steaks from these 100 carcasses were used to determine shear force on eight cooked beef muscles and taste panel ratings on three cooked beef muscles. It was discovered that the darkest-colored 20 to 25% of the beef carcasses sampled were less palatable and considerably less consistent than the other 75 to 80% sampled. Marbling score, by itself, explained 12% of the variation in beef palatability; hump height, by itself, explained 8% of the variation in beef palatability; measures of muscle color or pH, by themselves, explained 15 to 23% of the variation in beef palatability. When combined together, marbling score, hump height, and some measure of muscle color or pH explained 36 to 46% of the variation in beef palatability. Alternative quality grading systems were proposed to improve the accuracy and precision of sorting carcasses into palatability groups. The two proposed grading systems decreased palatability variation by 29% and 39%, respectively, within the Choice grade and decreased palatability variation by 37% and 12%, respectively, within the Select grade, when compared with current USDA standards. The percentage of unpalatable Choice carcasses was reduced from 14% under the current USDA grading standards to 4% and 1%, respectively, for the two proposed systems. The percentage of unpalatable Select carcasses was reduced from 36% under the current USDA standards to 7% and 29%, respectively, for the proposed systems. These grading systems, which included requirements for maturity, marbling, hump height, and colorimeter readings, could be implemented into the current USDA beef quality grading standards and improve the accuracy and precision of sorting beef carcasses into palatability groups. At the least, measurements of muscle color or pH could be used in a branded-beef program to increase the palatability consistency of its beef products.