EFFECTS OF PHYSIOLOGICAL MATURITY OF BEEF AND MARBLING OF RIB STEAKS ON EATING QUALITY

SUMMARY— Selected characteristics of beef rib steaks representing three physiological maturity levels and two marbling levels were investigated. Paired steaks at the 1lth thoracic vertebra were used to obtain cooking time and losses, palatability scores, Warner-Bratzter shear values, and selected histological data. In addition, steaks from the left 7th and right 8th thoracic vertebrae positions were used to measure cooking time and losses, Warner-Bratzfer shear values, waterholding capacity, pH, color-difference, and total moisture. Ether extract was obtained for raw longissimus dorsi at the 12th thoracic vertebra. Maturity and marbling affected told moisture (P < 0.001), quantity of fat in raw muscle (histological measurement, P < 0.01). ether extract (P < 0.001). and dripping losses (7th and 8th thoracic vertebrae P < 0.001). Other factors were not affected significantly. Maturity and marbling, at levels represented, had little effect on palatability of the steaks, although generally, measurements for fat content were higher and those for moisture lower at the higher marbling level. Most correlation coefficients for overall acceptability and histological measurements were low. Tenderness had more influence on the overall acceptability of the meat than flavor or juiciness. Moderate to high relationships occurred between cooking time and both initial weight of steaks and cooking losses. Generally, waterholding capacity was not related to pH, total moisture, or cooking losses. Correlation coefficients for pH vs. shear value and pH vs. color-difference were low.     

FACTORS RELATED TO LONGISSIMUS TENDERNESS AMONG ALTERNATE METHODS OF LEAN BEEF PRODUCTION

A 2³ factorial arrangement of treatments comparing bull versus steer, Angus versus Limousin, and zeranol implanted versus nonimplanted controls was used as a data source for this trial. Bulls had less intramuscular lipid and more total collagen than steers. Limousin had less intramuscular lipid, shorter sarcomere lengths and a higher percentage of fast-twitch glycolytic fibers than Angus cattle. Limousin and implanted cattle had more rapid postmortem temperature declines. Chemical, physical and histological traits as well as yield and quality grade traits were used in correlation procedures to examine their relationship with sensory panel tenderness and Warner-Bratzler shear force values of longissimus muscle steaks. The results of this trial indicate that postmortem muscle temperature decline plays a role in longissimus palatability and must be considered in the production of leaner beef.     

FACTORS AFFECTING THE HARDNESS OF FAT ON SIDES OF CHILLED BEEF

The influence of some factors on the hardness of subcutaneous fat on sides of chilled beef as measured by the average force resisting movement of a cutting pin (Ff) was investigated. Values of Ff determined at a fat temperature of 10°C on grass-fed animals denied water 24 h preslaughter were not significantly influenced by moisture content (5-11%) or fat depth (2-27 mm). There was a quadratic relationship (P<0.001) between the age of animals at slaughter (31-141 months) and Ff, and a linear one (P<0.001) between saturated fatty acid content (35-50%) and Ff. Values of Ffat a fat temperature of 5°C were not significantly related to moisture content (1-22%) but there was a linear relationship (P<0.01) with fat depth (5-13 mm). This had a common slope for the three feeding patterns: (1) grass-fed animals denied water 24 h preslaughter; (2) grass-fed animals given access to water 24 h preslaughter, and; (3) lot-fed animals given access to water 24 h preslaughter.     

CORRELATIONS BETWEEN SERUM CONCENTRATIONS OF LEPTIN AND BEEF CARCASS COMPOSITION AND QUALITY

Steers (n = 84) of various genotypes raised under diverse management conditions from the 2001 Missouri State Beef carcass contest were used to evaluate the relationship between serum concentrations of leptin and beef carcass composition and quality. Serum and carcass data including hot carcass weight; adjusted 12^th rib fat thickness; percentage kidney; pelvic and heart fat (KPH); marbling score; and USDA yield grades were measured at harvest. Leptin was correlated with back fat thickness over the 12^th rib, yield grade, and marbling score (r = 0.35, r = 0.19, r = 0.26 , P < 0.10; respectively), but not with hot carcass weight, ribeye area, or KPH (P > 0.10). Serum concentrations of leptin may be useful to objectively evaluate carcass composition in fed cattle and may provide a means by which carcass quality can be predicted in the live animal.     

USDA MATURITY INDICES AND PALATABILITY OF BEEF RIB STEAKS1

In a population of 195 beef carcasses, as maturity increased (by whole USDA groups) from A to B, flavor, tenderness and overall palatability ratings for rib steaks decreased (P < .05); further increases in maturity (B vs. E) resulted in subsequent decreases (P < .05) in tenderness and overall palatability. Subdivision of whole maturity groups into thirds and subsequent data analyses supported precepts in USDA grade standards of declining palatability with advancing maturity, but the declines, when they occurred, were nearly linear through the extremes (from A^? to E⁺) and did not support the concept, in USDA grade standards, of a precipitous decline in eating satisfaction at or near the B⁺/C^? maturity line. Among seven carcass maturity indices, all were similarly and singularly related (P < .05) to palatability of rib steaks, with some measure of skeletal maturity (the best of these was color/shape of the rib bones) plus some measure of muscle maturity (the best of these was color of the longissimus muscle) combining (by means of multiple regression analyses) to predict tenderness (panel ratings and shear values) with maximum precision. Neither total pigment concentration (a chemical measure of muscle color), amount of ether-extractable lipid (a chemical measure of intramuscular fatness) nor marbling score (a visual measure of intramuscular fatness) was able to explain more than about 7% of the observed variability in palatability ratings for cooked beef steaks. Data suggest that more attention should be paid to appearance of rib bones in a carcass (to better assess effects of maturity) and that less attention could be paid to differences between SLIGHT, SMALL and MODEST in marbling in the ribeyes, in attempting to predict, via USDA grading, the palatability of beef rib steaks.     

FACTORS AFFECTING COLOR PROPERTIES OF BEEF PATTIES COOKED ON AN OUTDOOR GAS GRILL

Visual and instrumental color properties were obtained on beef patties cooked on an outdoor gas grill. Factors evaluated as to their influence on color were fat content, (20–28% vs 6–10%) patty handling prior to cooking (fresh, thawed either as patties or bulk ground beef), endpoint in cooking (57, 66, 71C, slit in outer edge of patty during cooking showing brown color), lighting conditions and evaluation time post-cooking. Factors resulting in less pink/red color and more brown color in cooked patties were (1) higher fat content, (2) cooking bulk frozen, thawed, then pattied product, (3) higher endpoint temperature and longer time postcooking before evaluation. Termination of cooking by observing brown color in slits in patties cooked on a gas grill was not synonymous with a safe internal temperature.     

PHYSICAL AND SENSORY PROPERTIES OF LEAN GROUND BEEF PATTIES CONTAINING METHYLCELLULOSE AND HYDROXYPROPYLMETHYLCELLULOSE1

Broiled, lean ground beef patties containing no additives, two levels of methylcellulose (MC, 0.5 or 1.0%) and two levels of hydroxypropylmethylcellulose (HPMC, 0.5 or 1.0%) were evaluated for raw and cooked composition, cooking losses, sensory attributes and Instron compression measurements. MC or HPMC addition did not significantly affect the fat, moisture or protein content of the raw and cooked patties. Patties containing HPMC received greater tenderness, juiciness and off-flavor sensory scores when compared with patties containing MC or no additive. MC or HPMC addition increased patty gumminess sensory scores and decreased Instron compression values. Sensory cooked meat flavor decreased with gum addition.     

RELATIONSHIPS OF SERUM, MUSCLE AND SUBCUTANEOUS LIPIDS TO BEEF CARCASS TRAITS AND FLAVOR

ABSTRACT— An examination of the means and range coefficients of the total serum, intramuscular (longissimus) and subcutaneous lipids, the major lipid classes and fatty acid compositions of the 3 tissue sites from 30 heifers and 31 bulls of the Hereford breed revealed some interesting aspects of lipid metabolism. When placed on a concentration (percent of tissue) basis, significant differences due to sex, environment and sires were shown by an analysis of variance for many of the lipid components. Phenotypic correlations, also computed on a concentration basis, gave indications of the growth and development of the animals, in addition to showing the associations of various lipid components of the 3 tissue sites to various carcass cutout traits and flavor. With a few exceptions, low positive correlations were shown for the serum lipid components with flavor, whereas, most of the marbling and subcutaneous fat components exhibited low negative correlations with flavor.     

COOKED COLOR OF PATTIES PROCESSED FROM VARIOUS COMBINATIONS OF NORMAL OR HIGH pH BEEF AND LEAN FINELY TEXTURED BEEF

Color of cooked patties prepared from beef with a pH of 5.7 (normal = N) or pH = 6.2 (dark cutting = DC) beef and with either 0, 25, 50 or 75% lean finely textured beef (LFTB) was evaluated. Patties were cooked to 68.3C, 71C, or until >75% were "well-done". Inclusion of LFTB in N patties resulted in higher a*-values, but did not affect either visual color scores or myoglobin (Mb) denaturation. Inclusion of LFTB in DC patties did not affect pH. A higher LFTB content resulted in lower a*-values, higher hue-angle, a more well-done visual color and increased Mb denaturation. To appear well-done, DC patties without LFTB had to be cooked to 89C, whereas DC patties with 75% LFTB had to be cooked to 83C. Possibly, conditions during production of LFTB are responsible for the increased heat sensitivity of Mb from LFTB.     

FACTORS AFFECTING COLOR AND APPEARANCE OF CORN TORTILLAS

A study is described which examined the relative contributions of production and post-production variables on color and appearance of corn tortillas. Tortillas processed at three production sites were stored under exact marketing conditions in refrigerated display cases in three supermarkets. Reflectance measurements and visual evaluations immediately on delivery showed that processing variables contributed heavily to initial appearance and color differences. Rate of appearance deterioration on storage was affected by both processing and storage variables. The rate and magnitude of visually perceived changes on storage was not paralleled by a similar rate and magnitude of change in diffuse reflectance characteristics. This suggests that the visually perceived changes were due to structural rather than color changes.     

EARLY POSTMORTEM MUSCLE SHORTENING AND TENSION IN RELATION TO TENDERNESS IN BEEF M. LONGISSIMUS

The purpose of this study was to investigate muscle tension and shortening in relation to tenderness in beef M. longissimus. Initially, an intercalibration of six identical rigormeters using a polyacrylamide standard showed that the rigormeters gave reproducible results. This means that the rigormeter is a potentially valuable tool in studies of postmortem muscle tension and shortening. Tension and shortening of M. longissimus from 24 bulls carcasses exposed to two different chilling regimes were measured 1.5 to 20 h postmortem in the rigormeters. The muscle samples were separated into three groups; fast chilled (all tough), slow chilled (tough) and slow chilled (tender). On average, both the developed tension and accumulated shortening of muscle strips during this period were highest in tender, slow chilled samples and lowest in fast chilled samples. There was a relationship between glycolytic rate and the muscle contraction process, as the fast glycolyzing muscles exerted the fastest development of tension and contraction. This study indicates that tension and, shortening, as measured in the rigormeter, is related to WB shear force measured in aged meat.     

REALIMENTATION OF CULL BEEF COWS. I. LIVE PERFORMANCE, CARCASS TRAITS AND MUSCLE CHARACTERISTICS

The objective of this study was to determine whether culled beef cows fed a high-concentrate diet (FED) would have improved live performance, carcass traits and muscle characteristics compared with forage fed (CON) cows. In addition, ractopamine (RAC) supplementation was evaluated for added benefits over high concentrate alone. Live weight, average daily gain, hot carcass weight, ribeye area, marbling, quality grade and carcass fat measurements increased ( P ≤  0.05) by realimentation. As a percent of hot carcass weight, muscle yields did not differ ( P >  0.05). Lipid content increased ( P ≤  0.05) in 5 out of the 10 muscles from FED cows. Cows fed ractopamine showed some numeric improvements over feeding alone, but few statistical differences ( P >  0.05). This may result from variability associated with cull cows, and warrants investigation into the best dose/duration for ractopamine. However, realimentation by itself was able to improve cull cow quality.

PRACTICAL APPLICATION

The U.S. beef industry continues to explore new avenues to enhance undervalued sectors of the production system. Through realimentation, cull cow quality can be improved. The data presented herein demonstrate that feeding a high-concentrate diet to cull cows increases both live and carcass weights. In addition, high concentrate-fed cull cows display more marbling and whiter fat cover than those fed at maintenance level. Qualification for premium programs, heavier weights and overall higher quality may lead to increased value for this underutilized sector of the beef industry.     

THE EFFECTS OF DELAYED CHILLING AND ALTERED CARCASS SUSPENSION UPON BEEF MUSCLE: II. HISTOLOGICAL AND CHEMICAL PROPERTIES

A total of 60 bovine carcasses from “exotic”— crossbred heifers, 12 to 16 months of age with carcass weights of approximately 260 kg were utilized in two separate but related experiments to evaluate the effects of delayed chilling at 2 temperatures (13 and 22°C) for 12 or 24 h and altered carcass suspension on certain histological and chemical properties of beef muscle. Hip-free suspension (suspension by the os coxae from hooks inserted through the obturator foramen with the limbs hanging free) produced substantially greater alteration of the histological properties of the muscles evaluated than did delayed chilling. Such alterations resulted in longer semimembranosus (SM) and longissimus dorsi (LD) sarcomeres, shorter psoas major (PM) sarcomeres, smaller SM and LD muscle fiber diameters, larger PM muscle fiber diameters, fewer SM and LD wavy fibers, more PM wavy fibers, and shorter SM muscle fiber fragment lengths (P<0.05). Neither hip-free suspension nor delayed chilling produced consistent differences (P<0.05) in either the intramuscular collagen content, the heat solubility of the intramuscular collagen, or the histological properties of the intramuscular collagen fibers.