J. D. Crouse

The relationship of muscle fibre size to tenderness of beef.

Steaks were removed from loins of beef carcasses at 1, 3, 6 or 14 days post mortem for fragmentation index (MFI), Warner-Bratzler Shear Force (SF) and sensory panel tenderness evaluation. Also, after 1 day of storage, samples were removed for histological observations. Greatest improvement in tenderness, SF and MFI occurred within the first 6 days of storage. Sensory panel tenderness was correlated (P < 0·01) with SF and MFI. Average muscle fibre size was correlated (P < 0·01) with tenderness and SF at days 1 and 3, but not at days 6 and 14. Evidently, muscle fibre size is important to tenderness prior to post-mortem storage of meat and proteolysis, but becomes less of a factor in tenderness after 6 days of storage.

Factors associated with tenderness in young beef

One hundred and twenty-two crossbred steers of varying percentages of Bos Indicus and Bos Taurus breeding were slaughtered to determine the relationship of carcass and meat characteristics to tenderness. Carcasses were graded and longissimus dorsi muscle samples were evaluated for fibre type characteristics, sensory and shear force determination, sarcomere length, intramuscular fat content, collagen content and solubility and fragmentation index. Sarcomere length and collagen content and solubility were not significantly related to shear force values or sensory tenderness ratings. The fragmentation index was highly correlated to sensory tenderness ratings (r = -0·60) and shear force values (r = 0·53) indicating that variation in tenderness is associated with myofibrillar protein degradation. A four variable regression equation that included fragmentation index, lean colour, marbling and per cent red fibres accounted for 56% of the variation in sensory tenderness. Fragmentation index directly accounted for 30% of the variation in sensory tenderness in the four variable equation.

Attachment and Proliferation of Bacteria on Meat

The attachment of bacteria ( Serratia marcescens , Staphylococcus aureus , Streptococcus faecalis , Salmonella arizonae , Pseudomonas aeruginosa , and Listeria monocytogenes ), to lean muscle tissue and fat tissue was investigated. The number of cells attached to the meat was directly proportional to the initial cell concentrations present. There was no significant difference in the number of cells attached between the lean muscle tissue and fat tissues among the organisms tested. All bacteria tested except P. aeruginosa proliferated better on the lean muscle tissues than on the fat tissue at ambient temperature for 72 h. No significant attachment competition to tissue samples was seen between L. monocytogenes and P. aeruginosa , however, the numbers of P. aeruginosa were greater than L. monocytogenes (after 24 h). Similarly, no competitive attachments between S. aureus and S. marcescens , S. faecalis and S. arizonae were observed; but the numbers of S. marcescens were greater than S. aureus , and S. arizonae were greater than S. faecalis , when the inoculated meat was incubated at room temperature for 24 h.

Effect of feed energy intake on collagen characteristics and muscle quality of mature cows

Samples from mature cows fed a high-energy and maintenance-energy diet for 84 days prior to slaughter were used to compare collagen solubility and palatability traits. Cows fed a high-energy diet prior to slaughter had increased percentage heat-labile collagen, less sensory panel detectable connective tissue and lower shear force values than cows fed a maintenance-energy diet. Mature cows fed a high-energy diet were fatter and had more marbling than cows fed a maintenance-energy diet. The increased collagen solubility from feeding a high-energy diet to mature cows resulted in palatability and shear force ratings similar to those expected from young animals.

The influence of diet and time on feed on carcass traits and quality

Seventy-two Simmental-sired steer calves (approximately 8 months old) were randomly assigned to one of two pre-finishing dietary treatments (low energy or high energy). Energy intake was monitored to produce average daily gains of approximately 0·41 (low energy) or 0·68 (high energy) kg during a 6-month growth interval. At 14 months of age the steers were assigned to four finishing (time on feed) groups-0, 56, 112 or 168 days. Steers assigned to the 0-day group received their respective pre-finishing diets from 14 to 20 months of age. The other groups received a finishing diet for the final 56, 112 or 168 days of the experiment. All steers were slaughtered at 20 months. Steers backgrounded on high energy diets produced heavier (P < 0·01), fatter (P < 0·01) carcasses with higher (P < 0·01) marbling scores and quality grades and LD steaks with greater (P < 0·05) ease of fragmentation, less (P < 0·05) detectable connective tissue and higher (P < 0·05) tenderness ratings as compared to steers on low energy diets. After 112 days on feed, quality grades were similar for high energy and low energy steers; however, tenderness ratings still favored the high energy treatment. Increased time on feed was associated with higher quality grades, but only within the low energy treatment group. Additionally, tenderness of LD steaks improved with increased time on feed; howver, the greatest improvement was observed from 0 to 56 days.

Microbial decontamination and weight of carcass beef as affected by automated washing pressure and length of time of spray

Carcasses were obtained from 56 heifers that were fed a corn-corn silage diet to determine the effects of automated washing water spray pressures (SP) of 2412 kilopascal (kPa) or 4134 kPa and chain speeds (CS) of 3.9, 5.9 or 7.9 m/min on microflora and weight changes of carcass beef. Carcass beef sides were weighed before washing, 5 min after washing and 20 h after washing and storage at 0°C. Enterobacteriaceae and aerobic counts of forequarters and hindquarters were determined before and 20 h after washing. Carcass sides shrank 1.52 kg after 20 h of storage. This shrinkage was similar among all treatment groups. Washing reduced Enterobacteriaceae counts 1.57 log10 colony forming units (CFU)/200 cm2 and counts of aerobic bacteria 0.87 log10 CFU/200 cm2. All combinations of SP and CS were similar in effectiveness of reducing Enterobacteriaceae counts. However, the low SP tended (P<0.102) to be more effective in reducing aerobic counts. Forequarters possessed greater (P<0.051) aerobic counts (5.44 vs 5.29 log10 CFU/200 cm2) than hindquarters, but washing eliminated this differential. Automated carcass washing reduced bacterial counts of carcass beef, but within treatments applied, SP and CS had no effect on variation in carcass weight or variation in reduction of microflora. Research indicated that automated carcass washing was a useful procedure for reducing bacterial counts on carcass beef without affecting carcass weights.

Effect of subcutaneous fat and high temperature conditioning on bovine meat tenderness.

Effects of subcutaneous fat cover and high temperature conditioning on tenderness of meat were studied using 16 steer carcasses. Longissimus subcutaneous fat cover was completely removed from eight carcasses and the right and left sides were stored at either 0°C or 26°C. After 6 h at 26°C, the sides were transferred to the 0°C room; and after 24 h, all sides were transferred to a 1°C room for the duration of the experiment. Cold temperature and removal of fat cover reduced (P < 0·05) the longissimus muscle temperature at 6, 9 and 12 h post-mortem. The pH of the longissimus muscle was lower (P < 0·05) as the result of high temperature conditioning and fat cover 6, 9 and 12 h post-mortem. Consequently, conditions existed which would have been expected to promote cold shortening, yet high temperature conditioning and fat cover had no consistent effects on myofibrillar fragmentation index, sarcomere length or shear values.

Bovine Longissimus dorsi muscle glycogen and color response as affected by dietary regimen and post-mortem electrical stimulation in young bulls

Eighty bulls were assigned to one of two groups and fed a dietary regimen to defer or accelerate growth until slaughter. Bulls fed at an accelerated rate of growth (or high energy regimen) had higher post-mortem pH, and lower muscle glycogen stores, with darker lean color, and improved shear and palatability traits compared to deferred fed animals. Bulls fed at an accelerated rate of growth also had a higher degree of marbling and USDA quality grade. Electrical stimulation did not affect (P > 0·05) ultimate pH, but reduced (P < 0·05) glycogen values at 0 and 2 h post mortem. Electrical stimulation also improved muscle color, lowered cooking losses and improved the palatability of cooked longissimus dorsi steaks.

Effect of feeding regimen, breed and sex condition on carcass composition and feed efficiency

Eighty bulls and eighty steers representing four breed types (7/8 Angus. 7/8 Simmental, 7/8 Simmental × 7/8 Angus and 7/8 Simmental × 7/8 Hereford) were randomly assigned to two diets by sex class and breed type. Exotic breeds produced heavier, leaner, more muscular carcasses, with lower USDA quality grades and darker colored, coarser textured lean. Angus 9-10-11th rib composition showed that Angus tended to have less lean, more bone and the most fat when compared to the Simmental and Simmental crosses. Feeding the deferred diet resulted in carcasses with (P < 0·05) less fat, lower USDA quality grade, smaller ribeyes, more sensory panel detectable connective tissue, higher cooking losses and higher Instron shear values. Sex class caused differences (P < 0·05) in feed efficiency, carcass traits and sensory properties.

Palatability of beef from bulls administered exogenous hormones

One-hundred and forty four weanling bulls of Angus (A, n = 48), Simmental x Hereford (SH, n = 48) and Simmental (S, n = 48) breeding were either castrated, left intact, left intact and implanted with Ralgro or left intact and implanted with Synovex S. Cattle were slaughtered after either 190, 246 or 315 days of high-energy feeding, and the right side of each carcass was electrically stimulated. Sensory analysis was conducted on longissimus dorsi steaks after 5 days aging and Warner-Bratzler shear force (WBS) was measured after 5, 10 and 15 days aging. Steers had lower (P < 0·05) WBS and more desirable sensory panel scores for juiciness, ease of fragmentation, amount of connective tissue and overall tenderness than all intact treatments. The implanting of weanling bulls with synthetic steroid hormone compounds did not make a practical improvement in beef tenderness.