This study was undertaken to learn what method of cooking beef round of Commercial and Prime grades is most. satisfactory for palatability and tenderness. Fourteen cooking methods were compared with a standard braising method. These methods were evaluated by means of cooking losses, palatability, and shear. Cover (5, 6, 7) has observed that roasting meat at a very low temperature produces a more tender product than cooking meat in water at the same low temperature or roasting at higher temperatures. She has found that tenderness increases as speed of heat penetration decreases, and has questioned (6) whether moist heat is needed for making tough meat tender.Seasoned and unseasoned meat tenderizers containing papain were tested by Hay, Harrison, and Vail (8). Treated beef was found to be more tender but less juicy than untreated meat. The tenderizer had no significant effect on total cooking losses, aroma, or flavor of the beef. Lowe (9) reported that beef treated with a marinade containing vinegar had lower shear values than the control sample. EXPERIMENTAL PROCEDUREPaired right and left rounds from 6 steers were obtained from the Chicago stockyards. Four of these animals were from the bottom quarter of the Commercial grade; they were slaughtered under the grading system in use before December 29, 1950. However, the grade of these animals would have been Commercial under the system in use after that date. These 4 animals were of Hereford extraction, from the Middle West, and were about 3lh years old, except the second animal which was about 2 years old. The carcass weights were 572 to 587 pounds. The fifth and sixth pairs of rounds were of average Prime grade, and were purchased after the change in the grading system. The animals from which these rounds were obtained were Hereford steers about 2 years old, from the Middle West. These 2 carcasses weighed 579 and 582 pounds, which is light for Prime.On the fifth or sixth day after slaughter, the rounds were sliced. Starting at the rump end the slices were l%, M, l%, 1y2, 1 / , l%, I%, % in. thick. The l%-in. slices were cooked, while the thinner slices were used raw for chemical assays which are reported in a second paper. Each slice was divided immediately into top round, including the adductor and semimembranosus muscles, and bottom round, including the biceps femoris and semitendinosus muscles. The cooking samples of top round weighed 469 to 1439 g.; of bottom round 405 to 1290 g. The samples were stored in a refrigerator until they were cooked 6 to 8 days after slaughter. The cooking methods were arranged a
During a study of the effect of various methods of cooking beef round on the collagen content of the meat, the method of Hartley and Hall ( 4 ) was used for the first 31 cooked samples. Since collagen is hydrolyzed to gelatin during cooking, losses in collagen were expected for all the cooking methods. Therefore it was surprising to find that 21 of these cooked samples appeared to contain more collagen nitrogen, expressed as percentage of total nitrogen, than did the matched raw samples when analyzed by this method. Similarly, when the total amounts of collagen in the slice of round before and after cooking were compared, 19 of these 31 samples appeared to have gained collagen. EXPERIMENTAL METHODSTo study the analytical method, qualitative tests (Millon, Hopkins-Cole, xanthoproteic) were made on the filtrate obtained after autoclaving the samples. Since the Hartley-Hall method assumes that gelatin is the only source of nitrogen in this filtrate, and since gelatin contains no tryptophane and only a trace of tyrosine ( 8 ) , negative tests f o r these two amino acids were expected. However, qualitative tests of the filtrates from four raw samples indicated some contamination, while tests of six cooked samples indicated considerable contamination with tyrosine and tryptophane. Parallel tests of a solution of commercial gelatin calculated to contain twice as much nitrogen as the filtrates were negative. These tests appeared to indicate that the apparent gains of collagen found on cooking some of the samples were due to decomposition of proteins other than collagen during autoclaving. This decomposition of non-collagen proteins was evidently greater in the cooked than in the raw samples.Because of these findings, the method of Lowry, Gilligan, and Katersky ( 5 ) seemed a good choice f o r studying the effect of cooking on the collagen content of meat. In this method, protein other than collagen and elastin is removed by solution in 0.1 N .sodium hydroxide before autoclaving. When the method was followed as published, the last washing with sogium hydroxide gave a positive biuret test, and qualitative tests of the filtrate obtained after autoclaving were faintly positive f o r tyrosine and tryptophane. I f washing with sodium hydroxide was continued until a negative biuret test was obtained on the last filtrate, indicating the removal of all protein other than connective tissue, tests on the filtrate obtained after autoclaving were negative for tyrosine and tryptophane. However when washing with sodium hydroxide was done according to the original directions, followed by washing with water t o a negative biuret test, qualitative tests for tyrosine and tryptophane on the filtrate obtained after autoclaving were again positive. Evidently, non-collagen protein decomposed during autoclaving when the washing with sodium hydroxide was incomplete. Because of this fact, the method was modified to include washing with sodium hydroxide until a negative biuret test was obtained on the filtrates. The volume of 0.1 N . sodium hyd...
with more glycerol concentrations than were used in the rest of the work. Although the authors have no explanation for this abnormal solubility effect, they have enough supporting data to be convinced that it is real and not merely a consequence of experimental error.The tightness of the sleeve stoppers of the solution bottles was demonstrated by making Karl Fischer moisture determinations on four samples that had been immersed in the constant temperature bath for 46 days at 15°C. After deducting the dextrose, as determined with the saccharimeter, the water content of the solvent was found to be unchanged. Sample abed Original water concentration, % 75.1 49.9 37.4 25.1 Water by analysis after 46 days, % 75.0 51.1 37.65 25.0 AcknowledgmentThe pure dextrose used in this work was generously supplied by George R.
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