A Comparison of Two Methods for Determining the Collagen Content of Cooked Meat

Abstract

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...

The Effect of Two Methods of Cooking on Palatability Scores, Shear Force Values, and Collagen Content of Two Cuts of Beef

“…Collagen nitrogen was converted into collagen by using 18.6% as the nitrogen content of collagen (9) so that comparisons could be made with the values reported by other workers. The collagen content on the moist basis averaged 0.36% for lolzgissinzus dorsi and 0.57% for biceps femoris in the raw meat of the 26 animals.…”

“…The collagen content on the moist basis averaged 0.36% for lolzgissinzus dorsi and 0.57% for biceps femoris in the raw meat of the 26 animals. Briswold, using the Lowery procedure, reported collagen values of 0.87%, l.ll%, and 1.17% for semitendinosus muscle in bottom round (9) and a range of 0.5'7% to 1.13% for thrce muscles in two or more pairs of rounds (8). In none of her samples was the outside covering of the muscle removed.…”

Meat Tenderness Factors, Determination of Collagen in Raw and Cooked Beef from Two Muscles by Alkali-Insoluble, Autoclave-Soluble Nitrogen and by Hydroxyproline Content

“…In addition, they had found the quantity of nitrogen in collagen or gelatin to range from 17.5 to 18.7%. The figure of 18.6% has been used by Griswold and Leffler (5) and previously in this laboratory by Cover and Smith (4). Thus, collagen was calculated from hydroxyproline content using 13% as the conversion figure.…”

Collagen Determination, Comparison of Enzyme and Waring Blendor Methods for Determination of Collagen in Beef

“…Procedures reported for the separation of the organic acids of tomato fruits (2, 3, 7) were adaptations of the methods outlined by Isherwood (4) and Marvel and Rands (6). The Isherwood method, as employed by Bulen, Varner, and Burell (2) and Rice and Pederson (7), to isolate the organic acids in tomatoes required the use of sulfuric acid in the initial extraction of the organic acids as well as in the preparation of the silicic acid partition column. The author found in preliminary studies that the sulfuric acid was eluted in sufficiently high concentrations to mask the presence of acids eluted after citric acid.…”