SUMMARY —Free amino acid (FAA) analyses were conducted on 87 I. dorsi and 58 b. femoris samples from cattle varying in sex, breeding and age to study the relationships between these muscle constituents and Warner‐Bratzler Shear values. The b. femoris contained greater amounts of FAA than the I. dorsi and was significantly tougher. Muscles from a line of cattle that tended to be more tender possessed greater amounts of FAA. With few exceptions the I. dorsi of steers contained greater amounts of FAA than the same muscle from bulls. Differences in bull muscles due to age were not significant for any FAA. Steer muscle with low shear values tended to possess greater amounts of FAA than steers with high shear values. Although not significantly correlated individual and total FAA increased slightly with increasing tenderness within beef muscles.

Free amino acid analyses were conducted on the longissimus and biceps femoris muscles from carcasses aged 2, 7 and 21 days to determine the relationships between these muscle constituents and palatability. Many of the free amino acids increased during aging. Shear values for the longissimus decreased faster with increased aging time than did shear values for the biceps femoris. Nevertheless, no significant interaction between aging period and muscle existed for any of the free amino acids. This indicates that proteolysis progressed at about the same rate in both the longissimus and biceps femoris muscles. The greater tenderness increase in the longissimus then in the biceps femoris during aging was probably due to greater amounts of connective tissue in the biceps femoris rather than to changes in free amino acids. Relationships between free amino acids in muscle and tenderness and flavor were low.

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The protein quality of mechanically deboned red meat was investigated using amino acid analysis, protein efficiency ratio and the slope ratio technique. Nine different meat products were studied utilizing Sprague-Dawley weanling albino rats. Protein quality of the mechanically deboned meat varied greatly with the amount of lean left on the bones prior to mechanical deboning. Deboned meat which contained more lean, and less collagen, was superior in protein quality to the deboned meat obtained from bones which contained less lean and more collagen. Total sulfur amino acids (cystine and methionine) and isoleucine were the most limiting amino acids in all nine of the meat products when compared with lactalbumin. The contents of total sulfur amino acids and isoleucine, as well as the ratio of essential amino acids to total amino acids, reflected the protein quality of the meat.

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