Methylamino acids as robust unequivocal indices of lean meat in foods

Methods for the determination of 3-methylhistidine and Nε-methyllysine content of meat and meat products using an ion exchange chromatography technique are suggested. Concentrations of both 3-methylhistidine and Nε-methyllysine in lamb, beef and pork muscle hydrolysates are given. 3-methylhistidine titres showed less variation within a sample than did titres of Nε-methyHysine. In all species of meat studied, concentrations of proteinbound 3-methylhistidine were found to be reasonably constant about a mean value of 6.0 (± 0.7) mg/gN. The concentration of 3-methylhistidine in pork varied between 5 and 56 mg/gN, an increase in concentration being related to an increase in age. The higher concentrations of 3-methylhistidine in pork were found to be easily reduced to levels more representative of protein-bound 3-methylhistidine by a washing procedure with water. The presence of an unbound water soluble from of 3-methylhistidine was thus indicated. This form of 3-methylhistidine was not detected for the other meat species analysed. A similar interspecies variation in Nε-methyllysine was not apparent. 3-methylhistidine and Nε-methyllysine were absent from the non-meat proteins analysed. The similar interspecies value for the 3-methylhistidine bound to the myofibrillar proteins of meat is tentatively suggested as an index of the lean meat content of meat products. The application of the majority of techniques presently available for the determination of meat content are restricted to those products where processing treatments have not severely affected the constituent proteins. The methylamino acids, and in particular 3-methylhistidine, were therefore proposed by Hibbert and Lawrie (1972) for use as indices because they were heat stable and had been shown to be an integral constituent of the myofibrillar proteins. 3-methylhistidine has been found in both actin (Johnson, Harris and Perry, 1967) and myosin (Johnson and Perry, 1970) but it is believed to be absent from foetal and cardiac myosins (Kuehl and Adelstein, 1970). Nε-methyllysine has also been found in myosin but not from actin (Hardy et al., 1970).