Various instrumental and biochemical parameters as ageing indicators of beef Longissimus dorsi muscle and their relation to creatine and creatinine content

The main dietary source of creatine is red meat. Its ageing is accompanied by deep changes in chemical composition and structure of muscle tissues. The effect of ageing (nonaged-i.e. 24 h post mortem vs. 14 and 28 days post mortem at 1 degrees C) on the content of creatine and creatinine, on the creatine/creatinine ratio and on other ageing indicators, such as instrumentally measured colour values, pH(ultimate) values, length of myofibrilar fragments and total free amino acid content of beef Longissimus dorsi muscle. Muscles originated from eight commercially slaughtered Simmental bulls, 19-20 months old. Generally, all parameters measured were influenced by ageing time at the 5% level or less. Approximately 0.1 unit higher pH values and 1 unit higher colour L*, a* and b* values of ageing samples compared to nonaged was found. Length of myofibrilar fragments being in average the highest (69 mu m) for nonaged samples, 34 mu m for 14 days aged and the lowest (17 mu m) for 28 days aged sample. Higher content of total free amino acids released during 14 and 28 days of storage (10.19 and 18.71 mu mol/g) than from nonaged beef (19.75 mu mol/g) was found. Creatine content significantly declined with increasing days of ageing (nonaged 6.05 mg/g, 14 days 5.86 mg/g, 28 days 5.66 mg/g). On the contrary, the total content of creatine (creatine + 1.159 x creatinine) was not markedly affected by 14 days of ageing (nonaged 6.27 mg/g, 14 days 6.14 mg/g), although significant difference between nonaged and 28 days aged groups (5.95 mg/g) was observed. It was assumed that the creatinine/creatine ratio might be a good indicator of ageing rate for beef (R-2 = 0.974).