The impact of homogenizer type and speed on the determination of myofibrillar fragmentation.

The myofibrillar fragmentation index (MFI) was determined by the turbidity method on five samples of ovine Longissimus muscle, aged for either 1 or 5 days and processed from the frozen state over 3 weeks. These samples were homogenized at one of four speeds (11,000, 16,000, 19,000 or 22,000 rpm) with a shaft type homogenizer (Ystral) and at 15,000 rpm with a blade type homogenizer (Omni mixer). At all speeds except 15,000 or 22,000 rpm samples were homogenized for either one or two bursts of 30 s giving a total of eight different treatments. There was a significant interaction between ageing and treatment (P<0.05) and ageing and muscle sample (P<0.001). Regarding the Omni mixer result as a reference standard, the closest result from the Ystral homogenizer was obtained at 19,000 rpm after two bursts of 30 s. These two treatments gave similar mean values for samples aged 5 days. Repeatability between duplicates did not differ significantly for the various treatments (r=0.55). A large difference was found between samples aged for 1 and 5 days and the difference was greater for the Ystral homogenizer than the Omni mixer. The Omni mixer values for 1 day aged samples were 38 units less than for samples aged for 5 days while this difference for the Ystral homogenizer was 63 units. As speed of homogenization increased with the Ystral homogenizer the overall mean values increased and the values were always greater after two bursts of 30 s compared to one burst of 30 s. The results suggest that the Ystral homogenizer may be better for detecting differences between treatments than the Omni mixer. At the slower speeds myofibrils consist of more sarcomeres and intermyofibril linkages could still be observed. This contrast was also seen between samples aged for 1 or 5 days with much greater degradation visually observed in the latter samples. This was supported by the quantitative data.