A research note on factors affecting the determination of myofibrillar fragmentation.

The myofibrillar fragmentation index (MFI) was determined for a section of ovine Longissimus muscle, aged for either 1 or 3 days and processed from either the fresh or frozen state. Additionally samples were homogenized at one of three speeds (5000, 10,000 or 15,000 rpm). Speed of homogenisation and 'state' of the sample both had a significant effect (P < 0.001) on MFI values as did the interaction between speed and state (P < 0.001), with other interactions terms not being significant. Age of the sample had no significant (P > 0.05) effect on MFI values with least square means (s.e.) for Day 1 and Day 3 being 92 and 93 (1.16), respectively. As homogenisation speed increased, the difference between values for fresh and frozen samples was diminished, such that at 15,000 rpm there was no effect of 'state' on values. Overall the 'state' and the speed of homogenisation have a large impact on values and there was more variation between samples at the slowest speed (5000 rpm). At the slowest speed myofibrils consist of more sarcomeres and can be observed to still exhibit intermyofibril linkages. The results suggest a homogenisation speed of 15,000 rpm was preferable when determining MFI values.