Samples for shear force analysis were frozen after each ageing
time. Frozen samples were thawed overnight at 4 °C prior to heat
treatment. The samples were heat treated in vacuum bags for 55 min
in a 72 °C water bath, turned after 25 min, thereafter chilled in
running cold tap water for 30 min and then stored at 4 °C until the
next day. Samples of all treatments from the same animal were heat
treated at the same time. Instrumental tenderness was measured
using the Warner Bratzler method as described by Honikel (1998).
The samples were cut into strips minimum 30-mm-long with a 100-
mm2 (10×10 mm) cross-section area. The strips were cut parallel to
the longitudinal orientation of the muscle fibres. Shear force was
measured on a minimum of 12 strips from each sample with a Texture
Analyser HD 100 (Stable Micro Systems, Godalming, UK) equipped
with a Warner Bratzler shear force blade with a rectangular shaped
cutting area of 11 mm×15 mm. The cutting blade was 1 mmthick and
had the speed of 0.83 mm/s when cutting through the strips. Shear
force was analysed as peak force and total energy (area under the
curve).