Mechanisms of ultrastructural changes in electrically stimulated beef Longissimus muscle

Three steers, ranging in grade from USDA low to average Good, were used in the evaluation of the effect of electrical stimulation (ES) on structural properties of the beef longissimus muscle. The left sides were electrically stimulated with 1-A current (delivering 145-250 V through the sides) for 2 min by applying eight bursts of 15-s duration. The right sides were not stimulated (controls). Samples of the longissimus muscle were removed at the sixth lumbar area 48 h post mortem and processed for light and transmission electron microscopy. Light and electron micrographs of stimulated muscle revealed irregular (contraction) bands, superstretching of myofibrils, absent or ill-defined I-, A- or Z-lines, tearing of myofibrils, the presence of empty vesicles and fragmentations of myofibrils at the Z-lines. Therefore, some of the mechanisms of tenderisation of electrically stimulated muscle would appear to result from physical disruption of myofibrils and possibly autolytic proteolysis.