Effect of lamb age and electrical stimulation on the colour stability of fresh lamb meat

Abstract

The aim of this experiment was to compare the effects of electrical stimulation and lamb age on the retail colour stability of lamb meat. Poll Dorset Merino crossbred lambs that were 5 months (‘suckers’, SU) and 12 months (‘carryovers’, CO) finished on the same green annual pasture were slaughtered at a commercial abattoir. Half of the carcasses in each age group (10) were either electrically stimulated (ES) or not stimulated (NES) post-dressing with a commercial high voltage electrical stimulation system. Luminescence (L), hue angle (indication of redness), chroma (intensity), and oxy/met (a measure of browning) values were measured at 0 h (0 days), 21 h (0.86 days), 93 h (3.88 days), and 166 h (6.91 days) after meat had been cut 1 day after slaughter, over wrapped, and put under simulated retail display conditions. Three muscles, m. longissimus thoracis et lumborum (LL), m. gluteus medias (GM), and m. rectus femoris (RF), were measured in this way. A linear mixed model was used to fit a repeated-measurements model to the light measurements of L, hue angle, chroma, and oxy/met. Oxy/met rate of change was compared by fitting splines to predict the time required for oxy/met to reach an arbitrary benchmark value of 3. Colour and rate of colour change during display were affected by both age class and electrical stimulation but these effects depended on the muscle. The LL was the darkest (lowest L) and reddest (lowest hue angle), whilst RF was the most stable in colour (lowest rate of change for oxy/met) of the 3 muscles tested. Age class had a greater effect on oxy/met rate of change for the LL and GM compared with RF. Oxy/met of LL changed more rapidly for CO than SU lambs. ES increased the time for oxy/met to reach 3 in RF and GM for SU only but did so for both age groups in LL. ES decreased this time in RF and GM for CO. CO meat contained a higher concentration of myoglobin than SU meat. Negative effects of electrical stimulation on colour stability are more likely to occur in older lambs and in the GM and RF rather than in the LL.