Experimental
2.1. Animals, carcasses and muscle sampling
2.1.1. Lamb
Castrated male Romney lambs were raised on pasture
and processed at a commercial meat export plant. On
arrival at the processing plant lambs were swim-washed
and processed 18 h later under accelerated conditioning
and ageing (AC and A) conditions as recommended by
MIRINZ (1978). Just prior to slaughter, the lambs were
electrically stunned, immobilised by low voltage electrical
stimulation and the carcasses subsequently dressed
in accordance with standard New Zealand industry
practices. Six lamb carcasses weighing between 15.9 and
16.5 kg were randomly selected from a line of 40 lambs
for detailed investigation of their proteolytic enzyme
pro®les and meat quality characteristics.
On the processing chain, at 26 min post-stunning and
prior to high voltage electrical stimulation, a sample (5±
6 g) of the Longissimus lumborum et thoracis (LD) at the
13th rib was removed from the carcasses. High voltage
electrical stimulation (90 s at 14.3 pulses/s, 1.8±2 A and
1130 V peak) was applied according to Chrystall and
Devine (1983) to the carcasses within 28 min of stunning
to remain within the New Zealand AC and A processing
conditions. Serial measurements of pH and temperature
of the right LD at the 12th rib were taken from each
carcass using an Orion 8163 glass electrode and a temperature
probe attached to a Hanna HI 9025 portable
pH meter. Measurements were recorded on 14 occasions
between 25 min and 24 h post-mortem.
During the ®rst 24 h post-slaughter carcasses were
held in a conditioning room with the following regime:
15C for 8 h, 10C for 6 h and 10 h at 1C. At 6 and 12
h post-mortem, LD samples (45 mm long and 40 mm
thick) were removed from the left-hand side of carcasses
between the ®rst and fourth lumbar vertebrae for
enzyme and tenderness determinations. After 24 h the
carcasses were transferred to the cutting room and a 45
mm mid-loin chop (13th rib) removed from the right
side of the carcass. The remainder of the half mid-loin
from the ®rst to seventh lumbar vertebrae was vacuum
packed and stored at 4C. At 48 and 96 h post-mortem,
additional 45 mm bone-in chops were removed from the
vacuum packed half-mid loins for enzyme and tenderness
determinations. All LD samples for tenderness determinations
were frozen at ÿ20C at the time of sampling.
2.1.2. Beef
Angus cross steers raised on pasture and aged 24±28
months were slaughtered and processed at a commercial
meat export plant. The steers were stunned by captive
bolt and the carcasses dressed in accordance with standard
New Zealand industry practices. Six carcasses
ranging in weight from 250 to 278 kg were randomly
selected from a line of 20 animals. At 43 min postslaughter,
the LD was exposed by knife ventral/dorsal
surface cuts. At 44 min, prior to high voltage electrical
stimulation, the pH and temperature of the right LD
was recorded (using an Orion 8163 glass electrode and
temperature probe attached to a Hanna HI 9025 portable
pH meter) and a sample (5±10 g) of the LD over
the 13th rib was removed. High voltage electrical stimulation
of 900 V was applied within 50 min of stunning.
The carcasses were then held at 6C for 8 h and
4C for 16 h. The temperature and pH of the LD was
determined on 10 occasions between 50 min and 24 h
post-mortem. At 12 h, a 25 mm sample of the LD from
the right side between the 13th and 14th rib was taken
for enzyme and tenderness determinations.
After 24 h in the conditioning room the carcasses
were transferred to the cutting room and within 40 min
the LD from the ®rst to sixth thoracic vertebrae was
removed from the right side of the carcass. A 25 mm
length of the LD was removed for enzyme and tenderness
determinations. The remainder of the LD was
vacuum packed and held at 4±6C until 336 h postmortem.
At 48, 96, 168 and 336 h, further 25 mm
lengths of LD were removed sequentially from the
vacuum packed strip loin for enzyme and tenderness
determinations. All LD samples for tenderness determinations
were frozen at ÿ20C at the time of sampling.