The aim of this study was to evaluate the effect of freezing methods and post-mortem
ageing days for frozen beef m. longissimus lumborum (LL) on colour, moisture
characteristics; characteristics and sensory characteristics. There were 3 freezing
treatments: fresh, never frozen (FR); quick-frozen (QF), and slow-frozen (SF). All fresh
and frozen beef m. longissimus lumborum samples were aged for 3 or 14-days and
frozen beef samples were frozen before ageing.
Materials and methods
Three replications of 7 beef samples (steaks) per treatment (total of 3-days, n=126)
were used. Fresh beef samples (FR) were kept in a cold room at 3 °C until the next
morning (Day 3). Slow-frozen samples (SF) were packed in a single layer on 3 shelves
of a house hold freezer (AEG Skandiluxe) to reach a core temperature of -20 °C.
Quick-frozen samples (QF) were placed in a single layer on 3 shelves of an
IcematicT15-2P blast freezer to a reach to core temperature of -30°C in 3 hours. All
samples for the two freezing treatments were stored after the freezing processing at -
20°C freezer room and were then thawed in vacuum packages for 18 hours at 3 °C in
a dark chiller before analyses.
The freezing methods and ageing days had a significant effect (P<0.001) on moisture
characteristics but showed no effect on cooking losses. Drip loss and more pressed
out water were higher for samples aged for 3-days compared to 14-days ageing postmortem.
The effect of ageing days on moisture characterises was different for fresh
compared to frozen beef samples (interaction: P<0.001). Drip loss of frozen steaks
during 3-days ageing post-mortem was significantly higher (P<0.001) than those aged
for 14-days. Drip loss between fresh samples aged for 3 and 14-days nor between
frozen samples aged for 3 or 14-days. Colour characteristics
Most colour characteristics were significantly affected by freezing methods and postmortem
ageing days. Fresh beef samples had significantly higher (P<0.001) values
for redness (a*) and chroma, lower values (P<0.05) for hue (closer to typical red
colour) and were brighter (higher L*) than samples of both freezing methods. Higher
(P<0.001) OxyMb and lower MetMb were recorded for fresh compared to frozen
samples. Beef samples aged for 3-days had lower (P<0.05) b* (less yellow) and hue
angle values than those aged for 14-days. DeoxyMb and OxyMb were higher and
MetMb lower (P<0.05) in 3-days samples compared to 14-days samples.
Freezing method had a significant effect (P<0.001) on WBSF, tenderness related
sensory attributes and meat flavour. Fresh samples were tougher than frozen samples
according to WBSF and sensory scores for first bite, overall tenderness, and residual
connective tissue. In addition, quick-frozen samples were also significantly more
tender (P<0.001) than slow-frozen samples according to all three tenderness related
Overall, freezing methods and post-mortem ageing days influenced moisture and
colour characteristics of beef. Quick freezing method improves tenderness measured
as WBSF or sensory tenderness, but neither freezing method nor post-mortem ageing
period (day 3 and day 14) had a meaningful effect on cooking losses.
Dissertation (MInst (Agrar))--University of Pretoria, 2017.