The effect of freezing and post mortem ageing on beef quality

Abstract

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. Results Moisture characteristics 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. Sensory characteristics 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 sensory parameters. Conclusion 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.