Impact of MAP packaging on MSA Lamb loin and topside eating quality

Summary

Recent overseas studies (mainly in beef) have shown that the eating quality of Hi oxygen modified atmosphere packaging (Hi-Ox-MAP) packaged meat is less than optimal due to toughening of the meat and negative flavour changes. Vacuum or Cryovac® packaging (VP) has been used successfully for the storage of meat primals; however VP meat has traditionally been unacceptable for retail display due to the presence of the dark purple deoxymyoglobin in meat stored under this anaerobic environment.  Thus retailers have generally avoided using VP, because the purple colour is perceived negatively by consumers. Industry (Sealed Air Inc.) has recently developed new technologies for retail ready meat; Cryovac Darfresh® Barrier vacuum skin packaging (VSP) and Cryovac Darfresh® Bloom (Hi-Ox-DB) and now other packaging formats such as UltraDarfresh®. VSP uses an advanced barrier system which takes advantage of a novel composite polymer with two layers. The Hi-Ox-DB system incorporates elements of VSP, within a Hi-Ox-MAP tray; e.g. the headspace gas composition is also 80% O2 and 20% CO2 .

Lamb topside and backstrap muscles from animals of known genetics were sourced from Victorian producer demonstration sites. The muscles were directly cut into steaks without any prior vacuum wet aging and evenly allocated to either Hi-Ox-MAP, VSP or Hi-Ox-DB retail packaging treatments and stored at 1oC for either 5 or 10 days in a simulated retail display. After storage, the raw meat colour (L*a*b* tristimulus values) and pH were measured and meat was repackaged and frozen for later consumer sensory testing according to Meat Standards Australia (MSA) protocols. After 5 and 10 days storage both Hi-Ox-MAP and Hi-Ox-DB maintained a bright red colour in contrast to a characteristic purple colour for the VSP packaged lamb.

The effects on eating quality (CMQ4 scores) were consistent for each packaging format regardless of the muscle type, backstrap or topside. All sensory attributes were rated significantly lower for the topside samples compared to the backstrap. After 5 and 10-days storage CMQ4 scores indicated that Hi-Ox-MAP and Hi-Ox-DB systems were able to maintain "good everyday" quality, whereas VSP packaged backstrap was rated "better than everyday" quality.  CMQ4 scores were significantly lower for topside samples, with Hi-Ox-MAP stored topsides falling into an "unsatisfactory" quality category after 10 days. Overall, the MSA consumer testing clearly showed that the eating quality of VSP packaged lamb was better than Hi-Ox-MAP, despite the purple coloured meat. Hi-Ox-MAP and Hi-Ox-DB samples had low tenderness and flavour scores compared to VSP after 5 days of storage. The Hi-Ox-DB samples had only marginally better eating quality than the Hi-Ox-MAP samples at 10 days, despite the maintenance of a red meat colour in the pack.

All sensory attributes were rated significantly lower for the topside samples compared to the backstrap.  It was concluded that direct packaging of lamb under high oxygen MAP (Hi-Ox-MAP or Hi-Ox-DB) should not generally be recommended for retail ready packaging of lamb at 1 day post-slaughter. Although Hi-Ox-DB provided some modest gains in eating quality, it is uncertain whether it can be recommended as a viable solution for retail packaging of lamb.  It should be noted that current Australian guidelines require that lamb in first wet aged under vacuum for 5 days before repackaging into other retail ready formats.

There were minimal differences in the volatile profiles and odour quality of raw samples stored for 10 days under VSP, Hi-Ox-DB or Hi-Ox-MAP. This confirmed that no discernible or characteristic "off-odours" developed during storage for any of the evaluated packaging systems. Finally, there was little evidence of differences in proteolysis between the packaging treatments, as measured by concentrations of free amino acids or peptides.  This result was consistent with the hypothesis that the toughening of meat under Hi-Ox-MAP occurs primarily due to intermolecular cross-linking or other mechanisms, rather than inhibition of proteolytic enzymes.