Dry-ageing of Lean Beef and Lamb: Effect of Processing and Storage Factors on Product Quality and Acceptability
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Dry-ageing is a traditional post-mortem processing technique for the improvement of tenderness and flavour of meat. Most dry-aged meat is produced from well-marbled prime beef cuts rather than lean beef. The use of lean beef may offer advantages for storage stability and reduced off-flavours arising from oxidative and microbial spoilage. Lamb is another important red meat with characteristic flavour profile favoured by consumers around the world. The quality of wet-aged lamb has been studied with limited knowledge of its dry-aged equivalents. The current study aimed to produce dry-aged lean beef and lamb using in-bag dry-ageing (BD) technique. The study consisted of two stages: (1) Determine the impact of processing factors, including ageing air velocities, stepwise ageing and ageing time, and frozen storage on the quality and acceptability of dry-aged lean beef; and (2) Investigate the impact of BD on the quality, acceptability and biochemical changes of lamb compared to its widely available wet-aged equivalents. Lean bull beef longissimus lumborum (n = 30) were stepwise in-bag dry-aged in water-permeable ageing bags at 2 °C, RH 75% under three different air velocities: 0.5, 1.5 and 2.5 m.s-1 for 7 days followed by wet-ageing (W) for 14 days. The impact of processing factors and frozen storage on the quality and acceptability of the in-bag dry-aged lean beef was compared to the straight-dry-aged equivalents at 0.5 m.s-1 as a control. Increased air velocities accelerated dehydration process with no negative impact on all the quality traits determined in this study, including physicochemical quality, sensory acceptability, in vitro digestibility and metabolite profile. A total of 1705 metabolites were identified in dry-aged beef using Rapid Evaporative Ionisation Mass spectrometry (REIMS) fingerprinting. Stepwise ageing resulted in 692 metabolites which differed (P < 0.05) from the control. Stepwise processed dry-aged beef had equivalent quality, palatability, lipids and proteins oxidative stabilities, and lower level of surface microorganisms and higher yield compared to the control (P < 0.05). Free amino acids, small peptides and metabolites arising from lipid and protein oxidation increased significantly with ageing time in fresh beef, regardless of ageing regimes (straight BD/stepwise ageing). Frozen storage for 12 months had little or no effect on the quality and acceptability of the dry-aged lean beef. Oxidative stabilities and protein digestibility of in-bag dry-aged beef were improved during the frozen storage (-18 °C) compared to the unaged. Lamb hindlegs (Ram, n = 60) were used to produce the in-bag dry-aged lamb products in this study. Dry-aged lamb legs were produced using water-permeable ageing bags at 2 °C, 0.5 m.s-1 air velocity and RH 75%, for 21 days. The quality, acceptability and biochemical changes of in-bag dry-aged lamb were compared to the widely available wet-aged equivalents at -1.5 °C for 21 days. The dry- and wet-aged lamb were equally preferred by the consumer panellists suggesting the niche nature of dry-ageing products. Dry-aged lamb had harder and chewier texture profiles and lower colour attributes (L*, a* and b*) than the wet-aged (P < 0.05). BD resulted in higher yeast and lipid oxidation (TBARS) levels compared to the wet-aged (P < 0.05). There was no difference in the SDS-PAGE protein profile, fatty acids and protein carbonyl content between two ageing treatments. The gastric digestibility of dry-aged lamb was greater than wet-aged. A total of 1704 metabolites was identified using REIMS fingerprinting. There were 663 metabolites that differed (P < 0.05) between the ageing methods mainly arise from proteolysis and lipid metabolism. Different peptide profiles (< 10 kDa) were observed using peptidomic profiling between the two ageing techniques. Small peptides released from creatine kinase, LIM domain binding 3, nebulin, sHSP and myozenin were significantly higher for dry-aged, suggesting the potential as signature biomolecules to distinguish in-bag dry-aged from wet-aged. Outcomes of this study demonstrate the feasibility of producing dry-aged lean beef and lamb using BD technique. Ageing time was the main factor affecting the quality of in-bag dry-aged products rather than ageing air velocities which had no impact. Stepwise ageing regime could produce dry-aged lean beef products with acceptable sensory quality, improved oxidative stability and digestibility during long-term frozen storage up to 12 months. The use of REIMS to monitor processing in meat science is a novel application suggesting the potential as a rapid food authentication screening and quality control tool in the food industry. Outcomes in the present study could also have implications for industry to produce value-added dry-aged beef and lamb which are safe microbiologically, easy to handle and free of trimming for local and export markets.