| Tenderness is considered to be the most important quality trait in beef.The process of chilling has great impact on tenderness thus it should be optimized for minimal muscle contraction and maximal proteolysis, which can be achieved by controlling the pH/temperature decline in the muscle.The critical time during post mortem chilling is thepre-rigor period,when the relationship between pH and temperature is a decisive factor affecting meat tenderness.Many studies on muscle excisedpre-rigor have been undertaken and identified that the highest degree of tenderness was obtained at pre-rigor temperature of 12-18 °C.It is necessary to confirm whether this result obtained from excised muscles could be applied into carcasses in commercial slaughter plants to improve beef tenderness.The present study focuses on the temperature control, a stepwise chilling treatment of Chinese Yellow Cattle carcasses that ensure M. Longissimus lumborum(LL) reach a rigor center temperature window of 12-18 °C: a fast chilling(air temperature, –11±1 °C; air velocity, 0.5 m/s) for 2h, then the refrigeration was stopped(air velocity, 0 m/s) until 10 h post mortem, followed by a 1±1°C chilling(air velocity, 0.5m/s) to 48 h post mortem. The aim was to investigate the effects of this temperature control on tenderness of Chinese Yellow Cattle LL muscle during aging.One half-carcass was stepwise chilled and the other half-carcass was conventional chilled. Quality attributes of LL muscles were evaluated after aging for 1, 7 and 14 days.Pelvic suspension has a major influence on sarcomere lengthand tenderness, and has been shown to be especially efficient to avoid cold shortening when applied without electrical stimulation. However, studies of beef ultra-structure analysis between different suspension methods are lacking.Most studies examining suspension methods of beef carcasses were conducted under conventional chilling conditions. It is not clear whether carcasses under a higher pre-rigor temperature with pelvic suspension can also achieve higher tenderness compared with those suspended by the Achilles tendon. And it is controversial about the continuous benefits on meat quality by different suspension methods during post mortem aging. Therefore, the aim of this study was to investigate the effect of suspension method on meat quality and ultra-structure of 12-18 °C pre-rigor temperature control-chilled Chinese Yellow Cattle LL during aging.After slaughter, the right sides of carcasses were hung by the Achilles tendon, while the left sides were hung from the pelvic bone. Both sides went through the stepwise chilling.LL muscles were aged for 1, 7 and 14 days then evaluated for quality traits and ultra-structure.In this study, the main results were as follows:The stepwise chilling resultedin decreased(P < 0.05) Warner–Bratzler shear force, increased myofibril fragmentation indexand longer sarcomere length during aging compared with control. The WHC and meat color were improved by stepwise chilling. The stepwise chilled LL at 7 d post mortem had a lower(P < 0.001) WBSF than those of conventional chilled at 14 d, which indicated that stepwise chilling quickly decrease the WBSF in a shortened aging time and accelerate the rate of tenderization.Pelvic suspension under stepwise chilling had no significant effect on myofibril fragmentation index, but decreased the Warner–Bratzler shear force values especially after aging for 1d(12.7%, P < 0.05) and significantly decreased the purge loss. Electron microscopy and sarcomere length examination of LL showed that pelvic suspensin resulted in lengthened I-bands and sacomere length.To conclude, taking the enterprise economic benefit, meat quality and safety into consideration, the 12-18 °C pre-rigor temperature controlled stepwise chilling combined with pelvic suspension, could improve meat quality, shorten aging time, reduce the production cost and raise enterprise’s profit. So it should be introduced to the beef industry widely. |
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