Characterization of the myofibrillar proteome as a way to better understand differences in bovine meats having different ultimate pH values.

: Influence of ultimate pH (pHu) on the occurrence of defective meats known as Dark, Firm and Dry (DFD) meats was studied through a proteomic approach at early post-mortem times. The myofibrillar sub-proteome of Longissimus thoracis et lumborum muscle from twelve loin samples from Asturiana de los Valles x Friesian yearling bulls, previously classified into two groups of six samples according to their pH values (normal, pHu < 6.0 and high, pHu ≥ 6.0), was analysed at 24h post-mortem. Fractionation/enrichment of muscle samples was carried out by combining OFFGEL fractionation in the pH range 4-7 followed by SDS-PAGE of the retrieved liquid fractions. Four protein bands satisfactorily discriminated between meat samples with high and normal pHu. These bands were quantified by image analysis, and further identified by liquid chromatography-mass spectrometry as desmin, pyruvate kinase, myosin light chain and myosin heavy chain-1 and -2. Coupling OFFGEL and SDS-PAGE separation with MS provided detailed and reproducible myofibrillar protein profiles enabling comparison among the sample groups assayed. This makes feasible to identify biomarkers capable to better understand pre-slaughter stress condition susceptible to give DFD meats with high pHu values. Significance statement: Meat industry has moved towards producing animals that are efficient feed converters, fast growing, with high lean meat content and with minimum production cost. This resulted in the production of animals with higher muscle development and less muscle glycogen reserves, that in some cases are more susceptible to stress and consequently increasing the occurrence of meat quality defects in the production chain, such as dark-cutting beef. Dark cutting meats are generally linked to a low muscle glycogen content at slaughter caused by elevated glycogenolysis induced by on-farm nutrition, stress and exercise in the pre-slaughter period. This implies metabolism modifications of the post-mortem muscle resulting in an abnormal post-mortem acidification process. This defective meat cheracterized by high post-mortem pH has become a significant problem in the meat industry inflicting important economic losses (50 and 20 million dollars per annum for Australian and British industry, respectively). The present proteomic investigation constitutes a straightforward strategy to reveal differences in bovine muscle for an appropriate assessment of dark cutting meat, an issue of major importance due to its implications regarding security of consumers, animal welfare and economic benefits of the meat industry. This article is protected by copyright. All rights reserved.