Tackling proteome changes in the longissimus thoracis

25 Pre-slaughter stress has adverse effects on meat quality that can lead to the 26 occurrence of Dark Firm Dry (DFD) meat in cattle. This study explores the previously 27 uncharacterized proteome changes linked to pre-slaughter stress in the longissimus 28 thoracis (LT) bovine muscle. Differential proteome profiles of DFD and normal (non29 DFD) LT meat samples from male calves of Rubia Gallega breed were assessed by 230 DE coupled to MS analysis (LC-MS/MS and MALDI TOF/TOF MS). A total of seven 31 structural-contractile proteins (three different myosin light chain isoforms, two fast 32 skeletal myosin light chain 2 isoforms, troponin C type 2 and cofilin-2) and three 33 metabolism enzymes (triosephosphate isomerase, ATP synthase and beta-galactoside 34 alpha-2,6-sialyltransferase) were found to have statistically significant differential 35 abundance in sample groups. In addition, 2-DE in combination with the 36 phosphoprotein-specific fluorescent dye Pro-Q DPS revealed that highly 37 phosphorylated fast skeletal myosin regulatory light chain 2 isoforms underwent the 38 most intense relative change in muscle conversion to DFD meat. Therefore, they appear 39 to be the most sensitive biomarkers of stress just prior to slaughter in Rubia Gallega. 40 Overall, these findings will facilitate a more integrative understanding of the 41 biochemical processes associated with stress in cattle muscle and their effects in meat 42 quality. 43 44