Glycolytic potential and activity of adenosine monophosphate kinase (AMPK), glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE) in steer carcasses with normal (b 5.8) or high (N 5.9) 24 h pH determined in M. longissimus dorsi ☆ A. Apaoblaza a , A. Galaz b , P. Strobel b , A. Ramírez-Reveco b , N. Jeréz-Timaure c , C. Gallo b, ⁎ a Programa Doctorado en Ciencias Veterinarias, Escuela de Graduados, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Chile b Instituto de Ciencia Animal, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Chile c Departamento de Zootecnia, Facultad de Agronomía, Universidad del Zulia Núcleo Agropecuario, Maracaibo, Venezuela abstract article info Article history: Received 13 July 2014 Received in revised form 19 November 2014 Accepted 20 November 2014 Available online 25 November 2014 Keywords: Cattle Muscle pH Glycogen Glycolytic enzymes AMPK Muscle glycogen concentration (MGC) and lactate (LA), activity of glycogen debranching enzyme (GDE), glycogen phosphorylase (GP) and adenosine monophosphate kinase (AMPK) were determined at 0.5 h (T0) and 24 h (T24) post-mortem in Longissimus dorsi samples from 38 steers that produced high pH (N 5.9) and normal pH (b 5.8) carcasses at 24 h postmortem. MGC, LA and glycolytic potential were higher (P b 0.05) in normal pH carcasses. GDE activity was similar (P N 0.05) in both pH categories. GP activity increased between T0 and T24 only in normal pH carcasses. AMPK activity was four times higher in normal pH v/s high pH carcasses, without changing its activity over time. Results reinforce the idea that differences in postmortem glycogenolytic/glycolytic flow in L. dorsi of steers showing normal v/s high muscle pH at 24 h, could be explained not only by the higher initial MGC in normal pH carcasses, but also by a high and sustained activity of AMPK and an increased GP activity at 24 h postmortem. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Insufficient glycogen content in muscle at the moment of slaughtering results in low production of lactic acid; therefore meat has a high pH (N 5.8), high water holding capacity and an unattractive dark color; this condition is known as DFD (dark, firm and dry) meat (McVeigh & Tarrant, 1982). The measurement of muscle pH at 24 h after slaughter is a criterion routinely used at slaughterhouses to deter- mine meat quality and take further processing decisions. High pH is still an important problem in the Chilean beef industry (Gallo, 2004; Hargreaves, Barrales, Larraín, & Zamorano, 2003) as well as in other countries with extensive pasture fattening systems like México (Leyva-García, Figueroa-Saavedra, Sánchez-López, Pérez-Linares, & Barreras-Serrano, 2012). Studies in the main slaughterhouses in the south of Chile showed that the incidence of high pH meat varies between 17 and 40% on a yearly basis (Gallo, 2004) and the problem causes signif- icant losses to the meat industry (Vidal, Ferrando, Köpfer, & Almuna, 2009). Main risk factors related to high pH in Chile are long transport duration (steers transported for 24 h have been reported to show higher muscle pH than those transported for 3 h) and prolonged lairage time (steers that spent 24 h in lairage had higher muscle pH than those that spent 3 h in lairage) before slaughter (Amtmann, Gallo, Van Schaik, & Tadich, 2006; Gallo, Lizondo, & Knowles, 2003). As opposed to other countries, where this problem is more prevalent in bulls (Brown, Beavis, & Warriss, 1990), in Chile bull production is uncommon and the steers (young castrated males up to 4 permanent teeth) are mainly affected (Gallo, 2004). Other potentially glycogen-depleting stressors such as very low and high ambient temperatures before slaughter, as well as transportation conditions to slaughter, have been reported (Immonen, Ruusunen, Hissa, & Puolanne, 2000). Stress is an inevitable consequence of the process of transferring animals from farm to slaughter. The effects of chronic stress on muscle glycogen depletion and the consequent dark cutting condition have been well reviewed (Ferguson & Warner, 2008). The problem increases when there is a depletion of muscle glycogen due to exercise, stress, bad nutrition, fasting, weather (Hood & Tarrant, 1980) or due to fighting when different groups are mixed (Warriss, Kestin, Brown, & Wilkins, 1984). All these environmental factors will produce different responses according to intrinsic factors of cattle that make them more susceptible to present high pH, such as breed, sex, age and temperament (Voisinet, Grandin, Tatum, O'Connor, & Struthers, 1997). Due to the inability to completely avoid stress during pre-slaughter handling of livestock other strategies for reducing the effects of stress on meat quality have been studied, such as the use of high energy Meat Science 101 (2015) 83–89 ☆ Research project FONDECYT 1120757 Chile. ⁎ Corresponding author. E-mail address: cgallo@uach.cl (C. Gallo). http://dx.doi.org/10.1016/j.meatsci.2014.11.008 0309-1740/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Meat Science journal homepage: www.elsevier.com/locate/meatsci