Any link between integrin degradation and water-holding capacity in pork? Ida Krestine Straadt, Marianne Rasmussen, Jette Feveile Young, Hanne Christine Bertram * University of Aarhus, Faculty of Agricultural Sciences, Department of Food Science, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark article info Article history: Received 5 November 2007 Received in revised form 11 March 2008 Accepted 11 March 2008 Keywords: Integrin WHC Drip loss Confocal laser scanning microscopy CLSM Western blot Aging NMR Water distribution abstract In order to investigate a possible relationship between integrin degradation and water-holding capacity (WHC), integrin was quantified using western blot, and water mobility and distribution was measured by proton NMR T 2 relaxometry at 24 h postmortem in pork (n = 30) with a large variation in WHC (drip loss varying from 2.8% to 11.3%). Regression analyses revealed correlation coefficients of r = 0.32 (P = 0.08) and r = 0.40 (P = 0.03) for the correlations between the content of integrin determined by western blot analysis and WHC determined as either drip loss or by NMR, respectively. Water mobility and distribu- tion was also measured in 18 meat samples upon 7 days of aging, which revealed a correlation (r = 0.54) between integrin content determined by western blot analysis 24 h postmortem and the mobility of the myofibrillar water (T 21 relaxation time) at day 7. In contrast, no correlation could be established between integrin content 24 h postmortem and WHC at day 7 determined by NMR as the amount of extramyofibr- illar water (T 22 population) (r = 0.01). In conclusion, both visualisation by CLSM and quantification of integrin by western blot analyses of suggested that a strong link between integrin degradation and WHC in pork is questionable, whereas integrin degradation seems to have impact on the succeeding development in the mobility of the myofibrillar water. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Variations in water-holding capacity (WHC) of pork is a well recognized problem, and several investigations have elucidated factors of importance for the development in WHC. It has been demonstrated that pH and temperature during the initial time after slaughter are highly correlated to WHC of pork (Schäfer, Rosenvold, Purslow, Andersen, & Henckel, 2002). This can be ex- plained by the fact that these factors control the degree of protein denaturation (Offer, 1991), which changes the functionality of the proteins and thereby the ability of the muscle proteins to entrap water (Bertram, Whittaker, Andersen, & Karlsson, 2003a). Recently it has also been hypothesized that the degradation of cytoskeleton proteins plays a key role for WHC of pork, as such a degradation allows the myofibrils to swell (Kristensen & Purslow, 2001). Recently this hypothesis was supported by determination of spe- cific protein degradation analysed by western blot analyses (Huff-Lonergan & Lonergan, 2005; Zhang, Lonergan, Gardner, & Huff-Lonergan, 2006). In addition, it has been proposed that the integrin, which attaches the cytoskeleton to the extracellular matrix, should have impact on the formation of drip channels in pork (Lawson, 2004). It is noteworthy that while a negative corre- lation is proposed between drip loss and degradation of cytoskele- ton proteins such as desmin and talin (Zhang et al., 2006), the reverse relationship is suggested for degradation of integrin and formation of drip loss when integrin was examined during the first 24 h postmortem (Lawson, 2004). As calpains are expected to be responsible for both the degradation of desmin and talin (Bee, Anderson, Lonergan, & Huff-Lonergan, 2007) as well as the degra- dation of integrin (Lawson, 2004), the reverse correlations to WHC are unexpected and indicate that the role of integrin is far from fully understood. Consequently, the aim of the present study was to visualize the integrin degradation in extreme pork qualities; pale, soft, exudative (PSE), normal, and dark, firm, dry (DFD) pork aged for 1 or 7 days using confocal laser scanning microscopy (CLSM). Furthermore, we aimed to investigate if a relationship between integrin content quantified by western blot and WHC determined by two different methods (drip loss and proton NMR relaxometry) could be established on pork samples representing a wide range of WHC. 2. Materials and methods 2.1. Animals A total of 30 pigs, which were offspring of Duroc/Landrace boars cross-bred with Landrace/Yorkshire sows, were included in this study. In order to create a variation in the meat quality, 20 of the pigs were exercised on a treadmill by stepwise increasing speed from 0.4 km/h to on average 5.2 km/h with increments of 0.4 km/h every 2 min i.e. a total of approximately 26 min. The pigs were 0309-1740/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2008.03.012 * Corresponding author. Tel.: +45 89 99 15 06; fax: +45 89 99 15 64. E-mail address: HanneC.Bertram@agrsci.dk (H.C. Bertram). Meat Science 80 (2008) 722–727 Contents lists available at ScienceDirect Meat Science journal homepage: www.elsevier.com/locate/meatsci