NMR relaxometry and differential scanning calorimetry during meat cooking Hanne Christine Bertram a, * , Zhiyun Wu a , Frans van den Berg b , Henrik J. Andersen a a Department of Food Science, Danish Institute of Agricultural Sciences, P.O. Box 50, DK-8830 Tjele, Denmark b Department of Food Science, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark Received 23 October 2005; received in revised form 12 February 2006; accepted 9 May 2006 Abstract By combining simultaneous nuclear magnetic resonance (NMR) T 2 relaxometry and differential scanning calorimetry (DSC) on pork samples heated to nine temperature levels between 25 and 75 °C, the present study investigates the relationship between thermal dena- turation of meat proteins and heat-induced changes in water characteristics. Principal component analysis (PCA) on the distributed 1 H NMR T 2 relaxation data revealed that the major changes in water characteristics during heating occur between 40 and 50 °C. This is probably initiated by denaturation of myosin heads, which however, could not be detected in the DSC thermograms obtained directly on the meat. In contrast, the DSC thermograms revealed endothermic transitions at 54, 65 and 77 °C, probably reflecting the denatur- ation of myosin (rods and light chain), sarcoplasmic proteins together with collagen and actin, respectively. Simultaneous modelling of DSC and NMR data by partial least squares regression (PLSR) revealed a correlation between denaturation of myosin rods and light chains at 53–58 °C and heat-induced changes in myofibrillar water (T 2 relaxation time 10–60 ms) as well as between actin denatur- ation at 80–82 °C and expulsion of water from the meat. Accordingly, the present study demonstrates a direct relationship between thermal denaturation of specific proteins/protein structures and heat-induced changes in water mobility during heating of pork. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Water distribution; Heating, Pork; T 2 relaxation; DSC; Thermal denaturation 1. Introduction During cooking of meat severe structural changes, which influence the textural characteristics of the end product, are taking place (Hamm, 1977; Offer, 1984; Tornberg, 2005). Accordingly, a comprehensive under- standing of what triggers these changes is substantial for optimising cooked meat quality. Proton nuclear magnetic resonance (NMR) relaxometry provides direct informa- tion about interactions between water protons and exchangeable protons in proteins and thereby the chemi- cal–physical state of water in muscles and meat, and has been successfully applied in meat science (for a review, see Bertram & Andersen, 2004). Moreover, the fact that NMR is a non-destructive technique has been utilized to obtain dynamic information about the chemical–physical state of water during cooking of meat (Bertram, Engelsen, Busk, Karlsson, & Andersen, 2004; Micklander, Peshlov, Purslow, & Engelsen, 2002; Shaarani, Nott, & Laurance, 2006). As a result, 1 H NMR T 2 relaxation measurements taken continuously during cooking of meat have revealed a number of shifts in water properties at different temper- atures, which was suggested to reflect myosin denatur- ation and longitudinal shrinkage of the muscle fibres, respectively (Bertram et al., 2004; Micklander et al., 2002). However, no further evidence of a relationship between denaturation of meat components and simulta- neous changes in water properties was obtained in these studies. Differential scanning calorimetry (DSC) can be used to monitor protein denaturation, and DSC studies on meat have demonstrated three denaturation steps that have been ascribed to myosin denaturation (40–60 °C), sarcoplasmic protein and collagen denaturation (60– 0309-1740/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2006.05.020 * Corresponding author. Tel.: +45 8999 1506; fax: +45 8999 1564. E-mail address: HanneC.Bertram@agrsci.dk (H.C. Bertram). www.elsevier.com/locate/meatsci Meat Science 74 (2006) 684–689 MEAT SCIENCE