Water properties during cooking of pork studied by low-field NMR relaxation: effects of curing and the RN(-)-gene.

Using low-field NMR transverse relaxation measurements, the physico-chemical state of water in meat was followed continuously during cooking of 20 uncured and 20 cured pork samples from RN-carriers (n=20) and non-carriers (n=20). The obtained relaxation data were analysed using (i) distributed exponential fitting, and (ii) principal component analysis (PCA). Distributed exponential fitting revealed transition from a system with relatively well-separated components to a less well-defined system with a wide distribution of relaxation times and merged components during cooking. In addition, distributed exponential fitting analysis implied changes in relaxation characteristics that are tentatively ascribed to denaturation of myosin and subsequent shrinkage of the myofibrillar structures. The results are further suggested to reflect formation of new compartments in the myofibrillar lattice during the shrinkage of the existing structures with a succeeding redistribution of water. Nitrite curing was found to affect the distribution of water as well as the progress in the different water populations during cooking. PCA revealed two major shifts in relaxation characteristics around 43 and 56 °C in uncured samples and around 43 and 63 °C in cured samples, and the shift around 43 °C was found to be significantly affected by RN-genotype. The strong shift in water properties around 43 °C is suggested to be a result of myosin denaturation, and thus the results imply differences in myosin denaturation in meat from RN-carriers compared with meat from non-carriers. The second shift in water properties is suggested to reflect the onset of collagen shrinkage causing longitudinal shrinkage of meat, and accordingly the shift from 56 to 63 °C in the presence of salt points towards an effect of curing on structural alterations during cooking.