Two-Dimensional Correlation Spectroscopy Study of Visible and Near-Infrared Spectral Variations of Chicken Meats in Cold Storage

This paper reports the generalized two-dimensional (2D) visible/near-infrared (Vis/NIR) correlation spectroscopy study of chicken meats in cold storage. The 2D visible correlation analysis revealed that, besides the previously reported three absorption bands around 445, 485, and 560 nm ascribed to DeoxyMb, MetMb, and OxyMb, there is an additional band around 635 nm that could be assigned to SulfMb, a product from the reaction of myoglobin with H2S generated by bacteria. Unlike the spectral intensity reduction of the 440 and 560 nm bands, the intensities of the 490 and 635 nm bands increase with storage time. The asynchronous 2D visible correlation spectra indicated that OxyMb and MetMb produce SulfMb first; then complicated reactions such as the oxygenation and oxidization of DeoxyMb and the oxidization of OxyMb follow as storage is prolonged. In addition, several close and separated bands appearing around the 440, 490, and 560 coordinates could be a result of the changes in the molecular environment of the heme pigment portion. Hence, the decreasing intensity and the splitting of the 440 and 560 nm bands are responsible for the discoloration of meats. The 2D correlation spectra in the NIR region showed that the O-H/N-H bands change their spectral intensity before the C-H groups during the storage, suggesting a coordination process for hydrophilic O-H and N-H groups. It revealed two main possibilities: (1) water species interact with other meat components, and (2) the meat proteins undergo proteolysis and denaturation processes, which is associated with the development of tenderization during storage (aging). In addition, the asynchronous spectra correlating the spectral bands in both the visible and NIR regions suggested that the discoloration occurs earlier than other developments, such as tenderization process.