FTIR spectroscopy studies of high pressure-induced changes in pork macromolecular structure

Abstract

High pressure processing (HPP) allows to extend the shelf life of meat and meat products by pressurization of microorganisms. At the same time, HPP can induce changes of the protein structure. Vacuum-packed pork chops were HPP-treated at 300, 600 MPa for 1 or 15 min. Samples of raw, cooked and HPP-treated meat muscles and juice were analysed to evaluate the structure of macromolecules. HPP caused visible discolouration of pork chops; hence, the colour of pork meat surface was tested. The lightness (colour component L*) was directly proportional to the applied pressure, probably due to the increased protein denaturation by high pressure. Pork meat muscle and juice samples were analysed with FTIR high-throughput screening (FTIR HTS-XT, Bruker, Germany). FTIR spectra of meat muscle showed pressure and time dependent decrease of numbers of α-structures and β-sheet conformations of proteins. In spectra of cooked meat muscle, the number of α-helix structures and β-sheets, identified at 1682 cm−1, was the lowest. The decrease of intensities of absorption bands at 1655 cm−1 and 1454 cm−1, assigned to the collagen type I, was directly proportional to the pressure and treatment time, thus, suggesting the release of denatured collagen into meat juice. In spectra of meat released juice, changes of Amide band shapes, frequencies and the minimum between the Amide I and II bands, compared to those of control, indicated changes in the protein secondary structure and the ratio of α-helix to β-sheet. In spectra of all juice samples an absorption band at 1394 cm−1 assigned to CH3 groups in proteins Amide I and lipids was detected. The intensities of bands at 1394 and 1124 cm−1 increased proportionally to the increase of pressure and treatment time. It was shown that the absorption band at 1394 cm−1 can be used as a marker for assessment of the HPP induced changes in proteins. This study showed that HPP-induced changes in protein structure can be evaluated by FTIR high-throughput screening of pork meat muscles as well as released juice. FTIR analyses of the meat released juice is significantly faster and simpler method than analyses of muscle. This approach is especially effective for quick assessment of large sample sets and search of the most effective meat HPP treatment mode.