Infrared and fluorescence spectroscopy for monitoring protein structure and interaction changesduring cheese ripening

Abstract

Sixteen experimental semi-hard cheeses, varying in moisture (42.1 to 49.8%), protein (20.2 to 25.9%) and fat (23.7 to 31.1%) content, were manufactured and ripened under controlled conditions. Fluorescence (tryptophan) and mid-infrared (Amide I and II regions) spectra were collected at 1, 21, 51 and 81 days of ripening in order to test the ability of spectroscopy to highlight the molecular changes that occur during this process. The mid-infrared and fluorescence spectral data from the experimental cheeses were analysed firstly by principal component analysis. Secondly, the correlations between the chemical domain and the spectral domains were studied by canonical correlation analysis methods. These analyses showed that each spectroscopic technique provided relevant information related to the cheese protein structure, which was used to discriminate each ripening stage. In addition, some spectral characteristics of ripened cheeses, linked to the initial chemical composition and the initial protein network structure, were detected at the early stage of ripening. Finally, a canonical correlation analysis between the two sets of spectroscopic data was performed and allowed to clearly discriminate each stage of ripening and each cheese at the 4 ripening stages. A molecular interpretation of these results involving the modifications of proteins, minerals and water interactions during ripening was attempted. This result demonstrated the interest of coupling two complementary spectroscopic techniques. Such coupling allowed the description of global characteristics of the investigated samples, which can be used for their characterisation. cheese / ripening / protein / structure / spectroscopy