Protein determination in polychromed stone sculptures, stuccoes and gesso grounds

Various procedures were used to extract and determine proteinaceous material from artificial specimens and samples taken from works of art. Polychromed stone sculptures (twelfth-thirteenth century), the gesso ground from a wooden statue (fifteenth century), fresco plasters (sixteenth century) and stuccoes of various ages were examined. The best results were obtained by extracting protein with 1N NaOH at 80°C for 180 minutes and determination by a modified Folin phenol assay. The amino acid composition of proteins was determined by direct hydrolysis of the samples and desalting on a sulphonic resin. High performance liquid chromatography (HPLC) using phenyl isothiocyanate (PITC) derivatization permitted the identification of some of the proteins used in the works of art and demonstrated the presence of amino acids deriving from microorganism activity and environmental contamination. The extraction method used here and direct hydrolysis appeared to be complementary: the colorimetric procedure permits the quantitative determination of protein, rapidly screening a large number of samples, while amino acid analysis permits identification of the nature of the proteins and the presence of other amino acids which are not present in binding proteins.