*3.4. Amino Acid Composition*

The amino acid composition of native and acetylated PPC was determined by ionexchange chromatography after 23 h hydrolysis with 6 N HCl at 110 ◦C, according to the method described by Miedzianka et al. [24]. The hydrolysed amino acids were determined using an AAA-400 analyser (INGOS, Prague, Czech Republic). A photometric detector was used, working at two wavelengths, 440 and 570 nm. A column of 350 × 3.7 mm, packed with ion exchanger Ostion LG ANB (INGOS, Prague, Czech Republic), was utilized. Column temperature was kept at 60–74 ◦C and the detector at 121 ◦C. The prepared samples were analysed using the ninhydrine method. No analysis of tryptophan was carried out.
