Reactions of phenolic substances with lysozyme — physicochemical characterisation and proteolytic digestion of the derivatives

Lysozyme was modified by covalent attachment of selected phenolic compounds (m-, o-, p-dihydroxybenzenes, ferulic and gallic acid) at pH 9. The derivatives formed were characterized in terms of their physicochemical and digestion properties. The derivatization was accompanied by a reduction of lysine and tryptophan residues. Moreover, the solubility of the derivatives decreased over a broad pH range and the derivatization increased the hydrophobicity. The isoelectric points were shifted to lower pH values and formation of high molecular weight fractions occurred. In vitro experiments showed that, the peptic digestion of the derivatized lysozyme was adversely affected, whereas the tryptic, chymotryptic and pancreatic hydrolysis seemed to be favoured. The lytic activity of all the resulting lysozyme derivatives was reduced.