Quantification of l-lysine in cheese by a novel amperometric biosensor

Lysine quantification in cheese by a novel, highly selective amperometric biosensor is reported. Based on l-lysine-α-oxidase immobilized by co-crosslinking onto Platinum (Pt) electrodes modified by overoxidized polypyrrole, the sensor proved almost specific to lysine, sensitive and stable. The pure enzymatic nature of current signals was confirmed by a control electrode modified without enzyme. The precision of the method showed relative standard deviations of 4.7% and 9.2% respectively for Parmigiano Reggiano and Grana Padano cheese (n = 5). The recovery data on various cheese, spiked with lysine at 50-100% of the measured content, ranged from 85% to 99%. Different types of cheese were analysed showing lysine concentrations related to the ripening time and the manufacture technology, in agreement with literature data. Within dairy products, no appreciable lysine was detected in yogurts. The method adopted revealed suited to satisfy the demands for precise and sensitive detection of lysine with minimal sample preparation and clean-up.