Selective Determination of Lysine in Dry-Cured Meats Using a Sensor Based on Lysine-α-Oxidase Immobilised on a Nylon Membrane

Abstract

An enzymatic sensor employing lysine oxidase (LOx) with the immobilised enzyme system by crosslinking with glutaraldehyde using an immunodyne ABC nylon membrane, in combination with an oxygen electrode, has been optimised to determine the lysine content in dry-cured ham and dry-fermented sausage at different cured times. The amperometric signal obtained due to the oxygen depletion (consumed oxygen) during the lysine oxidation was recorded at 5 s in the immobilised enzyme sensor, and the reaction rates (slope) were related to the lysine content. A linear relationship between the consumed oxygen as a function of time (mg O2/l/s) and the lysine concentration in the range 10–250 μM (R 2 = 0.9946) for the immobilised enzyme system was found. The immobilised enzyme sensor showed a high specificity and sensibility. Nevertheless, the stability of the immobilised enzyme at the assay temperature was very poor, and thus, a new membrane was required for each analysis. The analysis of lysine with the immobilised enzyme system in cured meat samples revealed very good agreement with the determination performed through standard HPLC methodology, which validated the use of this sensor as an alternative technique to evaluate cured meat quality.