Selective determination of lysine in mozzarella cheese using a novel potentiometric biosensor

ABSTRACT The analysis of lysine represents a significant cost for the relevant food industries. The use of an enzymatic sensor would allow the reduction of time and cost of this analysis. An enzymatic sensor using lysine -α- oxidase (LOx) with a soluble enzyme sensor in combination with an oxygen electrode was optimized in this study to determine the lysine content in mozzarella cheese. Selective determination of lysine in mozzarella cheese is an indicator of quality and of ripening time. The potentiometric signal obtained due to oxygen depletion (consumed oxygen) during lysine oxidation was carried out during 100s in the soluble enzyme sensor. An optimal time sensor response to quantify the lysine content of 3.5s was calculated from the slope of reaction rates. The sensor was set at a potential of 0.6 mV. A positive linear relationship was found between consumed oxygen as a function of time (mg O2/L × s) and lysine concentration in the range of 30–1,300 µM, with a coefficient of R2 = 0.9968 for the soluble enzyme sensor. This system showed good specificity (KM = 0.03 mM), which continued during eight weeks of cheese ripening time. The analysis of lysine with the soluble enzyme sensor in mozzarella cheese samples revealed very good agreement with the determination performed through standard HPLC methodology, which validated the use of this sensor as an alternative and more efficient technique to evaluate dairy products.