Luminescent enzymatic flow sensor for d- and l-lactate assay in beer

Abstract

A bioluminescent flow sensor, previously developed for the determination of both d- and l-lactate in clinical samples, was utilized to carry out the same assay in beer. The sensor monitored the reduced form of nicotinamide adenine dinucleotide, produced by nylon-immobilized d- and l-lactate dehydrogenase, by means of bacterial bioluminescent enzymes immobilized on a separate nylon coil. The preparation of beer samples was very simple as only a modification of pH and a dilution were necessary. The recoveries ranged from 91% to 104%, and the relative standard deviations at the 1 mmol 1–1 level were 4.6% and 6.7% for l- and d-lactate respectively. The response was linear in the range 0.1–10 mmol 1–1 for both d- and l-lactate. The total amount of lactate determined by bioluminescent biosensor (x) and by HPLC (y) showed a very good correlation (y=0.654 x+88.1, n=29, r=0.918). The flow injection system developed allowed the determination of not only the total but also the individual contents of d- and l-lactate in beer, and the timely discovery of the unwanted presence of lactic acid bacteria.