Luminescent enzymatic flow sensor for D- and L-lactate assay in beer

A bioluminescent now sensor, previously developed for the determination of both D- and L-lactate in clinical samples, was utilized to carry out the sa me assay in beer. The sensor monitored the reduced form of nicotinamide ade nine dinucleotide, produced by nylon-immobilized D- and L-lactate dehydroge nase, by means of bacterial bioluminescent enzymes immobilized on a separat e nylon coil. The preparation of beer samples was very simple as only a mod ification of pH and a dilution were necessary. The recoveries ranged from 9 1% to 104%, and the relative standard deviations at the 1 mmol 1(-1) level were 4.6% and 6.7% for Land D-lactate respectively. The response was linear in the range 0.1-10mmol 1(-1) for both D- and L-lactate. The total amount of lactate determined by bioluminescent biosensor (x) and by PIPLC (y) show ed a very good correlation (y = 0.654 x + 88.1, n = 29, r = 0.918). The flo w injection system developed allowed the determination of not only the tota l but also the individual contents of D- and L-lactate in beer, and the tim ely discovery of the unwanted presence of lactic acid bacteria.