Enzymatic Spectrophotometric Determination of Nitrites in Beer

ABSTRACT A colorimetric assay for nitrite determination in beer based on c-type multiheme enzyme Nitrite reductase (NiR) isolated from Desulfovibrio desulfuricans ATCC 27774, was developed. Using the enzyme in solution, nitrite assay was linear in the 10−8 – 10−2 M range with a detection limit of 10−8 M and a recovery ranging from 90 to 107%. The imprecision ranged from 4 to 10% on the entire calibration curve. With NiR immobilised onto a nylon coil, a flow reactor was developed which showed a narrower linear range (10−5 – 10−2 M) and a higher detection limit (10−5 M) than with the enzyme in solution, but made it possible to reuse the enzyme up to 100 times (50% residual activity). Sample preparation was simple and fast: only degassing and beer dilution by buffer was needed. This enzymatic assay was in good agreement with the results obtained using commercial nitrite determination kits.