Lag Time Determinations in Beer Samples. Influence of Alcohol and PBN Concentration in EPR Spin Trapping Experiments

The beers’ lag time measured with the PBN (N-t-Butyl-α-phenylnitrone) spin trapping experiments coupled with EPR spectroscopy is related to their antioxidant capacity and shelf life. The effect on the lag time of the alcohol content of the beer (starting values, 9 and 13%) and PBN concentration (50 or 200 mM) was analyzed on three samples, a pilsner, a strong lager, and a blonde Ale heated at 60 °C to trigger the production of the 1-hydroxyethyl radical. The lag time was determined only for the strong lager beer, with the values depending on the experimental conditions, being higher when PBN had a lower concentration. The antioxidant activity of the three beers gave the following values: 0.9089 mL pilsner beer/mg DPPH, 0.8510 mL strong lager beer/mg DPPH, and 0.7184 mL blonde Ale beer/mg DPPH, indicating that the unsuccessful determination of the lag time was not due to stale beers. The EPR intensity of the PBN adduct after 150 min (I150) and the area under the curve (AUC) were also measured and related to the oxidative stability of beers. Further studies are needed to verify the influence of the heating temperature in samples that do not show a lag time at 60 °C.