Relationship among EPR oxidative stability and spectrophotometric parameters connected to antioxidant activity in beer samples

A relationship between EPR and spectrophotometric parameters related to beer staling and antioxidant activity, was identified. AUC (area under the curve), intensity at 150 min (T150), radical scavenging activity (RSA), total phenolic compounds (TPC), hydroxyl radical scavenging capacity (HRSC) and one parameter linked to staling degree of beers (thiobarbituric index, TBI) were related. Temperature was modified to find the proper working conditions for EPR spin-trapping experiments and it was found that it affected the kinetic of PBN adduct evolution. For the samples reaching a maximum intensity signal, the higher the heating temperature, the shorter the time interval needed to reach it. No linear relationship was detected among parameters obtained with EPR spin trapping experiments and RSA, TPC, TPI, and HRSC when correlating one parameter with another. On the contrary, a good linear relationship was found among AUC or T150 and a combination of RSA, TPC, TPI, and HRSC (R2 = 0.9562 and 0.9694, respectively). The goodness of fit increased to R2 = 1 when a combination of AUC and T150 was related to a combination of RSA, TPC, and TPI, and HRSC.