Studies On Free Radicals And Antioxidative Activity Of Beer

A new method, DPPH- spectrocolorimetery was established in this paper to detect the antioxidative capacity of beer, main conditions were as follows: put 2 mL of degassed beer with the dilution of 20 times of deioned water into a vial with a ground-glass stopper, then mixed with 2 mL DPPH- ethanol solution of 0.1 mmol/L, incubated under 0℃for 30min, then have the solution detected by spectrophotometer under 517nm, account the DPPH-scavenging ratio. This method has a effective estimation to antioxidative capacity of beer.Brewing process was reviewed and found that DPPH-scavenging ratio decreasing with the phase of mashing, from 87.17% at the beginning to 93% in the end; the high temperature of boiling made DPPH-scavenging ratio keep falling with 6.0%; some antioxidants were yielded by yeast during fermentation, DPPH-scavenging ratio had an obvious raise after 1-day fermentation, but a little decrease in the end.The free radicals were detected by Electron Spin Resonance(ESR) method, it was found that·OH was the typical free radical in bottled beer, which was yielded by the reaction of oxygen and materials in beer, the content of·OH increased with the staling degree. During the brewing process, the content of·OH increased a lot during boiling, decreasing after fermentation, and raising after filtration. An unreported free radical was detected in mashing wort for first time, and named FR1 temporarily. It was implied that FR1 had some relationship with·OH in the reaction chain. Oxygen is a great impulse to the yielding of free radicals during mashing.Based on the studies on bottled beer in this paper it was shown that lag time, which brought forward by Uchida, can neither token the antioxidative capacity nor indicate the staling degree of beer. SI (stability index) relates highly to the panel score of sensory analysis. SI could be used in both same brand beer and different ones, SI>200, fresh; 200-120, slight staling; 120-50, staling; <50, extreme staling.A speculation on categories of antioxidants in beer: categoryâ… andâ…¡have the effect mainly on lag time, generation speed of free radical respectively, while typical materials are SO₂ and polyphenols. Both categoryâ… andâ…¡effect the DPPH-scavenging ratio.