Evaluation of Antioxidant Properties of Hop and Hop Products.

Several techniques of sample preparation and assessment methods were tested for evaluation of antioxidant properties of hop and hop products. Hot water or methanol was used for extraction of antioxidants. The antioxidant activity was determined using the techniques based on the methods already published by Chapon (photometric determination with dipyridyl-ferric complex), Kaneda (determination with free radical DPPH) and Ushida (determination of the EPR-T150 value). The method according to Ushida is limitary usable due to small differences of reducing activities of individual samples. The method according to Chapon is basically usable but it is less sensitive in comparison with the method according to Kaneda (DPPH). Determination with DPPH was performed using photometric and EPR detections, results of both detection methods were in a good correlation. The reducing activity of methanol extracts was found to be higher than the reduction activity of hot water extracts. It is due to a different spectrum of extracted substances. Hot water extraction was used for further study of the antioxidant properties of various hops and hop products for simulation of conditions of hop boiling and the method of determination of the reducing activity with DPPH. Significant differences in reducing activities were proved among Czech hop varieties. Best results of reducing activity were found out for Saaz hops. No significant differences in reduction activities were found among hybrid varieties.Several techniques of sample preparation and assessment methods were tested for evaluation of antioxidant properties of hop and hop products. Hot water or methanol was used for extraction of antioxidants. The antioxidant activity was determined using the techniques based on the methods already published by Chapon (photometric determination with dipyridyl-ferric complex), Kaneda (determination with free radical DPPH) and Ushida (determination of the EPR-T150 value). The method according to Ushida is limitary usable due to small differences of reducing activities of individual samples. The method according to Chapon is basically usable but it is less sensitive in comparison with the method according to Kaneda (DPPH). Determination with DPPH was performed using photometric and EPR detections, results of both detection methods were in a good correlation. The reducing activity of methanol extracts was found to be higher than the reduction activity of hot water extracts. It is due to a different spectrum of extracted substances. Hot water extraction was used for further study of the antioxidant properties of various hops and hop products for simulation of conditions of hop boiling and the method of determination of the reducing activity with DPPH. Significant differences in reducing activities were proved among Czech hop varieties. Best results of reducing activity were found out for Saaz hops. No significant differences in reduction activities were found among hybrid varieties