EVALUATION OF ANTIOXIDANT PROPERTIES OF RAW HOP AND HOP PRODUCTS
The reducing activity was determined using the techniques based on the methods already published by Chapon (photometric determination with dipyridyl-ferric complex), Kaneda (determination with DPPH free radical) and Ushida (determination of the EPR-T150 value). The method according to Kaneda as well as the method according to Chapon is efficient for hop antioxidant properties determination; the method according to Chapon is less sensitive. Determination with DPPH was performed using photometric and EPR detections, results of both detection principles were in a good correlation. The reducing activity of methanol extracts of hops was higher than of hot water ones due to a different spectrum of extracted substances. Hot water extraction and reducing activity determination with DPPH were used for further study. Significant differences in reducing activities were proved among Czech hop varieties. Best results of reducing activity were found out for Saaz aroma hops. Small part of reducing activity of hops is lost in the course of hops drying; the decrease does not usually exceed 5% of origin reducing activity value. Drying in belt and chamber kilns is comparable from the hops antioxidative properties conservation point of view. Grinding and pelletizing has no conclusive effect on antioxidative properties of hops. Reducing activities of hops decreased in the course of long-term storage in dependence on storage temperature and hop form (raw hops, pellets). Storage temperature has no significant effect on reducing activity of hop pellets packed in multi-layer foil without air access.
Mikyska, A., Haskova, D. and Krofta, K. (2008). EVALUATION OF ANTIOXIDANT PROPERTIES OF RAW HOP AND HOP PRODUCTS. Acta Hortic. 778, 97-111
hops, reducing activity, DPPH, EPR, hop varieties, hops processing, hop ageing