To assess the quality of natural antioxidants used as food additives, it is important to establish method for evaluating antioxidant activity. In this study, the DPPH and ABTS radical scavenging methods were evaluated. The antioxidant activities of 21 reference antioxidants, including flavonoids, polyphenols, vitamins, amino acids, and peptides, were determined by these methods. In both assays, a catechol and a pyrogallol moiety contributed to antioxidant activity. In addition, a 3-hydroxyl group in the C-ring of the flavonoids and the gallic acid ester moiety of the catechins were also important for activity. The antioxidant activities determined by DPPH and ABTS were similar with the exception of catechol compounds, for which values were～1.3 μmol TE/μmol higher in the DPPH assay than in the ABTS assay. We conclude that DPPH reflects reactivation of the catechol moiety of the antioxidants. A correlation study of DPPH and ABTS with the FRAP method showed that the DPPH method reflected ferric-reducing ability more precisely than did the ABTS assay. We conclude that the DPPH assay would be suitable as a standard method for evaluating natural antioxidants as food additives.

　The rhizomes of diploid and tetraploid gingers (Zingiber officinale Roscoe) were studied for their composition of volatile and pungent compounds. The tetraploid ginger was derived from the diploid ginger by in vitro colchicine techniques. GC and GC-MS analyses revealed that the volatile compounds in the diploid and tetraploid gingers exhibited a similar compositional pattern. The pungent compounds were also isolated from the tetraploid ginger rhizomes and their structures were identified as [6]-gingerol and [6]-dehydroparadol by chemical and spectroscopic evidence. The HPLC analysis showed that the composition of pungent compounds in tetraploid ginger was not so different from that of diploid ginger. Therefore, tetraploid ginger showed a potential alternative to diploid ginger, since tetraploid ginger has several advantages over diploid ginger such as pollen fertility, germinability, and larger size.

　Broccoli (Brassica oleracea var. italica) has a high vitamin C (VC) content, which can be reduced during the cooking process. We therefore compared two methods, vacuum cooking and boiling, with respect to changes in VC content. We cut the broccoli, and divided it into 4 edible parts: the florets, branches, and inner and outer parts of the stalk. Thereafter, we applied the two cooking methods to the prepared broccoli samples, and analyzed the VC content using the post-column derivatization method. Samples were analyzed for total VC content/100g fresh weight. For raw samples, the VC content was greatest in the branches, followed by the inner stalk, florets, and outer stalk. Significantly more VC remained after vacuum cooking than boiling in all 4 parts based on the reduced VC content eluted out under vacuum cooking (p＜0.01). The sterilization process before vacuum-sealed packaging reduced the VC content in florets, whereas sterilization of the other 3 parts (branches, inner stalk, and outer stalk) showed minimal reduction of VC content (p＜0.05). We concluded that the major factors maintaining VC content during vacuum cooking are control of the outflow of VC in the cooking water and deactivation of enzyme decomposition of VC by sterilization.