CHARACTERIZATION OF CHLOROPHYLL PIGMENTS IN RIPENING CANOLA SEED (BRASSICA-NAPUS)

This study characterizes the chlorophyll pigments in ripening Brassica napus seed. Seed samples, collected weekly as the crop ripened, were analyzed by high-performance liquid chromatography to characterize chl orophyll pigment composition. Chlorophyll A, chlorophyll B, pheophytin A and pheophytin B were the predominant pigments, while pheophorbide A, methylpheophorbide A and pyropheophytin A were minor components. No differences in pigment composition were observed between the three cu ltivars tested or between early and late seeding dates. There were dif ferences in pigment composition between the two years of the study, wh ich may result either from seed aging during storage or from environme ntal influences. Pigment composition was dependent on seed maturity, w ith physiologically mature green seeds containing both chlorophylls an d pheophytins, but fully mature seeds containing only chlorophylls. Ph eophytins and the minor components appeared transiently, presumably fo rmed from the chlorophylls and subsequently degraded. The ratio of chl orophyll A/B increased during seed ripening, with fully mature canola seed having a chlorophyll A/B ratio twice that of physiologically matu re green seed. The ''B'' derivatives degraded faster than the ''A'' de rivatives, suggesting enzymatic reactions. The initial steps in the ch lorophyll breakdown pathway in canola seed appear to be: [GRAPHICS] Ra ncimat test but the order of stability was reversed in the thin-film U V test. Cocoa butter was much more stable in the Rancimat test than wh en assessed by the thin-film UV test.