The influence of genotype, ring specificity, gamma irradiation, location, soil type, and growth stage on the contents of the anticarcinogenic flavonol, quercetin, in onion (Allium cepa L.)

Abstract

The variation in quercetin content due to genotypes was investigated using reverse phase high perform ance liquid chrom atography (HPLC). D ifferent quercetin glucosides were hydrolyzed into aglycones. On a fresh weight basis, total quercetin content in yellow and red onions varied from 56.16 to 286.40 m g/kg in different genotypes. White onions contained only a trace amount of total quercetin. One o f the TAES genotypes'20272-G 'had the highest aglycone content 12.50 mg/kg. A decrease in total quercetin content was observed from the dry skin to the inner rings, and both m iddle rings (5-6) and inner rings (7-10) contained less total quercetin in all genotypes. The highest total quercetin content was observed in the dry skins o f'R ed Bone', while the white 'Contessa', contained the least amount. Among the edible parts, total quercetin content in outer scales of'K adavan' was the highest. Outer rings o f all genotypes except 'TG1015Y' and 'Contessa' contained moderate amounts o f the aglycone. The highest concentration o f aglycone was observed in 'Kadavan' skin. Total quercetin content in 'Dorado' (diced) and 'Cardinal' (whole bulb) increased significantly (P=0.05) both at 0.8 and 1.2 kGy. Aglycone content increased significantly (P=0.05) in diced onions treated both at 0.8 and 1.2 kGy in 'Cardinal', 'Dorado', and '20352G ' genotypes. A glycone content in whole bulbs did not show a significant increase. W ounding alone did not influence total quercetin content during seven days stored at -20C. Four genotypes showed significant differences in total quercetin content due to tw o locations. Total quercetin content in 'T G 10I5Y ' due to different growth stages indicated differences but they were not significant. At second growth stage (23 Mar.) onions grown in the sandy loam soil, exhibited a significant (P=0.05) increase in total quercetin content over those harvested at the first growth stage (9 Mar.). However, total quercetin content o f onions in both fields were found be m ore or less sim ilar on both first and the last growth stages (21 Apr.). Thus, quercetin content was influenced by both the location and growth stage.