Composition and flavonoid levels in onions (Allium cepa) grown in hydroponics in greenhouses and growth chambers
One-thousand eighty long-day onions (Allium cepa L. 'Purplette') grown ' hydroponically in a greenhouse were analyzed for composition and total edible biomass to determine the amount of variability as the plant matures. Plants were harvested at 14, 21, 28, 35, 42, 49, 63, 77 and 98 d after sowing. Plant height increased as plants aged, and a significant interaction between planting date and plant age was noted. Plant weight and net number of leaves increased with age and again an interaction between age and planting date was observed. Percent N decreased from 0.55-.34% (p < 0.05) as the plants aged. Percent C (C) decreased (p < 0.05) as the plants aged but after d 77 a significant increase occurred. Ash content increased (p < 0.05) as the plant aged, with means ranging from 0.09 -1.07%. Calcium (Ca) and magnesium (Mg) concentration decreased (p < 0.05) as the plant aged with means rangmg from 128.7 - 14.2 mg/100 g and 57.1 - 22.0 mg/100 g, respectively. Potassium (K) concentrations showed an interaction (p < 0.05) between age and plant age. Total flavonol (TF) content increased (p < 0.05) from 226.1 - 554.7 mg/100g, as the plant aged from 14 d to 98 d. Dry matter (DM) content and sulfur (S)concentration was unchanged (p > 0.05) as the plant aged. Mean values ranged from 10.47-10.70% and 185.2-193.6 mg/100 g for dry matter content and S concentration, respectively. Biomass production and proximate composition of onions varied significantly as the plant ages and underwent morphological changes.