Elevated Carbon Dioxide Alters Hydrocarbon Emissions and Flavor in Onion

Bulb onion (Allium cepa), non-bulbing Japanese bunching onion (A. fistulosum), common chives (A. schoenoprasum) and garlic chives (A. tuberosum) have markedly different harvest indices. With the onset of bulbing, leaf production ceases, photosynthates are reallocated to the bulb, lowering production of new shoots and crop canopy. Successive harvests from the same planting allow for a cumulative harvest index. In testing the influence of growing plants under different CO₂ conditions, a set of volatile methyl-ketones have been identified from onion that are emitted at higher levels when plants are grown at elevated CO₂ compared to controls grown at ambient CO₂ levels. Sensory panel taste testing has indicated differences in flavor for some cultivars when comparisons were made between plants grown at ambient and elevated CO₂ conditions. In future studies we will examine if thiosulfinates generated from the enzymatic conversion of alk(en)yl cysteine sulphoxides contribute to flavor differences detected between ambient and elevated CO₂ grown plants.