Biosynthesis of Volatiles in Brown Boronia Flowers after Harvest: Effect of Harvest Time and Incubation Conditions

Brown boronia flowers (Boronia megastigma) were incubated at 25 °C after harvest, increasing the concentration of a solvent extracted product by up to 25% (d. wt basis) and floral volatiles by up to 300% (d. wt). Open flowers produced more volatiles during post-harvest incubation than flower buds, whole flowers produced more than flowers treated to simulate harvester damage, and fresh flowers produced more than frozen and thawed flowers. Flowers incubated in bags purged with air produced more extract and volatiles than those purged with nitrogen gas; β-ionone was particularly depleted in nitrogen-purged flowers. Flowers and buds from three successive harvests (68, 82 and 90% open flowers) were incubated at several temperatures for up to 24 h. The greatest increase in the concentration of floral extract occurred in flowers harvested when 90% were open and incubated for 4 h at 12 °C, or 14 h at 23 °C. The largest increase in total volatiles occurred in material harvested at 82% open flowers and incubated for 25 h at 12 °C, or 13 h at 23 °C. The concentration of extract and volatiles declined after prolonged post-harvest incubations. Brown boronia flowers produce volatiles and other components of the floral extract after harvest when flowers with mature, intact enzyme systems are well supplied with oxygen, at temperatures at or below 25 °C. As flowers become visibly senescent, their ability to produce volatiles after harvest declines.