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

Brown boronia flowers (Boronia megastigma)were incubated at25 °C after harvest, increasing the concentration of a solventextracted product by up to 25% (d. wt basis) and floral volatilesby up to 300% (d. wt). Open flowers produced more volatilesduring post-harvest incubation than flower buds, whole flowersproduced 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 extractand volatiles than those purged with nitrogen gas; ß-iononewas particularly depleted in nitrogen-purged flowers. Flowersand buds from three successive harvests (68, 82 and 90% openflowers) were incubated at several temperatures for up to 24h. The greatest increase in the concentration of floral extractoccurred in flowers harvested when 90% were open and incubatedfor 4 h at 12 °C, or 14 h at 23 °C. The largest increasein total volatiles occurred in material harvested at 82% openflowers and incubated for 25 h at 12 °C, or 13 h at 23 °C.The concentration of extract and volatiles declined after prolongedpost-harvest incubations. Brown boronia flowers produce volatilesand other components of the floral extract after harvest whenflowers with mature, intact enzyme systems are well suppliedwith oxygen, at temperatures at or below 25 °C. As flowersbecome visibly senescent, their ability to produce volatilesafter harvest declines.Copyright 1998 Annals of Botany Company Boronia megastigma(Nees); brown boronia; essential oils; floral volatiles; ß-ionone; phenology; post-harvest storage.     

Volatiles in Different Floral Organs, and Effect of Floral Characteristics on Yield of Extract fromBoronia megastigma(Nees)

The relative amounts of volatile compounds in the extract andheadspace from each floral organ were assessed in order to identifythe main organs for accumulation and emission. The mass of flowers/organs,the number/density of oil glands and yield of volatiles wereexamined for their relationship with extract yield, in clonaland non-clonal plants. Boronia flowers were divided into componentorgans and the solvent extractable product and headspace aboveeach organ type was quantified. The petals comprised 50% ofthe weight of the flowers, and the stigma 20%; however, thestigma contributed 70% of the total volatile compounds to extractfrom the whole flower. Proportionately more ß-iononeand dodecyl acetate were emitted from the stigma and anthersthan were contained in the extract, compared with other volatiles.The sexual organs are morphologically equipped for emissionof volatiles to attract pollinators. Between non-clonal plants, there was a lower coefficient ofvariation for extract yield than for values relating to extractcomposition, indicating that the former is more heritable thanthe latter. Variation between clonal plants was reduced comparedwith variation between non-clonal plants. The environment modifiesyield and quality of extract in clonal plants, indicating thatboth have relatively low heritability. No significant relationshipsbetween any floral characteristics and extract yield were found.Biosynthetic potential to accumulate extract is therefore ofprime importance, and the effect of environment on this potentialshould be the subject of future work. Boronia megastigma; brown boronia; Rutaceae; essential oils; flower; stigma; oil gland; ß-ionone     

The Effect of Flower Maturity and Harvest Timing on Floral Extract fromBoronia megastigma(Nees)

Development of floral organs during maturation of flower budsinto fully open boronia flowers is described. The petals andfunctional anthers attain their maximum size prior to the non-functionalanthers and the stigma. Organoleptic properties of the floralextract change with successive stages of bud development. Theconcentrations of extract and volatiles in the extract (% byf. wt) increase as buds mature, the extract concentration beinghighest in large buds and open flowers and the concentrationof volatile compounds being highest in open flowers. The rateof flower and extract development was measured. Yields of flowermaterial and floral extract per plant, and the concentrationof total volatiles including ß-ionone reach maximumlevels when 70% of flowers have reached anthesis. All measuredfactors decline after this point, except extract concentration(% of f. and d. wt) which is maintained up to 83% open flowers. Boronia megastigma(Nees); brown boronia; Rutaceae; flower development; floral extract; solvent extraction; ß-ionone; essential oils