Studies on the carotenoid and glycosidic precursors of aroma and flavour compounds in Boronia megastigma (Nees)

Studies relating to the carotenoid precursors of C-13 norisoprenoids resulted in the identification of five C-27 apocarotenoids. The new compounds were 3-hydroxyapo-10'-carotenoic acid, methyl 3-hydroxy-apo-10'-caroteno ate, apo-10'-carotenoic acid, apo-10'-carotenal, and methyl apo-10'-carotenoate. This provided evidence for site specific cleavage of C-40 hydrocarbon carotenoids and xanthophylls in the 9, 10 position. Changes in the levels of these apocarotenoids, P-ionone and C-40 carotenoids demonstrated that metabolism relating to carotenoid cleavage increased during flower opening. Glycosides of monoterpenes, C-13 norisoprenoids and cucurbates were detected in boronia using an HPLC screening process followed by enzymatic hydrolysis of an extract using both a pectinase and B-D-glucosidase. Release of these conjugates was further demonstrated through a simple marc incubation process. The pattern of change over a ten day period demonstrated initial release of the compounds over 4 - 6 days of incubation followed by their disappearance. A commercial trial of the process demonstrated a 36% increase in the yield of extract after 4 days. GC / Olfactometry indicated that many of the compounds in the new extract had aroma properties compatible with the primary boronia extract. There was additionally evidence that tiglamides, cinnamate esters and 8-hydroxy linalool esters that were previously not considered as flavour and aroma compounds contributed positive aroma sensations. Endogenous fungi were isolated from boronia which have the capacity to breakdown glycosides of flavour and aroma compounds including monoterpenols, C-13 norisoprenoids and cucurbates. These fungi were tested in a model system using sterilised boronia marc. The impact of fungal treatment on 45 naturally occurring boronia compounds was measured over a 4 day incubation period. The results indicated a complex pattern of changes including hydrolysis of glycosides, further metabolism of released compounds, and metabolism of volatile compounds remaining after the primary flower extraction.