Commercial production of essential oils from blackcurrants (Ribes nigrum L.)

The aim of the research programme was to investigate factors influencing the production of extracts from blackcurrant buds. The results, indicate that a small, but viable production unit could be established within the framework of a broader essential oils industry in Tasmania. Various agronomic factors which influence the growth of blackcurrant crops were examined in a systematic fan design. Investigations for a source of bud material revealed that blackcurrant plants pruned each winter to ground level, provide the maximum bud yields. In this system, the blackcurrant bush will remain vegetative. The importance of maintaining a healthy balance between plant vigour and bud yield. needs to be appreciated, as the annual pruning regimen can potentially subject the plant to physiological stress and reduce bud yields in subsequent years. The form of the bud yield-plant density response is asymptotic as determined by non-linear regression analysis. Further, investigation of the relationship of total cane fresh weight and shoot numbers per plant to planting density revealed that plant site is decreased at high densities. Growth depression is observed, with respect to shoot length at both high and low planting densities. This is discussed in terms of competition for resources, in particular light. Basal cane girth is Shown to be related to yield parameters and is suggested as being a reliable estimator of plant productivity. Two canopy types are distinguished over the range of planting densities examined. The continuous, uniform canopy at high densities intercepts light more efficiently than the discontinuous, clumped canopy observed at low planting densities. The continuous canopy meets criteria laid down for an ideal canopy. In particular, it reaches maximum size quickly, before incident radiation reaches its summer peak, as well as being easy to maintain at maturity. The compositional and organoleptic methods used on a number of varieties in this assessment reveal White Bud as the preferred variety. This analysis confirms the relationships established by Todd in his identification key, based on phenotypic features. Scanning electron microscopy identified, late November - early December, as the period of most rapid increase in oil gland size. Gas chromatographic methods reveal that the rate of oil synthesis increases in early to mid January, corresponding to a period of increased photosynthate availability as leaf growth slowed. Investigation of oil quality during bud burst, under both glasshouse and field conditions, showed that the strength of the catty note increases as the buds break from dormancy. This raises questions concerning the complexity of biosynthetic changes that are occurring, particularly the relationship between terpene synthesis and abscisic acid. Components in blackcurrant bud oil were analysed by liquid chromatography on silica gel or florisil columns using a series of different polarity solvents. The catty note was not eluted using these techniques, however a reversed phase procedure employing High Performance Liquid Chromatography was successful in separating this compound. Compositional data and identification were obtained by gas chromatographic and mass spectrometry methods. One hundred and twenty-three components were detected, of which sixty-six were positively identified, and good quality mass spectra presented for fifty-seven unknowns. Some twenty-three components reported have not been previously identified in blackcurrant bud or fruit oils. Gas chromatographic effluent odours were associated with the corresponding peaks to determine their individual contribution to the overall aroma complex. Five regions of the aroma profile were shown to be important to the blackcurrant bud aroma, but the individual components were not identified. Various extraction solvents were investigated, and petroleum ether was shown to produce an extract resembling the French product. The superiority of liquid carbon dioxide extracts was demonstrated, and these hold much promise for future commercial operations. Both harvesting techniques examined were effective in removing buds. However, the mechanical harvester is better adapted for commercial operation due to lower labour inputs. This prototype consisted of a set of rotating brush rollers which act to lift the bud and break the petiole. Other rollers control the speed at which the cane passes these brushes. In contrast, the chemical method utilizes sprays of ethephon to cause abscission layer formation in the bud petiole. An economic analysis was undertaken, examining the effect of price, planting density and harvesting method on the internal rate of return of capital invested. A mechanical harvesting operation is preferable, returning a higher profit margin than manual harvesting, since the latter requires high labour inputs. Lower planting densities, than those considered desirable for agronomic reasons, are more profitable due to reduced establishment costs.