St. Kitts & Nevis is blessed with fertile soil which can produce a wide variety of crops suitable for the extraction of high value materials for use as food flavourings, fragrances, aromatherapy products or pharmaceuticals. There is therefore potential for creating a new industry in the twin island state; an industry which could create higher earnings from land use, as well as create job opportunities both on the land and in manufacturing.
The processes associated with the primary extraction of these materials are not difficult, these being.
Notwithstanding the technical differences, both processes lend themselves to operation in small factory locations.
Research is currently being carried out in the Department of Chemical Engineering of the St. Augustine Campus to investigate the potential for introducing the Supercritical Fluid Extraction technology in the Caribbean. This has included work on ginger, clove, nutmeg, orange peel, grapefruit peel, and jasmine flowers. The results to date have been promising. It is important to note that relevant comparisons with traditional processes, e.g. steam distillation, are generally made in this work in order to ensure the best choice of technology. Some of these results will be included in the presentation and used to project the potential for commercial application in St Kitts-Nevis.
Essential oils and plant extracts are the basis for the natural flavour and fragrance industry worldwide. Essential oils, or as they are sometimes called volatile oils are believed to be that small portion of the plant material which imparts the characteristic odour and flavour most closely associated with the vegetative matter which they are obtained (Reverchon, 1997)
Essential oils are extensively used globally for food flavouring, fragrances, aromatherapy and pharmaceuticals. The worldwide market for essential oils has been estimated at US$2.6 billion, with an annual growth rate of 7.5%.
The Caribbean has very few production plants which manufacture essential oils. These include pimento oil in Jamaica, nutmeg oil in Grenada, bay oil in Dominica, and anise oil in Trinidad. These manufacturing plants which are all small by international standards use the traditional method of steam distillation as the method of production. However, because of the high temperature associated with the steam, there is some inherent thermal degradation of the volatile oils.
Within the last twenty years a new technique has been developed and commercialized to prevent the loss of these volatile material, as well as offer greater flexibility in selectivity of exactly which components can be extracted from a particular matrix. The process is called Supercritical Fluid Extraction (SFE).
Steam distillation involves the comminution of material usually in a large vat and the application of live steam through the material. The steam percolates the material and vapourizes the essential oils from the matrix, from which the mixture of steam and essential oils goes to a condenser where it is liquefied. Subsequently the liquid mixture is separated using a settling tank or similar vessel.
Supercritical Fluid Extraction (SFE) with respect to the extraction of essential oils involves the use of carbon dioxide as the solvent. Carbon dioxide is cheap, inflammable, and leave no detectable residue. A typical SFE process shown in Figure 1 consists of two major segments, the extractor and the separator. The material to be extracted is packed into the extractor and supercritical carbon dioxide enters the extractor where it dissolves the volatile material in the plant. The CO2 and the extract then goes to the separator where the pressure is below critical thereby allowing the CO2 to revert to the gas phase and deposit the extract. The CO2 can then be recycled to the extractor vessel. In order for the CO2 to be in the supercritical state, the pressure and temperature must be above the critical point of CO2 i.e. 31oC and 74bars.
Figure 1: The Supercritical Fluid Extraction Process
In an effort to introduce this technology to the Caribbean, The University of the West Indies, through the Department of Chemical Engineering, St. Augustine Campus, acquired two (2) SFE units in 1997 from Applied Separations Inc. (Penn, USA), at a cost of US$120,000.00. The first was a laboratory scale unit which has extractor vessels with capacities of 25ml, 100ml, and 300ml. The unit has a maximum operating temperature of 250oC, and a maximum operating pressure of 680bars. The second unit, a pilot plant, has a 20l extractor vessel with operational limits of 150oC and 300bars. The unit also has a carbon dioxide recycle unit integrated into the main unit because of the large volume of CO2 used in the process.
Since SFE is only part of the overall production process, other equipment were also required to process the plant materials. These include dryers, mills, slicers, a refrigerator for storage of the extract, as well as a gas chromatograph for analysis of the extracted oils.
Extraction work has been carried out on a wide range of plant material which can be readily found in the West Indies. These include nutmegs, orange peels, grapefruit peels, jasmine flowers, tonka beans, cloves, and ginger. For illustrative purposes, only results for tonka beans and nutmegs will be discussed. Tonka beans and its extract are used as a flavouring agent in the confectionery industry as well as in the manufacture of fine perfumes and pharmaceuticals. An experimental program was undertaken to investigate the SFE of tonka beans, with the extraction pressure being varied from 150bars to 400bars in increments of 50bars, at a constant temperature of 40oC. This was done for plain dried tonka beans obtained from a local source, and cut into 2mm pieces before extraction.
Traditionally the tonka beans are presoaked with ethanol to facilitate solvent extraction with hexane. Therefore a comparison was done using SFE to extract tonka beans presoaked in ethanol, and plain dried beans in order to ascertain any advantages in using this technique. The results are illustrated in Figure 2.
Nutmeg oil is used extensively today in the food, cosmetic, and pharmaceutical industry. Nutmegs, obtained from Grenada, were milled to about 1mm particles and extracted from 100bars to 350bars in increments of 50bars, and at 35oC to 60oC in increments of 5oC. (These results can be seen in Figures 3 & 4). Analysis of these extracts was done on a UNICAM 4600 gas chromatograph equipped with a 60m capillary column, and a FID detector. The results were compared with a sample of oil obtained from the Grenada Cooperative Nutmeg Association (GCNA) and the results are shown in Figure 3.
Figure 2: SFE of Tonka Beans
Figure 3: Variation of Yield of Nutmeg Oil with Pressure
Figure 4: Variation of Yield of Nutmeg Oil with Temperature
Figure 5: Variation of Major Components of Nutmeg Oil at Varying Conditions
Run 1: 40C 100bars Run 2: 40C 150bars Run 3: 40C 200bars
Run 4: 40C 250bars Run 5: 40C 300bars Run 6: 40C 350bars
Run 7: 35C 350bars Run 8: 50C 350bars Run 9: CGNA oil
Tonka beans – From Figure 2, the maximum yield of tonka beans extract, i.e. 6.46%, occurred at 350bars and 40oC. The corresponding yields for the beans presoaked in ethanol extracted at the same conditions showed a maximum yield of 4.34% at 300bars, and generally lower yields than the plain beans. This indicates the traditional method of presoaking the beans in ethanol does not offer any advantage in SFE.
Nutmegs – Figures 3 and 4 show the optimum extraction conditions for nutmegs (yield – 22%) to be at 350bars and 50oC. Figure 5 which shows the quantity of the key nutmeg components extracted i.e. sabinene, alpha-pinene, myristicine, and beta-myrcene, indicates their quality does not vary significantly with different extraction conditions. At the optimum extraction conditions, 50oC and 350bars (run no. 8), the quantity of these components are similar to that of the sample obtained from GCNA (run no. 9).
From the experimental results presented in the previous section, it is clear that SFE offer an alternative to the traditional method of steam distillation in the production of essential oils. However the traditional method of steam distillation is still extensively used because it favours oils that are relatively low in value such as bay oil or anise oil. Even though the composition of the oils may be slightly different, the SFE oils and extracts have been found to be superior because of the amount of key components they contain. Additionally, by varying the extraction conditions, it is possible to extract different compounds from the plant material. Generally at higher pressures, heavier compounds such as resins are extracted. Hence there are definite advantages to the process. A major disadvantage though, is the capital cost associated with setting up a SFE processing plant, which is a bit more than a steam distillation plant. However an economic analysis done by McGaw et al (1998) shows that a SFE processing plant in the Caribbean can be quite profitable with a return on investment of 39%.
Additionally, it is must be emphasized that the previous examples of nutmegs and tonka beans are just potential crops which can be processed for essential oils and extracts. For St Kitts & Nevis, crops suitable to these islands must be explored, by first developing them agriculturally, then investigating which of the processes, steam distillation or SFE will be suitable for processing the material. It is therefore up to the respective authorities and entrepreneurs in the islands of St. Kitts and Nevis to make use of this opportunity which will not only generate income, but provide employment in the manufacturing and agricultural sectors.
Reverchon, E. (1997) Supercritical Fluid Extraction and Fractionation of Essential Oils and Related Products The Journal of Supercritical Fluids Vol 10:1 pp1-37.
McGaw, D.R., Paltoo, V., Chang Yen, I. (1999) Impact of Supercritical Fluid Extraction on the Flavour and Fragrance Industry of the Caribbean Proceedings of the 6th Meeting on Supercritical Fluids Nottingham, England, 10-13 April 1999 pp 495-499.
URL http://www.uwichill.edu.bb/bnccde/sk&n/conference/papers/DRMcGaw.html
© David R. McGaw and Vernon Paltoo, 2000. HTML prepared using 1st Page 2000, revised September 29th, 2000.