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Eng 2021, 2 616 In terms of the overall composition of the six major quality components, the data taken from Figures 4–6 show the highest cumulative percentage at 71%, also when operating at 25 ◦C and 65 bar pressure, with 51% at 25 ◦C and 68 bar and 53.2% at 25 ◦C and 71 bar. This percentage varied from 39.6% to 54.2% for the other operating conditions investigated with the lower values being at the higher pressures and temperatures. When the extraction curves for the individual components for this set of conditions, as shown in Figure 4, are compared to those operating under the other conditions investigated i.e., Figures 5 and 6, it is also seen that whereas the highest yields are always of ar- turmerone, there is a far bigger spread of the curlone and turmerone components when operating at 25 ◦C and 65 bar pressure. Therefore, it may be concluded that the optimum operating conditions for the extrac- tion of the essential oil from oven dried turmeric are 25 ◦C and 65 bar pressure, both from the point of view of overall yield and essential oil composition. However, if the objective is to obtain ar-turmerone, then the results show that a higher pressure should be used. All extractions were carried out over a 5 h period, and whereas many yield vs. time curves showed close to complete extraction, a few had not quite levelled off to that state. This was particularly true when operating at 30 ◦C; for 30 ◦C and 65 bar, it was still rising steadily after 5 h, which are conditions that are clearly unsuitable for commercial extraction. In commercial practice, extraction would be cut off rather earlier, typically 3 h when ≈90% of the extraction had been collected. The extra 2 h operating cost would not be worth the collection of the last ≈10%. It is important to note that no curcumin was obtained in any of the sub-critically extracted oils. Therefore, the sub-critical oils were pure essential oils uncontaminated by the turmeric oleoresin. 4.3. Comparison of Hydrodistillation with Sub-Critical Fluid Extraction The overall yields obtained from the hydrodistillation experiments, as indicated in Table 1, gave a yield of ≈6.2% dry weight basis, with preferred raw material being unpeeled fresh turmeric. The yields from the sub-critical extraction of unpeeled dried material, as detailed in Table 2, showed yields varying with operating conditions from 3.4% to 9.0% on a dry weight basis, with the highest yields at the lowest temperature of 25 ◦C. Therefore, sub-critical fluid extraction is preferred to hydrodistillation on the basis of yield. The component distribution identified in the hydrodistilled oil was fairly comparable to that identified in the sub-critically extracted oils, as shown in Table 3. Thus, the key components identified in the sub-critical extractions as being the most abundant in the extracts were α-curcumene, β-sesquiphellandrene, zingiberene, ar-turmerone, turmerone, and curlone. However, whereas one of the key components was not identified at all in the hydrodistilled oils, the other five key components were present. Several components other than the key components identified in the hydrodistilled oil were also found in the sub- critical oils, but in low concentrations. Overall, the sub-critical extractions provided a far superior product both in terms of quality and yield. Therefore, in terms of commercialising the process, subcritical extraction rather than hydrodistillation is the preferred method of extraction. Table 4 also indicates that the need to dry the turmeric prior to sub-critical fluid extraction does not seem to adversely affect the product quality. 4.4. Implications of Results The results show that sub-critical fluid extraction can give a higher yield than hy- drodistillation and that the extract is of higher quality. The extracts in each case are pure essential oils uncontaminated with oleoresin. Therefore, in terms of commercial application, the production of the essential oil of turmeric by sub-critical extraction is preferred, but it is appropriate that a financial comparison be made involving both capital and operating costs. In determining the operation costs of sub-critical extraction, the superficial flow rate of ≈1 L per min per cm2PDF Image | Sub-Critical Fluid Extraction Turmeric vs Hydrodistillation
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