There is a definite need for uncomplicated analytical methods to determine the quality of aloe gel in commercially important species. The Aloe vera industry is a well-established, multi-billion dollar industry with well developed processing and quality control methods which are not directly applicable to the local Aloe ferox industry. There is a lack of suitable parameters and quality standards for gel products. Gels from Aloe ferox leaves (and several other species) were extensively sampled to collect a wide range of data points as part of a first exploration of possible quality control parameters. Only three species of Aloe (A. vera, A. arborescens and A. ferox) have been commercialised despite the fact that there are more than 400 species in the genus. This study involves an evaluation of variables and methods which could have potential for describing, identifying and standardising aloe gels from different species. All known topical uses reported in the ethnobotanical literature for aloe are recorded, showing that perhaps many other aloes could have commercial potential. Apart from A. vera, A. arborescens and A. ferox, other species included in this study were A. greatheadii var. davyana, A. striata, A speciosa and A. marlothii. Leaf dimensions, gel yields and gel compositions in these species were studied in detail. Parameters investigated included free and hydrolysed sugars, organic acids, conductivity, acidity, phenolic contaminants and gel discolouration potential. Free sugars are surprisingly uniform in the Aloe genus with glucose found to be the only free sugar present in the gel parenchyma. Glucose levels ranged from 0.1 mg/mL to 3.3 mg/mL. Hydrolysed sugars released after hydrolysis with trifluoroacetic acid (TFA) have a gel fingerprinting potential. Commercially important gel from A. vera can be distinguished from the local A. ferox gel on the basis of hydrolysed sugars. Aloe vera gel contains mannose and A. ferox gel a combination of glucose, galactose and sometimes xylose. Further variation studies are however recommended for A. ferox gels as there appears to be three gel chemotypes. Organic acids currently used in the A. vera industry as markers of freshness are considered in other Aloe species.Seven species from 16 localities showed variation in their malic acid and lactic acid levels with lactic acid formation associated with older gel stored at room temperature. Lactic acid formation is a scribed to malolactic fermentation during which bacteria use malic acid and/or glucose to produce lactic acid. Conductivity proves to be a quality control variable with potential for quality control as it shows species-specific ranges in both fresh and aged gel. Seven species were analysed for conductivity level changes associated with storage. Aloe ferox gel shows aconductivity below 3000 ìS/cm in fresh gel and above 3100 ìS/cm in aged gel. In A. vera the values are 1670 ìS/cm in fresh gel and 1990 ìS/cm in older gel batches, while in A. arborescens the highest level is 3510 ìS/cm in fresh gel and above 4000 ìS/cm in aged gel. It is therefore possible to determine unknown commercial liquid gel batches using conductivity as a species-specific marker. Acidity (or pH) levels vary between acidic (4.7) and neutral (6.8) in fresh gel. Acidity (pH) was found to generally increase during ageing of gels but there is considerable variation with regard to species and gel age. Unwanted phenolic contaminants in aloe gel can easily be analysed by HPLC and shows some potential as a fingerprinting method for aloe gel products. The levels of these unwanted compounds in aloe gels can be reduced by treatment with activated charcoal. However, complete removal of aloin or aloesin proves difficult. The colour changing potential of various aloe gels (caused by unknown phenolic compounds which may turn an undesirable yellow or pink colour) can easily be determined using a crude sodium hydroxide test. The methods developed in this study can now be used to explore the full range of variability in commercial aloe gels and other species with commercial potential. Such studies will be necessary to set quality criteria and define standards for many species of Aloe. / Prof. B.E. van Wyk
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8333 |
| Date | 21 April 2008 |
| Creators | O'Brien, Chantal |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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