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

The drug aloes has been known since earliest times and is mentioned in the Ebers papyrus of circa 1,500 B.C. Alexander the Great is reported to have sent a commission to Socotra to investigate the aloes grown there. The chemical composition of aloes is complex, and being of plant origin, subject to variation. Both the complexity of the chemical constituents and their biological variation has resulted in a very large volume of conflicting material being published on this drug export. Since aloes is used as a purgative for both human and veterinary use, it is obviously important that the dosage and consequently the active constituents, should comply to an accurate means of standardisation. To date, despite extensive world wide research into this drug such standardisation has not been achieved. Even the methods used for the assay of the principal constituent, aloin, vary considerably in their results, and to complicate matters new chemical principles have been isolated from aloes in recent years. Consequently the purpose of this work has been to investigate the main chemical assay methods currently in use, and to determine which was the most accurate, and why discrepancies occurred in the selected assay methods. furthermore the results obtained by chemical assay have been compared with those obtained by biological assay in an attempt to correlate aloin content with purgative activity. Newly isolated compounds have been investigated biologically for the first time, and the biological assays of the resinous, glycosidal and other compounds of aloes have been performed. Intro. p.1-2.

Introduction: Despite the tremendous advances made with regard to synthetic organic medicinals within the last two decades, heavy reliance is still placed on plant products. This is especially true of the anthracene derivatives used medicinally as purgatives, and which are derived principally from senna, cascara, rhubarb, frangula and aloes. While particular attention has been paid to the chemistry of the former group in recent years, aloes has been largely neglected, possibly due to the fact that the Aloe species are confined largely to areas where extensive research facilities are lacking, such as Africa , India and the West Indies. Thus research in Europe has been confined largely to the lump aloes of commerce, derived from relatively few species. In 1953 a comprehensive report by Hodge (103) appeared on "The Drug Aloes of Commerce, with Special Reference to the Cape Species". Hodge observed that South Africa abounds in species just as abundant as A.ferox, (which is the prime source of Cape aloes), and advised that a systematic chemical survey might show certain of these to be not only higher yielders of bitter aloetic juice but also sources of a superior drug product. Consequently an investigation along these lines is presented here, and it is observed that several species apart from A.ferox not only contain aloin, but also yield a large volume of aloetic juice. Only pharmacologic studies can reveal if the juice of these species is as safe as that of A.ferox, but without doubt they could be used for the extraction of crystalline aloin. Concurrently, the distribution of the Aloe resins, said by some to be purgative themselves, has been studied. The investigation has revealed that the structurally similar compound homonataloin enjoys an equally wide distribution as aloin. However, almost invariably it is confined to small species yielding little aloetic juice, apart from which nothing is known regarding its pharmacologic properties. It is interesting to note that the resin distribution in the homonataloin-containing species is very similar to that of the aloin-containing species, but differs widely from. that of the species containing neither of these principles. Apart from aloin and homonataloin, aloinoside and chrysophanol also occur in Aloe species, and together with the resins, these indicate that when all the South African Aloe species have been investigated, they may well be of chemotaxonomic value. Within the comparatively short space of the last decade some work has been performed on aspects of the metabolism of such anthracene-containing species as Rheum, Rhamnus and Rumex. These investigations have shown that the anthracene derivatives are not merely waste products, but perform definite metabolic functions. The latter portion of this work has been devoted to this relatively neglected aspect of the Aloe species.

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