and (E)-2-hexanal (Umano etal., 1999). Elsewhere, citric, malic and formic acids were found in various aloes (Ishikawa etal, 1987) and again, malic acid was determined as 1.3% of unspecified 'raw material' (Bereshvili etal, 1989). Malic acid has been used as a marker to validate gels offered for sale as aloe-derived (Chapter 6). Previously, an extensive survey of leaf and perianth waxes of 63 Aloe species showed that the major component in most samples was hentriacontane (C3]}. Occurrence of other hydrocarbons had a taxonomic correlation (Herbin and Robins, 1968). An extract of whole A. vera plants yielded 0.7% non-polar lipids, of which the major components were stigmas-terol (18.4% of sample) and its stearate (21.3%), with lesser amounts of cholesterol (12.5%), methyl oleate (7.1%), triolein (2%) and oleic acid (1.3%). The polar lipids (0.9%) contained principally phosphatidic acid (47.3% of sample), with some sulfoqui-novosyl diglyceride (16.8%), phosphatidylcholine (12.1%) and phosphatidyleth-anolamine (12%) (Afzal etal, 1991). Hydrolysis of the lipid fraction yielded mainly Y-linolenic acid (42% of fraction), with a lesser amount of arachidonic acid (3.1%) which together were postulated as precursors of prostaglandins. Another analysis of A. vera gel by thin-layer chromatography claims the presence of sterols, saponins, triterpe-noids and naphthoquinones (Vazquez etal., 1996). The simple sugars, glucose, fructose and sucrose are present in large amounts in the nectar of aloes (Van Wyk etal., 1993) and a survey of 82 species revealed two groups in which sucrose was found at very high or very low levels.
As well as the organic substances described above there is of course an inorganic component in any plant material. An early report showed 3.3% ash content of A. vera leaf 'rind' and 0.2% (wet weight) ash in leaf 'pulp', which contained calcium oxalate (Rowe and Parks, 1941). Another report at that time gave the ash content of a purified gel as 12.9% (dry weight) (Roboz and Haagen-Smith, 1948). Twenty years later an analysis of A. vera freeze-dried 'juice' revealed a high level of chlorine (12.2%), accompanied by potassium (6.6%) and calcium (4.7%) (Bouchey and Gjersted, 1969). Analysis of an A. arborescens, incinerated, whole-leaf 'juice' also showed potassium (57%) as the main metallic component, accompanied by sodium (32%), manganese (9%), magnesium (2%) and calcium (1%) (Hirata and Suga, 1977). Calcium and magnesium lactates were found in fresh leaves of A. arborescens, together with 11 other metallic cations (Kodym, 1988). Calcium (0.3%) was a major component of a sample of A. vera gel (Baudo, 1992). A later analysis of A. vera, freeze-dried, gel gave prominence to calcium (3.5%), followed by magnesium (0.7%) and sodium (0.2%) (Yamaguchi etal, 1993). The detailed analysis of Femenia etal. (1999) also gave potassium (4.1%) as a major component, followed by sodium (3.7%) and calcium (3.6%) based on the freeze-dried gel. It is noteworthy that they also found a relatively high calcium content (3.3%) of the alcohol insoluble polysaccharides.
Was this article helpful?