Compositional features of polysaccharides from Aloe vera (Aloe barbadensis Miller) plant tissues ´ ´ Antoni Femenia*, Emma S. Sanchez, Susana Simal, Carmen Rossello ´ ´ Enginyeria Quımica, Departament de Quımica. Universitat de les Illes Balears, Ctra. Valldemossa km 7.5, 07071 Palma de Mallorca, Illes Balears, Spain Received 22 September 1998; received in revised form 27 October 1998; accepted 20 November 1998
Abstract A complete chemical characterisation of Aloe vera plant (Aloe barbadensis Miller) was carried out from the dissection of the plant whole leaves in ﬁlets and skin. In addition, a mucilaginous gel extracted from the ﬁlets was also characterised. Extraction with ethanol of lyophilised Aloe fractions (AIRs) allowed to concentrate the major fraction composed of carbohydrates up to 80%. The composition of the main type of polysaccharides present in the Aloe AIRs was determined. Mannose and cellulosic glucose were the major polysaccharide components in all AIRs, signiﬁcant amounts of pectic polysaccharides were also detected. Sequential extraction of polysaccharides present in Aloe vera plant portions, revealed that two main types of mannose-containing polymers were present in the Aloe vera plant. The polysaccharide detected in the ﬁlet and in the gel fractions corresponded to a storage polysaccharide located within the protoplast of the parenchymatous cells. Its structural and compositional features corresponded to the active polysaccharide known as acemannan. On the contrary, in the skin tissue, the mannosyl residues arose from a structural polysaccharide located within the cell wall matrix. Structural and compositional differences between both polymers were conﬁrmed by methylation analysis. The fact that acemannan is a reserve polysaccharide might help to explain most of the compositional variations reported in the literature for Aloe vera carbohydrates. Further, sequential extraction allowed us to identify several pectic polysaccharides, rich in uronic acids, with a composition similar to that of several antitumoral polymers found in different plant tissues. 1999 Elsevier Science Ltd. All rights reserved. Keywords: Aloe barbadensis; Polysaccharides; Bioactive polymers; Cell walls
1. Introduction Aloe vera (Aloe barbadensis Miller) is a perennial plant with turgid green leaves joined at the stem in a rosette pattern. Aloe leaves are formed by a thick epidermis (skin) covered with cuticles surrounding the mesophyll, which can be differentiated into chlorenchyma cells and thinner walled cells forming the parenchyma (ﬁlet). The parenchyma cells contain a transparent mucilaginous jelly which is referred to as Aloe vera gel. Aloe vera has enjoyed a long history of lay acceptance as possessing curative or healing qualities (Coats and Ahola, 1979; Davis et al., 1994; Visuthikosol et al., 1995) and it has been featured extensively in the area of dermatology, especially for treating radiation-caused skin conditions (Davis et al., 1989; Kaufman et al., 1989). The body of scientiﬁc literature documenting medical applications in digestive problems, as a virucidal, bactericidal, and a fungicidal * Corresponding author. E-mail address: email@example.com (A. Femenia) 0144-8617/99/$ - see front matter PII: S0144-861 7(98)00163-5
agent and in gynaecological conditions is also extensive (Grindlay and Reynolds, 1986; Shelton, 1991). According to the literature, the chemical composition of Aloe plants is largely dependant on the species analysed. A prominent feature of Aloe vera ﬁlet is its high water content, ranging from 98.5% to 99.5% of fresh matter. More than 60% of the remaining solid being made up of polysaccharides (McAnalley, 1993). Presently, the controversy over the identity of the active substance(s) in Aloe vera has not been settled. It is therefore important to clearly distinguish between the composition of the different parts which form the Aloe vera plant. There is...