Available online at www.sciencedirect.com South African Journal of Botany 77 (2011) 988–995 www.elsevier.com/locate/sajb Physical and chemical characteristics of Aloe ferox leaf gel ⁎ C. O'Brien, B.-E. Van Wyk , F.R. Van Heerden 1 Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, Johannesburg, South Africa Abstract Aloe ferox leaf gel differs substantially from that of Aloe vera but almost no commercially relevant data is available this species. Leaf dimen- sions, gel yields and gel compositions were studied, based on samples from several natural populations. Glucose is the only free sugar in aloe gel (0.1 to 0.4 mg ml− 1 in A. ferox). Monosaccharides released after hydrolysis show potential for gel fingerprinting and allow for a distinction be- tween A. ferox and A. vera. The former yields various combinations of glucose and galactose as main monosaccharides, while the latter yields only mannose. Further variation studies are recommended because A. ferox appears to have three different gel chemotypes. Conductivity shows species- specific ranges — in A. ferox below 3000 μScm− 1 in fresh gel and above 3100 μScm−1 in aged gel (corresponding values for A. vera were 1670 and 1990 μScm− 1). The level of phenolic (bitter) compounds in A. ferox gel can be reduced by treatment with activated charcoal, resulting in a small loss of total dissolved solids. Alcohol precipitable solids and insolubility are useful variables for quality control of gel powder. The methods and data presented are the first steps towards developing quality criteria for A. ferox leaf gel. © 2011 SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Free sugars; Gel composition; Gel conductivity; Gel yield; Hydrolyzed sugars; Organic acids; Quality control 1. Introduction or “Kidachi aloe”) is another possible alternative source of gel products (Van Wyk et al., 2009). Aloe ferox Mill. (=Aloe candelabrum A.Berger), commonly A. ferox has been used since ancient times as traditional med- known as the bitter aloe or Cape aloe (also khala, umhlaba, bit- icine — a San rock painting depicts the plant (Reynolds, 1950) teraalwyn) is a polymorphic species indigenous to the Cape and it has a well-documented history of use as medicine (see coastal region, from Swellendam in the west to the southern Grace, 2011). However, the use of the inner, non-bitter gel as a parts of KwaZulu-Natal in the east (Reynolds, 1950; Van food supplement is a recent development — no documentation Wyk and Smith, 1996; Glen and Hardy, 2000). It is a single- of a food use is found in the literature except the production of stemmed aloe with erect racemes of red, orange, yellow or rare- jam (preserve) by Cape farmers (Palmer and Pitman, 1972; ly white flowers and spreading or gracefully curved thorny Fox and Norwood Young, 1982; Palmer, 1985; Rood, 1994). leaves. Northern forms of the species, previously known as A. The gel of Aloe maculata All. and Aloe zebrina Baker, however, candelabrum, are morphologically, genetically and chemically is used as famine food in case of an emergency, and the flowers within the range of variation of A. ferox (Viljoen et al., 1996). of several species, including A. ferox, contain nectar which is Aloe marlothii A.Berger is a possible alternative source of eaten by children (Fox and Norwood Young, 1982). gel products. This species formed the basis of a pharmaceutical Aloe vera L. is undoubtedly one of the most important me- product known as “Natal aloes” that was discontinued in the dicinal plants of the world. The plant provides the raw materials late 19th century. Aloe arborescens Mill., currently under com- for a well-researched, well-established, multi-billion dollar in- mercial development in Japan and Italy (known as “Japan aloe” dustry with an estimated annual turnover exceeding 110 billion US dollars (International Aloe Science Council, 2004). The gel ⁎ from this species is used mainly in cosmetics and as a tonic Corresponding author. drink but there are numerous other uses in the food industry E-mail address: [email protected] (B.-E. Van Wyk). 1 Current address: School of Chemistry, University of KwaZulu-Natal Pieter- (Grindley and Reynolds, 1986; Reynolds and Dweck, 1999; maritzburg, Private Bag X01, Scottsville 3209, South Africa. World Health Organization, 1999; Waller et al., 2004); see 0254-6299/$ - see front matter © 2011 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2011.08.004 C. O'Brien et al. / South African Journal Of Botany 77 (2011) 988–995 989 also Reynolds (2004), Park and Lee (2006), Du Preez (2008), with A. vera releasing mannose (Choi and Chung, 2003) after Grace et al. (2008, 2009) and Grace (2011). a hydrolysis treatment and A. ferox releasing mainly glucose In South Africa, the A. ferox gel industry has gained momen- and galactose (Mabusela et al., 1990). tum since 1994 when the first gel was produced through a patent- Since almost all published information is only applicable to ed process in a factory at Albertinia (Botha, 1994; Newton and A. vera gel, this study was conducted to explore some chemical Vaughan, 1996). Despite the increasing commercial importance and physical characteristics of the leaf parenchyma gel of A. of A. ferox gel, only one scientific study of the gel components ferox. Leaf dimensions, gel fillet yields and gel powder yields has been published (Mabusela et al., 1990). In view of the large were studied in detail. Other parameters investigated included number of Aloe species, it is surprising that no research has total dissolved solids, free and hydrolysed sugars, conductivity, been done to investigate the commercial potential of other spe- alcohol precipitable solids and solubility. The expectation was cies. In 2007, Standards South Africa (a division of the South Af- that such data can provide a better understanding of the basic rican Bureau of Standards) published a South African National principles underlying gel variability, with possible applications Standard for Aloe raw materials (Standards South Africa, 2007). in chemotaxonomy and especially in developing commercial The scope of the standard is to specify the “requirements and quality control procedures for A. ferox gel. test methods for A. ferox raw material intended for use in consum- er products including health, cosmetic, health food, medicinal, 2. Materials and methods veterinary and industrial products”. Gel composition at a species level differs substantially. 2.1. Materials Available published information shows that the gel composi- tion of A. vera (Choi and Chung, 2003; Waller et al., 2004) dif- Mature leaves were harvested from various individual plants fers from that of A. ferox (Mabusela et al., 1990), and A. at several different localities throughout most of the natural dis- arborescens (Yagi et al., 1985). These species differ in their tribution area of A. ferox (with permission from the land acetylated polysaccharides. Nuclear magnetic resonance spec- owners). Locality details and voucher specimens are listed troscopy (NMR) is used as a quality control method for A. with the results in Tables 1 to 4. vera gel but the absence of acetylated compounds in A. ferox complicates the application of NMR methods in this species. 2.2. Leaf dimensions and gel firmness Thus, quality control methods that are applied to A. vera gel cannot be applied with the same success to A. ferox gel. The Leaf width and leaf thickness measurements were taken at gel polysaccharides are different within these two species, the base of the leaf. A penetrometer was used to determine Table 1 Leaf dimensions and gel firmness in eight populations of Aloe ferox (six leaves from three individual plants were sampled). The values given are averages for six leaves per plant. Locality and voucher specimens (all in JRAU) Plants Leaf weight Leaf length Leaf width Leaf thickness Gel firmness (g) (mm) (mm) (mm) (kg pressure) 1. Albertinia (S 34° 05.532′; E 21° 38.528′) O'Brien 60 1 726.0 471.7 101.7 19.5 10.5 2 532.7 437.2 106.0 16.2 10.0 3 628.6 462.7 107.8 17.2 7.1 2. Albertinia (S 34° 08.689′; E 21° 39.309′) O'Brien 61 1 523.0 401.7 132.8 10.8 9.6 2 334.4 323.3 96.8 14.3 6.4 3 305.0 336.7 88.3 13.5 8.1 3. Seweweekspoort (S 33° 27.480′; E 21° 25.485′) O'Brien 62 1 917.7 597.7 119.7 18.7 8.0 2 950.7 596.7 127.5 22.2 6.9 3 994.7 534.2 136.3 20.2 6.2 4. Uniondale (S 33° 47.003′; E 23° 29.115′) O'Brien 63 1 612.0 480.5 101.5 11.8 8.8 2 868.2 554.3 100.3 18.3 8.1 3 469.3 472.5 94.2 11.8 9.3 5. Uniondale (S 33° 34.582′; E 23° 10.390′) O'Brien 64 1 1028.2 619.5 109.8 18.7 7.4 2 800.5 493.7 106.3 18.2 12.0 3 773.7 519.0 104.2 17.5 11.1 6. Fort Beaufort (S 32° 55.119′; E 26° 28.647′) O'Brien 65 1 474.0 449.7 104.0 14.5 7.9 2 480.8 425.3 90.0 17.0 9.3 3 569.8 460.4 98.5 14.1 8.4 7. Balfour (S 32° 32.318′; E 26° 41.414′) O'Brien 66 1 224.1 406.7 83.7 08.3 5.7 2 753.9 528.0 132.4 18.4 6.3 3 333.0 384.8 89.8 11.2 9.4 8.