Flavonoid and polyphenol content of Aloe vera (Aloe barbadensis Mill.) flowers and their in vitro antioxidative capacity

Aloe vera has become very popular in cosmetics and nutraceutical formulations due to the ascribed beneficial properties of the inner gel from the fleshy leaves (Aloe vera gel). The big yellow flowers of A. barbadensis are not of commercial interest yet although the Aloe flowers were shown to contain various biologically active substances like e.g. phenolcarboxylic acids and flavonoids [1,2,3] and a few products, e.g. „Aloe flower herbal tea“, have appeared on the market. The aim of this study was to investigate the correlation of the polyphenol content and the antioxidative capacity. Therefore the polyphenols and their flavonoid portions of three batches of the years 2003, 2004, and 2005 were determined and the in vitro antioxidative capacity was measured. The polyphenol content was analysed with the Folin-Ciocalteu reagent (λ=760 nm, water extracts) and the flavonoid content with oxalic/boric acid (λ=410 nm, 60% ethanolic extracts). The antioxidative capacity was determined by the TEAC method [4] and the ORAC method [5].

The polyphenol content of the dried Aloe flowers ranged between 0.73% –1.01% (±0.05%) and the flavonoid content between 0.24% –0.34% (±0.01%) correlating from batch to batch. The hydrophilic antioxidative capacity amounted to 85.7–94.9 (±0.50)µmol Trolox equivalent (TE)/g dried Aloe vera flowers (TEAC) and 79.8–134.2 (±5.6)µmol TE/g dried Aloe vera flowers (ORAC). The individual data show a direct correlation between the antioxidative capacity and the polyphenol content on the one side and the flavonoid content on the other side.

References: [1] Keyhanian, S., Stahl-Biskup, E. (2007) Planta Med.: in press. [2] Hou, D.Y. et al. (2004) J Zhejiang University 31: 438–41. [3] Sigler, A., Rauwald, H.W. (1994) Z. Naturforsch. 49 c: 286–92. [4] Re, R. et al. (1999) Free Radic. Biol. Med. 26: 1231–37. [5] Prior, R. L. et al. (2003) J. Agric. Food Chem. 51: 3273–79.