Geographic and intraspecific variability of mesquitol amounts in Prosopis juliflora trees from Kenya

Abstract

Several studies have shown that the heartwood of Prosopis juliflora contains high amounts of a naturally rare flavan-3-ol compound identified as 2-(3,4-dihydroxyphenyl)chromane-3,7,8-triol otherwise known as (−)-mesquitol (1). It is known to possess strong antioxidant properties, which may be of valuable interest for further valorization. However, no data exists so far showing the variations of its abundance depending on the different geographic habitats of the tree, the age and the different parts of the tree stem. The variability of flavan-3-ols depending on the geographical area and intra-specific variability within P. juliflora trees from Kenya was addressed in this substantive study. The study was done using wood extracts from three different counties in Kenya (Baringo, Garissa and Turkana Counties). Wood samples were separated into two categories of ages; small trees, aged less than 4 years and the big trees, aged more than 8 years. Each sample was divided into five different parts, which included the bark, sapwood, knot wood, heartwood and the pith. Serial extractions were done by the Dionex accelerated solvent extractor using four solvents in increasing polarity (dichloromethane, acetone, toluene: ethanol (2:1 v/v) and finally water). Gas chromatographic analysis coupled to mass spectrometry was employed to identify the different compounds present in the extracts. LC–MS/MS method was thereafter developed and used to confirm the identity and quantify the amounts of mesquitol present. Two other flavan-3-ols identified and quantified included catechin (2) and 4′-O-methylgallocatechin (3). A systematic study on the mass spectra and the observed fragmentations of the flavonoids showed that mesquitol compound is the most abundant compound in P. juliflora with high amounts being found in the heartwood and pith of the acetonic extract (47–72%). Mesquitol abundance was also found to vary depending on the age of the tree and on the geographical areas.