Different grades of genuine and counterfeit Fraxinus excelsior exudates, marketed as natural sweeteners or mild laxatives, were evaluated for their proximate composition and for saccharidic, organic acids, lipidic and phenolic profile by means of GC-MS and (1)H NMR. Genuine samples contained mannitol (39-48 g/100 g, according to the grade), fructose (9-16 g/100 g), glucose (2-3.7 g/100 g), sorbitol (0,5-0,6 g/100 g), galactose (0.02-0.74 g/100 g), oligosaccharides as mannotriose (13-22 g/100 g) and stachyose (1-11 g/100 g), and traces of myo-inositol, mannose, sucrose. On the contrary, counterfeit samples contained mostly mannitol and sorbitol, with traces of fructose, glucose and mannose. Differences in ash, total polyphenolic content and fatty acid composition allowed a quick identification of counterfeit products, confirmed by a distinct mono-, oligosaccharidic and phenolic pattern. Elenolic acid (63-1628 mg/kg), tyrosol (15-774 mg/kg), homovanillic acid (2,39-52.8 mg/Kg), dopaol (0.8-63 mg/kg), pinoresinol (4.2-18.5 mg/kg) and fraxetin (0.25-11.64 mg/kg), albeit showing a wide concentration range, were the most abundant substances detected in the phenolic fraction of Fraxinus manna, while esculetin, p-hydroxybenzoic acid, 4-hydroxyphenacetic acid, 3,4 hydroxybenzoic acid, hydroxy-pinoresinol, medioresinol and siringaresinol were present in low amounts. The polyphenolic profile may be used as a marker for authentication and should be considered in the evaluation of nutritional and health properties ascribed to Fraxinus manna.
Keywords: Fraxinus; Lignans; Manna ash composition; Natural sweeteners; Polyphenols; Quality control.
© 2013.