Abstract:

Orthogonal array design was used to optimize the extraction conditions for phenols from longan (Dimocarpus
longan Lour.) seeds by evaluating the effect of four crucial variables including alcohol concentration, solid-to-solvent ratio,
extraction temperature and extraction time on the yield of phenols. The optimum conditions were determined as follows:
ethanol concentration 40%, solid-to-solvent ratio 1:20 (g/mL), extraction temperature 70 ℃, and extraction time 90 min.
Under these conditions, the maximum yield of phenols of 36.15 mg/g was obtained. D3520 resin was selected to purify
longan seed phenols by comparing static absorption and dynamic desorption capacity of four macroporous resins, and
40% ethanol was chosen as the best elution solvent. The structural properties of longan seed phenols were preliminarily
analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and the results showed that longan
seed phenols were mainly composed of hydrolyzable tannins with small molecular weights, such as ellagic acid and its
derivatives. Ellagic acid and (S)-flavogallonic acid were confirmed as two abundant compounds from longan seeds by NMR,
UV spectroscopy and IR spectroscopy. (S)-Flavogallonic was identified as a derivative of ellagic acid.

Key words: longan seeds, phenols, separation and purification, structural analysisanalysis;Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS)