Racemization at C-2 of naringin in pummelo (Citrus grandis) with increasing maturity determined by chiral high-performance liquid chromatography

The relative content of (2S)- and (2R)-naringin in the albedo of pummelo during maturation in the entire season was determined by normal-phase HPLC using Chiralpak IB, a polysaccharide-derived chiral stationary phase, and n-hexane/ethanol doped with 0.5% TFA as mobile phase. A sigmoid curve was obtained showing variation from 95.3% of (2S)-naringin in very immature fruits to 53% in mature fruit samples (2.3 and 14.4 cm diameter, respectively). A comparison was made with previous results obtained for grapefruit and sour orange and a tentative explanation of the bitter taste of sour orange is proposed. The Chiralpak IB is much more efficient with respect to the Chiralcel OD used for the other two Citrus species and separation and resolution factors of 1.73 and 9.2, respectively, were achieved. Authentic samples of naringin and neohesperidin were also separated into their C-2 diastereomers with Chiralpak IB and isolation of the pure diastereomers of naringin was accomplished.