Optimization of ultrasonic-assisted extraction of oil from the seed kernels and isolation of monoterpene glycosides from the oil residue of Paeonia lactiflora Pall.

Abstract

Ultrasonic-assisted extraction of oil from Paeonia lactiflora Pall. seeds with hexane as the solvent was studied, and the chemical composition of the oil was analyzed by gas chromatography–mass spectrometry (GC–MS). Based on single-factor tests, the effects of the extraction parameters, including ultrasonic time, ultrasonic temperature and ultrasonic power, on the extraction yield of P. lactiflora seed oil were optimized by response surface methodology. The chemical constituents of the oil residue of P. lactiflora were isolated using a silica gel column: Toyopearl HW-40, Sephadex LH-20, and preparative HPLC chromatographies. The structures of the isolated compounds were elucidated based on 1H-NMR, 13C-NMR and MS data analysis. An HPLC method for the simultaneous determination of six monoterpene glycosides in the seed cake and seed shell of P. lactiflora was established. The optimum conditions were as follows: extraction time of 18min, extraction temperature of 35°C, and extraction power of 445W. Under these conditions, the extraction yield values of the oil were 28.85%. The predominant fatty acids in P. lactiflora seed oil were linolenic acid (34.12%), linoleic acid (26.47%), and oleic acid (27.87%), among others. The percentage of unsaturated fatty acids relative to total fatty acids exceeded 85%. Eight monoterpene glycosides, including 4″-hydroxyl-albiflorin (1), oxypaeoniflorin (2), albiflorin (3), paeoniflorin (4), paeonidanin (5), albiflorin R1 (6), 4-O-methyl-paeoniflorin (7) and oxypaeonidanin (8), were isolated from the oil residue of P. lactiflora. All the compounds were isolated from the seeds of P. lactiflora for the first time. The contents of 4″-hydroxyl-albiflorin, oxypaeoniflorin, albiflorin, paeoniflorin, paeonidanin and albiflorin R1 in the oil residue of P. lactiflora were 0.0113%, 0.0277%, 0.0655%, 0.589%, 0.0118% and 0.00486%, respectively. The contents of monoterpene glycosides in the oil residue were higher than those in the seed shell of P. lactiflora. These findings indicated that the seeds of P. lactiflora could be a good bioresource for the preparation of edible oil and total monoterpene glycosides. Therefore, P. lactiflora seeds have important research value as well as development and utilization prospects.