Abstract:

The aim of this study was to investigate three main parameters (inclusion time, temperature and number) affecting ulrea inclusion of gamma linolenic acid (GLA) from evening primrose oil by single factor and orthogonal array design methods. Single factor experiments were carried out to examine the effects of the parameters on the crystal morphology of urea inclusion compounds observed using naked eyes and microscopy and GLA purity. Gas chromatography was used to determine GLA purity. A 4-factor, 3-level orthogonal array design involving 9 experiments was employed to examine the effects of the parameters on GLA yield and purity. Results showed that under the conditions of longer inclusion time and lower inclusion temperature, more urea inclusion compounds were obtained and the crystal shape was longer in length and thicker in diameter. Urea inclusion compounds obtained by either twice, three- or four-time inclusion exhibited longer length and thicker diameter in crystal shape than those obtained by once inclusion. The optimal values of inclusion time, temperature and number for improved crystal morphology of urea inclusion compounds were 36 h, －15 ℃ and 4, respectively. When they were modified to be 60 h, －15 ℃ and 3, respectively, a maximum GLA purity of up to 78.996% was obtained. All these parameters exhibited a significant effect on the formation of urea inclusion compounds. Thus, observations on changing trends in the crystal morphology and amount of urea inclusion compounds provides a feasible guidance for the optimization of urea inclusion of GLA from plant seed oil.

Key words: evening primrose oil, gamma linolenic acid (GLA), urea inclusion, urea inclusion compound