Isolation of punicic acid from pomegranate seed oil by modified freeze crystallization and response surface methodology

A modified freeze crystallization method based on the different melting points of fatty acids was employed to isolate punicic acid (PA), a C18 polyunsaturated fatty acid (PUFA), from pomegranate seed oil (PSO). The purification process was optimized by response surface methodology. The complex effects of factors as well as their interactions on the purity, content, and yield of PA were simulated by the second-order polynomial equations. It indicates that repeated freezing and thawing help to separate PA from the impurities with close melting points. Under the optimum conditions (solvent-to-material ratio of 12 ml/g, three freeze–thaw cycles, retaining the last 30% melting fraction), the content and purity of PA reached 950.00 ± 1.38 mg/g and 95.39 ± 0.66%, which were equivalent to 2.54 and 1.21 folds of original sample, respectively. The chemical structure of PA was confirmed by UV, IR, NMR, and GC–MS. PA exhibited a much stronger capacity in inhibiting various bacteria than PSO. Novelty impact statement Freeze crystallization combined with urea complex is a commonly used method to isolate PUFA, which has multiple beneficial effects on human health. However, the procedure is time-consuming, low yield, and accompanied with potential toxic degradation products from urea. The study provides an efficient, safe, and convenient approach to separate fatty acids with different melting points and holds immerse prospective to be utilized in PUFA manufacture.