Different Extraction Methods For Tree Peony Seed Oil And Its Oxidation Stability

Peony seed oils from the ‘Fengdan’ cultivar were extracted by supercritical CO2 extraction,cold pressing,and organic solvent extraction,respectively.The objective was to explore the effects of different extraction methods on oil yield,physicochemical properties,fatty acid composition and antioxidant capacity in vitro.Moreover,The effects of temperature,air,light and natural antioxidants on the oxidative stability of peony seed oil were also investigated.The results are shown as follows:First,we analyzed oil yield of peony seed oil extracted using three methods.The results revealed that organicsolvent extraction produced the highest oil yield(28.61%),with supercritical CO2 extraction being in the middle(28.17%),andcold pressing producing the lowest oil yield(19.14%).Second,we also analyzed and evaluated physicochemical properties.There were no significant variations in saponification value,refractive index or relative density among three extracted oils,while considerable variations in acid value,peroxidevalue,iodine value,moisture and volatiles,and color were observed.Acid value of supercritical CO2 extraction(5.08 mg KOH/g)was higher than that of cold pressing(3.20 mgKOH/g)and organic solvent extraction(2.02 mgKOH/g).The results of peroxide values were showed that cold pressing(6.46 meq/kg)>organic solvent extraction(1.42 meq/kg)>supercritical CO2 extraction(0.50 meq/kg).The iodine values of peony seed oils extracted through supercritical CO2 extraction,cold pressing,and organic solvent extraction were 184.01 gI2/100 g,193.45 gI2/100 g,and 174.38 gI2/100 g,respectively.The content of water and volatile matter of the peony seed oil obtained by organic solvent extraction(8.92%)was significantly higher than that of supercritical CO2 extraction(0.17%)and cold pressing(0.22%)(P<0.05).In these three methods,the color of peony seed oil obtained from cold pressing is deepest.Third,these oil samples had nearly identicalfatty acid composition and content as measured by gas chromatography-mass spectrometry(GC-MS).We detected five dominant fatty acids which were mainly unsaturated fatty acid(89%~91%).The alpha linolenic acid content was the highest(43%~45%),followed by linoleic acid(around 25%)and oleic acid(18%~21%).Forth,theirantioxidant activities in vitro were significantly different with the decreasing order of organic solvent extraction >cold pressing > supercritical CO2 extraction in terms of DPPH(1,1-diphenyl-2-picrylhydrazyl)radical-scavenging rate andEC50(concentration for 50% of maximal effect).Fifth,temperature,air,and light are important factors affecting theoxidation stability of peony seed oil.High temperature,air,and light can accelerate the oxidation rate of peony seed oil and promote oxidation and rancidity.Sixth,the effects of different concentrations of natural antioxidants on the oxidation stability of peony seed oil were different from each other.In a certain range,the antioxidant capacity of natural antioxidants was enhanced with increases of antioxidant concentration.Moreover,the effects of different natural antioxidants at same concentrationon the oxidation stability of peony seed oil were different from each other.At the concentration of 0.02%,tea polyphenols antioxidant effect most significant among natural antioxidants,while propolis worst.In addition,the antioxidant activities of natural antioxidants were relatively improved at optimized concentration.Among them,the best and worst antioxidant effects were tea polyphenols and propolis,respectively.The antioxidant effects of seven natural antioxidants except propolis was better than that of BHA and BHT and the antioxidant effect of tea polyphenols was the closest to that of TBHQ.In conclusion,each method has both advantages and disadvantages for theextraction of peony seed oil.Cold pressing is advantageous with respect to lower cost,easier operation,simpler process,andhigher safety over the other two methods and therefore it is more suitable for the extraction of high quality peony seed oil.Natural antioxidants in the peony seed oil system have good antioxidant effects and other health benefits on human,which are ideal substitutes for synthetic antioxidants.