| Pomegranate seed oil is rich in punicic acid and a variety of bioactive substances.It has a wide spread of applications in food,cosmetic,and medical industry owing to its beneficial effects of antioxidant,anti-cancer,and anti-inflammatory.At present,the research on pomegranate seed oil mainly focuses on its extraction and characterization of its physicochemical properties,while there are few reports on the effects of different extraction methods on the oil yield and physicochemical properties of pomegranate seed oil as well as the lipid composition analysis of pomegranate seed oil and its modification.In this research,the effects of different extraction methods on the oil yield of pomegranate seeds and the physicochemical properties of pomegranate seed oil were studied and the lipid composition of pomegranate seed oil was also analyzed.Finally,the pomegranate seed oil was employed to prepare punicic acid-rich diacylglycerols.The main experimental results are as follows:(1)We compared the effects of the different extraction method on the oil yield of pomegranate seeds and the physicochemical properties of pomegranate seed oil,and found that the oil yield of soxhlet extraction,vibration extraction,microwave extraction,ultrasonic extraction and subcritical extraction ranged from 11.24%to 15.46%.The oil yield of soxhlet extraction is highest(15.46%).Comparatively,n-hexane was more suitable for the extraction of pomegranate seed oil than petroleum ether.The extracted pomegranate seed oil by the above five methods had good physicochemical properties.The acid value ranged from 0.9 to 1.44 mg KOH/g and the peroxide value was undetectable.Additionally,the oxidation stability(0.35-0.56 h)of pomegranate seed oil was significantly lower than that of commercially available soybean oil(2.33 h).Through the observation of the scanning electron microscope images before and after the extraction of pomegranate seeds,it can be seen that different extraction methods achieve different extraction effects by causing different degree of damage to the raw materials during extraction.(2)Through analysis of the glyceride composition of pomegranate seed oil,it was found that pomegranate seed oil was mainly composed of 12 kinds of triacylglycerols with the content of 96.3%?96.64%,followed by diacylglycerols with the content of 2.75%?2.89%.Through analysis of the fatty acid composition of pomegranate seed oil,it was found that the content of unsaturated fatty acid ranged from 92.05%to 94.46%and the content of punicic acid ranged from 75.2%to 77.54%.Besides,it was found that the content of calendic acid(punicic acid,?-eleostearic acid,catalpa acid and ?-eleostearic acid)ranged from 81.05%to 83.45%,and the extraction conditions affect the mutual transformation between punicic acid and its isomers.Further analysis on the molecular types of triacylglycerols revealed that pomegranate seed oil was mainly composed of 12 kinds of triacylglycerol molecule with PiPiPi(45.12%?53.65%)being the most abundant.Subsequently,the lipid concomitants in pomegranate seed oil were analyzed,it was found that the content of ?-sterol ranged from 2.98 to 3.69 mg/g and the content of squalene ranged from 1.22 to 1.62 mg/g.The total content of tocopherol ranged from 336.19 to 378.22 mg/100g,including ?-tocopherol(15.35?21.67 mg/100g),?-tocopherol(310.75?345.21 mg/100g)and ?-tocopherol(8.23?12.08 mg/100g).Besides,the lipid concomitants in pomegranated seed oil extracted by different extraction methods were significantly different.The content of squalene in pomegranate seed oil extracted by vibration extraction method was the highest of 1.62 mg/g and the content of ?-sterol in pomegranate seed oil extracted by microwave extraction was the highest of 3.69 mg/g.Additionally,the content of total tocopherol,?-tocopherol,?-tocopherol in pomegranate seed oil extracted by soxhlet extraction were the highest of 378.22 mg/100g,21.67 mg/100 g and 345.21 mg/100 g,respectively.Moreover,the content of ?-tocopherol in pomegranate seed oil extracted by subcritical extraction method was the highest of 12.08 mg/100g.Furthermore,the content of ?-tocopherol was the highest in the extracted pomegranate seed oil,followed by ?-tocopherol and ?-tocopherol.Finally,it was found that the microwave extraction could achieve high oil yield in short time and the acid value of pomegranate seed oil was low.Additionally,the content of polyunsaturated fatty acids,punicic acid,?-sterol and squalene were higher than other methods.Therefore,we can conclude that the microwave extraction was the most suitable method for the extraction of pomegranate seed oil.(3)To avoid the negative effects of high reaction temperature and long reaction time on the quality of pomegranate seed oil,we used enzymatic alcoholysis to prepare punicic acid-rich diacylglycerols and examined the effects of the different commercial enzymes and the reaction factors on the enzymatic alcoholysis reaction,which found that Lipozyme 435 showed the best catalytic effect.Under the optimized reaction conditions(the molar ratio of pomegranate seed oil and ethanol of 1:50,enzyme loading of 6%reaction temperature of 30?,reaction time of 1 h),the content of diacylglycerols in the product was 32.86%.The scale-up reaction was performed under the optimized conditions and the content of diacylglycerols was 33.14%in the product mixture.The product mixture was further separated and purified by short-path molecular distillation and the content of diacylglycerols reached to 51.83%with the punicic acid content of 76.55%.The acid value and peroxide value of the products were 0 and 1.45 mmol/kg,respectively,which indicated that the established enzymatic alcoholysis method could produce punic acid-rich diacylglycerols with good quality. |
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