Optimization Of The Extraction Parameters, Composition Analysis And Determination Of The Nutritional Value Of Silkworm Pupal Oil

As one of the insect oils,silkworm pupal oil which is rich in unsaturated fatty acids, especially alpha-linolenic acid(ALA) contains many nutritive components and can bring significant economic benefits.Desilked silkworm pupae which are one of the byproduct of the silk industry were used to extract silkworm pupal oil.Optimization of the organic solvent and supercritical carbon dioxide extraction of silkworm pupal oil,analysis of fatty acid composition of the silkworm pupal oil extracted and determination of the nutritional value of the oil were studied in the paper.Single factor experiments and orthogonal array design were adopted to optimize the parameters of silkworm pupal oil extraction by hexane.The effects of independent parameters,including temperature,extraction time,solvent volume and oscillation rate on the yield of oil were studied.The statistical analysis show that the solvent volume was the most significant variable followed by extraction time,oscillation rate and the interactions between temperature and oscillation rate.The optimal extraction condition for oil yield was temperature 38℃,extraction time 2 hours,solvent volume 4 mL/g and oscillation rate 160 r/min.Under this condition,the extracting rate of pupal oil was measured about 28.17%.Response surface methodology(RSM) was applied to optimize the parameters of SC-CO₂ extraction.The effects of independent variables,including pressure,temperature, CO₂ flow rate,and extraction time,on the yield of oil were investigated.The statistical analysis showed that the pressure,extraction time,and the quadratics of pressure, extraction time,and CO₂ flow rate,as well as the interactions between pressure and temperature,and temperature and flow rate,showed significant effects on oil yield.The optimal extraction condition for oil yield within the experimental range of the variables researched was at 324.5 bar,39.6℃,131.2 min,and 19.3 L/h.At this condition,the yield of oil was predicted to be 29.73%.Fatty acid composition of pupal oil obtained was analyzed by GC and GC/MS.The results indicated that the silkworm pupae oil was rich in unsaturated fatty acids which accounted for more than 68%of the total fatty acids.The main unsaturated fatty acids are Oleic acid(approximately 33%),α-linolenic acid(27.99%) and linoleic acid(7.12%).The main saturated acid in the silkworm pupal oil was palmitic acid(21.77%),followed by stearic acid(7.02%).Male rats were divided into four groups,the first group represented control group,fed with standard diet,the second group represented SPO group fed with control diet supplemented with silkworm pupal oil(SPO 1.0%ml/ wt),the third group represented HFD group fed with the high fat diet,and the fourth group represented HFD+SPO group fed with high fat diet supplement with SPO(1.0%ml/ wt).These rats were used to investigate the effect of the silkworm pupal oil on growth parameters and lipid metabolism of rats fed with high fat diet by animal experiment in vivo.The results demonstrated that SPO rich in unsaturated fatty acids especially alpha-linolenic acid(ALA) supplementation reduced the body weight gain and relative liver weight,significantly lowered serum total cholesterol(TC),triglycerides(TG),low-density lipoprotein -cholesterol(LDL-C) levels and increased the high-density lipoprotein -cholesterol(HDL-C) levels in HFD fed rats, indicating its hypolipidemic activity.Oral administration of SPO significantly reduced liver TC,TG levels and raised the liver HDL-C levels in HFD fed rats,indicating it can regulated the lipid metabolism in liver.Hepatic protection by SPO is further substantiated by the normal liver histological findings in HFD fed rats.The results of of SPO on LPL mRNA level in liver of rats showed that SPO could relieve the negative effect on the LPL mRNA level in liver caused by HFD,which further confirmed that silkworm pupal oil could regulate the lipid metabolism in rats.