| Hemp seed oil has high content of polyunsaturated fatty acids,in which the proportion of n-6 and n-3 fatty acids is nearly 3:1,and is beneficial to human health.Tetrahydrocannabinol(THC)is a kind of psychoactive compound in hemp seeds that is easily dissolved into hemp seed oil during extraction,and reduces the quality of oil.In this study,firstly,pretreatment method for detecting THC in hemp seed oil was improved.Secondly,microwave method was applied to pretreat hemp seeds and the effects of microwave pretreatment on cannabinoids contents and qualities of hemp seed oil were evaluated.Finally,the refining process of hemp seed oil was optimized.This study intended to provide the foundation for the preparation of domestic hemp seed oil with low THC content.The main contents and results were as follows:Firstly,the pretreatment method of THC in hemp seed oil before determination was improved.The results showed that the optimal condition of extraction solvent was acetonitrile,shaking time was 60 s,freezing temperature was-20?,freezing time was 120 min and amount of Alumina-N was 25 mg.Under the above conditions,the matrix co-extract content was 1.94 mg/m L.The standard curves of THC and CBN were y = 0.0225 x + 0.0089 and y = 0.0141 x + 0.0128,with the linear ranges of 2.50~100.00 ?g/mL and 2.50~20.00 ?g/mL,respectively.The LODs were 0.72 ?g/mL and 0.81 ?g/mL,respectively.The recoveries of THC were 92.3~94.9% and the RSDs were 1.8~4.7%.The recoveries of CBN were 91.2~95.7% and the RSDs were 2.2~3.7%.Secondly,the changes of THC and CBN contents in hemp seed oil after different thermal pretreatments were determinated,and the transformation rule was verified.The THC content in cold press hemp seed oil was 122.63 mg/kg.THC contents significantly decreased and CBN contents increased after pretreatments.Samples with microwave pretreatment showed lowest content of THC that decreased to 57.33 mg/kg and the CBN content increased to 27.58 mg/kg in hemp seed oil.Moreover,the qualities of hemp seed oil after microwave pretreatments were evaluated.The results showed that the acid value and the peroxide value of hemp seed oil slightly increased,the color was darker and the oxidation stability was better after microwave pretreatment.Under the condition of microwave time(15 min)and power(1000 W),the residual oil ratio of hemp seed cake decreased to 9.98%,and the acid value and peroxide value increased to 3.72 mg KOH/g and 3.85 mg/g,respectively.The OSI value increased to 3.02 h,and the tocopherol content was 716.88 mg/kg,while the fatty acid composition showed no significant change.In consideration of THC and CBN contents,color and other quality indexes of hemp seed oil,the optimal pretreatment conditions were that the microwave time was 15 min and the microwave power was 1000 W.Finally,hemp seed crude oil was refined,and single factor experiments were designed to optimize the process of degumming and clay adsorption.The results showed the optimal degumming conditions were that the concentration of citric acid was 50%,acid reaction temperature was 70? and acid reaction time was 20 min.The phosphorus content of hemp seed oil decreased to 17.4 mg/kg.The bleaching rate was 83.5% under the optimal bleaching conditions that clay content was 4%,bleaching temperature was 110?,bleaching time was 30 min.After the refining process,phospholipids,pigments and other impurities in hemp seed crude oil were removed,the THC content decreased and the high quality of hemp oil was maintained.Cannabinoids contents in hemp seed oil were effectively reduced during degumming and bleaching process and the removal rates of THC and CBN were 68.9% and 67.7%,respectively.The THC content of refined hemp seed oil decreased to 17.83 mg/kg,which is in accordance with domestic enterprise standard and Swiss and German standards.Under the optimum refining conditions,the acid value and the peroxide value of hemp seed oil were 2.97 mg KOH/g and 2.83 mmol/kg,respectively.The color was 2.6R and no significant change of fatty acid composition was found. |
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