Extraction And Equilibrium Of α-LNA In Supercritical Carbon Dioxide

α-linolenic acid is known as"the 21st century green nutritional and health care food", as it has numerous physiological functions of antiatheroscloresis, lowering blood pressure, promoting the development of nervous system and so on. So health products and medicine usingα-linolenic acid as raw materials or additives are popular in order to improve the intake ofα-linolenic acid in many countries.As is well known, the resources of silkworm chrysalis are abundant in our country. The oil, accounting for more than 30 percents of the quality of dry silkworm chrysalis, contains 30 percents ofα-linolenic acid. So investigation on the process of extractingα-linolenic acid is significant for the full utilization of silkworm chrysalis and development of alpha linolenic acid.Firstly, the process of supercritical CO₂ (SC-CO₂) extraction, Soxhlet and microwave extraction of oil from silkworm chrysalis have been investigated, respectively. And the three extraction methods were compared through extraction conditions, quality of products on the optimal conditions obtained experimentally. Then the extraction mechanisms were analyzed through the changes of structure between raw material and extraction residues. The results indicated that SC-CO₂ extraction was dominant in lower extraction temperature, higher yield, the light color of product and without solvent recovery and pollution, but the requirement of equipment was higher than others as its high-pressure conditions. The equipment of soxhlet extraction was simple and yield was high, but the extraction consumed a long time and a large quantity of solvent. Microwave extraction just cost 50s, and extraction conditions were mild, but the yield was low.Then, extraction of fatty acids and fatty acid ethyl ester with SC-CO₂ distillation and extraction of fatty acids with SC-CO₂ extraction combined with freeze crystallization process were investigated, respectively. The experimental results showed that SC-CO₂ distillation extraction can increase the content of alpha-linolenic acid in fatty acids from 28.44% to 39.11%, and the content in fatty acid ethyl ester from 28.37% to 45.78%. It was found that the content ofα-linolenic acid is up to 64.63% when SC-CO₂ distillation and freeze crystallization were united. The combination improved the purity ofα-linolenic acid more effectively.Finally, the phase equilibrium of fatty acid ethyl ester-CO₂ system was studied. The pressure at the point of being homogeneous phase and the solubility in two phases at different conditions were measured. The curves of partition coefficient showed that there was little difference of partition coefficient between unsaturated fatty acids when the length of carbon chain and the number of double bonds approached. Thus, it was difficult to separate these unsaturated fatty acids by supercritical fluid extraction.The solubility under the experimental conditions was associated with Chrastil equation to obtain equation. The relative error of solubility between calculated by the equation and experimental measured was 8.9%. The improved Chrastil equation in which k was expressed as a function of the temperature was applied to correlate the solubility data of fatty acid ethyl ester in supercritical CO₂. The relative error calculated by this equation was 3.69%.