Subcritical Extraction And Oxidative Stability Of Flaxseed Oil

Flaxseed oil,one of the healthy vegetable oils due to its nutritional and healthy attributes,which is rich inα-linolenic and multiple bioactive components.However,the lipid oxidation of flaxseed oil is a vital issue during processing and storage because of the high content of unsaturated fatty acids,especially theα-linolenic with three unsaturated double bonds.In comparing with the conventional technology,the oxidation degradation of vegetable oils could be alleviated during the method of subcritical extraction under the oxygen-free environment.The protein of the raw material can also be protected in the mild extraction conditions.Moreover,subcritical extraction is widely used in the extraction of natural products.Therefore,subcritical extraction was applied to extraction of flaxseed oil in this study,the extraction conditions of flaxseed oil were optimized and the quality changes of flaxseed oil during the storage were evaluated.The main research contents and conclusions are as follows:（1）Flaxseed oil was prepared by the methods of subcritical butane extraction,supercritical CO₂ extraction,cold pressing,hot pressing and Soxhlet extraction.The physicochemical properties,fatty acid composition,thermal properties,phytochemical,oxidative stability and volatile components of flaxseed oil were investigated.The results showed that the flaxseed oil obtained by the five methods conformed to the national standard of China,and the flaxseed oil extracted by subcritical butane has lower initial oxidation degree,higher content of tocopherols（74.60 mg/100g）and carotenoids（46.56 mg/kg）and longer oxidation induction time（9.26 h）.The analysis of volatile components showed that the content of sulfides with earthy smell in flaxseed oil was low.（2）The parameters of subcritical extraction were optimized.Firstly,the extraction solvent was selected according to the yield and physicochemical properties.Then,the effects of extraction temperature,extraction time,liquid-solid ratio and extraction times on the yield of flaxseed oil were investigated.Moreover,response surface method was applied to further optimize the extraction process.Finally,the kinetics of subcritical extraction was estimated.The results showed that different solvents had a slight effect on the fatty acid composition of flaxseed oil,but the quality of oil extracted by butane was better.In addition,Subcritical butane extraction has lower operating pressure and better safety.The results of response surface optimization showed that the extraction temperature,extraction time and liquid-solid ratio had significant effects on yield of flaxseed oil.The optimum extraction conditions were as follows:extraction temperature 54℃,extraction time 57 min,liquid-solid ratio 20:1 m L/g,Under the above conditions,the actual yield of flaxseed oil was 28.75%.The kinetic results show that the model proposed by Patricelli et al.can well describe the extraction process of flaxseed oil.（3）The effects on the quality of flaxseed oil prepared by subcritical extraction were evaluated under the condition of accelerated storage（60℃）and natural storage（25℃）.The results showed that the oxidation degree of flaxseed oil increased in different degrees during the two types of storage with tocopherol decreased.The fatty acid composition results showed that the fatty acid composition of flaxseed oil changed slightly during the oxidation process.The main volatile compounds produced by accelerated storage were aldehydes and ketones,while natural oxidation mainly produces aldehydes,unsaturated olefins.Compared with natural oxidation,the effect of accelerated oxidation on volatile components is multiple,which not only accelerates the oxidation process,but also promotes the oxidation of oxygen and other complex changes such as decomposition and transformation of chemical products.This project focused on subcritical extraction of flaxseed oil.The results showed that the subcritical butane extraction process had the characteristics of low temperature,low pressure and high efficiency.subcritical butane extraction could help to improve the quality of flaxseed oil to a certain extent,and provided new ideas for enriching the extraction process of flaxseed oil.