Microwave Assisted Catalytic Synthesis Of Phytosterol Esters

Phytosterols have the functions of reducing cholesterol and inhibiting the growth of cancer cells,which greatly increases the market demand for phytosterols-rich products and attracts much attention for its safety.Studies show that the quality and extraction process of phytosterols are significantly affected by the raw materials(deodorization distillate),but there is a lack of quality analysis of phytosterols raw materials,especially for the evaluation of the content of phytosterols and hazard factors.Meanwhile,phytosterols have poor oil solubility,and the application of phytosterols is mainly in the form of phytosterol esters in food and medicine industries.However,there are widespread problems in the industrial production of phytosterol esters,such as high reaction temperature,long reaction time and serious substrate oxidation.Based on this,the oil deodorization distillates from different origins were comprehensively analyzed and an efficient synthesis process of phytosterol esters at low temperature was developed in this paper.The specific contents were as follows:Firstly,the physicochemical properties,unsaponifiable matter content and hazardous factors content of oil deodorization distillate samples from 35 different origins were systematically analyzed.The results showed that the acid value was 68.1～191.3 mg KOH/g,with peroxide value of 0.043～0.149 g/100 g,water content of 0.18%～1.98%,ash content of less than 0.3 g/100 g and saponification value of 125.0～205.8 mg KOH/g.The contents of unsaponifiable matter ranged from 2.80% to 35.71%,including phytosterols(0.81%～23.24%),vitamin E(0.13%～9.44%)and squalene(0.09%～2.56%).The contents of four EU limited polycyclic aromatic hydrocarbons(PAH4)in deodorizing distillate ranged from 6.74 μg/kg to61.98 μg/kg,and the individual levels of seven phthalate esters(PAEs)ranged from 0.02 mg/kg to 5.65 mg/kg.The residual risk of PAHs and PAEs in phytosterols should be concerned.Secondly,the synthesis process of phytosterol esters was optimized.The effects of different reaction conditions on the synthesis efficiency of phytosterol esters were investigated by using the esterification rate of phytosterol esters as index,and the product identification and reaction kinetics were studied.The results showed that the conditions of traditional heating method were as follows: molar ratio of substrate 4:1,reaction temperature 200℃,reaction time4 h,the esterification rate reached 93.25%.Under the condition of substrate molar ratio 4:1 and reaction temperature 180℃,microwave irradiation can shorten the reaction time to 60 min,and the esterification rate was 93.21%.In order to further reduce the reaction temperature,microwave assisted dodecylbenzenesulfonic acid was applied to catalyze the synthesis of phytosterol esters.Under the optimal conditions of substrate molar ratio of 2.5:1,reaction temperature of 60℃,catalyst dosage of 20%(number of phytosterols moles)and reaction time of 60 min,the esterification rate reached 94.27%.The results of fourier transform infrared spectroscopy and mass spectrometry demonstrated that phytosterol esters were successfully synthesized.The kinetic study of microwave assisted catalytic synthesis of phytosterol esters showed that the kinetic model with high correlation coefficient could effectively predict the synthesis effect of phytosterol esters.Finally,the phytosterol esters with different saturation fatty acids were synthesized by microwave assisted dodecyl benzene sulfonic acid,and the oxidative stability of phytosterol esters in the process of preparation and accelerated storage was investigated.The results showed that the process conditions effectively reduce the oxidation level of the reaction system.At the end of esterification,the distribution of anisidine values of different phytosterols ranged from1.75 to 3.62.The oxidation stability of phytosterol esters decreased with the increase of storage temperature,time and fatty acid unsaturation.In addition,the increase in the number of fatty acid double bonds in phytosterol esters increased the probability of phytosterols oxidation,which made it easier to produce phytosterol oxides.In summary,35 samples of oil deodorization distillate from different origins were systematically analyzed in this paper,which provided theoretical guidance for the optimization of phytosterols production process and the improvement of product safety.In addition,microwave assisted dodecyl benzene sulfonic acid realized the efficient synthesis of phytosterol esters at low temperature,providing an effective solution for reducing the substrate oxidation level.This paper provided reference for the production and utilization of phytosterol esters and the improvement of their quality and safety.