Effects Of Raw Material Pretreatments On Lignans And Comprehensive Quality Of Sesame Oil

Sesame oil has a large content of nutritive substances which are beneficial and essential to humans,.It is enjoyed by our people because of its attractive fragrance.In addition to its rich nutritional value and mellow aroma,sesame oil has significantly better oxidation stability than other types of vegetable oils.In addition to the role of tocopherol contained in sesame oil,the most important reason is that sesame oil also contains a bioactive component named sesame lignans.Sesamolin,sesamol and sesamin are rich biological active substances in sesame lignans.which play a part in scavenging free radicals,protecting the liver and reducing blood lipids in the human’s body.The proportion of sesame lignans in sesame oil has made outstanding contributions to improving and promoting the quality and nutritional value of sesame oil.Based on this,this paper studies the influence of high temperature roasting and microwave roasting on the content of lignans in sesame oil produced by pressing method,in order to find out the best roasting conditions of the two roasting methods,and analyze and compare the quality and oxidation stability with cold pressed sesame oil and leaching of sesame oil,which provides a theoretical reference for the production and development of sesame oil rich in lignans.The main research contents and conclusions are as follows:(1)Sesame oil was prepared by roasting sesame as raw material,and then squeezed oil with hydraulic oil press.The single factor experiment was carried out with roasting temperature,roasting time and initial moisture content as the inspection indexes to explore the effect of these three factors on the lignans content in sesame oil.Taking the content of sesame lignans in sesame oil as the response value,the roasting conditions were further optimized through response surface optimization design,and the optimal process conditions were achieved as follows: roasting temperature was 204 ℃,roasting time was 35 min,and initial moisture content was 15%.Under this condition,the content of sesame lignans was808.267mg/100 g,which was basically consistent with the theoretical value of809.264mg/100 g.The influence of roasting temperature,roasting time and initial moisture content on the total content of lignans in sesame oil was that roasting temperature > roasting time > initial moisture content.(2)Sesame oil was prepared from sesame by microwave roasting,and then pressed by hydraulic oil press.The single factor experiment was carried out with roasting temperature,roasting time and initial moisture content as the inspection indexes to explore the influence of these three factors on the lignans content in sesame oil.Taking the content of sesame lignans in sesame oil as the response value,the roasting conditions were further optimized through response surface optimization design,and the optimal roasting conditions were obtained: 800 w microwave power,5 min microwave time,18% initial moisture content.Under this condition,the content of sesame lignans was 1355.16mg/100 g,which was basically consistent with the theoretical value of 1360.39mg/100 g.The order of the factors affecting lignans content in roasting process was microwave power > initial moisture content >microwave time.The contents of sesame lignans were relatively different obtained by the two kinds of roasting methods,microwave roasting and high-temperature roasting,and it was speculated that the reason for the large difference may be that the heating mechanism of microwave treatment and high-temperature roasting was different,and the mechanism of microwave heating was dipole rotation and ion polarization,which belonged to radiation heat transfer;While the mechanism of roasting heating was thermal motion of microscopic particles,genus conduction heat transfer.Because of the difference in the mechanism of action,it resulted in the difference between the texture and the content of the minor components of sesame seeds after treatment,and it also caused the large difference in the lignan content of sesame seeds between the prepared oils(3)With cold pressed sesame oil,roasted pressed sesame oil,microwave roasted pressed sesame oil,sesame oil extracted by roasted sesame cake and sesame oil extracted by microwave cake as the research object,the composition of fatty acid,and the physicochemical properties,tocopherol and sterol,oxidation stability and volatile components of five sesame oil samples were determined.The results showed that the five sesame oil samples met the requirements of the national standard in terms of physical indicators such as refractive index and physicochemical indicators such as iodide value,saponification value,acid valence(AV)and peroxidation value(POV).The color of roasted pressed sesame oil was darker than that of the other four sesame oils.Compared with roasted pressed sesame oil,microwave roasted pressed sesame oil had lower acid value and peroxide value,indicating that microwave treatment conditions are more moderate.On the whole,the fatty acid composition of sesame oil prepared by the five processes had little difference.The sesame oil produced by microwave roasting and pressing had a higher content of tocopherol and phytosterol.Compared with the sesame oil produced by cold pressing,the sesame oil produced by roasting and pressing had a higher content of phytosterol.However,the content of tocopherol decreased due to the higher roasting temperature,which indicated that heat treatment had a greater impact on the bioactive components of the oil.The oxidation induction time of roasted and pressed sesame oil(20.03h)and microwave roasted and pressed sesame oil(15.09h)was much longer than that of cold pressed sesame oil(7.46h).The oxidation stability of the two sesame oils was better.However,from other oxidation indicators,after high temperature heat treatment,the roasted pressed sesame oil received a certain degree of oxidative damage in the freshly prepared sesame oil,while the microwave roasted and pressed sesame oil had less oxidative damage.Due to the different preparation processes of the five sesame oil samples,the volatile components of the sesame oil obtained were different.The volatile components of cold pressed sesame oil were mainly olefins and terpenes.The roasted pressed sesame oil mainly contained pyrazine,pyrrole and other heterocyclic substances,which made a great contribution to the flavor of sesame oil.The main volatile components in sesame oil produced by microwave roasting and pressing were aldehydes,esters and alkanes In addition to pyrazine,the sesame oil extracted by roasted sesame cake and also contained aldehydes,esters and other volatile components,Alkanes and ketones in sesame oil extracted by microwave roasted cake were the main flavor substances.(4)The changes of oil quality of cold pressed sesame oil,roasted pressed sesame oil,microwave roasted pressed sesame oil,sesame oil extracted by roasted sesame cake,sesame oil extracted by microwave sesame cake in accelerated storage test(60 ℃)were investigated.The peroxide value,p-anisidine value,conjugated diene,conjugated triene values,thiobarbituric acid values of five sesame oils increased to various degrees with increasing storage time,and the acid values fluctuated.There was no significant variety in the content of fatty acids in the five sesame oils.However,the tocopherol content of the five sesame oils gradually decreased,and the content of cold pressed sesame oil decreased the most,with a loss rate of 49.21%.High temperature accelerated the oxidation of tocopherol.Generally,microwave roasting sesame oil had better oxidation stability.