| Sesame lignans such as sesamin,sesamolin,and sesamol,are a group of compounds formed by oxidative coupling ofρ-hydroxyphenylpropane.Sesamin and sesamolin are the two major lignans exist in raw sesame seed,which possessing lipid-lowering and liver-protecting effects.Sesamol may be released from sesamolin in the oil processing process,which has an excellent anti-oxidation capacity.The structures and the contents of sesamin,sesamolin,and sesamol play an important role in the aspects of quality and nutritional value of the sesame oil.In this work,analytical methods for simultaneous determination of sesamin,sesamolin,and sesamol were established,their contents in various sesame cultivars and sesame oils produced from different techniques were investigated,their changes in sesame oil processing process were studied,and the effects of sesamin,sesamolin,and sesamol on oxidative stress and lipid metabolism were compared using cell model.The main contents are as follows:Firstly,two kinds of analytical methods for simultaneous determination of sesamin,sesamolin,and sesamol were established based on normal/reversed-phase liquid chromatography.For the reversed-phase liquid chromatography method,three analytes were linear over the concentration ranges with R~2 ranging from 0.9998 to 1.0000(2.48-396.4μg/mL for sesamin,2.84-226.8μg/mL for sesamolin,and 2.55-204.0μg/mL for sesamol).The LOQs for the three analytes were 0.37,0.10,and 0.03μg/mL,respectively,and the recoveries at three spiked levels were 87.4%-103.8%,with the limits of RSDs lower than 8%.For the normal-phase liquid chromatography method,three analytes were linear over the concentration ranges with R~2 ranging from 0.9999 to 1.0000(1.00-400.0μg/mL for sesamin,1.50-300.0μg/mL for sesamolin,and 1.25-250.0μg/mL for sesamol).The LOQs for the three analytes were 0.10,0.03,and 0.03μg/mL,respectively,and the recoveries at three spiked levels were 94.5%-103.4%,with the limits of RSDs lower than 5%.The normal-phase liquid chromatography method exhibited higher recovery,better precision,lower LOQ,wider linearity range,and lower solvent used,shorter preparation and analysis times,which was a suitable alternative for rapid determination of these three lignans in sesame oils.Secondly,the concentrations of sesamin,sesamolin,and sesamol in one-hundred sesame cultivars and fifty-six kinds of hot pressed,cold pressed,small mill,and refined sesame oils were determined based on the established methods.The results showed that the contents of sesamin in four cultivars such as jinzhi-1(4.75 mg/g)and wanzhi-6(3.83 mg/g)were high,the contents of sesamolin in five cultivars such as zhengzhi-12(2.46 mg/g)and liaozhi-6(2.32mg/g)were high.Meanwhile,sesamin and sesamolin amounts in muzhenbai(9.41 and 3.35mg/g)and zhuzhulian-1(6.63 and 2.51mg/g)cultivars were both at high levels,however,their contents in jinzhi-3 cultivar were both at low levels of 1.61 and 1.05 mg/g,respectively.In addition,jizhi 9014 cultivar showed the lowest sesamin amount(1.11 mg/g)and ezhi-6 cultivar showed the lowest sesamolin amount(0.20 mg/g).Hot pressed and small mill sesame oils exhibited significantly higher sesamol contents(0.15 and 0.16 mg/g)than that in cold pressed sesame oil(0.02 mg/g),and sesamolin contents in those two kinds of sesame oils(2.81 and 2.75mg/g)were lower than that in the latter(3.39 mg/g),but higher than that in refined sesame oil(1.47 mg/g),thus indicating that roasting and refining processes showed significant influence on the changes of sesamolin and sesamol in the sesame oils.Thirdly,the change of sesamolin in the high temperature roasting process was studied.The results showed that the conversion rate of sesamolin to sesamol gradually increased with the increases of the roasting temperature and time,and the roasting temperature showed much higher effects on the conversion process.When the roasting temperature was low(170℃),the change of sesamolin was not obvious,even if the roasting time increased to 40 min,the content of sesamolin only decreased from 2.47 mg/g to 2.42 mg/g,with a low conversion rate of 2.02%.When the roasting conditions were changed to190℃and 30 min as well as 210℃and 20 min,the conversion rate of sesamolin to sesamol increased significantly,and the contents of sesamolin decreased to 2.34 and 2.32 mg/g,respectively,while the contents of sesamol reached to 0.10 and 0.09 mg/g,respectively.When the roasting temperature was 230℃and the roasting time was 40 min,the content of sesamolin decreased to 1.95 mg/g and the content of sesamol reached to 0.29 mg/g.At this time,the conversion rate of sesamolin to sesamol was 21.05%,which was the highest.Based on the above results,and taking into account the influences of roasting process on the color,flavor,and PAHs of the sesame oil,the suitable conditions of moderate roasting for sesamol-riched sesame oils were as follows:the roasting temperature was210℃and the roasting time was 30 min.At this time,sesamolin content in sesame oil decreased from 2.47 mg/g to 2.21 mg/g,with a conversion rate of 10.52%,and the content of sesamol reached to 0.16 mg/g and the oxidation induction time of the sesame oil increased significantly from 8.41 h to 15.08 h.Furthermore,the changes of three lignans in the refining process were studied,and the effects of adsorbent types on the contents of their amounts were investigated.The results showed that degumming and deacidification had no significant effects on the contents of sesamin,sesamin,and sesamol,however,deodorization significantly reduced the amounts of three lignans by 36.47%,41.64%,and 47.59%,respectively.Additionally,the contents of sesamin and sesamin decreased by 12.61%and 50.80%,respectively,and the content of sesamin increased by 29.41%in the bleaching process using activated clay as the adsorbent.In contrast,although Norit and WY activated carbons decolorization reduced the content of sesamol by 23.89%and 15.33%,respectively,they showed good retention effects on sesamin and sesamolin,which were the best adsorbents for the production of sesamin and sesamolin-riched sesame oils.Based on the above results,and taking into account the influences of adsorption refining process on the flavor,oxidation stability,and removal rate of PAHs,the suitable conditions of adsorption refining for sesamin and sesamolin-riched sesame oils were as follows:sesame oil was adsorbed by 0.5%of WY activated carbon at 100℃for 30 min.Fourthly,high fat and high cholesterol cell evaluation model was established using oleic acid/cholesterol(300/25μM)co-induction method,and the effects of sesamin,sesamolin,and sesamol on oxidative stress of the steatotic cells were investigated.The results showed that three lignans reduced the cellular ROS level and MDA content,decreased the levels of intracellular oxygen free radical and lipid peroxidation and alleviated the oxidative damage of the HepG2 cells.At high intervention concentration,sesamin lowered the ROS level and MDA content by 62%and 51%,respectively,when compared with the model group,which were much better than those of sesamolin and sesamol.Further,three lignans increased the activities of SOD,CAT,and GR as well as the content of GSH,thus improving the redox status of the hepatic steatosis cell.Sesamin exhibited the best regulation effect on SOD at three intervention concentrations,improving the activities of SOD by 3.07,2.43,and 1.50 times higher than that of the model group,respectively,which were much better than those of sesamolin and sesamol.At high intervention concentration,sesamol had the best regulation effects on CAT,GR,and GSH,thus increasing their levels by 1.97,2.31,and 2.30 times of the model group,respectively.Finally,the effects of sesamin,sesamolin,and sesamol on lipid metabolism of the steatotic cells were studied and the underlying molecular mechanisms were elucidated.The results showed that three lignans exhibited the most obvious inhibitory effect on the lipid accumulation in the HepG2 cells at the high intervention concentration,thus resulting in the number of the lipid droplets in the cells were significantly decreased.Sesamol reduced the contents of triglyceride and cholesterol by 61%and 63%,respectively,when compared with the model group,which were much better than those of sesamin and sesamolin.Three lignans down-regulated the expressions of fat synthesis genes and cholesterol synthesis and intake genes,thus suppressing the intracellular lipid generation and uptake.Additionally,they up-regulated the expressions of fat oxidation and cholesterol efflux and transformation genes,thus promoting the intracellular lipid decomposition and transport.PPAR pathway played an important role in the regulation process.On the one hand,it can promote fat oxidation by activating the PPARα-CPT-1A pathway;on the other hand,it can induce cholesterol efflux and conversion by activating the PPARγ-LXRα-ABCG1 and LXRα-CYP7A1 pathways,respectively,which were the main molecular mechanisms by which sesamin,sesamolin,and sesamol lower the levels of cellular triglyceride and cholesterol,and regulate the abnormal lipid accumulation in the steatotic HepG2 cells. |
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