| Dietary oil intake and composition has been strongly associated with a progression of hypercholesterolaemia.An appropriate selection of edible oils could play a positive role both in preventing and delaying disease progression.Fragrant rapeseed oil is a characteristic rapeseed oil with long history for consumption in China.Not only it has higher nutritional value than ordinary rapeseed oil,but also a rich flavour and pure taste,which is well-loved among consumers.Currently,studies domestically and internationally focused on flavour formation and aroma profile construction,whereas roasting temperature was the key process control point during actual production.However,there remains a lack of systematic and comprehensive research on whether variations in nutrient retention and risk factor production caused by different roasting temperatures affect their potential biological functions.Therefore,the present study aimed to investigate the component variation between refined rapeseed oil(RO)and fragrant rapeseed oil(FO)at three roasting temperatures(120℃,150℃ and 180℃)and their ameliorative effects on hypercholesterolaemic model rats,as well as exploring the possible action mechanisms and explanation for the differences,with a view to providing a valuable theoretical basis for the moderate processing and nutritional health benefits of FO.Specific research contents and findings are as follows.Firstly,the physicochemical parameters,main hazards and active ingredients of rapeseed oils were measured.Results showed that the acid value(0.08 mg KOH/g to 2.55 mg KOH/g),peroxide value(1.68 mmol/kg to 5.90 mmol/kg)and benzo(a)pyrene(ND to 1.91 μg/kg)of the four rapeseed oils were in compliance with China’s secondary rapeseed oil standards.No 3-MCPE,2-MCPE and glycidyl esters were detected in FO.Roasting temperatures(150°C and180°C)substantially increased the total phenolic and flavonoid contents of FO(1738.10 mg GAE/kg and 1050.16 mg RE/kg,1750.92 mg GAE/kg and 1125.40 mg GAE/kg,respectively),about 1% reduction in α-linolenic acid and trace amounts of stigmasterol output occurring at180°C.However,roasting temperature had no effect on the major fatty acid composition,phytosterol monomers,total tocopherols,and their monomer content.Also,refining nearly removed the total phenols and flavonoids of RO(only 19.79 mg GAE/kg and 8.81 mg RE/kg),while α-linolenic acid,brassicasterol and α-tocopherol were also markedly reduced.Then,eight main phenolic compounds were identified by Ultra performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spetrometry(UPLCQTOF-MS),including 4-ethenyl-2,6-dimethoxyphenol,sinapine,sinapinic acid,trans-ferulic acid,acetosyringone,scoparone,methyl vanillate and kaempferol.Of these,4-ethenyl-2,6-dimethoxyphenol(654.72 mg/kg to 694.55 mg/kg),sinapine(19.85 mg/kg to 35.90 mg/kg)and sinapinic acid(8.18 mg/kg to 8.31 mg/kg)were plentiful at FO-120 and FO-150,but 4-ethenyl-2,6-dimethoxyphenol and sinapinic acid declined notably at FO-180,with losses of 24.32% and51.22%,respectively.Next,the effect of fragrant and refined rapeseed oils on cholesterol metabolism were investigated in hypercholesterolaemic model rats.Seventy SD male rats were randomly divided into seven experimental groups: normal group(LCD,fed maintenance diet),hypercholesterolaemic model group(HCD,fed high fat high cholesterol diet),positive control group(HCD supplemented with 3% cholestyramine),and fragrant and refined rapeseed oil group(HCD replaced lard with 15% FO or RO).Findings showed that FO suppressed exogenous cholesterol absorption and increased faecal bile acid excretion,particularly FO-120 and FO-150,effectively reduced plasma total cholesterol levels by 18% and total hepatic cholesterol accumulation by modulating hepatic related metabolic enzymes(Cyp7a1 and Hmgcr)expression to inhibit hepatic cholesterol synthesis and promote cholesterol conversion to bile acids.Despite increasing cholesterol excretion,RO showed no positive effect on hepatic cholesterol metabolism.In addition,compared with RO,FO could significantly upregulate unsaturated fatty acid synthesis genes(Fads1 and Fads2),increase hepatic α-linolenic acid(C18:3)accumulation and eicosapentaenoic acid(EPA)and docosahexaenoic acid(DHA)production,as well as effectively reduce plasma and hepatic lipid peroxidation,particularly FO-120 and FO-150 markedly activated Nrf2 antioxidant pathway,upregulated downstream factors(Ho-1,Nqo-1)expression and enhanced hepatic total antioxidant capacity.Finally,a correlation analysis revealed that FO-120 and FO-150,rich in polyunsaturated fatty acids(C18:2 and C18:3),total phytosterols and polyphenolic compounds(4-ethenyl-2,6-dimethoxyphenol,sinapinic acid and sinapine),contributed comparatively more to the improvement in hypercholesterolemic rats,probably accounting for their greater cholesterollowering advantage.In conclusion,roasting temperature and refining altered the compositional properties of rapeseed oil,and the type and content of polyphenols in fragrant rapeseed oils were more sensitive to roasting temperature.Phenolic monomers(4-ethenyl-2,6-dimethoxyphenol,sinapinic acid and sinapine)and polyunsaturated fatty acids(C18:2 and C18:3)acted as important cholesterol-lowering active components of rapeseed oil. |
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