| Rapeseed oil also named rape oil,it showed a unique flavor and contains abundant nutritions,as one of the common cooking oil on the market and the main oil crops in our country,rapeseed oil is popular with the masses.The contents of unsaturated fatty acid contents of rapeseed oil was more than 85%,of which oleic acid and linoleic acid are the main unsaturated fatty acid,absorption rate of rapeseed oil of human,s body is as high as 99%.Rapeseed oil contains abundant Vitamin E,polyphenols,squalene,sterol and so on,which are natural active ingredients.Rapeseed oil of different varieties,the producing areas and processing technology may influence the flavor types of rapeseed oil.Therefore,our research studied physical and chemical properties,nutrients and volatile flavour compounds of 32 kinds of rapeseed oil samples of different brands,different producing areas and different processing technology,in addition we also studied the volatile flavour compounds of different accelerating oxidation time and different refining stages.1,The acid value,peroxide value,oxidation induction period,anisidine value,total oxidation value and polyphenols of 32 kinds of rapeseed oil samples were determined by titration method,rancimat method and spectrophotometry.The results showed that the acid value of rapeseed oil ranged from 0.06 to 2.08 mg/g,the peroxide value ranged from 0.85 to12.08 mmol/kg and most of them were less than 6mmol/kg.Oxidation induction period ranged from 5.60 to 13.82 h and most of them concentrated in 10 h.Anisidine value were from 0.01 to 5.97,total oxidation value were from 3.41 to 51.66.The polyphenol contents of rapeseed oil showed with tannic acid contents,the polyphenol contents of four levels of rapeseed oil were from 10.012-28.091 mg/100 g,while three levels of rapeseed oil were 5.189-21.980 mg/100 g,one levels of rapeseed oil were 2.005-4.888 mg/100 g.Polyphenols contents of rapeseed oil were related with processing technic,polyphenols were loss in refining process.The fatty acid composition,vitamin E contents and squalene contents of rapeseed oil were detected by gas chromatography and liquid chromatography.The relative percentage of saturated fatty acid ranged from 6.698% to 14.689%,of which palmitic acid and stearic acid were the main fatty acids.The contents of monounsaturated fatty acid were 42.634-66.574%,of which oleic acid was the major ingredient.The contents of polyunsaturated fatty acid were 23.926-41.047%,linoleic acid and Linolenic acid were the main components,The contents of trans fatty acid were 0.622-1.564%.three kinds of vitamin E were detected,?-vitamin E presented the highest for 228.164-496.795 mg/kg,whereas ?-vitamin E were 73.799-271.952 mg/kg,?-vitamin E were 0-93.810 mg/kg and the total vitamin E were 323.046-671.644 mg/kg.Squalene contents were from 1.746 to 26.334 mg/kg.There were correlation between nutrients and physical and chemical indicators,the reasons main related to the forming factors of the contents and refining process,the research can provide theoretical support for finding source,quality assessment,identification adulteration.2,comparing simultaneous distillation-extraction and solid phase microextraction in extracting the volatile components of rapeseed oil,results indicated that solid phase microextraction was more suitable for extracting the volatile flavor compounds of rapeseed oil,optimum extraction conditions were established by the use of a DVB/CAR/PDMS fiber,extracting temperature 70?,balanced 20 min,extraction for 40 min,desorption for 4 min,flow rate was set as 0.8 mL/min.3,The volatile flavor compounds of rapeseed oil were detected by gas chromatography-mass spectrometry-olfactory.Results showed that the volatile compounds of four levels of rapeseed oil were superior to three levels of rapeseed oil and one levels of rapeseed oil in terms of the variety and contents of the volatile compounds,the numbers of volatile compounds were respectively 241,154 and 110.characteristic flavor compounds of rapeseed oil of four levels were 5-Cyano-1-pentene,2,5-dimethyl Pyrazine,3-methyl-2-Butenenitrile,3-ethyl-2,5-dimethyl-Pyrazine,2-methyl Pyrazine,2,4-Pentadienenitrile,2-ethyl-5-methyl-Pyrazine,Nonanal,Hexanal,Heptanal of which present roast,green,seed,fatty odor.Characteristic flavor compounds of rapeseed oil of three levels were 2,4-Pentadienenitrile,2-methyl Pyrazine,ethyl Pyrazine,2,3-dimethyl Pyrazine,2-ethyl-5-methyl-Pyrazine,3-methyl-2-Butenenitrile,2,5-dimethyl Pyrazine,3-ethyl-2,5-dimethyl-Pyrazine,4-isothiocyanato-1-Butene,(E,E)-2,4-Heptadienal,(E)-2-Octenal,(E,E)-2,4-Decadienal,characteristic flavor compounds present roast,green,fatty.Characteristic flavor compounds of rapeseed oil of one level were Hexanal,(E)-2-Pentenal,(E)-2-Octenal,(E)-2-Decenal,which presented an weak fatty odor.4,After refining,the acid value and peroxide value of rapeseed oil decresed,in addition the contents of monounsaturated fatty acids and trans fatty acids decresed,while the contents of polyunsaturated fatty acids and saturated fatty acids increased.The contents of polyphenols,squalene and vitamin E reduced in the refining process,respectively,decreased by 5.241%,5.483% and 16.361%.Aldehydes,glucosinolates glucose degradation product and heterocyclic were the main volatile flavour compounds.Aldehydes increased in the alkali refining process and washing process,and decreased in the decolorization process and deodorization process.Glucosinolates glucose degradation product increased in the alkali refining process and decreased in the washing,decolorization,and deodorization process.Heterocyclic continue reduced in whole refining process,and dereased by 94.098%.The volatile flavor composition significantly changed during decolorization,and deodorization process,so we can effectively decreased the loss of flavor compounds by control refining conditions.5,The acid value and peroxide value of rapeseed oil increased in the process of accelerated oxidation,in addition,the percentage amount of the saturated fatty acids,monounsaturated fatty acids,erucic acid and trans fatty acids were also increased,while polyunsaturated fatty acids decreased.In addition,the contents of Vitamin E and polyphenols continues decreased,oxidation rate of Vitamin E were ?-VE>?-VE>?-VE.Aldehydes significantly increased because of the oxidation degradation of unsaturated fatty acid during the accelerating oxidation process,and a high concentration of aldehydes may cause rancidity odor of rapeseed oil.Sulfur glucoside of glucose degradation products of rapeseed green odor and pyrazine of roast odor sharply reduced until disappear.It lead to oxidized rapeseed oil lacking rapeseed green and baking aroma.1,5-hexadien-3-ol and 3',5'-dimethoxyacetophenone significantly decreased during accelerating oxidation process6,Electronic nose combined with discriminant analysis and principal component analysis can better distinguish the rapeseed oil samples of different accelerated oxidation process and refining stages,but can not be better distinguish 32 kinds of rapeseed oil. |
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