Effect Of Infrared Pretreatment Of Rapeseed On The Oxidative Stability And Flavor Of Oil

As an edible vegetable oil,rapeseed oil is very popular among consumers.It contains80%～90% of unsaturated fatty acids in an appropriate proportion,which is beneficial to human absorption.Rapeseed oil is also rich in endogenous active ingredients,such as tocopherols,phytosterols and erucic acid.The producer roasted the rapeseed by traditional roller roasting(TRR)to obtain a higher oil yield and better flavor than the cold pressing(CP)one,but due to the limitations of the TRR,the rapeseed will be heated during the production process unevenness,deep black color of rapeseed oil,poor oil stability and burnt smell.Therefore,this paper introduces a new type of seed roasting technology,infrared ray roasting(IRR)to explore the appropriate process conditions for seed roasting,and to reveal the impact of IRR technology on the quality of rapeseed oil.The main research contents are as follows:Firstly,this paper took the pressed rapeseed oil processed by TRR,IRR,CP and MW as the research object,to investigate the effects of different methods of seed roasting on the oil yield,AV,PV,OSI,and phenolic acid content.The results showed that the quality of rapeseed oil roasted by IRR was better than TRR.Compared with TRR,the oil yield of rapeseed oil treated with IRR is 1.5% higher than TRR and 5.04% higher than CP;its AV and PV are lower than TRR at the same temperature and time;its OSI is 14.79% higher than TRR,61.24% higher than CP;its phenolic acid content is 27.72% higher than TRR and 164.33% higher than CP.Secondly,this paper took the rapeseed roasted by IRR as the research object,to investigate the oil extraction rate,fatty acid composition,color,AV,PV,OSI,free radical elimination ability,volatile compounds and odor characteristics.The results show that IRR can significantly improve the oxidative stability and flavor of rapeseed oil.IRR at 150℃ for 40 minutes increased OY by 23.21%;AV increased to 0.51 mg/kg;PV increased to 1.27 mmol/kg;OSI increased by 65.31%;free radical elimination ability increased by 17.03%,and fatty acid composition had no significant change.At the same time,three types of volatile compounds were identified in the rapeseed oil treated with IRR: aldehydes and hexenals with fatty taste as the odor characteristics,such as hexanal and(E,E)-2,4-decadienal;Pyrazines and furans with roasted aroma as the odor characteristics,such as 2,5-dimethylpyrazine and 2-furaldehyde;isothiocyanates and nitriles with pungent and pungent odor characteristics,such as 4-isothiocyanate-1-butene,methallyl nitrile.The quality of rapeseed oil treated by IRR is better than rapeseed oil treated by other methods because of the increase in antioxidants and flavor compounds.In addition,this paper took tocopherol and 4-vinylsyringol(Canolol)in rapeseed oil as the research object,to explore the mechanism for the change of phenolic acid content in the IRR process and the correlation between phenolic acid content and OSI.The results showed that the content of phenolic acid increased by 164%,the content of tocopherol increased by 16.39%,and the content of Canolol increased by 90.5 folds.Scanning electron microscopy reveals that the structure of rapeseed cells is fully destroyed by IRR,and the oil body protein network structure and function are lost,which is beneficial to increase the oil yield and promote the dissolution and production of phenolic compounds.In addition,the antioxidant capacity of tocopherol and Canolol was evaluated,and the results showed that in the refined oil matrix(ROM),Canolol showed better antioxidant capacity than tocopherol,which was verified in the Schaal storage experiment.The AV and PV of the Canolol-ROM system are lower than that of the tocopherol-ROM.It is worth noting that the ROM system with equal amounts of tocopherol and Canolol shows a synergistic effect.The antioxidant loss analysis shows that under the same conditions,the loss rate of Canolol is higher than that of tocopherol.This may be due to the different groups on the phenol ring of the two antioxidants,leading to different effects on the elimination of free radicals in the system.Finally,our work focused on the traceability investigation of the three types of compounds summarized in the flavor-table.The results showed that aldehydes and hexenals compounds increased by 2.59～3.70 folds,which came from the thermal oxidation of unsaturated fatty acids during the baking process,and their main flavor characteristics were oily and rancidity;pyrazine furan compounds came from this process The Maillard reaction of reducing sugars and free amino acids has the main flavor characteristics of roasted flavor and clear flavor;isothiocyanates and nitriles mainly come from the degradation reaction of glucosinolate compounds in this process,and their main flavor characteristics are spicy and pungent flavor.In summary,this paper explored the effect of IRR technology on the oxidative stability and flavor of rapeseed oil.This paper obtained the best seed roasting conditions,and revealed the synergistic effect of tocopherol and Canolol in antioxidant process.The classification and traceability analysis of volatile compounds clarified the important contribution of oil oxidation,Maillard reaction and glucosinolate degradation to the formation of rapeseed oil flavor.This paper is of great significance to the production of rapeseed oil.