Autoxidative Change And Its Law Of Edible Oils During Storage

Edible oil oxidation not only causes the loss of edible oil,but also brings a lot of food safety hazards.At present,limited information is available regarding the basic research on oxidative change and its law of edible oils during storage.For a practical approach,the oxidative stability is determined under conditions of accelerated oxidation,usually at elevated temperatures.An ideal method for evaluating the oxidative stability and monitoring the oxidation process of edible oil should provide information about a variety of chemical species simultaneously in real time,should be sensitive and reproducible,and should be amenable to longer time frames that moderate oxidative conditions might entail.The detecting techniques of Fourier infrared spectrum(FTIR)can provide the information on groups of C/H/O,which is very suitable for monitoring of edible oil oxidation process.Taken the common edible oils in our country as raw material,we monitored some functional groups correspond to oil oxidation in real time during ambient storage by mesh cell-based FTIR method.Furthermore,a practical means of evaluating the edible oil oxidative stability during ambient storage was established.Headspace solid-phase microextraction/gas chromatography–mass spectrometry(HS-SPME/GC–MS)was used to monitor changes of key volatiles composition in edible oil during ambient storage.Meanwhile,we explored the different factors affecting the oxidation of edible oil and offered a suggestion for edible oil storage at ambient temperature.The oxidation change of the bottled edible oil in daily life was also studied.The main results were obtained as follows:(1)Owing to the high surface-to-volume ratio provided by the mesh cell,the oxidative process can be further accelerated with air flow over the mesh cell.Edible oils oxidized on the mesh cells reached the peroxide value(PV)end point(20 and 100 meq/kg-1)nearly2.6–4.2 times faster than the oils oxidized in bulk under the same conditions.Meanwhile,the changes in ROOH(3471 cm-1),isolated trans double bond(968 cm-1),FFA n(C=O)absorbance(1706 cm-1),cis-fatty acid absorbance(914 cm-1),and carbon chain skeleton vibration absorbance(723 cm-1)can be monitored in real time during ambient storage.Therefore,the mesh cell-based oxidation method is a flexible,simple,fast,and convenientmethod.The rapid rate of oil oxidation on these mesh cells makes it practical to evaluate the oxidative stability during ambient storage and facilitates real time monitoring of oxidative changes.(2)HS-SPME/GC–MS analysis was used to monitor changes in key volatile compounds in edible oil during ambient storage.Volatile composition and oxidation process were compared among edible oil samples.The differences in the volatile contents of edible oils led to their characteristic flavor.Aldehydes featured a relatively high content and low odor threshold and mainly contributed to the flavor of edible oils.The key flavor compounds included pentanal,hexanal,octanal,nonanal,trans-2-heptenal,and benzaldehyde,which are important oxidative degradation products of oleic acid and linoleic acid.The formation of key volatile oxidation compounds was affected by different oxidation processes during ambient storage.Certain aldehydes increased with oxidation level,whereas other aldehydes initially increased then decreased.Correlation analysis showed that the concentrations of several volatile compounds progressively increased during oxidation.(3)Azobisisoheptonitrile as free radical initiator and chlorophyll as a photosensitizer both increased the rate of edible oil autoxidation.Their ultimate role is to increase the free radicals in edible oils,promote the chain initiation and accelerate the autoxidation process.TBHQ can prolong the time of edible oil induction period,and it can play a good role in inhibiting the oxidation and rancidity of edible oil.After the addition of a certain amount of antioxidant,the oxidation process of lineed oil has not reached induced period(PV less than10 meq/kg)after 47 d oxidation at ambient temperature.The PV of linseed oil filled with nitrogen reached 62.5 meq/kg lower than 200 meq/kg of the control group at 47 d.When the oil was stored in nitrogen,the oxygen in the oils could be discharged by continuously filling the nitrogen which played a role in inhibiting oil oxidation.The PV of the linseed oil stored in the 4oC refrigerator was only 14.3 meq/kg at 47 d.Therefore,in order to prevent the edible oil oxidation,some measures can be taken: avoiding light,avoiding high temperature,removing chlorophyll and other photosensitive substances and a variety of free radical initiator,minimizing contact with oxygen,filling with nitrogen,adding antioxidants and so on can improve the stability of edible oil.Meanwhile,it has been shown that the addition of antioxidants and low temperature storage were more effective than the addition of nitrogen.(4)The oxidation of bottled linseed is easier than other edible oils;Bottle wall's residual edible oil can promote the oxidation of remaining oil in the bottle;At ambient temperature,the peroxide values of different parts of the linseed oil(upper,middle and lower layers)after9d increased to 15.1 meq/kg,12.6 meq/kg,10.8 meq/kg,respectively,and the peroxide valueof different parts of bottled peanut oil after 9d increased to 9.4 meq/kg,8.8 meq/kg,8.4 meq/kg,respectively.The oxidation speed of bottled linseed oil and peanut oil's upper oil is greater than the middle,middle oil oxidation speed is greater than the lower.Barrel wall's residual oil can promote the oxidation of remaining oil in barrel;The oxidation speed in upper barrel oil is greater than the middle,middle oil oxidation speed is greater than the lower.Owing to more laminar air flow in the upper layer,the oxidation rate was faster.More attention should be payed to the cleaning of oil drums to avoid residual oil on the barrel wall and oil drums should not be reused in the daily life.The edible oils should try to avoid excessive contact with the air.