Migration And Transformation Rules Of Tertiary Butyl Hydroquinone (TBHQ) And Its Antioxidation Mechanism Under Thermal Treatment

Test and evaluation method for tert-butyl hydroquinone (TBHQ) loss in oils duringheating was established in this article. The relationship between thermal loss of TBHQ withthe rapid dropping of the oil quality under high temperature treatment was studied.Temperature effects on the loss mechanism of TBHQ was discussed. Impact of peroxidevalue and acid value of oils on the TBHQ loss was described, and the related mechanisms ofthat was deduced.500g Samples of oils were heated at setting temperature in the oven. The maximumRSD(relative standard deviation) of two parallel samples at150℃over a heating period (24h)was3.04%.The concentration of the antioxidant TBHQ was determined by HPLC, therecocery was in a rang of97.3to102.8%(RSD=2.9%), and the minimum detection limitwas0.01μg/mL.TBHQ loss was in direct proportion to the heating temperature and the heating time.With the increasing loss rate of TBHQ, the inhibition to the increase of Totox value(TV) ofoils was significantly reduced. In addition, TV can be used as a sensitive indicator of lipidoxidation degree.That means, the rapid dropping of the oil quality under high temperaturetreatment was closely related to significant thermal loss of TBHQ.Volatilization was the major pathway for TBHQ loss in the oils at hightemperatures.Volatiles contains orther transformation or degradation products, wherein,tert-butyl-benzoquinone (TQ) was the main transformation product of TBHQ in heating oils.Loss rules of TBHQ in the samples of oils of different degrees of unsaturation, namelysoybean oil and palm oil, was contrasted in different heating temperatures. The resultsindicated that：the loss of TBHQ was more rapid in the soybean oil, which had a higherunsaturation degree, at relatively low temperatures (≤135℃),while there were oppositebehaviors under higher temperatures（≥150℃）.There may exists competition relationbetween antioxidant loss and volatile and degradation loss of TBHQ in the heating oils. Itcould be explained that, at lower temperature, TBHQ loss was primarily concerned with freeredical mechanism. Under this condition, the autoxidation reactions taking place throughchain reactions of free radicals are relatively slow in the less unsaturated oil.Thus, much moreProton have been transfered from phenolic to a peroxyl radical in the more unsaturated oil,and the higher level of free radicals produced by hydrogen transfer were exhausted by combining with another lipid peroxyl radical in a series of termination reactions to yieldnonradical oxidation products. However, besides free redical reaction, there existvolatilization and degradation, which were regarded as the main pathway of TBHQ loss athigh temperature. Based on the studies, we put forward that there exists a temperature turningpoint in competition relation between antioxidant loss and volatilization and degradation lossof TBHQ during heating. The turning point is affected by oils’ saturation significantly.Impact of peroxide value and acid value of oils on the TBHQ loss was described. It isshowed that the loss of TBHQ was increase With the increasing oxidation degree and the acidvalue. The oxidative coupling reaction between phenol radicals and peroxyl radicals of thelipids was the most reasonable explanation for this phenominon.