Study On The Spectrum And Antioxidant Mechanism Of Main Food Antioxidants

Food antioxidants are important food additives.It can effectively delay the oxidation of food and ensure food safety.At present,Butyl hydroxyanisole(BHA),Butylated hydroxytoluene(BHT),Tert-butyl hydroquinone(TBHQ),Propyl gallate(PG)and vitamin E are the most widely used food antioxidants.Among them,BHA and TBHQ have been widely used in animal and vegetable oils,fatty foods and other foods due to their excellent antioxidant capacity,and have become the main food antioxidants.However,excessive use of BHA and TBHQ may cause harm to the body.Experimentally,Fourier transform infrared spectrometer(FTIR)was used to measure the IR spectra of samples by KBr tablet method.The UV spectra of the samples were determined in the ethanol solvent by ultraviolet visible spectrophotometer.Based on density functional theory,the B3LYP functional was used to optimize the geometric configuration and calculate the frequency of BHA and TBHQ in gas phase at the level of 6-311g(d,p)basis set by Gaussian software.Then plot IR spectra.On this basis,based on the time-dependent density functional theory,SMD implicit solvent model was selected,and the first 50 excited states of molecule in ethanol solvent were calculated by using B3LYP functional and def2-TZVP basis set.Then plot UV spectra.Multiwfn software is used to calculate the Hirshfeld atomic charge,Fukui function,double descriptor,and electrostatic potential of BHA and TBHQ to predict their electrophilic reactive sites.By comparative analysis,it can be seen that the theoretical spectra are in good agreement with the experimental spectra.The characteristic absorption peaks of each group in the IR spectra are obvious,and the theoretical peaks are in good agreement with the position of the measured peaks.The hydrogen bonding of dimers and polymers in the TBHQ sample would weaken the O-H bond strength of a single molecule,which would weaken the vibration frequency of the O-H bond,resulting in a wide peak at 3670-3070 cm^-1 in the experimental IR spectrum.The UV spectra of BHA are mainly formed from the ground state to the first,second,sixth and seventh excited states.The maximum absorption peak in the UV spectrum is below 200 nm and is formed by the transitions of???^*and???^*.The absorption peaks at 269.2 nm and 223.7 nm are formed by the transitions of n??^*and???^*.It can be seen from the electron-hole distribution diagram that these four excitations are all electron local excitation.The UV spectra of TBHQ are mainly formed from the ground state to the first,second,sixth and seventh excited states.The maximum absorption peak in the UV spectrum is below 200 nm and is formed by the transitions of???^*and???^*.The absorption peaks at 268.8 nm and 221.4 nm are formed by the transitions of n??^*and???^*.It can be seen from the electron-hole distribution diagram that these four excitations are all electron local excitation.The analysis of electrophilic reactive sites shows that the four methods can well predict that the oxygen atoms on the phenolic hydroxyl group and on the ether bond of the BHA molecule may be the electrophilic reactive sites and the oxygen atoms on the two phenolic hydroxyl groups of TBHQ molecule may be electrophilic reactive sites.When the BHA is attacked by electrophilic reagents such as peroxide radicals,the oxygen atoms on the ether bond first undergo electrophilic substitution reaction,resulting in the C-O bond breaking and being replaced by hydrogen atoms to form phenolic hydroxyl groups.It becomes TBHQ with stronger antioxidant effect.On the one hand,this research is of great significance for the detection of food antioxidants BHA and TBHQ.On the other hand,it also provides an important method for the theoretical study of antioxidant mechanism.