Effect Of Pulsed Electric Fields On The Structre Activity Of Glycine And Small Molecule Compounds And Its Mechanism Investigation

Pulsed electric fields（PEF）is widely used as a novel non-thermal processing technology in the liquid food sterilization.Compared to other processing techniques,the advantage of pulsed electric fields is that it can achieve continuous,low temperature and rapid sterilization process and less damage to food nutrients during processing.Although there are many reports on the effect of pulsed electric field on food active ingredients in the prcessing,there are few reports on the effect of pulsed electric field on struction of food components.Therefore,the different molecular weights and special functional groups compounds,such as amino acids,vitamin C,chlorophyll and carotenoids,were selected as the object to study the effects of different electric field intensity and electric field treatment time on the structure and physicochemical properties.Moreover,the preliminary mechanism of the effect of pulsed electric fields on the structure was proposed.The results are as follows:The effect of PEF treatment on the reaction process of glycine chelating iron was studied and compared with the heat treatment.The results show that both heat and PEF treatment can increase the yield and chelating ability of glycine-iron complex.In addition,the infrared spectra showed that the structure the glycine-iron complex obtained by PEF treatment was basically the same as that of heat treatment,but the intensity of absorption peak is greater at1110 cm^-1 with PEF treatment.The XRD patterns showed that the crystal structure of the complex obtained by heat and PEF treatment was similar to which showed the main diffraction peaks 2θat 11.1,16.7,23.8 and 25.7°,respectively,but the intensity of diffraction peak is greater at 18.9°with PEF treatment.The thermogravimetric analysis showed that the PEF treatment has had the same thermal stability properties as the glycine-iron complex obtained by the heat treatment,which hashad three stages of decomposition process.The effect of PEF on the reaction of L-phenylalanine andβ-cyclodextrin was studied.The results show that the different electric field intensity of PEF can affect the fluorescence intensity of phenylalanine-β-cyclodextrin complex and the stability coefficient ofβ-CD-L-Phe complex by PEF treatment increased from 147 M^-1 to 250 M^-1.The presence of hydrogen bonds in the phenylalanine-beta-cyclodextrin complex was demonstrated by molecular docking processing.Raman spectroscopy showed that the complex molecules showed new absorption peaks at 620 and 1207 cm^-1 after PEF treatment.In addition,the thermogravimetric（TGA）and differential scanning calorimetry（DSC）showed that the electric field intensity treatment could increase the weight loss rate,maximum decomposition temperature（T_m）and the enthalpy of theβ-CD-L-Phe complex in the 340-355°C range compared with the without PEF treatment sample.The effect of PEF on the structure and physicochemical properties of vitamin C was studied.The results show that the fluorescence intensity of the reaction product derived from vitamin C and o-phenylenediamine is enhanced with the increase of electric field intensity and treatment time.The vibrational peak of the infrared spectrum of vitamin C after PEF treatment appeared blue shifted(3379 cm^-1)and the intensity of some absorption peaks changed with electric field intensity was changed(3300,1680 and 1600 cm^-1).In addition,the relative content of vitamin C were increased by the high-performance liquid chromatography（HPLC）,and the antioxidant activity（DPPH radical scavenging ability and total reducing power）was significantly higher than untreated sample（p<0.05）.The effects of PEF on the extraction of pigment in spinach leaves were studied under 20,35 and 45 ^oC.The results showed that the contents of chlorophyll a,chlorophyll b and carotene in pigment solution treated with different electric field intensity were higher than those without PEF treatment（p<0.05）.It can be seen from the UV-Vis spectrophotometer that the intensity of the UV absorption peak at 468,615 and 664 nm is increased by PEF treatment.In addition,the absorption peak intensity(1734,826,800 and 767 cm^-1)of the infrared spectrum changed with the increase of electric field intensity,and a new absorption peak appeared at 1317 cm^-1 by FT-IR spectroscopy.In addition,the X-ray diffraction spectra show that the pulsed electric field can change the intensity of the diffraction peaks 2θ（27.3,28.3,29.8 and 32.7°）under the low temperature and a new diffraction peak appeared atnear2θ19.0°.When the temperature rises to 45°C,almost all of the diffraction peaks disappeared.In addition,the DPPH radical scavenging activity of the spinach pigment solution after PEF treatment at different temperature was significantly higher than without PEF treatment sample（p<0.05）.The mechanism of influence of the PEF on the structure and properties of food compounds was discussed through the above results.The results showed that PEF can change the ionization process of glycine,and promote the formation of zwitterions,thus increasing the ability of glycine to bind to ferrous ions.Moreover,the PEF can change the polarity of the benzene ring in the molecular structure of L-phe,and promote the formation of hydrogen bond between L-phe andβ-CD,which enhance the stability of the reaction product.In addition,the PEF can change the equilibrium between the enol and the ketone configuration of vitamin C,promote the transiton from the cis-to the trans-configuration of the carotenoids,and the interaction btween the magnesium ions and the amino group in the pyrrole ring of the chlorophyll.From the above results,it can be proven that the PEF can change some weak chemical bonds or forces and small molecular weight of compounds,and then change of the corresponding of physicochemicalproperties.The mechanism of the effect of PEF on food compositions is mainly free radical theory and high energy electronic theory.