| Latic acid-ethanol-water system was a simulation system of rice wine.Pulsed electric field was used to research its effect on esterification of lactic acid and ethanol、reverse reaction and lactic acid-water solution in this paper. Gas chromatography mass spectrometry (GC-MS) and Fourier transform infrared spectrum(FTIR) was applied to study the change of the lactic acid-water solution microscopic structure.1. The influences of electric field intensity, single treatment time with the temperature on the esterification were studied. Then, the variation of activation energy during the esterification was explored. The results indicated that when the reaction temperature was30℃, flow rate was50mL/min, by applying15,20,25kV/cm PEF for10h, the productions of ethyl lactate were1.7,1.9,2.1times of PEF untreated sample, so the reaction was enhanced with increasing intensity; the productions of ethyl lactate were increased with increasing single treat time when the other condition were same; the reaction was enhanced obviously compared to untreated sample at the same temperature; the activation energy was changed by applying PEF,it is significantly decreased from the original43.43kJ/mol to25.05kJ/mol by applying20kV/cm PEF treatment.2. The influences of ethanol/lactic acid molar ratio and electric conductivity on the etherification were analyzed and non-thermal effect of PEF was explored at high electric conductivity system. The results indicated that as the molar ratio between ethanol and lactic acid was increased from0.5:1to2:1, the production of ethyl lactate was increased gradually as the four systems adjusted the same electric conductivity; when the four systems were not adjusted the electric conductivity, the production of ethyl lactate decreased gradually exhibited an order as1:1,0.5:1,1.5:1,2:1systems; non-thermal effect of PEF was more than30%of the total enhancement at the high electric conductivity system.3. Effect of PEF on esterification reverse reaction was studied. It was demonstrated that the pH of the ethyl lactate-water solution have a little change by applying PEF treatment, the enhancement of ethyl lactate hydrolysis was very weak; the electric conductivity of the ethyl lactate-water solution increased with increasing PEF intensity.4. The macroscopic and microscopic structure change of lactic acid-water solution by applying PEF treatment was explored. The results indicated that electric conductivity and viscosity of the lactic acid-water solution almost have no change after PEF treatment while the pH has a little decrease; GC-MS detection result indicated that no new substance emerged by PEF treatment, so there was no new impurity disturbed the esterification of lactic acid and ethanol; FTIR results indicated that O-H stretching band move to low wave number area with increasing intensity from0kV/cm to33.3kV/cm while C=O and acid O-H,acid C-O stretching band have little change; treatment times were0,0.5,1,1.5,2,2.5,3,3.5,4h, respectively.O-H stretching band fluctuated in a small range then tend to low wave number area while C=O and acid O-H、acid C-O stretching band have not a notable change.The strength of hydrogen bonding at Latic acid and water systems which have been treated by PEF was weaker compared to the former after55days storage. |
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