L-苯丙氨酸对谷氨酸结晶的影响研究

Effects of L-Phenylalanine on Crystallization And Nucleation of L-Glutamic Acid

用稀硫酸调节谷氨酸一钠(MSG)溶液pH使谷氨酸等电点结晶,模拟谷氨酸(L-Glu)发酵液等电结晶操作,研究外源添加L-苯丙氨酸(L-Phe)对谷氨酸结晶的影响。结果表明,实验范围内L-Phe的添加量对谷氨酸溶解度无影响,但在谷氨酸结晶过程中,L-Phe可以吸附到谷氨酸晶体表面并被包埋到晶体内部,从而能够抑制谷氨酸β型晶体的生长,同时对α型晶体的生长也有抑制作用,使α型晶体形态发生改变,晶体粒径随添加量的增加而减小。通过数学推导建立了结晶诱导时间与过饱和度之间的定量关系,在此基础上进一步研究了L-Phe添加量与谷氨酸结晶诱导时间的关系,结果表明L-苯丙氨酸的添加可以降低谷氨酸成核的固-液表面张力σ、成核自由能△G和临界成核半径r_c,同时降低了最大成核速率A,使得谷氨酸成核速率(J)随着L-Phe的添加量的增加而降低。

The effects of L-Phenylalanine(L-Phe) on crystallization and nucleation of L-Glutamic acid(L-Glu) were investigated in this study by = simulating L-glutamic acid precipitation process through changing pH of monosodium glutamate solution with diluted sulphuric acid.The results indicated that the amount of L-Phe did not affect the L-Glu solubility,but the addition of L-Phe could be absorbed and imbedded on the surface/inside of the crystals of LGlu, thus repressing the crystals production withβform and changing the size distribution of the crystals with a form(crystals sizes decreases with the increased L-Phe addition amount). The mathematical analysis/model revealed that the nucleation kinetics parameters,solid/liquid surface tension(σ),free energy(△G),critical nucleation radius(rc) and maximum nucleation rate(A) in L-Glu crystallization were reduced,leading a lower nucleation rate(J) of L-Glu when increasing the L-Phe addition amount.