L-苏氨酸发酵液稳定性探究及副产物测定

Investigation of the stability of L-threonine fermentation broth and determination of by-products

由于在L-苏氨酸发酵液提取过程中杂质甘氨酸质量浓度过高,导致产品质量下降,笔者对L-苏氨酸分解产生甘氨酸的机理进行了探究,并采用设置不同pH和温度条件的方法进行验证。将样液pH调整为0.4,6.0和13.1,分别20,40,60,80,100℃水浴处理30 min。处理后的样液采用高效液相色谱法(HPLC)测定氨基酸质量浓度,利用邻苯二甲醛(OPA)衍生测L-苏氨酸、甘氨酸质量浓度;利用2,4-二硝基苯肼(DNPH)衍生测乙醛质量浓度。实验结果表明:L-苏氨酸在酸性、中性加热条件下稳定;在碱性加热条件下分解为甘氨酸和乙醛,其中甘氨酸质量浓度增加了3.5 g/L,L-苏氨酸质量浓度降低了9 g/L;温度和pH是导致L-苏氨酸分解的关键因素。

In the extraction process of L-threonine fermentation liquid,the high concentration of impurity glycine decreased the quality of the final product.The mechanism of producing glycine from the decomposition of threonine was investigated and confirmed by varying the pH and temperature.The pH of the samples was adjusted to 0.4,6.0,and 13.1,and the samples were subjected to 30 min water baths at 20,40,60,80 and 100℃,respectively.The concentration of amino acids was determined by HPLC,and the concentrations of threonine and glycine were determined by o-phenyldiformaldehyde(OPA)derivations.The mass concentration of acetaldehyde was determined by derivatization with 2,4-dinitrophenylhydrazine(DNPH).L-threonine was stable under acidic and neutral heating conditions,according to the results.Under the conditions of alkaline heating,the decomposition of threonine into glycine and acetaldehyde resulted in an increase of glycine mass concentration by 3.5 g/L,and a decrease of threonine mass concentration by 9 g/L.Therefore,temperature and pH are the key factors in the L-threonine decomposition.