不同的中和剂对L(+)-乳酸发酵的影响

分别利用CaCO3、6 mol/L氨水和6 mol/L NaOH溶液调控乳酸发酵过程的pH,得到的乳酸浓度为169.1g/L、187.9g/L和170.1g/L(以发酵液的初始体积计算),分别是无pH调控发酵过程的4.9倍、5.4倍和4.9倍;得到的OD620分别为19.3、21.6和16.4,分别是无pH调控(OD620为8.5)的2.3倍、2.5倍和1.9倍.相对于氨水和NaOH来说,CaCO3粉末是一种缓慢型的酸中和剂,pH调节能力有限,只能将pH维持在4.9～5.2.但CaCO3可以将乳酸以生成乳酸钙的形式沉淀下来,给下游乳酸的分离提取带来一定的方便.因此对于传统的分批式发酵,CaCO3仍不失为一种较好的选择.氨水和NaOH溶液都可以很好地将发酵液的pH调控在6.0,其中氨水是一种最理想的酸中和剂,既有利于乳酸的生物合成又能促进乳酸菌的生长.

Effects of different neutralizers on L(+)-lactic acid fermentation

Using CaCO3, 6 mol/L NH4OH and 6 mol/L NaOH as neutralizers, maximum lactic acid concentrations of 169.1 g/L, 187.9 g/L and 170.1 g/L were obtained respectively, which were 4.9, 5.4 and 4.9 times higher than that of no pH adjusting. And maximum OD620 value of 19.3, 21.6 and 16.4 were obtained, respectively, which were 2.3, 2.5 and 1.9 times higher than that of no pH adjusting. CaCO3 was found to be a kind of mild neutralizers, which could only control pH keeping at 4.9- 5.2 during the lactic acid fermentation process by Lactobacillus paracasei. While using CaCO3as neutralizer, lactic acid could be deposited in the form of calcium lactate, which facilitated the subsequent separation process. Therefore, CaCO3 was still a suitable neutralizer for lactic acid production in conventional batch fermentation. On the contrary, both aqueous ammonia and NaOH solution could adjust pH value at 6.0 very well. Aqueous ammonia was a perfect neutralizer, which was in favor of lactic acid production as well as the growth of Lactobacillus paracasei.