Exogenous Leucine Improved the Acid Tolerance of Lactococcus lactis Under Acid Stress

Abstract:

The addition of leucine was proved to improve the tolerance of Lactococcus lactis NZ9000 to acid stress. When cultivated with leucine under acid stress(pH 5.0),the biomass of L. lactis NZ9000(Leu+) increased 1.24 fold,compared to L. lactis NZ9000(Leu-) (without leucine addition). After challenged at pH 4.0 for 5 h,the survival rate of L. lactis NZ9000(Leu+) increased 28.5 fold,compared to L. lactis NZ9000(Leu-). Further measurements indicated that the addition of leucine could improve the concentration of intracellular NH4+,help to maintain the intracellular pH(pHin) at a relatively high level and protect the activity of lactate dehydrogenase(LDH). Therefore,the addition of leucine could enhance the acid tolerance of L. lactis.