PURPOSE: To ensure the sourness of fruit juice to be mitigated by degrading the organic acids, in particular, citric acid in the fruit juice using a novel lactic acid bacteria Leuconostoc sp.KS-0002 having organic acid assimilability.

CONSTITUTION: Lactic acid bacteria in pieces of somewhat deteriorated mandarin orange sarcocarp are specifically proliferated in a relevant GYP medium comprising glucose, yeast extract and a citrate and then incubated in an appropriate agar-agar medium containing components similar to those mentioned above into a colony. This colony is then separated using a plate colony technique, thus obtaining the objective lactic acid bacteria Leuconostoc sp.KS-0002 with organic acid assimilability (FERM P-10313). The present bacterial can grow in fruit juice of high sourness with low pH such as from grape fruits or oranges, having such activity as to degrade the organic acids of high sourness in the fruit juice, in particular, citric acid. Thereby, treatment of a 100% natural fruit juice of high sourness with the present bacteria will convert it to a tasty natural fruit juice with mitigated sourness.