Process for producing lactic acid or its salts from fermentation using thermotolerance Bacillus bacteria

A process for producing lactic acid or its salts, comprising the steps of:

• (a) cultivating thermotolerant Bacillus genus bacteria to obtain a seed culture having an initial optical density (OD);
• (b) increasing the cell number of the thermotolerant Bacillus genus bacteria by inoculating the seed culture obtained from step (a) into a fermenter containing an initial carbon source at an initial concentration under an aerobic condition for a period of time;
• (c) fermenting the seed culture obtained from step (b) in the fermenter under a microaerobic condition to obtain lactic acid or its salts;
• wherein step (b) further comprises at least one addition of the carbon source under any one of the following conditions, which are independent of each other, to increase the concentration of the carbon source:
• when the concentration of the carbon source in the fermenter reduces to 50% or less compared to the initial concentration;
• when step (b) is carried out after at least one third (⅓) of the said period of time has elapsed;
• when the optical density (OD) of bacteria cells in the fermenter increases by at least 10 times compared to the initial optical density (OD).