1. Introduction
Lactic acid provides a profound application as a chemical feedstock for several industries such as food industry, pharmaceutical industry, leather and textile industries. Recently, the use of lactic acid for production of polylactic acid (PLA) [1], the most well-known bioplastics, leads to a substantial increase in world consumption of lactic acid. However, the price of lactic acid is still too high for its economical use in PLA production. Thus, several attempts have been devoted to develop the cost effective approaches for lactic acid production by seeking for the non-or low cost substrates and the efficient microorganisms, and/or optimizing the fermentation process [2] and [3].
Although the starches have been substituted to the refine sugars for lactic acid production, the high production costs still exist due to the high costs in substrate pretreatment [4]. Currently, an achievement of simultaneous saccharification and fermentation (SSF) of starch to lactic acid by the amylolytic lactic acid bacteria has been noted [3]-[5]. However, these studies were mostly performed by using batch fermentation and under a sterile condition which increased the production costs due to an inoculum preparation and resterilization of the fermentation vessels. In order to reduce the production costs, therefore, the present research is aimed at producing lactic acid from the repeated-batch and simultaneous saccharification and fermentation of a synthetic cassava starch wastewater by an amylolytic Lactobacillus plantarum MSUL 702 under a non-sterile condition. The viable lactic acid bacteria (LAB) in the reactor and treatment efficiency of the SSF processes were also investigated.